5-1

5. ENGINEERING AND DESIGN ANALYSIS

Overview

The company has undertaken a technical analysis of the LIC network and the events

during the July heat wave in order to determine whether planning or system design

played any part in the event. We have also analyzed certain equipment failures in order to

establish why the equipment failed. We have performed a retrospective analysis of the

event in order to determine where and when the damage occurred to the secondary

network occurred that resulted in the customer outages. This latter analysis is set forth in

Section 5.9. It has also been used to reinforce the LIC network to ensure system

reliability in the future.

As set forth below, the pre-summer planning for the LIC network was appropriate and

played no part in the event. The load experienced during the heat wave both by the

overall Con Edison service area, and in the LIC network in particular, was below the

forecast peak load for the summer of 2006. The Con Edison system, including the LIC

network, was designed to handle that load. In addition, the pre-summer reliability work

performed in the LIC network was in compliance with Con Edison specifications and

resulted in a robust network that could carry peak load with any two feeders out of

service without overloading any equipment. We also examined the company’s current

tools for appropriately allocating reliability resources among networks and feeders, and

we found that the reliability index and the hi-pot program are appropriate tools for that

purpose.

5-2

The network design was also found to be appropriate. Our analysis revealed that the

feeder diversity was appropriate for supplying the secondary grid. We identified six

individual customers who are not connected to the grid, but instead receive power

directly from high voltage primary feeders, for whom better diversity could be achieved.

This issue did not impact the event. We have also undertaken to study whether the effect

of transient overvoltages, which can occur during fault inception, fault clearing or when

re-energizing a feeder, had any impact on the event.

The company also compared the actual secondary damage to the predictive damage using

a modeling application as a measure of the adequacy of its models. The company

reviewed the primary failures caused by secondary events and the effect of secondary

damage in clearing alive-on-backfeed conditions.

5.1. Demand Forecasting

Overview

Con Edison’s system peak demand occurs during the summer months and is driven by the

increase in electrical consumption caused by high temperatures and humidity. At the end

of each summer, Con Edison reviews summer peak demand for its electric distribution

system and various networks. The company then forecasts the demand for the next

summer based on the prior summer’s demand, along with statistical information such as

population growth and new business development in each network. Based on this

calculation, the electric system is then reinforced to carry the forecast load in preparation

for the next summer’s peak period. This section of the report describes the process for

determining the Con Edison demand forecast.

5-3

5.1.1. Review of Forecast – Con Edison System

The system peak load that was forecast for the summer of 2006 for the Con Edison

service area was 13,400 MW. The actual system peak load on July 17, 2006, was 12,760

MW for the hour ending (HE) 18:00. The company estimates that the system peak load of

12,760 MW would have been approximately 70 MW higher had the load not been

reduced by implementation of the New York Power Authority’s Peak Load Management

Program (45 MW) and the customer outages in the Granite Hill area of Westchester

County (25 MW).

The actual system peak load on July 18, 2006, was 12,829 MW at HE 17:00. The

company estimates that the system peak load of 12,829 MW would have been

approximately 400 to 481 MW higher, but again, load was reduced by the

implementation of the New York Independent System Operator (NYISO) Emergency

Demand Response Program - Special Case Resources (EDRP-SCR) (300 to 400 MW)

and the customer service outages that were experienced in the LIC network (81 MW that

day).

5-4

5.1.2. Review of Forecast – LIC Network

The LIC network peak load forecast for summer 2006 was 395 MW. The actual peak

load on July 17, 2006, was 381 MW at HE 17:00. The LIC network actual peak load on

July 18, 2006, was 309 MW at HE 12:00.

5.1.3. Review of LIC Network Load Cycle

The Daily Load Factors and Daily Loss Factors are used to detect changes in load cycle

patterns. These factors are used to adjust equipment ratings to reflect the unique load

characteristics of a network. They are defined as:

Daily Load Factor: the ratio of the average of the 24 hourly readings of amperes

(or MW) to the maximum ampere (or MW) hourly reading of the load for the 24-

hour period.

Daily Loss Factor: the ratio of the average power loss, over a 24-hour period, to

the maximum power loss occurring in that period.

A review of the 24-hour load cycles for the LIC network for the previous peak days,

which occurred during the summers of 2003, 2004, 2005, and 2006 showed very little

change in the load-cycle pattern. The LIC network load factors ranged from 83% to 85%,

while the loss factors ranged from 72% to 73%. The calculated network load factor,

based on summer 2006 experience, was 83%. This is based on the peak day prior to the

Long Island City event, June 19, 2006, when the network was in normal operating

5-5

conditions. The projected load factor was 83%. Similarly, the calculated network loss

factor based on summer 2006 was 72%, compared to a projected daily loss factor of 72%.

5.1.4. Load Cycle Impact on Ratings

The calculations of the summer normal ratings and the emergency ratings of the LIC

primary network feeders reflect the LIC network peak-load cycle. The calculations of

summer normal ratings and the emergency ratings of the LIC network transformers

reflect the individual network transformer peak-load cycles.

• The LIC network feeder ratings are calculated using the Poly Voltage Load Flow

(PVL) program, incorporating several factors, including the network load cycle.

• The LIC network transformer ratings are calculated incorporating several factors,

including the individual network transformer load cycle.

5.1.5. Review of Load Cycle

A comparison of the LIC network load forecast of 395 MW for summer 2006 with the

actual peak load of 381 MW, recorded this summer before July 17, shows that the

network load projection was not exceeded prior to the beginning of the Long Island City

event.

There were no significant changes in the 24-hour peak-load cycle pattern in a comparison

of the LIC network load-cycle pattern before July 17 against the load cycles experienced

during the previous three years. The load cycle for the LIC network, used to calculate the

load factor and the loss factor, has been very steady for the past three years and does not

5-6

require a change at the present time. The company will continue to analyze the network

load cycles for each summer period to determine if and when a change is required.

5.1.6. Load Cycle Analysis

The load-cycle analysis for the LIC network has confirmed that the projected load cycle

for summer 2006 was accurate, and therefore does not warrant a revision of the network

loss factor.

5.1.7. Long Island City Network Primary Feeders

Table 5-1 shows the summer 2006 normal and emergency primary feeder peak-load

projections, normal and emergency feeder capability, and the percentage of feeder

loadings for the LIC network. All of the LIC network feeders were projected to be within

their ratings under normal and design-contingency conditions.

5-7

Long Island City Network Supply Based on the Network/Area Load Forecast of September 2, 2005

Independent Feeder Normal & Emergency Amperes - Summer Peaks Summer 2006

Network Projected Independent Peak Load: 395 MW Supply Area Substation: North Queens

Feeder Normal Emergency Number Load Capability % Loading Load Capability % Loading 1Q01 492 565 87% 784 807 97% 1Q02 465 590 79% 743 758 98% 1Q03 382 406 94% 570 609 94% 1Q04 402 423 95% 598 625 96% 1Q05 406 489 83% 589 695 85% 1Q06 379 458 83% 568 633 90% 1Q07 474 549 86% 666 685 97% 1Q08 439 479 92% 618 663 93% 1Q09 491 527 93% 692 711 97% 1Q11 476 500 95% 678 688 99% 1Q12 395 443 89% 577 621 93% 1Q13 417 454 92% 551 630 87% 1Q14 457 565 81% 752 829 91% 1Q15 401 549 73% 696 926 75% 1Q16 539 620 87% 770 824 93% 1Q17 551 620 89% 834 904 92% 1Q18 393 410 96% 522 606 86% 1Q19 437 493 89% 631 665 95% 1Q20 459 493 93% 616 627 98% 1Q21 479 565 85% 703 773 91% 1Q22 375 410 91% 588 620 95% 1Q23 383 410 93% 586 613 96%

Table 5-1

5.2. Network Design

Overview

The basic components of a secondary network system are high-voltage primary

distribution feeders; three-phase network transformers; network protectors (automatic

switches that connect the transformer to the secondary grid); secondary cables (“mains”);

cable limiters (a type of fuse designed to isolate sections of secondary cable from severe

5-8

overloads or fault conditions); and customer service wires. Feeders and transformers are

connected to the secondary network in a pattern that ensures a diverse power supply

under contingency-design conditions.

The following are network design criteria and practices described in this section:

• Network contingency design • Bus and feeder diversity • Basic impulse level (BIL) rating • Network size and density considerations • Network analyses for summer preparations

5.2.1. Network Contingency Design Considerations

The LIC network has an “N-2” contingency design (also known as second contingency),

which means that the network can supply customers’ peak electric demand with any two

network feeders out of service without stressing network components beyond design

limits. Customers with a dedicated transformer supply also have an “N-2” design, so that

their peak demand is met even with two transformers out of service. This second

contingency design criterion for the primary system, coupled with the secondary network

(i.e., “mesh”) design, is what makes the Con Edison system highly reliable.

Con Edison establishes a diversified mesh design to support its second contingency

design. In order to meet design requirements, two feeders are usually installed in a duct

system and follow a diversified pattern over the network area. Networks with a large

number of feeders are permitted to have more than two feeders installed in the same duct

5-9

bank (independent duct system), provided that no more than two are associated

electrically, i.e. supply the secondary grid in contiguous portions of the network.

A significant portion of the LIC network is underground, which limits its exposure to

severe weather conditions, such as wind, ice, and precipitation, and adds to the overall

reliability of the system. During an extended heat wave, however, the underground

system is subjected to equipment loadings and higher ambient earth temperatures

generating heat that increases the incidence of failures. Nonetheless, when compared to

an overhead radial system, outages on an underground network system are 50 times less

frequent. It is more difficult, however, to locate and repair problems in an underground

system, which results in outages that typically last twice as long as those associated with

an overhead system.

5.3. Overview of System Tools

The Poly Voltage Load (PVL) model comprises two components: the primary-flow and

the secondary-flow programs. The primary-load-flow program is a power-flow analysis

tool used for simulating balanced, three-phase electric distribution systems. Using base

models for the design criteria of normal, first, and, where applicable, second contingency

conditions, the company is able to identify projected primary feeder cable overloads that

require reinforcement. The program simulates distribution systems that have network and

radial primary feeders supplying secondary network systems, including isolated network

installations, high-tension customers (customers supplied directly from primary feeders),

unit substations, auto loops, and automatic transfer switches.

5-10

Similar to PVL, but used for real time operation, WOLF is a load flow program that uses

real time data to calculate loading on feeder components and can assist operators in

prioritizing feeder restoration. WOLF uses data from a dynamic network model which

includes feeder sections, transformers and secondary mains. This model is updated in

real time as system components both become unavailable and are subsequently restored.

During the LIC event, WOLF was not fully operational due primarily to issues with

updating the network model. Operators were able to use a number of alternate sources of

information to prioritize feeder restoration. These alternate sources included the

locations of specific feeders in the network, RMS transformer data, SOCCSX feeder

loading and field information such as low voltage reports. It is also unclear to what

extent WOLF would have produced accurate real time results given the high levels of

contingencies experienced during the LIC event. The problems with WOLF did not

impact feeder restoration, as WOLF is only one source of information that helps

operators direct resources.

5.4. Bus and Feeder Diversity

Part of the network design criteria involves the design of substations and the connection

of the primary feeders to the substation. The substation contains an electrical “bus” to

which a number of feeders are connected through a circuit breaker for each feeder. The

groups of feeders that are connected to each bus have a diversity design to prevent local

impact on the network when the bus section is removed from service for testing or

maintenance.

5-11

Network feeders generally run in bands, (two feeders in a common duct bank supplying

the same network) with no more than two associated feeders in the same duct bank so

that a manhole fire or duct collapse will not cause more than a second contingency. In a

network, there are typically four or more bands. By increasing feeder diversity, which is

equivalent to decreasing the average number of related feeders (feeders in the same or

adjacent bands or supplying a substantial amount of load in the same area), Con Edison is

able to design a more reliable network.

Feeder bands are designed so that a bus-section outage at the substation will have

minimum effect on feeder loading. When a feeder goes out of service, or “de-energizes,”

the load that was supplied from that feeder is picked up by nearby feeders, i.e., feeder

loading increases. This is accomplished at the area substation, as often as is possible, by

connecting only unrelated feeders to each bus section.

5.4.1. Bus and Feeder Diversity Analysis

Feeder diversity has a particular impact on customers who receive their electricity

directly from high-voltage feeders rather than from the low-voltage secondary grid. Con

Edison evaluated the bus feeder diversity at the North Queens substation as it relates to

these customers. Using the Net Report and Customer Matrix data systems, which provide

information on how customers are connected to the Con Edison system, high tension

services, isolated networks, spot networks, and multi-bank locations were analyzed to

identify any bus conflicts. A conflict is defined as having two or more transformers on

one feeder, or when a customer is directly supplied by more than one feeder on the same

5-12

bus section. Each location was reviewed to see if any customer outages would result from

a particular bus section being taken out of service. Using the PVL model, each bus

section was simulated to be out of service to see if any overloads occurred in order to

identify any design issues. The study identified six customers with bus diversity conflicts

where improvements could be made in the diversity of their electric service. Those

conflicts were not a factor in the LIC event, and are scheduled for correction before

summer 2007.

5.5. BIL Design Criterion

The design of an electrical system includes using insulation that meets the standard

insulator basic impulse level (BIL) for the voltage level on the system. BIL is defined as

the voltage level that can flash over the leakage distance of an insulator. Con Edison uses

this design characteristic to handle above-normal voltages. These voltage surges can

come from lightning strikes (primarily a concern for overhead equipment), and also from

feeder switching and feeder faults. Equipment such as transformers have a BIL voltage

level, which represents the amount of voltage a transformer can withstand before it is

damaged. For the 27-kV network system, the transformers are designed to meet a BIL of

200 kV, which protects them against the voltage surges that can be experienced in the

network system.

All new transformers installed are given a high-voltage impulse test, which verifies that

the transformer meets the minimum BIL requirement. In addition, all reconditioned

transformers are also given the high-voltage impulse test.

5-13

5.6. Network Size and Density Considerations

Con Edison’s network and feeder systems are designed to reliably, efficiently, and safely

meet customer demand for electricity. The LIC network has relatively long primary

feeders and a secondary network that covers approximately 10 square miles. By contrast,

Manhattan networks, because of higher load density and a lower primary operating

voltage of 13 kV, have shorter primary feeders and fewer transformers per feeder. In

addition, the location of the North Queens substation – in the northern part of the network

– requires longer feeders to supply the southern portion of the network. Long primary

feeders generally have more components than short feeders, and as a result, have higher

feeder-outage rates.

5.7. Network Reliability Probabilistic Model

Overview In order to maintain a high level of reliability, the company developed a probabilistic

model to measure network reliability. This model forecasts the probability of a complete

network contingency and ranks all company networks based on a calculated reliability

index. The network ranking from 2002 through 2006 is shown in Table 5-2 (networks

without a ranking available are noted in italics). In this index, the better-predicted

network performance corresponds to higher-ranking numbers. Even networks with low

rankings have a very low probability of experiencing a severe contingency because of

their design configuration. As a result of system enhancements over the years, the LIC

network ranking improved from four in 2002 to its current ranking of nine.

5-14

2002 2003 2004 2005 2006Network Ranking Ranking Ranking Ranking Ranking

Battery Park City 54 55 57 57 57Bay Ridge 24 22 20 17 18Beekman 49 48 48 40 45Borough Hall 14 9 13 12 10Bowling Green 44 46 45 39 37Brighton Beach n/a 47 22 24 24Canal 47 50 51 50 48Central Bronx 20 16 5 15 16Central Park 30 32 34 36 33Chelsea 22 23 30 30 34City Hall 37 31 31 31 27Columbus Circle 40 41 44 46 47Cooper Square 26 26 32 28 26Cortlandt 53 51 52 53 54Crown Heights 10 5 19 14 5Fashion n/a n/a 56 55 55Flatbush 1 1 1 1 8Flushing 2 4 4 4 11Fordham 6 3 3 2 1Fulton 38 36 38 37 40Grand Central 27 28 27 27 25Greeley Square 33 35 39 38 38Greenwich 52 52 47 52 52Harlem 18 19 21 21 21Herald Square 42 45 49 43 41Hudson n/a 56 53 56 56Hunter 50 53 54 54 50Jackson Heights 25 24 25 25 28Jamaica 3 2 6 6 3Kips Bay 43 38 40 47 46Lenox Hill 32 34 29 29 29Lincoln Square 36 42 46 42 42Long Island City 4 6 8 8 9Madison Square 28 25 26 26 31Maspeth 5 7 10 13 19Northeast Bronx 35 27 23 23 23Ocean Parkway 9 20 24 22 22Park Place 51 54 55 51 53Park Slope 8 11 14 7 7Pennsylvania 23 30 33 33 32Plaza 34 33 35 35 36Rego Park 13 17 18 20 20Richmond Hill 12 10 11 18 14Ridgewood 16 15 12 5 12Riverdale 21 21 9 19 15Rockefeller Center 39 40 42 45 43Roosevelt 48 49 50 49 51Sheepshead Bay 17 14 15 3 4Sheridan Square 31 37 36 34 35Southeast Bronx 19 18 7 11 13Sutton 41 39 43 44 39Times Square 45 43 37 41 44Turtle Bay 46 44 41 48 49Washington Hts 29 29 28 32 30West Bronx 15 12 2 9 2Williamsburg 11 8 16 10 6Yorkville 7 13 17 16 17

Table 5-2: Relative Network Reliability Ranking Based on Probabilistic Analysis

5-15

5.7.1. Calculating the Reliability Index

The Con Edison reliability model uses two programs:

- The contingency-planning program shows the reliability of the networks over a 20-year period; and

- The monitor-operating program assesses the reliability of the networks during a heat wave for a fixed number of days.

Both programs seek to gauge the relative reliability of a network by measuring the

probability for patterns of multiple associated feeder outages over time as caused by

component failures. The programs identify the probability that feeders in related bands

might experience outages simultaneously. Con Edison takes into account several factors

when determining the reliability of specific feeders.

Data for these programs is derived from many sources, including the PVL application and

the Vision-Mapping database. Table 5-3 contains the physical and behavioral information

used in the contingency program to determine the reliability of the individual networks.

The reliability is calculated using a probabilistic approach by simulating the feeder

component failures in the network. The model uses failure indices for cable sections,

joints, transformers, and related equipment and is further defined according to age and

vintage patterns, heat wave performance, temperature, and voltage levels.

5-16

Physical Characteristic Table:Name Description Source NecessityAWD* Index AWD Temperatures since 1995 Forecast Group RequiredBus Substation Bus Connectivity Hi Tension Diagrams OptionalFeeders Feeder load and rating data Engineering Book RequiredFixed Feeder cable section data Vision Mapping RequiredJoints Feeder joint data Inferred from Vision RequiredLocate Switch Sectionalizing Switch data Calculated by ProgramM_BQ_X_CC Customer data Emopsys OptionalManhole Congestion Manholes w/ cable/section counts Distribution Engineering RequiredNetworks Network ID and load data Engineering Book RequiredNewSwitch Sectionalizing Switch data Regional Engineering OptionalPickup1 1st Contingency Feeder Pickups PVL RequiredPickup2 2nd Contingency Feeder Pickups PVL RequiredShift1 1st Contingency Feeder Shifts PVL RequiredShift2 2nd Contingency Feeder Shifts PVL RequiredTransformers Transformer ID Information CINDE RequiredVacuum Recloser Switch (VRS) VRS ID Information Regional Engineering OptionalWater Wet Manhole Identifiers CIMOES Required

Behavioral Information Table:Name Description Source NecessityCongestion Factors for congested manholes Analysis RequiredCosts Repair costs for failed components Distribution Engineering RequiredDefault Repair Default time Repair / Restore feeder Distribution Engineering RequiredFailure Rates Component Failure Rates Analysis RequiredFinancial Discount Rate, Start and End Years Distribution Engineering RequiredInflation Inflation rates for 20 years Distribution Engineering RequiredLoad Load Factor Multipliers Analysis RequiredOverload Overload Multiplication Factors Analysis RequiredSwitchTimeConstant Default Time for SF6 Switching Distribution Engineering Required*Average Wet-Dry Bulb Index

Table 5-3: Physical Characteristics and Behavioral Information

The contingency program is designed to run a 20-year simulation for up to 10,000

iterations and to predict the frequency of network feeder failures and network

contingencies. It produces a reliability index based on the outage frequency of feeders in

related bands over the 20-year period. During the Long Island City event, the company

appropriately prioritized feeder restoration by using the summer model to determine the

next-worst-case scenario. Models were used to determine the next-worst-case scenario

5-17

using the summer model that allowed Con Edison to appropriately prioritize the

restoration of feeders.

5.7.2. Improving Reliability in LIC

In order to meet the increasing demand in the LIC network, by 2015 the company plans

to establish an additional substation in the southern portion of the network. Part of the

load currently served by the North Queens substation will be transferred to this new

substation. The addition of this substation may enhance electrical reliability in the area in

that there will be additional sources of electrical supply feeding substantially the same

numbers of customers.

A review of potential projects within the affected areas of the network concluded that

reliability would be improved by adding two new feeders at the North Queens Substation.

Feeders 1Q16, and 1Q17, will be de-loaded onto new feeders 1Q24 and 1Q25, taking into

consideration bus diversity, existing feeder loadings, and available conduit outlet

systems. This would have the following impact on loading and reliability indexes:

5-18

LIC Feeder Loadings

Before After Feeder Amps Feeder Amps 1Q16 540 1Q16 252 1Q17 501 1Q17 328 1Q24 325 1Q25 181

Reliability LIC Network Before After 0.0036 0.0034 Before After Feeder Reliability Index Feeder Reliability Index 1Q16 5.89 1Q16 1.88 1Q17 7.96 1Q17 2.25 1Q24 2.38 1Q25 2.38

Feeder 1Q16 currently runs along 21st Avenue and enters the network on 44th Street. The

feeder has four major branches: the first on 21st Avenue, the second on 30th Avenue, the

third on Skillman Avenue, and the fourth on 48th Avenue. Feeder 1Q24 will supply two

of the four branches, including the branches on 21st Avenue and 30th Avenue. Cubicle

24W will be used at the North Queens Substation to establish this feeder. The remaining

two branches on Skillman Avenue and 48th Avenue will remain on 1Q16.

Feeder 1Q17 currently runs along 21st Avenue and then enters the network on 44th Street.

The feeder has five major branches: the first on Berrian Boulevard, the second on 21st

Avenue, the third on 30th Avenue, the fourth on Skillman Avenue, and the fifth on 48th

5-19

Avenue. Feeder 1Q25 will supply two of the five branches including the branches on

Berrian Boulevard and on 21st Avenue. Cubicle 14E will be used at the North Queens

Substation to establish this feeder. The remaining three branches on Skillman Avenue,

30th Avenue, and 48th Avenue will remain on 1Q17.

These new feeders will require the installation of nine new manholes, 5,500 feet of

conduit, and 65 sections of primary cable. During the LIC event, feeder 1Q16 faulted

seven times and 1Q17 six times. The new feeders will help improve the performance of

the LIC network by balancing the load between new and existing feeders and increasing

feeder and transformer availability in the event of a future feeder failure.

5.8. Transient Study on Primary System

Overview In Long Island City, several faults occurred when operators attempted to re-energize a

feeder after it had been repaired. This condition is known as “close in, open auto”

(CIOA). There is a possibility that transient overvoltages during switching, which can

occur during fault inception, fault clearing, or subsequent re-energizing of cable, may be

responsible for contributing to the dielectric failure of the cables, joints, and transformers.

Siemens Power Transmission and Distribution, Inc. (PTI) was contracted to study these

overvoltages.

5.8.1. Electro-Magnetic Transient Program (EMTP) Study for Long Island City

An engineering study to simulate the transient overvoltages associated with the switching

operations of the 22 network feeders supplying the LIC network has been performed. The

purpose of the study was to determine the magnitude and duration of transient

5-20

overvoltages associated with various switching/fault events and compare them to the

dielectric- withstand capability of the cables, joints, and transformers. The objective of

the study was to identify whether switching operations may be correlated to failures

experienced during the event.

Con Edison initiated an Electro-Magnetic Transients Program (EMTP) study for the LIC

network to determine the magnitude of sub-cycle voltages during switching. Specifically,

the study focused on the impact of the direct current (DC) high potential (hi-pot) test and

the impact of “failed on test” cases that result in overvoltages on the remaining

components of the feeder.

5.8.2. Feeder 1Q21 and Bus-Section Trip

On July 17, 2006, at 18:48, the B-phase primary termination on network transformer

TM804 connected to feeder 1Q21 failed. Normally, this would result in feeder 1Q21

alone being isolated by its station breaker, however, the breaker (34W) did not operate as

designed (see Section 3, Chronology), which resulted in the bus back-up overcurrent

protection operating approximately 1.63 seconds after fault initiation.

The bus back-up overcurrent protection normally opens all breakers associated with the

bus. Breaker 34W (1Q21) and breaker 34E (1Q81), however, both had incomplete DC

trip circuits and failed to open. The fact that both of these breakers failed to open left the

unusual circuit configuration of feeders 1Q21 and 1Q81 isolated from the station source

but connected together through bus section 3S.

5-21

Feeder 1Q21 is a primary network feeder supplying 55 network transformers and two

high-tension customers, having a combined total of just under 40 MVA of connected

transformer capacity. The 27-kV windings on all of the transformers connected to

feeder1Q21 are delta connected. Also connected to the feeder is a 300-kVA shunt reactor.

The total primary cable length of feeder 1Q21 is 60,100 feet (11.4 miles), with a charging

capacitance of 1,064 kVARs.

Feeder 1Q81 is a non-network feeder connected to two independently owned gas turbines

(GT7 and GT8) via a 40-MVA generator step-up (GSU) transformer. This GSU

transformer is an autotransformer with no tertiary winding that would affect backfeed

voltages. Feeder 1Q81 also supplies a 15-MVA start-up transformer at a New York

Power Authority generator, as well as a 500-kVA unit connected to the generator

pressuring plant, both with 27-kV delta windings. GT 8 was on line at the time of this

incident, and GT 7 was off line. The total primary cable length of feeder 1Q81 is 7944

feet (1.5 miles) with a charging capacitance of 288 kVARs.

As a result of the bus section 3S event, the GT-8 generator came off line via generator

protection in less than a second. Because the associated 40 MVA GSU autotransformer

has no 27-kV breaker, however, it remained connected to Feeder1Q81.

Operational data from both breaker 34W (1Q21) and the 27-kV side of the

autotransformer indicated that during the bus section open auto, a backfeed condition

existed on 1Q21 for approximately 15 minutes.

5-22

PTI was engaged to perform an Electro-Magnetic Transient Program (EMTP) study on

this unusual backfeed situation. They modeled the backfeed condition assuming the worst

case of a single 500-kVA transformer backfeeding to the effectively combined 1Q21/81

feeder. Results of the study indicated that peak voltages on the unfaulted phases (A and C

phase) were not in excess of the voltages that would have been experienced during a back

feed on feeder 1Q21 alone.

5.8.3. Line to Ground Fault and Bus Section Outage Event Model Results

The models were completed for the single-line-to-ground fault (B phase) on 1Q21 and

bus section 3S outage event. Following are the preliminary results of the Siemens/PTI

EMTP study. NOTE: All are EMTP study results, except for Figure 5-2, which is the

station fault PQ recorder data from Transformer No.1 at the North Queens Substation. It

is provided for comparison against the EMTP results (Figure 5-1) for the same scenario.

5-23

Figure 5-1: (EMTP Study) Bus 3S voltage steady state then fault at 0.254 seconds. The temporary overvoltage (30.4 kV on phase C) continues for 1.7 seconds until the bus section clears.

(file f21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.00 0.02 0.04 0.06 0.08 0.10[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

5-24

Figure 5-2: (Station Fault Recorder PQ Data) – same as Figure 5-1

-30000

-20000

-10000

0

10000

20000

30000

0.00 0.02 0.04 0.06 0.08 0.10

NORTHQNS - 7/17/2006 18:47:38.563

EPRI Solutions/Electrotek PQView®

Volta

ge (V

)

Time (s)

Va Vb Vc

5-25

Figure 5-3: (EMTP Study) The temporary overvoltage increases to 38 kV on phases A and C when the bus section 3S clears. 1Q07 and 1Q15 open auto leaving 1Q21 and 1Q81 connected to bus 3S. The Gas Turbine 8 is still on line and all of the network protectors remain closed.

(file f21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.08 0.10 0.12 0.14 0.16 0.18 0.20[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

5-26

Figure 5-4: (EMTP Study) Same as Figure 5-3 except that 1Q81 trips off. TOV is 37 kV

(f ile b21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.08 0.10 0.12 0.14 0.16 0.18 0.20[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

5-27

Figure 5-5: (EMTP Study) GT 8 is off at 0.3 seconds in this simulation but the bus 3S temporary overvoltage remains about the same at 38 kV. Once the GT is off line, network protectors should start to open.

(file f21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.28 0.30 0.32 0.34 0.36 0.38 0.40[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

5-28

Figure 5-6: (EMTP Study) The simulated voltage of the back feed from a single 500 kVA network transformer is less than 1.00 per unit because of the impact of the No. 8 GSU, which acts as a grounding transformer. Note: The 1.00 per-unit voltage is 21.213-kV line-to-ground peak based upon 15-kV rms line to ground.

(file f21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.60 0.62 0.64 0.66 0.68 0.70[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

5-29

Figure 5-7: Without feeder 1Q81, the voltage from the back feed from a single 500-kVA network transformer would be about 39 kV (1.84 per unit).

(f ile b21e.pl4; x-var t) v:BUS3SA v:BUS3SB v:BUS3SC v:P1PU01 v:M1PU01 0.40 0.42 0.44 0.46 0.48 0.50[s]

-50.0

-37.5

-25.0

-12.5

0.0

12.5

25.0

37.5

50.0[kV]

Conclusions While results of the study indicated that peak voltages on the unfaulted phases (A and C

phase) were not in excess of the voltages that would have been experienced during a back

feed on feeder 1Q21 alone, the temporary overvoltage increased to 38 kV on phases A

and C when bus section 3S clears. Because this is within the BIL of the associated cable

and joints, it is unlikely that this event caused significant additional failures. It is

possible, however, that incipient failures (such as heat-sensitive cable splices) were

further damaged by the exposure to the higher voltages.

The B-phase current transducer on breaker 34W (1Q21) and the Watt/VAR transducers

on the 27-kV terminals of the 40 MVA auto-transformer both show the current gradually

5-30

declining from 28 A down to 0 A over a 15-minute period. Investigations will continue in

an effort to find an explanation for this gradual decline.

5.9. Secondary System

Overview This section analyzes the performance of the secondary system in the LIC network

through the various contingencies and estimates when and where damage on the

secondary occurred. To perform the post-LIC-event assessment on the secondary system,

load flows on the secondary system were simulated using the PVL model data as adjusted

to reflect known conditions. The results of the PVL analysis were compared with actual

damaged reported from the field to develop an estimated time line of secondary damage

and causes of customer outages.

5.9.1. Secondary-Cable Limiters

In a secondary-network system, such as the LIC network, low-voltage secondary-cable

limiters (electrical connectors with reduced and fusible midsections) are installed at

strategic locations, generally at the intersection of interconnecting secondary mains, to

isolate secondary cable faults. The limiters mitigate the possible damage to adjacent

cables that supply current to the fault and maintain the flow of power in the network.

They are not designed to operate during an N-2 criteria event.

To ensure reliability and minimize the effect of the harsh environment in underground

structures, the limiters are encased in the secondary-splice connection, as part of a sealed

unit with several connecting points. Their primary purpose is to protect the low-voltage

5-31

grid against severe faults or overloads on the secondary cable and prevent the fault from

spreading in multiple directions. While these limiters are designed to isolate a faulted or

severely overloaded cable from the grid, they do not operate for low-level arcing or

intermittent sparking conditions. The arcing fault, a relatively low-current fault, will

consume cable insulation, which eventually results in cable failures.

To ensure that each of the protective components in the low-voltage grid operates to

maintain the reliability of the network, limiters are designed to coordinate with the fuses

in the network protector switch. During backfeed conditions, the limiters should not

operate.

There are generally multiple sets of low-voltage secondary mains (cables) in an

underground-network grid. Under normal system conditions, the limiter, the network

protector fuse, and the network protector switch coordinate with each other. When a large

number of cables become isolated, because of either a fault or damage, these components

will not coordinate properly.

All network switch fuses and limiters are designed in accordance with Time Current

Characteristic (TCC) curves. These curves are plotted based on the actual laboratory tests

at 25 degrees Celsius (see Figure 5-8).

5-32

Figure 5-8: Sample Limiter TCC Curve

5.9.2. Secondary Modeling versus Actual Conditions

To simulate the sequence of events that occurred on the primary feeders in the LIC

network, the PVL load-flow cases were remodeled for the secondary system using known

system conditions. The system conditions include: removing defective transformers;

modeling transformers that were taken off the system (i.e., live end capped, cables cut,

and the cable end left ungrounded); and known open mains. The load for each load flow

was redistributed using actual RMS data from the LIC network event and the associated

time stamp for each network transformer on each primary feeder event.

5-33

To represent the secondary load, the network-load model reflected the Load Profile Data

System (LPDS) data for high-tension customers and the RMS data for all secondary

network transformers. The demand data was verified and adjusted when necessary

against the recorded network demand found on the System Operation Computer Control

System expansion (SOCCS-X) megawatt data recorder at the North Queens substation

bus. PVL cases were run sequentially for each primary-feeder event. For each primary-

feeder event, secondary-main sections were removed from the model for any cases where

the current flow in the secondary mains exceeded the time-current characteristics of the

cable limiters. For the subsequent case, secondary demand was re-estimated using RMS

and the modified secondary network model.

5.9.3. Model Limitations

The PVL model cases used to simulate the events assumed that all secondary mains were

equipped with limiters, which may be different from actual field conditions. Therefore,

the results of the simulation could result in a higher number of blown limiters than the

actual field conditions.

All load models in PVL are a constant kVA model. Within the N-2 design criteria, the

voltage change does not significantly change the load model. When the N-2 criterion is

exceeded, however, the amperes flowing on the secondary main might be exaggerated

and, as the voltage decreases, the model becomes less accurate. The constant kVA

situation is true for reactive loads, however, the voltage and current relationship varies

5-34

depending on the model used. Because the composition of the load on the grid is a mix of

different load types, the errors associated with a constant kVA model are reduced.

5.9.4. Analysis

A simulation of secondary network condition was performed for each primary feeder

outage and restoration. These results were then compared to the actual work performed

on the system as depicted in Figure 5-9.

Figure 5-9: Overload Model Analysis versus Actual Damage in LIC Network

After this initial simulation using the PVL program, a second scenario was run where the

current flow in the secondary mains was compared to the time-current characteristics of

the cable limiters to determine the location of operated limiters. Open mains (secondary

5-35

mains out of service) due to limiters isolating the cable sections, were removed from the

model for subsequent load flows. This scenario better represented the actual system

conditions during the event.

The actual damage was identified through field-response efforts during the customer

restoration process and follow-up field inspections. There were more than 500 manhole

inspections performed following the restoration effort. It has been determined that 377

secondary cable sections failed, 125 cable shunts were installed, and 67 transformer fuses

opened. The open-limiter information is not complete because there was no formal

method to track the limiter status during emergency response efforts. Field crews focused

on repairs such as secondary splicing, cable installation, and cable shunts.

The post-event model review identified additional cable sections that would have been

overloaded based on the sequence of events used in the network model simulation. The

difference between the actual damage and the model results is attributed to the model

limitations detailed above. Field inspection of the cable sections identified by the model

as “overloaded” has found that there was no actual damage in more than 80% of the

modeled cases.

5.10. Impact of feeder Outages on LIC Network Areas

To ease the analysis process, the LIC network was separated into five areas based on

mains and services (M&S) plates, as seen in Figure 5-10. As the contingencies

progressed, the secondary damage was assessed by the M&S plate groupings.

5-36

Figure 5-10: Area Impacted by LIC Event

The secondary system in the five affected areas was reviewed and analyzed to establish a

time line of the secondary system failures, and to gain a better understanding of the

secondary damage that occurred.

Each of the five areas was analyzed as an individual region, as well as plate by plate, to

5-37

determine the first case (when the event started) and worst case (when the most damage

occurred) for each area, using the feeder contingency cases as defined in Section 3:

Chronology.

To determine when damage to the secondary system started and when the damage

peaked, the local secondary system data on each M&S plate was compared to the primary

failure time line for transformers supplying the area. Areas with local primary failures

were compared to the documented records of secondary cable failures. A preliminary

assessment of secondary damage was made using all data sources available, such as

RMS, ECS, and Vision Mapping data base (mapping system). For instances where there

was insufficient information, the secondary-failure time was estimated to be when a

customer outage was reported. Equipment status was determined using the following

available data:

• Real-time transformer voltage and loading

• Telephone reports of manhole events (smoking, fire, and explosion)

• Records of installed shunt cables

• PVL models of secondary loading

• Results of blown limiter inspections

• Customer calls of power outages and voltage problems

• Records of transformers and mains in service

• System maps of secondary network (which show feeders supplying the network at all points)

Below are three scenarios that may result in secondary damage:

5-38

1. Network support removed: Feeder outages removed all local transformers from service, causing limiters to open. The area experiences outages, but relatively minimal secondary damage.

2. Island effect: Few transformers remain in service, and are subjected to large loads from the network. Transformers may subsequently exceed temperature rating, have fuses operate, fail internally, have damaged secondary cables, and/or cable limiters that operated.

3. Feeder restorations in severely affected areas: When single transformers are energized in an area with several transformers out of service, the associated secondary cables could exceed rated capacity because of the re-energized transformer not having sufficient support from the rest of the network.

The secondary modeling results for the five areas are summarized below:

5.10.1. Area One Secondary Event Summary

Secondary events began on July 17, 2006, at approximately 20:00 (Section 3: Case 7).

Initial problems were characterized by low voltage and overloaded mains, as modeled by

PVL after the event and supported by the initial reports of flickering lights and power

outages. During this initial case, few manhole events were reported and RMS data shows

that only one transformer exceeded its temperature rating

Further south, the significant cases occurred on the afternoon of July 18, 2006 (Section 3:

Cases 13 and 14), when the area lost feeder 1Q17 followed by feeder 1Q18. This case

was characterized by the following damage: three transformers exceeded ratings, two

secondary riser failures (underground cables that are run up utility poles to connect to the

overhead secondary cable), and several network protectors with fuses that operated. Four

plates with transformers that remained had “island” effects. PVL models indicate mains

operated beyond rated capacity in the area. All of Area One experienced low voltage,

5-39

supported by low voltage reports (80 tickets), and the secondary damage was localized to

the immediate vicinity of the few transformers still in service.

5.10.2. Area Two Secondary Event Summary

On July 17, 2006, a secondary-cable failure on M&S plate 67AE damaged feeder 1Q17

and feeder 1Q16. Secondary events began on July 17, 2006, at around 21:49 (Section 3:

Case 8) in the central part of Area Two. Low-voltage complaints and flickering lights

were reported from this area. Customers in the southwestern portion of Area Two

experienced outages caused by the feeder outages. On the morning of July 18, 2006, the

fifth contingency caused the loss of supply to many of the transformers supplying the

residential neighborhoods in parts of central Area Two. Smoking secondary mains were

reported during this time. While customers experienced low voltage, the secondary

damage was localized to the immediate vicinity of the few transformers still in service

because they were the remaining supply source for the local area.

Area Two was most impacted from 20:38 on July 18, 2006 (Section 3: Case 18) to 06:19

on July 19, 2006 (Section 3: Case 26). During these events, 8 to 10 feeders were out of

service and reported outages were greater. Based on the RMS data and field inspections

for limiters, it is believed that the few transformers, energized earlier in the day, became

isolated from the secondary system by limiters, fuses, or open mains. Several manhole

events and secondary burnouts were reported. The southeastern portion of Area Two

experienced low voltage conditions, since it was only partially affected by the feeder

outages.

5-40

5.10.3. Area Three Secondary Event Summary

Secondary events began on July 17, 2006, at approximately 21:00 (Section 3: Case 5) for

plates 72AF, 73AF, 72AG, and 73AG, located in the central part of Area Three. The

northwestern part of Area Three was only partly affected by the feeder outages. At

around 21:40 on July 17, 2006, the loss of five feeders resulted in a loss of supply to most

of the transformers supplying the area. While no manhole problems were reported,

several secondary burnouts were reported. The entire area experienced low voltage as

determined by customer calls on July 17, but secondary damage was localized to the

immediate vicinity of the few transformers still in service.

Area Three was the most impacted from 20:38 on July 18, 2006 (Section 3: Case 18) to

06:19 on July 19, 2006 (Section 3: Case 26). It experienced similar damage to that of

Area Two. Based on post-event review of RMS and ECS low-voltage tickets, the

southwestern portion of Area Three was experiencing low-voltage conditions.

5.10.4. Area Four Secondary Event Summary

Secondary events began on July 17, 2006, for all Area Four M&S plates, except those on

the southern border, which are primarily commercial. Most problems began in Case 8, at

approximately 21:49 on July 17, 2006. At this point, the loss of five feeders caused the

loss of supply to most or all of the transformers feeding M&S plates in the dense

residential neighborhoods located in the central and northern parts of Area Four. The

entire area experienced low voltage, however secondary damage was localized to the

immediate vicinity of the few transformers still in service, as these transformers were the

5-41

remaining supply sources for the area.

The worst interval for Area Four was from 20:05 on July 18, 2006 (Section 3: Case 15) to

06:19 on July 19, 2006 (Section 3: Case 26). During the night, 8 to 10 feeders were out of

service and area outages were reported. The few transformers that were still in service the

night before were either out of service or isolated from the secondary system via limiters,

fuses, or open mains. Some manhole events were reported. On the morning of July 19,

some secondary damage occurred as individual transformers were placed in service while

surrounding transformers were still out of service

5.10.5. Area Five Secondary Event Summary

Secondary events in Area Five began between 19:00 and 20:00 on July 17, 2006 (Section

3: Case 6). In most cases, secondary problems developed when feeder contingencies

removed a majority of the area transformers from service. Typically, damage began in

Area Five when about 60% of the transformers in a plate lost supply. Most M&S plates

experienced low voltage and some secondary cables were above rated capacity. One or

more transformers exceeded their temperature rating in 5 of 12 plates. Of the 12 plates

analyzed in Area Five, eight began to experience secondary damage before Case 8.

The worst case in Area Five occurred on July 18, 2006 (Section 3: Cases 11 to 23), when

a large number of feeders were out of service. In southern portion of Area Five, the worst

case occurred later, on the night of July 18, 2006, around Case 23. On average, 85% of

transformers on each plate were out of service at one time for the worst case. PVL

indicated secondary mains above rated capacity on most M&S plates, and five had one or

5-42

more transformers exceeding their temperature rating. In the worst-case scenario, four

transformers also failed. Manhole events did not occur until well after this case, when the

neighborhood feeders returned to service.

Considering the first and worst cases, it appears that secondary damage occurred mostly

while the network was transitioning into or out of multiple-feeder contingency

conditions. At first, when the network went into multiple contingencies, the remaining

transformers took on large additional loads, causing initial damage to the secondary

system. On July 19, 2006, since remaining cable sections and limiters supplied the

connected load in the area, the recovered transformers (as some feeders returned to

service) took on very high load levels and caused secondary damage. In some cases, the

transformers failed, contributing to additional feeder outages, and in other areas all

transformers went off line initially, which created a brownout or blackout condition. In

these cases, no secondary damage occurred in the beginning, but may have occurred as

feeders came back into service.

5.11. Secondary Events Impacting Primary

Six primary failures that have been attributed to secondary events were reviewed.

Through post-event modeling, it was determined that five of these events had secondary

sections with overloads that may have contributed to the failure. At one location, the

model also indicated that there were no overloads.

Event 1: SB1345 43-19 30th Avenue 1Q17 OA on July 17, 2006, at 15:50

1Q16 OA on July 17, 2006, at 16:22

5-43

Event one was studied in detail. A fire in SB1345 involving two sections of 3-500, 2-4/0

cable migrated from the service box into the wood duct system in the direction of

SB30112. Outside of SB1345, as reported by field crews, the wood duct system was in

direct contact with another wood duct system that contained feeders 1Q16 and 1Q17. The

failure of feeders 1Q16 and 1Q17 was caused by external heating from the secondary

electrical fire within the conduit system adjacent to SB1345. The ultimate cause of the

secondary fire is undetermined. The subsequent excavation of the damaged cable and

conduits revealed that the wood secondary conduits were stacked directly over the

primary conduit along 30th Avenue between 44th and 24th Streets.

Under projected peak load conditions with V9426 out of service, the review indicated

that the sections of secondary cable involved in the electrical fire in SB1345 were

marginally over the cable ratings at the time of failure. These two sections were projected

to be loaded to 105% and 108% of the emergency rating under peak load conditions.

Event 2: M820 Ditmars Boulevard and 45th Street 1Q02 OA on July 18, 2006, at 08:23

A sixth contingency was experienced on July 17, 2006, at 21:49, with 1Q01, 1Q07,

1Q16, 1Q17, 1Q20, and 1Q21 already out of service. The secondary mains (four sets of

3-500 cable) from M820 to TM6398 were calculated by the PVL study to be overloaded

by 143% of emergency rating. The secondary mains were overloaded for 11 hours and

subsequently caused the failure of feeder 1Q02. At 10:01, a smoking manhole condition

was reported in M820 located on Ditmars Boulevard and 45th Street.

5-44

Event 3: M14503 20th Avenue and 49th Street 1Q02 OA on July 18, 2006, at 08:23

In addition to the events in M820 described in Event 2 above, the secondary mains

sections (two sets of 8-4/0) from SB60970 and M14503 were overloaded by 176%

causing damage to feeder 1Q02 in MH14503.

Event 4: M8405 21st Avenue and 75th Street On July 17, at 20:40, a cut in open auto (CIOA) occurred on feeder 1Q16. A primary

section on 1Q16 was damaged caused by a burning secondary cable in the M8405,

located on 21st Avenue and 75th Street. According to the PVL study, there was an

overloaded secondary main section during the fourth (1Q16, 1Q17, 1Q07, 1Q21)

contingency on July 17, 2006, at 19:10, and fifth contingency (1Q16, 1Q17, 1Q07, 1Q07

and 1Q02) on July 17, 2006, at 19:48. Four sets of 3-500 cable from M8405 to V5582

became overloaded to 149% during the fourth contingency, and these cable overloaded to

193% during the fifth contingency.

Event 5: M2554 Newtown Avenue and 30th Street On July 17, at 17:11, a CIOA occurred on feeder 1Q21. The failure took place in a “two-

way-one-way” disconnectable splice between single-conductor EPR and XLPE insulated

cable on feeder 1Q21 in M2554, which was located on Newtown Avenue and 30th Street.

Based on field reports, the splice failure was caused by the burning of secondary cable.

During the fifth contingency on July 17, 2006 at 18:48, the secondary cable sections in

the structure were overloaded to 149% and 189%.

5-45

5.12. Secondary Network System – Alive on Back Feed

Overview

When a primary feeder goes out of service, the network protector switch on the low-

voltage secondary side of the transformer senses the reverse power current into the feeder

from the low-voltage network. Under these conditions, the network protector switch is

designed to open at low backfeed current levels to prevent this reversal of flow. In the

event that a network protector switch fails to open, it is also equipped with fuses that will

isolate the low-voltage secondary system from the transformer and the primary feeder.

These fuses are coordinated with the cable limiters that are on the secondary mains in

manholes and service structures such that the fuse will operate before the limiter during

backfeed conditions (see limiter section for design of limiters). If the network protector

switch and the fuses remain closed, the secondary mains continue to back feed into the

primary fault. This condition is called “alive on back feed” (ABF). Whenever a feeder

remains alive on back feed, it delays the fault-locating and repair process until the ABF

condition is found and eliminated. One means of clearing the back feed is to apply

grounds at the substation to blow the fuses at the network protector and isolate the feeder

from the secondary system. If this is not successful, the back feed has to be located by

field crews visiting the network switches. Long Island City feeders have an average of 54

switches per feeder, hence an ABF condition results in a considerable effort and delay in

restoring a faulted feeder.

There are three basic reasons a network protector switch fails to open. They can fail

because of a mechanical problem, an electrical problem, or insufficient voltage on the

secondary to operate the relays. A network protector is equipped with relays (either

5-46

electromechanical, microprocessor, or solid state) that control the operation of the

network protector. These relays operate the control motors and mechanical linkages

required to operate the network protector. A failure of any of the mechanical parts or

relays will cause the protector switch to remain closed.

During multiple network-feeder outages, the power flow in the secondary network can

cause limiters to open and isolate sections of the secondary cables from the grid. If

enough secondary cables are disconnected within an area in a network grid, the drop in

voltage on the secondary network may cause relays on the network protectors to become

inoperable because of insufficient current. This condition would prevent the network

protector switch from opening and the primary feeder will remain alive on back feed.

5.12.1. ABF Analysis

During the LIC event, seven primary feeders remained alive on back feed. These were

feeders 1Q02, 1Q13, 1Q15, 1Q16, 1Q17, 1Q18, and 1Q19.

In order to understand the conditions for ABF on these feeders, Con Edison completed

computer modeling to determine the secondary voltage levels and the backfeed current at

the transformers suspected of causing the ABF condition. As stated above, network

protector switches are equipped with one of the three types of relays. The microprocessor

relays can operate with a minimum of 13 volts on any one phase, the solid-state model

can operate on 50 volts on B-phase, and the electro-mechanical model requires a

minimum of 60 volts on all three phases.

5-47

The model, while useful in assessing primary feeder and transformer load flow, has some

distinct limitations when analyzing secondary-system conditions. One key limitation in

the simulations is that individual customer loads are aggregated at the transformer

locations and not at individual service points. This limits the accuracy of the predicted

load flow on the secondary mains. Another limitation is actual field conditions

experienced during the event that cannot be accurately modeled, such as voltage

reduction and unbalanced loading of the secondary system due to open fuses and cable.

With these limitations, the simulation model estimated approximately 61 volts on the

secondary grid during a 10th contingency. The model could not factor in the 8% voltage

reduction implemented in the network, therefore, the actual voltage could be lower. RMS

telemetry showed voltages as low as 26 volts for transformers with network protectors

indicated as closed. The RMS-measured voltage on those transformers was insufficient to

operate the solid-state and electro-mechanical relays.

The second criterion investigated was whether the backfeed current was sufficient to

operate the fuses in the network protector. Seven instances of feeders that were ABF

during the Long Island City contingency were modeled using PVL. The model was

refined to include secondary cables and transformers that were disconnected during the

event. In four of the seven cases, the backfeed current was not sufficient to operate the

network protector fuses.

During the first and second contingencies, there was sufficient backfeed current to

operate the network protector fuses. As the contingencies progressed to six feeders out of

5-48

service and beyond, the network switches did not have sufficient backfeed current

available to operate the network protector fuses.

Table 5-4 indicates the amount of backfeed current available for each case examined.

Table 5-4 Contingency Feeder Vault Fuse Rating

(A) Available Backfeed Current (A)

Fuses Should Operate

1 1Q15 VS5297 5,700 7,704 Yes 2 1Q16 VS8139 5,700 15,562 Yes 5 1Q02 TM5963 5,700 15,883 Yes 6 1Q02 TM6768 5,700 4,472 No 7 1Q17 TM950 5,200 770 No 8 1Q18 TM6056 5,700 769 No 9 1Q19 TM5989 5,200 1,598 No

As stated above, the company can employ a technique to clear an ABF condition without

searching for the closed switch. This technique is to apply a three-phase ground at the

substation on the feeder. Grounding phases is intended to draw sufficient backfeed

current from the secondary system to operate the relays or fuses in the network protector.

During the LIC event, the company applied a three-phase ground on four of the seven

ABF feeders. Of the four feeders subjected to this three-phase ground, only one ABF

condition (feeder 1Q16) was eliminated. This further confirms that sufficient backfeed

current was not available to operate the network protector fuses.

5-49

Long Island City Network Feeder ABF Duration

8:14

8:05

1:22

4:05

0:18

0:40

6:03

2:52

2:11

2:11

Monday, July 17 Tuesday, July 18 Wednesday, July 19 Thursday, July 20 Friday, July 21 Saturday, July 22 Sunday, July 23 Monday, July 24

1Q16

1Q02

1Q13

1Q18

1Q19

1Q17

1Q15

Feed

er

0

2

4

6

8

10

12

Con

tinge

ncy

Leve

l

Figure 5-11: Alive on Back Feed during Multiple Contingencies

Figure 5-11 illustrates that as the contingencies progressed past the sixth contingency,

more feeders tended to remain ABF for longer periods of time. When a sixth contingency

was reached on July 19, 2006, the ABF duration began to lengthen significantly.

In summary, as the events progressed to the sixth contingency and greater, it is

reasonably clear that insufficient backfeed current was available to operate the network

protector relays or fuses, which caused feeders to remain alive on back feed.

Conclusions Based on a review of the actual damage, the ECS-ticket activity, the manhole events, and

the post-event model assessment, the secondary cable and limiter damage peaked

between 20:00 on July 18 through 06:00 on July 19. When the secondary system

5-50

experienced elevated contingencies beyond the N-2 design criteria for extended periods,

the limiters opened, mitigating cable failures. While the primary function of the limiter is

to isolate a secondary cable fault, the heavy load currents experienced on the secondary

system during the Long Island City event resulted in an unusual amount of open limiters.

While there is no complete record of the limiter damage location and repairs, field

responders reported that manholes supplied by transformers and manholes with

intersecting mains experienced the most limiter damage. There were cable failures and

manhole events caused by the limiters not opening. In these cases, when high loads break

down the insulation, an intermittent arcing fault could be produced. This fluctuating

current will not produce current values high enough to open the limiter and will consume

the cable at the point of the arcing fault.

The manhole events were reviewed and the results indicate that most cable failures

occurred in the ducts. This is because of cable insulation breakdown from excessive

heating within the duct from the overloaded cables.

In addition, long-duration overloads experienced by transformer network protector fuses

changed the fuse-curve characteristics and resulted in failure. The weakening of the fuse

element resulted in a failure of coordination between the limiters and fuses during

extended overloads. The fuses failed before the limiters in approximately 60 cases.

5-51

The ability for network protectors to open and clear ABF was compromised during high

multiple-feeder contingencies, typically above a fifth contingency, and after the

secondary system experienced significant damage. This was probably because of the low

voltage experienced in the network. The transformer fuses are the back-up protection to

clear the feeder from the secondary system. However, when the LIC network was above a

fifth contingency, and there was significant damage on the secondary system, a ground

applied at the station could not generate enough backfeed current to open the fuses.

The high loads carried on the secondary system during the Long Island City event caused

manhole fires and burning within ducts. These events occurred because the limiters did

not open due to arcing faults.

5.13. Primary Cable, Splice and Termination Overview

The Long Island City network experienced 37 primary component failures from July 17

through July 25. Table 5-5, below, lists the 37 failures by component type with their

average age at the time they failed.

5-52

Table 5-5: LIC Event Component Failures This section of the report will review the primary cable, splice, and termination failures.

Con Edison’s analysis of the cable and splice failures showed that no new programs

specific to the LIC network or for the Con Edison system in general are required to

address the reliability of those primary feeder components. The company has previously

identified and is addressing problems related to components such as premolded

disconnectable 2W-1W (known as, 2 way–1 way) stop-joint splices through existing

programs.

5.13.1. Long Island City Network Feeder Composition

There are three basic types of cable in the LIC network: ethylene propylene rubber

(EPR), cross-linked polyethylene (XLP), and paper insulated lead covered (PILC). Table

5-6 lists the three cable types, the number of miles of each in the LIC network, the

percent of the network, and average age.

Component Failure Count (OA/FOT) Average Age Years

Cables 7 17

Splices 15 11

Terminations 2 Not Available

Transformers 13 32

Totals 37

5-53

Table 5-6: LIC Network Feeders - Cable Types

The LIC network primary feeder cable has an average age of 22 years compared to a

system-wide average of 25 years. Nearly 50% of the cable in the LIC network is EPR

cable with an average age of 10 years.

The entire Con Edison distribution system contains approximately 8,000 circuit miles of

primary feeder cable. Of these feeders, 27% is PILC cable and 73% is EPR and XLP

cable. Of the 73% that is EPR and XLP, there is about half of each type.

PILC is among the oldest type of cable in the Con Edison system. This cable is typically

constructed with the three phase conductors bundled together under a single lead sheath.

The phase conductors, which are usually copper, are individually insulated with oil-

impregnated paper tape. The sheath serves to protect the insulated conductors and

provide a path back to the substation for neutral current. Figures 5-12 and 5-13 present a

typical PILC cable construction.

Cable Type Miles Percent in LIC Ave. Age

PILC 39 13% 46

EPR 133 47% 10

XLP 113 40% 22

Totals 285 100% 22

5-54

Figure 5-12: Cross Section of PILC Cable Figure 5-13: Typical PILC Cable

The EPR and XLP insulated cable used in the underground distribution system is

typically constructed as a single insulated conductor covered by either a lead sheath or a

plastic jacket. When the cable does not include a lead sheath, a series of flat copper straps

is placed under the plastic jacket to provide a path back to the substation for neutral

current. This type of cable has been used on the primary feeder system since the late

1960s and has become the Con Edison standard for medium-voltage applications. Figure

5-14 shows the construction of a typical EPR distribution cable rated for 15 kV.

5-55

Figure 5-14: Typical EPR Cable Construction for 15kV

Table 5-7 shows the cable composition for each network in the Con Edison service area

by percent of cable type (PILC, EPR, or XLP) in that network. In Figure 5-15, the LIC

network is designated as 1Q. At 13%, the LIC network has one of the lowest percentages

of the older PILC cable on the Con Edison system. The cable in Table 5-7 listed as

“Other” is comprised of small quantities of rubber-insulated cable, overhead wire, and

cable in the database with no assigned cable type.

5-56

Table 5-7: Percent of Cable Type per Network

5.13.2. Long Island City Primary Feeder Splice Composition

There are approximately 5,000 primary feeder splices in the LIC network. A splice is

needed any time one section of feeder cable is connected to another. There are three main

types of splices: (1) solid, (2) stop-joint, and (3) lead-wipe.

Borough Network_ID EPR PAPER XLP OTHER

Brooklyn 1B 29.0% 33.1% 37.9% 0.0%

Brooklyn 2B 43.6% 26.4% 30.0% 0.0%

Brooklyn 3B 31.8% 39.6% 28.7% 0.0%

Brooklyn 4B 35.5% 21.7% 42.7% 0.1%

Brooklyn 5B 26.1% 15.5% 58.4% 0.0%

Brooklyn 6B 34.5% 25.7% 39.8% 0.0%

Brooklyn 7B 37.4% 20.2% 42.4% 0.0%

Brooklyn 8B 44.8% 7.7% 47.5% 0.0%

Brooklyn 10B 28.6% 38.3% 33.1% 0.0%

Brooklyn 11B 28.1% 13.2% 58.7% 0.0%

Manhattan 1M 61.6% 22.8% 15.5% 0.0%

Manhattan 2M 45.2% 28.9% 25.9% 0.0%

Manhattan 3M 63.0% 18.4% 18.6% 0.0%

Manhattan 4M 28.6% 41.7% 29.7% 0.0%

Manhattan 5M 29.7% 12.4% 57.9% 0.0%

Manhattan 6M 45.5% 28.0% 26.5% 0.0%

Manhattan 7M 44.3% 28.0% 27.7% 0.0%

Manhattan 8M 36.3% 27.8% 35.9% 0.0%

Manhattan 9M 34.5% 31.8% 33.7% 0.0%

Manhattan 10M 52.6% 21.5% 25.9% 0.0%

Manhattan 11M 49.9% 19.1% 31.0% 0.0%

Manhattan 13M 54.2% 21.4% 24.4% 0.0%

Manhattan 15M 65.0% 15.7% 19.3% 0.0%

Manhattan 16M 38.5% 28.3% 33.2% 0.0%

Manhattan 17M 54.1% 23.1% 22.8% 0.0%

Manhattan 18M 62.0% 0.0% 38.0% 0.0%

Manhattan 19M 33.8% 40.3% 25.9% 0.0%

Manhattan 20M 31.4% 39.4% 29.2% 0.0%

Borough Network_ID EPR PAPER XLP OTHER

Manhattan 21M 48.7% 20.5% 30.8% 0.0%

Manhattan 22M 32.1% 37.0% 30.9% 0.0%

Manhattan 23M 43.3% 28.1% 28.5% 0.0%

Manhattan 24M 40.4% 25.6% 33.9% 0.0%

Manhattan 25M 41.9% 27.2% 30.9% 0.0%

Manhattan 26M 31.6% 39.4% 29.0% 0.0%

Manhattan 27M 42.8% 14.6% 42.6% 0.0%

Manhattan 28M 17.9% 23.2% 58.9% 0.0%

Manhattan 29M 33.9% 20.4% 45.8% 0.0%

Manhattan 30M 50.8% 33.6% 15.6% 0.0%

Manhattan 31M 39.6% 23.6% 36.9% 0.0%

Manhattan 32M 35.4% 43.0% 21.6% 0.0%

Manhattan 34M 41.3% 20.2% 38.5% 0.0%

Manhattan 39M 41.8% 31.1% 27.0% 0.0%

Manhattan 40M 65.5% 12.5% 22.0% 0.0%

Manhattan 43M 37.1% 32.7% 30.2% 0.0%

Queens 1Q 47.4% 13.1% 39.5% 0.0%

Queens 3Q 29.6% 20.2% 50.1% 0.0%

Queens 5Q 36.1% 18.5% 45.2% 0.3%

Queens 6Q 34.5% 30.6% 34.6% 0.3%

Queens 7Q 45.0% 10.2% 42.2% 2.6%

Queens 9B 36.7% 22.4% 37.8% 3.0%

Queens 9Q 44.1% 22.4% 33.0% 0.5%

Bronx 1X 23.9% 37.7% 26.4% 11.9%

Bronx 2X 48.9% 27.4% 23.7% 0.0%

Bronx 3X 40.0% 36.3% 23.5% 0.2%

Bronx 4X 29.3% 41.8% 28.9% 0.0%

Bronx 5X 27.7% 40.2% 32.1% 0.0%

Bronx 7X 24.5% 28.9% 39.8% 6.8%

5-57

1. Solid Splice A solid splice is used to connect one polymeric cable (EPR or XLP) to another polymeric

cable. These are manufactured splices that are constructed with materials similar to the

insulation and are field assembled as a complete unit. They are called solid splices

because they do not require the addition of an insulating dielectric fluid. Solid splices

tend to be the newest on the system. There are four major types of solid splices based on

their construction and application: premolded, premolded disconnectable, heat-shrink,

and cold-shrink.

1a. Premolded Splice

Premolded splices are typically assembled with an insulating sleeve that slides over

the cable connector. They are used on single conductor cables requiring three

individual splices for three-phase distribution. Figures 5-15 and 5-16 show examples

of a typical premolded splices used on the Con Edison system.

Figure 5-15: Fully Assembled Premolded Splice

5-58

Figure 5-16: Cut-Away Premolded Splice

1b. Premolded Disconnectable Splice

The cables using a premolded disconnectable splice connect through a removable

insulated yoke, or bus bar, to facilitate disassembly in the field. To assemble this

splice, lug connectors are attached to the conductor of each cable and then each

cable is bolted to one end of the yoke through the lug. An insulation sleeve is then

slid over each connection point to insulate and protect the assembly.

These splices are usually used in a “Y” configuration where two legs of the “Y”

are the main-run cable and the third taps off the main run to supply a network

transformer or an isolated feeder spur. In Con Edison nomenclature, a “Y” splice

is designated as a 2W-1W because one end of the splice connects one cable and

the other end connects two cables. In this application, disconnecting a leg from

the splice can easily isolate a faulted transformer or a failure on a spur. The rest of

the feeder can then be put back into service to continue supplying the network

load.

5-59

1c. Heat-Shrink Splice

Heat-shrink splices are constructed by shrinking heat-activated sleeves over the

connecting cables. These concentric sleeves are shrunk over each other with each

individual sleeve providing either electrical-stress control or insulation. The

manufacturer also provides a special moisture barrier tape that is applied over

moisture-sensitive areas inside the splice. The heat used to shrink the sleeves is

supplied from a hand-held propane torch.

In the LIC network, heat-shrink splices are used primarily to connect one single

conductor polymeric cable to another. In Con Edison nomenclature, this splice

configuration is designated as a 1W-1W (known as, 1 way – 1 way) because each

end of the splice connects only one cable.

A cross sectional representation of a typical 1W-1W solid heat-shrink splice is

shown in Figure 5-17.

5-60

Figure 5-17: Typical 1W-1W Heat-Shrink Splice

1d. Cold-Shrink Splices

Cold-shrink splices, much like heat-shrink splices, are constructed by shrinking

concentric sleeves over the cable connector. Cold-shrink splices, however, are

pre-stretched over a removable plastic core that expands the splice sleeves greater

than their “shrunk-down” diameter. The core, with the sleeve, is slid over the

connector area and removed, causing the sleeves to shrink over the connected

cables. This type of construction is called cold-shrink because heat is not required

to shrink the insulating sleeves.

In the LIC network, all cold-shrink splices have a 1W-1W configuration. Figure

5-18 show a typical cold-shrink splice installation on a 27-kV feeder. The core

and shrink sleeves have been positioned over the cable connector area.

5-61

Figure 5-18: Cold-Shrink Splice Installation

2. Stop-Joint Splice

A stop-joint, or transition, splice is used to connect a polymeric cable to a PILC cable.

Because the dielectric fluid (usually a mineral or synthetic oil) in the PILC cable can

degrade the polymeric insulation over time, a stop-joint incorporates an oil-stop feature to

hold the oil inside the PILC cable. These splices have their origins in the 1970s when

there was a move away from PILC cable to polymeric (solid dielectric) cable. Instead of

segregating these very different types of cables, many utilities chose to replace the PILC

cable on a section by section. This replacement strategy required the use of stop-joint

splices where the PILC cable was connected to the newer solid dielectric cable.

The type of stop-joint splice currently installed on the Con Edison system is the heat-

shrink splice shown in Figure 5-19. The oil-stop feature employed on this splice is a clear

plastic tube shrunk over the exposed paper tapes. The oil stop keeps the PILC cable oil

5-62

from migrating over the cable connector to contaminate the polymeric insulation on the

solid dielectric cable. Figure 5-19 also shows a cut-away Raychem 3W-1W transition

splice. A 3W-1W (known as, 3 way – 1 way) splice has one cable (in Figure 5-19, a

three-conductor/three-phase PILC cable) spliced to three cables (in Figure 5-19, three

single-conductor/single-phase EPR cables). Note the clear oil-stop tube shrunk over the

PILC cable insulation.

Figure 5-19: 3W-1W Stop-Joint

A heat-shrink stop-joint is also used to connect single conductor PILC cable to single

conductor polymeric cable. This splice is installed in a 1W-1W configuration and uses

the same oil-stop feature as the 3W-1W stop-joint splice.

Older types of transition splices that are still in service on the Con Edison distribution

system include the 2W-1W stop-joint splice. This splice is usually used to connect a

polymeric main cable run to a PILC cable spur or tap-off to a network transformer. It has

all the features of the premolded disconnectable splice shown in Figure 10, with the

inclusion of an oil stop on the PILC cable leg.

These early stop-joints were constructed from a 2W-1W premolded disconnectable

splice, manufactured by Elastimold, fitted with an oil-stop feature. The oil stop was built

5-63

up with overlapping layers of rubber adhesive, silicone tape, rubber insulating tape,

semiconducting tape, and plastic tape. The use of these splices was discontinued by 1999.

3. Lead-Wipe Splice A lead-wipe splice connects one lead covered cable to another. These are the oldest

splices on the system and usually connect PILC cable. There are some lead-wipe splices

that were used with early vintage lead-covered XLP or EPR cable, but as the solid

dielectric splices became available, the use of lead-wipe splices in these applications was

discontinued.

A lead-wipe splice is constructed by soldering a lead sleeve over the connector area

between the two cables. The ends on the lead sleeve are soldered to the lead jacket of

each cable to seal the splice and provide electrical continuity to the lead sheath. The

splice is typically filled with a dielectric fluid to prevent partial discharge from occurring

inside the splice cavity.

Figure 5-20 is a design drawing for a typical lead-wipe splice. Note the lead sleeve

soldered over the cable sheath.

5-64

Figure 5-20: Typical Lead-Wipe Splice

Table 5-8-a: Splice Composition of Networks

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

01B 22 771 35.05 40.93 14 1652 75.09 11.94 23 638 29.00 8.96 8

02B 16 642 40.13 44.52 8 1999 124.94 8.65 14 440 27.50 7.66 10

03B 16 770 48.13 43.64 5 1271 79.44 10.09 22 548 34.25 8.16 4

04B 16 737 46.06 41.64 6 3164 197.75 11.07 1 334 20.88 7.99 21

05B 12 367 30.58 42.14 17 2259 188.25 15.63 3 295 24.58 8.65 12

06B 18 727 40.39 44.59 7 2366 131.44 10.81 10 595 33.06 8.91 5

07B 12 294 24.50 41.70 21 1454 121.17 11.36 16 234 19.50 8.41 23

08B 12 158 13.17 42.06 36 2333 194.42 10.98 2 166 13.83 8.28 38

09B 18 672 37.33 39.55 12 2522 140.11 13.61 6 406 22.56 10.62 17

10B 12 659 54.92 38.56 4 1169 97.42 11.30 17 428 35.67 8.72 2

11B 10 187 18.70 38.45 28 1401 140.10 14.66 7 148 14.80 9.30 35

01M 20 302 15.10 47.81 32 1307 65.35 7.59 24 260 13.00 8.57 40

02M 28 659 23.54 42.03 24 1804 64.43 8.37 25 641 22.89 8.75 16

03M 29 812 28.00 43.16 18 3784 130.48 9.33 11 628 21.66 10.54 20

04M 24 410 17.08 44.74 31 636 26.50 13.47 53 382 15.92 9.96 29

05M 16 87 5.44 44.26 53 703 43.94 13.64 32 127 7.94 9.27 51

06M 24 314 13.08 39.14 37 880 36.67 8.39 39 355 14.79 8.37 36

07M 24 445 18.54 38.46 29 1265 52.71 8.68 29 358 14.92 9.14 34

08M 23 292 12.70 37.66 38 787 34.22 10.42 44 266 11.57 10.01 44

09M 12 96 8.00 36.51 47 227 18.92 10.96 56 110 9.17 10.74 49

10M 16 213 13.31 41.33 35 980 61.25 9.36 26 248 15.50 8.62 31

11M 18 160 8.89 37.14 45 685 38.06 9.32 37 194 10.78 8.40 45

13M 27 158 5.85 38.58 51 689 25.52 5.78 54 242 8.96 7.30 50

15M 12 67 5.58 39.49 52 362 30.17 6.55 49 71 5.92 8.44 55

16M 24 281 11.71 38.23 39 791 32.96 8.90 45 315 13.13 8.48 39

17M 20 282 14.10 41.79 33 1178 58.90 9.86 27 311 15.55 8.69 30

18M 8 2 0.25 22.00 57 336 42.00 8.25 34 7 0.88 19.71 57

19M 12 293 24.42 44.02 22 358 29.83 12.51 50 186 15.50 11.33 32

20M 12 264 22.00 38.95 26 393 32.75 11.79 46 220 18.33 11.62 25

Network ID

Number of

Feeders

Solid Dielectric Splice Stop-JointLead-Wipe Splice

5-65

Table 5-8-b: Splice Composition of Networks

Tables 5-8 a and b show that more than 75% of the primary splices in the LIC network

are the solid dielectric type with an average in-service age of less than 10 years. With

only 13% PILC cable and more than 75% solid dielectric splicers, the LIC network is a

relatively young network.

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

Number of Splices Splice/Feeder Average Age

YearsNetwork Ranking

21M 14 109 7.79 36.38 48 643 45.93 10.26 31 178 12.71 9.47 42

22M 12 140 11.67 37.47 40 328 27.33 10.60 51 193 16.08 10.13 28

23M 13 129 9.92 40.73 43 447 34.38 8.65 43 197 15.15 8.86 33

24M 24 214 8.92 40.11 44 827 34.46 11.44 42 303 12.63 10.25 43

25M 12 164 13.67 40.08 34 520 43.33 11.58 33 153 12.75 10.15 41

26M 12 331 27.58 41.31 19 436 36.33 10.87 40 263 21.92 9.97 19

27M 24 76 3.17 39.61 56 644 26.83 12.69 52 121 5.04 8.92 56

28M 12 122 10.17 40.08 42 562 46.83 17.37 30 219 18.25 12.47 26

29M 16 97 6.06 38.11 50 488 30.50 11.78 48 116 7.25 10.57 53

30M 12 65 5.42 38.72 54 189 15.75 4.59 57 118 9.83 7.91 48

31M 12 131 10.92 36.05 41 494 41.17 11.28 35 120 10.00 11.74 46

32M 8 191 23.88 42.39 23 277 34.63 8.57 41 163 20.38 10.26 22

34M 12 59 4.92 34.00 55 374 31.17 10.59 47 88 7.33 8.64 52

39M 8 70 8.75 35.67 46 182 22.75 8.00 55 79 9.88 7.11 47

40M 18 117 6.50 48.39 49 676 37.56 6.87 38 108 6.00 10.35 54

43M 12 220 18.33 37.87 30 493 41.08 11.16 36 167 13.92 9.90 37

01Q 22 509 23.14 39.10 25 3707 168.50 9.90 5 529 24.05 10.26 14

03Q 16 596 37.25 37.97 13 2182 136.38 15.25 8 460 28.75 11.10 9

05Q 28 741 26.46 37.58 20 3529 126.04 14.16 13 509 18.18 10.54 27

06Q 15 864 57.60 40.44 2 1947 129.80 12.13 12 376 25.07 9.74 11

07Q 24 485 20.21 36.25 27 4345 181.04 12.29 4 449 18.71 9.75 24

09Q 10 344 34.40 41.04 15 1347 134.70 9.80 9 302 30.20 10.09 7

01X 12 697 58.08 39.78 1 1054 87.83 14.28 18 507 42.25 12.57 1

02X 15 600 40.00 45.60 9 1823 121.53 8.93 15 520 34.67 11.58 3

03X 22 854 38.82 43.83 10 1831 83.23 9.65 19 514 23.36 11.13 15

04X 15 826 55.07 46.27 3 1194 79.60 12.22 21 485 32.33 12.39 6

05X 12 454 37.83 41.63 11 647 53.92 12.17 28 292 24.33 12.05 13

07X 19 629 33.11 39.83 16 1517 79.84 13.50 20 419 22.05 12.79 18

Stop-JointNetwork

ID

Number of

Feeders

Lead-Wipe Splice Solid Dielectric Splice

5-66

5.14. Component Failures and Autopsy Results in the LIC Network, July 17 through July 25, 2006

This section presents the findings of the analysis Con Edison conducted of the LIC

primary component failures. The analysis covered primary cable, splice, and termination

failures that occurred in the LIC network from July 17 at 1550, through July 25.

Table 5-9 is a table of the primary cable, splice, and termination failures during the LIC

event. The data show that the ratio of splice to cable failures was about two, which,

historically, is typical for heat waves similar to the weather conditions during the LIC

event. The average age of the cable failures in the LIC event, 17 years, is considerable

lower than the 31 years seen system wide. This is due, in part, to the relatively newer

cable in service in the LIC network.

Tables 5-16a-d list all feeder outages during the LIC event, including cable, splice, and

termination failures.

Table 5-9: LIC Event Component Failures

Component Failure Count (OA/FOT)

Average Age Years

Cables 7 17

Splices 15 11

Terminations 2 Not Available

Totals 24

5-67

5.14.1. Cable Failures

Table 5-10 is a breakout of the primary cable failures during the LIC event by insulation

type. As has been typical in recent years, failures of PILC cable sections were low, with

only one failure due to damage sustained from a collapsed conduit.

Table 5-10: LIC Event Cable Failures

Table 5-11 lists the LIC event cable failures by the cause and location of failure. Six out

of the seven cables, or 86percent, are known to have failed due to causes external to the

cable. Three EPR and two XLP cables were damaged from fire, and one PILC cable was

damaged by a collapsed conduit. One failed EPR cable was never recovered, so no

specimen was available for examination. No cable sections were known to have failed

due to dielectric breakdown of the insulation.

Cable Type Insulation

Failure Count (OA/FOT)

Average Age Years

EPR 4 4

Paper 1 59

XLP 2 22

Totals 7 17

5-68

Table 5-11: LIC Event Cable Failures by Cause and Location

Six primary component failures caused by damage from secondary fires occurred during

the LIC event. Four of these failures involved cable sections and two were splices. Table

5-12 lists the primary failures caused by secondary burnouts.

The secondary mains involved in the July 17 failures of 1Q17 and 1Q16 were only 3% to

6 % over their first contingency ratings. These marginal overloads, by themselves, do not

usually result in cable insulation damage. These secondary mains most likely had a pre-

existing condition that lead to the fire.

Cable Type Insulation

Failure Count OA/FOT Failure Cause Count Failure Location

1 Duct between manholes

2 Manhole

Not examined, lost 1 Duct between manholes

Paper 1 Defective duct 1 Duct between manholes

Manhole fire, other that secondary 1 Transformer

manholeDamaged by

secondary fire 1 Duct between manholes

XLP 2

Damaged by secondary fireEPR 4

5-69

Primary failures due to secondary fires account for approximately 5% of all cable and

splice failures system wide. During the LIC event, 16% of primary component failures

were attributed to secondary cable fires.

Table 5-12: Primary Failures Cause by Secondary Fires

Cable Failure Details (failure IDs can be referred to Table 5-16 a-d) Feeder Outage 1Q17 on July 17 at 15:50, ID 75500 At 15:50 on July 17, feeder 1Q17 opened auto due to a fault. The outage was attributed to

a secondary cable fire that damaged a section of single conductor cable between

manholes M11711 and M11645 (see Figure 5-21). The damaged was incurred on a 2/0-

XLP.

This cable run was located on 30th Avenue between 44th and 43rd Streets in Queens. At

the time of the 1Q17 failure, there were reports of manhole and service box fires in the

Feeder Date & Time Equipment Oveloaded Mains

Structure Number Locaion

1Q17 7/17/2006 15:50 Cable Yes M11711 Conduit

1Q16 7/17/2006 16:22 Cable Yes M11711 Conduit

1Q02 7/18/2006 8:24 Cable Yes M820 Manhole

1Q02 7/18/2006 8:24 Splice Yes M14503 Manhole

1Q21 7/18/206 17:11 Splice No M2554 Manhole

1Q16 7/18/2006 21:49 Cable Yes M8405 Manhole

5-70

area around M11711 (emergency ticket QE06028057 was issued). There was one report

of a fire at service box SB1345 on 30th Avenue between 44th and 43rd Streets that

damaged two vehicles parked over the structure. This service box is located 120 feet west

of M1171. Figure 5-21, Conduit and Duct Occupancy Plate Q67AE, contains details of

the structure and conduit layout.

The damaged section between manholes M11711 and M11645 was located in a conduit

adjacent to the burning service box SB1354. It was reported that construction crews cut

and capped (live end-cap) the feeder in manhole M11711 at 22:02.

A visual failure examination, or autopsy, was performed on a sample of the failed cable

by Cable Technology Laboratories, Inc. The autopsy was performed at the Con Edison

Cable and Splice Center for Excellence. The cables (three-phase legs) showed evidence

of exposure to high temperatures from an external source. From all available evidence,

Con Edison concluded that the failure was caused by the secondary cable fire.

The results from the visual failure analysis are consistent with the secondary events

reported in ticket QE06028057. Field forces reported fires in SB1345, which the conduit

plate, shown in Figure 5-21, shows as directly above or adjacent to the conduit that

carried feeder 1Q17. Field crews also reported that both the primary and secondary cable

conduits involved in this incident were constructed of wood. The wood conduits were

initially found to be burning due to failing secondary cable.

5-71

Field crews reported that at the location of the 1Q17 (as well as the 1Q16) failure, the

wood secondary conduits were stacked directly over the primary conduit. The proximity

of the primary cable to the burning secondary cable and conduits supports the assertion

that fire from the burning secondary cable caused the failure of 1Q17. A visual inspection

of manhole M11711 showed the secondary conduit at least two feet above the primary

conduit at the west wall. The failure of the feeder was not related to any conditions found

in that structure.

The manhole, M11711, was last inspected on February 6, 2006. The inspection report

recommended the replacement of a set of secondary cable mains. A subsequent

inspection of the manhole after the event indicated that the set of mains targeted for

replacement were not involved in the incident. Their condition was noted as not being of

immediate concern.

5-72

Figure 5-21: Conduit and Duct Occupancy Plate Q67AE for M11711

Prior to July 17, the electric facilities in SB1345 consisted of four sets of mains cable,

one building service, and one streetlight service. The cables in SB1345 consist of (see

Figure 5-22 for layout):

1Q17 and 1Q16 damaged here.

5-73

• 1 set of 8-4/0 copper mains cable running west to M11645 tied locally in the

structure.

• 1 set of 3-500 2 4/0 copper mains cable running east to M30112 tied locally in the

structure.

• 1 set 4-4/0 copper service cable serving a building in a parochial school complex

located 43-19 30th Avenue tied to the local mains sets.

• 1 set 2 #4 aluminum streetlight service cable serving a streetlight on the south side

of 30th Avenue 83 feet from the service box.

• 1 set of 8-350 aluminum mains cables running west to M11645 tied express in the

structure.

• 1 set of 3-500 2 4/0 copper mains cable running east to M30112 tied express in

the structure.

At the time of the secondary incident in SB1345 (ticket QE06028057), a 1000 kVA

transformer (V9426) located at the corner of 43rd Street and 30th Avenue (see Figure 5-22

for the layout details) was off the system due to defect. This transformer was removed

from the system on July 12. The transformer in V9426 was identified as defective and

dropped from the system via a live end-cap in M11645. The engineering evaluation

indicated that dropping the transformer in V9426 with a live end-cap was acceptable.

There were additional transformers in the area that were out of service but no reported

open mains (secondary cable out of service).

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The closest nearby transformer off the system, in addition to V9426, was V5447. The

transformer in V5447 is a 500-kVA transformer located at 25th Avenue and 42nd Street.

The engineering evaluation indicated that there would be no impact to the system with

this transformer out of service.

Figure 5-22 shows the secondary mains and services detail of V9426 and its proximity to

service box SB1345.

Figure 5-22-: V9426 Mains and Services

To determine if loading in the area and dropping V9426 from the system was a

contributing factor in the electrical fire in SB1345 that damaged feeder 1Q16 and 1Q17, a

detailed secondary-load flow analysis was conducted for the area surrounding SB1345,

including V9426.

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This study indicated that the sections of secondary cable involved in the electrical fire in

SB1345 were marginally over the cable ratings at the time of failure. The two sections of

cable (three single 600-volt, 500-kcmil EPR cables with 2 4/0 bare neutrals) from

M30112 to SB1345 that failed were 3% to 6% over their first contingency rating. These

cables ran in a conduit system that was common with feeders 1Q16 and 1Q17. While

these cables may have exceeded their rating for some period before the failure, Con

Edison’s experience with secondary distribution cables shows that the high load alone

was not sufficient to have caused a catastrophic cable failure. The cable most likely had a

preexisting condition that contributed to the failure.

Additional tests were performed on the 1Q17 failure samples at Cable Technologies

Laboratories, Inc. These included:

• stripping tension

• dimensional analysis

• volume resistivity

• microscopic examination

• water tree count

The additional tests found no abnormalities and indicated that the insulation was in very

good condition.

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Feeder Outage 1Q16 on July 17 at 16:22, ID 75501 On July 17, feeder 1Q16 opened auto due to a fault. The outage was attributed to a failed

section of single conductor cable between manholes M11711 and M11645. This cable

run was located on 30th Avenue between 43rd and 44th Streets and was adjacent to feeder

1Q17, which had failed one-half hour earlier.

Both 1Q16 and 1Q17 failed during the same event and for the same reason: damage due

to a secondary cable fire. For details on the 1Q16 failure, see above section on the July 17

failure of 1Q17 (ID 75500).

Additional tests were performed on the 1Q17 failure samples at Cable Technology

Laboratories, Inc. These included:

• stripping tension

• dimensional analysis

• volume resistivity

• microscopic examination

• water tree count

• ac five-minute step breakdown test

The tests found no abnormalities beyond those that were the result of the fire damage.

The cable section withstood the 92,000 volts in the ac-breakdown test before the cable

terminations “flashed over.” That is six times the normal operating voltage level of that

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cable. This result shows the good condition of the insulation on the intact portion of the

cable.

Feeder Outage 1Q01 on July 17 at 21:56, ID 75507 On July 17, at 21:56, feeder 1Q01 experienced a cut-in open auto (CIOA). This outage

followed an automatic breaker operation at 21:49 on the same day that an unsuccessful

attempt was made to re-energize the feeder after a seven-minute outage. The failure

occurred in manhole M820, located on the northwest corner of Ditmars Boulevard and

45th Street, on a single conductor 500-kcmil EPR cable. The failed cable was

manufactured by BICC General and installed in 2000. A specimen for this fault was not

recovered for a visual examination.

The feeder was repaired by replacing the damaged cable in M820. The feeder was

energized on July 18 at 20:53.

Feeder Outage 1Q02 on July 18 at 08:23, ID 75549 On July 18, feeder 1Q02 opened auto due to a fault. The failure occurred on a single-

conductor 2/0 EPR cable section installed in manhole M820 in 2005. The cause of the

primary cable failure was damage from a secondary cable fire.

The manhole was located on the corner of Ditmars Boulevard and 45th Street. On July 18

at 10:01, a smoking-manhole condition was found in M820 and reported in ticket

QE06028609. Field crews reported damage to the single-conductor cable connected to a

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premolded disconnectable joint on July 18 at 12:18. The construction permit requested a

live-end cap in M820 to drop one transformer bank. The feeder was energized on July 18

at 13:09.

At the time of the outage, the network was in a fifth contingency with feeders 1Q01,

1Q16, 1Q07, 1Q20, and 1Q21 out of service. A load-flow study of the area surrounding

M820 found four sets of secondary mains from M820 to TM6398 overloaded by 43%.

The overloaded condition most likely damaged the secondary cable and caused the fire in

M820.

Cable Technology Laboratories, Inc. performed a visual examination of the failure at the

Con Edison Cable and Splice Center for Excellence. The autopsy results of the cable

specimen submitted from M820 attributed the fault to damage from a secondary cable

fire. This autopsy is consistent with the emergency ticket generated as a result of a

smoking manhole in M820.

A safety inspection of M820 was performed on April 4, 2006. No abnormalities were

reported.

Additional tests were performed on the 1Q02 failure samples at Cable Technology

Laboratories, Inc. These included:

• stripping tension

• dimensional analysis

• volume resistivity

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• microscopic examination

• water tree count

• ac five-minute step breakdown test

The tests found no abnormalities except those that resulted from the fire damage. The

cable section withstood the 92,000 volts in the ac breakdown test before the cable

terminations “flashed over,” which is six times the normal operating voltage level of that

cable. This result shows that the unburned portion of the cable insulation was in

acceptable condition. Cable Technology Laboratories, Inc. reported that, overall, all

tested cable characteristics demonstrated the good performance of the cable.

Feeder Outage 1Q12 on July 18 at 20:32, ID 75564 On July 18, feeder 1Q12 opened auto at 20:32 due to a fault. Subsequent cable damage

was caused by a transformer failure in transformer manhole TM838 located on 30th

Street, 32 feet north of Broadway.

The transformer failure resulted in a tank rupture and manhole fire that damaged the

primary cable on the high-voltage side of the transformer. On July 19, at 03:04, a fault

was found on single-conductor, cross-linked polyethylene (XLPE) insulated cable. The

cable fault was attributed to the transformer failure and resultant fire. A visual failure

examination was performed at the Con Edison Cable and Splice Center for Excellence.

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Feeder Outage 1Q16 July 18 at 21:49, ID 75566 On July 18, at 21:50, feeder 1Q16 tripped off line due to a cut-in open auto (CIOA). This

outage followed an automatic breaker operation at 20:38 on the same day. The failed

component was a single conductor 2/0 EPR cable installed in 2002. The cause of failure

was attributed to damage from a secondary fire in manhole M8405. A visual examination

of the failed cable was performed at Con Edison Cable and Splice Center for Excellence.

A load-flow analysis indicated overloaded secondary mains in the area surrounding

M8405. At 19:48, under a fifth network contingency, mains cables in M8405 were

overloaded by 93%. When 1Q16 opened auto at 20:33, the network was put onto a tenth

contingency. The overloaded mains cables most likely caused the fire in M8405 and

damaged the primary cable.

On July 19 at 12:02, a permit was issued to repair damaged cable in manhole M8405. The

feeder experienced several DC hi-pot test failures (FOTs) before being returned to service

on July 21 at 07:48.

Feeder outage 1Q01 on July 19 at 11:39, ID 75596 On July 19 feeder 1Q01 opened auto at 11:39 due to a feeder fault. The feeder outage was

attributed to a failed 3-conductor 2/0 PILC cable manufactured by Phelps Dodge. The

failed cable was located between M1892 and M15263, on the west side of Steinway

Street opposite 25th Avenue. An inspection of the failed component determined that the

damage was the result of a defective duct. The Con Edison Cable and Splice Center for

Excellence performed the visual inspection of the failed cable.

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A work permit was issued on July 20 at 12:47 to replace the defective cable section. After

the cable replacement, the feeder failed a DC hi-pot test. This FOT was caused by the

failure of a single conductor splice in manhole M1593. The feeder was returned to

service on July 21 at 08:00.

Table 5-13: LIC Event Splice Failures

5.14.2. Splice Failures

Table 5-13 lists the LIC event splice failures. Stop-joints splices accounted for more than

half the splice failures, although they make up only about 8% of the LIC network splice

population. The five premolded disconnectable 2W-1W stop-joints that failed during the

LIC event were all manufactured by Elastimold. These splices have not been installed on

the Con Edison system since 1999 and are currently targeted for removal. The heat-shrink

3W-1W stop-joints were manufactured by Raychem and are currently being installed on

the Con Edison distribution system.

Failures 5 4 1 4 0 1

Average Age Years 14 13 Not Available 6 0 1

Cold Shrink

Premolded 2W-1W

Heat-Shrink 3W-1W Premolded

Solid Dielectric Joints

Lead-Wipe Paper Heat

Shrink

Stop-Joint

LIC Joint Failures

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Component Failure Rate Failure Units

PILC Cable 0.23 Failures/100 sections

EPR Cable 0.07 Failures/100 sections

XLP Cable 0.12 Failures/100 sections

Paper-Paper Lead-Wipe splice 0.19 Failures/100 joints

Solid Dielectric Splices 0.12 Failures/100 joints

ALL Stop-Joint Splices 0.80 Failures/100 joints

Raychem 3W-1W Stop-Joint 0.95 Failures/100 joints

Elastimold 2W-1W Stop-Joint 2.78 Failures/100 joints

Distribution Component Failure Rates

Based on the summer failure rates of both types of stop-joint splices, one could expect

that at least three Elastimold 2W-1W stop-joints and three Raychem 3W-1W stop-joints

would fail. In fact, this event had five Elastimold failures and four Raychem failures.

These two types of stop-joint splices, Elastimold 2W-1W and Raychem 3W-1W, have

historically provided a lower level of performance when compared to other splice

designs. The LIC network, however, contains fewer than 100 of the Elastimold 2W-1W

stop-joints and approximately 300 of the Raychem 3W-1Ws. This compares to almost

1,000 Elastimold 2W-1W stop-joints and 11,000 Raychem 3W-1W stop-joints system

wide.

Table 5-14 shows the 2005 system-wide summer failure rates for the Raychem and

Elastimold stop-joint splices, as well as other major distribution components.

Table 5-14: Distribution Component Failure Rates

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The first installations of the Elastimold 2W-1W stop-joints began as XLP cable become

more prevalent on our primary system. As previously discussed, these stop-joints have an

oil-stop that prevents the dielectric fluid inside the paper insulation from migrating over

to the solid dielectric cable insulation. A secondary function of the oil-stop is to keep

outside moisture from infiltrating into the paper insulation. Moisture can degrade the

dielectric strength of the paper insulation. The oil-stop feature on the Elastimold 2W-1W

splice was not adequate for the application.

The most prevalent mode of failure for these splices is for moisture to infiltrate into the

paper insulation on the PlLC cable leg of the splice, resulting in its eventual dielectric

failure. The design, with multiple layers of tape over the paper insulation, does not

effectively seal the PILC cable from moisture intrusion. Several design changes have

been made to the oil-stop since its inception, but the failure rate remains undesirably

high.

Raychem 3W-1W stop-joints were introduced into the Con Edison system in 1985-86.

Around 1987, they underwent a design change that replaced the one-piece outer jacket

sleeve with a split sleeve. The split sleeve was constructed from a more robust material,

and the split allowed it to be wrapped around the splice and shrunk down over the

insulating tubes. This made the splice easier to assemble in congested manholes.

The original Raychem was constructed by shrinking three tubes over the cable connector,

one electrical stress-control tube followed by two insulating tubes. Many failures of these

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early splices involved the improper shrinking of these multiple tubes. Moisture and other

contaminants were sometimes left on the lower tube while the upper was shrunk down.

This led to “tracking” failures between the layers. The contamination provided a

conductive path to ground for the voltage that builds up in the insulation. The current

then tracks along that path to ground for a subsequent feeder failure.

Another problem with the multiple layers was the difficulty of installing all three layers

over the connector area. If these multiple heat-shrink tubes were not properly shrunk over

each other, air voids tended to build up between the layers. Over time, and in an electrical

field, the air in these voids would ionize and lead to high levels of partial discharge

(partial discharge develops into small electrical arcs that erode the insulating material of

the heat-shrink tube) and an eventual failure.

In 1994, another redesign of the Raychem stop-joint was implemented on the Con Edison

system. The two insulation tubes were combined into one tube (called the ECIC tube),

more effective sealants were added under the outer jacket, and tell-tale marks were added

to all heat-shrink tubes for better indication of a proper shrink. These changes in 1994

were also coupled with more thorough and effective training from our splicing school.

These changes appear to have improved the reliability of the Raychem 3W-1W stop-joint

splice. The age of the majority of Raychem 3W-1W stop-joint splice at the time of

failure, for the summers of 2005 and 2006, is between 10 and 13 years. These splices

were installed just before and after the design change of 1994. Splices installed after 2000

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do have a significantly lower failure rate – about half that of those installed before that

time. The combination of a better design and more effective training, over time, has

reduced the failure rate of these splices.

The failures of the pre-1994 stop-joint splices were the result of assembly problems and

not with the electrical design of the splice. When properly assembled, these older splices

have about the same failure rate as the post-1994 design. On the whole, the improperly

assembled older splices have failed and were removed from the population, leaving the

two populations of splices with a similar failure rate. Raychem 3W-1W stop-joints

installed before 1994 are no longer targeted for replacement. Table 16 shows a breakout

of the LIC event splice failures by cause of failure.

Three Elastimold 2W-1W stop-joints, failed because of defective oil-stop features. The

oil-stop feature on the Elastimold 2W-1W stop-joints, as previously stated, was an

inadequate design for the application. These splices are targeted for removal.

One of the July 20 failures of 1Q07 involved an Elastimold 2W-1W stop-joint that failed

due to paper ionization. The failure resulted from partial discharge inside the PILC cable

side of the splice. Voids in the paper insulation were created by the natural migration of

the dielectric oil throughout the high-stress areas of the splice (in this case the area of the

PILC cable in the vicinity of the oil-stop). The combination of the voids and the high

electrical fields created the conditions for partial discharge. The partial discharge, in turn,

created a solid wax from the cable oil that blocked the oil’s return to dryer areas in the

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paper insulation. This condition created larger voids and higher levels of partial

discharge. The partial discharge, over time, degraded the insulation, which led to a

dielectric failure.

The two splices that failed due to overheating were not overloaded at the time of failure.

The first was a Raychem stop-joint that failed on 1Q16 on July 17, at 23:37. The feeder

was returning to service and cut in opened auto after an outage (open auto) earlier that

day (at 16:22). Prior to the 1Q16 outage, the failed component was operating at 7% of its

emergency rating of 660 amps. It failed immediately after the circuit breaker was closed.

The PILC cable connected to one side of the splice showed signs of long-term thermal

degradation, with brittle and discolored paper insulation tapes found close to the

conductor. This was a condition that seemed to affect the entire cable and not one hot

spot. This cable could have experienced periods of high load over the course of its years

of service.

The second overheated splice failed on 1Q15 on July 21. This was a 1W-1W lead-wipe

splice connecting one section of PILC cable to another. This splice was located in a

customer manhole on customer-owned cable and was most likely constructed by the

customer’s electrician. The splice was not constructed to any Con Edison splicing

specifications. As with the other overheated splice, the cable insulation had indications of

long-term thermal degradation. The splice was not filled with insulating dielectric fluid,

which is the standard Con Edison practice when assembling these types of splices. This

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condition added to the normal electrical stress present in the splice and could have

hastened the failure.

The Pirelli splice that failed on 1Q01 on July 20 was a 1W-1W cold-shrink splice. The

failure occurred during a dc high-potential (hi-pot) test on the XLP cable connected to

one side of the splice and not on the splice itself. Because the cable where the failure

occurred was beneath the outer protective splice jacket, this event was classified as a

splice failure. The XLP cable experienced a dielectric failure. This vintage of XLP cable

has well-documented manufacturing defects that leave it vulnerable to failure, especially

under a dc hi-pot test.

The failures caused by “leaky seam or seal on shrink joints,” “inherent heat-shrink

problems: interlayer voids,” and “improper shielding” are all related to assembly

problems with Raychem 3W-1W stop-joints.

The “inherent heat-shrink problems: interlayer voids” failure occurred on a 14-year-old

splice. This issue was addressed in the 1994 redesign of the Raychem splice. The other

two failures occurred on the new Raychem design and were addressed through enhanced

splicer training.

The failure of the 2W-2W splice on 1Q07 was due to damage from a previous remake of

the splice. See the splice-failure details that follow.

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There were two termination failures during the LIC event. Both were elbow connections

to the high-voltage side of transformers, and neither failure sample was recovered for

examination.

A system-wide examination of transformer termination failures shows that three failure

modes contribute to more than half the failures. Since January 2003, 31% can be

attributed to a breakdown at the transformer bushing; 12% were the result of moisture

contamination in the elbow/cable interface; and 8% experienced mechanical damage.

More than half of the LIC event splice failures involved PILC cable (stop-joints are one-

half PILC cable). Failures of stop-joints due to breakdowns of the PILC cable, however,

are classified as splice failures because it was the process of splicing that created the

failure. The failure rate for PILC cable sections is significantly lower than the failure rate

for stop-joints based on percent of their populations. Raychem 3W-1W stop-joints have a

summer failure rate of 0.95 in percent of population, while PILC cable has a failure rate

of 0.23. If the problem were the cable and not the splice, the rates would be similar.

In addition to the company’s Elastimold stop-joint elimination program, Con Edison is

actively removing the PILC cable from its primary distribution system and replacing it

with a modern polymeric cable. This will eliminate both the stop-joints and the PILC

cable. The current plan is to remove all PILC cable by 2024.

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Splice and Termination Failure Details Feeder Outage 1Q21 on July 17 at 19:03, ID 75504 On July 17, at 19:03, 1Q21 experienced a cut-in open auto (CIOA) following its

restoration from a bus section outage at the North Queens Substation. The fault was

reported to be on the high-voltage terminations (elbows or hammerheads) to the

transformer in TM804, located on 28th Avenue, 26 feet west of 37th Street. The fault was

identified after a visual examination revealed indications of electrical tracking on the

elbow sleeve to ground. A specimen was not recovered from this event.

This was the first of three cut-in open autos on 1Q21 following the North Queens bus

outage. It is most likely that the reported problem on the elbow in TM804 was not the

actual faulted component. The actual failed component appears to be an Elastimold 2W-

1W stop-joint in manhole M14669, which caused the second consecutive cut in open auto

on 1Q21 on July 18, at 02:49 (ID 75546).

It should be noted that both the first and second cut-in open autos on 1Q21 showed B-

phase targets at the substation. The elbow that flashed over in TM 804 was on the B-

phase as was the Elastimold stop-joint that failed in M14669. The feeder was live-end

capped in M2820, isolating the damaged section going to TM804 and returned to service

on July 19 at 06:15.

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Feeder Outage 1Q07 on July 17 at 19:09, ID 75503 On July 17, at 19:09, feeder 1Q07 experienced a cut-in open auto (CIOA) following its

restoration from a bus section outage at the North Queens Substation. The failure

occurred on an Elastimold premolded disconnectable joint in manhole MH3881 located

on Crescent Street, 54 feet north of 30th Avenue. The joint configuration is a 2W-2W

disconnectable splice that connects XLP cables to EPR cables. On July 18 at 08:49, a

permit was issued to remake the failed disconnectable joint in manhole M3881. Feeder

1Q07 was returned to service July 18 at 11:29.

The autopsy analysis of the submitted 2W-2W joint removed from MH3881 indicated the

cause of failure was damage due to a previous remake of the splice.

The 2W-2W Elastimold splice was installed on 1Q07, in manhole M3881, in April of

1992. At that time the cable configuration was: two legs were 2/0-XLP (feeding two

banks, VS5685 and VS9687); one leg was 1999 500-EPR; and one leg was 1972 500-

XLP.

In May 2006, the feeder was out for scheduled work and both of 500 legs of the 2W-1W

splice in manhole 3881 were replaced with 750-EPR. The 2/0 legs were not replaced.

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Feeder Outage 1Q16 on July 17 at 23:37, ID 75511 On July 17, at 23:37, feeder 1Q16 experienced a cut-in open auto (CIOA). This CIOA

outage followed an automatic breaker operation at 16:22 of the same day (see ID 75501).

The fault occurred in manhole M1188 on the corner of Roosevelt Avenue and 62nd Street.

The failed component was a 12-year-old Raychem 3W-1W stop-joint splice that

connected one 3-conductor 500-kcmil PILC cable to three single-conductor 2/0 XLP

cables.

Cable Technologies Laboratories, Inc. examined the failure at the Con Edison Cable and

Splice Center for Excellence. The results of a visual examination of the failed specimen

indicated a thermal degradation of the paper insulation due to high loads. This

degradation occurred over time and did not appear to be the result of a single episode of

very high load. Given the vintage of the PILC cable this high-load condition could have

existed years ago. The station fault targets and PQ-node indicated a B-phase fault. The

actual failure had no indication of which phase faulted although it was a single phase-to-

ground fault.

Construction crews installed live-end caps in M1183 and dropped the defective joint in

M1188, as well as two transformer banks, VS5265 and TM6594. The feeder was re-

energized on July 18 at 09:37.

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Feeder Outage 1Q21 on July 18 at 02:49, ID 75646 On July 18, at 02:49, feeder 1Q21 experienced a cut-in open auto (CIOA). This was the

second CIOA on this feeder. The failed component was an Elastimold 2W-1W stop-joint

installed in 1994. The fault occurred in manhole M14669 on Ditmars Boulevard and 73rd

Street. The splice connected two legs of single-conductor 500-kcmil XLP to one single-

conductor 2/0 PILC insulated cable. Con Edison attributed the failure to an improperly

made oil-stop feature. A visual examination of the failed splice was performed by Cable

Technology Laboratories, Inc. at the Con Edison Cable and Splice Center for Excellence.

The work permit requested that construction drop 10 transformers and one high-tension

customer vault utilizing a known point splice (KPS) in M10705. The feeder was

energized on July 18 at 17:11 when it experienced a third cut-in open auto.

Feeder Outage 1Q20 on July 18 at 05:53, ID 75548 On July 18, at 05:53, feeder 1Q20 experienced a cut in open auto. This followed a cut in

opened auto on that feeder on the previous day. The failed component was a Raychem

3W-1W stop-joint installed in 1992. The splice connected one 23-year-old 3-conductor

500-kcmil PILC cable to three 15-year-old single-conductor 500-kcmil XLP cables. The

fault occurred in manhole M1699 on 34th Avenue, 116 feet east of 42nd Street.

A visual failure examination was performed at the Con Edison Cable and Splice Center

for Excellence. The fault was attributed to an interlayer void between the heat-shrink

tubes used in the installation of the joint.

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The work permit requested construction to remake the damaged joint in M1699. The

feeder was energized on July 19, at 13:09.

Feeder Outage 1Q02 on July 18 at 08:23 On July 18, at 08:23, feeder 1Q02 opened auto at 08:23 due to a fault. The outage was the

result of the failure of a premolded disconnectable 2W-1W splice in manhole M14503

located on 20th Avenue 42 feet west of 49th Street. The splice was damaged due to a

secondary cable fire in that manhole. A visual examination of the failed component was

performed at the Con Edison Cable and Splice Center for Excellence.

Field forces located the fault in M14503 on July 18 at 12:56. This was the second fault

location found on the feeder during this outage. The feeder was energized on July 18 at

18:54 when it cut in opened auto.

Feeder Outage 1Q21 on July 18 at 17:11 On July 18, at 17:11, feeder 1Q21 experienced a cut in open auto. This was the third

consecutive cut-in open auto on this feeder since the North Queens bus section trip on

July 17. The failure component was a premolded disconnectable 2W-1W splice in

manhole M2554, located at the intersection of Newtown Avenue and 30th Street. The

splice connected one leg of 1994 single-conductor 500-kcmil EPR cable, one leg of 1988

single-conductor 500-kcmil XLP cable, and one leg of 1989 single-conductor 2/0 XLP

cable. The splice failure was attributed to damage from a secondary cable fire. A visual

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examination of the failed component was performed at Con Edison Cable and Splice

Center for Excellence.

At 20:26, a permit was issued to replace three sections of cable between manhole M2554

and manholes M12547, M2553, and M12542. The feeder was put back into service on

July 19 at 06:17.

A load-flow study was performed on the network area surrounding manhole M2554 to

determine if overloaded secondary mains could have contributed to the cable fire. The

study did not detect any overloaded secondary cable in M2554 just prior to the event.

Based on PVL analysis, several mains in the vicinity of this damage were overloaded.

Feeder Outage 1Q02 on July 18 at 18:56, ID 75558

On July 18, at 17:11, feeder 1Q02 opened auto after being cut in following a previous

event. The failure occurred in a transition splice between three-conductor PILC cable and

three single-conductor EPR cables. The splice was located in manhole M1699 on 47

Street, 68 feet south of Queens Boulevard. The splice failure was attributed to a leaking

seam or seal in the heat-shrink joint. Visual examination was performed at Con Edison

Cable and Splice Center for Excellence.

At 08:25, the fault was identified as the transition splice in manhole M1699. At 09:17, a

permit was issued to remake the damaged splice. The cable was energized on July 19 at

19:05.

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Feeder Outage 1Q17 7/19/06 at 08:50, ID 75593

On July 19, at 08:50, feeder 1Q17 opened auto after being cut in following a previous

event. The failure occurred in a 2W -1W disconnectable splice connecting PILC cable to

EPR insulated cable. The splice was located in manhole M11730 on 48th Avenue, 38 feet

west of 42nd Street. The splice failure was attributed to an improperly made oil stop,

allowing potential for dielectric fluid to enter the EPR insulation and/or moisture to enter

the paper insulation. Visual examination was performed at the Con Edison Cable and

Splice Center for Excellence.

At 12:50, the fault was identified as being located in manhole M11730. At 15:09, a

permit was issued to drop the transformer in transformer manhole TM810 and cable

section by making live-end caps in manhole M11730. The feeder was energized on July

19 at 20:44.

Feeder outage 1Q14 on 7/19/06 at 08:54, ID 75594

On July 19, at 08:54, feeder 1Q14 opened auto. The failure was attributed to a failed

joint, a 2W-1W X-E Elastimold manufactured in 1991, in M908 located on west side of

Steinway Street opposite 25th Avenue. A work permit was issued on July 19 at 22:21 to

install live end caps in M908, dropping TM932 and VS7684 and various sections of

cable. Visual failure analysis was done by Cable Technology Laboratories, Inc.

The feeder was restored to service on July 20 at 06:36.

5-96

Feeder outage 1Q15 on 7/19/2006 at 16:05, ID 75598

On July 19, at 16:05, feeder 1Q15 failed a modified DC high-voltage (hi-pot) test (30 kV

for 5 minutes) after 3 minutes. The failure resulted in a manhole fire and was attributed to

a LEC termination in M1810 located at the northwest corner of 47th Avenue and 40th

Street. This LEC was installed on July 18 in order to drop the failed transformer in

VS339. The failure specimen received was insufficient to perform analysis. An additional

fault was located on Rikers Island. An additional LEC was installed in M12996, dropping

10 transformers. Visual failure analysis was done by Cable Technology Laboratories, Inc.

A work permit was issued on July 19 at 18:30 to remake the LECs in MH1810. An

additional fault was located on Rikers Island. On July 20 at 05:21, an additional work

permit was issued to install a LEC in M12996 to drop 10 transformers on Rikers Island.

The feeder was restored to service on July 20 at 13:48.

Feeder outage 1Q07 on 7/20/06 at 13:39, ID 75616

On July 20, at 13:39, feeder 1Q07 opened auto. The failure was attributed to a failed

joint, a 2W-1W P-X Elastimold manufactured in 1991, located in M523 on 47th Avenue

and 31st Street. The cause of failure was determined to be an improper oil-stop feature.

Visual failure analysis was done by the Cable and Splice Center for Excellence.

The fault was inspected at 14:36. On July 20 at 17:41, a work permit was issued to install

an LEC in M523, dropping V-3385 and two cable sections. On July 20 at 21:01, 1Q07

failed a hi-pot test.

5-97

Feeder outage 1Q01 on 7/20/06 at 20:22, ID 75619

On July 20, at 20:22, feeder 1Q01 failed a modified DC hi-pot test. The failure was

attributed to a joint, 1W-1W X-E Pirelli, manufactured in 2005 and located in M1593 on

the west side of 33rd Street, north of Hunters Point Avenue. The cause of failure was

determined to be dielectric breakdown of the XLP cable under the joint. Visual failure

analysis was done by the Cable and Splice Center for Excellence.

On July 21 at 02:42, a work permit was issued to install a LEC in M1593, dropping

V3385 and two cable sections via LEC in MH523. The feeder was restored to service on

July 21 at 08:00.

Feeder outage 1Q07 on 7/20/06 at 21:03, ID 75620

On July 20, at 21:03, feeder 1Q07 failed a modified dc hi-pot test. The failure was

attributed to a joint, a 2W-1W P-X Elastimold, installed in 1992 in structure PB783

located on the west side of Crescent Street, north of 40th Avenue. The failure was due to

the deterioration of paper tapes and there was evidence of oil draining and waxing

indicating that partial discharge had occurred. Visual failure analysis was done by the

Cable and Splice Center for Excellence.

On July 21 at 02:36, a work permit was issued to install LEC in PB 783 and drop TM632.

On July 21 at 06:37, the feeder was restored to service

5-98

Feeder outage 1Q15 on 7/21/06 at 10:05, ID 75627

On July 21, at 10:05, feeder 1Q15 opened auto. The failure was attributed to a joint, 1W-

1W P-P Leadwipe, in customer MA6B on Rikers Island east of Gate 5. The splice

appeared to be constructed by the customer. The failure was determined to be caused by

overload (thermal degradation over the long term). Visual failure analysis was done by

Cable Technology Laboratories, Inc.

A second fault, located at 19:08, was a damaged section of 1-conductor cable between

M1951 and M1810. On July 21 at 22:38, a work permit was issued to spear and cut the

blown joint and install a cable insert in customer MA6B.

Feeder outage 1Q15 on 7/22/06 at 07:34, ID 75641

On July 22, at 07:34, feeder 1Q15 failed a modified dc hi-pot test. The failure was

attributed to a failed joint, a 2W-1W P-X Elastimold manufactured in 1995, in M12995

located on the north side of 19th Avenue west of 48th Street. The failure specimen

received was insufficient to perform analysis. Visual failure analysis was done by Cable

Technology Laboratories, Inc.

On July 22 at 10:12, a work permit was issued to remake blown mechanical 2W-1W

joints in M12995. The feeder failed a DC hi-pot test at 0 kV on July 22 at 14:36.

5-99

Feeder Outage 1Q14 on 7/23/06 at 22:08, ID 75652

On July 23, at 22:08, feeder 1Q14 failed a dc hi-pot test. The failure occurred in a

transition splice between 3-conductor PILC cable and three single-conductor XLPE

insulated cables. The splice was located in manhole M12995 at the intersection of 19th

Avenue and 48th Street. The splice failure was attributed to an improperly terminated

copper shielding tape. During splicing, the tape was left with a sharp edge following

termination. Physical dissection was performed by Cable Technologies Laboratories, Inc.

This feeder had originally opened auto on July 19 at 08:54. A modified DC hi-pot test

was performed on July 23 beginning at 20:29 in order to confirm its integrity before

being put back in service. The feeder failed during this test on July 23 at 22:08. On July

24 at 0032: the fault was identified as a blown transition splice. On July 24 at 03:00, a

permit was issued to replace the cable between M12995 and M12996 on 19th Avenue

between 48th and 49th Streets. The cable was energized on July 25 at 07:26.

The LIC network experienced seven primary cable-section failures during the event. Six

failures were caused by conditions on the network, such as secondary cable fires and

damaged conduit. These failures were caused by events external to the cable. One section

was not recovered.

The LIC network experienced 15 splice failures during the event. Stop-joints accounted

for more than half of these failures. Five of these stop-joints were premolded

disconnectable 2W-1W splices manufactured by Elastimold. These splices are no longer

5-100

being installed on the Con Edison system, and there is currently a program to remove all

existing splices.

Four of the failed stop-joints were 3W-1W heat-shrink splices manufactured by

Raychem. The failure mode for three of these 3W-1W stop-joint failures has been

addressed by a redesign of the splice in 1994 and enhanced splicer training. One of the

3W-1Ws failed due to long-term thermal degradation of PILC cable insulation and not a

problem with the splice itself.

There was one failure of a customer-owned single-conductor lead-wipe splice and a dc

hi-pot test failure on the XLP cable on a cold-shrink splice.

Four of the splice failures were premolded disconnectable non-stop-joint splices. Two of

these splices failed due to damage from a secondary cable fire; one was damaged when

the splice was reassembled; and one was not recovered for inspection.

Problems associated with the premolded disconnectable 2W-1W stop-joints are well

documented and are being addressed through a replacement program. The installation of

all stop-joints will be reduced as the company replaces PILC cable through its routine

maintenance practices and reliability programs.

5-101

Conclusions

An analysis of the cable and splice failures leads to the conclusion that no new programs

specific to LIC or the Con Edison system are required to address the reliability of these

primary feeder components. Problems related to components, such as premolded

disconnectable 2W-1W stop-joint splices, have previously been identified and are

currently being addressed by existing programs. In addition, improved methods to protect

primary feeders from external fire and heat would serve to increase feeder reliability.

5-102

Failure count Manufacturer Configuration Stop-Joint Failure Discription Feeder ID Failure

Date Comments

1 Elastimold 2W-1W P-E Yes Defective oil-stop feature 1Q17 7/19/2006 PILC Cable 50 years old

Defective oil-stop feature 1Q21 7/18/2006 PILC Cable 34 years old

Defective oil-stop feature 1Q07 7/20/2006 PILC cable 27 years old

Paper - Ionization 1Q07 7/20/2006 PILC Cable 34 years old

Unknown: Insufficient Specimen 1Q15 7/22/2006 PILC cable 59 years old

Damage by secondary fire 1Q21 7/18/2006

Unknown: Insufficient Specimen 1Q14 7/19/2006

1 Elastimold 2W-2W X-E No Damage Due To Remake 1Q07 7/17/2006

1 Lead-Wipe 1W-1W P-P No Overheating 1Q15 7/21/2006Long-term thermal degradation.

Customer assembled with no dielectric filler

1 Pirelli 1W-1W X-E No Dielectric Breakdown - XLP 1Q01 7/20/2006 XLP cable failed under outer splice jacket

1 Raychem 3W-1W P-E Yes Leaky Seam or Seal on Shrink Joints 1Q02 718/2006 No PILC cable age available

Inherent Heat Shrink Problem: Interlayer Void 1Q20 7/18/2006 PILC cable 23 years old

Overheating 1Q16 7/17/2006 Long-term thermal degradation. 1950's vintage PIL cable

Improper Shielding 1Q14 7/23/2006 PILC cable 48 years old

1 Richards 2W-1W X-E No Damage by secondary fire 1Q02 7/18/2006

3 Raychem 3W-1W P-X Yes

4 Elastimold 2W-1W P-X Yes

2 Elastimold 2W-1W X-E No

Table 5-15 Network Event Splice Failures

5-103

Details of LIC Network Event Component Failures

Table 5-16a: LIC Network Feeder Outages

5-104

Figure 5-16b: LIC Network Feeder Outages

5-105

Table 5-16c: LIC Network Feeder Outages

ID Region Volt Feeder Outage Fail Date & Time Equipment Joint/Cable Config* Stop Joint Manufacturer Manufacture Date Age Fail Code Remarks

75500 Q 27 1Q17 OA 7/17/2006 15:50 CABLE 3-1/c 2/0 XLP ANACONDA 1985 21 81 External Damage from Secondary burnout

75501 Q 27 1Q16 OA 7/17/2006 16:22 CABLE 3-1/c 500 EPR BICC GEN. 2000 6 81 External Damage from Secondary burnout

***** Q 27 1QO7 OA - BUS TRIP 7/17/2006 18:47

***** Q 27 1Q21 OA - BUS TRIP 7/17/2006 18:47

***** Q 27 1Q81 OA - BUS TRIP 7/17/2006 18:47

***** Q 27 1Q15 OA - BUS TRIP 7/17/2006 18:47

75504 Q 27 1Q21 CIOA - BUS TRIP 7/17/2006 19:03 TERMINATION NOT AVAILABLE 94 No Failure Sample Recovered

75503 Q 27 1Q07 CIOA 7/17/2006 19:09 SPLICE 2W-2W X-E ELASTIMOLD 2006 0 145 Damaged from Reassembly of Splice

75506 Q 27 1Q02 OA 7/17/2006 19:50NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

***** Q 27 1Q20 OA 7/17/2006 21:42NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

***** Q 27 1Q01 OA 7/17/2006 21:49NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75508 Q 27 1Q20 CIOA 7/17/2006 21:56 TRANSFORMER GE 1966 40 601 Overheating

***** Q 27 1Q01 CIOA 7/17/2006 21:56 TRANSFORMER GE 1984 22 601 Overheating

75507 Q 27 1Q01 CIOA 7/17/2006 21:56 CABLE 3-1/c-500-EPR BICC GEN. 2000 6 94 No Failure Sample Recovered

75511 Q 27 1Q16 CIOA 7/17/2006 23:37 SPLICE 3W-1W P-X Yes RAYCHEM 1994 12 80 Overload (thermal degradation over time)

75546 Q 27 1Q21 CIOA 7/18/2006 2:49 SPLICE 2W-1W P-X Yes ELASTIMOLD 1994 12 43 Improper Oil Stop

75548 Q 27 1Q20 CIOA 7/18/2006 5:53 SPLICE 3W-1W P-X Yes RAYCHEM 1992 14 165 Inherent Heat Shrink Problem; Interlayer Void

75549 Q 27 1Q02 OA 7/18/2006 8:24 CABLE 3-1/c-2/0-EPR BICC GEN. 2005 1 81 Damaged from Secondary Fire

75589 Q 27 1Q02 OA 7/18/2006 8:24 SPLICE 2W-1W X-E RICHARDS 2003 3 81 Damaged from Secondary Fire

75550 Q 27 1Q17 OA 7/18/2006 11:50NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75552 Q 27 1Q18 OA 7/18/2006 15:16 TRANSFORMER GE 1988 18 601 Overheating

75553 Q 27 1Q21 CIOA 7/18/2006 17:11 SPLICE 2W-1W X-E ELASTIMOLD 1994 12 81 Damaged from Secondary Fire

75558 Q 27 1Q02 CIOA 7/18/2006 18:56 SPLICE 3W-1W P-E Yes RAYCHEM 1994 12 31 Leaky Seam or Seals on Heat or Cold Shrink Splice

75561 Q 27 1Q13 OA 7/18/2006 20:04NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75564 Q 27 1Q12 OA 7/18/2006 20:32 TRANSFORMER GE 1985 21 601 Overheating

75564 Q 27 1Q12 OA 7/18/2006 20:32 CABLE 3-1/c-2/0-XLP PHEL.DODGE 1984 22 160 Damaged from Manhole Fire, Other than Secondary Fire

75565 Q 27 1Q15 OA 7/18/2006 20:35 TRANSFORMER GE 1963 43 601 Overheating

Breaker opened but no fault was found. . Feeder put back into service. 7 minute outage. Subsequent CIOA see 1Q01 7/17 at 21:56

Breaker opened but no fault found. The feeder was put back into service. 9 hour outage. Subsequent CIOA, see 1Q17 on 7/18 at 20:55

Breaker opened but no fault was found. Feeder was put back into service. 1 hour outage

LIC NETWORK FEEDER OUTAGES 7/17/06 TO 7/25/2006

Bus Outage at North Queens Substation

Breaker opened but no fault was found. Feeder was put back into service. 1 hour outage.

Breaker opened but no fault was found. Feeder was put back into service. 13 minute outage. Subsequent CIOA, see 1Q20 7/17 at 21:56

5-106

Table 5-16d: LIC Network Feeder Outages

ID Region Volt Feeder Outage Fail Date & Time Equipment Joint/Cable Config* Stop Joint Manufacturer Manufacture Date Age Fail Code Remarks

***** Q 27 1Q16 OA 7/18/2006 20:37 No Fault Found

75567 Q 27 1Q17 CIOA 7/18/2006 20:55 TRANSFORMER GE 1961 45 601 Corrosion

75623 Q 27 1Q16 CIOA 7/18/2006 21:49 TRANSFORMER GE 1964 42 601 Overheating

75566 Q 27 1Q16 CIOA 7/18/2006 21:49 CABLE 3-1/c-2/0-EPR BICC GEN. 2002 4 81 Damaged From Secondary Fire

75568 Q 27 1Q18 OA 7/18/2006 21:50NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75569 Q 27 1Q19 OA 7/18/2006 22:24NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75572 Q 27 1Q18 CIOA 7/18/2006 23:57 TRANSFORMER GE 1988 18 601 Overheating

75573 Q 27 1Q19 OA 7/19/2006 0:09 TRANSFORMER GE 1969 37 601 Overheating

75593 Q 27 1Q17 CIOA 7/19/2006 8:50 SPLICE 2W-1W P-E Yes ELASTIMOLD 1990 16 164 Defective oi-stop feature

75594 Q 27 1Q14 OA 7/19/2006 8:54 SPLICE 2W-1W X-E ELASTIMOLD 1991 15 89 Insufficient Specimen Available to Perform Analysis

75595 Q 27 1Q12 FOT - Mod. Hipot 7/19/2006 11:15NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75596 Q 27 1Q01 OA 7/19/2006 11:39 CABLE 1-3/c-2/0-PILC PHEL.DODGE 1947 59 67 Damaged From Defective Duct

75598 Q 27 1Q15 FOT - Mod. Hipot 7/19/2006 16:05 TERMINATION 89 Insufficient Specimen Available to Perform Analysis

75601 Q 27 1Q16FOT - Ammeter

Clear7/19/2006 19:45

NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found - No Specimen Delivered

75603 Q 27 1Q17 OA 7/19/2006 21:34 TRANSFORMER GE 1972 34 601 Overheating

75613 Q 27 1Q16FOT - Ammeter

Clear7/20/2006 8:11 TRANSFORMER GE 1993 13 601

Third attempt to pass ammeter clear. Transformer Failure: Primary Bushing Failure

75616 Q 27 1Q07 OA 7/20/2006 13:39 SPLICE 2W-1W P-X Yes ELASTIMOLD 1991 15 164 Defective oi-stop feature

75618 Q 27 1Q16FOT - Ammeter

Clear7/20/2006 19:43

NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75619 Q 27 1Q01 FOT - Mod. Hipot 7/20/2006 20:22 SPLICE 1W-1W X-E PIRELLI US 2005 1 122 Dielectric Breakdown--XLP

75620 Q 27 1Q07 FOT - Mod. Hipot 7/20/2006 21:03 SPLICE 2W-1W P-X Yes ELASTIMOLD 1992 14 13 Paper Ionization (Found Pd damage)

75627 Q 27 1Q15 OA 7/21/2006 10:05 SPLICE 1W-1W P-P LEAD WIPE NOT AVAILABLE 80Overload (thermal degradation over time). The splice

appeared to be constructed by customer

75633 Q 27 1Q19 OA 7/21/2006 17:25 TRANSFORMER GE 1978 28 Secondary Bushing Assembly Leak

75641 Q 27 1Q15 FOT 7/22/2006 7:34 SPLICE 2W-1W P-X Yes ELASTIMOLD 1995 11 89 Insufficient Specimen Available to Perform Analysis

75643 Q 27 1Q15FOT - Ammeter

Clear7/22/2006 14:36

NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75644 Q 27 1Q17 OA 7/22/2006 20:35 TRANSFORMER GE 1993 13 601 Overheating

75651 Q 27 1Q14 CIOA 7/23/2006 19:47NOT CABLE, SPLICE OR TRANSFORMER

No Fault Found

75652 Q 27 1Q14 FOT 7/23/2006 22:08 SPLICE 3W-1W P-X Yes RAYCHEM 1994 12 34 Poor Shielding (shielding cutback left with sharp edges)

LIC NETWORK FEEDER OUTAGES 7/17/06 TO 7/25/2006

Breaker opened but no fault was found. Feeder was put back into service. 1 hour outage. Subsequent CIOA, see 1Q16 0n 7/18 at 21:49

Breaker opened but no fault was found. Feeder was put back into service. 2 hour outage. Subsequent CIOA, see 1Q18 on 7/18 at 23:57

Breaker opened but no fault was found. Feeder was put back into service. 2 hour outage

Feeder passed a modified HiPot test and was put back into service. Outage duration was 2 hours

Feeder failed a subsequent hipot test. See FOT on July 23 22:08

Feeder failed hipot test but no fault was found. Feeder was put back into service. 2 hour outage

Received 1 leg of a 2W-1W mechanical splice with XLP cable attached. The termination end of the cable was not sent. No indication of a failure.

Failed test while restoring feeder from 7/18 outage but no fault was found. The feeder was not re-energized before it FOT'd.

Opened a transformer network protector, feeder passed ammeter clear returned to service.

5-107

5.15. Transformer and Protector Analysis

Background The Long Island City network has 1,198 network transformers with an average transformer age

of 20.8 years. In comparison, the average age of the 24,569 underground transformers on the

Con Edison system is 21.6 years. Thirteen transformer failures are associated with the Long

Island City event of July 2006. Two of these failures occurred after all of the primary feeders had

been restored. Eleven transformers were rated for 500 kVA (Figure 5-23), and two were rated

1000 kVA (Figure 5-24). The average age of the 13 transformers that failed is 32 years.

Figure 5-23: Typical 500-kVA transformer

5-108

Figure 5-24: Typical 1000-kVA transformer

Transformers are connected to the low-voltage secondary grid through automatic switches called

network protectors. The network protector is normally closed, allowing the electricity to flow

from the transformer to supply the grid. When a feeder trips and the transformer becomes de-

energized, the network protector automatically opens to disconnect the de-energized transformer

from the energized secondary grid. This prevents electricity from flowing back into the de-

energized transformer and feeder. When the electricity from the secondary system does flow

back (backfeeds) through the network protector into the transformer and feeder, the condition is

called “alive on back feed” (ABF). Network protectors are designed to prevent ABF.

A transformer has three internal coils made of alternating layers of paper insulation and

conductors. The coils are submerged in transformer oil within a sealed tank. The electric load on

a transformer generates heat within the coil assembly. The heat is dissipated away from the coils

through the oil into a radiator system on the exterior of the transformer tank. Overheating occurs

5-109

when more heat is generated than the transformer can dissipate. The transformer fluid not only

conducts heat away from the coils, it also acts as an electrical insulating medium and preserves

the paper insulation. When the oil deteriorates due to overheating, its cooling and insulating

properties become diminished, and the transformer can fail if localized hot spots burn through

the electrical conductors.

A forensic analysis to determine the root cause of the 13 transformer failures was conducted by

the independent engineering firm of Engineering Systems Inc. (ESI), with support from

representatives of the company’s Engineering Department. This process included draining the

transformer oil, cleaning the exterior, removing the internal components, and testing and

examining each transformer. ETI Richards, an independent network-protector manufacturer,

analyzed the network protectors associated with each of the failed transformers. The analysis of

each transformer and network protector follows the overview of the monitoring system.

5.15.1. Overview of Remote Monitoring System

Recognizing the benefit of having near-real-time load and status data from network transformers,

the company worked with a vendor to develop a system to monitor underground network

transformers. The Remote Monitoring System (RMS) was installed beginning in 1982. Today,

there are approximately 25,000 RMS transmitters providing individual transformer load and

network-protector switch-position data throughout the Con Edison system. The data, which is

typically used by control room operators and distribution engineers, can be displayed on any

company personal computer. The information is collected by a transmitter in the transformer

vault and is electronically sent over the feeder cable to a receiver in the substation. Figure 5-25 is

5-110

PICKUP COIL

SUBSTATION

5B21

TX

TX TX

TX

TX

TX

VDAMS

USER

USER

USER

RECEIVERFRAME LINE

PHONE LINE

2

3

4

1

TX - TRANSMITTER

a simplified diagram of the system components showing the data flow from the transformer to

computer terminal.

System Diagram

Figure 5-25: Typical Network RMS System

RMS is the main line of data acquisition for network protectors and transformers. The original

RMS system monitored the load on each phase as an analog value and up to five status flags. The

five status flags include open network protector, oil temperature greater than 90oC, vault access,

water level, and sump oil detection. In the early 1990s Con Edison worked with the original

RMS vendor to improve the transmitters and receivers to add five analog values, including the

voltage on each phase and three status flags. Since 1996, approximately 8,000 of these second-

generation units have been installed.

After the original patents expired on this technology, Con Edison identified another vendor that

was qualified to provide replacement equipment. At that time, the company enhanced the design

to improve the transmitter reporting rates and to incorporate analog oil-temperature and

transformer tank-pressure data. Transformer oil-level and stray-voltage status flags were also

added as reportable data. In January 2006, the company started deploying the new RMS

5-111

transmitters, and more than 750 have been installed system-wide; 48 of them are in the LIC

network.

The company has been at the forefront of developing, implementing, and improving the RMS

system. The RMS system is broad and complex, and at any time a certain number of units do not

report data as designed. The performance of the RMS system is evaluated by the number of units

that are not reporting (UNR). UNR occurs for a variety of reasons, including equipment

problems. The transmitters are installed within the harsh underground environment of

transformer vaults. There are also inherent limitations in the ability to transmit data signals over

27-kV power cables.

Con Edison is working with an independent vendor to enhance the receiver capability. The latest

receivers have the ability to perform diagnostics on each feeder pickup coil, thus allowing better

monitoring of performance.

5.15.2. Long Island City Incident RMS Analysis

The RMS in the Long Island City network is unique because the number of transformers, and the

corresponding number of required transmitters, exceed the design limits of the standard

receivers. This limitation was resolved by using two receivers, one on each of two phases, which

increased the number of transmitters that could be installed in the network.

Prior to the event, on July 14, with all 22 feeders in service, the LIC network reported an RMS

availability rate of 79.5%.

5-112

FORENSIC ANALYSIS OF FAILED TRANSFORMER

JULY 2006 LONG ISLAND CITY EVENT VS 0477 – SERIAL # F525458

Incident Description: Feeder 1Q01 cut in opened auto (CIOA) on 07/17/06 at 21:56. The Long Island City network remained in a sixth contingency at the time of failure. The fault was identified in transformer vault VS 0477. The following are the particulars of the transformer:

Vault: VS 0477 Serial Number: F525458 Feeder #: 1Q01 Trip Mode: CIOA Field Address: 41st Avenue and 67th Street Received Date: 10/1/1964 Installed Date: 7/31/1984 (after reconditioning) Transformer Class: GA8S KVA: 500 NWP Serial #: 710005 Rupture: No

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer tank had visible signs of corrosion at the top. The tank was bulged, and it passed a pressure test. The maximum-reading dial on the temperature gauge was over 160°C. The network protector was evaluated at an offsite facility. All three primary coils failed and showed characteristics of overheating damage in their hot-spot regions and in the interphase region of the coils. Evaluation: The transformer sustained an internal failure of all three primary coils. As indicated by the temperature gauge maximum reading of over 160°C, the calculated operating temperatures exceeded the design limits for this transformer. According to the RT3 system, the winding hot spot was calculated to have reached 164°C (designed to 135°C), and the top oil temperature was calculated to have reached 141°C (designed to 125° C). Testing of the network protector established that it operated properly to automatically trip when the transformer faulted. Conclusion: Based on the physical appearance of the coil assembly and the associated load and temperature information at the time of failure, this failure is attributed to overheating of the coils.

5-113

Figure 5-26: F525458 – Core/coil assembly showing faulted coils

Figure 5-27: F525458 – Coil windings showing loss of insulation coating

5-114

Figure 5-28: F525458 – Coil winding fault damage

Figure 5-29: Real-Time Temperature of Transformer (RT3) VS0477 in Long Island City

5-115

FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

V7813 – SERIAL # F529863

Incident Description: Feeder 1Q20 cut in open auto (CIOA) on 07/17/06 at 21:56. The Long Island City network remained in a sixth contingency at the time of the failure. The fault was identified in transformer vault V7813. The following are the particulars of the transformer:

Vault: V7813 Serial Number: F529863 Feeder #: 1Q20 Trip Mode: CIOA Field Address: 28th Avenue and 42nd Street Received Date: 1/1/1966 Installed Date: 6/1/1967 Transformer Class: GU8N KVA: 1000 NWP Serial #: 18204 Rupture: No

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer tank was in good condition. The transformer failed the pressure test due to leaks at the secondary bushings. The network protector was evaluated at an offsite facility. The RMS variation of the PQ node indicated a three-phase fault. It was also noted that prior to the CIOA on 7/17/06 at 21:56, the feeder opened auto (OA) on 7/17/06 at 21:43. Evaluation: The transformer sustained an internal failure of all three primary coils. The tank subsequently bulged, and all three secondary bushings cracked and leaked insulating fluid. The associated calculated operating temperatures exceeded the design limits and continued to climb up to the point of failure. According to the RT3 system, the winding hot spot was calculated to have reached 160°C (designed to 135°C) and the top oil temperature was calculated to have reached 140°C (designed to 125°C). Re-energizing the feeder after it originally opened auto caused the damage to the transformer. Based upon an inspection of the coils and a review of the data, it was decided that the cause of the failure could be determined without disassembling the core and coil assembly. The core and coil assembly was placed back into the transformer, and the transformer was put in secure storage.

Testing of the network protector, found in the open (tripped) position as brought from the field, showed that it operated properly to trip automatically when a substitute test network relay was used. The substitute relay was used for testing because the original relay sustained internal power-supply damage from the fault.

5-116

Conclusion: Based upon the observed coil damage, and the load and temperature information at the time of failure, this failure is attributed to overheating of the coils.

Figure 5-30: F529863 – Core/coil assembly fault damage

Figure 5-31: Real-Time Temperature of Transformer (RT3) V 7813 in Long Island City

5-117

FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 9819 – SERIAL # M174194

Incident Description: Feeder 1Q18 opened auto (OA) on 07/18/06 at 15:14. The Long Island City network went into a sixth contingency at the time of the failure. The fault was identified in transformer vault TM 9819. The following are the particulars of the transformer:

Vault: TM 9819 Serial Number: M174194 Feeder #: 1Q18 Trip Mode: OA Field Address: West Service Road of the Brooklyn-Queens Expressway and Berkley Avenue Received Date: 6/20/1988 Installed Date: 9/23/1988 Transformer Class: HIGAIT KVA: 500 NWP Serial #: 810706 Rupture: Yes

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer cover weld ruptured along one of the long sides. The network protector was dry and clean; it was evaluated at an offsite facility. One fuse was blown and the other two started to melt. The temperature gauge was damaged. The primary A-phase and B-phase bushings were damaged. Evaluation: The transformer sustained an internal failure. According to the RT3 system, the winding hot spot was calculated to have reached 150°C (design to 150°C), and the top oil temperature was calculated to have reached 128°C (designed to 125°C).

The oil was at the normal level before the failure occurred and approximately 20 inches below normal after the failure. The B-phase winding had a melted-wire, moist-paper insulation, and high-low shield damage. Despite the shield damage, high voltage did not penetrate to low voltage. The damage was found in the interphase area. The C-phase winding had its outer shield burned and was wrinkled by the force of the wire. The wires in the winding were bundled up and had multiple turn-to-turn faults. The first turn of the secondary burned to the high-to-low voltage barrier. The A-phase winding punctured high voltage to low voltage.

Testing of the network protector revealed that the protector functioned properly to trip automatically due to the transformer fault. Conclusion: Based on the physical appearance of the coils and information that the load and temperature exceeded the unit’s rating, this failure is attributed to the overheating of the coils.

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Figure 5-32: M174194 Section view of coil showing faulted primary and secondary winding

Figure 5-33: M174194 Showing faulted coil on unwinding machine

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Figure 5-34: Real-Time Temperature of Transformer (RT3) TM9819 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 0838 – SERIAL # M133783

Incident Description: Feeder 1Q12 opened auto (OA) on 07/18/06 at 20:33. The Long Island City network went into an eighth contingency at the time of the failure. The fault was identified in transformer vault TM 0838. The following are the particulars of the transformer:

Vault: TM 0838 Serial Number: M133783 Feeder #: 1Q12 Trip Mode: OA Field Address: 30th Street and Broadway Received Date: 5/1/1985 Installed Date: 12/1/1985 Transformer Class: HIGAIT KVA: 500 NWP Serial #: 706035 Rupture: Yes

Findings: The transformer tank was bulged and the top was corroded. The transformer cover ruptured. The exterior of the transformer and network housing were damaged by fire. The inside of the network protector was also damaged by fire. The primary elbows and bushings were damaged. The temperature gauge could not be read because of the fire damage. The sight glass of the network-protector housing melted, and the glass had been pushed outward. When the network-protector housing door was opened, water from the fire-fighting effort poured out of the housing. Evaluation: The bottom of the B-phase winding had melted aluminum across the layers. A cross-section of the C-phase winding showed the primary turns bundled, indented, and distorted, both turn to turn and layer to layer. The secondary of this phase was in good condition. The A-phase winding did not fail. The network protector, evaluated at an offsite facility, was found in the open (tripped) position, as would be expected, due to the transformer fault. The protector sustained heavy damage from the transformer fire. Conclusion: The damage found in the B-phase and C-phase windings of this transformer indicates a failure caused by overheating.

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Figure 5-35: M133783 Core/coil assembly showing faulted coil

Figure 5-36: M133783 Faulted primary coil

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FORENSIC ANALYSIS OF FAILED TRANSFORMER

JULY 2006 LONG ISLAND CITY EVENT VS 0339 – SERIAL # F124281

Incident Description: Feeder 1Q15 failed open auto (OA) on 07/18/06 at 20:33. The Long Island City network went into a ninth contingency at the time of the failure. The fault was identified in transformer vault VS 0339. The following are the particulars of the transformer:

Vault: VS 0339 Serial Number: F124281 Feeder #: 1Q15 Trip Mode: OA Field Address: 40th Street and 47th Avenue Received Date: 12/1/1963 Installed Date: 4/1/1964 Transformer Class: GA8S KVA: 500 NWP Serial #: 702533 Rupture: Yes

Findings: The transformer was analyzed at the Astoria Transformer Shop. The bayonet connector for the H3 connection to the transformer was missing. It appeared that the solder melted from the heat, and the connector fell off. The H3 phase burned through the phase tube and arced to ground. The A-phase primary winding showed indications of burning, heat damage, and broken wires. The B-phase winding showed layer-to-layer damage and deformation, as well as broken wires. The top of the C-phase winding burned layer to layer, was deformed, and had broken wires. The two spot-weld areas on the radiator panel failed. The weld remained intact, but surrounding material was pulled from the panel. There was an oil line halfway down the inside of the transformer tank, which was at the same height as the two weld failures. The network protector was evaluated at an offsite facility. Evaluation: Finite-element and metallurgical analysis were performed on the failed radiator. The sealed tank with integral radiator can fail due to over-pressurization by expansion of the insulating fluid. The most probable cause of over-pressurization is overheating of the transformer oil beyond the maximum 125°C operating design temperature.

Testing of the network protector showed that it operated properly to trip automatically to

clear the transformer fault from the secondary grid.

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Conclusion: The failed radiator panel welds resulted in a reduced oil volume. This reduced oil volume resulted in a lack of insulating- and cooling-fluid circulation, which in turn caused overheating and the failure of all of the windings.

Figure 5-37: F124281 – as received from the field

Figure 5-38: F124281 showing faulted coil

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Figure 5-39- Real-Time Temperature of Transformer (RT3) VS0339 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

VS 0479 – SERIAL # F124624

Incident Description: Feeder 1Q16 cut in opened auto (CIOA) on 07/18/06 at 21:49. The Long Island City network remained in a seventh contingency at the time of the failure. The fault was identified in transformer vault VS 0479. The following are the particulars of the transformer:

Vault: VS 0479 Serial Number: F124624 Feeder #: 1Q16 Trip Mode: CIOA Field Address: 30th Avenue and Hobart Street Received Date: 3/1/1964 Installed Date: 4/1/1964 Transformer Class: GA8S KVA: 500 NWP Serial #: 702579 Rupture: No

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer tank was slightly deformed, and one of the radiator panel spot welds had failed. All three of the associated network-protector fuses were found intact. The network protector was evaluated at an offsite facility. However, calculated loading of the unit at time of failure is approximately 45% of its rating. Evaluation: There are two spot welds located at the approximate midpoint of the vertical dimension of the radiator panel. These welds prevent the panel sides from expanding. One of these spot-weld areas failed, causing a hole in the panel. When the weld failed, the oil leaked, and the level in the transformer dropped, thereby exposing the high-voltage components. Upon examination of the tank’s inner surfaces, the oil line was observed at the same height as the hole in the panel, which confirmed this theory. All three coils failed.

A finite-element and metallurgical analysis was performed on the failed radiator. It has been concluded that the electrical failure (fault) occurred because of a lack of insulating fluid after the radiator failed. The sealed transformer tank with integral radiator can fail due to over-pressurization caused by expansion of the insulating fluid. The likely cause of over-pressurization is that the oil temperature exceeded the maximum 125°C.

The network-protector testing showed it would not trip due to an inoperable network

relay. However, it is believed to have operated properly at the time of the fault because it automatically tripped when a substitute test relay was installed and because it was received from

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the field in the open position. Such network relay damage can occur from the high-voltage transients created during faults. Conclusion: The failure of the radiator-weld area was caused by the pressure buildup in the tank. The transformer oil leaked from the site of the weld failure and resulted in all the windings becoming exposed, which in turn caused the faulting of all three phases to ground. .

Figure 5-40: F124624 Core/coil assembly showing faulted coils

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Figure 5-41: F124624 showing faulted coil

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

VS 7995 – SERIAL # D514708 PRELIMINARY REPORT

Incident Description:

Feeder 1Q17 cut in opened auto (CIOA) on 07/18/06 at 20:55. The Long Island City network remained in a ninth contingency at the time of the failure. The fault was identified in transformer vault VS 7995. The following are the particulars of the transformer:

Vault: VS 7995 Serial Number: D514708 Feeder #: 1Q17 Trip Mode: CIOA Field Address: 43rd Street and Skillman Avenue Received Date: 4/1/1961 Installed Date: 6/1/1967 Transformer Class: GA8S KVA: 500 NWP Serial #: 700963 Rupture: No

Findings:

The transformer was analyzed at the Astoria Transformer Shop. The transformer tank had signs of corrosion at the top and pitting corrosion on two sides toward the bottom of the tank. It was observed that oil seeped through the porous tank wall in this region. The transformer failed a pressure test due to leaks at the (A-phase) cable gland and tap-changer plug. The protector arrived without fuses. The network protector was evaluated at an offsite facility. Calculated loading based upon the network PVL model indicates that the transformer was loaded to a maximum of 44% during the LIC event. Area station fault recorders indicated a three-phase fault correlation to this failure. Evaluation:

The transformer tank was found to be porous on two sides. This resulted in the loss of transformer oil. The transformer failed when the live high-voltage components of the ground switch and tap changer, normally submerged under the oil, became exposed, resulting in all three phases arcing to ground. The primary H1 – H3 (C-phase) coil also failed. The oil-level gauge was not functioning and was frozen in the max-level state. The leaks at the (A-phase) cable gland and tap-changer plug did not contribute to the failure. The transformer had a field inspection performed on 10/29/02. This inspection report indicated corrosion was present, with moderate corrosion at the top of the transformer. In addition, the oil-level gauge was found to be defective. Testing of the network protector revealed it tripped automatically to properly clear the transformer fault from the secondary grid.

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Conclusion: The lower side of the transformer tank corroded, which resulted in the loss of dielectric fluid. The loss of dielectric fluid exposed the high-voltage components, resulting in all three phases arcing to ground. This caused the internal failure of the transformer and the resulting feeder opened auto (OA).

Figure 5-42: D514708 showing corrosion

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Figure 5-43: D514708 showing faulted tap-changer

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TRANSFORMER FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

VS8807 – SERIAL # M174722

Incident Description: Feeder 1Q18 cut in opened auto (CIOA) on 07/18/06 at 23:57. The Long Island City network remained in a ninth contingency at the time of the failure. The fault was identified in transformer vault TM 8807. The following are the particulars of the transformer:

Vault: VS 8807 Serial Number: M174722 Feeder #: 1Q18 Trip Mode: CIOA Field Address: 69th Street east of 38th Avenue Received Date: 10/3/1988 Installed Date: 12/27/2004 (after reconditioning) Transformer Class: HIGAIT KVA: 500 NWP Serial #: 812547 Rupture: No

Findings: The transformer and network protector were both reconditioned in 2004. The transformer was analyzed at the Astoria Transformer Shop. The transformer was slightly bulged. The tank was clean, and the temperature gauge maximum reading was 155°C. The tank passed the pressure test. There was a normal oil-level line on the inside of the tank. This unit had supplemental cooling by flooding the vault on 7/18 prior to failure. The network protector was evaluated at an offsite facility. Evaluation: The RT3 readings indicated that the transformer load reached 200%, exceeding its rating. According to the RT3 system, the winding hot spot was calculated to have reached 200°C (designed to 135°C), and the top oil temperature was calculated to have reached 175°C (designed to 125°C. The C-phase winding failed at the top. Upon teardown, three distinct faults were found. The first failure in the winding was adjacent to the interphase area. The wire movement on the top of the coil caused the other two relatively minor faults. Partial discharge (PD) may have been present, but it did not contribute to the failure. The A-phase and B-phase windings passed continuity, megger, and transformer turns ratio test (TTR) tests. Testing of the network protector revealed that it operated properly to trip automatically to clear the transformer fault from the secondary grid. Conclusion:

The transformer was operating above its rating. A primary fault developed and the feeder tripped.

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Figure 5-44: M174722 showing faulted coil

Figure 5-45: Real-Time Temperature of Transformer (RT3) VS8807 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 0624 – SERIAL # H260569

Incident Description: Feeder 1Q19 opened auto (OA) on 07/19/06 at 00:06. The Long Island City network went into a ninth contingency at the time of failure. The fault was identified in transformer vault TM 0624. The following are the particulars of the transformer:

Vault: TM 0624 Serial Number: H260569 Feeder #: 1Q19 Trip Mode: OA Field Address: 49th Street and 43rd Avenue Received Date: 7/1/1969 Installed Date: 7/12/1999 (after reconditioning) Transformer Class: GA8S KVA: 500 NWP Serial #: 806969 Rupture: No

Findings: This transformer was reconditioned in 1999, and the network protector in 2004. The transformer was analyzed at the Astoria Transformer Shop. The transformer was bulged, and the top-cover weld was cracked. The top of the transformer was burned. The high-voltage bushings appeared to be in good condition. The color of the inside of the tank was dark. The network protector was evaluated at an offsite facility. Evaluation: The transformer sustained an internal failure. According to the RT3 system, the winding hot spot was calculated to have reached 214°C (designed to 135° C), and the top oil temperature was calculated to have reached 183°C (designed to 125°C). The oil level appeared to be normal at the time of failure. The cooling panels expanded outward due to the increased pressure inside the tank. The A-phase winding collar had brittle paper. Some of the wire and paper were indented on certain layers. There was no high-voltage-to-low-voltage penetration. B-phase high voltage had problem conductors. There was damage to the high-voltage shield, and it was also deformed. The C-phase winding was deformed. The load was rising at this time. The network-protector testing showed that it would not trip due to an inoperable network relay. However, it is believed to have operated properly at the time of the fault, because the switch was found in the open position as received from the field and because it automatically tripped when a substitute relay was used for testing. Network-relay damage, as found in this protector, can be caused by the high-voltage transients created during faults. Conclusion:

Based upon the physical appearance of the coils, and the associated load and temperature information at the time of failure, this failure is attributed to the overheating of the coils.

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Figure 5-46: Real-Time Temperature of Transformer (RT3) TM 0624 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 7981– SERIAL # H309368

Incident Description: Feeder 1Q17 opened auto (OA) on 07/19/06 at 21:29. The feeder trip put the Long Island City network into a seventh contingency. The fault was identified in transformer vault TM 7981. The following are the particulars of the transformer:

Vault TM 7981 Serial Number: H309368 Feeder #: 1Q17 Trip Mode: OA Field Address: 62nd Street and Roosevelt Avenue Received Date: 12/1/1972 Installed Date: 1/1/1973 Transformer Class: HIGAO KVA: 500 NWP Serial #: 806420 Rupture: Yes

Findings: The top and sides of the transformer tank were bulged. The temperature gauge was missing. The bottom of the end of the fins had separated from the tank at the base as a result of the fault. Two of the fins had leaked oil into the vault. The network protector was evaluated at an offsite facility. Evaluation: The tap-changer shield was found cracked. The A-phase and B-phase windings were damaged, and the C-phase winding was intact. The low-voltage copper bus was reddish in color, an indication of overheating. The high- and low-voltage windings in this unit were aluminum. The B-phase was distorted and burned. There was a burn through the high-voltage/low-voltage shield that consumed the paper separator, but had not perforated the shield. The high-voltage shield was distorted, and the winding turns had separated throughout the winding. The RMS data indicates that the loading exceeded the second-contingency rating by 152%.

Testing of the network protector, found in the open (trip) position as received from the field, showed it operated properly and automatically tripped when a substitute test network relay was used, since the relay returned with it sustained damage believed to be from the fault. Conclusion: The nature of the damage to the A-phase and B-phase coils, as well as the signs of overheating at the low-voltage copper bus, indicate that the cause of this failure was overheating.

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Figure 5-47: H309368 showing faulted coils

Figure 5-48: Real-Time Temperature of Transformer (RT3) VS7981 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 6531 – SERIAL # Q115445

Incident Description: Feeder 1Q16 failed on test (FOT) when the feeder was hi-potted on 07/20/06 at 08:11. The Long Island City network was in a fourth contingency at the time of the failure. The fault was identified in transformer vault TM 6531. The following are the particulars of the transformer:

Vault: TM 6531 Serial Number: Q115445 Feeder #: 1Q16 Trip Mode: FOT Field Address: Review Avenue and 37th Street Received Date: 9/29/1993 Installed Date: 11/12/1993 Transformer Class: HIGAZA KVA: 500 NWP Serial #: 0288A554751 Rupture: No

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer tank was in very good condition and was intact, but failed the pressure test through a leak at the C-phase primary bushing. Visual inspection revealed that this bushing was damaged. All three phases of the network protector fuses were blown. The network protector was evaluated at an offsite facility. Data interpolation from the RMS indicates that the unit was operated within its rating. Evaluation: The transformer sustained a primary C-phase bushing failure from phase to ground. The bushing failure was a high-voltage puncture through the epoxy to ground. The bushing is an ESNA bushing, which is a disconnectable elbow termination. After the bushing was isolated, the transformer passed continuity, insulation resistance (megger), and turns ratio tests, indicating that the fault was contained to the primary bushing.

Testing of the network protector revealed an inoperable network relay. The protector was found in the electrically closed position as received from the field but with manual operating handle in the trip (open) position, indicating the protector may not have operated properly to clear the transformer fault from the secondary grid. The protector did operate properly when a substitute test network relay was used. Conclusion:

The failed component was sent to NEETRAC laboratory for root-cause analysis. The failure of the bushing is attributed to mechanical damage.

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Figure 5-49: Q115445 showing faulted primary bushing; fault at lower left

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

TM 6682 – SERIAL # M105273

Incident Description: Feeder 1Q19 opened auto (OA) on 07/21/06 at 17:25. The Long Island City network went into a second contingency at the time of the failure. The fault was identified in transformer vault TM 6682. The following are the particulars of the transformer:

Vault: TM 6682 Serial Number: M105273 Feeder #: 1Q19 Trip Mode: OA Field Address: 25th Avenue and 46th Street Received Date: 12/1/1977 Installed Date: 1/1/1978 Transformer Class: HIGAIT KVA: 500 NWP Serial #: 706338 Rupture: Yes

Findings: The transformer was analyzed at the Astoria Transformer Shop. The transformer tank had visible signs of corrosion at the top, but did not appear to be porous, and the tank was ruptured. The network-protector housing, which was previously opened in the field, showed signs of oil inside. The network protector was evaluated at an offsite facility. Evaluation: The transformer sustained an internal three-phase failure. The transformer tank leaked through the low-voltage secondary bushing assembly into the network-protector compartment. The secondary bushing assembly was removed and sent for evaluation. Subsequent metallurgical evaluation revealed that the leak resulted from stress-corrosion failure, attributed to exposure to high concentrations of chlorides (salts). The leak resulted in a low oil level within the transformer. This was confirmed by an inspection of the internal tank. The examination showed that prior to failure, the oil level was at the height of the secondary bushings. The transformer failed when the live high-voltage components of the ground switch and tap-changer were exposed above the oil level. This resulted in all three phases arcing to ground.

The windings were tested, and passed both insulation resistance (megger) and TTR tests, confirming that the coils were not part of this failure. According to the RT3 system, the winding hot spot was calculated to have reached 160°C (designed to 150°C), and the top oil temperature was calculated to have reached 130°C (designed to 125°C).

Testing of the network protector showed that it operated properly and tripped automatically to clear the transformer fault from the secondary grid.

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Conclusion: The leak at the low-voltage secondary bushing assembly resulted in lowering the dielectric fluid level inside the transformer. Exposing the high-voltage components caused all three phases to arc to ground. The leak was attributed to stress-corrosion cracking at the weld area of the low-voltage bushing assembly.

Figure 5-50: M105273 showing faulted coil

Figure 5-51: Real-Time Temperature of Transformer (RT3) TM6682 in Long Island City

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FORENSIC ANALYSIS OF FAILED TRANSFORMER JULY 2006 LONG ISLAND CITY EVENT

VS 7388 – SERIAL # F531695

Incident Description: Feeder 1Q17 opened auto (OA) on 07/22/06 at 20:33. The fault was identified in transformer vault VS 7388. The following are the particulars of the transformer:

Vault: VS 7388 Serial Number: F531695 Feeder #: 1Q17 Failure Mode: OA Field Address: 31st Street and Ditmars Boulevard Received Date: 10/1/1965 Installed Date: 6/29/1993(after reconditioning) Transformer Class: GU8N KVA: 1000 NWP Serial #: 801039 Rupture: No

Findings: This transformer and the network protector were reconditioned at the Astoria Transformer Shop in 1993. The transformer was analyzed at the Astoria Transformer Shop. The high-voltage tubes and the high-voltage bushings were in good condition. There was evidence of arcing on the jaw of the ground switch (H1 phase). The low-voltage bushings were damaged and had leaked. There was an oil-level line below the low-voltage bushings (12” down from the top). There was coil damage (B-phase and C-phase) at the interphase region. Connections from the A-phase coil had pulled out of the tap-changer. Oil was released from the transformer secondary bushings and started a fire in the upper region of the network-protector housing. The network protector was evaluated at an offsite facility. Evaluation: According to the RT3 system, the winding hot spot was calculated to have reached 160°C (designed to 135°C), and the top oil temperature was calculated to have reached 137°C (designed to 125°C). The network protector, found in the open position as received from the field, sustained damage from the oil fire attributed to subsequent release of oil from the faulted transformer’s secondary bushings. Conclusion: The transformer was operated above its rating, resulting in a primary fault, which caused the feeder to trip.

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Figure 5-52: F531695 showing faulted coils

Figure 5-53: Real-Time Temperature of Transformer (RT3) V 7388 in Long Island City

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Transformer Analysis and Conclusions

Transformer manufacturers specify a normal-load rating for continuous operation and a higher

emergency-load rating for contingency operation. The company monitors the load on

transformers through its remote monitoring system (RMS). The RMS data from the LIC event

indicate that 175 transformers exceeded their rating at some point during the event. A PVL load

study performed after the event indicated that 218 transformers had exceeded their rating at some

point. Based upon an analysis of the RMS data performed by BQ Engineering during the event,

98 transformers required load mitigation or supplemental cooling. The BQ Equipment group

addressed 73 of these transformers, 59 by supplemental cooling methods. Only one cooled

transformer failed.

In 10 of the 13 transformers analyzed, the failures were caused by overheating. Seven of the 10

overheating failures were attributed to operating in an overloaded state. The available load data

for the other three failures did not indicate overloading that would result in overheating damage,

but the forensic analysis did support a conclusion that the transformer had overheated.

During forensic analysis, overheating damage to the coils was observed in an area called the

interphase region. In a three-phase transformer, each coil is made up of a primary and a

secondary winding, and the three different phase coils are mounted in a row adjacent to each

other. The interphase region, where the coils contact each other, is typically the winding’s hottest

area. Heat damage to insulation and subsequent layer-to-layer faults were found in multiple coils.

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Overheating can also cause over-pressurization that can damage the integrity of the transformer’s

sealed tank, resulting in a loss of oil, which in turn can cause the transformer to fail. This

occurred on two of the 10 transformers that failed due to overheating, when their radiators

sustained mechanical damage owing to over-pressurization. These transformers failed when the

transformer fluid leaked from the site of the mechanical damage.

Two transformer failures were attributed to leaks resulting from corrosion on the exterior of the

transformer tank. The failures occurred when the loss of transformer oil caused the internal high-

voltage electrical components, which are normally submerged in the oil, to become exposed. The

electrical components faulted due to lack of insulation. The faulted region and the lower-than-

normal oil-level line on the inner tank wall were observed during the forensic analysis.

One unit experienced a fault at a primary bushing that was attributed to mechanical stress

damage.

During the LIC event, the network transformers were operated at high loads that on occasion

exceeded load ratings. Some highly loaded transformers were subject to contingency operation,

which calls for supplemental cooling to network transformers. Supplemental cooling methods

include flooding vaults with water for submersible units, spraying water for nonsubmersible

units, and employing portable cold-air blowers. These techniques effectively provide the

transformers with additional cooling to lower their temperatures and mitigate damage from

overheating. During the LIC event, a total of 59 jobs were generated for supplemental cooling of

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transformers. Seven transformers that were overloaded during the incident eventually short

circuited. One of these transformers had been cooled prior to short circuiting.

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Network-Protector Analysis and Conclusions

The network protectors that were associated with the 13 failed transformers were analyzed at an

offsite facility. The protectors were tested in their ‘as-found’ condition, with the network relays

in place as received from the field.

Ten of the 13 protectors operated properly and are believed to have cleared the transformer fault

from the secondary grid. Of the 10, four had damaged network relays. These four required

substitute test relays used in place of the damaged relays to test the protector. Such relay damage

can occur from high-voltage transients created during the fault. Two of 13 network protectors

were found in the tripped-open position and showed heavy damage attributed to fire that

occurred at the time of the transformer failure. These were not tested because of the fire damage.

One of the 13 protectors also had a damaged relay. It did operate normally using a substitute test

relay. This protector was found in the closed position with the manual operating handle in the

open position. This indicated that the unit might not have tripped automatically during the

transformer fault.

The company had reconditioned three of the 13 protectors. The analysis revealed no abnormal

findings associated with the reconditioning work. The remaining 10 units were as originally

manufactured.

Four of the 10 network protectors that operated properly to trip automatically required substitute

relays for testing because the original relays were damaged when the faults occurred.

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Trip Date and Time

Trip Type

Transformer Serial

Number

Switch Serial Number (Network Protector) Fe

eder

Vaul

t #

Equi

pmen

t C

lass

Age Install Date Mfr Date kVA

Rup

ture

Root Cause

7/17/2006 21:56 CIOA F525458 710005 1Q01 477 GA8S 41 7/31/1984 10/1/1964 500 Overheating

7/17/2006 21:56 CIOA F529863 18204 1Q20 7813 GU8N 40 6/1/1967 1/1/1966 1000 Overheating

7/18/2006 15:14 OA M174194 810706 1Q18 9819 HIGAIT 18 9/23/1988 6/20/1988 500 Y Overheating

7/18/2006 20:33 OA M133783 706035 1Q12 838 HIGAIT 21 12/1/1985 5/1/1985 500 Y Overheating

7/18/2006 20:33 OA F124281 702533 1Q15 0339 GA8S 43 4/1/1964 12/1/1963 500 Y Overheating

7/18/2006 21:49 CIOA F124624 702579 1Q16 0479 GA8S 42 4/1/1964 3/1/1964 500 Y Overheating

7/18/2006 20:55 CIOA D514708 700963 1Q17 7995 GA8S 45 6/1/1967 4/1/1961 500 Corrosion

7/18/2006 23:57 CIOA M174722 812547 1Q18 8807 HIGAIT 18 12/27/2004 10/3/1988 500 Overheating

7/19/2006 0:06 OA H260569 806969 1Q19 0624 GA8S 37 7/12/1999 7/1/1969 500 Overheating

7/19/2006 21:29 OA H309368 806420 1Q17 7981 HIGAO 34 1/1/1973 12/1/1972 500 Y Overheating

7/20/2006 8:11 FOT Q115445 0288A554751 1Q16 6531 HIGAZA 13 11/12/1993 9/29/1993 500 Mechanical damage to

Primary bushing

7/21/2006 17:25 OA M105273 706338 1Q19 6682 HIGAIT 29 1/1/1978 12/1/1977 500 Y Corrosion

7/22/2006 20:33 OA F531695 801039 1Q17 7388 GU8N 41 6/29/1993 10/1/1965 1000 Overheating

Table 5-17: Failed Transformers From Long Island City July 2006 Event

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