Southwest Power Pool MINIMUM DESIGN STANDARDS TASK …

Southwest Power Pool

MINIMUM DESIGN STANDARDS TASK FORCE WORKING GROUP

MEETING

May 24, 2016

Teleconference

(2:00 PM – 4:00 PM)

• M I N U T E S •

Agenda Item 1: Administrative Items

MDSTF Meeting

Item 1a: Call to Order and Introductions

Secretary Doug Bowman (SPP), called the meeting to order around 2:00 PM, welcomed those in

attendance, and asked for introductions. (Attachment 1 – MDSTF Attendance 5-24-2016)

Item 1b: Receipt of Proxies

There were no proxies.

Item 1c: Approve minutes of previous meetings

The previous meeting minutes were not reviewed during the meeting.

Item 1d: Agenda

Agenda Presented. (Attachment 2 – MDSTF Agenda 5-24-2016)

Agenda Item 2: Review of Past Action Items

No past action items were discussed. (Attachment 3 - MDSTF Action Items 5-24-2016)

Agenda Item 3: Minimum Transmission Design Standard for Competitive Upgrades Rev 2

Proposed Changes

The TF reviewed the proposed changes to the MTDS received from both stakeholders and the

Industry Expert Panel (IEP) involved in the completion of the first Transmission Owner

Selection Process finalized at the SPP Board of Directors meeting on April 26th. (Attachment 4 –

Minimum Transmission Design Standard)

Jeff Stebbins (TCEC) shared his comments with the group regarding potential clarification points

in the SPP Effective 2016 Planning Criteria. He asked the TF members to review his comments

internally to discuss at the next meeting. (Attachment 5 – SPP Effective 2016 Planning Criteria

with Highlights)

Action Items:

TF members to review Jeff’s highlights to the SPP Effective 2016 Planning Criteria internally to

discuss at the next meeting.

Agenda Item 4: Other Items

No other items were brought up for discussion.

Agenda Item 5: Discussion of Future Meetings

Remaining Meetings (Meet as needed):

June (via doodle poll)

Agenda Item 6: Closing Administrative Duties

The Action Items were summarized, the meeting adjourned, and a request for availability in June

will be sent to schedule our next meeting.

Respectfully Submitted,

Douglas Bowman

MDSTF Staff Secretary

Attachments Attachment 1 – MDSTF Attendance 5-24-2016 Attachment 2 – MDSTF Agenda 5-24-2016 Attachment 3 - MDSTF Action Items 5-24-2016 Attachment 4 – Draft Minimum Transmission Design Standard Rev 2 Attachment 5 – SPP Effective 2016 Planning Criteria with Highlights

Southwest Power Pool

MINIMUM DESIGN STANDARDS TASK FORCE WORKING GROUP

MEETING

May 24, 2016

Teleconference

(2:00 pm – 4:00 pm)

Participant Name Email

1 Doug Bowman [email protected]

2 Jarred Miland [email protected]

3 Chris Giles [email protected]

4 Pat Hayes [email protected]

5 Jeff Stebbins (TCEC) [email protected]

6 Brian Johnson - AEP [email protected]

7 Dave Parrish [email protected]

8 graybigl [email protected]

9 Kenny Munsell (Xcel Energy) [email protected]

10 Erin Keeler - ITC [email protected]

11 Clarence D. Suppes (SEPC) [email protected]

12 William Pim [email protected]

13 Melanie Hill (SPP) [email protected]

14 Mark Kuhlenengel (OPPD) [email protected]

15 David Binkley [email protected]

16 Paul Sedlacek (Westar) [email protected]

17 Dan Slaven KCPL [email protected]

18 Brian Jack [email protected]

19 Jerrod Nelson [email protected]

20 Michael Wegner (ITC) [email protected]

21 Kyle Drees (WR) [email protected]

22 Robert Nasset [email protected]

23 Dawn-Marie Coggins [email protected]

24 allen ackland [email protected]

25 Jeff Stebbins (TCEC) [email protected]

26 Jay [email protected]

27 Aaron Shipley [email protected]

mailto:[email protected]

mailto:[email protected]

Relationship-Based • Member-Driven • Independence Through Diversity

Evolutionary vs. Revolutionary • Reliability & Economics Inseparable

Southwest Power Pool, Inc.

MINIMUM DESIGN STANDARD TASK FORCE

May 24, 2016

Net Conference

• A G E N D A •

1. Administrative Items ............................................................................................................ Jeff Stebbins a. Call to order b. Proxies c. Approve minutes of previous meeting d. Approve agenda

2. Review of Past Action Items…………………………………………………………………….Doug Bowman

3. Minimum Transmission Design Standard Rev 2 Proposed Changes…….……..………….. Jeff Stebbins a. Comments from Industry Experts Panel b. Comments from ITC

4. Other Topics for Discussion.…………………………………………………………………............. Group

5. Discussion of Future Meetings (Proposed Meeting Dates)……….………………………… Jeff Stebbins a. 2016 (Net Conference; Doodle Poll)

6. Closing Administrative Duties………………………………………………………………….. Doug Bowman

a. Summarize Action Items b. Adjourn meeting

Action

Item

Date

OriginatedAction Item Comments

Status(Not Started, In Progress,

Closure Pending, On

Hold, Closed)

1. 04/11/16SPP staff to review approval cycle of

Minimum Transmission Design Standard.In Progress

2. 04/11/16SPP staff to get the SPCWG to review the

MTDS Protection and Controls comments.5-9-2016 Received 1 comment In Progress

3. 04/11/16SPP staff to schedule a meeting for the second

week of May.

4/21/2016 - meeting scheduled for

May 9Complete

4. 04/11/16SPP staff to send AEP Rev 2 comments on

proposed changes to TF.Sent to TF on 4/12. Complete

5. 04/11/16

SPP staff to review lessons learned from

Order 1000 process to determine if updates to

the MTDS are necessary.

Sent to TF on 4/25. Posted to

MDSTF Exploder 5/4.Complete

6. 05/09/16

SPP staff to provide the MDSTF with Rev 2

Minimum Transmission Design Standard

draft, the updated RFP Response Form, and a

link to the IEP Public Report.

Sent to TF on 5/9. Complete

7. 05/24/16

TF members to review Jeff’s highlights to the

SPP Effective 2016 Planning Criteria

internally to discuss at the June meeting.

Document posted to MDSTF

Meeting Materials on 5/25.

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Working Group Action Items

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Minimum Transmis s ion

Des ign S tandards for

Compet i t ive Upgrades

January 23, 2015May 2016

Minimum Design Standards Task Force


Minimum Transmission Design Standards for Competitive Upgrades

1

Revision History

Date or Version

Number

Author Change Description Comments

12/17/2014

Revision IR

MDSTF Original Approved by MDSTF

and PCWG

1/23/2015

Revision 1

MDSTF Changed the 230 kV

rating in the transmission

circuit design to 1,200

amps minimum in table

on page 8

Changed per MOPC

request and approved by

MDSTF



2

Table of Contents

Revision History .......................................................................................................................1

Acronyms and Definitions .......................................................................................................3

Introduction ..............................................................................................................................4

Transmission Lines ..................................................................................................................6

Transmission Substations ......................................................................................................10

Transmission Protection and Control Design .....................................................................18



3

Acronyms and Definitions

ACI American Concrete Institute

ADSS All-Dielectric Self Supporting

AISC American Institute of Steel Construction

AISI American Iron and Steel Institute

ANSI American National Standards Institute

ASCE American Society of Civil Engineers

BIL Basic Insulation Level

CFR Code of Federal Regulation

CIGRE International Council on Large Electric Systems

CT Current Transformers

CVT Capacitive Voltage Transformer

DETC De-energized Tap Changer

DME Disturbance Monitoring Equipment

DTT Direct Transfer Trip

FAC Facilities Design, Connections, and Maintenance

FAC-008 Facility Ratings Methodology

GPS Global Positioning System

IEC International Electrotechnical Commission

IEDs Intelligent Electronic Devices

IEEE Institute of Electrical and Electronics Engineers

LTC Load Tap Changer

MOP Manual of Practice

MTDS SPP Minimum Transmission Design Standards

NEMA National Electrical Manufacturers Association

NERC North American Electric Reliability Corporation

NESC National Electrical Safety Code

OLTC On-Load Tap Changer Transformer

OPGW Optical Ground Wire

OSHA Occupational Safety & Health Administration

PLC Power Line Carrier

PMU Phasor Measurement Unit

RFP Request for Proposal

PT Potential Transformer

RTU Remote Terminal Unit

SCADA Supervisory Control and Data Acquisition

TO Transmission Owner

TOSP Transmission Owner Selection Process

TPL Transmission Planning

VAR Volt Ampere Reactive



4

Introduction

Applicability

A Request for Proposal (“RFP”) shallwill be published for each Competitive Upgrade which is

approved for construction by the SPP Board of Directors after January 1, 2015. Competitive

Upgrades will beare subject to the Transmission Owner Selection Process (“TOSP”) outlined set

forth in Section III of Attachment Y of the SPP Open Access Transmission Tariff (“SPP Tariff”) and

associated SPP Business Practices.

SPP shallwill issue an RFP for a Competitive Upgrade to solicit proposals from Qualified RFP

Participants or QRPs, as defined in Attachment Y of the SPP Tariff, (“Respondent”). These SPP

Minimum Transmission Design Standards (“MTDS”) outline the minimum design standards to be

used by the Respondent in its response to such RFP issued by SPP pursuant to the TOSP for

Competitive Upgrades. If a particular RFP states a value greater than that shown in the MTDS, the

RFP shall govern what the Respondent shall use in its RFP Response. SPP shall, as part of the

project portfolio proposal to the BOD for approval of the project, document the need for any

standard deviating from that set forth in the SPP MTDS. If there is a conflict between the RFP and

the SPP Tariff or Business Practices, the SPP Tariff and Business Practices shall govern.

The MTDS represent the minimum design standards by which a Competitive Upgrade must be

designed unless the project approved by the BOD and set forth in the RFP specifies different values

than those provided in the MTDS. The MTDS facilitate the design of transmission facilities in a

manner that is compliant with NERC requirements and SPP Criteria; are consistent with Good

Utility Practice, as defined in the SPP Tariff1; and are consistent with current industry standards

specified herein, such as NESC, IEEE, ASCE, CIGRE, and ANSI, at the time the RFP is issued.

The MTDS ensure that the Respondent has the necessary information for the Competitive Upgrade

to be constructed within the parameters requested by SPP. Individual sections within this document

contain minimum design standards for transmission lines and transmission substations. If the

Respondent has questions regarding the MTDS or the RFP design requirements, it is the

Respondent’s sole responsibility to direct such questions to the SPP in the manner specified by SPP

1 The SPP Tariff defines Good Utility Practice as follows: “Good Utility Practice: Any of the practices, methods and acts

engaged in or approved by a significant portion of the electric utility industry during the relevant time period, or any of

the practices, methods and acts which, in the exercise of reasonable judgment in light of the facts known at the t ime the

decision was made, could have been expected to accomplish the desired result at a reasonable cost consistent with good

business practices, reliability, safety and expedition. Good Utility Practice is not intended to be limited to the optimum

practice, method, or act to the exclusion of all others, but rather to be acceptable practices, methods, or acts generally

accepted in the region, including those practices required by Federal Power Act section 215(a)(4).”



5

in the RFP. SPP bears no responsibility if the Respondent does not understand the MTDS or RFP

design requirements. The Respondent is encouraged to clarify such questions prior to the RFP

Response due date allowing time for SPP to address such questions.

Any RFP Response submitted to SPP in the TOSP that exceeds the RFP design requirements is

submitted solely at the discretion of the Responder. Responders are highly encouraged to provide

sufficient information for any such deviation to provide the Industry Expert Panel information that

can be used in the evaluation of the RFP Response.

In no instance shall the Minimum Design Standard for a Project for a Competitive Project exceed the

design standards of the Transmission Owner(s) to which the project connects, unless specifically

detailed by SPP as part of the proposed project and approved by the SPP BOD. Further, in no

instance shall a design requirement for a Competitive Project exceed the prevailing design standards

in the SPP region unless explicitly approved by the SPP BOD.

All references to standards contained herein through reference mean standards as of the date

the project was initially approved by the SPP BOD.



6

Transmission Lines

General

Transmission lines shall be designed to meet all applicable federal, state, and local environmental

and regulatory requirements.

Electrical Clearances

Design clearances shall meet the requirements of the NESC. To account for survey and construction

tolerances, a minimum design margin of 2 feet shall be applied to ensure the NESC clearances are

maintained after construction. This margin shall be applied to conductor-to-ground and conductor-

to-underlying or –adjacent object clearances, but need not be applied to conductor-to-transmission

structure clearances. These clearances shall be maintained for all NESC requirements and during the

ice with concurrent wind event as defined in the Structure Design Loads Section. In regions

susceptible to conductor galloping, phase-to-phase and phase-to-shield wire clearances during these

conditions shall be considered.

Sufficient space to maintain OSHA minimum approach distances in place at the date of project

approval, either with or without tools, shall be provided. When live-line maintenance is anticipated,

designs shall be suitable to support the type of work that will be performed (e.g., insulator assembly

replacement) and the methods employed (i.e., hot stick, bucket truck, or helicopter work, etc.).

Structural Design Loads

All structure types (deadends, tangents, and angles), insulators, hardware, and foundations shall be

designed to withstand the following combinations of gravity, wind, ice, conductor tension,

construction, and maintenance loads.” The magnitude of all weather-related loads, except for NESC

or other legislated loads shall be determined using a 100 year mean return period and the basic wind

speed and ice with concurrent wind maps defined in the ASCE Manual of Practice (MOP) 74. SPP

shall provide values for any number used in a calculation (Extreme Wind, Extreme Ice, etc.) to

determine the MTDS either in an Appendix to this document and such numbers shall be reviewed at

least every five years. With the exception of the NESC or other legislated loads that specify

otherwise, overload factors shall be a minimum of 1.0.

Loads with All Wires Intact

NESC Grade B, Heavy Loading

Other legislated loads



7

Extreme wind applied at 90º to the conductor and structure

Extreme wind applied at 45º to the conductor and structure

Ice with concurrent wind

Extreme ice loading

Unbalanced Loads (applies to tangent structures only)

Longitudinal loads due to unbalanced ice conditions, considering 1/2’’radial ice, no wind in

one span, no ice on adjacent span, with all wires intact at 32º Fahrenheit final tension. This

load case does not apply to insulators; however, insulators must be designed such that they

do not detach from the supporting structure.

Longitudinal loads due to one broken ground wire or one phase position (the phase may

consist of multiple sub-conductors). For single conductor phases, use 0” ice, 70 mph wind,

0º F and for multi-bundled phases use no wind, 60º F. Alternatively, for lines rated below

200 kV, provide stop structures at appropriate intervals to minimize the risk of cascading

failures. This load case does not apply to insulators; however, insulators must be designed

such that they do not detach from the supporting structure.

Construction and Maintenance Loads

Construction and maintenance loads shall be applied based on the recommendations of ASCE

MOP 74.

Structure and Foundation Design

Structures and foundations shall be designed to the requirements of the applicable publications:

ASCE Standard No. 10, Design of Latticed Steel Transmission Structures

ASCE Standard No. 48, Design of Steel Transmission Pole Structures

ASCE Manual No. 91, Design of Guyed Electrical Transmission Structures

ASCE Manual No. 104, Recommended Practice for Fiber-Reinforced Polymer Products for

Overhead Utility Line Structures

ASCE Manual No. 123, Prestressed Concrete Transmission Pole Structures

ANSI 05-1, Specifications and Dimensions for Wood Poles

IEEE Std. 751, Trial-Use Design Guide for Wood Transmission Structures

ACI 318 Building Code Requirements for Structural Concrete and Commentary

Proper clearances with design margins shall be maintained under deflected structure conditions.



8

A geotechnical study shall be the basis of the final foundation design parameters.

Insulation Coordination, Shielding, and Grounding

Insulation, grounding, and shielding of the transmission system (line and station) shall be

coordinated between the Designated Transmission Owner and the Transmission Owner(s) to which

the project interconnects to ensure acceptable facility performance.

All metal transmission line structures, and all metal parts on wood and concrete structures shall be

grounded. Overhead shield wires shall also be grounded, or a low impulse flashover path to ground

shall be provided. Grounding requirements shall be in accordance with the NESC.

Phase Conductors

The minimum amperage capability of phase conductors shall meet or exceed the values shown

below, unless otherwise specified by SPP. If otherwise specified by SPP, the SPP value shall

govern. The amperage values shown in the table shall be considered to be associated with

emergency operating conditions.

The emergency rating is the amperage the circuit can carry for the time sufficient for adjustment of

transfer schedules, generation dispatch, or line switching in an orderly manner with acceptable loss

of life to the circuit involved. Conductors shall be selected such that they will lose no more than 10

percent of their original strength due to anticipated periodic operation above the normal rating.

Voltage (kV) Emergency

Rating

(Amps)

100 - 200 1,200

230 1,200

345 3,000

500 3,000

765 4,000

Normal circuit ratings shall be established by the Respondent such that the conductor can operate

continuously without loss of strength. Respondents shall document Consideration shall be given to

electrical system performance (voltage, stability, losses, impedance, corona, and audible noise), and

Commented [MH1]: Stopped here 5/24/2016

Commented [AS2]: What does “Consideration” mean? Might consider stronger wording such as “required to document” or something if the items in parentheticals are important enough to be

part of any RFP Response. “Consideration” can be very open-ended

language from a standards document perspective.

Commented [AS3]: Are there any standards for these variables that should be documented as acceptable here?



9

for the effects of the high electric fields when selecting the size and arrangement of phase conductors

and sub-conductors.

The conversion from conductor ampacity to conductor temperature shall be based on IEEE Publication

No. 738, Standard for Calculating the Current-Temperature Relationship of Bare Overhead

Conductors, SPP Criteria 12.2, or another documented approach that complies with the current FAC-

008.

Shield Wire

Fiber shall be installed on all new transmission lines being constructed, consisting of OPGW,

underground fiber, or ADSS fiber. Where there are multiple shield wires and OPGW is utilized,

only one need be OPGW. The shield design shall be determined based on the anticipated fault

currents generating from the terminal substations.

Adequate provisions shall be made for fiber repeater redundancy as well as power supply

redundancy at each repeater.

The minimum number of fiber strands per cable shall be 36.

Reactive Compensation Final reactive compensation shall be provided as specified by SPP.

Other Considerations

Wind Induced Vibration

The design shall consider providing mitigation for the effects of wind induced vibration for

wire systems.

Commented [AS4]: Update to match new SPP Planning Criteria version 12/1/2015. This section was not edited but the numbering

was modified.

Commented [AS5]: Should there be just one reference here and

not 3? 3 poses a couple potential problems 1)Do these varying methods/standards contradict each other

through either different acceptable variables or methods for

evaluating this conversion? This can be a challenge to account for in a 60-90 day evaluation period across multiple responses. IF

one is acceptable why not just use it alone as the conversion

method. 2)The “or” option is very open-ended and if not properly

documented by a respondent, could be a potential issue for the

IEP evaluations. It also negates any standards prescribed in the IEEE or SPP Criteria options and would not be as widely known

as the IEEE or SPP Criteria. At least those two methods are

known either by the industry (IEEE) or SPP region (SPP Criteria). Company specific approaches is what we see with the “or” option

and that can potentially be an issue in a competitive environment

when placing a conductor in a territory of another TO with

different standards that may be lower or higher than what was

used in the RFP Respondents evaluation

Commented [MAK6R5]: I think this area needs better definition and clarity. The way this was recently applied was not fully

consistent with SPP Criteria 12.2. perhaps Criteria 12.2 should be

the standard as I believe it refers back to IEE 738.

Commented [MH7R5]: TF to take to own companies to determine if referring only to 7.2 is acceptable

Commented [AS8]: Might could use some expansion on this point. The word consider might should be stronger or more of a

requirement. Are there any standards/numbers to associate with

galloping that are acceptable? At minimum may include a requirement to document how this was

evaluated and the results of the wind induced vibration evaluations

as part of a rfp response. Word as needed.



10

Transmission Substations

Substation Site Development

Transmission substations shall be sited and designed to meet all applicable environmental and

regulatory requirements. Each shall be developed to accommodate the intended electrical purpose.

Sufficient property shall be provided to accommodate predicted growth and expansion throughout

the anticipated planning horizon and as defined in the RFP. The final size shall consider future

maintenance and major equipment replacement needs.

The design and development of the substation property shall be completed with due consideration to

the existing terrain and geotechnical conditions. Storm water management plans and structures must

comply with all federal, state, and local regulations. The substation pad shall be graded such that it

is at or above the 100-year flood level, however alternate methods such as elevating equipment may

be considered by SPP.

Electrical Clearances

All design and working clearances shall meet the requirements of the NESC. Additional vertical

clearance to conductors and bus shall be provided in areas where foot and vehicular traffic may be

present. Phase spacing shall meet IEEE C37.32 and NESC requirements.

Sufficient space to maintain OSHA minimum approach distances, either with or without tools, shall

be provided. When live-line maintenance is anticipated, designs shall be suitable to support the type

of work that will be performed (e.g., insulator assembly replacement) and the methods employed

(i.e., hot stick, bucket truck work, etc.). This requirement is not intended to force working clearances

on structures not intended to be worked from.

Structural Design Loads

Structures, insulators, hardware, bus, and foundations shall be designed to withstand the following

combinations of gravity, wind, ice, conductor tension, fault loads, and seismic loads (where

applicable). The magnitude of all weather-related loads, except for NESC or other legislated loads

shall be determined using the 100 year mean return period and the basic wind speed and ice with

concurrent wind maps defined in the ASCE Manual of Practice (MOP) 113. The load combinations

and overload factors defined in ASCE MOP 113 or a similar documented procedure shall be used.

Line Structures and Shield Wire Poles

NESC Grade B, Heavy Loading



11

Other legislated loads

Extreme wind applied at 90 degrees to the conductor and structure

Extreme wind applied at 45 degrees to the conductor and structure


Extreme ice loading, based on regional weather studies

Equipment Structures and Shield Poles without Shield Wires

Extreme wind, no ice


Forces due to line tension, fault currents and thermal loads

In the above loading cases, wind loads shall be applied separately in three directions (two

orthogonal directions and at 45 degrees, if applicable).

Structure and Foundation Design

Structures and foundations shall be designed to the requirements of the applicable publications:

ASCE Standard No. 10, Design of Latticed Steel Transmission Structures

ASCE Standard No. 48, Design of Steel Transmission Pole Structures

ASCE Standard No. 113, Substation Structure Design Guide

AISC 360 Specification for Structural Steel Buildings

ACI 318 Building Code Requirements for Structural Concrete and Commentary

Deflection of structures shall be limited such that equipment function or operation is not impaired,

and that proper clearances are maintained. The load combinations, overload factors, and deflection

limits defined in ASCE MOP 113 or a similar documented procedure shall be used.

A site-specific geotechnical study shall be the basis of the final foundation design parameters.

Grounding and Shielding

The substation ground grid shall be designed in accordance with the latest version of IEEE Std. 80,

Guide for Safety in AC Substation Grounding, using the fault currents defined in the Minimum

Design Fault Current Levels section.



12

All bus and equipment shall be protected from direct lightning strikes using the Rolling Sphere

Method. IEEE Std. 998, Guide for Direct Lightning Stroke Shielding of Substations.

Surge protection (with the appropriate energy rating determined through system studies) shall be

applied on all line terminals and power transformers.

Bus Design

Substation bus shall be designed in accordance with IEEE Std. 605, Guide for Bus Design in Air

Insulated Substations and ASCE Manuel 113.

Bus Configuration

Substations shall be designed using the bus configurations shown in the table below or as specified

by SPP. All stations shall be developed to accommodate predicted growth and expansion (e.g.,

converting ring bus to a breaker and a half as terminals are added) throughout the anticipated

planning horizon and as defined by SPP. For the purposes of this table, terminals are considered

transmission lines, BES transformers, generator interconnections. Capacitor banks, reactor banks,

and non-BES transformer connections are not considered to be a terminal.

Voltage (kV) Number of Terminals Substation Arrangement

100 - 200 One or Two Single Bus

Three to Six Ring Bus

More than Six Breaker-and-a-half

201 - 765 One to Four Ring Bus

More than Four Breaker-and-a-half

Commented [MH9]: Each TF member to vet internally to determine if wording is acceptable



13

Rating of Bus Conductors

The minimum amperage capability of substation bus conductors shall meet or exceed the values

shown below, unless otherwise specified by SPP. If otherwise specified by SPP, the SPP value shall

govern. The amperage values shown in the table shall be considered to be associated with

emergency operating conditions.

The emergency rating is the amperage that the circuit can carry for the time sufficient for adjustment

of transfer schedules, generation dispatch, or line switching in an orderly manner with acceptable

loss of life to the circuit involved. Conductors shall be selected such that they will lose no more than

10 percent of their original strength due to anticipated periodic operation above the normal rating.

Voltage (kV) Emergency

Rating

(Amps)

100 - 200 1,22,000

230 2,000

345 3,000

500 3,000

765 4,000


continuously without loss of strength. Consideration shall be given to electrical system performance

(voltage, stability, losses, impedance, corona, and audible noise), and for the effects of the high

electric fields when selecting the size and arrangement of phase conductors and sub-conductors.

For bare, stranded conductors, the conversion from conductor ampacity to conductor temperature

shall be based on IEEE Publication No. 738, Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors, SPP Criteria 12.2.2, or other similar documented

approaches.

For rigid bus conductors, the conversion to conductor operating temperature shall be based on IEEE

Std. 605, Guide for Bus Design in Air Insulated Substations, SPP Criteria 12.2.2 as applicable, or

other similar documented approaches.”

Commented [AS10]: Same concerns on this paragraph and varying methods to evaluate as detailed in the Transmission Line

section on page 8.

Commented [AS11]: Update reference to match new Planning Criteria published 12/1/2015

Commented [AS12]: Same concern with this language as the

previous section. Why “or”? Why not just 1 acceptable reference?



14

Substation Equipment

All substation equipment should be specified such that audible sound levels at the edge of the

substation property are appropriate to the facility’s location.

Minimum Basic Insulation Levels (BIL)

Substation insulators, power transformer windings and bushings, potential transformer bushings,

current transformer bushings, and power PTs shall meet the minimum BIL levels shown in the tables

below. When placed in areas of heavy contamination (coastal, agricultural, and industrial), extra-

creep insulators, special coatings to extra-creep porcelain insulators, or polymer insulators shall be

used.

Substation Insulators

Nominal System L-L

Voltage (kV)

BIL

(kV Crest)

BIL (kV Crest) Heavy

Contaminated Environment

115 - 138 550 650 (Extra Creep)

161 650 750 (Extra Creep)

230 750 900 (Extra Creep)

345 1050 1300 (Extra Creep)

500 1550 1800 (Standard Creep)

765 2050 2050 (Standard Creep)

Power Transformers, Potential Transformers and Current Transformers

Nominal

System L-L

Voltage (kV)

Power Transformer

Winding BIL

(kV Crest)

Power PTs

(kV Crest)

PT and CT BIL

(kV Crest)

Circuit Breaker BIL

(kV Crest)

115 450 550 550 550

138 550 650 650 650

161 650 650 650 650

230 750 900 900 900

345 1050 1300 1300 1300



15

500 1425 N/A 1550 / 1800 1800

765 2050 N/A 2050 2050

Power Transformers

Power transformers shall comply with the latest revisions of ANSI/IEEE C57, NEMA TR-1, and

IEC 76. NEMA TR-1 shall apply only to details not specified by ANSI/IEEE C57, and IEC shall

apply to details not specified by ANSI/IEEE C57 or NEMA TR-1.

For transformers with low voltage winding below 200kV, On-Load Tap Changing transformers

(OLTC) shall be equipped with automatically and manually operated “tap-changing-under-load”

equipment. This shall have a range of 10% above and below the rated low voltage in 32 steps

(33 positions). The LTC shall allow the tertiary voltage where applicable to follow the high side

voltage throughout the entire tap range (i.e., the effective HV-TV turns ratio shall remain constant

within 0.5%).

De-energized Tap Changing (DETC) transformers shall have five high voltage full capacity taps

designed for operation with the unit de-energized.

Minimum Design Fault Current Levels

Substations shall be designed to withstand the calculated available symmetrical fault current

including predicted growth and expansion throughout the anticipated planning horizon. Design

values will be determined from system models provided by SPP.

Minimum Rating of Line Terminal Equipment

Terminal definition – point of demarcation between the transmission line and the substation. The

transmission line terminal shall be considered the substation deadend structure.

Terminal Equipment definition – All equipment located within the substation that is considered, for

ratings purposes, to be a part of the transmission line. This equipment consists of jumpers, devices,

switches, bus, etc., through which line current flows to the common substation bus.



16

The minimum amperage capability of substation terminal equipment shall meet or exceed the

ratingvalues of the associated transmission lineshown in the table below, unless otherwise specified

by SPP. If otherwise specified by SPP, the SPP value shall govern. The amperage values shown in

the table shall be considered to be associated with emergency operating conditions.

The emergency rating is the amperage that the circuit can carry for the time sufficient for adjustment

of transfer schedules, generation dispatch, or line switching in an orderly manner with acceptable

loss of life to the circuit involved. Equipment shall be rated in accordance with the applicable IEEE

Standard, SPP Criteria 12, or another documented approach that complies with the current FAC-008.


continuously without loss of strength. Consideration shall be given to electrical system performance

(voltage, stability, losses, impedance, corona, and audible noise), and for the effects of the high

electric fields when selecting the size and arrangement of phase conductors and sub-conductors.

Substation Service

Two sources of AC substation service, preferred and backup shall be provided. This shall be

accomplished by using the tertiary winding of an autotransformer, power PTs connected to the bus,

distribution lines or a generator. Distribution lines shall not be used as a primary source unless no

other feasible alternative exists. Generators shall not be used as a primary source.

Control Enclosures

Control enclosures shall be designed to the requirements of the applicable publications:

Voltage

(kV)

Emergency

Rating (Amps)

100 - 200 1,200

230 2,000

345 3,000

500 3,000

765 4,000

Commented [AS13]: Update reference.

Commented [AS14]: Same concern as stated previously.

Commented [AS15]: Stronger language than “consider” Require or detail what is expected for to be documented for these

variables.



17

ASCE 7, Minimum Design Loads for Buildings and Other Structures

AISC 360 Specification for Structural Steel Buildings

AISI Specification for the Design of Cold-Formed Steel Structural Members

ACI 530/530.1, Building Code Requirements and Specification for Masonry Structures and

Related Commentaries

ACI 318, Building Code Requirements for Structural Concrete and Commentary

NESC

OSHA

Design loads and load combinations shall be based on the requirements of the International Building

Code or as directed by the jurisdiction having authority. Weather loads shall be based on a 100 year

mean return period.

Wall and roof insulation shall be designed in accordance with the latest edition of the International

Energy Conservation Code for the applicable Climate Zone.

Oil Containment

Secondary oil containment shall be provided around oil-filled electrical equipment and storage tanks

in accordance with the requirements found in 40 CFR 112 of the United States EPA and local

ordinances.

Metering

Intertie metering shall be installed in accordance with SPP Criteria 7.0 and the Interconnect

Agreement with the incumbent Transmission Owner(s) (TOs). Metering criteria should match those

of the connected TO and Transmission Operator.



18

Transmission Protection and Control Design

General

Substation protection and control equipment must adhere to NERC Reliability Standards and SPP

Criteria, and be compatible with the incumbent TO standards. It is the responsibility of the

successful Respondent to contact the incumbent TO(s) to ensure proper coordination of both the

communication channel and the relay systems

For all new substations, all Intelligent Electronic Devices (IEDs) shall be synchronized through the

use of a satellite GPS clock system.

Communication Systems

Power Line Carrier (PLC) equipment, microwave, or fiber shall be specified as the communication

medium in pilot protection schemes. PLC equipment may be used on existing transmission lines.

For existing transmission lines less than 5 miles, forms other than PLC shall be considered and made

compatible with the incumbent TO(s) equipment. PLC is not preferable for lines less than 5 miles

due to the reliability characteristics of the equipment. Fiber protection schemes shall be considered

on all new transmission lines.

Voltage and Current Sensing Devices

For primary and secondary protection schemes, independent current transformers (CTs) and

independent secondary windings of the same voltage source shall be used.

CTs used for relaying shall be C800 with a thermal rating factor of 2.0 or greater.

CVTs and wound PTs used in relaying shall be designed and tested to meet all applicable ANSI and

NEMA standards. CVTs and wound PTs shall have an accuracy class of CL 1.2 WXYZ for relaying

and CL 0.3 WXYZ for metering.

DC Systems

For new substations greater than 200 kV, redundant battery systems shall be installed.

Commented [AS16]: Does this mean required? Do you want Fiber Protection schemes on all new Tlines? IF so require here.



19

At all voltage levels, battery system(s) of sufficient capacity to support station requirements for a

minimum duration of 8 hours without AC power shall be installed. DC systems shall be designed in

accordance with NERC standards and SPP Criteria.

Primary and Secondary Protection Schemes

Primary and secondary protection schemes shall be required for all lines and be capable of detecting

all faults on the line. The primary scheme shall provide communications-assisted, high-speed

simultaneous tripping of all line terminals at speeds that will provide fault clearing times for system

stability as defined in the most recent version of the NERC Transmission Planning and Reliability

Standards (TPL).

The following criteria shall be used to determine if one or two high speed protection systems are

required on a line. While it is possible that the minimum protective relay system and redundancy

requirements outlined below could change as NERC Planning and Reliability Standards evolve, it

will be the responsibility of the Respondent to assess the protection systems and make any necessary

modifications to comply with these changes.

Line Applications

General

Alarms shall be provided for loss of communication channels and relay failure.

Automatic check-back features shall be installed on PLC-based protection schemes using) on/off

carrier to ensure the communication channel is working properly at all substations.

Local breaker failure protection shall be provided for all breakers.

765 kV / 500 kV

At least two high speed pilot schemes using a redundant battery design, and dual direct transfer

trip (DTT) are required. Protection communications require redundant paths as required by

NERC reliability standards. Power Line Carrier requires Mode 1 coupling (three phase

coupling).

230 kV/345 kV

Dual high speed communications-assisted schemes using a redundant battery design and one

direct transfer trip (DTT) system are required. Dual DTT systems are required for direct

equipment protection (reactors or capacitors). Protection communications require redundant



20

paths as required by NERC reliability standards. Power Line Carrier requires single or two

phase coupling.

Below 230 kV

A minimum of one high speed communications-assisted scheme is required.

Single phase coupling for PLC is acceptable. Breaker failure DTT system is required if remote

clearing time is not acceptable based on the TPL assessment. Dual pilot schemes may be

required for proper relay coordination or system dynamic performance requirements. When dual

high speed systems are needed, redundant communication paths shall be used. Dual DTT

systems are required for direct equipment protection (reactors or capacitors).

Transformer Applications

High Voltage Winding Above 200 kV

Transformer protection shall be designed with a redundant station battery configuration, with the

protection divided into two systems using redundant overlapping zones of protection. Each

system must provide differential protection schemes and have independent lockout

function. Also, at least one system must provide backup overcurrent protection, and sudden

pressure alarm or tripping.

High Voltage Winding 100 kV to 200 kV

Transformer protection shall be designed with the protection divided into two systems using

redundant overlapping zones of protection. Each system must provide differential protection

schemes and have independent lockout function. Also, at least one system must provide backup

overcurrent protection, and sudden pressure alarm or tripping.

Bus Applications

200 kV and Above

Bus protection shall be designed using a redundant station battery configuration with the

protection divided into two systems. Each system must provide differential protection schemes

and have independent lockout function.

Below 200 kV

Bus protection shall be designed with the protection divided into two systems. Each system must

provide differential protection schemes and have independent lockout function. Bus one-shot

schemes are also permitted.

Commented [MH17]: Dave Parrish – Brian Johnson Power Line Carrier requires two phase coupling if Power Line

Carrier is the only communication path.

Commented [MH18]: Dave Parrish – Brian Johnson Breaker failure DTT system is required if remote clearing time or

remote auto-reclosure is not acceptable based on the TPL

assessment.



21

Other Substation Equipment

For substation devices, such as capacitor banks, static VAR compensators, reactors, etc., appropriate

protection systems shall be incorporated. Redundant schemes shall be provided according to NERC

requirements.

Sync Potential and Sync Scopes

Sync potential sources (wire wound PTs or CCVTs) and synchronizing equipment shall be installed

where required.

Disturbance Monitoring Equipment (DME)

DME shall be installed in accordance with the SPP Criteria 7.0 and NERC requirements DME

equipment includes fault recorders, long term (dynamic) disturbance recorders, and sequence-of-

event recorders.

Phasor Measurement Units (PMUs) PMU capability through the use of Intelligent Electronic Devices (IEDs) or other devices capable of

providing PMU measurements, shall be installed in all new substations above 200 kV. One or more

PMU capable devices at each voltage level above 100 kV within the substation shall be provided.

SCADA and RTUs

SCADA and RTUs shall be installed in all substations. Points and protocols should match those of

the connected TO and Transmission Operator.

APPENDIX of Values to be Used in Calculations for Standards Referenced Herein

Extreme Wind

Extreme Ice

Etc.

Commented [MH19]: Dave Parrish – Jay Zeek Shouldn’t some minimum direction be provided? I.E. all

interconnect interfaces (TO-GO or TO-TO) as well as all terminals

defined in a system restoration plan as part of a cranking path.

Commented [MH20]: Dave Parrish – Jay Zeek NERC PRC-002 requirements

Commented [MH21]: Dave Parrish – Jay Zeek This is very unclear.

PMU capability through the use of Intelligent Electronic Devices (IEDs) or other devices capable of providing PMU measurements,

shall be installed in all new substations above 200 kV. PMU’s are

required to monitor bus voltage, transmission line current, and transformer current (either high side or low side). PMU equipment

must be able to stream data to a regional control center and save

sufficient data to meet NERC PRC-002 requirements.

SPP Planning Criteria

Version 1.0 11/20/2015 68

(i) The data must include the most recent 3 years.

(ii) Values may be calculated from wind or solar data, if measured MW values

are not yet available. Wind data correlated with a reference tower beyond

fifty miles is subject to Generation Working Group approval. Solar data

correlated with a reference measuring device beyond two hundred miles is

subject to Generation Working Group approval. For calculated values, at

least one year must be based on site specific data.

(iii) If the Load Serving Entity chooses not to perform the net capability

calculations as described above during the first 3 years of commercial

operation, the Load Serving Entity may submit 5% for wind facilities and

10% for solar facilities of the site facility’s nameplate rating.

(f) Facilities in commercial operation 4 years and greater:

(i) The data must include all available data up to the most recent 10 years of

commercial operation.

(ii) Only metered hourly net power output (MWH) data may be used.

(iii) After three years of commercial operations, if the Load Serving Entity

does not perform or provide the net capability calculations to SPP as

described above, then the net capability for the resource will be 0 MW.

(g) The net capability calculation shall be updated at least once every three years.

7.2 Rating of Transmission Circuits

Each SPP member shall rate transmission circuits operated at 69 kV and above in accordance

with this criteria. A transmission circuit shall consist of all elements load carrying between

circuit breakers or the comparable switching devices. Transformers with both primary and

secondary windings energized at 69 kV or above are subject to this criteria. All circuit ratings

shall be computed with the system operated in its normal state (all lines and buses in-service, all

breakers with normal status, all loads served from their normal source). The circuit ratings will

be specified in "MVA" and are taken as the minimum ratings of all of the elements in series.

The minimum circuit rating shall be determined as described in this criteria and members shall

maintain transmission right-of-way to operate at this rating. However, SPP members may use

circuit ratings higher than these minimums. Each element of a circuit shall have a normal and an


Version 1.0 11/20/2015 69

emergency rating. For certain equipment, (switches, wave traps, current transformers and circuit

breakers), these two ratings are identical and are defined as follows:

(1) NORMAL RATING: Normal circuit ratings specify the level of power flow that

facilities can carry continuously without loss of life to the facility involved.

(2) EMERGENCY RATING: Emergency circuit ratings specify the level of power flow that

a facility can carry for the time sufficient for adjustment of transfer schedules, generation

dispatch, or line switching in an orderly manner with acceptable loss of life to the facility

involved.

At a minimum, each member shall compute summer and winter seasonal ratings for each circuit

element. The summer season is defined by the months June, July, August and September. The

winter season is defined by the months December, January, February and March. The seasonal

rating shall be based upon an ambient temperature (either maximum or average) developed using

the methodology described in Appendix PL-2.A. A member may elect to compute a third set of

seasonal ratings for the remaining months of the year (April, May, October and November). If

that election is not made, summer ratings shall be used for these remaining months.

7.2.1 Power Transformer

Power transformer ratings are discussed in ANSI/IEEE C5791, IEEE Guide for Loading

Mineral-Oil-Immersed Power Transformers. Every transformer has a distinct temperature rise

capability used in setting its nameplate rating (either 55°C or 65°C). These temperature rise

amounts reflect the average winding temperature rise over ambient that a transformer may

operate on a continuous basis and still provide normal life expectancy.

7.2.1.1 Normal Rating

The normal circuit rating for power transformers shall be its highest nameplate rating. The

nameplate rating shall include the effects of forced cooling equipment if it is available. For

multi-rated transformer (OA/FA, OA/FA/FA, OA/FOA/FOA, OA/FA/FOA) with all or part of

forced cooling inoperative, nameplate rating used is based upon the maximum cooling available

for operation. Normal life expectancy will occur with a transformer operated at continuous

nameplate rating.


Version 1.0 11/20/2015 70

7.2.1.2 Emergency Rating

When operated for one or more load cycles above nameplate rating, the transformer insulation

deteriorates at a faster rate than normal. The emergency circuit rating for power transformers

shall be a minimum of 100% of its highest nameplate rating. Member systems may use a higher

emergency rating if they are willing to experience more transformer loss-of-life.

7.2.1.3 Loss of Life

In ANSI/IEEE C57.91, a 65°C rise transformer can operate at 120% for an 8 hour peak load

cycle and will experience a 0.25% loss of life. If a 65°C rise transformer experiences 4 incidents

where it operates at or below 120% for an 8 hour peak load cycle, it will still be within the target

of 1% loss of life per year. In ANSI/IEEE C57.91, a 55°C rise transformer can operate at 123%

for an 8 hour peak load cycle and will experience a 0.25% loss of life. Likewise, if a 55°C rise

transformer experiences 4 incidents where it operates at or below 123% for an 8 hour peak load

cycle, it will still be within the target of 1% loss of life per year.

7.2.1.4 Ambient Temperature

Average ambient temperature is an important factor in determining the load capability of a

transformer since the temperature rise for any load must be added to the ambient to determine

operating temperature. Transformers designed according to ANSI standards use a 30°C average

ambient temperature (average temperature for 24 consecutive hours) when setting nameplate

rating. Transformer overloads can be increased at lower average ambient temperatures and still

experience the same loss of life. This allows seasonal ratings with higher normal and emergency

ratings. However, this circuit rating criteria does not call for seasonal transformer ratings. In

ANSI/IEEE C57.91, transformers can be loaded above 110% and experience no loss of life when

the average ambient temperature is below 78°F. By not having seasonal ratings, the four

occurrences that contribute to loss of life are limited to days when the average ambient

temperature exceeds 78°F. The Power Transformer Rating Factors include:

(1) Nameplate rating, normal loss of life for 55°C and 65°C rise transformers with cooling

equipment operating.

(2) Average ambient temperature, 30°C.

(3) Equivalent load before peak load, 90% of nameplate rating.

(4) Hours of peak load, 8 hour load cycle.


Version 1.0 11/20/2015 71

(5) Acceptable annual loss of life, 1%.

7.2.2 Overhead Conductor

Overhead conductor ratings are discussed in IEEE Standard 738, IEEE Standard for Calculating

the Current-Temperature Relationship of Bare Overhead Conductors. Ampacity values are to be

determined using the fundamental heat balance equation outlined in the House and Tuttle

method. Because of the amount and complexity of the equations, this method lends itself to

computer application. The recommended computer programs to be used for this calculation

either include the BASIC program listed in Annex B of IEEE Standard 738 or an equivalent

program, such as the DYNMAP program which is part of the EPRI TLWorkstation TM software

package. While tables and graphs may be convenient to use, they fail to take into account the

geographic location of the line and often lack either the desired ambient temperature and/or the

desired conductor temperature. The use of tables and graphs is not acceptable.

7.2.2.1 Conductor Properties

Some computer programs used to compute ampacity values have a conductor property library

whereby a user simply specifies the conductor code name and the program will search the

conductor property file and select the proper input properties. Those using the BASIC program

from Annex B of IEEE Standard 738 or another computer program that does not have a

conductor property library will obtain conductor properties from an appropriate data source

(Aluminum Electrical Conductor Handbook, EPRI Transmission Line Reference Book 345 kV

and Above, Westinghouse Transmission and Distribution Book, etc.).

7.2.2.2 Line Geographic Location

These factors specify the location of the line, its predominant direction and its predominant

inclination. These numbers can either be line specific or they can represent a general line within

the control area. One ambient temperature shall be agreed upon for tie lines traversing several

geographic areas and interconnections among different control areas.

7.2.2.3 Radiation Properties

The two radiative properties of conductor material are solar absorptivity and infrared emissivity.

Solar Absorptivity The fraction of incident solar radiant energy that is absorbed by the

conductor surface. This value shall be between 0 and 1. Recommended

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values are given in the following tables:

COPPER CONDUCTORS

ALUMINUM CONDUCTORS

Oxidation Level

Absorptivity

Service Years

Absorptivity

None

Light

Normal

Heavy

0.23

0.5

0.7

1.0

0<5

0.43

1.00

Source: Glenn A. Davidson, Thomas E. Donoho, George Hakun III, P. W. Hofmann, T. E

Bethke, Pierre R. H. Landrieu and Robert T. McElhaney, "Thermal Ratings for

Bare Overhead Conductors", IEEE Trans., PAS Vol. 88, No.3, pp. 200-05, March

1969.

Infrared Emissivity The ratio of infrared radiant energy emitted by the

conductor surface to the infrared radiant energy emitted by a blackbody at the

same temperature. This value shall be between 0 and 1. Recommended values

are given in tables below:

COPPER CONDUCTORS

ALUMINUM CONDUCTORS

Oxidation Level

Emissivity

Service Years

Emissivity

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None

Light

Normal

Heavy

0.03

0.3

0.5

0.8

0

5-10

10-20

0.23

0.82

0.88

0.90

Source: W. S. Rigdon, H. E. House, R. J. Grosh and W. B. Cottingham, "Emissivity of

Weathered Conductors After Service in Rural and Industrial Environments,"

AIEE Trans., Vol. 82, pp. 891-896, Feb. 1963.

7.2.2.4 Weather Conditions

Ambient temperature represents the maximum seasonal temperature the line may experience for

summer and winter conditions. Appendix PL-2.A contains a methodology to compute maximum

ambient temperature. Wind speed is assumed at 2 ft/sec (1.4 mph) or higher. Wind direction is

assumed perpendicular to the conductor.

7.2.2.5 Maximum Conductor Temperature

The selection of a maximum conductor temperature affects both the operation and design of

transmission lines. Existing transmission lines were designed to meet some operating standard

that was in effect at the time the line was built. That standard specified the maximum conductor

temperature which maintained acceptable ground clearance while allowing for acceptable loss of

strength. Over time, the required amount of ground clearance and the maximum conductor

temperature needed to maintain acceptable ground clearance have changed. The changes are

reflected in the revisions that have been made to the National Electric Safety Code (NESC) over

the years. Although this Criteria specifies a maximum conductor temperature that could be met

by current line design practices, consideration must be given to existing lines that were built

according to an earlier standard. This Circuit Rating Criteria specifies a maximum conductor

temperature (for both normal and emergency operating conditions) that shall be used for seasonal

circuit ratings. For those existing lines that were designed to meet an earlier standard, it is the

responsibility of the line owner to establish a rating that is consistent with the NESC design

standards being practiced at the time the line was built. This Criteria specifies the use of

maximum conductor temperatures that either maintain acceptable ground clearance requirements

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from earlier NESC's or meet the temperature requirements in SPP Planning Criteria section

7.2.2.6, whichever is lower.

7.2.2.6 Determination of Maximum Conductor Temperature

The maximum conductor temperature for normal ratings may be limited by conductor clearance

concerns. Normal ratings are at a level where loss of strength is not a concern. The maximum

conductor temperature for emergency ratings have both conductor clearance and loss of strength

concerns. By setting a maximum conductor temperature and the length of time a conductor may

operate at this temperature, the maximum allowable loss of strength over the life of the

conductor is prescribed. Unless conductor clearance concerns dictate otherwise, at least the

following maximum conductor temperatures shall be used. This allows for the efficient

utilization of the transmission system while accepting minimal risk of loss of conductor strength

during emergency operating conditions. These conductor temperatures are a result of the

examination of SPP members practices.

Maximum Conductor Temperature

Normal Rating

Emergency Rating

ACSR

85°C

100°C

ACAR

85°C

100°C

Copper

85°C

100°C

Copperweld

85°C

100°C

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AAC 85°C 100°C

AAAC

85°C

100°C

SSAC

200°C

200°C

Note: Annealing of copper and aluminum begins near 100°C.

7.2.2.7 Hours of Operation at Emergency Rating

The effect of conductor heating due to operating at the maximum temperature during emergency

conditions is cumulative. If a conductor is heated under emergency loading for 4 hours 8 times

during the year, the total effect is nearly the same as heating the conductor continuously at the

temperature for 32 hours. Using a useful conductor life of 30 years, the conductor will have

been heated to the maximum temperature for 1000 hours. For an all aluminum conductor

(AAC), this results in a 7% reduction from initial strength. Since the steel core of an ACSR

conductor is essentially unaffected by the temperature range considered for emergency loadings,

for an ACSR conductor, this results in a 3% reduction from initial strength. Both of these

amounts are acceptable loss of strength. The daily load cycle for operating at the emergency

rating shall not exceed 4 hours. This load cycle duration for conductors operating at the

emergency rating is more restrictive than power transformers because power transformers have a

delay in the time required to reach a stable temperature following any change in load (caused by

a thermal lag in oil rise) and because seasonal ratings shall allow transmission lines to achieve a

maximum conductor temperature throughout the year, not just days when the ambient exceeds

78°F.

7.2.3 Underground Cables

Ampacities are calculated by solving the thermal equivalent of Ohm's Law. Conceptually, the

solution is simple, however the careful selection of the values of the components of the circuit is

necessary to ensure an accurate ampacity calculation. The recognized standard for almost all

steady-state ampacity calculations, in the United States, is taken from a publication, "The


Version 1.0 11/20/2015 76

Calculation of the Temperature Rise and Load Capability of Cable Systems," by J.H. Neher and

M.H. McGrath, 1957, hereafter referred to as the Neher-McGrath method. The procedure is

relatively simple to follow and has been verified through testing. In recent years, some of the

parameters have been updated, but the method is still the basis of all ampacity calculations.

7.2.3.1 Cable Ampacity

Cable ampacity is dependent upon the allowable conductor temperature for the particular

insulation being used. Conductor temperature is influenced by the following factors:

(1) Peak current and load-cycle shape;

(2) Conductor size, material and construction;

(3) Dielectric loss in the insulation;

(4) Current-dependent losses in conductor, shields, sheath and pipe;

(5) Thermal resistances of insulation, sheaths and coverings, filling medium, pipe or duct and

covering, and earth;

(6) Thermal capacitances of these components of the thermal circuit;

(7) Mutual-heating effects of other cables and other heat sources; and

(8) Ambient earth temperatures.

Both steady-state and emergency ampacities depend upon these factors, although emergency

ratings have a greater dependency upon the thermal capacitances of each of the thermal circuit

components.

7.2.3.2 Conductor Temperature

The maximum allowable conductor temperature is 85°C for high-pressure fluid-filled (HPFF),

pipe-type cables and 90°C for crosslinked, extruded-dielectric cables.

The table below summarizes allowable conductor temperatures for different insulation materials.

Two values are given for each cable insulation. The higher temperature may be used if the

thermal environment of the cable is well-known along the entire route, or if controlled backfill is

used, or if fluid circulation is present in an HPFF circuit. The maximum conductor temperatures

allowed under steady-state conditions are limited by the thermal aging characteristics of the

insulation structure of the cable. For emergency-overload operating conditions, maximum


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conductor temperatures are also limited by the thermal aging characteristics. The temperature is

also limited by the melting temperature range of the insulation structure of the cable, its

deformation characteristic with temperatures, restraints imposed by the metallic shield,

deformation characteristic of the jacket, and the decrease in ac and impulse strengths with

increases in temperature.

Insulation Material

Maximum Temperature

Normal

Emergency

Impregnated paper (AEIC CS2-90 for

HPFF and HPGF

(AEIC CS4-79 for SCLF)

85°C

(75°C)

105°C for 100 hr

100°C for 300 hr

Laminated paper-polypropylene (AEIC

CS2-90)

85°C

(75°C)

105°C for 100 hr

100°C for 300 hr

Crosslinked polyethylene (AEIC CS7-87)

90°C

(80°C)

105°C

cumulative for 1500 hr

Ethylene-propylene rubber (AEIC CS6-87)

90°C

(80°C)

105°C*

cumulative for 1500 hr

Electronegative gas/spacer

Consult manufacturer for specific designs

* Emergency operation at conductor temperatures up to 130°C may be used if mutually agreed

between purchaser and manufacturer and verified by qualification and prequalification tests.


Version 1.0 11/20/2015 78

7.2.3.3 Ambient Temperature

The ambient temperature is measured at the specified burial depth for buried cables and the

ambient air temperature is used for cables installed above ground. IEC Standard 287-1982 (2-5)

recommends that in the absence of national or local temperature data the following should be

used:

Climate

Ambient Air

Temperature °C

Ambient Ground

Temperature °C

Tropical

55

40

Sub-tropical

40

30

Temperature

25

20

The electrical resistance is composed of conductor dc resistance, ac increments due to skin and

proximity effects, losses due to induced currents in the cable shield and sheath and induced

magnetic losses in the steel pipe. Heat generated in the cable system will flow to ambient earth

and then to the earth surface. This heat passes through the thermal resistances of the cable

insulation, cable jacket, duct or pipe space, pipe covering and soil. Adjacent heat sources, such

as other cables or steam mains, will provide impedance to the heat flow and thus reduce cable

ampacity. Further information concerning the components of the ampacity calculations are

summarized in Appendix PL-2.B and fully detailed in the EPRI Underground Transmission

Systems Reference Book. An example calculation, from the EPRI book, is also provided in

Appendix PL-2.B.

7.2.4 Switches

Appendix PL-2.C contains a discussion on developing ratings for switches. In general, switches

have seasonal ratings that are a function of the maximum ambient temperature. A switch part

class designation is used to differentiate loadability curves that give factors which can be

multiplied by the rated continuous current of the switch to determine temperature adjusted

normal and 4 hour emergency ratings. The summer normal and emergency switch ratings can be


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computed by selecting the appropriate loadability factor curve for the switch part class, reading

the loadability factors that are appropriate for the summer maximum ambient temperature (40°C

or the summer maximum ambient temperature determined in Appendix PL-2.A), and multiplying

the continuous current ratings by the loadability factor. The switch winter normal and

emergency ratings can be computed by multiplying the continuous current rating by the normal

and emergency loadability factors that are appropriate for the winter maximum ambient

temperature (0°C or the winter maximum ambient temperature determined in Appendix PL-2.A).

Appendix PL-2.C contains loadability factor curves (both normal and emergency) for various

switch part classes. The ANSI/IEEE standard referenced in Appendix PL-2.C allows for

emergency ratings to be greater than normal ratings. This Criteria does not require the

emergency rating to be greater than the normal rating.

7.2.5 Wave Traps

Appendix PL-2.D contains a discussion on developing ratings for wave traps. The two types of

wave traps are the older air-core type and the newer epoxy-encapsulated type. In general, both

types have a continuous current rating based on a 40°C maximum ambient temperature. Both

types have a loadability factor that can be used to determine seasonal ratings that are a function

of the maximum ambient temperature. However, the older air-core type has another loadability

factor that can be used to determine a four-hour emergency rating that is also a function of the

maximum ambient temperature. The newer epoxy encapsulated type does not have an

emergency rating.

7.2.6 Current Transformers

Appendix PL-2.E contains a discussion on developing ratings for current transformers. The two

types of current transformers are the separately-mounted type and the bushing type. In general,

both types have a continuous current rating based on a 30°C average ambient temperature.

7.2.6.1 Separately Mounted Current Tranformers

The separately-mounted type has an ambient-adjusted continuous thermal current rating factor

that can be multiplied by the rated primary current of the current transformer to determine

seasonal ratings. Separately-mounted current transformers do not have emergency ratings.


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7.2.6.2 Bushing Current Transformers

Bushing current transformers are subject to and influenced by the environment of the power

apparatus in which they are mounted. Bushing current transformers can be located within circuit

breakers and power transformers. Since bushing current transformers are subject to the

environment within the power apparatus, they do not have ambient adjusted continuous thermal

current rating factors. Rather, if the primary current rating of the ratio being used is less than the

continuous current rating of the breaker or the power transformer, this restricts the breaker or

power transformer to operate below its rated current which reduces the current transformer

temperature. This allows the current transformer to be operated at a continuous thermal rating

factor greater than 1.0. Having a bushing current transformer whose primary current rating of

the ratio being used is less than the continuous current rating of the breaker or the power

transformer is an unusual case. However, the formula to develop the rating factor for this case is

located in Appendix PL-2.E. Although bushing current transformers have some short-term

emergency overload capability, it must be coordinated with the overall application limitation of

the other equipment affected by the current transformer loading. Consequently, this criteria does

not recognize an emergency rating for bushing current transformers.

7.2.7 Circuit Breakers

Appendix PL-2.F contains a discussion on developing ratings for circuit breakers. This

discussion centers on the use of specific circuit breaker design information to set seasonal and

emergency ratings. This design information is not readily available to the owners of such

equipment. To use the rating methodology discussed in Appendix PL-2.F would require

contacting the manufacturer for detailed design information for each circuit breaker being rated.

Rather than doing that, this circuit rating criteria specifies that the nameplate rating shall be used

for seasonal normal and emergency ratings. The nameplate rating is based on a maximum

ambient temperature of 40°C. If a circuit breaker is found to be a limiting element in a circuit

and is experiencing loadings that limit operations, a member system may pursue the

methodology outlined in Appendix PL-2.F to determine the circuit breakers seasonal normal and

emergency rating.

7.2.8 Ratings of Series and Reactive Elements

The series transmission elements rating will be in amps, ohms, and MVA. The series

transmission elements current (amps) rating will be taken as the minimum rating of all internal


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components (e.g., breakers) that are in series with the interconnected transmission circuit. Shunt

reactive elements (e.g., capacitors, reactors) MVA ratings will be based on the nominal

transmission interconnecting voltage.

The documentation of the methodology(ies) used to determine the rating of series and reactive

elements shall be provided to SPP and/or NERC on request within five business days.

7.2.9 Ratings of Energy Storage Devices

The available real power rating, reactive power rating, control points, and availability of each

electrical energy storage device will be provided to SPP upon request. The documentation of the

methodology(ies) used to rate electrical energy storage devices shall be provided to SPP and/or

NERC on request within five business days.

7.2.10 Circuit Rating Issues

7.2.10.1 Dynamic (Real Time) Ratings

The calculation of static thermal ratings specified in SPP Planning Criteria section 7.2.2.6 uses

worst case thermal and operational factors and therefore apply under all conditions. Often times,

these worst case thermal and operational factors do not all occur at the same time. Consequently,

a static rating may understate the thermal capacity of the circuit. For operation purposes, some

members have elected to monitor the factors that affect circuit ratings and use this information to

set dynamic ratings. A member can develop and use a rating that exceeds the static thermal

rating for operating purposes. The ratings developed by using this criteria are not intended to

restrict daily operations but set a minimum rating that can be increased when factors for

determining the equipment rating have changed. However, if transmission line ratings are

changed dynamically, the required clearances shall still be met.

7.2.10.2 Non-Thermal Limitations

There may be instances when the flow on a transmission circuit is limited by factors other than

the thermal capacity of its elements. The limit may be caused by other factors such as dynamics,

phase angle difference, relay settings or voltage limited.


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7.2.10.3 Tie Lines

When a tie line exists between two member systems, use of this criteria shall result in a uniform

circuit rating that is determined on a consistent basis between the two systems. For tie lines

between a SPP member and a non-member, the member shall follow this criteria to rate the

circuit elements owned by them and shall coordinate the rating of the tie line with the non-

member system such that it utilizes the lowest rating between the two systems.

7.2.10.4 Rating Inconsistencies

A member may have a contractual interest in a joint ownership transmission line whereby the

capacity of the line is allocated among the owners. The allocated capacity may be based upon

the thermal capacity of the line or other considerations. Members shall use good faith effort to

amend their transmission line agreements to reflect the effects of new circuit ratings. There may

exist other transmission agreements or regulatory mandates that use the thermal capacity of

transmission circuits in allocation of cost and determination of network usage formulas (for

example, the MW-mile in ERCOT). These agreements and mandates may specify a

methodology and/or factors for computing thermal capacity used in the formulas. Since these

amounts are only used in assignment of cost or usage responsibility and not in actual operations

of the transmission system, there is no conflict with using a different set of ratings for this

specific purpose.

7.2.10.5 Damaged Equipment

There may be instances when a derating of a transmission line element is required due to

damaged equipment. The limit may be caused by such factors as broken strands, damaged

connectors, failed cooling fans, or other damage reducing the thermal capability.

7.2.11 Reporting Requirements

Each member will administer this Criteria and will make available upon request the application

of this Criteria for those facilities that impact another member (i.e. force them to curtail

schedules due to line loadings, denies them access to transmission service or requires them to

build new transmission facilities or pay opportunity costs to receive transmission service).

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