08 - Device Coordination

ETAP 5.0ETAP 5.0

Copyright 2004 Operation Technology, Inc.

Protective DeviceCoordination

Copyright 2004 Operation Technology, Inc. – Workshop Notes: Protective Device Coordination Slide 2

Agenda• OC Protective Device Coordination

– Concepts & Applications

• STAR 5.0.0 Overview– Features & Capabilities

• STAR Example 1

– Advance Topics• STAR Example 2

– PD Sequence of Operation– Device Libraries– ETAP ARTTS


Definition

• Overcurrent Coordination– A systematic study of current responsive

devices in an electrical power system.


Objective

• To determine the ratings and settings offuses, breakers, relay, etc.

• To isolate the fault or overloads.


Criteria

• Economics

• Available Measures of Fault

• Operating Practices

• Previous Experience


Design

• Open only PD upstream of the fault oroverload

• Provide satisfactory protection for overloads

• Interrupt SC as rapidly (instantaneously) aspossible

• Comply with all applicable standards andcodes

• Plot the Time Current Characteristics ofdifferent PDs


Analysis

When:

• New electrical systems

• Plant electrical system expansion/retrofits

• Coordination failure in an existing plant


Protection vs. Coordination

• Coordination is not an exact science

• Compromise between protection andcoordination– Reliability

– Speed

– Performance

– Economics

– Simplicity


Protection

• Prevent injury to personnel

• Minimize damage to components

– Quickly isolate the affected portion of the system

– Minimize the magnitude of available short-circuit


Spectrum Of Currents

• Load Current– Up to 100% of full-load

– 115-125% (mild overload)

• Overcurrent– Abnormal loading condition (Locked-Rotor)

• Fault Current– Fault condition

– Ten times the full-load current and higher


Coordination

• Limit the extent and duration of serviceinterruption

• Selective fault isolation

• Provide alternate circuits


Coordination

t

I

C B A

C

D

D B

A


Equipment

• Motor

• Transformer

• Generator

• Cable

• Busway


Capability / Damage Curves

t

I

I22t

Gen

I2t

MotorXfmr

I2t

Cable

I2t


Transformer CategoryANSI/IEEE C-57.109

Minimumnameplate (kVA)Category Single-phase Three-phase

I 5-500 15-500II 501-1667 501-5000III 1668-10,000 5001-30,000IV above 1000 above 30,000


Infrequent Fault Incidence Zones for Category II & III Transformers

* Should be selected by reference to the frequent-fault-incidence protection curve or fortransformers serving industrial, commercial and institutional power systems with secondary-sideconductors enclosed in conduit, bus duct, etc., the feeder protective device may be selected byreference to the infrequent-fault-incidence protection curve.

Source: IEEE C57

Source

Transformer primary-side protective device(fuses, relayed circuit breakers, etc.) may beselected by reference to the infrequent-fault-incidence protection curve

Category II or III Transformer

Fault will be cleared by transformerprimary-side protective device

Optional main secondary –side protective device.May be selected by reference to the infrequent-fault-incidence protection curve

Feeder protective device

Fault will be cleared by transformer primary-sideprotective device or by optional main secondary-side protection device

Fault will be cleared byfeeder protective device

Infrequent-FaultIncidence Zone*

Feeders

Frequent-FaultIncidence Zone*


Transformer

t(sec)

I (pu)

Thermal200

2.5

I2t = 1250

2

25Isc

Mechanical

K=(1/Z)2t

(D-D LL) 0.87

(D-R LG) 0.58

Frequent Fault

Infrequent Fault

Inrush

FLA



Transformer Protection

MAXIMUM RATING OR SETTING FOR OVERCURRENT DEVICEPRIMARY SECONDARY

Over 600 Volts Over 600 Volts 600 Volts or Below

TransformerRated

Impedance

CircuitBreakerSetting

FuseRating

CircuitBreakerSetting

FuseRating

Circuit BreakerSetting or Fuse

Rating

Not more than6%

600 % 300 % 300 % 250% 125%(250% supervised)

More than 6%and not more

than 10%

400 % 300 % 250% 225% 125%(250% supervised)

Table 450-3(a) source: NEC


Protective Devices• Fuse

• Relay (50/51 P, N, G, SG, 51V, 67, 46, 79, 21, …)

• Thermal Magnetic

• Low Voltage Solid State Trip

• Electro-Mechanical

• MCP

• Overload Heater


Fuse

• Non Adjustable Device

• Continuous and Interrupting Rating

• Voltage Levels

• Characteristic Curves

– Min. Melting

– Total Clearing

• Application


Minimum MeltingTime Curve

Total ClearingTime Curve


Current Limiting Fuse(CLF)• Limits the peak current of short-circuit

• Reduces magnetic stresses (mechanicaldamage)

• Reduces thermal energy


Symmetrical RMS Amperes

Pea

k Le

t-Thr

ough

Am

pere

s

100 A

60 A

15% PF (X/R = 6.6)

12,500

5,200

230,000

300 A

100,000

Let-Through Chart


Fuse

Generally:

• CLF is a better short-circuit protection

• Non-CLF (expulsion fuse) is a betterOverload protection


Selectivity Criteria

Typically:

• Non-CLF: 140% of full load

• CLF: 150% of full load


Molder Case CB

• Thermal-Magnetic

• Magnetic Only

• Integrally Fused

• Current Limiting

• High InterruptingCapacity

Types

• Frame Size

• Trip Rating

• Interrupting Capability

• Voltage


Thermal Minimum

Thermal Maximum

Magnetic(instantaneous)


LVPCB

• Voltage and Frequency Ratings

• Continuous Current / Frame Size

– Override (12 times cont. current)

• Interrupting Rating

• Short-Time Rating (30 cycle)

• Fairly Simple to Coordinate

480 kV

CB 2

CB 1

CB 2CB 1

IT

ST PU

ST Band

LT PU

LT Band

If =30 kA


Motor Protection

• Motor Starting Curve

• Thermal Protection

• Locked Rotor Protection

• Fault Protection


Motor Overload Protection(NEC Art 430-32)

• Thermal O/L (Device 49)

• Motors with SF not less than 1.15– 125% of FLA

• Motors with temp. rise not over 40– 125% of FLA

• All other motors– 115% of FLA


Locked Rotor Protection

• Thermal Locked Rotor (Device 51)

• Starting Time (TS < TLR)

• LRA– LRA sym

– LRA asym (1.5-1.6 x LRA sym) + 10% margin


Fault Protection(NEC Art 430-52)

• Non-Time Delay Fuses– 300% of FLA

• Dual Element (Time-Delay Fuses)– 175% of FLA

• Instantaneous Trip Breaker– 800% of FLA*

• Inverse Time Breakers– 250% of FLA

*MCPs can be set higher

200 HP

MCPO/L

Starting Curve

I2T(49)

MCP (50)

(51)ts

tLR

LRAs LRAasym


Overcurrent Relay

• Time-Delay (51 – I>)

• Short-Time Instantaneous ( I>>)

• Instantaneous (50 – I>>>)

• Electromagnetic (induction Disc)

• Solid State (Multi Function / Multi Level)

• Application


Time-Overcurrent Unit

• Ampere Tap Calculation– Ampere Pickup (P.U.) = CT Ratio x A.T. Setting

– Relay Current (IR) = Actual Line Current (IL) / CTRatio

– Multiples of A.T. = IR/A.T. Setting

= IL/(CT Ratio x A.T. Setting)IL

IR

CT

51


Instantaneous Unit

• Instantaneous Calculation– Ampere Pickup (P.U.) = CT Ratio x IT Setting

– Relay Current (IR) = Actual Line Current (IL) / CTRatio

– Multiples of IT = IR/IT Setting

= IL/(CT Ratio x IT Setting)IL

IR

CT

50


Relay Coordination• Time margins should be maintained between T/C

curves• Adjustment should be made for CB opening time• Shorter time intervals may be used for solid state

relays• Upstream relay should have the same inverse T/C

characteristic as the downstream relay (CO-8 toCO-8) or be less inverse (CO-8 upstream to CO-6downstream)

• Extremely inverse relays coordinates very well withCLFs


Fixed Points

• Motor starting curves

• Transformer damage curves &inrush points

• Cable damage curves

• SC maximum fault points

• Cable ampacities

Points or curves which do not changeregardless of protective device settings:


Situation

Calculate Relay Setting (Tap, Inst. Tap & Time Dial)For This System

4.16 kV

DS 5 MVA

Cable

1-3/C 500 kcmilCU - EPR

CB

Isc = 30,000 A

6 %

50/51 Relay: IFC 53CT 800:5


Solution

AInrsuh 328,869412I =×=

A338.4800

5II LR =×=

Transformer: AkV

kVAL 694

16.43000,5I =×

=

IL

CTRIR

Set Relay:

A551.52800

5328,8)50(

1)38.1(6/4.3380.6

4.5338.4%125

=>=×=

==

=×=

AInst

TDATAP

A


Question

What is ANSI Shift Curve?


Answer

• For delta-delta connected transformers, withline-to-line faults on the secondary side, thecurve must be reduced to 87% (shift to theleft by a factor of 0.87)

• For delta-wye connection, with single line-to-ground faults on the secondary side, thecurve values must be reduced to 58% (shiftto the left by a factor of 0.58)


Question

What is meant by Frequent andInfrequent for transformers?


AnswerInfrequent Fault Incidence Zones for Category II & III Transformers

Source

Transformer primary-side protective device(fuses, relayed circuit breakers, etc.) May beselected by reference to the infrequent-fault-incidence protection curve

Category II or III Transformer

Fault will be cleared by transformerprimary-side protective device

Optional main secondary –side protective device.May be selected by reference to the infrequent-fault-incidence protection curve

Feeder protective device

Fault will be cleared by transformer primary-sideprotective device or by optional main secondary-side protection device

Fault will be cleared byfeeder protective device

Infrequent-FaultIncidence Zone*

Feeders

Frequent-FaultIncidence Zone*


Question

What T/C Coordination interval should bemaintained between relays?


Answer

At

I

B

CB Opening Time

+

Induction Disc Overtravel (0.1 sec)

+

Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.)


Question

What is Class 10 and Class 20Thermal OLR curves?


Answer

• Class 10 for fast trip, 10 seconds or less

• Class 20 for, 20 seconds or less

• There is also a Class 30 for long trip time


Answer

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08 - Device Coordination