oc relay seting

7/31/2019 Oc Relay Seting

1/34

Power System

Protection

S.A.Soman

Principles ofOvercurrentProtection

Limitations of a Fuse

Algorithm for

Overcurrent RelayTime Multiplier

Setting

Classificationof OvercurrentRelay

Lack of Coordination

Problem

IEC Standard

Equations

IEEE Standard

Equations

Pick upCurrentSetting

Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary

Power System Protection

S.A.Soman

Department of Electrical EngineeringIIT Bombay

Fundamentals of Overcurrent Protection
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Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


1 Principles of Overcurrent ProtectionLimitations of a Fuse

Algorithm for Overcurrent Relay

Time Multiplier Setting

2 Classification of Overcurrent RelayLack of Coordination Problem

IEC Standard Equations

IEEE Standard Equations

3

Pick up Current SettingGuidelines

Primary and Back up Relays

Setting and Coordination

4 Summary
http://find/


3/34

Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary








3




4 Summary
http://find/


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Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



It is difficult to control the time to trip.This makes primary backup relay coordination difficult.

Once fuse melts, it has to be replaced for

reenergization of the equipment.

Thus it is difficult to have remote operation.
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Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary








3




4 Summary
http://find/http://goback/


6/34

Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



Set reference or threshold for discriminating

overcurrent Iref.Measure device current I.

Compute the ratio abs( IIref) which is known as the Plug

Setting Multiplier.

Trip the device, if PSM is above the threshold. Thethreshold is always greater than 1.


7/34

Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



8/34

Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary








3 Pick up Current Setting

Guidelines



4 Summary
http://find/


9/34

Power System

Protection

S.A.Soman



Algorithm for


Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



Overcurrent relays normally play the dual roles of

primary and backup protection.

Backup action requires a wait state.By providing the additional setting feature of TMS, this

can be achieved.

TMS is defined as the ratio TTm

, where T is the desired

relay operating time for a given PSM and Tm is the

corresponding operating time at TMS=1.

Relay operating time can be varied by varying the TMS

setting.


10/34

Power System

Protection

S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary

http://find/


11/34

Power System

Protection

S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


Classification of Overcurrent Relay

Instantaneous relay

Its action is very fast.It has only pick up setting.It does not have any TMS setting.This relay is not suitable for backup protection.
http://find/


12/34

Power System

Protection

S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



Instantaneous relay

Its action is very fast.It has only pick up setting.It does not have any TMS setting.This relay is not suitable for backup protection.

Time delayed definite time relay

It can be adjusted to issue trip decision after a specified

delay.This delay is independant of PSM value.It has both time setting and pick up setting.It is used for short length feeders.
http://find/


13/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


Overcurrent Protection Using Definite Time Relay

R1 trips without any intentional time delay.

R2 has to coordinate with R1 and its operation is

delayed by CTI.

R3 has to back up R2 and it is again time delayed.
http://find/


14/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary









Guidelines



4 Summary
http://find/


15/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


Lack of Coordination Between Fuse and DT relay

DT relay R1 has to back

up fuse.

After point X relay acts

faster than fuse.

This lack of coordination

is due to different

characteristics of fuse

and relay.This lead to the

development of inverse

characteristics for

overcurrent relay.
http://find/


16/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary



Inverse definite minimum time relayIt is inverse in the initial part and tends to approach adefinite minimum operating time characteristics as thecurrent becomes high.This is the most widely used characteristics.
http://find/


17/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE Standard

Equations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary





2

Classification of Overcurrent RelayLack of Coordination Problem




Guidelines



4 Summary


18/34

Power System

ProtectionS.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations

IEEE StandardEquations


Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


IEC Standard Equations for Inverse Characteristics

Standard Inverse Characteristics

t = TMS0.14

(I/Is)0.02 1

Very Inverse Characteristics

t = TMS13.5

(I/Is) 1

Extremely Inverse Characteristics

t = TMS80

(I/Is)2 1
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19/34

Power SystemProtection

S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary





2





Guidelines



4 Summary
http://find/


20/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


IEEE Stanard Equations for Inverse Characteristics

Moderately inverse: t= TD7

0.0515

(I/Is)0.021

+ 0.114

Very inverse: t=TD

7

19.61(I/Is)21+ 0.491

Extremely Inverse: t= TD7

28.2

(I/Is)21

+ 0.1217

US CO8 Inverse: t=TD

7 5.95

(I/Is)2

1+ 0.18

US CO2 Inverse: t= TD7

0.02394

(I/Is)0.021

+ 0.01694
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S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


IEEE Standard Curves
http://find/


22/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary





2





Guidelines



4 Summary
http://find/


23/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


Faults are classified into two:

Phase fault which do not involve ground.

Earth fault which involve ground.
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24/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary

Guidelines for Setting Pickup Current for Phase Fault

Relays

Pickup current should be above the maximum load

current.Pickup current should be below minimum fault current.

Pickup current should also be below the minimum fault

current of the feeder that it has to back up.

The back up relay also should provide time for primaryrelay to operate. This time interval is known as

coordination time interval.

F d l f O P i
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25/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary





2





Guidelines



4 Summary
http://find/


26/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary

Algorithm for Identifying Primary and Backup Relays

Identify leaf nodes and

root nodes.

Find the parents of theactive child nodes.

The corresponding

relays should back up

the leaf node relays.

Update active child

nodes to corresponding

parent node.

F d t l f O t P t ti
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27/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


F d t l f O t P t ti
http://find/


28/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


http://find/


29/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time Multiplier

Setting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary




30/34


S.A.Soman



Algorithm for

Overcurrent Relay

Time MultiplierSetting



Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary

http://find/


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S.A.Soman



Algorithm for

Overcurrent Relay




Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary





2 Classification of Overcurrent Relay

Lack of Coordination Problem




GuidelinesPrimary and Back up Relays


4 Summary

http://find/


33/34


S.A.Soman



Algorithm for

Overcurrent Relay




Problem

IEC Standard

Equations



Guidelines

Primary and Back up

Relays

Setting and

Coordination

Summary


Algorithm for Setting and Coordination of Overcurrent

Relays in a Radial System

Initialize the coordination tree.

Are there any leaf nodes except the root? If yes, go to

step 3, else go to step 7.

Identify the leaf node in coordination tree.

If the PSM of these relays are not set so far, set their

PSM.

Identify the parents of leaf nodes in step 3. Compute

their PSM and TMS for backup protection andcoordination.

Delete the leaf nodes. Update the coordination tree and

go back to step 2.

Coordination activity is complete.
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oc relay seting

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