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Oleg BAGLEYBTER

Sankara SUBRAMANIAN

ENHANCING DIFFERENTIAL PROTECTIONSTABILITY DURING CT SATURATION WITH

TRANSIENT BIAS

GRID

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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subjectto change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particularpurpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Preventing CT saturation

IEEE Guide for the Application of Current TransformersUsed for Protective Relaying Purposes. IEEE Std

C37.110-2007.

..1

)1(

up

s

x

REM

RXRIV

+>

Westinghouse equation

Remanent flux up to 80%X/R = 20 (typical transmission)

=

> RIRIV ss

x 1058.0121

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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subjectto change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particularpurpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Simple Transient Bias

Decaying

( ) )()()( ... nInISLOPEnI BIASTRBIASTHRDIFF +=

)()1()( .. nISnIDnI BIASBIASTRBIASTR +=

Incrementing

0)( > nIBIASIf

!!!OPERATING TIME FOR INTERNAL FAULTS!!!

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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subjectto change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particularpurpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Transient Bias with External Fault Detector

)()1()( .. nISnIDnI BIASBIASTRBIASTR +=

)1()( .. = nIDnI BIASTRBIASTR

1SI

2SIBIAS

IBias current

DIFFI

1

K

2K

[ ])(),( nInI DIFFBIAS

[ ])(),( nInI DIFFBIAS

[ ])1(),1( nInI DIFFBIAS

External fault

Internal fault or

CT saturation

2KR >

2KR

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