Differential Biased Trip Logic; Figure 46: Differential Biased Trip Logic - GE P642 Technical Manual

Chapter 6 - Transformer Differential Protection
3.9

DIFFERENTIAL BIASED TRIP LOGIC

The differential biased trip is affected by both the CT Saturation technique and by the No Gap detection technique.
If the second harmonic blocking is asserted and either the CT Saturation Detection or No Gap detection technique
is asserted, then the biased differential trip is unblocked.
CT Saturation Detection and No Gap detection act independently from 5th harmonic blocking, however. A biased
differential trip will occur only if the fifth harmonic blocking is not asserted and the bias differential start signal is
asserted. The differential biased trip logic is described below.
Cross blocking
Enabled
CT Saturation A
No Gap A
External Fault A
IA2H Diff Start
CT Saturation B
No Gap B
External Fault B
IB2H Diff Start
CT Saturation C
No Gap C
External Fault C
IC2H Diff Start
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Figure 46: Differential biased trip logic

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1
1 1
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1
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1
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IA5H Diff Start
& &
Id Bias Start A
1
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IB5H Diff Start
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Id Bias Start B
1
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IC5H Diff Start
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Id Bias Start C
1
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P64x
Id Bias Trip A
Id Bias Trip B
Id Bias Trip C
P64x-TM-EN-1.3