GE P742

Operation
P74x/EN OP/N
a7
MiCOM P741, P742, P743
(OP) 5-
1
OP
CONTENTS
1. OPERATION OF INDIVIDUAL PROTECTION FUNCTIONS 5
1.1 Busbar Biased Current Differential Protection 5
1.1.1 Operating principle 5
1.1.2 Application of Kirchoffs law 5
1.2 Busbar Protection 7
1.2.1 Bias Characteristic and Differential current setting 7
1.2.2 Scheme supervision by "check zone” element 7
1.2.3 Scheme Earth characteristic element 8
1.2.4 Threshold coherency. 9
1.2.5 Signal Quality 10
1.2.6 Tripping Criteria 10
1.2.7 Trip duration 11
1.2.8 Current Circuit Supervision 11
1.3 Additional protections 15
1.3.1 Dead Zone protection (DZ) 15
1.3.2 Stub protection 15
1.3.3 Circuit Breaker Fail (CBF) 16
1.4 Three Phase Overcurrent Protection 25
1.5 Earth Fault Protection 26
1.5.1 EF time delay characteristics 26
1.5.2 External Fault Detection by High-Set Overcurrent or Earth Fault Element 26
1.5.3 Supervision 26
1.5.4 Zero Sequence Current (Ι
O
) Supervision. 26
1.5.5 CT Supervision 27
1.5.6 InterMiCOM teleprotection introduction 27
1.5.7 EIA(RS)232 InterMiCOM (“MODEM InterMiCOM”) 29
1.5.8 InterMiCOM statistics & diagnostics 33
2. CURRENT TRANSFORMERS 34
2.1 CT Saturation detection 34
3. ISOLATOR AND CIRCUIT BREAKER FUNCTION 38
3.1 Isolator State Monitoring Features 38
3.2 Circuit Breaker State Monitoring Features 38
3.3 Circuit Breaker Control 40
4. OPERATION OF NON PROTECTION FUNCTIONS 42
4.1 Programmable scheme logic 42
4.1.1 Level settings 42
4.1.2 Accuracy 42
4.2 IRIG-B signal (P741) only 42
4.3 Differential current display 42
5. COMMUNICATIONS BETWEEN PU AND CU 43
5.1 Communications link 43
5.2 Direct optical fibre link, 850nm multi-mode fibre 43