Transformer Diff Protection Problem during the TF Energization
Transformer Diff Protection Problem during the TF Energization
(OP)
Hello every one; now a days i am having a big issue related to the transformer differential relay.
Let me tell you the schemes and parameters:
2 generators (each 125MW) connected with the 1 stepup Transformer(350MVA/15kV-400kV); between generator & TF there is 52G and also two Auxiliary Transformer (15kV to 6.6kV). Aux TF is feeding the MV Switchgear & also stepdown TF (6.6kV to 440V) for LV switchgear.
Differential Protection taking the feedback (through CTs) from HV(400kV), tertiary(15kV) and MV (6.6kV) side. 87 also have REF, 50/51N, Thrmal OL, Overfluxing, Voltage & Frequency Protection...
Problem Case:
1-when we energized the transformer (close Line Breaker); suddenly 87 operate (current differential) and trip the Line breaker.
2-By disable the diff protection; transformer energized and then again we enable it, transformer still energized in healthy condition but when we start 6.6kV induction motor (for cranking the turbine), this relay again trip (87) the line breaker.
If we disable the 87 protection and energize the TF and crank the turbine, after synch the generator we enable 87 then it works properly but during the above cases it trip the line breaker.
Can any body please explain why this is happening?
I think the relay settings for the 87 is not correct; if you want relay settings and trip record (disturbance record); i will share.
Any help regarding to the above cases will be highly appreciated
Let me tell you the schemes and parameters:
2 generators (each 125MW) connected with the 1 stepup Transformer(350MVA/15kV-400kV); between generator & TF there is 52G and also two Auxiliary Transformer (15kV to 6.6kV). Aux TF is feeding the MV Switchgear & also stepdown TF (6.6kV to 440V) for LV switchgear.
Differential Protection taking the feedback (through CTs) from HV(400kV), tertiary(15kV) and MV (6.6kV) side. 87 also have REF, 50/51N, Thrmal OL, Overfluxing, Voltage & Frequency Protection...
Problem Case:
1-when we energized the transformer (close Line Breaker); suddenly 87 operate (current differential) and trip the Line breaker.
2-By disable the diff protection; transformer energized and then again we enable it, transformer still energized in healthy condition but when we start 6.6kV induction motor (for cranking the turbine), this relay again trip (87) the line breaker.
If we disable the 87 protection and energize the TF and crank the turbine, after synch the generator we enable 87 then it works properly but during the above cases it trip the line breaker.
Can any body please explain why this is happening?
I think the relay settings for the 87 is not correct; if you want relay settings and trip record (disturbance record); i will share.
Any help regarding to the above cases will be highly appreciated






RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
2. Check the restraint elements
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
https://1drv.ms/f/s!AsmTiLrMNRoZpjoyYI3MX9oFyKZn
or
COMTRADE & Setting FIles
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
Channel 1 looks bad too, with A and B in phase with each other and C 180 degrees out from the other two.
The schematic indicates every CT secondary neutral is grounded twice, one ground through a switch. Unless the switch is open, you may find that stray ground currents have an improper path through a relay coil.
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
RE: Transformer Diff Protection Problem during the TF Energization
If this is a typical gas turbine system, the heaviest 6kV load occurs during turbine starting. Maybe during normal operation, the 6 kV current is less than pickup so no tripping. Or it could be a setting issue or the multiple grounds on CT's.