Sackeyfio
Electrical
- Oct 22, 2003
- 10
There are 3 identical generator step-up transformers T1,T2,T3,2 step-up transformers, 2 identical generator step-up transformers(these were added later) GSU1,GSU2 and 2 identical station service transformers SST1 and SST2.
Realized that when generator is in service only
GE Digital generator Protection relays for T1 and T2 trips spuriously on differential when either GSU1 or GSU2 transformers is energised on no-load from the HV busbar. Because GSU1 and GSU2 are normally kept energised even with generator off-line this problem of spurious tripping comes about when GSU1 and GSU2 have to be taken out for maintenance isolation and restored to service afterwards.
Observation Made so far:
1. GSU1 and GSU2 have lower impedances than the other transformers.
2. Current oscillographs taken from DGP relay after the trip show waveform distortion on system side current without any corresponding distortion on return-side current. This is likely to come from harmonics associated with the inrush.
3. Energizing T1,T2, SST1 and SST2 no load does not trip the differential.
4. DGP relay for T1 and T2 are ver 4.12400F 1995-1997 whilst DGP for T3 is ver 4.12500F 1997-1998. DGP for T3 does trip on differential when on line.
5. Most of the spurious trips occur on phase C
6. Relay has been checked for stability OK for phase C.
7. CT ratios checked OK.
Anybody has some experience with these DGP relays ver 4.12400F. What do you think could be the causes of these spurious trips? I will appreciate your contributions. I have contacted GE Multilin who asked me to send oscillographs to them which I did.
Realized that when generator is in service only
GE Digital generator Protection relays for T1 and T2 trips spuriously on differential when either GSU1 or GSU2 transformers is energised on no-load from the HV busbar. Because GSU1 and GSU2 are normally kept energised even with generator off-line this problem of spurious tripping comes about when GSU1 and GSU2 have to be taken out for maintenance isolation and restored to service afterwards.
Observation Made so far:
1. GSU1 and GSU2 have lower impedances than the other transformers.
2. Current oscillographs taken from DGP relay after the trip show waveform distortion on system side current without any corresponding distortion on return-side current. This is likely to come from harmonics associated with the inrush.
3. Energizing T1,T2, SST1 and SST2 no load does not trip the differential.
4. DGP relay for T1 and T2 are ver 4.12400F 1995-1997 whilst DGP for T3 is ver 4.12500F 1997-1998. DGP for T3 does trip on differential when on line.
5. Most of the spurious trips occur on phase C
6. Relay has been checked for stability OK for phase C.
7. CT ratios checked OK.
Anybody has some experience with these DGP relays ver 4.12400F. What do you think could be the causes of these spurious trips? I will appreciate your contributions. I have contacted GE Multilin who asked me to send oscillographs to them which I did.