S
Sir,
I was selecting a main incomer VCB for a turbo generator TG of 16000KW. I assumed ISc 31.5KA but an expert provided me calculation which I am sending you. He calculated total fault level 23.62KA and advised to select VCB of 25KA. I am also sending single line diagram of power house.
In calculation
* Considered sub transient reactance Xd" while I think should be considered transient reactance Xd'
* 1200KW diesel generator DG set Xd" is assumed 14%. I am not clear for this selected value is it assumed correctly?
* 20MVA transformer Z% is assumed 9%. I think it should not be assumed more then 7%. Am I right?
The expert told that DG set and grid transformer will contribute the fault current and the fault level as whole will increase than individual levels.I think that incomer VCB will have to bear just contributed part of ISc KA that is 8.33KA he suggested then why not select VCB of fault level 8.33KA?
In the single line diagram here are some more outgoing transformers of 2500 and 2000KVA I would like to know whether these out going other transformers at same bus bar would not considered in fault level calculation and these transformers will not contribute in fault level?
Your guidance is requested.
Regards
Shaheed
I was selecting a main incomer VCB for a turbo generator TG of 16000KW. I assumed ISc 31.5KA but an expert provided me calculation which I am sending you. He calculated total fault level 23.62KA and advised to select VCB of 25KA. I am also sending single line diagram of power house.
In calculation
* Considered sub transient reactance Xd" while I think should be considered transient reactance Xd'
* 1200KW diesel generator DG set Xd" is assumed 14%. I am not clear for this selected value is it assumed correctly?
* 20MVA transformer Z% is assumed 9%. I think it should not be assumed more then 7%. Am I right?
The expert told that DG set and grid transformer will contribute the fault current and the fault level as whole will increase than individual levels.I think that incomer VCB will have to bear just contributed part of ISc KA that is 8.33KA he suggested then why not select VCB of fault level 8.33KA?
In the single line diagram here are some more outgoing transformers of 2500 and 2000KVA I would like to know whether these out going other transformers at same bus bar would not considered in fault level calculation and these transformers will not contribute in fault level?
Your guidance is requested.
Regards
Shaheed