Transformer primary feeder sizing.
Transformer primary feeder sizing.
(OP)
Dear Friends, I have a question regarding sizing of the breaker for primary side of transformer.
I have 160kVA, 415 to 11kV, Z=4.5%, ONAN transformer. Its full load current is 223A. What should be the size of the feeder. I referred to NEC & it says 125% of FLC of transformer. I have chosen Schneider Electric's CVS 320A MCCB with 35kA for 1 Sec & LSI protections. Just wanted to cross check with you..
I have 160kVA, 415 to 11kV, Z=4.5%, ONAN transformer. Its full load current is 223A. What should be the size of the feeder. I referred to NEC & it says 125% of FLC of transformer. I have chosen Schneider Electric's CVS 320A MCCB with 35kA for 1 Sec & LSI protections. Just wanted to cross check with you..






RE: Transformer primary feeder sizing.
Current rating seems OK if you are ensuring that the 320A rating corresponds to the site rated design ambient temperature.
Make sure the MCCB fault level matches with the 415V bus fault level.
Don't you want to have earth fault protection for the feeder. LSI release doesn't include the same (LSIG release is the right one)!!
RE: Transformer primary feeder sizing.
RE: Transformer primary feeder sizing.
125% margin in the feeder rating ensures that the feeder is not going to impose any constraint in utilising the overload withstand capabilities of the trafo.
IEC says the busbars etc. in switchgears cannot have any sustained overload ratings.