Two sets of 3 phase transformers
Two sets of 3 phase transformers
(OP)
Hello all,
I'm trying to figure out what would happen when one phase is blown or removed if two sets of three phase transformers were all connected to the same load. The transformers are all 750 KVA & impedence of 5.3%, secondary cables are of equal length. Any ideas?
I'm trying to figure out what would happen when one phase is blown or removed if two sets of three phase transformers were all connected to the same load. The transformers are all 750 KVA & impedence of 5.3%, secondary cables are of equal length. Any ideas?






RE: Two sets of 3 phase transformers
Transformers themselves would not care. 3 phase motors won't like it too much. Most will stop running, some may keep running with single phasing, some would get damaged. Single phase load on the lost phase would not work, other single phase loads on sound phases may keep on working. Depending upon the protective set up, the device feeding the transformer may just trip.
Rafiq Bulsara
http://www.srengineersct.com
RE: Two sets of 3 phase transformers
I attached a diagram of what Im dealing with. Im just wondering if one of these transformers were to fail would it effect the distribution and how? I can't seem to figure it out. I believe you're correct though, the device feeding the transformer may just trip, but would it trip after a certain period of time after installation?
RE: Two sets of 3 phase transformers
RE: Two sets of 3 phase transformers
I could not get your drawing. Something is wrong. I too am having trouble understanding the transformers connected to the same load.
RE: Two sets of 3 phase transformers
a) 2 paralleled transformers or
b) at least 2 feeding a common low side bus but not paralleled on the primary.
RE: Two sets of 3 phase transformers
RE: Two sets of 3 phase transformers
RE: Two sets of 3 phase transformers
If they were delta-wye, then it would depend on what failed. If it was one phase within the transformer, the transformer would act as an open-delta primary and the transformer capacity would be 57.7% of original rating. If it was a phase conductor, then you would have a much more complex situation: voltages from secondary would keep primary currents flowing in transformer, but only one phase of the delta would have full source power (B-C phase primary). A-phase bushing would still have potential and there current would still flow in A-B and A-C primary windings--they would just be a load sourced from the secondary, however.
If your transformers are three-phase and one phase of the transformer had a fault, it would probably be only a matter of time before conditions inside the transformer (combustion products in oil, etc) would give your trouble on the rest of the transformer.