Machine Parts

Each phase of a three phase transformer must be considered as a single phase transformer when determining loading. For example: A 45 KVA three phase transformer with a 208Y/120 volt secondary is to service 4 loads at 120 volts single phase each. These loads are 10 KVA, 5 KVA, 8 KVA, and 4 KVA. That maximum loading on any phase does not exceed 10 KVA. Each phase has a 15 KVA capacity.  45 KVA = 15 KVA per phase         _____        3 phase  If incorrect method is used, phase B will have an 18 KVA load which is 3 KVA above its normal capacity of 15 KVA and failure will result even though we only have a total load of 27 KVA on a 45 KVA transformer.