Single Phase Loads on Three Phase Transformers
Single Phase Loads on Three Phase Transformers
(OP)
This is a question that has sparked some debate around here so any input will appreciated. How does one go about calculating how much single phase current is available from a three phase transformer? For example, if I have a 75kVA 230V 3 Phase transformer, what is the maximum single phase load (amps) that I can connect to each phase? A 75kVA @ 230V transformer should yeild 188A of 3 phase current, so would it not be that I have 1/3 of this available at each phase for single phase loads? Thanks for the help.






RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
Three phase at 230 volts is a legacy delta voltage so the following remarks pertain to a delta transformer.
CAUTIO: Some three phase transformers do not like single phase loads.
The maximum stand alone single phase load will be 2/3 of the rating of the bank, or 50 kVA. If you add a single phase load on each phase, they become a three phase load. For equal single phase loads, the load equals a three phase load, three times the rating of one single phase load. eg:, Three 10 kVA single phase loads equal one 30 kVA three phase load. The calculations for adding single phase loads to a transformer that is partially loaded with three phase loads are more challenging, particularly when the loads have differing power factors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
In the case of a 75kVA transformer running single phase loads, wouldn't each phase be limited to the maximum of 25kVA or run the risk of overloading that phase core of the transformer?
RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
RE: Single Phase Loads on Three Phase Transformers
Thanks for the heads up on the 230/400V.
I agree with you completely on the loading.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Single Phase Loads on Three Phase Transformers
3 phase power = 3* single phase power
single phase power = V(Ø-N)* I(Ø)
therefore
3 phase power = 3 * V (Ø-N) * I(Ø)
or
3 phase power = SQRT(3) * V (Ø-Ø) * I (Ø)
therefore
I (Ø) = 3 phase power / ( SQRT(3) * V(Ø-Ø) )