Low PF out of a Transformer

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Branden Donovan

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I'm having a PF problem on a transformer. Phase b an c have very low PF with no load and phase a is at .95 the other two are at .38 to .41. Can the transformer produce this with no load? This is a 3000A service. V on all 3 phases is 478-500. This is with all load disconnected. Thanks for your time.
Branden
 
090928-0903 EST

Branden Donovan:

There is something strange about your transformer or your description.

I just measured a small, 175 VA, transformer and the PF was 0.13 and this is a reasonable value. Remember that under unloaded conditions looking into the primary side of a transformer that it looks very inductive, and the losses are low. Thus, PF should be low.

Is your transformer really 3 single phase transformers wound on separate cores, or a true 3 phase transformer?

Is the primary Y or delta?

What kind of instrumentation did you use and how was it connected?

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Low PF

Low PF

The same is true under load also, A is .94 and phase b and c are .30- .45. And three feeders are .18 pf on b and c. The transformer is a Y. I've have had two other electrical company's verify my findings. But no cause found yet.
 
090928-2011 EST

Branden Donovan:

You have indicated you have a Y input (primary), and I am assuming a Y secondary.

Your PF instrument should measure the current in one input leg, and the voltage from that leg to neutral. With no load on the secondary of this phase your PF should be low. As you add resistive load to the secondary the PF viewed at the primary should increase. Maybe being within 0.90 to 1.00 at full load with a resistive load only.

Can you describe your PF instrument? However, it may not mean anything to me.

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