# Power factor for transformers

I have read that transformers operate on high power factor but I cannot get what is the reason behind it..?? I mean..what if we are having a low power factor..how is that going to affect the working of transformer??

## Answers and Replies

PF depends on leakage inductance of xfm and the load itself.

but what's the reason behind high pf??

but what's the reason behind high pf??
relatively small leakage inductance of xfm + operation near rated load point

actually I have studied that pf is inversely proportional to the current...so I was seeing whether this thing point is the reason..??

The no-load transformer p.f. is low [approx.0.1]. However, a transformer does not change much the load p.f.Since the active no-load power and reactive no-load power are low the load power factor [at full load] does not decrease more than 2% [usually].
Of course, if the load will be low the p.f. could decrease more [up to 0.1 at no-load!].

Another extreme case is a short circuit case where I>>Inom. PF also low.

jim hardy
Science Advisor
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I have read that transformers operate on high power factor but I cannot get what is the reason behind it..?? I mean..what if we are having a low power factor..how is that going to affect the working of transformer??

That's a bit ambiguous question.
I'd suggest the source from which you extracted that tidbit was suggesting that it is usual practice to use power transformers at reasonably highPF because:
Z of transformer is largely inductive
Draw your phasors..
When PF of load is unity,what is phase angle between applied voltage and I X Z drop in transformer?
When PF of load is zero, what is that angle?

At high PF your transformer I X Z drop is at right angle to applied voltage so doesn't change it much, because the hypotenuse and long side of a right triangle are nearly the same when vertex angle is small. That's elementary geometry.
At zero PF that I X Z drop Is in phase with applied voltage and subtracts or adds to it volt for volt.

So you'll get better regulation with a load having reasonably high PF.