Power factor for transformers

  • Thread starter ranju
  • Start date
  • #1
223
3

Main Question or Discussion Point

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

  • #2
1,184
221
PF depends on leakage inductance of xfm and the load itself.
 
  • #3
223
3
but what's the reason behind high pf??
 
  • #4
1,184
221
but what's the reason behind high pf??
relatively small leakage inductance of xfm + operation near rated load point
 
  • #5
223
3
actually I have studied that pf is inversely proportional to the current...so I was seeing whether this thing point is the reason..??
 
  • #6
427
119
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!].
 
  • #7
1,184
221
Another extreme case is a short circuit case where I>>Inom. PF also low.
 
  • #8
jim hardy
Science Advisor
Gold Member
2019 Award
Dearly Missed
9,839
4,869
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.
 

Related Threads on Power factor for transformers

  • Last Post
Replies
3
Views
721
  • Last Post
Replies
7
Views
3K
  • Last Post
Replies
1
Views
2K
Replies
6
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
1
Views
6K
  • Last Post
Replies
4
Views
2K
Top