# Determination of Parameters (Transformers)

Discussion in 'Homework Help' started by jegues, Dec 17, 2011.

1. ### jegues Thread Starter Well-Known Member

Sep 13, 2010
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43
I've been reading through the notes for my course and in the section where we are determining the parameters for transformers.

For the OCT they give,

240V, 1.066A, 136.6W

From this they calculate Rc and Xm which I understand how to do but underneath in bold it says,

"Calculate the power factor of the transformer during the OCT and comment."

Wouldn't the PF of the transformer just be,

$PF = \frac{136.6W}{240V \cdot 1.066A} = 0.533$

Is there something to take away from this? It wouldn't be put in bold in my notes for no reason.

What am I to conlcude from this?

2. ### jegues Thread Starter Well-Known Member

Sep 13, 2010
735
43
Bump, Should I be drawing a particular conclusion here!?

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Nothing particularly startling about the low excitation power factor. Would one not expect that to be normal?

4. ### jegues Thread Starter Well-Known Member

Sep 13, 2010
735
43
I don't know.

This point was put in bold within my professors typed up notes for the course, so I'm sure there's something he wants us to take note of or realize here, I just can't figure out what.

5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Trying to second guessing a professor has its pitfalls. Does he/she want an erudite dissertation or simply a brief sentence or two?

I would offer a reasonable explanation as to why I would expect the excitation power factor to be low and what are the practical aspects of the magnetic circuit design that have any bearing on this.

Secondly I would offer some engineering justification as to why one can't reach 'perfection' on that score.

What is a reasonable design compromise on the excitation power factor? Could one, for instance, achieve an excitation power factor of 0.1 say and if so what cost penalty would the designer incur in achieving this? How does one adjust the excitation power factor in the design process? Is the excitation power factor really all that important from the designer's perspective?