# Inductance of a Transformer

Discussion in 'General Electronics Chat' started by Management, Sep 13, 2010.

1. ### Management Thread Starter Active Member

Sep 18, 2007
306
0
Hi Everyone,

I would like to measure the inductance of a transformer for the purposes of creating a LR model.

Background:I know looking into the secondary side of a transformer looks like a low pass filter for high frequency signals due to the high inductance. I want to figure out a filter model and characteristic.

How can I get the L, R, Xl of that transformer and construct a proper lumped element model of that port.

I have access to a good amount of test equipment. Also, this is no small transformer.

Regards,

Dru

2. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
8
1) put xformer in series with known inductance
2) apply known frequency at known amplitude across both
3) measure voltage drop across xformer
4) run the math

3. ### davebee Well-Known Member

Oct 22, 2008
539
47
If it is a large transformer then it may have enough internal capacitance between the windings to result in quite a complex frequency response at higher frequencies, so be sure to test it over the frequency range thatyou are interested in using.

This might give you an idea of what you'll be looking at:

4. ### timrobbins Senior Member

Aug 29, 2009
318
18
One inconsistancy you will find is that the winding inductance will vary considerably with excitation voltage - this is due to the core material characteristic of permeability versus flux density.

Another good reference includes: http://www.pmillett.com/tecnical_books_online.htm 1955 Lee Electronic transformers and circuits.

5. ### Management Thread Starter Active Member

Sep 18, 2007
306
0
Hey guys thank you for the information.

I have a question ... is it possible to use an LCR Meter to L, R, & C to come up with a lumped element model?

Like you all said I would have to do this at different frequencies. I think we have a meter that will do a frequency sweeping for L, R, & C. Let me know if this makes sense or not?

Essentially I am looking for the quickest and dirtiest way of getting the frequency response or a model i can get it from on a computer.

I also though i can hook up a signal generator to on side and a scope to the other side of the transformer. Wouldn't this help? Not sure how to connect it up though.

Last edited: Sep 14, 2010
6. ### Management Thread Starter Active Member

Sep 18, 2007
306
0
Thank you again for your response but can you add a few more details. Transformers are kind of not my thing.

7. ### timrobbins Senior Member

Aug 29, 2009
318
18
Your LCR meter may be able to identify the impedance maxima/minima with frequency, and the impedance magnitude at those frequencies. You can try and tune the lumped model to those peaks/troughs - especially for the first one or two. That will lead you to controlling the Q/ESR of each peak/trough. That may be all you need. You will get some insight into the lumped model and the various R and C contributions when doing that iterative simulation tuning.