# Transformer: Excitation Frequency and Turns Ratio

1. Jun 3, 2009

Another transformer question: if I have an oil-filled transformer coil and I calculate the turns ratio with voltage in / voltage out at 60 Hz, why, when I increase the frequency to 23 kHz would the turns ratio appear to change? Is it because of the inductance of the primary coil? My boss' question, but I didn't have a good answer for him.

2. Jun 3, 2009

### Staff: Mentor

Welcome to the PF. I think we'll need a little clarification on your question. If you start at 60Hz, it is a decrease to 23Hz, not an increase. In the general case, the turns ratio does not depend on the excitation frequency. The total number of turns may depend on frequency, depending on the type of transformer and its use. Also,l 50/60Hz transformers are not generally made to be used at other frequencies -- they are optimized for 50/60Hz, and will experience large losses at frequencies much away from 50/60Hz.

3. Jun 3, 2009

Re: Transformer: secondary coil question

Excuse me, I should have said inductive reactance. I think I've answered my own question. The reactance of an inductor increases with frequency, so it's the reactance of the primary coil itself that lowers the voltage in, therefore, the voltage out would reduce by the turns ratio. Thanks for your help! :)

4. Jun 3, 2009

### BackEMF

Funny, that's what I read too, but he actually did say 23 kHz - "kilohertz".

5. Jun 3, 2009

### Staff: Mentor

Oh wow, you're right! Glad I wasn't the only one.

MadHattah, do NOT try to run a 60Hz transformer up in frequency. There's a good chance it will smoke. Don't ask me how I know that. The losses are huge when you get above the intended operating frequency of 50/60Hz transformers.

6. Jun 3, 2009