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Transformer: Excitation Frequency and Turns Ratio 
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#1
Jun309, 02:53 PM

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Another transformer question: if I have an oilfilled 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
Jun309, 04:24 PM

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#3
Jun309, 04:26 PM

P: 3

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
Jun309, 04:41 PM

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Transformer: Excitation Frequency and Turns Ratio



#5
Jun309, 04:44 PM

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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
Jun309, 05:50 PM

P: 3

Hey, wow, I thought my posts were just disappearing. Anyway, the transformer we're using is from a car, and is usually operated in the 200  1000 Hz range, apparently we are using it from 600 to 1000 Hz not 23 kHz (that's a different unit with a different transformer). It seems to me that the transformer is optimized to be used mostly at the lower end of its range with occasional jumps to higher frequencies (i.e. accelerating in your car), but we're using them at the higher range occasionally jumping higher than the single kHz it's designed for. But even so, the confusion comes from the fact that at low frequency we get a certain turns ratio based on voltage out over voltage in, but at higher frequencies the ratio changes. I really think that it's because of the reactance of the primary coil at the higher frequency dropping voltage, maybe? So there's less voltage available to induce magnetic flux?



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