Transformer: Excitation Frequency and Turns Ratio

In summary: These are both off the top of my head.In summary, the turns ratio of an oil-filled transformer coil may appear to change when the frequency is increased from 60 Hz to 23 kHz. This could be due to the inductance of the primary coil itself, which increases with frequency and can lower the voltage in, resulting in a reduction in the voltage out. Additionally, using a 50/60 Hz transformer at higher frequencies could lead to large losses and potential damage. It is important to consider the operating frequency and intended use when selecting a transformer.
  • #1
MadHattah
3
0
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.
 
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  • #2
MadHattah said:
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.

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


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
berkeman said:
...If you start at 60Hz, it is a decrease to 23Hz, not an increase...

Funny, that's what I read too, but he actually did say 23 kHz - "kilohertz".
 
  • #5
BackEMF said:
Funny, that's what I read too, but he actually did say 23 kHz - "kilohertz".

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
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?
 
  • #7
At higher frequencies, you may be getting less AC voltage out due to core losses being higher. At lower frequencies, you could get less AC voltage out because of core saturation.
 

1. What is excitation frequency in a transformer?

Excitation frequency in a transformer refers to the frequency of the alternating current (AC) that is used to energize the primary winding of the transformer. This frequency is typically measured in Hertz (Hz) and determines the rate at which the transformer converts electrical energy from one circuit to another.

2. How does excitation frequency affect the performance of a transformer?

The excitation frequency is directly related to the transformer's turns ratio, which is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. As the frequency increases, the turns ratio decreases, resulting in a higher output voltage and lower output current. This can affect the efficiency and power handling capability of the transformer.

3. What is the ideal turns ratio for a transformer?

The ideal turns ratio for a transformer is determined by the desired output voltage and the input voltage. The turns ratio is calculated by dividing the output voltage by the input voltage. For example, if the input voltage is 120 volts and the desired output voltage is 24 volts, the ideal turns ratio would be 5:1.

4. How does the turns ratio affect the frequency response of a transformer?

The turns ratio has a direct impact on the frequency response of a transformer. A higher turns ratio means a higher output voltage and lower output current, resulting in a wider frequency response and better performance at higher frequencies. Conversely, a lower turns ratio will result in a narrower frequency response and lower performance at higher frequencies.

5. Can the excitation frequency and turns ratio be adjusted in a transformer?

Yes, the excitation frequency can be adjusted by changing the input voltage or by using a variable frequency power supply. The turns ratio can also be adjusted by using different numbers of turns in the primary and secondary windings. However, it is important to note that changing these parameters can affect the performance and efficiency of the transformer.

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