Transformer: Excitation Frequency and Turns Ratio

Click For Summary

Discussion Overview

The discussion revolves around the behavior of a transformer when the excitation frequency is changed, specifically examining the turns ratio at different frequencies, including 60 Hz and 23 kHz. Participants explore the implications of frequency on inductance, reactance, and core losses, as well as the suitability of transformers designed for specific frequency ranges.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the turns ratio appears to change when the frequency is increased from 60 Hz to 23 kHz, suggesting it may relate to the inductance of the primary coil.
  • Another participant clarifies that the turns ratio generally does not depend on excitation frequency, although the total number of turns may vary based on transformer type and application.
  • A participant acknowledges their misunderstanding and suggests that the reactance of the primary coil increases with frequency, which could lower the input voltage and thus affect the output voltage relative to the turns ratio.
  • Concerns are raised about operating a 60 Hz transformer at higher frequencies, with warnings about potential overheating and losses.
  • A participant describes a specific transformer used in a car, noting it operates in the 200 - 1000 Hz range and discusses how the turns ratio changes with frequency, attributing this to reactance affecting voltage availability for inducing magnetic flux.
  • Another participant mentions that at higher frequencies, core losses may increase, potentially leading to reduced AC voltage output, while at lower frequencies, core saturation could also affect output.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between frequency and turns ratio, with some suggesting that frequency impacts the effective turns ratio due to reactance and core losses, while others maintain that the turns ratio itself is not frequency-dependent. The discussion remains unresolved regarding the specific effects of frequency on transformer performance.

Contextual Notes

Participants note that transformers designed for 50/60 Hz may not perform well at significantly different frequencies, highlighting potential issues with losses and overheating. There is also mention of specific operational ranges for certain transformers, indicating that assumptions about frequency effects may depend on the type of transformer in use.

MadHattah
Messages
3
Reaction score
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.
 
Engineering news on Phys.org
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.
 


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! :)
 
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".
 
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.
 
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?
 
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.
 

Similar threads

Motor / transformer variable frequency control
  • · Replies 11 ·
Replies
11
Views
3K
How to wind a 5K audio tube amplifier transformer?
  • · Replies 9 ·
Replies
9
Views
3K
Why is impedance given as a simple Ohms unit when it's frequency dependent?
  • · Replies 10 ·
Replies
10
Views
3K
Induction heater using Bicycle Dynamo Generator @ 24 V 60HZ Supply
  • · Replies 10 ·
Replies
10
Views
3K
How might electronics be different if AC voltage was 72V at 45 Hz?
  • · Replies 30 ·
2
Replies
30
Views
3K
Ampere turn balance (MMF balance) in transformers
  • · Replies 36 ·
2
Replies
36
Views
13K
Magnetic flux in tap changing transformers
  • · Replies 5 ·
Replies
5
Views
5K
I Don't Understand Transformers/How to Apply Them
  • · Replies 81 ·
3
Replies
81
Views
8K
Switch mode DC transformer equations?
  • · Replies 10 ·
Replies
10
Views
2K
Understanding a Single Transistor Flyback Transformer Driver?
  • · Replies 3 ·
Replies
3
Views
3K