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I have seen in many places where people mention that as the frequency of the input signal increases then the size of the transformer decreases. But as far as I have seen the formula for the transformer size. It is related to the core area. As the core area increases the size will be more and hence the power would be more.As shown: enter image description here

The frequency only changes the number of turns as shown in the formula: enter image description here

Link:Transformer Calculations

This means that the core area or the size of the transformer is not related to the frequency of the transformer, its only related to the power. Meaning If I want to make a high power transformer, even if it is high frequency my trnasfomer size will be the same but the turns will be comparatively less. Is this correct? Kindly correct me If I am wrong.

  • The second formula does show that for the same core and wire size, voltage per turn is proportional to frequency. So a 1.2 kVA 120V to 12 V 50/60 Hz transformer can handle ten times the voltage at the same current. So it would be 10 A at 1200 V to 100 A at 120 V, or 12 kVA, at 500/600 Hz. However, there will be more core losses for laminated iron, which will limit the performance. – PStechPaul Jun 07 '23 at 20:49
  • You are correct based on the parameters you have mentioned. Could there be any parameters you are missing? In particular, consider what must be true if wire diameter approaches zero, or infinity (since wire size / copper area is otherwise undefined so far!). – Tim Williams Jun 07 '23 at 23:09

1 Answers1

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No it's not correct.

The reason why the website formulas don't have frequency in them is because the website and formulas, or rather, the approximate rules of thumb, have already been calculated with the assumption that you are working with big and chunky low frequency mains voltage transformers.

And so by increasing frequency you can use smaller transformers.

The website just does not have formulas with frequecy for approximating transformer size with higher frequencies than 50/60 Hz.

Justme
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  • So the power calculations for a high frequency transformed will be different then? The formula given won't be used? –  Jun 07 '23 at 20:04
  • Could you provide me a general equation for power which can be used for both high and low frequency. Or provide me some link where I can get information or any derivation from that formula which resulted in the equations I gave above? –  Jun 07 '23 at 20:11
  • Yes you can't use same power handling formula meant for 50 Hz laminated iron cores and for 20 kHz ferrite cores. And the formulas are not exact. They are just very hand-wavy rules of thumb to approximate how much iron you need to be able to handle the power level you need, with no real specs how much the transformer losses make the transformer to just heat up and what's your limit for the generates heat. They simply give you a ballpark figure to very rough approximate the size for transformer. It may be an empirically found value with a lot of variables all squished down to single number. – Justme Jun 07 '23 at 20:23
  • Could you provide me some information regarding the formula for other frequencies as well. Like if I am designing for 20KHz or 50kHz which formula shall be used then. –  Jun 07 '23 at 21:00
  • @EEK21 See this [posting](https://electronics.stackexchange.com/questions/635417/is-there-a-simple-method-to-estimate-the-copper-loss-of-litz-wire/635448#635448) and this [posting](https://electronics.stackexchange.com/questions/666346/transformer-design-problem/666379#666379) about transformer design. There is no singular formula for transformer design. The process is iterative, but with experience the design can be done in perhaps 2 or 3 iterations. Not mentioned in the posts is core loss. Core loss parameters are found in the data sheets for the core material. – qrk Jun 08 '23 at 00:03