Why Size of transformer/motor reduces as frequency of operation increases ?

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Discussion Overview

The discussion revolves around the relationship between the frequency of operation and the size of transformers and motors, particularly in the context of aircraft electrical systems operating at 400 Hz. Participants seek to understand the theoretical basis for why equipment size and weight decrease with increasing frequency.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the amount of iron needed in transformers increases with peak magnetic flux, which is proportional to the time integral of voltage.
  • Another participant explains that the amount of iron required is related to the area under each half cycle of the voltage/time graph.
  • A request for references is made to support the claims regarding magnetic flux and its implications.
  • A reference list is provided, including definitions and laws related to flux density and Faraday's Law of Induction.
  • It is mentioned that for motors, the operating speed is crucial, as maximum torque is linked to flux and current linkage, allowing for more power in smaller AC machines at higher frequencies.

Areas of Agreement / Disagreement

Participants express various viewpoints on the relationship between frequency, size, and performance of transformers and motors, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

Limitations include the need for further clarification on how specific formulas apply to the reduction in size and the dependence on definitions of terms like flux and torque.

Who May Find This Useful

Individuals interested in electrical engineering, particularly those focusing on transformer and motor design, as well as applications in aviation and high-frequency systems.

gkraju
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In aircraft the frequency of operation of electrical systems used is mostly is 400hz. The reason given is that the size/weight of the equipment reduces as the frequency increases. can anyone please explain me the theory behind this with some formula, please do not stop with formula. How and why the size reduces ?
 
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- The amount of "iron" that you need increases as the peak magnetic flux increases.

- The peak magnetic flux is proportional to the time integral of voltage. \Delta \Phi = \int v \, dt

Essentially this means that the amount of iron you need is directly related to the area under each half cycle of the voltage/time graph.
 
Last edited:
Uart, could you provide some references for this?
 
Ref :

1. The definition of flux density.
2. Faraday's Law of Induction.
3. The Fundamental Theorem of Calculus.
 
BTW. The above relates more to transformers, why you can get roughly the same voltage and current ratings with less "iron" (or other soft magnetic material) section.

With respect to motors the operating speed is very significant. Here the maximum torque is related to the flux and the current linkage (ampere turns), so that tends to be fixed for a given size machine. Power being the product of torque times speed means that you can get more power in a smaller AC machine if it operates at higher frequencies.
 

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