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I need a fast (not to much elaborated) approximation figure of how lighter will be a transformer or motor designed to run on 400 Hz compared with an equivalent machine with the same power capacity designed to run on 50/60 Hz.

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  • \$\begingroup\$ To put it succinctly: A lot lighter. \$\endgroup\$
    – Hearth
    May 5, 2018 at 14:34
  • \$\begingroup\$ Can you think of any physical reasons that would determine the ratio? \$\endgroup\$
    – user16324
    May 5, 2018 at 14:46
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    \$\begingroup\$ Assuming the same transformer is used (to avoid long "elaboration"), the core cross-section is the same and it can support the same flux density. That means the same number of Webers (flux.) The wire will have the same cross-section too and can support the same maximum (peak) current. So both (X) Webers and (Y) Amps hasn't changed. The only remaining thing that has changed is frequency. Power = Webers * Amps * f. So about 8 times more power for the same transformer. It's pretty easy from there to work out the weight savings. \$\endgroup\$
    – jonk
    May 5, 2018 at 16:06
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    \$\begingroup\$ Or also see: core volume. (Note that in the above I didn't comment further on how well such a transformer designed for a lower frequency might work for a higher one (eddy current losses differences, for example.) \$\endgroup\$
    – jonk
    May 5, 2018 at 16:07

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With motors, the rated torque is fairly closely related to the size/weight of the machine. The rated power is not so much related. A 400 Hz motor of a given size/weight will produce about the same torque as a comparable 50 Hz machine, but the rated speed will be eight times as fast. Since rated power is rated torque X rated speed X units of measure factor, the rated power will be multiplied by eight. That does not take into account some increase in losses due to increased speed and frequency.

In order to produce 8X power at the same torque and current, 8X voltage would be required. The core would support that magnetically, but the winding insulation would not. Higher voltage rated insulation might require some additional space.

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