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When the frequency is too low, the inductance of the primary transformer coil becomes less effective = less efficiency, more wasted current and even lower Hz will lead to a short circuit.

Let's say, instead of 50 Hz (Europe, Asia, Japan) or 60 Hz (Americas), the primary AC frequency is frequency is 70 Hz, 80 Hz, 100 Hz, 200 Hz, 500 Hz, 1 kHz or even more.

What would happen? Which is the first part that would fail, and why?

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  • \$\begingroup\$ "When the frequency is too low, the inductance of the primary transformer coil becomes less effective = less efficiency, more wasted current" Please show how with an example. \$\endgroup\$
    – winny
    Jul 17 '19 at 13:26
  • \$\begingroup\$ @winny Because inductive coils resist changes in current. But on lower frequencies, the current changes less, therefore less impedance. \$\endgroup\$
    – neverMind9
    Jul 17 '19 at 13:33
  • \$\begingroup\$ Please show with a calculation example how this affects the efficiency of the transformer. \$\endgroup\$
    – winny
    Jul 17 '19 at 13:36
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    \$\begingroup\$ No, my point is that you are not correct and the best way to show you that would be for you to realize it with a calculation so you get to see it yourself. Efficiency will increase with decreased frecuency due to lower eddy current losses. Saturation is however the limiting factor here and magnitizing current would increase, but neither have anything to do with efficiency. Neat word. I learned something today. \$\endgroup\$
    – winny
    Jul 17 '19 at 14:17
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    \$\begingroup\$ Tiny correction on the above, the increased primary current to support the magnitizing would flow though the primary windings resistance, so that would increase the no-load windiwng losses slightly. Can't tell for sure if it would under, fully or overcompensate for the decreased eddy current losses. My point is that the normal or full load efficiency would not be different. \$\endgroup\$
    – winny
    Jul 17 '19 at 14:34
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Hysteresis losses (due to core imperfections of various kinds) increase linearly with increasing frequency because the magnetic domains must change direction more often. This increases transformer heating.

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  • \$\begingroup\$ As the impedance also increases with frequency, could that result in less transformer heating overall, or is it a case of "it depends..."? \$\endgroup\$ Jul 17 '19 at 15:18
  • \$\begingroup\$ @AndrewMorton Inductance have very little to do with transformer heating. \$\endgroup\$
    – winny
    Jul 17 '19 at 15:55
  • \$\begingroup\$ @winny I thought that maybe the reduced current (Z ∝ f) would result in less power being available to be wasted as heat. But then I just found a thesis Frequency Dependence of Transformer Losses that shows there are many parameters that need to be considered. \$\endgroup\$ Jul 17 '19 at 17:58
  • \$\begingroup\$ @AndrewMorton My old university! Excellent report you found there. \$\endgroup\$
    – winny
    Jul 17 '19 at 18:07

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