If a three phase generator is stated as 200kVA, 440V, 60Hz therefore a current output of 262A. If said generator is changed to deliver 50Hz power at 440V, would that reduce the power available? so the 200kVA generator would effectively be 166kVA ?


1 Answer 1


For the generator to deliver 50 Hz, it would need to operate at 5/6ths or 83.3% of the original speed. To deliver the same power, the torque would need to increase by 20%. The prime mover may or may not be capable of that. In addition, the generator excitation would need to be increased to supply the same voltage at a slower speed. The generator may or may not be able to tolerate that.

It is also important to be aware of the difference between real power (kW) and apparent power (kVA). If the kVA is constant but the kW is reduced, the prime mover would not require more torque at the lower frequency. The kW/kVA (power factor) also has an effect of the required excitation.

  • \$\begingroup\$ ok... So I know they have a 500kVA that we switched from 440V 60Hz to 50Hz. So it is possible to maintain the kVA rating of the generator when reducing the frequency, it's not like the reduction causes the generator to be de-rated providing the generator is designed to switch frequencies. \$\endgroup\$
    – noName
    Mar 24, 2020 at 16:35
  • \$\begingroup\$ You need to check the detailed specifications for the generator to know for sure. Equipment that is advertised as 50/60 Hz capable doesn't necessarily have all the same specifications with either frequency. It may have, but you need to read the fine print to know for sure. \$\endgroup\$
    – user80875
    Mar 24, 2020 at 17:01
  • \$\begingroup\$ I think what you've said answers my question. Providing the generator is designed to do it, power output is not affected when changing the frequency. Therefore a 200kVA generator at 60Hz, will still be a 200kVA generator at 50Hz. \$\endgroup\$
    – noName
    Mar 24, 2020 at 17:20

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