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A synchronous generator is made to rotate at constant speed and it only has a voltmeter connected to its terminals between line and neutral. In this scenario the terminal voltage will be equal to the induced EMF. Is it permissible to increase the field current so that the induced EMF (which is same as terminal voltage here) exceeds the rated terminal voltage?

The question arises in my mind since no current (or very little current) will be drawn so I think it will be okay to go beyond the rated voltage.

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is it permissible to increase the field current so that induced emf(which is same as terminal voltage here) exceeds the rated terminal voltage

If the voltage exceeds the maximum specified terminal voltage by an (unspecified) amount, it may cause an insulation breakdown in the conductors or at least a weakness in the insulation. Not desirable at all.

The question arises in my mind since no current(or feeble amount) will be drawn so I think it will be okay to go beyond rated voltage

There may be no load current to speak of but, if the insulation fails due to excessive voltage then, there might be significant damage due to excessive current arcing within the windings.

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  • \$\begingroup\$ Yes I agree that we need to make sure we don't cross the insulation limits and also within the limits of rated field current. But suppose these conditions limits me to be under 600 volts and the rated voltage is 420 volts then can I go beyond 420volts let say 550 volts \$\endgroup\$
    – dRIFT sPEED
    Commented Mar 1, 2023 at 15:33
  • \$\begingroup\$ You can only go as far as the manufacturer's specified limits. Anything beyond that cannot be justified without extensive and possibly costly testing. Of course you could use an appropriately rated transformer on the output to raise the voltage as much as you want. \$\endgroup\$
    – Andy aka
    Commented Mar 1, 2023 at 15:40

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