question

You will hear the boom.

See the fire.

Smell the smoke.

Momentarily the regulator should attempt to increase voltage in response to the fault conditions.

Another view;;;

If there is no excitation voltage at the regulator output nothing will happen,

If you are able to contorl the voltage carefully , you can induce full load current.This mehtod used to remove moisture.

Regards,

Hareesha

All the previous answers are valid. Thing is, the residual magnetism by itself can generate such a high voltage causing a damaging current to the generator ( even without the AVR kicking in). If you can regulate the voltage somehow to get a low or zero voltage before shorting the phases then the drying thing is possible as you gradually increase the voltage while monitoring the currents. With an AVR this is not desirable. The automatic function will try to raise the voltage to set(operating) value. If it has overexcitation protection it MIGHT trip before it goes BOOM.