Electrical Machines
What is/are the necessary conditions for voltage build up in self excited generator?

 Poles should contain residual flux.
 Field winding resistance should be less than critical resistance.
All of these
 Field winding should be properly connected to armature winding.

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Electrical Machines
Cogging and crawling are phenomena associated with

 cage induction machines and they are essentially the same.
 any of the above.
 the former during starting and the latter at a fraction of its rated speed.
 the former at a fraction of its rate speed and the latter during starting.

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Electrical Machines
A DC shunt generator builds up to a voltage of 220 V at no load while running at its rated speed. If the speed of the generator is raised by 25% kepping the circuit conditions unaltered, then the Voltage to which the machine would build up will

 increase to 1.25 times 220 V
 increase to a value greater than 1.25 times 220 V
 increase to value lying between 220 V and 1.25 times 220 V
 not change and remain at 220 V

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