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

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

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Electrical Machines
A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

 ½ ( ф + фᵢ ) in two diametrically opposite quadrants and ½ ( ф - фᵢ ) in the remaining two Quadrants
 ½ ( ф + фᵢ ) in all the four quadrants
 ½ ( ф - фᵢ ) in all the four quadrants
 ½ ( ф + фᵢ ) in two adjacent quadrants and ½ ( ф - фᵢ ) in the remaining two quadrants

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