Electrical Machines
Under which of the following conditions hunting of synchronous motor is likely to occur ?

  Over-loading for long period.
  Periodic variation of load.
  Over-excitation.
  Small and constant load.

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Electrical Machines
Commutation in a DC machine may be explained as a process

 how alternate flux affects the main field flux.
  in which magnetic field is set up.
 by virtue of which emf is induced in the armature conductors.
  by which electric current in a coil is reversed.

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

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