Electrical Machines
Direct-on-line (DOL) starters are not suitable for starting large DC motors, because

 the motor may run away.
 the motor may not start.
 the starting torque becomes low.
 the starting current will be enormously high.

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

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

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

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