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

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

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Electrical Machines
Interpoles in a DC motor must be

 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.

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