Electrical Machines
A cumulatively compounded dc motor delivers rated load power at rated speed. If the series field is short-circuited, then

 both decrese
 Ia increases and ωm decreses
 Ia remains constant but ωm increase
 both armature current Ia and speed ωm increase

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Electrical Machines
Slip speed is the

  half of the sum of synchronous and rotor speeds.
  difference of actual rotor speed and synchronous speed.
  sum of synchronous and rotor speeds.
  difference of synchronous speed and actual rotor speed.

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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.
 Shunt excited and should have the same polarity as that of the ahead 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.

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