Electrical Machines
The volt-ampere euation for a long-shunt compound motor is given by

 Vt = Ea + Ia(ra + rs)
 Vt = Ea + Iara+ ILrs
 Vt= Ea + Iara
 Vt= Ea– Iara

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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 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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