Interpole Connections in a Motor

Author: E.E. Kimberly

When the machine G₁ in Fig. 11-2 (b) is used as a motor, the directions of the currents in all its armature conductors are reversed from those of Fig. 10-21 (a). The effect of this condition on the total field is shown in Fig. 11-3.

Fig. 11-3. Effect of Armature Reaction in a Motor

Whereas the north pole of armature flux is at the bottom in Fig. 10-21 (a), where the machine is assumed to operate as a generator, the north pole is at the top in Fig. 11-3, where the machine is treated as a motor. Therefore, the interpole polarity in a d-c machine used as a motor must be opposite to that of the machine when it is used as a generator with the same direction of rotation and with the same magnetic-field polarity. In a direct-current motor the polarity of any interpole must be opposite to that of the main pole which it just precedes in the direction of rotation^

Interpoles in either a generator or a motor maintain the commutating zones midway between the main poles. This condition permits operation of the machine in either direction of rotation without shifting the brushes.