Ratio of starting torque to full load torque is minimum in
A. Shunt motor.
B. Series motor.
C. Differential compound motor.
D. Cumulative compound motor.
Answer: C
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The ratio of starting torque to full load torque is minimum in a differential compound motor.
In different types of DC motors, the starting torque refers to the torque generated by the motor when it starts from rest, while the full load torque is the torque produced by the motor when it is operating at its maximum designed load.
Among the given options:
A. Shunt motor: A shunt motor has a relatively constant field flux and provides good starting torque. However, its ratio of starting torque to full load torque is not the minimum.
B. Series motor: A series motor provides high starting torque due to its high starting current. Therefore, its ratio of starting torque to full load torque is not the minimum.
C. Differential compound motor: A differential compound motor has both a series and a shunt field winding. The series winding provides high starting torque, while the shunt winding provides a constant field flux. However, the interaction between the two windings results in a reduction in the starting torque compared to the full load torque. Therefore, the ratio of starting torque to full load torque is minimum in a differential compound motor.
D. Cumulative compound motor: A cumulative compound motor has both a series and a shunt field winding, similar to a differential compound motor. However, the cumulative compound motor has a higher starting torque due to the additive effect of the series and shunt fields. Therefore, the ratio of starting torque to full load torque is not the minimum in a cumulative compound motor.
Hence, the correct answer is C: Differential compound motor.