If the speed of a dc motor increases with load torque, then it is a
A. series motor
B. permanent magnet motor
C. differentially compounded motor
D. comulatively compounded motor
Answer: C
Share your understanding of this question with the correct explanation.
If the speed of a DC motor increases with load torque, then it is a differentially compounded motor.
In a differentially compounded DC motor, the field winding is wound in such a way that the series field flux opposes the shunt field flux. As a result, the effective field flux decreases with an increase in load torque. This reduction in field flux causes the motor to speed up as the load torque increases.
This behavior is opposite to what is observed in a normally compounded motor (cumulatively compounded motor) or a series motor. In a normally compounded motor, the field flux strengthens with an increase in load torque, causing the motor speed to decrease. In a series motor, the speed also decreases with an increase in load torque.
Therefore, if the speed of a DC motor increases with load torque, it indicates that the motor is a differentially compounded motor.