A DC cumulatively compounded motor delivers rated load torque at rated speed.
If the series field is short-circuited, then the armature current and speed will
A. both increase
B. both decrease
C. increase and decrease respectively
D. decrease and increase respectively
Answer: A
Share your understanding of this question with the correct explanation.
If the series field of a cumulatively compounded DC motor is short-circuited, it means that the series field current becomes zero. In this case, the motor essentially becomes a shunt motor.
In a shunt motor, the armature current and speed are both directly proportional to the applied voltage. When the series field is short-circuited, the applied voltage remains the same, so the armature current and speed both increase.
Therefore, the correct answer is A. Both the armature current and speed will increase when the series field is short-circuited in a cumulatively compounded DC motor.