A dc shunt motor has external resistance Ra and Rf in the armature and field circuits respectively.
Armature current at starting can be reduced by keeping
A. Rf maximum and Ra minimum
B. Ra maximum and Rf maximum
C. Ra minimum and Rf minimum
D. Ra maximum and Rf minimum
Answer: D
Share your understanding of this question with the correct explanation.
The armature current at starting in a DC shunt motor can be reduced by keeping the armature resistance (Ra) maximum and the field resistance (Rf) minimum.
When the motor is starting, a high armature resistance helps to limit the initial surge of current in the armature circuit. This is important because a high starting current can cause excessive heating and potential damage to the motor.
On the other hand, keeping the field resistance (Rf) at its minimum value ensures that the field current is not limited and allows for sufficient field flux to be produced. This is necessary for proper motor operation and torque generation.
Therefore, the correct answer is D. Ra maximum and Rf minimum.