A cumulative compound long shunt motor is driving a load at rated torque and rated speed. If the series is shunted by a resistance equal to the resistance of the series field, keeping the torque constant.
Right Answer is:
The armature current increase
The torque developed by a d.c motor is directly proportional to Flux per pole × Armature Resistance i.e
T ∝ ΦIa
The diagram of the above question is given below
In a cumulative compound long shunt motor, a load is being driven at rated torque and rated speed and its series field is shunted by a resistance equal to series field resistance with constant torque. Due to new resistance, the current is halved of its original value. Therefore, the armature current will have to increase to keep torque constant. Hence, the armature current increases to keep torque constant.