For some percentage increase in the torque, which DC motor will have the least percentage increase of input current?(a) Series motor(b) Shunt motor(c) Cumulative compound motor(d) Separately exited motorThe question was posed to me during an interview for a job.My question is based upon Operating Characteristics of DC Shunt Motor topic in division Characteristics of DC Motors of DC Machines

For some percentage increase in the torque, which DC motor will have t

1.	For some percentage increase in the torque, which DC motor will have the least percentage increase of input current?(a) Series motor(b) Shunt motor(c) Cumulative compound motor(d) Separately exited motorThe question was posed to me during an interview for a job.My question is based upon Operating Characteristics of DC Shunt Motor topic in division Characteristics of DC Motors of DC Machines
Answer» Correct answer is (a) Series motor The best I can explain: The mechanical torque T is directly PROPORTIONAL to the PRODUCT of flux per pole φ and armature current. In case of DC series motor, up to saturation point flux is proportional to field current because Ia = If. Now if small percentage increase in armature current (before saturation) will occur the same percentage of torque will increase. WHEREAS in DC series motor the torque is proportional to square of the armature current (before saturation).

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