Question

2. A 10 horsepower shunt excited DC motor connected to a 230V supply voltage draws 20A when it drives a load at the speed of 1200 rpm. The motor’s armature resistance is 2 ohms and its field resistance is 115 ohms.

a) Calculate the efficiency of the motor.

b) What torque does the load require if the rotational losses are 500W?

c) With an external resistor, the field current is reduced to 1.8A.

Calculate the armature current and the speed of the motor, (the motor is magnetic linear and the torque is unchanged)

Answer 1

a) motor's efficiency= 65%

b) Load torque = 23.8 Newton-meter

c) Motor's speed= 1197.5 rpm, Armature current = 18.2 Ampere