A 230 V dc shunt motor having armature resistance of 2 \Omega draws an armature current of 5 A to drive a constant torque load at 1250 rpm. At no load it draws a current of 1 A.
(a) A resistance of 15 \Omega is added in series to the armature. Find the motor speed with load torque as above. Also determine the speed regulation.
(b) A resistance of 15 \Omega is shunted across the armature and 10 \Omega in series with the supply line (as in Fig. 7.96(a). Calculate the load speed and speed regulation.
(c) Compare the power wasted in external resistance (s) in parts (a) and (b).
Rotational loss torque is negligible. The armature reaction effect is to be ignored.