1. A 240-V series motor has an armature resistance of 0.42 Q and a series-field resistance of 0.18 Q. If the speed is 500 r/min when the current is 36 A, what will be the motor speed when the load reduces the line current to 21 A? (Assume a 3-V brush drop and that the flux is proportional to the current.)
2. A 220-V DC shunt motor has an armature resistance of 0.2 Q and a rated armature current of 50 A. Find a. The voltage generated in the armature. b. The power developed.
3. A 550-V series motor takes 112 A and operates at 820 r/min when the load is 75 hp. If the effective Ra = 0.1 Q Rf = 100 Q When running at 1,100 r/min with no load connected to the shaft, the motor draws 4 A from the line. Find E and the rotational losses at 1,100 r/min (assuming that the stray-load losses can be neglected).