A dc, separately excited motor is driving a hoist. The motor has an armature resistance of 1.5 ?, and a field constant (K?) equals to 3.5 Vs. The terminals of the armature circuit are connected directly across a 240 V, dc source. The field circuit is connected to an ac/dc, full-wave, solid-state converter. The control circuit of the converter is designed to maintain the speed of the motor constant. At full load, when the field current is at its rated value, the motor speed is 600 rpm. One day while the motor was operating at full-load conditions, a failure in the dc source caused the armature voltage to change suddenly. The control circuit of the field converter acted rapidly to maintain the motor speed at 600 rpm. Due to the action of the control circuit, the field flux was reduced by

Question

25%. What was the percentage change in the armature voltage? Indicate whether the change was a voltage increase or decrease.

What will be an ideal response?

Answer 1