Dc Motors Objectives Part 04
61 . A dc shunt motor has rated rpm of 480. Certain industrial application requires this motor to run at 540rpm for some time. Which speed control will be desirable Field resistance control.
62 . A dc shunt motor has rated rpm of 480. Certain industrial application requires this motor to run at 600rpm for some time. Which type of control should be selected Field resistance control.
63 . The supply terminals for a dc shunt motor are reversed. What will be the effect on motor? It will run in reverse direction.
64 . A dc motor develops a torque of 100N-m at 400rpm. At 300rpm the motor will develop a torque of 100N-m.
65 . What will happen when back emf of a dc motor suddenly vanishes motor will burn.
66 . Which test can be used to determine the no load losses of a shunt motor? Swinburne’s test
67 . Which test can be used to determine the no stray losses? Running down test.
68 . Which of the following tests on dc machines need minimum two machines? Back to back set.
69 . A brake test is usually restricted to small horse power motor.
70 . In Swinburne’s test the no load power input to the armature supplies which of the following
a) Iron losses in core (b)friction and windage losses (c) armature copper losses
71 . Which of the following is assumption in Swinburne’s test decrease in flux due to increase in shunt resistance by heating is negligible.
72 . Hopkinson’s test is conducted at Full load.
73 . Which of the following test can be conducted on all types of dc machines
74 . Which of the following test can be conducted on other than shunt machines?
75 . In case of shunt motor if the supply voltage is increased by 20%, which of the following will decrease? Full load current.
76 . A 230V dc motor takes a no-load current of 2A and runs at 1200rpm. In case of full load current is 40A, the speed at full load will be 1150rpm.
77 . A 200V dc motor will be subjected to a high voltage test at 1400V .
78 . In a dc motor which of the following can sustain the maximum temperature rise? Field windings.
79 . In class B dc motor, the maximum permissible temperature rise in armature windings is 75C.
80 . A 230V dc motor has an armature circuit resistance of 0.6ohm. If the full load armature current is 30A and no-load armature current is 4A, the change in back emf no load to full load will be 15.6V.