DC Motors Objectives Part 01
01 . The fully load current of a 20HP 500V Dc motor will be closer to 35A
02 . The speed of a dc motor may be varied by varying (a)field current (b)applied voltage (c)resistance in series with armature(d) any of above
03 . In dc motor, the conditions for maximum power is Back emf=1/2(supply voltage)
04 . If conditions for maximum power for a dc motor are established, the efficiency of motor will be less than 50%
05 . A 200 V dc machine has an armature resistance of 0.5 ohm. If the full Armature current is 30A, the induced emf when machine acts as
a) generator (b) motor will be 120V,210V
06 . The speed of a dc motor is directly proportional to back emf.
07 . The ratio of starting torque to fully load torque is least in case of shunt motors
08 . Which of the following is not necessarily the advantage of dc motors over ac motors Low Cost
09 . Which motor will have least percentage increase of input current for the same percentage increase in torque series motor.
10 . The mechanical power developed by a dc motor is maximum when the ratio of back emf/applied voltage is 0.5
11 . The speed of a series-wound dc motor increases as flux decreases
12 . Following controls play significant role in the speed control of dc motors
a) Control of flux (b) armature resistance control (c)supply voltage control
13 . The speed regulation of a dc motor is (No load speed-full load speed)/Full load speed
14 . A dc motor having full load speed of 800 and speed regulation of 8% will have no load speed of 864 rpm.
15 . For a series motor if Ta be the torque and Ia the armature current, then
which relation is valid for the conditions before saturation Ta ∞ Ia2.
16 . In the dc series motor, shaft torque is less than the armature torque due to
17 . Dc motor with self-loading properties is differentially compound motor.
18 . The current drawn by a 120V dc motor of armature resistance 0.4 ohm and back emf 112V is 20A.
19 . If the load current and flux of a dc motor are held constant and voltage applied across its armature is increased by 5 percent, the speed of motor will be increase by about 5%
20 . A dc motor develops a torque of 140N-m at 1400 rpm. If the motor now runs at 1000rpm, the torque developed will be 140 N-m