Multiple choice questions on dc motor # 11



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objectives of electrical engineering on dc motors 11


1) The shunt armature control method of speed control for dc shunt motors is
A) less expensive
B) less wasteful
C) suitable for rapidly changing loads
D) none of the above

Ans:C

2) Ward leonard control is basically a ................ control method
A) armature control
B) field
C) field divertor
D) armature resistance

Ans:A

3) Ward-leonard control provides speed control
A) in one direction only
B) in both directions
C) above rated speed
D) below rated speed

Ans:B

4) The main disadvantage of the ward leonard system is
A) high initial cost
B) poor overall efficiency
C) high maintenance cost
D) all of the above

Ans:D

5) The armature voltage control is considered suitable for a dc motor driven at constant
A) torque
B) speed
C) power
D) current

Ans:A

6) Variation in speed by ward Leonard control of dc motors occurs due to variation in
A) field excitation
B) armature current
C) armature voltage
D) supply voltage

Ans:C

7) For a constant supply voltage, what are the effects of inserting a series resistance in the field circuit of a dc shunt motor, on its speed and torque?
A) speed will decrease and the torque will decrease
B) speed will increase and the torque will increase
C) speed will increase and the torque will decrease
D) speed will decrease and the torque will increase

Ans:C

8) In ward leonard system, the lower limit of speed is imposed by
A) armature resistance
B) field resistance
C) residual magnetism of the generator
D) none of the above

Ans:C

9) Ward-Leonard system for controlling the speed of a dc motor is used where
A) the speed in both the directions is required
B) very fine speed control over the whole range from zero to normal speed is required
C) the accuracy in speed control is required
D) all of the above

Ans:D

10) For very sensitive and wide speed control, the preferable control method is
A) field control
B) armature control
C) multiple voltage control
D) Ward Leonard system

Ans:D

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