1. Which D.C. motor has got
maximum self relieving property ?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded motor
(D) Differentially compounded motor
Ans: A
2. Which D.C. motor is
generally preferred for cranes and hoists ?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded motor
(D) Differentially compounded motor
3. For which types of D.C.
motor, dynamic braking is generally used ?
(A) Shunt motors
(B) Series motors
(C) Compound motors
(D) All of the above
Ans: D
4. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
(A) Low cost
(B) Wide speed range
(C) Stability
(D) High starting torque.
Ans: A
5. The armature voltage control of D.C. motor provides
(A) constant voltage drive
(B) constant current drive
(C) constant torque drive
(D) none of the above
Ans: C
6. The speed of a D.C. shunt motor can be increased by
(A) increasing the resistance in armature circuit
(B) increasing the resistance in field circuit
(C) reducing the resistance in the field circuit
(D) reducing the resistance in the armature circuit
Ans: B
7. In a differentially compounded D.C. motor, if shunt field suddenly
opens
(A) the motor will first stop and then run in opposite direction as series
motor
(B) the motor will work as series motor and run at slow speed in the same
direction
(C) the motor will work as series motor and run at high speed in the same
direction
(D) the motor will not work and come to stop
Ans: A
8. Which of the following motor has the poorest speed regulation ?
(A) Shunt motor
(B) Series motor
(C) Differential compound motor
(D) Cumulative compound motor
Ans: B
9. Buses, trains, trolleys, hoists, cranes require high starting
torque and therefore make use of
(A) D.C. series motor
(B) D.C. shunt motor
(C) induction motor
(D) all of above motors
Ans: A
10. If I2 be the armature current, then speed of a D.C. shunt motor is
(A) independent of Ia
(B) proportional to la
(C) varies as (Ia)
(D) varies as la
Ans: A
11. Following motor is used where high starting torque and wide speed range control is required.
(A) Single phase capacitor start
(B) Induction motor
(C) Synchronous motor
(D) D.C. motor
Ans: D
12. The speed of a D.C. motor can be varied by varying
(A) field current
(B) applied voltage
(C) resistance in series with armature
(D) any of the above
Ans: D
13. If a D.C. motor designed for 40°C ambient temperature is to be used
for 50°C ambient temperature, then the motor
(A) of lower H.P. should be selected
(B) of higher H.P. should be selected
(C) can be used for 50°C ambient temperature also
(D) is to be derated by a factor recommended by manufacturer and select the
next higher H.P. motor
Ans: D
14. If the terminals of armature of D.C. motor are interchanged, this
action will offer following kind of braking
(A) regenerative
(B) plugging
(C) dynamic braking
(D) none of the above
Ans: B
15. Which of the following motors is most suitable for signalling
devices and many kinds of timers ?
(A) D.C. shunt motor
(B) D.C. series motor
(C) Induction motor
(D) Reluctance motor
Ans: D
16. Which motor should not be started on no-load ?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded motor
(D) Differentially compounded motor.
Ans: A
17. Why are the D.C. motors preferred for traction applications ?
(A) Torque and speed are inversely proportional to armature current
(B) Torque is proportional to armature current
(C) Torque is proportional to square root of armature current
(D) The speed is inversely proportional to the torque and the torque is proportional to square of armature current
Ans: D
18. Ward-Leonard control is basically a
(A) voltage control method
(B) field diverter method
(C) field control method
(D) armature resistance control method
Ans: A
19. For constant torque drive which speed control method is preferred ?
(A) Field control
(B) Armature voltage control
(C) Shunt armature control
(D) Mechanical loading system
Ans: B
20. In Ward-Leonard control the lower limit of speed is imposed by
(A) residual magnetism of the generator
(B) core losses of motor
(C) mechanical losses of motor and generator together
(D) all of the above
Ans: A
