Monday, 29 October 2012

Synchronous Motors Multiple Choice Questions and Answers Preparation for Competition exams pdf

1.    Synchronous motors are generally not self-starting because
(a)    the direction of rotation is not fixed
(b)    the direction of instantaneous torque reverses after half cycle
(c)    startes cannot be used on these machines
(d)    starting winding is not provided on the machines
Ans: b

2.    In case one phase of a three-phase synchronous motor is short-circuited the motor will
(a)     not start
(b)     run at 2/3 of synchronous speed
(c)    run with excessive vibrations
(d)    take less than the rated load
Ans: a

3.    A pony motor is basically a
(a)    small induction motor
(b)    D.C. series motor
(c)    D.C. shunt motor
(d)    double winding A.C./D.C. motor
Ans: a

4.    A synchronous motor can develop synchronous torque
(a)    when under loaded
(b)    while over-excited
(c)    only at synchronous speed
(d)    below or above synchronous speed
Ans: c

5.   A synchronous motor can be started by
(a)    pony motor
(b)    D.C. compound motor
(c)    providing damper winding
(d)    any of the above
Ans: d
6. A three-phase synchronous motor will have
(a) no slip-rings     
(b) one slip-ring
(c) two slip-rings   
(d) three slip-rings
Ans: c

7. Under which of the following conditions hunting of synchronous motor is likely to occur ?
(a)    Periodic variation of load
(b)    Over-excitation
(c)    Over-loading for long periods
(d)    Small and constant load
Ans: a

8.    When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
(a)    the motor stops
(b)    it runs as a reluctance motor at the same speed
(c)    it runs as a reluctance motor at a lower speed
(d)    none of the above
Ans: a

9.    When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
(a) V   
(b) V312
(c) V2   
(d) 1/V
Ans: a

10.    The power developed by a synchronous motor will be maximum when the load angle is
(a) zero   
(b) 45°
(c) 90°   
(d) 120°
Ans: c

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shubham kawale on 22 April 2016 at 20:40 said...

Great quetion admin

shubham kawale on 22 April 2016 at 20:40 said...

Great quetion admin

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