|
1) Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ? a. Phase to phase winding resistance b. Stator winding to earthed frame c. Rotor winding to earthed shaft d. All of the above
|
||||
|
2) The speed of a synchronous motor: a. increases as the load increases b. decreases as the load decreases c. always remains constant d. none of the above
|
||||
|
3) When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way a. augments it directly b. directly opposes it c. cross-magnetises it d. none of the above
|
||||
|
4) If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________? a. become more b. become less c. remain constant d. none of the above
|
||||
|
5) Change of D.C. excitation of a synchronous motor changes: a. applied voltage of the motor b. power factor of power drawn by the motor c. motor speed d. none of the these e. all of the these
|
||||
|
6) The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________? a. zero degree b. two degrees c. five degrees d. ten degrees
|
||||
|
7) An important advantage of a synchronous motor over wound round induction motor is that a. its power factor may be varied at will b. its speed is independent of supply frequency c. its speed may be controlled more easily d. none of the above
|
||||
|
8) The angle between the rotating stator flux and rotor poles is called _________ angle. a. synchronizing b. obtuse c. torque d. power factor
|
||||
|
9) Slip-rings in a synchronous motor carry____________? a. direct current b. alternating current c. no current d. all of the above
|
||||
|
10) A synchronous motor working at leading power factor can be used as____________? a. voltage booster b. phase advancer c. noise generator d. mechanical synchronizer
|
||||
|
11) The standard full-load power factor ratings for synchronous motors are___________? a. zero or 0.8 leading b. unity or 0.8 lagging c. unity or 0.8 leading d. unity or zero
|
||||
|
12) The rotor copper losses, in a synchronous motor, are met by____________? a. d.c. source b. armature input c. motor input d. supply lines
|
||||
|
13) A synchronous motor will always stop when:______________? a. supply voltage fluctuates b. load in motor varies c. excitation winding gets disconnected d. supply voltage frequency changes
|
||||
|
14) The speed regulation of a synchronous motor is always___________? a. 1% b. 0.5% c. positive d. zero
|
||||
|
15) In a synchronous motor which loss varies with load ? a. Windage loss b. Bearing friction loss c. Copper loss d. Core loss
|
||||
|
16) For V-curves for a synchronous motor the graph is drawn between:_______________? a. armature current and power factor b. terminal voltage and load factor c. power factor and field current d. field current and armature current
|
||||
|
17) An over-excited synchronous motor takes__________? a. leading current b. lagging current c. both A. and (b) d. none of the above
|
||||
|
18) The synchronous motor is not inherently self-starting because_______________? a. the force required to accelerate the rotor to the synchronous speed in an instant is absent b. the starting device to accelerate the rotor to near synchronous speed is absent c. a rotating magnetic field does not have enough poles d. the rotating magnetic field is produced by only 50 Hz frequency currents
|
||||
|
19) 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
|
||||
|
20) A three-phase synchronous motor will have_____________? a. no slip-rings b. one slip-ring c. two slip-rings d. three slip-rings
|
||||
|
21) 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
|
||||
|
22) 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
|
||||
