 ## electrical

### Synchronous Motor MCQ Objective Questions and Answers Page - 2

1.
 The phase of emf induced in the armature of a synchronous motor (Eb) depends upon A Rotor speed B Load C Both load and speed D None of the above Answer : Select Correct Ans Explanation :
2.
 In a synchronous motor, the synchronizing power come into action when A Rotor speed either exceeds or falls below the synchronous speed B Rotor speed is equal to synchronous speeds C Rotor speed falls  below the synchronous speed D Rotor speed exceeds the synchronous speed Answer : Select Correct Ans Explanation :
3.
 Synchronizing power  of a synchronous motor varies A Directly  as synchronous reactance Xs B Directly as the square of the synchronous reactance Xs2 C Inversely as the synchronous reactance 1/Xs D None of the above Answer : Select Correct Ans Explanation :
4.
 The coupling  angle or load angle of a synchronous motor is defiend as the space angle between the A Rotor and stator poles of the same polarity B Rotor and stator poles of opposite polarity C Rotor and stator teeth D None of the above Answer : Select Correct Ans Explanation :
5.
 The torque angle is defined as the space angle between A Stator field axis and resultant field axis B Rotor field axis and resultant field axis C Stator field axis and rotor field axis D Stator field axis and mutual field axis Answer : Select Correct Ans Explanation :
6.
 The value of load angle for a synchronous motor depends mainly upon its A Excitation B Load C Speed D Supply voltage Answer : Select Correct Ans Explanation :
7.
 Electromagnetic torque  is present in rotating machines when A Stator winding carried current B Rotor winding carried current C both stator and rotor windings carry current D None of the above Answer : Select Correct Ans Explanation :
8.
 In a synchronous motor electromagnetic power varies A Directly as applied voltage B Directly as square of the applied voltage C Inversely as applied voltage D None of the above Answer : Select Correct Ans Explanation :
9.
 The interaction  torque in a synchronous motor depends upon A Stator field strength alone B Rotor field strength alone C Torque angle alone D All of the above i.e on stator field and rotor field strengths and torque angle Answer : Select Correct Ans Explanation :
10.
 The breakdown torque of a synchronous motor varies as A Applied voltage V B V2 C 1/V D √V Answer : Select Correct Ans Explanation :
11.
 A 3-phse synchronous motor connected to an infinite bus bar with constant excitation is driving a certain load and operating is leading power factor. If the shaft load is reduced A The load angle will increase B The load angle will decrease C Power factor will increase D Owner factor will decrease Answer : Select Correct Ans Explanation :
12.
 A synchronous motor is supplying a load at unity pf . If the load on the motor is increased keeping its excitation and terminal voltage constant , the power factor A Will remain the same B Will become leading C Will become lagging D None of the above Answer : Select Correct Ans Explanation :
13.
 When does a synchronous  motor operate with leading power factor current A While it is underexcited B While it is critically excited C While it is overexcited D While it is heavily loaded Answer : Select Correct Ans Explanation :
14.
 A synchronous generator connected to an infinite bus is over excited. Considering only he reactive power, from the point of view of the system  the machine acts as A Capacitor B Inductor C Resistor D None of the above Answer : Select Correct Ans Explanation :
15.
 A synchronous machine connected to a power system , grid bus-bar is operating as a generator . To make the machine operate as a motor the A Direction of rotation is to be reversed B Phase sequence is to be changed C Field excitation is to be decreased D Mechanical input is to be less than the losses at the shaft Answer : Select Correct Ans Explanation :
16.
 A salient  pole synchronous motor  is running on no load. If its excitation is made off, it will A Continue running at synchronous speed B Continue running but at a speed slightly less than synchronous one C Stop D None of these Answer : Select Correct Ans Explanation :
17.
 What is the effect of the field failure of salient pole synchronous motor connected with infinite bus A Reduce motor torque and speed B Not charge motor torque and speed C Stop the motor D Reduce motor torque but motor will continue to run at synchronous speed Answer : Select Correct Ans Explanation :
18.
 A salient pole synchronous motor continues running even if its excitation current is reduced to zero. This is due to A Rotating magnetic field of stator B Rotating magnetic field of rotor C Magnetization of rotor salient poles by stator magnetic field D Inter looking action between stator and rotor rotating magnetic fields Answer : Select Correct Ans Explanation :
19.
 When the excitation of normally operaitn unloaded salient pole synchronous motor suddenly gets disconnected, it continues to run as a A Charge motor B Spherical motor C Switched reluctance motor D Variable reluctance motor Answer : Select Correct Ans Explanation :
20.
 A smooth cylindrical synchronous motor will always stop when A Excitation winding gets disconnected B Load varies C Supply voltage fluctuates D Supply frequency varies Answer : Select Correct Ans Explanation :