EM 2

A synchronous motor operates on the principle of

• Lenz’s Law

• 
  b) Faraday’s Law
  

• 
  c) Magnetic locking between stator and rotor

• 
  d) Fleming’s Left-Hand Rule
  
  

The rotor of a synchronous motor rotates at

• Less than synchronous speed

• More than synchronous speed

• Exactly synchronous speed
  

• Variable speed
  
  

The rotor of a synchronous motor is generally made of

• Aluminum
  
  

• Silicon steel

• Cast iron

• Copper
  
  

Which of the following is NOT a difference between synchronous and induction motors?

• Synchronous motors run at a fixed speed, while induction motors have slip

• Synchronous motors require DC excitation, while induction motors do not

• Induction motors operate at synchronous speed, while synchronous motors do not

• Synchronous motors can operate at both lagging and leading power factors

Compared to an induction motor, a synchronous motor is preferred when:

• High starting torque is required
  
  

• Variable speed operation is needed
  
  

• Power factor correction is desired

• Frequent starts and stops are required
  
  

If the load on a synchronous motor increases while excitation remains constant, the motor will:

• Speed up
  
  

• Slow down

• Maintain synchronous speed but with increased torque

• Stop immediately
  
  

Increasing the excitation of a synchronous motor at a constant load will

• Decrease the power factor
  
  

• Improve the power factor leading
  
  

• Have no effect on the power factor

• Stop the motor
  
  

The V-curve of a synchronous motor represents the relation between:

• Armature current and power factor
  
  

• Torque and speed
  
  

• Power factor and voltage
  
  

• Armature current and power factor

An inverted V-curve is obtained by plotting:

• Load current vs excitation

• Power factor vs excitation

• Armature current vs load
  
  

• Speed vs torque

Hunting in a synchronous motor is:

• The loss of excitation

• The oscillation of the rotor about its steady-state position
  
  

• The sudden increase in speed
  
  

• The gradual reduction in speed