SYNCHRONOUS MOTORS

A synchronous motor has _____.

• Constant speed
• High speed at low torque
• Low speed at high torque
• Slight drop in speed at full load

Damper (amortisseur) winding in a synchronous motor _____.

• a. Prevents hunting of the motor
• b. Serves to start the motor
• c. Improves power factor of the motor
• d. Both A and B

A synchronous motor when running has slip of _____%.

• 0
• 1
• 2
• 5

The synchronous speed of 10 pole, 60 HZ 3 phase synchronous motor is _____ rpm.

• 50
• 600
• 720
• 900

A synchronous motor is capable of being operated at _____.

• Lagging or leading pf
• Leading power factor only
• Lagging power factor only
• None of these

When the stator winding of a synchronous motor is connected in such a way that the number of poles are made half, the speed of the rotor _____.

• Increases to two times the original value
• Decreases to one half of the original value
• Remains the same as the original value
• Tends to become zero

Synchronizing power of a synchronous machine is _____.

• Directly proportional to the synchronous reactance
• Inversely proportional to the synchronous reactance
• Equal to the synchronous reactance
• None of these

An over-excited synchronous motor has _____.

• Unity pf
• Leading pf
• Lagging pf
• Leading or lagging pf

When the excitation of an unleaded salient pole synchronous motor is suddenly disconnected, then _____.

• It runs at higher speed
• It runs at lower speed
• It run at the same speed
• The motor stops

A 3 phase, 60 HZ, 4 pole synchronous motor has a torque angle of 10 electrical degrees. The torque angle in mechanical degrees is _____.

• 4
• 5
• 10
• 20