Deck 32: Synchronous Motors

Question 1

What two conditions indicate that normal excitation has taken place?

Answer 1

Two conditions indicate when normal excitation has been achieved:
1) The current supplied to the motor drops to its lowest level.
2) The power factor will be 100 percent or unity.

Question 2

With a self-excited direct generator mounted on the rotor shaft, the amount of excitation current is adjusted by controlling the ____________________ of the generator.

Answer 2

field current

Question 3

A switch called the ____________________ switch is used to connect the excitation current to the motor.

Answer 3

field discharge

Question 4

The amortisseur winding provides good starting torque and a relatively high starting current.

Question 5

What is a brushless exciter?

Question 6

Synchronous motors are sometimes operated without load to help correct plant power factor. In this mode of operation, they are called ____________________.

Question 7

What is the function of the field discharge resistor?

Question 8

What is the polarized field frequency relay responsible for?

Question 9

The excitation current should be connected to the rotor only after it has accelerated to a speed that is close to synchronous speed.

Question 10

What happens when overexcitation takes place?

Question 11

A synchronous motor cannot be made to produce a leading power factor.

Question 12

The ____________________ relay is actually a timer that contains a current operated coil instead of a voltage operated coil.

Question 13

A special squirrel cage winding, called ____________________, is used to start a synchronous motor.

Question 14

A synchronous motor should never be started with excitation applied to the rotor.

Question 15

Synchronous motors are able to operate at the speed of the rotating magnetic field because they are not induction motors.