Deck 32: Synchronous Motors

Question 1

What happens when overexcitation takes place?

Answer 1

In this condition, the DC excitation current overmagnetizes the iron of the motor and part of the AC line current is used to de-magnetize the iron. The de-magnetizing process causes the AC line current to lead the voltage in the same manner as a capacitor.

Question 2

What is the polarized field frequency relay responsible for?

Answer 2

The polarized field frequency relay is responsible for sensing the speed of the rotor and controlling the operation of the field contactor.

Question 3

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

Answer 3

True

Question 4

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

Question 5

What two conditions indicate that normal excitation has taken place?

Question 6

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

Question 7

What is a brushless exciter?

Question 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

What is the function of the field discharge resistor?

Question 14

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

Question 15

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