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

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

Answer 2

out-of-step
out of step

Question 3

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

Answer 3

True

Question 4

What is the function of the field discharge resistor?

Question 5

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

Question 6

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

Question 7

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

Question 8

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

Question 9

What is the polarized field frequency relay responsible for?

Question 10

What is a brushless exciter?

Question 11

What two conditions indicate that normal excitation has taken place?

Question 12

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

Question 13

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

Question 14

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 15

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