Deck 17: The Synchronous Motor

Question 1

The ____________________ motor is a three-phase AC motor that operates at a constant speed from a no-load condition to full load.

Answer 1

synchronous

Question 2

The direction of rotation of a synchronous motor is reversed by interchanging any two of the three ____________________ feeding the stator winding.

Answer 2

line leads

Question 3

A synchronous motor must always be started as a three-phase AC induction motor with the DC field excitation connected.

Answer 3

False

Question 4

Briefly explain the reason that a three-phase synchronous motor is often connected to a three-phase industrial feeder circuit with a low lagging power factor.

Question 5

With normal full-field excitation of a synchronous motor, the power factor has a peak value of unity, or 100%, and the AC stator current is at its highest value.

Question 6

The synchronous speed of the magnetic field depends on the frequency of the three-phase voltage and the number of ____________________.

Question 7

A squirrel-cage, or amortisseur, winding is provided for starting because the synchronous motor is not self-starting without this feature.

Question 8

The value of DC field excitation required to achieve unity power factor is called ____________________ excitation.

Question 9

When starting synchronous motors of larger sizes through a starting compensator or an automatic starter, the voltage applied to the motor terminals at the instant of start is about half the value of the rated line voltage, and the starting surge of current is limited.

Question 10

List two industrial applications of the synchronous motor.

Question 11

When the synchronous motor is used only to correct the power factor and does not drive any mechanical load, serving the same purpose as a bank of capacitors used for power factor correction, the motor is called a(n) ____________________.

Question 12

Briefly explain why the three-phase synchronous motor will not start if an attempt is made to first energize the DC field circuit and then apply the three-phase voltage to the stator windings.

Question 13

The synchronous motor can be implemented to correct or improve the power factor of three-phase industrial circuits, thereby reducing operating costs.

Question 14

What are the basic parts in the construction of a synchronous motor?

Question 15

Outline two general methods used to provide a DC field for the rotor in larger three-phase synchronous motors.