SYNC MOTORS - Vee + Bell

Question 1

What is PF when the lowest current is across the stator field?

Answer 1

PF = 1 (unity)

Question 2

What happens to excitation as load is added?

Answer 2

It increases

Question 3

The torque angle on a phaser diagram on a sync motor is between which values?

Answer 3

180 reference line and Egen

Question 4

PF is the cosine angle between which values?

Answer 4

I arm and V phase

Question 5

A Vee curve is a plot of:

Answer 5

Armature current vs Field current

Question 6

Unity Power Factor (PF) operation means the lowest line current for a particular load condition.

Answer 6

True.

Question 7

Normal excitation results in lagging power factor.

Answer 7

True

Question 8

High excitation results in leading power factor.

Answer 8

True

Question 9

The Input apparent power (S) to the motor is.

Answer 9

3 x Vphase x Iarm

Question 10

A slightly loaded sync motor is operating at a leading PF. What would adding load cause?

Answer 10

Less leading.

Question 11

What are sync motors operating at a leading PF also called?

Answer 11

Synchronous condensers or Rotary Capacitors

Question 12

Three levels of excitation

Answer 12

Normal excitation
Under excited
Over excited

Question 13

What condition does under excited sync motor provide?

Answer 13

Lagging PF. Larger torque angle. Iarm decreases

Question 14

What condition does over excited on a sync motor provide

Answer 14

Leading power factor. Decreased torque angle. Iarm increase

Question 15

Normal excitation is when the state of the sync motor is;

Answer 15

At a unity PF

Question 16

What does a bell curve represent?

Answer 16

PF vs field current

Question 17

How do you calculate Erestant.

Answer 17

Vectorly with Egen and Vphase

Question 18

What are the four possible load conditions for a SYNC motor

Answer 18

No load/no losses
Light load and Leading PF
Rated load and unity PF
Overload and lagging PF

Question 19

What is the torque angle of a sync motor running in a no losses/no load operation?

Answer 19

Zero.

Egen is at 180 out-of-phase with Vphase

Question 20

What is the combination which equates ‘synchronous reactance’

Answer 20

Inductive reactance of the armature AND armature reaction.

Question 21

What has the greats affect on torque angle?

Answer 21

Mechanical load

Question 22

Changing DC excitation drastically changes the torque angle of a sync motor; (T/F)

Answer 22

False

Question 23

It is normal for a sync motor to run at a lagging PF ; (T/F)

Answer 23

False;
Usually operated at unity or leading

Question 24

A synchronous motor running with a constant mechanical load and minimal line current is known at what excitation?

Answer 24

Normal excitation

Question 25

Synchronous motors can be used for PF correction: (T/F)

Answer 25

True