Synchronous Motors Flashcards

1
Q

What is a synchronous motor called when used solely for power factor correction?

A

A synchronous condenser.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why would a synchronous motor be used to power factor correct instead of a capacitor bank?

A

It is much easier to adjust the amount of correction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a disadvantage of a permanent pole motor?

A

This design cannot alter the power factor of the machine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are three advantages of a synchronous motor over a SCIM?

A

Operate at a leading power factor to correct a building;

Constant speed from no load to full load;

Higher efficiency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are four disadvantages of a synchronous motor when compared to a SCIM?

A

DC excitation required;

May fall out of synchronism if overloaded;

Assistance to get to speed is required;

Does not work well with frequent starting.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why does a stator and rotor of a synchronous motor need to be constructed with the same number of poles?

A

So that the motor can magnetically lock and operate at synchronous speed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does a synchronous motor magnetically lock?

A

A dc excitation source is applied to the rotor poles, which creates permanent magnetic poles, these poles lock onto the rotating magnetic field of the three phase supply.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are three methods to start a synchronous motor?

A

Use a shaft mounted induction motor with 2 fewer poles;

Use the load, i.e. DC dynamo;

Use amortisseur windings and a field discharge resistor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is torque angle?

A

The angle between the center of magnetically locked poles, the angle exists due to rotational drag and mechanical load.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

When does pull out torque typically occur on cylindrical rotors?

A

At 90 degrees.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the four possible load conditions of a synchronous motor?

A

No losses and no load;

Light load and leading power factor;

Rated load and unity power factor;

Overload and lagging power factor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

As the load on a synchronous motor increases, how is the torque angle affected?

A

It will increase.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is normal excitation?

A

The amount required to operate the motor at unity power factor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is under excitation?

A

When excitation results in a lagging power factor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the condition when the amount of excitation current results in a synchronous motor running at a leading power factor.

A

Over excitation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Changing the field excitation of a synchronous motor changes the …?

A

Power factor.

17
Q

What is another name for a synchronous condenser?

A

A rotary capacitor.

18
Q

What power factor are most synchronous motors operated at?

A

Unity, 0.9 lead or 0.8 lead.