Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AC Machines > Mid Term > Flashcards

Mid Term Flashcards

1
Q

Connection to the armature of an alternator is normally done using what

A

Slip rings

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

The higher power output alternators use a

A

Revolving field

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

Non rotating part of an alternator

A

Stator

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

Rotating part of an alternator

A

Rotor

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

An alternator that has a separate mall alternator mounted on the shaft of its rotor is equipped with a

A

Brushless exciter

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

Output frequency of an alternator is controlled by

A

Number of stator poles

Rotor speed

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

Alternators should be connected in

A

Parallel

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

What is a field discharge resistor used for?

A

A field discharge resistor is used to limit voltage and prevent damage to an alternator when rotor dc excitation is removed.

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

What can be used instead of a field discharge resistor?

A

Diode

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

What does a synchroscope do?

A

Test phase angle of an armature

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

Advantages of a brushless exciter?

A

Less parts to wear. (No brushes)

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

Max kva of a rotating armature alternator?

A

25kva

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

The amount of emf produced in an alternator is proportional to what?

A

Number of conductors in the armature
Magnetic field strength
Speed of rotation

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

Describe a salient pole rotor

A

Has many poles on the outside of the rotor. Turned at low speeds.

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

Describe a cylindrical pole rotor

A

Have 2-4 poles
Used at high speeds
Cylindrical shape with poles inside

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

Purpose of “f” leads on an alternator

A

Provide excitation or field current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Two types of stators in a rotating armature alternator?

A

Permenant magnet

Electro magnet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Purpose of a rotor in a rotating field alternator?

A

The rotor is rotated by the prime mover to produce a current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is a prime mover?

A

The force used to rotate the armature in an alternator. (Harry)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are 4 conditions that must be met when paralleling alternators?

A

Phase rotation must be the same
Phase sequence must be the same
Frequency
Voltage output

21
Q

Output frequency of an alternator is dependent on?

A

Speed

Number of poles

22
Q

3 factors that determine output voltage of an alternator

A

Number of conductors in armature
Magnetic field strength
Speed of rotation

23
Q

What is electromagnetic induction?

A

When a conductor cuts magnetic lines of force, a voltage is induced into the conductor

24
Q

Describe lenzs law

A

When a closed loop of wire cuts through magnetic lines of flux, current is induced into the loop, creating a magnetic field. This magnetic field opposes the original field.

25
Q

Is a synchronous motor an induction motor?

A

No

26
Q

What is synchronous speed?

A

Speed of rotating magnetic field in a motor

27
Q

How is a squirrel cage rotor constructed?

A

Bars between 2 end rings

28
Q

Motor with high starting current?

A

Squirrel cage

29
Q

Typical percent slip of a squirrel cage motor?

A

2-5%

30
Q

Describe single phasing

A

Lose a single phase of a 3 phase of a three phase motor.

31
Q

Motor with low starting current and high starting torque?

A

Wound rotor motor

32
Q

What are amortisseur windings?

A

A set of squirrel cage bars on the rotor of a synchronous motor used to start the motor.

33
Q

What is a synchronous condenser?

A

A synchronous motor with no load used to correct the power factor of another motor or set of motors.

34
Q

How is the rotor in a seldom motor constructed?

A

3 windings connected in wye

35
Q

What are wound rotors motors used for?

A

High starting torque, low inrush current

Variable speed control

36
Q

How are 3 phase motors alike?

A

All operate on the principle of a rotating magnetic field

All have the same stator design

37
Q

How are 3 phase motors different?

A

Have different rotor designs

38
Q

What is the purpose of the m leads?

A

Connect your rotor circuit to the resistors in a wound rotor motor.

39
Q

Describe the starting sequence of a wound rotor motor

A

Resistance is connected to the rotor circuit to limit inrush current
Energize stator, creating rotating magnetic field
Voltage induced in the rotor is shunted out through the resistors
Resistance is removed making the rotor start to turn
At full rpm all resistance is removed

40
Q

Starting sequence of the synchronous motor

A

Energize stator, creating rotating magnetic field
Field cuts amortisseur winding
Current through the amortisseur winding produces a magnetic field that is attracted to the stator field causing the winding to turn
When close to synchronous speed dc is applied to the rotor, causing the rotor windings to become electromagnets
Rotor and stator fields lock in step and rotate at synchronous speed

41
Q

Describe the wiring configuration of the stator in a wound rotor motor

A

Windings 120 degrees apart setting up a rotating magnetic field
Stator is the same in all 3 phase motors

42
Q

Describe the construction of a squirrel cage rotor

A

Bars connected to 2 end rings

43
Q

Describe the construction of a wound rotor motor

A

Has 3 separate windings 120 degrees apart
Same poles per phase as the stator
Coils connected to slip rings on the rotor shaft

44
Q

Describe the construction of a synchronous motor

A

Dc excited wound coil with a squirrel cage added to it

45
Q

What are the brushes in a synchronous motor used for?

A

Dc excitation to the rotor

46
Q

Describe how a rotating magnetic field is set up by the stator

A

The pairs of poles in the stator are wound so that when current flows flow through the winding they develop opposite polarities.
When the stator is energized a rotating field is set up which we call phase rotation.
It rotates at synchronous speed
Windings are 120 degrees apart

47
Q

How are shynchronous and wound rotor motors the same?

A

Same stator

Both use wound coils. Wound rotor has 3, synchronous has 1

48
Q

How are synchronous and squirrel cage motors the same?

A

Same stator

Synchronous motor used a set of squirrel cage bars in the rotor that are used to start the motor. (Amortisseur winding)

49
Q

Why are motors important

A

Cause fuck you that’s why

AC Machines (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions