Brainscape's Knowledge GenomeTM

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


See full index

Electrical Level 3 > Final Review > Flashcards

Final Review Flashcards

1
Q

Define armature reaction

A

Distortion of the main field flux caused by current flowing from the armature to the conductors

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

What is flat compound?

A

Where the terminal voltage is flat or constant with respect to the load

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

What is over compound?

A

The rise in voltage at the terminals of the generator compensates for the line drop at the load

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

The condition under which the magnetic flux of the series and shunt fields oppose each other is called __________

A

Differential compound

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

What application is differential compound most commonly used in?

A

DC arc welding

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

Heat produced by current flowing through the armature and field coils is called ________________

A

Copper losses

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

Interpole winds consist of _______________

A

Small number of turns of large-gauge wire

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

The effects of armature reaction can be minimized by placing windings called __________________ in the main pole faces

A

Compensating windings

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

In practice, speed control of series motors is accomplished using _____________

A

Solid-state drives

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

The speed at which a DC motor operates without speed control devices is called __________

A

Base speed

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

Define torque

A

Torque is a twisting or turning force that is capable of producing rotation about an axis

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

Define the term slip speed

A

Slip speed is the difference between synchronous speed and rotor speed.

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

How is the direction of rotation reversed in a squirrel-cage induction motor?

A

By reversing the direction of the rotating field. This is accomplished by interchanging any two of the stator line connections to the source

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

How is the direction of rotation reversed in a split-phase motor?

A

By reversing the direction of current through the auxiliary winding

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

How is the direction of rotation reversed in a series motor?

A

By interchanging the two armature leads, or the two series field leads

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

How is the direction of rotation of a shaded-pole face motor reversed?

A

By removing the stator and turning it end-for-end before replacing it over the rotor

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

Define the term breakdown torque

A

The breakdown torque of a motor is the maximum torque the motor will produce

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

Why does a standard split-phase motor (without a starting capacitor) have a low starting torque compared to a capacitor-start, split-phase motor?

A

The standard split-phase motor has a phase shift between the main and auxiliary winding of 30–50 electrical degrees. The capacitor-start, split-phase motor has a phase shift of 90 electrical degrees, which corresponds better with the physical displacement of the poles in the motor

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

Which type of split-phase motor combines good starting torque with good overload capacity?

A

The capacitor-start, capacitor-run split-phase motor

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

What are the two types of windings in the stator of a shaded-pole motor?

A

Exciter winding, shading coil

21
Q

In what direction does the field move across the pole face in a shaded-pole motor?

A

From the unshaded portion to the shaded portion

22
Q

Is the starting torque of a shaded-pole motor high or low compared to a split-phase motor?

A

Low

23
Q

What is the purpose of the tertiary winding included in some wye-connected autotransformer banks?

A

It permits the flow of third-harmonic currents. This eliminates the third-harmonic voltages in the wye-connected windings

24
Q

What advantage does the extended-delta autotransformer have over the standard-delta autotransformer?

A

It permits transformations in ratios higher than 2:1

25
Q

Which autotransformer connection would likely be used to achieve a desired phase displacement between the primary and secondary systems?

A

The closed-delta connection

26
Q

What is the “form factor” commonly used for the three-phase half-wave rectifier

A

1.17 × AC phase (rms) value

27
Q

What is the “form factor” commonly used for the three-phase full-wave rectifier

A

1.35 × AC line (rms) value

28
Q

What advantage is offered by using SCRs instead of diodes in three-phase rectifier circuits?

A

SCRs can be phase-controlled to offer a variable DC output.

29
Q

How is an SCR normally turned on?

A

By applying a small amount of power to the gate terminal

30
Q

How does the power-handling ability of the SCR compare to that of a transistor?

A

SCRs can handle much more power.

31
Q

What happens if the SCR’s reverse-blocking voltage is exceeded?

A

The SCR will conduct in the reverse direction and will be permanently damaged.

32
Q

What happens if the SCR’s forward-blocking voltage is exceeded?

A

The SCR will be turned on without a gate signal.

33
Q

If resistor triggering is used, the SCR can be fired between ________ degrees up to ________ degrees in the positive half-cycle

A

0 to 90

34
Q

If resistor-capacitor triggering is used, the SCR can be fired from ________ degrees up to ________ degrees in the positive half-cycle

A

0 to 180

35
Q

Whereas the SCR is a unidirectional device, a triac is a ________ device

A

Bidirectional

36
Q

The action of a triac could be likened to two ________ connected back-to-back

A

SCR’s

37
Q

Triacs are available in rms current ratings up to a maximum of about ________ A

A

45

38
Q

What is the difference between a reduced-voltage starter with an open transition and a reduced-voltage starter with a closed transition?

A

For open-transition starters, there is a momentary loss of voltage (power) to the motor as the control transfers from the starting to the running stage.

But for closed-transition operation, there is no interruption of voltage

39
Q

What is anti-plugging protection?

A

Anti-plugging uses a zero-speed switch to prevent a motor from reversing until it has come to a complete stop

40
Q

Explain what is meant by the term plugging

A

Plugging is a control function that provides braking by reversing the motor line voltage polarity or phase sequence so that the motor develops a counter-torque that exerts a retarding force

41
Q

What conditions must be met in order that alternators may be paralleled?

A

Same: voltage, frequency, phase rotation. ( then phase opposition for sync. point.)

42
Q

What happens when a coil is rotated between a pair of opposite polarity field magnetic poles?

A

AC voltage is induced into the coil

43
Q

Brushes are positioned to short out a coil when it is ___________

A

Crossing the neutral plane

44
Q

Increasing the firing angle for an SCR from 0 75 degrees would result in _________

A

Less power supplied to the load

45
Q

The output of a revolving field 3 phase AC machine is taken from _____________

A

Slip rings and brushes

46
Q

Eddy currents and hysteresis losses are referred to as __________

A

Core losses

47
Q

The variable resistance placed into the rotor circuit is mainly for the purpose of __________

A

Varying the torque

48
Q

The maximum value of torque in a SCIM will ______

A

Occur when the rotor has XL = Resistance

49
Q

When a holding contact is wired into the control circuit, the motor is considered to have ________

A

Low voltage protection

Electrical Level 3 (9 decks)

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