Brainscape's Knowledge GenomeTM

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


See full index

2nd 6 Month Final > 3 Phase Systems > Flashcards

3 Phase Systems Flashcards

1
Q

A four-pole, three-phase motor has _____ coils.

A

12

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

The speed at which the magnetic field of an induction motor rotates is called the:

A

Synchronous speed

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

On starting, the slip of the induction motor is ____% of the synchronous speed.

A

100%

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

In general, the power factor of an induction motor increases with the load until the maximum power factor is reached at:

A

Full load

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

In an induction motor, maximum torque is always developed when the

A

Reactance and the resistance of the rotor are equal

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

Specifically, the core, the conductors, the end rings, and the shaft are the main parts of the squirrel-cage:

A

Rotor

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

When taking air-gap measurements on large motors, you should:
- keep a record fo the measurements and compare regularly
- take measurements about 90% apart
- take one measurement in the direction in which the load bears on the bearing
- all of the above

A

ALL OF THE ABOVE

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

In a squirrel cage motor, low starting torque is a result of

A

Low resistance and high reactance

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

A wound-rotor motor is always started with _________ in the rotor circuit.

A

Maximum resistance.

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

To improve a motors service life, you should do all of the following EXCEPT:

A

Remove the windings insulation

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

A synchronous motor requires:

A

Both AC and DC power

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

When DC power is applied to the rotor of a synchronous motor….

A

A set of north and south poles is produced.

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

With a low DC field current, the AC current:

A

Lags the potential difference

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

Slipping a pole causes a(n):

A

Surge of current in the DC line

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

The power factor of a synchronous motor will be less than 100% if the DC current in the rotor winding is:

A

Either too high or too low

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

A motor with a single winding can be connected for:

A

Either four-pole or eight-pole operation

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

Variable torque motors are designed to give:

A

An increase in torque with an increase in speed

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

In a constant horsepower motor, the torque:

A

Doubles when the speed is cut in half

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

When you reconnect the coils of an induction motor designed to run on a potential difference of 240V so that it will run on 480V

A

You reconnect the coils in series

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

A two-parallel-Y connection:

A

Requires a lower potential difference than a series-Y connection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

When removing grease and oil from a motor, you should avoid using too much solvent because it

A

Can damage the insulation

22
Q

40degrees C is the

A

Standard temp for measuring insulation resistance

23
Q

A lack of torque, a decrease in speed, and a growling noises are all indications of a(n)

A

Open rotor circuit

24
Q

Angular loads are caused by forces applied to the bearing

A

Both parallel and perpendicular to the shaft

25
Q

200degrees F (95C) is the

A

Maximum temp at which bearings can be operated safely

26
Q

The capacity of the power supply does NOT limit the

A

Normal running speed of the motor

27
Q

At full load a motor connected to the line will do all of the following except:

A

Decrease its internal temperature

28
Q

A motor rated at 2HP at full load can develop ___to_____ hp if it delivers at max torque

A

3 to 4.5

29
Q

An inductor connected in series with the motor windings is found in a(n)

A

Reactor starter

30
Q

To ensure that three phase motor control equipment is in good operating condition, you should:

A

Maintain a regular plan of inspections

31
Q

Which of the following stops a motor when the potential difference falls too low and automatically restarts the motor when the potential difference returns to normal?

A

Low-voltage release

32
Q

During plugging, the current in an induction motor is higher than the locked-rotor current causing a(n)

A

Power loss

33
Q

A controller that provides both surge and backspin protection for a motor that drives a pump has a(n)

A

On-delay relay plus an off-delay relay

34
Q

Reduced voltage starters for three phase motors change the potential difference across the motor by means of:

A

Auto transformers or resistors

35
Q

When smooth starting is necessary but more than two steps are required, ________ is used.

A

Resistance starting

36
Q

The supply winding in an alternator

A

Can be part of either the rotor or the stator

37
Q

If the field winding has 4 poles, how many poles does the armature of the alternator have?

A

4

38
Q

There is no current in the armature of the alternator when the

A

Regulator is disconnected

39
Q

The size of the conductors in the winding determines the

A

Current an alternator can conduct without overheating

40
Q

If the load driven by an alternator is purely inductive, the current:

A

Lags the potential difference.

41
Q

When interlocks are used in motor-starting circuits to overcome voltage drop problems, which motor in the circuit is started first?

A

The largest

42
Q

In most automatic installations, power failure relays act if the potential difference drops to _______ of the rated value

A

70% or less

43
Q

Whenever an engine starts, it should run until all parts reach:

A

Their normal operating temperatures

44
Q

In order to avoid damaging an engine when only one cranking period is provided, the cranking attempt should last at least _______ seconds.

A

15

45
Q

In establishing for inspecting generators you should match the schedule to the maintenance schedule of the:

A

Prime mover

46
Q

The potential difference where the electric system of the utility company and the plant are connected is called the ________ voltage.

A

Service

47
Q

All of the following are benefits of system grounding, EXCEPT:

A

Allows service to be maintained in entire circuit until the fault is located

48
Q

A relay with inverse-time characteristics operates:

A

Faster as the current increases

49
Q

In a cascade system having large air-gap circuit breakers, there should not be more than ___ cascade step(s).

A

2

50
Q

In general, three phase motors will give satisfactory service when operated at what percent of their rated potential difference?

A

90%

2nd 6 Month Final (11 decks)

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