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CE1 September exam > NEETS MODULE 5; CHAPTER 1,2,3,4; > Flashcards

NEETS MODULE 5; CHAPTER 1,2,3,4; Flashcards

1
Q

Which is cheaper AC motors or DC motors?

A

AC motors are cheaper

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2
Q

What are the three basic types of ac motors?

A

series, synchronous, and

induction motors

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3
Q

Series motors are generally used to operate what type of equipment?

A

To power small appliances.

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4
Q

Why are series motors sometimes called universal motors?

A

They operate on either ac or dc.

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5
Q

characteristics of a series ac motor?

A

It has low speeds for large loads and high speeds for light loads. It is a
varying-speed machine.

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6
Q

synchronous and induction types of motors rely on rotating _______ in their
stators to cause their rotors to turn.

A

magnetic fields

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7
Q

What determines the number of field poles required to establish a rotating magnetic
field in a multiphase motor stator?

A

The number of phases in the applied voltage.

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8
Q

What is the angular displacement between field poles in a two-phase motor stator?

A

90º.

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9
Q

What is the major difference between a two-phase and a three-phase stator?

A

Number and location of field poles

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10
Q

Synchronous motors have the characteristic of?

A

constant speed between no load and full load. capable of correcting the low
power factor of an inductive circuit

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11
Q

disadvantages of a synchronous

motor is that it cannot be started from a standstill by applying ______ ac power to the stator.

A

three-phase

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12
Q

The induction motor is the most commonly used type of?

A

AC motor

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13
Q

. Why is the ac induction motor used more often than other types?

A

They are simple and inexpensive to make.

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14
Q

examples of induction motors?

A

washing machines, refrigerator

compressors, bench grinders, and table saws.

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15
Q

The difference between

the speed of the rotating stator field and the rotor speed is called?

A

the slip

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16
Q

What determines the amount of slip in an induction motor?

A

Load

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17
Q

the most common type of winding in a induction motor?

A

The most common is

the squirrel-cage winding.

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18
Q

This other type of winding contains actual coils placed in the
rotor slots.

A

wound rotor

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19
Q

. What type of ac motor is most widely used?

A

Single-phase induction motor.

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20
Q

Split-phase motors are designed to use inductance, __________, or
resistance to develop a starting torque.

A

capacitance

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21
Q

How do split-phase induction motors become self-starting?

A

By using combinations of inductance and capacitance to apply out-of phase
currents in starting windings.

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22
Q

Why are shaded-pole motors used to drive only very small devices?

A

They have very weak starting torques.

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23
Q

SYNCHRONOUS SPEED?

A

is the speed of stator field rotation. It is determined by the
number of poles and the frequency of the input voltage

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24
Q

Magnetic induction occurs when there is relative motion between what two
elements?

A

A conductor and a magnetic field.

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25
Q

A rotating armature requires _______ and ______ to conduct the current from the
armature to the load.

A

slip rings and brushes

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26
Q

What is the part of an alternator in which the output voltage is generated?

A

Armature

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27
Q

What are the two basic types of alternators?

A

Rotating armature and rotating field.

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28
Q

What is the main advantage of the rotating field alternator?

A

. Output voltage is taken directly from the armature

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29
Q

. Most large alternators have a small dc generator built into them. What is its
purpose?

A

To provide dc current for the rotating field

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30
Q

Prime movers are divided into two classes?

A

generators-high-speed and low-speed.

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31
Q

There are two types of rotors used in rotating-field alternators?

A

turbine-driven and salient-pole rotors.

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32
Q

How are alternators usually rated?

A

Kilovolt-amperes (volt amperes).

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33
Q

Salient-pole rotors may be used in alternators driven by what types of prime movers?

A

Internal combustion engines, water force and electric motors.

34
Q

What does the term single phase indicate?

A

One voltage (one output).

35
Q

in single-phase alternators, in order for the voltages induced in all the armature
windings to add together for a single output, how must the windings be connected?

A

In series.

36
Q

. What determines the phase relationship between the voltages in a two-phase ac
generator

A

Placement of armature coils.

37
Q

How many voltage outputs are available from a two-phase three-wire alternator?

A

Three.

38
Q

. What are the two methods of connecting the outputs from a three-phase alternator
to the load?

A

Wye and Delta.

39
Q

What generator characteristics must be considered when alternators are
synchronized for parallel operation?

A

. Output voltage, frequency, and phase relationships

40
Q

How is output voltage controlled in practical alternators?

A

By varying the voltage applied to the field windings.

41
Q

What factors determine the direction of rotation in a dc motor?

A

. Direction of armature current, and direction of magnetic flux in field

42
Q

The right-hand rule for motors is used to find the relationship between what motor
characteristics?

A

Direction of conductor movement (rotation), direction of flux, and the direction of
current flow.

43
Q

. What causes counter emf in a dc motor?

A

Generator action.

44
Q

What motor characteristic is affected by counter emf?

A

Speed.

45
Q

What is the load on a dc motor?

A

The device to be driven by the motor.

46
Q

What is the main disadvantage of a dc series motor?

A

. It must have a load connected to avoid damage from excess speed.

47
Q

What is the main advantage of a dc series motor?

A

High torque (turning force) at low speed.

48
Q

What advantage does a shunt motor have over a series motor? (DC)

A

It maintains a constant speed under varying loads.

49
Q

As with dc generators, dc motors can be constructed using one of two types of armatures?

A

Drum-wound and gramme-ring

50
Q

Why is the Gramme-ring armature not more widely used?

A

Only outside of coils cut flux (inefficient).

51
Q

How is the disadvantage of the Gramme-ring armature overcome in the drum-wound armature?

A

By winding the armature in a way that places the entire coil where it is exposed to
maximum flux.

52
Q

In a dc motor that must be able to rotate in both directions, how is the direction
changed?

A

By reversing either field or armature connections.

53
Q

What is the effect on motor speed if the field current is increased?

A

Motor will slow down.

54
Q

Armature reaction in a dc motor causes a shift of the neutral plane in which
direction?

A

Opposite the rotation.

55
Q

What current flows in the interpole windings?

A

Armature current.

56
Q

What is the purpose of starting resistors?

A

To limit armature current until counter emf builds up

57
Q

A generator is a machine that converts mechanical energy into?

A

electrical energy.

58
Q

Generators convert mechanical motion to electrical energy using what principle?

A

Magnetic induction.

59
Q

What rule should you use to determine the direction of induced emf in a coil?

A

The left-hand rule for generators.

60
Q

What is the purpose of the slip rings?

A

To conduct the currents induced in the armature to an external load.

61
Q

Why is no emf induced in a rotating coil when it passes through the neutral plane?

A

No flux lines are cut.

62
Q

What component causes a generator to produce dc voltage rather than ac voltage at
its output terminals?

A

A commutator

63
Q

At what point should brush contact change from one commutator segment to the
next?

A

The point at which the voltage is zero across the two segments.

64
Q

An elementary, single coil, dc generator will have an output voltage with how many
pulsations per revolution?

A

Two.

65
Q

How many commutator segments are required in a two-coil generator?

A

Four

66
Q

How can field strength be varied in a practical dc generator?

A

By varying the input voltage to the field coils.

67
Q

What causes sparking between the brushes and the commutator?

A

Improper commutation

68
Q

What is armature reaction?

A

Distortion of the main field due to the effects of armature current.

69
Q

What is the purpose of interpoles?

A

To counter act armature reaction.

70
Q

What is the effect of motor reaction in a dc generator?

A

A force which causes opposition to applied turning force.

71
Q

How can eddy current be reduced?

A

By laminating the core material.

72
Q

Why are drum-type armatures preferred over the Gramme-ring armature in modern
dc generators?

A

Drum-type armatures are more efficient, because flux lines are cut by both sides of
each coil.

73
Q

Lap windings are used in generators designed for what type of application?

A

Higher currents

74
Q

What are the three classifications of dc generators?

A

Series-wound, shunt-wound, and compound-wound.

75
Q

What is the main disadvantage of series generators?

A

Output voltage varies as the load varies.

76
Q

What term applies to the voltage variation from no-load to full-load conditions and
is expressed as a percentage?

A

Voltage regulation.

77
Q

What term applies to the use of two or more generators to supply a common load?

A

Parallel operation.

78
Q

What is the purpose of a dc generator that has been modified to function as an
amplidyne?

A

It can serve as a power amplifier.

79
Q

What is the formula used to determine the gain of an amplifying device?

A

Gain = output ÷ input.

80
Q

What are the two inputs to an amplidyne?

A

The mechanical force applied to turn the amplidyne, and the electrical input signal

81
Q

Laminations in a small generator armature may be as thin as?

A

1/64 inch

CE1 September exam (17 decks)

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