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

Question 1

Which is cheaper AC motors or DC motors?

Answer 1

AC motors are cheaper

Question 2

What are the three basic types of ac motors?

Answer 2

series, synchronous, and

induction motors

Question 3

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

Answer 3

To power small appliances.

Question 4

Why are series motors sometimes called universal motors?

Answer 4

They operate on either ac or dc.

Question 5

characteristics of a series ac motor?

Answer 5

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

Question 6

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

Answer 6

magnetic fields

Question 7

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

Answer 7

The number of phases in the applied voltage.

Question 8

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

Answer 8

90º.

Question 9

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

Answer 9

Number and location of field poles

Question 10

Synchronous motors have the characteristic of?

Answer 10

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

Question 11

disadvantages of a synchronous

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

Answer 11

three-phase

Question 12

The induction motor is the most commonly used type of?

Answer 12

AC motor

Question 13

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

Answer 13

They are simple and inexpensive to make.

Question 14

examples of induction motors?

Answer 14

washing machines, refrigerator

compressors, bench grinders, and table saws.

Question 15

The difference between

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

Answer 15

the slip

Question 16

What determines the amount of slip in an induction motor?

Answer 16

Load

Question 17

the most common type of winding in a induction motor?

Answer 17

The most common is

the squirrel-cage winding.

Question 18

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

Answer 18

wound rotor

Question 19

. What type of ac motor is most widely used?

Answer 19

Single-phase induction motor.

Question 20

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

Answer 20

capacitance

Question 21

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

Answer 21

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

Question 22

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

Answer 22

They have very weak starting torques.

Question 23

SYNCHRONOUS SPEED?

Answer 23

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

Question 24

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

Answer 24

A conductor and a magnetic field.

Question 25

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

Answer 25

slip rings and brushes

Question 26

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

Answer 26

Armature

Question 27

What are the two basic types of alternators?

Answer 27

Rotating armature and rotating field.

Question 28

What is the main advantage of the rotating field alternator?

Answer 28

. Output voltage is taken directly from the armature

Question 29

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

Answer 29

To provide dc current for the rotating field

Question 30

Prime movers are divided into two classes?

Answer 30

generators-high-speed and low-speed.

Question 31

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

Answer 31

turbine-driven and salient-pole rotors.

Question 32

How are alternators usually rated?

Answer 32

Kilovolt-amperes (volt amperes).

Question 33

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

Answer 33

Internal combustion engines, water force and electric motors.

Question 34

What does the term single phase indicate?

Answer 34

One voltage (one output).

Question 35

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?

Answer 35

In series.

Question 36

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

Answer 36

Placement of armature coils.

Question 37

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

Answer 37

Three.

Question 38

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

Answer 38

Wye and Delta.

Question 39

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

Answer 39

. Output voltage, frequency, and phase relationships

Question 40

How is output voltage controlled in practical alternators?

Answer 40

By varying the voltage applied to the field windings.

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

. What causes counter emf in a dc motor?

Answer 43

Generator action.

Question 44

What motor characteristic is affected by counter emf?

Answer 44

Speed.

Question 45

What is the load on a dc motor?

Answer 45

The device to be driven by the motor.

Question 46

What is the main disadvantage of a dc series motor?

Answer 46

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

Question 47

What is the main advantage of a dc series motor?

Answer 47

High torque (turning force) at low speed.

Question 48

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

Answer 48

It maintains a constant speed under varying loads.

Question 49

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

Answer 49

Drum-wound and gramme-ring

Question 50

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

Answer 50

Only outside of coils cut flux (inefficient).

Question 51

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

Answer 51

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

Question 52

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

Answer 52

By reversing either field or armature connections.

Question 53

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

Answer 53

Motor will slow down.

Question 54

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

Answer 54

Opposite the rotation.

Question 55

What current flows in the interpole windings?

Answer 55

Armature current.

Question 56

What is the purpose of starting resistors?

Answer 56

To limit armature current until counter emf builds up

Question 57

A generator is a machine that converts mechanical energy into?

Answer 57

electrical energy.

Question 58

Generators convert mechanical motion to electrical energy using what principle?

Answer 58

Magnetic induction.

Question 59

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

Answer 59

The left-hand rule for generators.

Question 60

What is the purpose of the slip rings?

Answer 60

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

Question 61

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

Answer 61

No flux lines are cut.

Question 62

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

Answer 62

A commutator

Question 63

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

Answer 63

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

Question 64

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

Answer 64

Two.

Question 65

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

Answer 65

Four

Question 66

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

Answer 66

By varying the input voltage to the field coils.

Question 67

What causes sparking between the brushes and the commutator?

Answer 67

Improper commutation

Question 68

What is armature reaction?

Answer 68

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

Question 69

What is the purpose of interpoles?

Answer 69

To counter act armature reaction.

Question 70

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

Answer 70

A force which causes opposition to applied turning force.

Question 71

How can eddy current be reduced?

Answer 71

By laminating the core material.

Question 72

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

Answer 72

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

Question 73

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

Answer 73

Higher currents

Question 74

What are the three classifications of dc generators?

Answer 74

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

Question 75

What is the main disadvantage of series generators?

Answer 75

Output voltage varies as the load varies.

Question 76

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

Answer 76

Voltage regulation.

Question 77

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

Answer 77

Parallel operation.

Question 78

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

Answer 78

It can serve as a power amplifier.

Question 79

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

Answer 79

Gain = output ÷ input.

Question 80

What are the two inputs to an amplidyne?

Answer 80

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

Question 81

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

Answer 81

1/64 inch