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Common Course > Electrical Machine Principles > Flashcards

Electrical Machine Principles Flashcards

1
Q

How does a magnetic field and current carrying conductor interact to produce a force in the conductor?

A

All at 90 degrees to each other
Fleming left hand rule

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2
Q

How does a commutator enable a DC motor to produce rotation in a uniform direction?

A
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3
Q

What is the purpose in laminating the armature core and pole pieces in a DC electric motor?

A
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4
Q

What two quantities combine to produce torque in an electric motor?

A
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5
Q

What is back EMF and how is it produced in a DC motor?`

A
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6
Q

Explain why it is brushes on a DC motor are normally placed on the MNA

A
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7
Q

Briefly explain why the MNA tends to move when a motor is placed on a load

A
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8
Q

What are the two main effects of armature reaction in a DC motor?

A
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9
Q

2 methods that can be used to decrease sparking in a DC motor affected by armature reactions?

A
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10
Q

Why is a series motor not started on no load?

A
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11
Q

How does a shunt field differ physically from a series field in a DC motor?

A
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12
Q

What effect causes a curve to turn to a straight line?

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13
Q

State 3 methods of speed control for DC motors

A
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14
Q

Explain how field control is achieved for shunt and series motors

A
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15
Q

Give 2 disadvantages of field control

A
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16
Q

Advantages and disadvantages of armature resistance control

A
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17
Q

Why should terminal voltage control only be applied to the armature of a dc motor?

A
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18
Q

What effect on torque produced by a motor does an increase in its speed generally produce?

A
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19
Q

Why are starters needed on DC motors?

A
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20
Q

What are the basic requirements of a DC motor starter?

A
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21
Q

What is the operation of the faceplate starter?

A
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22
Q

Purpose of the ‘no volt’ release coil on the faceplate starter?

A
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23
Q

How does the faceplate starter protect a motor from excessive current?

A
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24
Q

Compare operating principles of modern starter with faceplate starter

A
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25
Q

Explain why the armature of most AC generators is on the stator instead of the rotor

A
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26
Q

Why does a DC machine have commutator and brushes but an AC machine has slip rings?

A
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27
Q

Explain 3 ways to increase EMF on an AC generator

A
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28
Q

Explain 2 ways of increasing the frequency output of an AC generator

A
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29
Q

Describe 2 types of 3 phase connections

A
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30
Q

Advantages of 3-phase systems?

A
31
Q

What is the relationship between phase and line voltages in a Star connected 3-phase system?

A
32
Q

Explain the one wattmeter and two wattmeter methods of measuring 3-phase power

A
33
Q

Why do you use an unearthed electrical system onboard ship?

A
34
Q

Explain why it is lethal to touch a bare conductor in an unearthed system

A
35
Q

What is the purpose of the DC exciter in an AC generator?

A
36
Q

Advantages of the brushless generator over the conventional generator?

A
37
Q

2 types of generator rotors and their application?

A
38
Q

How is field current applied to the rotor of the conventional and brushless generators?

A
39
Q

Describe the construction of the stator of an AC generator?

A
40
Q

Why is a voltage regulator necessary?

A
41
Q

How is hand control of a generator achieved?

A
42
Q

What are the two main operating parameters required of an AVR by the Royal Navy?

A
43
Q

What is the purpose of the thyristor bridge in an AVR?

A
44
Q

Explain two reasons for paralleling AC generators

A
45
Q

4 conditions that must be met before generators are paralleled?

A
46
Q

How do you parallel two AC generators using a synchroscope?

A
47
Q

Operation of a synchroscope?

A
48
Q

Relationship between True, Reactive and Apparent power?

A
49
Q

How does the speed of the prime mover and setting of the AVR affect the load sharing of an AC generator set?

A
50
Q

Explain why a generator requires a droop characteristic in order to operate in parallel with another generator?

A
51
Q

What is the normal voltage droop supply?

A
52
Q

Application for a high frequency generator?

A
53
Q

How does a 1600 Hz generator produce high frequency output at a relatively low prime mover speed?

A
54
Q

How does a rotating magnetic field be produced using 3 phase AC?

A
55
Q

Operation of a 3-phase synchronous motor?

A
56
Q

Difficulties when starting a synchronous AC motor?

A
57
Q

Application of synchronous motor?

A
58
Q

Construction of a squirrel cage rotor?

A
59
Q

Why can the rotor speed never equal the synchronous speed in a three-phase induction motor?

A
60
Q

What does the term ‘slip’ in an induction motor?

A
61
Q

How can the starting torque of an induction motor be improved?

A
62
Q

How is torque produced by the conducting bars in a squirrel cage rotor?

A
63
Q

How can synchronous speed of a motor be changed?

A
64
Q

Difference between stator switching and pole changing?

A
65
Q

How is pole changing achieved?

A
66
Q

What is the main disadvantage in rotor resistance control as a method of varying the speed of an induction motor?

A
67
Q

4 ways the speed of an AC induction motor can be altered?

A
68
Q

4 results of common motor faults?

A
69
Q

Symptoms exhibited by a single-phasing motor?

A
70
Q

How are motors protected from each type of fault?

A
71
Q

Purpose of the MTPU?

A
72
Q

3 possible causes of single-phasing in 3-phase motor?

A
73
Q

What are the requirements for the performance of an under-voltage protection unit?

A

Common Course (5 decks)

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