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EM1 > AC Power Distribution Systems > Flashcards

AC Power Distribution Systems Flashcards

1
Q

Which systems make up the power distribution system?

A

The casualty power system
The emergency power system
The ships service system

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2
Q

What is the function of the switchboard bus ties

A

Top permit switchboards to be cross connected and to allow paralleling of generators

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3
Q

On small ships, locating distribution panels centrally with respect to the load and feeding them directly from the generators has which if the following advantages?

A

Simplifies the installation
Reduced the weight and space requirements
Reduces the equipment requirements

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4
Q

What information is contained on circuit information plates located on distribution panels

A

The circuit number, the name of the circuit controlled, and the space served

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5
Q

You are troubleshooting a circuit and you want to know the max allowed current. This information is marked on which, if any, of the following plates?

A

Distribution panel circuit information plate

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6
Q

For what reason if any is the phase sequence important to the distribution system aboard ship

A

The phase sequence determines the direction of rotation of three phase motors

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7
Q

What is the advantage of using an MBT as an alternate power source to a vital load

A

Circuit conditions can be met before energizing

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8
Q

What service is provided by bus transfer equipment

A

Two sources of power to equipment that is vital to the ship

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9
Q

Aboard ships, switchgear groups are physically separated as much as practical for what reason?

A

To afford greater protection from damage during battle

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10
Q

What is not a function provided by switchboards aboard ships

A

Automatic shifting of power to alternate sources if normal power is lost

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11
Q

What is the purpose of the disconnect links

A
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12
Q

The output of all ac generators is generated in what winding

A

The armature winding

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13
Q

Revolving armature generators are seldom used for what reason

A

They are subject to arc-over at high voltages

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14
Q

When dealing with the load rating of ac generators, what factor must be accounted for?

A

The internal heat the generator can withstand

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15
Q

What statement defines the term power factor

A

The expression of the losses within the electrical distribution system

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16
Q

AC generator sets may be divided into what two classes

A

Low-speed, engine driven and high speed, turbine driven

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17
Q

The rotary force used to provide the rotating action in generators may be supplied by which of the following prime movers?

A

An electric motor
A turbine
An internal combustion engine

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18
Q

The rotary force from the prime mover is transmitted to the ac generator by which of the following components

A

Rotor drive shaft

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19
Q

When you use vectors to analyze ac circuits, what rotation direction represents (a) positive and (b) negative polarity

A

Counterclockwise

Clockwise

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20
Q

In transformers electrical energy is transferred from one circuit to another through which of the following

A

Electromagnetic induction

21
Q

When a transformer transfers electrical energy, what Elements are either increased or decreased by the transformer

A

Current and voltage only

22
Q

In a transformer what winding is designated as the primary

A

The one that receives energy from and ac source

23
Q

You can reduce eddy current losses in the core of a transformer by installing which if the following components

A

Thin, insulated lamination

24
Q

In a transformer, the low-voltage winding is placed next to the core instead of the high-voltage winding for what reason

A

To reduce leakage flux

25
Q

In each winding of a transformer, the total induced voltage has what relationship to the number of turns in that winding

A

Proportional

26
Q

Because of damage caused by heat, you should NOT operate a transformer rated at 400 hertz at which if the following frequencies

A

340

27
Q

A transformers efficiency is stated as a ratio of what factor of the transformers input it output

A

Power

28
Q

Which if the following losses does NOT affect the efficiency of a transformer

A

Leakage reactance losses

29
Q

To obtain max current output from a single-phase transformer you should connect the sections of the secondary windings in what configuration

A

Parallel- opposing

30
Q

When a large number of single phase loads are supplied from a three phase transformer bank what is the desirable connection of the transformer secondary

A

High voltage

31
Q

Which if the following types of equipment are used to supply 400hz power to a transformer

A

Motor generator units and static converters

32
Q

What are the two principal types of transformer construction

A

Core and shell

33
Q

By what means are hysteresis losses kept to a minimum in transformers

A

By using grain- oriented silicon steel laminations in the core

34
Q

What is the main purpose of the casualty power system

A

To make temporary connections to vital circuits

35
Q

Casualty power bulkhead terminals are permanently installed on opposite sides of the bulkhead for what reason

A

To transmit power through compartments without loss of watertight integrity

36
Q

A portable cable used to rig ac casualty power systems can carry (a) what max current for (b) what max number of hours

A

(A) 200A (b) 4

37
Q

When unrigging casualty power what procedure should you follow?

A

Remove both ends of the first cable at the power source, remove both ends of the last cable at the load, and then until the remaining cables

38
Q

Shore power connections aboard the ship may be used to supply power to another ship alongside

A

True

39
Q

When testing shore power cables, what should be used as the shore ground resistance?

A

The enclosure that houses the shore power terminals or receptacles

40
Q

The casualty power system provides a good means of testing repaired equipment without jeopardizing the normal electrical distribution system

A

False

41
Q

What person is authorized to order the energization of the casualty power system

A

Electrical officer

42
Q

What is the normal current carrying g capacity of portable casualty power cables and the casualty current carrying capacity

A

93A

200A

43
Q

An exercise in rigging casualty power is not considered completed until damage control central receives the report stating that what action(a) have been completed

A

The equipment is operating on normal power and all portable cables have been restored

44
Q

What publication should you refer for the insulation resistance requirements for shore power cables

A

NSTM 300

45
Q

When using spliced cables what action should you take

A

Make sure the phases are continuous and have not been altered at the splice

46
Q

What is the key component of the phase sequence indicator

A

The three phase induction motor

47
Q

When if ever is it permissible to move energized shore power cables

A

Never

48
Q

In the formula Eg=KØN what does the K represent

A

The constant determined by the construction

49
Q

Which of the following conditions causes the efficiency of a power transformer to be less than 100%

A

The copper losses in the windings and the hysteresis and eddy current losses in the core

EM1 (12 decks)

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