AC Power Distribution Systems

Question 1

Which systems make up the power distribution system?

Answer 1

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

Question 2

What is the function of the switchboard bus ties

Answer 2

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

Question 3

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?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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?

Answer 5

Distribution panel circuit information plate

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Circuit conditions can be met before energizing

Question 8

What service is provided by bus transfer equipment

Answer 8

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

Question 9

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

Answer 9

To afford greater protection from damage during battle

Question 10

What is not a function provided by switchboards aboard ships

Answer 10

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

Question 11

What is the purpose of the disconnect links

Question 12

The output of all ac generators is generated in what winding

Answer 12

The armature winding

Question 13

Revolving armature generators are seldom used for what reason

Answer 13

They are subject to arc-over at high voltages

Question 14

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

Answer 14

The internal heat the generator can withstand

Question 15

What statement defines the term power factor

Answer 15

The expression of the losses within the electrical distribution system

Question 16

AC generator sets may be divided into what two classes

Answer 16

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

Question 17

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

Answer 17

An electric motor
A turbine
An internal combustion engine

Question 18

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

Answer 18

Rotor drive shaft

Question 19

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

Answer 19

Counterclockwise

Clockwise

Question 20

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

Answer 20

Electromagnetic induction

Question 21

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

Answer 21

Current and voltage only

Question 22

In a transformer what winding is designated as the primary

Answer 22

The one that receives energy from and ac source

Question 23

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

Answer 23

Thin, insulated lamination

Question 24

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

Answer 24

To reduce leakage flux

Question 25

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

Answer 25

Proportional

Question 26

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

Answer 26

340

Question 27

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

Answer 27

Power

Question 28

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

Answer 28

Leakage reactance losses

Question 29

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

Answer 29

Parallel- opposing

Question 30

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

Answer 30

High voltage

Question 31

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

Answer 31

Motor generator units and static converters

Question 32

What are the two principal types of transformer construction

Answer 32

Core and shell

Question 33

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

Answer 33

By using grain- oriented silicon steel laminations in the core

Question 34

What is the main purpose of the casualty power system

Answer 34

To make temporary connections to vital circuits

Question 35

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

Answer 35

To transmit power through compartments without loss of watertight integrity

Question 36

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

Answer 36

(A) 200A (b) 4

Question 37

When unrigging casualty power what procedure should you follow?

Answer 37

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

Question 38

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

Answer 38

True

Question 39

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

Answer 39

The enclosure that houses the shore power terminals or receptacles

Question 40

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

Answer 40

False

Question 41

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

Answer 41

Electrical officer

Question 42

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

Answer 42

93A | 200A

Question 43

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

Answer 43

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

Question 44

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

Answer 44

NSTM 300

Question 45

When using spliced cables what action should you take

Answer 45

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

Question 46

What is the key component of the phase sequence indicator

Answer 46

The three phase induction motor

Question 47

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

Answer 47

Never

Question 48

In the formula Eg=KØN what does the K represent

Answer 48

The constant determined by the construction

Question 49

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

Answer 49

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