AC Power Distribution Systems Flashcards
Which systems make up the power distribution system?
The casualty power system
The emergency power system
The ships service system
What is the function of the switchboard bus ties
Top permit switchboards to be cross connected and to allow paralleling of generators
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?
Simplifies the installation
Reduced the weight and space requirements
Reduces the equipment requirements
What information is contained on circuit information plates located on distribution panels
The circuit number, the name of the circuit controlled, and the space served
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?
Distribution panel circuit information plate
For what reason if any is the phase sequence important to the distribution system aboard ship
The phase sequence determines the direction of rotation of three phase motors
What is the advantage of using an MBT as an alternate power source to a vital load
Circuit conditions can be met before energizing
What service is provided by bus transfer equipment
Two sources of power to equipment that is vital to the ship
Aboard ships, switchgear groups are physically separated as much as practical for what reason?
To afford greater protection from damage during battle
What is not a function provided by switchboards aboard ships
Automatic shifting of power to alternate sources if normal power is lost
What is the purpose of the disconnect links
The output of all ac generators is generated in what winding
The armature winding
Revolving armature generators are seldom used for what reason
They are subject to arc-over at high voltages
When dealing with the load rating of ac generators, what factor must be accounted for?
The internal heat the generator can withstand
What statement defines the term power factor
The expression of the losses within the electrical distribution system
AC generator sets may be divided into what two classes
Low-speed, engine driven and high speed, turbine driven
The rotary force used to provide the rotating action in generators may be supplied by which of the following prime movers?
An electric motor
A turbine
An internal combustion engine
The rotary force from the prime mover is transmitted to the ac generator by which of the following components
Rotor drive shaft
When you use vectors to analyze ac circuits, what rotation direction represents (a) positive and (b) negative polarity
Counterclockwise
Clockwise
In transformers electrical energy is transferred from one circuit to another through which of the following
Electromagnetic induction
When a transformer transfers electrical energy, what Elements are either increased or decreased by the transformer
Current and voltage only
In a transformer what winding is designated as the primary
The one that receives energy from and ac source
You can reduce eddy current losses in the core of a transformer by installing which if the following components
Thin, insulated lamination
In a transformer, the low-voltage winding is placed next to the core instead of the high-voltage winding for what reason
To reduce leakage flux
In each winding of a transformer, the total induced voltage has what relationship to the number of turns in that winding
Proportional
Because of damage caused by heat, you should NOT operate a transformer rated at 400 hertz at which if the following frequencies
340
A transformers efficiency is stated as a ratio of what factor of the transformers input it output
Power
Which if the following losses does NOT affect the efficiency of a transformer
Leakage reactance losses
To obtain max current output from a single-phase transformer you should connect the sections of the secondary windings in what configuration
Parallel- opposing
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
High voltage
Which if the following types of equipment are used to supply 400hz power to a transformer
Motor generator units and static converters
What are the two principal types of transformer construction
Core and shell
By what means are hysteresis losses kept to a minimum in transformers
By using grain- oriented silicon steel laminations in the core
What is the main purpose of the casualty power system
To make temporary connections to vital circuits
Casualty power bulkhead terminals are permanently installed on opposite sides of the bulkhead for what reason
To transmit power through compartments without loss of watertight integrity
A portable cable used to rig ac casualty power systems can carry (a) what max current for (b) what max number of hours
(A) 200A (b) 4
When unrigging casualty power what procedure should you follow?
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
Shore power connections aboard the ship may be used to supply power to another ship alongside
True
When testing shore power cables, what should be used as the shore ground resistance?
The enclosure that houses the shore power terminals or receptacles
The casualty power system provides a good means of testing repaired equipment without jeopardizing the normal electrical distribution system
False
What person is authorized to order the energization of the casualty power system
Electrical officer
What is the normal current carrying g capacity of portable casualty power cables and the casualty current carrying capacity
93A
200A
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
The equipment is operating on normal power and all portable cables have been restored
What publication should you refer for the insulation resistance requirements for shore power cables
NSTM 300
When using spliced cables what action should you take
Make sure the phases are continuous and have not been altered at the splice
What is the key component of the phase sequence indicator
The three phase induction motor
When if ever is it permissible to move energized shore power cables
Never
In the formula Eg=KØN what does the K represent
The constant determined by the construction
Which of the following conditions causes the efficiency of a power transformer to be less than 100%
The copper losses in the windings and the hysteresis and eddy current losses in the core
