7.5 Electrical Fundamentals - 7.5 Electrical Fundamentals Flashcards

1
Q

Basic terminology of Electricity

A

Conductor
Current “I”
Voltage “V or E”
Resistance “R” or “?”
Insulator
Direct Current “DC”
Alternating Current “AC”

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2
Q

Ohm’s Law
E or V = IR

A

The current in a resistive circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance.

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3
Q

Faraday’s Law

A

The induced voltage in a coil of wire equals the number of turns in that coil times the rate of change of the magnetic flux.

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4
Q

Three factors required to produce electricity

A

Conductor
Magnetic Field
Relative Motion

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5
Q

Generator

A

The machine that combines the Conductor, Magnetic Field, and Relative Motion

Relative Motion is provided by a Prime Mover
Three types:
Gas Turbines
Diesel
Steam Turbines

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6
Q

Electricity outputs in the Navy

A

450V, 60Hz, 3? (three-phase) electrical power

Carriers will produce 4160V, 60Hz, 3? electrical power instead due to the large electrical demands
The 4160V is then supplied to the 450V AC system through transformers

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7
Q

Three-Phase Power

A

Efficient system
A 3? system produces greater power density than a 1? (single-phase) system at the same amperage allowing wiring size to be smaller thus keeping the weight and cost down

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8
Q

Shore Power

A

400 amp receptacles are provided for a shore power connection.
Portable cables can be attached to them from the shore or from a ship alongside.

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9
Q

Switchboard

A

An electrical panel or group of electrical panels
used to distribute power throughout the ship

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10
Q

Load Center

A

Are located centrally to their loads and supply their
electricity with the goal to minimize the size, weight, and length of cabling

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11
Q

Distribution Panel

A

Divides the electricity into subordinate
circuits

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12
Q

Fuse or Breaker Panel

A

Divide the source of electricity
into separate circuits/equipment, each one is protected from
overcurrent by a safety device called a fuse, or a breaker depending
on ship configuration

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13
Q

Transformer

A

Transfers energy from one circuit to another
by raising or lowering the voltage to the receiving circuit
-Step-Down transformers lower voltage
-Step-Up transformers raise voltage

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14
Q

Bus Transfer Devices

A

Used to supply vital load panels with a normal and alternate power supply.

Two types:
Manual Bus Transfer (MBT)
Automatic Bus Transfer(ABT)
-Power Seeking: stays on current power even if normal power returns
-Normal Seeking: transfers back to the normal source when voltage is back to 85-95% of rated voltage

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15
Q

Automatic Bus Transfer (ABT) examples

A

AFFF pumps
Collective protection system class W ventilationEmergency lighting
Fire extinguishing auxiliaries and controls
Fire pumps
IC switchboard and panels
Steering gear power panel
Close In Weapons System (CIWS)
Some lighting distribution

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16
Q

Manual Bus Transfer (MBT) examples

A

Air Conditioning Units400 Hz
Combat System Equipment
All consoles in Combat Information Center (CIC)
Radio
Sonar
All other vital equipment requiring sequential start-up
Some lighting distribution

17
Q

400 Hz Distribution

A

Used due to high stability and regulation characteristics. It also allows for higher motor speeds, and lighter, smaller transformers and motors.

Examples of 400 Hz loads:
Comms. Equipment
Combat Systems Equipment
Nav Equipment
Aircraft starting and Servicing systems

18
Q

Home electrical systems

A

Grounded system

The system is physically connected to the earth at the ground point forming a zero voltage point, and all other voltages in the circuit are referenced to this point
-Can cause circuit breaker to trip and interrupt power

Picture

19
Q

Ship electrical systems

A

Ungrounded for reliability of operation

We do not want to cause power interruption if possible!

If a single phase is accidentally grounded (to the hull), there is no short circuit, because no other point of the circuit is connected to ground (the hull)

Picture

20
Q

Ungrounded System aka Ship

A

Ungrounded systems provide reliable service
If a ground momentarily or permanently occurs to any one phase of the system, the system can still operate

In a “perfectly ungrounded” system, you could touch a hot wire and no current would flow through you (No shock)

However, such perfectly grounded systems DO NOT EXIST!