7.5 Electrical Fundamentals - 7.5 Electrical Fundamentals Flashcards
Basic terminology of Electricity
Conductor
Current “I”
Voltage “V or E”
Resistance “R” or “?”
Insulator
Direct Current “DC”
Alternating Current “AC”
Ohm’s Law
E or V = IR
The current in a resistive circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance.
Faraday’s Law
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.
Three factors required to produce electricity
Conductor
Magnetic Field
Relative Motion
Generator
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
Electricity outputs in the Navy
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
Three-Phase Power
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
Shore Power
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.
Switchboard
An electrical panel or group of electrical panels
used to distribute power throughout the ship
Load Center
Are located centrally to their loads and supply their
electricity with the goal to minimize the size, weight, and length of cabling
Distribution Panel
Divides the electricity into subordinate
circuits
Fuse or Breaker Panel
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
Transformer
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
Bus Transfer Devices
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
Automatic Bus Transfer (ABT) examples
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
