Electrical systems
Basic operation of an aircraft electrical system
Engine driven generators supply electric current to the electrical system and maintain a sufficient electrical charge in the battery.
The battery provides electrical power for starting (APU, engine) (or ground power can be used) and a limited supply of energy in the event of a generator failure. Turning on the battery master switch provides electrical energy to all of the electrical equipment circuits.
A bus bar system is used to connect the main electrical system to the equipment using electricity as a source of power. Voltage and amps are monitored and regulated, with multiple circuit protection devices.
Methods of producing electricity in aircraft
-Ground power
-Battery
-Generator (engine driven, APU, ADG)
Function of aircraft electrical components
-Generators: engine driven, generate electricity by moving permanent magnets around a coil of wire, thereby motivating electron flow in the coil. Voltage = output of electrical pressure, Current = output volume or flow (measured in amps).
Normally generate AC current and must produce adequate amperage to power all of the components on its circuit(s) (or load shedding)
-Generator Control Units (GCU): voltage regulators, direct generator current to the battery when necessary for recharging, provide circuit and generator protection by disconnecting the generator from the system when electrical abnormalities occur.
-Battery: power reservoir that stores electrical energy in a chemical form. Must have lower voltage than the system to charge. Rated at amp-hours.
-Starter: driven electrically by a battery
Ni-cad: put out sustained voltage over a longer period of time, subject to memory characteristic (low use limits ability to handle high demand) and thermal runaway (excessive current is drawn from and then replaced to the battery causing it to overheat)
-Relays: remotely control electric circuits carrying large amounts of current
-Solenoid: electrically powered remote control device, moves a shaft over a short distance (hydraulic and pneumatic valves)
Transformers: used to step aircraft voltage (usually down) Transformer-rectifier units (TRU) convert AC to DC power
-Inverters: convert DC power to AC power
-Circuit breakers: disconnect individual components that are drawing too much current
Fuses: open circuits that are drawing too much current
-Diodes: one-way check valves
-Bus ties: switches or relays used to connect or disconnect buses from one another in order to isolate failed buses
Aircraft electrical distribution system
-Electrical bus bar system: aircraft’s electrical system is carefully organized into separate but interconnected circuits. Important circuits can be isolated from one another and supplied by alternate power sources. Redundancy is also provided.
