AC Distribution Flashcards
Bus bars
Transmit power from source to consumer.
A low resistance conductor usually copper or aluminium and forms a common connection point for loads and consumers,
Connected in parallel, as loads are switched on, bus bar current increase. because ach load draws additional electrical power from the system. Also reduced resistance (parallel).
AC bus
3 phase distribution bus with no directly connected loads. Used for supply and fault monitoring.
DC bus
Main DC supply supply bus with no directly connected loads, also used for supply adn monitoring.
Emergency bus
Loads essential for flight are powered from here. During emergency electrical configuration the essential buses remain powered.
Battery bus
Allows the battery to be connected to the DC bus for distribution or battery power or battery charging..
Hot bus
Directly connected to the battery terminals and unswitched (permanently live) used for permanent connections to certain functions: flight deck clock, dome light, fire detection system.
Ground or maintenance bus
Allows connection of external AC power. Allows for cleaners and engineers to use Ac and DC electrical equipment whilst on the ground: power outlets cabin and maintenance lights yellow hydraulic pump (A320) and refuelling equipent.
Shed bus
Non-essential loads connected via this bus allowing load shedding in an emergency to be carried out.
Connections
Cables can be connected to components by:
Uni-pole: metallic airframes and uses the structures the common earth return.
Dipole: Composite airframes. features 2 wire connection as the structure is effectively an insulator.
Uni-pole and dipole
Unipole - busbar only conncetd to 2/4 loads one way.
Dipole - busbar connected to 3.4 loads both ways.
Power priority
Generator 90kva
External power unlimited
APU 90kva
RAT 5kva
Batteries 1kva
Load sharing
Parallel system.
Generator outputs connected to same bus bar.
In an AC circuit following must match prior to closing tie breaker:
Voltage
Frequency
Phase angle
Reactive loads
Load shedding
Turning off non essential loads in the vent of power supply loss.
Switches off loads connected to the shed bus.
Will increase power available.
Split bus
Buses are kept separate from each other. Two generators never power the same bus simultaneously. If one fails operation continues as normal.
AC distribution
No loads connected directly to these bus bars and throughout the aircraft further bus bars are located to transfer power directly to end consumer via switches and circuit breakers.
Where single phase is required, 3-phase supplies can easily be seperated through the connection methods.
AC is transmitted to the TRU for conversion to DC for the DC system or charging of the batteries.
