electrical power supply systems 7705 Flashcards
what do A/C generators do?
generators convert mechanical energy derived from the aircraft engines or rotor heads into electrical energy by electro-magnetic induction
describe batteries
and their role in A/C
batteries produce DC electrical power by chemical reaction.
provide an emergency source of power,
power source for engine starting
limited system testing,
and recharge when the main generators come on line
auxiliary power unit (APU)
capable of providing power during emergencies to augment or replace the aircraft primary power generation system
such units typically consist of a generator powered by a small gas turbine engine
power conversion equipment
aircraft having a 200/115v three-phase AC generation system will often require the AC supply to be ‘stepped down’ to power instruments or rectified to provide a 28v DC supply to DC components
control and protection units
the protection devices will isolate the generator from the bus bars by removing the excitation filed at the generator.
voltage regulation ensures satisfactory operation, the output voltage must be maintained within a set tolerance over a wide range of engine speeds and electrical loads
protection devices
abnormal conditions or faults, may arise in an electricla circuit for a variety of reason,
devices circuit breakers are essential components in an electrical system. additionally we often employ switches as potential isolation devices
electriclal distribution
emergency services - fed diectly by main batteries, services such as flot, extinguishers, hoist cutter
essential services - services required to ensure safe flight, connected to busbars so that they can be fed by generator or batteries, using invertors and TRU’s
non-essesntial/ general services - considered non essential for flight, if they fail they will limit he A/C only,
bonding and earthing
bondng leads are used to achieve good bonding between structures or components,
will be similar in constructuion to an airframe, earth point and protected by blue paint
cable and component marking
coding method applicable to that aircraft type as laid down in the relevent topic 10’s (CIETP) such as:
system / circuit
location on the aircraft
the position within the circuit
type of supply (if AC, which phase it is)
component / equipment it is supplying
describe circuit breakers
a bi- metallic device opens the circuit in event of an electrical overload and release the actuating button
actuating button can be pulled out to isolate a circuit, pushed back in to reset the circuit.
contacts are opened by springs, the actuatting button is released to reveal a white collar to indicate tripped condition
manual switches
consists of two contact surfaces which can be brought together to make a circuit or separated to break a circuit
Types of toggle ships
1 pole, 2 posn. on-off
1 pole, 2 way, 2 posn
1 pole, 2 way, 3 posn
2 pole, 2 way, 2 posn
mechanical switches
these swithces are made as the result of some mechanical action or force
micro switches
float switches
pressure swithces
centrifugal switches
electrical switches
circuits can be made or broken by rapid movement of contacts which reduce the effects of sparking.
relays normally have more than one contact and can therefore provide multi-circuit switching
automatic or semi-automatic cotrol over circuits
heavy current circuits can be completed or isolated using low current control circuits
control circuits can be quite remote, allowing heavy cirrent carrying cables to be of minium length
heavy duty single coil relays
a relay which is used to switch a heavy current necessitates a powerful, fast build-up of electromagnetic force
this causes heat in the coil which may be severe, if the coil is energised for a considerable time
only fitted in circuits which are used to periodically for a short duration
heavy duty double coil relays
where a relay is needed to be energised for a long period of time, two coils are used, a low impedance high current coil is used to energise the relay via an auxilary contact
high impedance coil is inserted in series with the operating coil, reduces the current flow through the two coils reducing the heat
light duty relays
here the contacts are housed in a sealed unit which plugs into a fixed base, connecting the external circuits
inspection practices
servicing or maintenance is carried out whenever a fault has been reported, during flight servicing, periodicities laid down, aircraft, maintenace regime, modification are required or technical instruction
what checks are carried put
maintenance is either prevengtative or corrosive defined within MAPs
cleanliness
sign of corrosion
areas/equipment correctly protected against corrosion
damage/ faults in surrounding are and equipment
security of attachments and electrical connections
damage caused by wear and tear
sign of overheating
signs of fluid leaks
simple construction of battery
positive plate, negative plate and electrolyte
specific substance of which is dependant on battery
what is a cell
two unlike metals in a conducting solution (the electrolyte)
how is a battery made up
number of cells connected together
what is a primary cell
a cell, which once discharged, can only be recharged by replacing the chemicals in it
what is a secondary cell
a cell, which can be restored to its original state, after discharged, by passing a reverse current through it
