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AV Laet QC > electrical power supply systems 7705 > Flashcards

electrical power supply systems 7705 Flashcards

1
Q

what do A/C generators do?

A

generators convert mechanical energy derived from the aircraft engines or rotor heads into electrical energy by electro-magnetic induction

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2
Q

describe batteries

and their role in A/C

A

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

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3
Q

auxiliary power unit (APU)

A

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

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4
Q

power conversion equipment

A

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

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5
Q

control and protection units

A

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

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6
Q

protection devices

A

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

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7
Q

electriclal distribution

A

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,

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8
Q

bonding and earthing

A

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

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9
Q

cable and component marking

A

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

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10
Q

describe circuit breakers

A

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

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11
Q

manual switches

A

consists of two contact surfaces which can be brought together to make a circuit or separated to break a circuit

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12
Q

Types of toggle ships

A

1 pole, 2 posn. on-off

1 pole, 2 way, 2 posn

1 pole, 2 way, 3 posn

2 pole, 2 way, 2 posn

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13
Q

mechanical switches

A

these swithces are made as the result of some mechanical action or force

micro switches

float switches

pressure swithces

centrifugal switches

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14
Q

electrical switches

A

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

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15
Q

heavy duty single coil relays

A

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

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16
Q

heavy duty double coil relays

A

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

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17
Q

light duty relays

A

here the contacts are housed in a sealed unit which plugs into a fixed base, connecting the external circuits

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18
Q

inspection practices

A

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

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19
Q

what checks are carried put

A

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

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20
Q

simple construction of battery

A

positive plate, negative plate and electrolyte

specific substance of which is dependant on battery

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21
Q

what is a cell

A

two unlike metals in a conducting solution (the electrolyte)

22
Q

how is a battery made up

A

number of cells connected together

23
Q

what is a primary cell

A

a cell, which once discharged, can only be recharged by replacing the chemicals in it

24
Q

what is a secondary cell

A

a cell, which can be restored to its original state, after discharged, by passing a reverse current through it

25
Q

what is EMF

A

electro motive force

total electrical pressure produced by a cell

26
Q

internal resistance

A

resistance to current flow through the cell itself

if a battery is connected in a circuit the terminal voltage will be less than the EMF

27
Q

capacity of a batery

A

the amount of electricity a cell/battery will deliver between the fully charged and discharged state

28
Q

rated capacity

A

dependant on electrolyte

the rate at which a battery is discharched affects the amount of electricity it can deliver

29
Q

efficiency of a battery

A

this is a measure of the performance of a battery.

as a bettery deteriorates with use and age, it will no longer produce its rated performance

30
Q

construction of a lead acid batteries

A

positive plates are made of lead peroxide and the negative plates are made of spongy lead

electrolyte is dilute sulphuric acid

each cell voltage is 2v

31
Q

construction of an alkaline battery

A

nickel hydroxide positive plates, cadmium hydroxide negative plates, potassium hydroxide electrolyte, seperated by synthethic fibre. the cell is made of steel nylon

32
Q

what are the discharge characterisitics of lead acid battery

A

steadily decreasing

33
Q

discharge characteristics of a alkaline battery

A

remains constant until fully discharged

34
Q

what is thermal runaway? what conditions can cause it

A

alkaline and li-ion suffer from rare instances of thermal runaway, caused by an increase in internal temperature of the battery causing a chain reaction of temperature rises,

adverse operationg conditions

poor battery maintenance

battery damage

high battery usage

35
Q

explain battery servicing

A

batteries are installed removed IAW topic 1, topic 5C and topic 5A1

battery maintenance is staffed by civi’s ashore and navy afloat,

battery maintenance TEM are provided for those personnel who need the experiance and specific detail

36
Q

what types of battery servicing are there

A

commission charge: carried out on all new batteries prior to first use

routine charge: carried out on ‘not in use batteries’ not connected to aircraft, but are servicable, or ‘in use’ batteries when charge state is unkown

full maintenance/charge carried out on all ‘in use’ and ‘not in use’ batteries and is carried out at periodicity laid down in topic 5C

chargeing methods depends on the battery type

37
Q

what are the checks for battery compartments

A

general cleanliness

electrolyte spillage

corrosion

damage to battery or battery tray

vent pipes attached and secure

38
Q

explain a capacity test (lead acid and alkaline)

A

a capacity charge is used to force discharge an A/C battery, at its 1 hour rate until the trip voltage of 20V is reached

a digital counter indicates capacity percentage

a capacity of over 80% shows is fit for A/C use

39
Q

describe how a slab battery is dishcarged

A

deep discharge is undesirable

and batteries are discharged for 48 mins, if it doesnt reach its trip voltage in that time, then it is considered to be at least 80% efficient and fit for use

40
Q

explain the procedure for battery spillage in an aircraft

A

entry in Mod form 700C pt1 (placing aircraft unservicable

soak up spillage

dispose of contaminated rags IAW local orders

use neutralising agent

wash and dry area to minimise any free fluid and residual contamination

use litmus paper to test for residual contamination

have area surveyed, by an authorised person for any possible skin repairs

refinish area as required

clear the entry Mod form 700C pt 1

41
Q

battery eye contamination

A

flush with eye irrigator, or clean water holding eye open for min 15 min until medical help arrives

inform sickbay of all relevent info

do not leave patient alone or let them make there own way to sickbay

42
Q
A
43
Q

what is load sharing

A

if one output voltage is slightly higher than the other, the high generator will provide a greater share of the load.

an equalising circuit operates via both generator control units (GCU) to adjust the output voltage of the generators to maintain equal load sharing

44
Q

when inspecting a generator what do we look for

A

general wear

burring, pitting or scoring of the commutator segments

thrown solder

brushes are checked for:

acceptable length and even wear

cracking, chipping or scoring

frayed or broken pigtail connections

freedom of movement in brush holder

correct spring tension

45
Q

what does the GCU provide protection from

A

generator control unit

protect the generators and distribution circuits from:

over and under voltage

over excitation

overspeed

current limiting

reverse current

reverse polarity

short circuit / overload protection

46
Q

what is the prupose of the GCU

A

generator control unit

maintains the output voltage of the DC starter generator at a constant level of 28.5V, as well as control of contactors

GCU’s are also responsible for load sharing

47
Q

what does the PDU do

A

power distribution unit provides primary distribution of DC electrical power to the aircraft

48
Q

what does the main battery do

A

it supplies DC power to the essential busbar in the event of failure of the main generation power

49
Q

what are the advanatages of using AC generators as a primary power source

A
  • Better power to weight ratio
  • AC generators sre robust and simpler in construction
  • generating AC at a higher voltage reduces the size and weight of the current carrying cables
  • can be stepped up or down efficiently by use of transformers
  • easily rectified
  • brushless AC generators design removes the servicing and the problems associated with the brushes
50
Q

what is load shedding

A

in an aircraft generators are connected to separate busbars, but there has to be a method of ensuring essential loads to incase of a single generator failure

by using bus tie contactors if a generator fails the working generator, APU or GI can have power diverted from them to power essential systems while isolating non-essential

51
Q

what do GCU’s protect against (additionally)

A
  • over voltage
  • under voltage
  • under frequency
  • over current
  • differential current (between load and busbars)
  • current unbalance (different current between phases)
  • dead bus (prevents a generator being connected to a bus bar if frequncies are out of phase)
52
Q

What do EPCU monitor

A

external power control units

incorrect phase

under frequency

under/over voltage

AV Laet QC (13 decks)

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