AES Flashcards
What are Primary batteries in aviation?
Primary - Are capable of producing current as soon as they are constructed and are unable to be recharged.
What are Secondary batteries in aviation?
Secondary batteries are rechargeable and are used for starting engines or auxiliary power units
(APU), powering aircraft systems before starting, allowing technicians to test systems on the
ground and as an emergency source of power in the air.
Where would you use a primary battery in aviation?
In aviation they are used
cockpit voice recorders (CVR), flight data recorders (FDR), emergence locator transmitters (ELT)
and life vest lights
How must secondary batteries be constructed in aviation
They must be able to
cope with large temperature variations, atmospheric pressure variations and cope well with
inversion, vibration and impact
The two most common secondary aircraft battery types?
- Lead acid
- Nickel Cadmium (NiCad)
What are the methods to keep batteries held in position during flight?
Typically, hold down points are manufactured into the lid of the
case that are used to secure the battery to battery tray or the airframe.
No hold down points available: Positioned using brackets
In general aviation batteries can have posts located on top that accept bolts. What must be done to prevent damage when torquing the battery
These bolts must be torqued to the manufacturer’s specifications to prevent damage
What can be combined to make electrolyte in lead acid batteries?
Electrolyte used in lead acid batteries is sulphuric acid combined with
distilled water.
With regards to Lead Acid Batteries, what is the nominal voltage of each cell?
What is the nominal voltage of a battery in aviation, which are typically comprised of 12 cells.
Each cell in a lead acid battery has a nominal voltage of 2V DC.
Aviation batteries are typically comprised of 12 cells joined in series giving a total nominal voltage of 24V DC
What is the reccomended voltage do Lead acid batteries need to be charged at?
When charging lead acid batteries out of an aircraft, constant potential charging is usually the best method of restoring a lead acid batteries charge. A voltage of
approximately 2.4V DC per cell is the recommended voltage. With a 12-cellbattery, this equates to 28.8V DC at the output of our battery charger
What is the limiting voltage?
Once the cells have dropped to 1.75V DC per cell, this is considered to be the limiting voltage.
What is the C1 Rating?
Aviation batteries have a 1-hour rating referred to as the C1 rating. This is the average current that a battery is capable of supplying without interruption for an
interval of 1 hour.
Thus, if a battery can deliver 20 amperes continuously for 1 hour, the battery has a rating of 20 Ah.
The 20Ah battery mentioned above supplied 20A for 1 hours (C1
rating) before the battery discharged to a voltage of 21V (12 cells x 1.75V DC each).
The average current the battery is capable of supplying without interruption for an
interval of 1 hour.
Lead acid batteries are made up of what components?
- Battery case
- Connectors
- Cells
What is the typical range of Cold Cranking Amps (CCA) Ratings of aircraft secondary batteries?
Typical CCA ratings can range from 300A for general aviation up to 1000A for turbine-based
aircraft.
300A-1000A
Aircraft battery cells consist of which 3 main components?
Cells in a lead acid battery are made up of what components?
- Plates (positve plate have lead dioxide paste added to the grive and negative plates have a pasteof sponge lead added to the grid)
-
Separator Seperators are placed between the positve plate (anode) and the negative plate (cathode)
Alternating layers of plates and separators are used to form a cell
- Electrolyte
Electrolyte used in lead acid batteries is sulphuric acid combined with
distilled water
What makes Nickel Cadmium Different to Lead Acid Batteries?
Nickel cadium case can be opened and indiviual cells can replaced with new cells
The capacity of a battery is measure in what?
Ampere-hour (Ah)
How many cells are found in a NiCad battery?
What is the nominal voltage of each cell?
A typical NiCad battery has 20 individual cells fitted into the case. Each cell is a nominal 1.2 V DC
How are the cells in a NiCad battery joined together?
Each cell is joined to another in series giving the battery the required voltage.
Nickel plated copper solid links are used for the interconnections
- Nickle plated copper used to interlink the cells
- Linked in series
In a Nickel Cadium Battery what range do the vent caps, vent at?
Most vented NiCad’s vent
at between two and ten PSI.
What connector is used for a NiCad battery
A Elcon style connector
What is a major danger regarding NiCad batteries?/
Define thermal runaway?
A Ni-Cad battery is able to operate over a wider temperature range than
a lead-acid battery. However, they need to be watched very closely in
high temperatures and high charging rates as they become unstable. This
can cause thermal runaway which is an uncontrolled increase in battery
temperature potentially leading to a discharge of toxic fumes and the risk of
ignition and fire
- Uncontrollable increase in the temperature of a battery
- Leads to discharge or toxic fumes or ignition
High temp / high changing rate = battery becomes unstable
How are the State of Charge and State of Health Calculations done?
The temperature of the cells is an important factor for
determining the battery’s SOC and SOH calculations,
Using the temperature
Label the component
Cockpit Control Panel
At what temperature does the WMC illuminate the ‘batt temp’ warning light?
When the WMC detects an overheat condition, the WMC will illuminate the “BAT TEMP”
annunciator light on the Central Warning Panel (CWP).
This occurs when the thermostat
senses an internal battery temperature that exceeds 71°C ± 2.8°C
71 Degrees with a 2.8 degree tolerance
What is a Transformer Rectifier Unit (TRU)?
The transformer rectifier unit (TRU) provides a source of DC power on an aircraft with an AC
power generation system.
What does the TRU convert 115V AC into?
Ask the inverse question
What does the TRU convert 28V DC from?
The TRU converts the 3-phase 115V AC into 28V DC.
What are the components of a basic TRU?
- three phase transformer
- three phase full wave rectifier
- filter unit
- cooling circuit
- overtemp warning switch.
What is the Primary Purpose of an aircraft battery?
What is the Secondary purpose of an aircraft battery?
And what type of battery is it?
The primary purpose of the battery is to provide emergency
power to the aircraft in the event of all other sources of
power being lost.
The secondary purpose, depending on aircraft type, is to
either start the main engine or, if the aircraft has one, the
Auxiliary Power Unit (APU).
This means the battery type is Secondary
What is the empty box in the following image?
A voltage regulator
What does a voltage regulator do?
What type of voltage has to be applied to the field?
The regulator controls the output voltage of the generator, by varying the voltage applied to the generator field.
DC Voltage
What are the three types of voltage regulators?
- Vibrating point (Sparking - overcomes spring tension, 50-200 times a second - feedback path is through the resistor)
- Carbon pile (Carbon wears down)
- Transistor (electronic switch connected to an earthing point so when the contact open and close it stops the return path)
How is a voltage regulator connected?
It is connected parallel with the generator
Anything to do with voltage is measured in Parallel
What type of regulator has varies the voltage ofa generator, by varying the resistance of the discs?
The carbon discs contained within the pile will vary the resistance, depending
on the contact area and the pressure with which the two surfaces are held
together.
How does the carbon pile regulator achieve voltage regulation?
The carbon pile regulator achieves voltage regulation by altering the field
winding circuit resistance, therefore increasing or decreasing the field current.
What regulator is this image?
Vibrating Point Regulator
In a transistorised regulator what is the purposes of the transistor?
The transistorised regulator is a solid-state switch, which acts as an ON/OFF switch, and a vibrating point relay
In some DC generator systems what device is intstalled which reduces the generator output voltage whenver the maximum safe load is exceeded?
Current Limiter
What is the purpose of a Reverse Current Relay (RCR)?
The Reverse Current Relay (RCR) is the device used to
prevent the battery from discharging through the generator
and to disconnect the generator automatically, whenever the
generator voltage is lower than that of the batteries
Stops the battery from discharging back into the generator. Stop’s it going flat with the generator isn’t online (AC is switched off)
What the components of a RCR?
- voltage coil
- current coil
- a pair of contact points.
How does the RCR disconnect the battery?
When the aircraft engine is shut down, the generator voltage will decrease falling below that
of the battery. The battery will begin to discharge back through the generator via the relay
current winding.
This current flow will create its own field in the current winding to oppose the field of the
voltage winding. This results in a weakening of the total field of the relay. As a result, the
contact points open due to spring tension, and the generator is disconnected from the
battery
What the three main busbars in aviation?
- Non-essential
- Essential
- Vital / Emergency /Hot Battery
What is the primary function of a Busbar in a DC distribution sytem?
The primary function of the busbars, in a DC distribution system, is to supply the various
aircraft DC loads with power in all operating conditions
What is the purpose of the non-essential bus?
It is designed to isolate non-essential
loads during a failure of the primary power source
If a DC generator should fail, which busbar will become offline first and what components disengages it?
- Non-essential bus
- the auxiliary contacts of the DC generator’s reverse current relay will open, removing the
earth from the load shed relay. - when the earth to the load shed relay’s coil is removed, the relay will de-energise, causing
its main contacts to open and disconnect the non-essential bus from the essential bus. - with the isolation of the non-essential bus from the essential bus, all power will be
removed from the non-essential DC loads
What happens if power is subsequently restored to the generator?
If the failed DC generator should recover or reset, and return to a serviceable condition, then
the reverse will occur, and the non-essential bus will be re-connected to the DC generator
How is the battery and vital loads reconnected to the essential bus?
It would be essential for the continued operation of the aircraft,
that the battery and vital loads be reconnected to the essential bus. This can be accomplished
by simply turning the battery switch to “ON”
The two systems used to distribute DC power within a multi-generator system are?
- split bus distribution system
- tied bus distribution system.
What is the name of the DC distribution system that has one generator
supplying the essential loads while a second independent generator supplies
the non-essential loads?
Split bus system
What is the name of the DC distribution system that has two or more
generators connected in parallel to a common busbar?
Tied Bus System
In a split bus system what device connects both busses together when one generator fails or is turned off?
Bus Tie Breaker
In a split bus sytem, while the bus tie relay is open. How do the two generators operate?
Both supply systems will operate independently of each
other (bus tie relay open).
Under a generator fail situation which component in a split bus links the no.1 generator?
Bus tie relay
If the No.1 generator fail light has illuminated in the cockpit:
* What other related indication would be expected?
* What power source would now be supplying the DC distribution system?
* What busbars would be supplied with 28 VDC?
- Bus tie indication light. (illuminates when the bus tie relay energises)
- The remaining No.2 Generator
- Both the essential and non-essential buses
Which of the two distribution systems would most likely be used in an
aircraft to distribute the power generated by four DC generators?
Tied bus because if one generator fails, there will be no interruption in the
output
What component will be used as the primary source of power for the DC
loads in an aircraft that is fitted with only AC generators?
Transformer Rectifier Unit (TRU)
In a split bus DC distrubution system if a generator fails. What will remain operational?
If one generator in a split bus DC distribution system fails, then the remaining operational
generator will supply power to both the essential and non-essential buses
What component in a tied bus ensures the generators are sharing the load?
Equalising voltage controller
Advantage of a tied bus system compared to a split bus system?
The Aircrafts generators are tied together in parrellel. This means that the high current drawn by the aircraft’s operating DC loads will be distributed evenly between the aircraft’s generators and not supplied by any
individual generator.
- Voltage is always constant / 28v across the bus bar regardless of how many generators are lost
In a tied bus system the equalising circuit can only correct small differences in generator voltage. What is the output voltage tolerence?
The output voltages of all generators therefore, should be adjusted to within 0.5 Volts
of each other during installation or scheduled aircraft servicing.
What is the purpose of an inverter?
An inverter is a device that converts direct current (DC) into alternating current (AC) at the frequency and voltage required for operating aircraft AC equipment.
Converts 28 DC voltage to 115 VAC
What is a common application of inverters in aviation?
Inverters are commonly used in aircraft that have a DC generator system to supply AC to flight instruments, radio, radar equipment and electronic equipment
Rotary Inverter
What are the two classes of inverters?
- Rotary inverter
- Static inverter
What is the nominal output frequency and voltage rating in a rotary inverter?
- the nominal output voltage rating for inverters is 115 V
AC single or 200 V AC three phase - the nominal output frequency rating for inverters is 400 Hz
What is the construction of a rotary inverter?
Rotary inverters generally have the rotating field windings electrically connected
via slip rings and brushes
Why are slip rings and brushes used in a rotary inverter?
To supply power to the magnetic field in a AC generator
Where is the 115 VAC and 400 Hz taken from in a rotary inverter?
The stator
What are the advantages of a static inverter over a rotary inverter?
- lighter weight
- negligible noise
- smaller size for a comparable output
- no moving parts - therefore maintenance problems will be less for static
inverters than for rotary inverters.
What electric components do static inverters/solid state inverters consist of ?
Internally, a static or solid state inverter consists of standard
electric and electronic components, such as diodes,
transistors, capacitors, transformers, etc.
Where are the components in a static inverter located?
The components
are located within a well-ventilated housing that protects the
internal circuitry from foreign object damage
Electrolyte combination in a Nickle Cadium (Nicad) battery?
The electrolyte is a combination of 30% potassium hydroxide (KOH) and 70% distilled water
Static inverter output?
115v AC
Label the components of a static inverter block diagram?
A) Square wave generator
B) Power amplifier
C) Sinewave shaping network
D) Feedback
What is the purpose of a Generator Control Unit (GCU)?
The generator control unit will maintain the output voltage at the correct
voltage and frequency. It is also responsible for ensuring that the IDG is
running with the same phase rotation as the other AC power sources already
on-line.
Label the components on the AC Split Bus Distribution System
A) External Power Relay
B) Auxiliary Power Relay
C) & I)Generator Circuit Breaker/ Generator Control Breaker
D) Inverter
E) & F)Transformer Rectificer Unit
G) & H) Bus Tie Breaker
In a AC generating system what is the purpose of the Generator Circuit Breaker’s?
To connect or disconnect the relevant AC generator to its bus bar
What is the function of an AC multi-generator distribution system?
To supply power to various AC loads
In a AC generating system what is the purpose of the Bust Tie Breakers (BTB’s)?
To tie or disconnect generators to the bus system
To tie or disconnect generators to the bus system
What are the fundamental requirements for an AC tie bus system?
- AC generators must be in synchronism (voltage, phase
and frequency) before they are connected in parallel - once connected to a common bus the AC generators
must be maintained in synchronism throughout system
operations.
How are the generators synchronised in an AC tied bus system?
Electronic Load
Management System (ELMS)
In an AC tied bus system with 4 generators, if generator 4 fails, what will happen?
- GCB4 will open breaking the circuit to generator 4
- Gen 1, 2 and 3 will supply power to bus 4 (will remain closed)
In an AC tied bus system with 4 generators, if generators 2, 3 and 4 fail, What will happen?
- GCB2, GCB3 and GCB4 will open, breaking the circuit to generator 2, 3 and 4
- Gen 1 is not capable of powering itself and 3 other generators on its own, therefore bus 2, 3 and 4 will remain disengaged
What is ELMS and what does it do?
Electronic load management system
- Manages all the switches via Auto-Synchronisation
Label the Switches in the diagram
A) GCB 1
B) GCB 2
C) GCB 3
D) GCB 4
E) BTB 1
F) BTB 2
G) BTB 3
H) BTB 4
What does the GCU do when a generator in a system fails?
If a generator in the system fails, the generator’s GCU in
conjunction with the electronic load management system (ELMS)
will trip its respective GCB
Where is calibration and adjustments carriet out?
Calibration and adjustments
are carried out at a workshop or deeper level maintenance facility.
Aircraft electrical system and components may also be subject to periodic
maintenance such as a bay service, overhaul or calibration check as detailed in
the applicable Technical Maintenance Plan (TMP)
What is all maintenance, testing, troubleshooting, utiliastion of fault and diagnosise guides TBCO IAW?
TBCO-To be carried out. IAW-In accordance with
All maintenance, including testing troubleshooting and the utilisation of fault
diagnosis guides, are to be carried out in accordance with authorised data (ICA, MM’s, Serice bulletins and airworthiness directives)
and only by authorised personnel.
When you are presented with Aircraft Faults in which you lack the knowledge and experience to rectify Who would you seek out ?
In these instances you will
be required to seek the advice of senior and more experienced technicians
within your trade. You may also find that you require the experience of
technicians outside your trade for advice
What do you do when the advice of senior and more experienced technicicans are insufficient?
Aircraft faults that extend beyond these solutions may require the
intervention of Continuing Airworthiness Management Organisation (CAMO)
or DASR Part 21 Design Organisation.
It is their job to seek further clarification of the presented problem in which
they will then seek advice and recommendations for you to proceed with
your work. This may go as far as to obtaining approved specialist equipment,
having maintenance procedures changed or even develop modifications to
the aircraft or equipment to be incorporated.
When do we service primary batteries?
Specific maintenance schedule as dictated by the equipment / aircraft manufacture
Why is nickle cadimum a popular choice in aviation?
- Good starting current
- Deliver a linear output
- Handle extreme temps reasonably well
How is a non essential bus isolated during failure of a primary power supply?
Load shed
Why is a current limiter used?
Reduces the generator output voltage whenever the maximum safe load is exceeded
What is the vital bus directly connected to?
- The aircraft battery
- This ensures power is supplied to the aircrafts emergency loads at all times
How is an essential bus isolated and then reconnected?
- By turning the battery switch off
- By turning on the switch
Where are split bus commonly used?
Commonly used in light aircrafts with 2 generators
Advantages of the tied bus bar?
- Tied together in parallel
- Load is distributed evenly between the aircraft generators, not supplied by an individual generator
Difference between split bus and tied bus?
Split - Series
Tied - Parallel
What does the equalising voltage controller do?
It ensures that the load carried by the generators is shared evenly
What must the voltage be within for the equalising voltage controller?
28v DC
+/- 0.5v
Required AC voltage and frequency used for aircrafts?
115vac
400Hz
What controls the frequency and voltage in a rotary inverter?
Frequency is controlled by the speed of rotation and
voltage by generator field excitation current.
What parts of the aircraft are connected to the vital bus?
- fire detection and extinguishers
- cockpit warning lights
- emergency interior lighting
- emergency radio
- DC and AC generator control (single battery aircraft
only) - engine ignition and relight (single battery aircraft only)
- ejection seat (if fitted)
- canopy and stores jettison (if fitted).
What should be followed when carrying out troubleshooting?
Repair and overhaul manuals
What must be carried out after a component is removed or disconnected?
Following any maintenance on an aircraft electrical system that
required disconnection of any component, an operational test of that system
is required
Where can the periodic maintenance be found?
Technical maintenance plan (TMP)
When inspecting a static inverter what would you be looking for?
- Inspect it for signs of overheating, security, damage, or defects
- Pay attention to sign of contamination around the vent holes
- Inspect the receptacle for signs of damage, corrosion and foreign objects
. Describe one sign that you are looking out for when inspecting busbars?
- damage and defects
- contamination by oil, grease and hydraulic fluid
- signs of discolouration/overheating
- contamination and foreign objects
For a static inverter, what is monitored at the feedback stage?
- Voltage
- Frequency
- Current
What connector is used for lead acid batteries?
MIL Spec connector
What does the capacity of a battery depend on?
- Area of plate in contact with electrolyte
- Quantity and specific gravity of electrolyte
- Type of separater
- General condition of battery
- Final limiting voltage
What are the components of a AC split bus system?
- Two Intergrated Drive Genarators
- Auxillary Power Unit
- Genarator Control Units
- Transformer Rectifier Units
- Static inverter
- External power supply
- Generator Circuit Breaker
- Bus Tie Breaker
What are three sources of internal DC supply in an aircraft?
- Battery
- DC generator
- TRU
Name two components unique to an emergency power system?
- Emergency Battery
- Standby Inverter
In an AC tied bus system, what must we ensure before the connection of
multiple generators?
Before AC generators are connected to the tied bus, they
must be checked to ensure they have the same voltage,
frequency, and that each incoming generator is in phase (phase sync)
with the on line power
