11.6 Electrical Power Flashcards
What type of battery systems are used within aircraft?
Negative ground or single wire earth returns system
What do they mean by negative ground/ single wire earth system?
Negative terminal of battery is connected directly to the metallic portion of the aircraft structure placing the structure at a negative potential.
What type of electrical system is required on composite aircrafts?
two-wire electrical system
What is the purpose of a solenoid/contactor?
Remotely control a large current source with a small conductor and switch.
What is the purpose of a freewheeling diode?
Eliminate spikes when the master switch is opened and the magnetic field from the coil collapses.
Describe the operation of a free wheeling diode.
Allows induced EMF to feed back into itself rather than back into the distribution system.
How is thermal runaway prevented on an aircraft with and without the charger unit.
Isolate battery when external DC power is applied, or the battery charger unit automatically disconnects the charging current above a pre-set battery temp.
What indications do aircrafts have with nicad batteries fitted?
Battery temperature monitor system and a high temperature warning.
What gassing does lead acid batteries give off when charging?
Hydrogen and oxygen.
What methods are there of ventilating the aircraft batteries?
System A: neutralising agent in a sump jar
B: typical light aircraft/ ram air.
C: pressurisation system air through non return valve.
What can be done to prevent corrosion on aircraft lugs?
Smear lugs with an approved lubricant/ white petroleum jelly for quick disconnects
If there is no inbuilt locking device on quick disconnects what must be done?
Lockwired closed with 26 AWG copper wire.
Aircraft batteries must be firmly mounted into?
Mounting cradle.
When connecting the aircraft battery always connect which lead first?
Positive.
When removing the battery from the aircraft always disconnect which lead first?
Negative.
What should be checked before installing the battery?
Mounting tray/box in good corrosion free condition, vent and drain lines in good condition/not blocked, neutralising jar is serviceable.
What solution is used to neutralize lead acid batteries?
Bi-carb and water
What solution is used to neutralize ni-cad batteries?
Chromic acid.
What should you flush acid spills on your skin with?
Water only.
A DC alternator produces?
AC voltage and uses internal rectifiers to produce a dc output.
On larger aircraft normal DC power is supplied by?
Transformer Rectifier Units (TRU’s) 115 V AC to 28 V DC
What are used in emergency power situations?
AC generators driven by APU’s or RAT’s
Alternators are classified according to?
Voltage, ampereage, phase, power output.
EXAM: What are your four main AC power systems?
- Left engine driven generator
- Right engine driven generator
- APU generator or starter generator
- External power.
On a turbine aircraft the engine driven generators a driven by?
CSD - Constant speed drive and
IDG - Integrated drive generator.
What do generators supply?
AC 3 phase 115/200 volts at 400hz
What does a static inverter supply?
115V AC.
What does a CSD system consist of?
- Axial Gear Differential AGD
2 Fly-weight type governor - Variable delivery hydraulic pump.
- Quick attach/detach adapted QAD.
To remove a CSD generator from the aircraft how is this achieved?
Release the QAD using one fastener.
What does the IDG system consist of?
Both the generator and CSD all in one unit, reduces wight and the size of a traditional two unit system
What electrical sub assemblies make up an IDG?
- Permanent magnet generator
- Exciter generator and rectifier assembly
- Main generator.
What should be closely monitored in regards to CSD and IDG’s
Oil level monitored periodically using the sight glass.
An IDG system installation consists of?
- Alternating current generator
- hydraulic transmission with mechanical control governing the rotational speed of the alternating current generator.
What is in the governing section of the CSD?
spring-biased flyweight operated hydraulic control valve.
How is the CSD disconnected and reconnected?
Electrically decoupled, to reconnect when engine is stationary pulling out on reset handle until solenoid snaps into position.
Emergency generators are normally without exception?
Permanent magnet alternators and do not require battery power to function.
What provides emergency hydraulic power for the flight control if hydraulic power is lost on both engines?
RAT, automatically deployed if both engine driven generators fail.
What is the RAT made up of?
- Hydraulic constant speed motor and AC generator (CSM/G)
- Generator Control Unit (CSM/G GCU)
Efficient operation of electrical equipment in an aircraft depends on?
Maintaining a fixed supply voltage under varying load requirements
L4 current widning consists of?
few turns of heavy wire.
L5 voltage winding consists of?
Many turns of fine wire.
What is this?
Grounded field type solid state voltage regulator
What is this?
Grounded regulator type solid stage voltage regulator
What is this?
Carbon pile voltage regulator
What is this?
Transistorized voltage regulator circuit.
What is the order of hierarchy for bus systems?
- Hot battery bus
- Essential DC Bus
- AC Bus
- AC Essential Bus
- AC Non-essential bus
Describe Essential DC Bus
referred to as Battery bus, connected to hot battery bus via a contactor.
Describe AC Bus
Fed from respective main generator
Describe Essential AC Busses
Essential lighting, flight control systems, comms, navs, required to ensure safe flight in emergency,
Describe Non essential bus
galley power, non essential lightingm low priority electrical,referred to as shed busses or isolation busses.
If one generator fails what is used to connect bus1 and bus 2 together?
But tie breakers (normally open)
If a tied AC bus system is tied it means the AC generators are connected or in parallel what conditions must be met?
AC Generators must be matched so their output waveforms are the same.
1.Voltages
2. Frequencies
3. voltages in phase
4. same phase rotation (3 phase)
The split system breaker will not close if.
if the buses properties are outside the limits of voltage, phase rotation or frequency.
Relays are used for?
Low-current switching applications
The part of the relay attracted by electromagnet to close the contact points is called the?
Armature
Breaker =?
High Current
Relays =
Low Current Switching
Bus tie breakers contain 3 heavy duty contacts which connect three phase power to?
generator bus bars where it is distributed to the aircraft loads.
What is the job of the Generator circuit breaker?
- Connect AC gen to bus if serviceable
- when gen connected to gen bus, bus tie breaker is tripped therefor ensuring ac loads receive power from only 1 power source.
- Isolate generator output from aircraft if fault occurs.
Inverts are used to?
Convert DC to AC at a frequency of 400hz
What is this?
Rotary AC inverter
What is this?
Static inverter
What are the advantages of a static inverter?
No moving parts, less maintenance, less problems.
Label these
- Filter Network (cleans)
- 400hz OSC (square)
- Pulse shaper (square)
- Power Driver (28-115)
- Harmonic filter (cleaner not 400hz)
- Output stage & final filter (sine wave)
- Voltage current/freq sense (ensures correct voltage and frequency)
Static inverters produce?
115V single phase alternating current 400 Hz from a 18-30 V DC input
Transformers allow the values of AC voltage and current to be changed using?
Mutual inductance.
Rectifiers typically use what to convert AC to DC?
Diodes allowing current flow in only 1 direction.
Transformer rectifier units are designed to operate on?
3 Phase AC inputs and provide continuous DC output. A star to deltas transformer input and output are 30 degree’s out of phase.
A fuse should only be replaced with one of?
The same voltage and current rating.
What are these?
Fuses
Describe current limiters
2 TIMES THEIR RATED CURRENT, 6 TIMES LONGER TO OPEN THAN A FAST BLOW. High current DC power systems, behaves more like a fusible link rather than fast blow, designed for HARD faults,
Advantages of circuit breakers?
Can be reset once the fault is found., visual indication.
What are the 2 types of circuit breakers?
Magnetic and thermal circuit breakers.
Thermal circuit breakers use what to trip?
bi-metallic strips, contact type switch, mechanical latching mechanism.
What is the primary reason why circuit breakers are so close to the bus bar?
Protect the wiring run from short circuits which would cause a overload and possible fire.
What is the secondary reason for circuit breakers?
Protect the component at the end of the wiring.
How do you tell a circuit breaker is tripped?
Small white band.
A non trip free circuit breaker can be? (magnetic-hold in)
Reset and/or held on even if an overload or excessive heat condition is present.
A trip free (thermal) circuit breaker is a?
CB that will trip open even if the operating mechanism is held in the ON position.
What must be done when a circuit breaker trips?
Isolate the faulty or component and repair it, then reset the circuit breaker.
Reverse current circuit breakers are designed to?
Remain in the “locked out” condition to ensure complete isolation of a circuit until the fault has been cleared.
Describe the Merz protection system.
When a fault occurs, an unbalanced condition occurs causing current to flow through the coils of the relays thereby energizing them so as to open the line at each end.
On a DC power receptacle what is the smaller pin used for?
Interlock sensing and polarity check, in event of plug being withdrawn, the external power relay will de-energize before the main pins are disengaged to prevent arcing.
How is an AC external power receptacle identified?
by its 6 pins
