13.5 Electrical Power Extra Questions Flashcards
The battery charger has shutdown automatically. A possible fault could be:
a) the sensed battery voltage is measured at 22.5 volts
b) an over-temperature of 45°C is sensed
c) the input voltage is over 134 volts AC
The input voltage is over 134 volts AC
Initial output excitation in a starter/generator is normally provided by:
a) direct battery voltage through the generator field relay
b) residual magnetism released to the voltage regulator when the generator field relay is energised
c) a shaft mounted permanent magnet provided DC excitation through a rectifier unit
Residual magnetism released to the voltage regulator when the generator field relay is energised
A shunt wound DC generator ‘off load’ experiences output regulation failure. The resultant would:
a) reducing the field to zero losing all excitation
b) bring the generator to a constant voltage output regardless of load
c) lead to an increase in field strength until eventually the generator would ‘burn-out’
Lead to an increase in field strength until eventually the generator would ‘burn-out’
The use of interpoles is the most satisfactory way of maintaining a constant neutral plane. The windings of the interpoles are:
a) in series with the load, of an opposite polarity to that of the armature field and produce an effect in proportion to the load
b) in parallel with the load, of the same polarity to that of the armature field and produce an effect directly in proportion to the load
c) in series with the load, of the same polarity to that of the armature field production, in effect inversely proportional to the load
In series with the load, of an opposite polarity to that of the armature field and produce an effect in proportion to the load
A very low resistance develops between A and C phase of the exciter rotor in a 200 volts brushless AC generator. The resultant voltage and frequency output would initially show:
a) an increase in frequency but a drop in voltage
b) no change in frequency but with a marked reduction in voltage
c) a decrease in both frequency and voltage
No change in frequency but with a marked reduction in voltage
A three phase TRU often features a:
a) star-delta combination to give a sixty degrees phase shift
b) star-star combination to give a sixty degrees phase shift
c) star-delta combination to give a thirty degrees phase shift
Star-delta combination to give a sixty degrees phase shift
Typically, a GCU sensing protection condition will open both GCR (generator control relay) and GCB. The condition causing GCB only opening is:
a) pre-engine start load shedding
b) an Overvoltage condition
c) an IDG (integrated drive generator) underspeed condition
An IDG underspeed condition, as a logic system is installed to inhibit the tripping of the GFR on normal shutdown
What does the differential sensing coil sense?
a) current
b) volts
c) power
Current
Where does the GCU get its power under normal conditions?
a) PMG
b) battery
c) RAT
PMG
When a load is shed from a busbar, the:
a) busbar voltage increases
b) current consumption from the bar decreases
c) busbar voltage decreases
Current consumption from the bar decreases
Sharing of electrical loads by paralleled DC generators is controlled by:
a) equalising circuits which control the speed of the generators
b) equalising circuits which control the field excitation of the generators
c) automatic load shedding
Equalising circuits which control the field excitation of the generators
Over voltage protection circuits are activated:
a) before the over voltage limit is exceeded
b) dependent on the magnitude of the over voltage
c) after a fixed time delay
Dependent on the magnitude of the overvoltage
Whilst operating paralleled AC constant frequency generators, it is important to maintain generator outputs at the same voltage:
a) to prevent a circulating current developing between two or more TRUs
b) to prevent a circulating current of considerable magnitude developing between two or more generators
c) to prevent CSD shock loading
To prevent a circulating current of considerable magnitude developing between two or more generators
CSD warning lights on the flight deck normally indicate:
a) high oil pressure, low oil temp
b) low oil pressure, high oil temp
c) low oil pressure, under frequency
Low oil pressure and high oil temperature
An overvoltage condition trips the AC generator. The time taken to trip the GCU depends on:
a) closing of fuel and hydraulic valves
b) amplitude of voltage
c) flash delay response
Amplitude of voltage
Speed of hydraulic motor within the CSDU is controlled by a:
a) swash plate
b) GCR unit
c) differential unit
Swash plate
An external power plug has two short pins, these are used for:
a) the interlock circuit
b) ground handling bus
c) charging the aircraft batteries
The interlock circuit
In a carbon pile regulator, the resistive element is:
a) in series with the field and changes resistance with changing length
b) in series with the field and changes resistance with surface area contact
c) in parallel with the field and changes resistance with changing length
In series with the field and changes resistance with surface area contact
In a transistor voltage regulator, the voltage output is controlled by:
a) transformers and transistors
b) diodes and transformers
c) zener and transistors
Zener and transistors
When resetting the CSD on the ground, the engine should be:
a) stationary
b) rotating at idle
c) rotating at Nsync
Stationary
If voltage and frequency of the generator drop to zero in flight, it would be an indication that the:
a) CSD drive shaft shear point has sheared
b) phase sequence detection circuit has operated
c) bus tie interlock is inoperative
CSD drive shafe shear point has sheared
Generator output indications are:
a) KW
b) KW & KVAR
c) KVA & KW
KW & KVAR
A metal tray to hold a battery would hold what type of battery?
a) dry cell battery
b) alkaline battery
c) lead acid battery
Alkaline battery
A flight crew member has reported an acrid, acidic smell in the cockpit, what could be wrong?
a) the non-return valve is stuck open
b) the aircrew had a curry last night
c) the non-return valve has stuck closed
The non-return valve is stuck open
When does a RAT become insufficient, and what happens to the system?
a) when the RAT has eaten too much cheese and the system becomes flatulent
b) when the slipstream is too slow and the system reverts to batteries
c) when the slipstream is too slow and the system reverts to APU
When the slipstream is too slow and the system reverts to batteries
What piece of equipment operates at very high speeds on reverse currents of approximately 500 amps?
a) voltage regulator
b) reverse current circuit breaker
c) differential cut-out
Reverse current circuit breaker
The trimmer resistor in a carbon pile regulator is adjusted by:
a) the pilot, during an air test
b) the engineer, during a ground run
c) the engineer, before battery replacement
The engineer, during a ground run
In some twin turboprop powered aircraft, when the battery switching relay is operated, the batteries are:
a) switched from a parallel configuration to a series configuration for initial engine starting
b) connected in parallel if one engine has failed in order to increase the overall capacity and available power time
c) switched to supply direct power for static inverter operation when a double generator failure occurs
Switched from a parallel configuration to a series configuration for initial engine starting
Differential protection in a generating system:
a) detects voltage difference between source and load
b) detects current difference between source and load
c) uses the volts coil to trip the GCR
Detects current difference between source and load
In an AC paralleling system, reactive load sharing is achieved by using a load sharing loop:
a) with mutual reactors which affect the speed of the generators
b) error sensors which affect the speed of the generators
c) with mutual reactors which affect the excitation of the generators
With mutual reactors which affect the excitation of the generators
What pins are used as interlock pins on an AC plug or socket?
a) A and B
b) A and E
c) E and F
E and F
A trip free circuit breaker:
a) will not operate even if there is a fault
b) cannot be manually overridden
c) can be held closed against a fault
Cannot be manually overridden
Alkaline batteries fitted in an aircraft are normally charged by:
a) a higher initial charging current and then pulse charged
b) the constant current method
c) AC from the main output winding of the generator
A higher initial charging current and then pulse charged
Voltage regulation of a DC generator is achieved by:
a) controlling the amount of current through the armature
b) moving the brushes either backwards or forwards
c) controlling the amount of current in the field winding
Controlling the amount of current in the field winding
The purpose of the Hold Off relay in a DC powered aircraft:
a) disconnect the battery charger in the event of a battery overheat
b) prevent the battery or generator from being connected to the busbar if ground power is on
c) prevent the generator from being connected to the busbar until it has reached its full voltage
Prevent the battery or generator from being connected to the busbar if ground power is on
A frequency wild AC generator:
a) gives an output of 115V single phase, can only be paralleled with generators of the same voltage output
b) gives an output of 200V three phase, and can only supply resistive loads
c) cannot be used to supply transformer rectifier units to obtain DC supplies
Gives an output of 200V three phase, and can only supply resistive loads
In a frequency wild AC generator system, if an overvoltage occurs:
a) the Constant Speed Drive Unit (CSDU) will slow down the generator to reduce the voltage
b) the voltage regulator will increase the excitation of the generator
c) the generator will be de-excited and removed from the busbar
The generator will be de-excited and removed from the busbar
The Constant Speed Drive Unit (CSDU) will be automatically disconnected:
a) if an overvoltage above 220V is detected
b) if an internal oil temperature above 168°C is detected
c) if a frequency above 440 Hz is detected
If an internal oil temperature above 168°C is detected
Initial excitation of a brushless AC generator comes from:
a) permanent magnets on the rotor
b) permanent magnets on the stator
c) the aircraft batteries
Permanent magnets on the rotor
A Variable Speed Constant Frequency (VSCF) Generator produces:
a) 200V single phase 400 Hz directly from the generator using a constant speed drive unit
b) 115V three phase 400 Hz by rectifying the generator output, changing it to a pulsed AC with an inverter and then filtering it to produce constant frequency AC
c) 200V three phase from a transformer rectifier unit
115V three phase 400 Hz by rectifying the generator output, changing it to a pulsed AC with an inverter and then filtering it to produce constant frequency AC
The point of regulation in an AC power generation system:
a) describes the voltage at which the cut will close
b) should be as close to the generator as possible
c) should be as close to the busbar as possible, but before the generator breaker
Should be as close to the busbar as possible, but before the generator breaker
In a split busbar AC power generation system, if one generator fails:
a) its line contactor will open, bus tie breakers will close and the other generator will take over its load
b) its line contactor will remain closed and its bus tie breaker will close, connecting both generators together
c) the loads on the failed generator’s busbars cannot be supplied
Its line contactor will open, bus tie breakers will close and the other generator will take over its load
In a parallel AC generator system, reactive load sharing is achieved by;
a) modifying the generator drive torque
b) switching off reactive loads and connecting real loads
c) modifying the generator excitation
Modifying the generator excitation
If a differential fault is detected in one generator in a parallel AC system:
a) all BTBs will trip
b) the faulty Generator Field Relay (GFR) will trip but not the Generator Relay (GR)
c) the faulty Generator Field Relay (GFR) will trip
The faulty Generator Field Relay (GFR) will trip
On constant speed generators, operation of the disconnect solenoid will disconnect the generator drive. This can be reset:
a) when all loads are switched off
b) only when the engines are shut down and the aircraft is on the ground
c) automatically when the fault clears
Only when the engines are shut down and the aircraft is on the ground
In a brushless generator, the purpose of the PMG is to:
a) provide initial excitation only
b) supply the generator protection circuits only
c) provide initial excitation and supply the protection circuits
Provide initial excitation and supply the protection circuits
Over excitation is a protection circuit which is used in:
a) DC generating system
b) AC split busbar system
c) AC paralleling busbar system
AC paralleling busbar system
The purpose of BTB and GCB auxiliary contacts in a load sharing loop is to:
a) prevent damage to the current transformer when the generator is offline
b) short out the load sharing circuit of a generator not paralleled
c) prevent excessive current to the field of a faulty generator
Short out the load sharing circuit of a generator not paralleled
In a frequency wild generating system:
a) frequency varies with the engine/generator speed
b) voltage varies with the engine/generator speed
c) frequency and voltage varies with engine/generator speed
Frequency varies with the engine/generator speed
In a frequency wild system, the AC supply is used for:
a) anti-icing systems
b) navigation instruments
c) general aircraft instruments
Anti-icing systems
An inverter supplies:
a) AC from a DC input
b) DC from an AC input
c) AC from lower DC input
AC from a lower DC input
Using a pulsed width voltage regulation system, with an increase in generator voltage output, the pulse:
a) width increases
b) width decreases
c) frequency increases
Width decreases
In a constant frequency system, the reactive load sharing is achieved by regulating the generator:
a) excitation
b) drive torque
c) speed
Excitation
Flight deck indications for a Constant Speed Drive Unit (CSDU) are:
a) over temperature
b) temperature and low oil pressure
c) speed
Temperature and low oil pressure
In an AC parallel power system, the normal flight state of the bus tie breakers is:
a) open
b) closed
c) closed only if there is a fault
Closed
The GCR directly controls the:
a) exciter field
b) GCB
c) BTB
Exciter field
The Reverse Current Circuit Breaker (RCCB) in a generator system trips the generator offline:
a) during normal engine shutdown to prevent the battery motoring the generator
b) if the generator output current rises above 450 to 500 amps
c) when a large current flows from the busbar to the generator
When a large current flows from the busbar to the generator
When a serious over excitation fault develops in a twin DC generator system:
a) the overexcited generator is de-excited by the overvoltage relay tripping
b) the differential cutout de-excites the field
c) the voltage regulator senses the fault and de-excites the field
The overexcited generator is de-excited by the overvoltage relay tripping
Differential protection monitors for:
a) difference between the generator line voltages
b) difference between generator line currents
c) feeder cable faults
Difference between generator line currents
A mutual reactor’s output is mainly dependent on the generator’s:
a) active load current
b) excitor field current
c) reactive load current
Reactive load current
The unit that houses both AC generators and constant speed drive units is called the:
a) integrated drive generator
b) generator control unit
c) auxiliary power unit
Integrated drive generator
Over excitation protection applies to:
a) non parallel AC generation systems only
b) parallel AC generation systems only
c) either non parallel or a parallel AC generation system
Either non parallel or a parallel AC generation system
In a parallel busbar aircraft, the normal contactor positions in flight are:
a) bus tie breakers (BTB) open, generator control breakers (GCB) closed, generator field relay (GFR) closed
b) BTBs closed, GCBs open, GFRs closed
c) BTBs closed, GCBs closed, GFRs closed
BTBs closed, GCBs closed, GFRs closed
Which of the following is inhibited on engine shutdown?
a) under voltage
b) over voltage and over frequency
c) under voltage and under frequency
Under voltage and under frequency
Compounding transformers are used in … generators to … ?
a) integrated drive , provide negative feedback
b) frequency wild , assist the voltage regulator
c) variable speed constant frequency , convert the frequency wild AC output into 270V DC
Frequency wild , assist the voltage regulator
A main power breaker or latching relay:
a) has a non-polarised armature, with a single input supply, power is applied constantly to the selected coil
b) has a polarised armature, with a two input supply, power is removed from the coil once the armature has moved to the desired position
c) has a polarised armature, with a two input supply, power remains on the coil to keep the relay energised to protect against ‘g’ forces
Has a polarised armature, with a two input supply, power is removed from the coil once the armature has moved to the desired position
A fault which would cause all the bus tie breakers (BTBs) to trip in a parallel AC system:
a) over excitation
b) differential protection
c) negative sequence voltage
Negative sequence voltage
Emergency power is provided from a ram air turbine (RAT) when:
a) all generators fail
b) the static inverter fail
c) the battery busbar fails
All generators fail
Electrical load on aircraft is controlled by:
a) IPS
b) BPCU
c) GCU
BPCU
Excessive commutator sparking can be caused by:
a) brushes positioned on MNA
b) weak spring tension
c) rotating field diode failure
Brushes positioned on MNA
An AC generator used with a CSD:
a) needs a voltage controller to maintain voltage with increasing load
b) does not need a voltage controller because voltage is kept constant
c) does not need a voltage controller because current is kept constant
Needs a voltage controller to maintain voltage with increasing load
A DC generator fails to excite, a possible cause is:
a) incorrect brush position needing correction
b) excessive load which must be reduced
c) loss of residual magnetism which needs restoring
Loss of residual magnetism which needs restoring
Two methods of bringing the second generator on-line in a DC parallel system are:
a) boost resistor or equalising circuit
b) boost resistor or pick up relay
c) pick up relay or equalising circuit
Boost resistor or equalising circuit
In some aircraft onboard battery charging systems, SCRs when operated ensure:
a) full and functional control monitoring and switching via temperature and reference voltage control circuits
b) a maximum pre-set charging current cannot be exceeded
c) de-energising of the AC and DC charger relays on main power failure
Full and functional control monitoring and switching via temperature and reference voltage control circuits
The formation of white crystals on a properly serviced nickel-cadmium battery, installed in aircraft are:
a) potassium hydroxide, harmless, but indicate the presence of high humidity
b) potassium carbonate, the result of a reaction of expelled electrolyte vapour with carbon dioxide and may indicate overcharging
c) sodium carbonate, caused by high carbon dioxide concentration reacting with potassium hydroxide
Potassium carbonate, the result of a reaction of expelled electrolyte vapour with carbon dioxide and may indicate overcharging
The neutral forming transformer inside the inverter module of a Variable Speed Constant Frequency converter (VSCF):
a) adds a neutral lead to the three-wire output of the control transistors allowing sharing of an unbalanced load
b) changes the pulse-width modulated waveform to three phase sinusoidal
c) monitors the output current of the VSCF converter
Adds a neutral lead to the three-wire output of the control transistors allowing sharing of an unbalanced load
A thermistor, mounted on the exciter frame of a constant speed drive generator:
a) blocks current flow in one of the parallel field lines at high operating temperatures allowing better output control
b) allows current flow to increase with temperature rise compensating for heat losses
c) drops to a negligible value at increased temperature providing temperature compensation and allowing balanced current flow in the parallel field lines
Drops to a negligible value at increased temperature providing temperature compensation and allowing balanced current flow in the parallel field lines
The GCU provides a BTB lockout protection junction, which prevents BTB closure if:
a) an undervoltage and underfrequency condition exists at the same time on the associated generator
b) an undervoltage and overload condition exists on the associated generator
c) an underspeed condition exists on the associated generator
An undervoltage and overload condition exists on the associated generator
In an over frequency fault condition the generator field relay (GFR) and the Generator Breaker (GB) … , and the Constant Speed Drive Unit (CSDU) is put into … ?
a) are tripped , overdrive
b) are tripped , underdrive
c) remain energised , the mechanical governed condition
Are tripped , underdrive
Under normal operating conditions in a constant frequency AC system, the inverter is:
a) switched off, and will not come online until all AC power fails
b) switched off, and will not come online until the load shedding circuits are operated during an inflight generator failure
c) switched on constantly and supplies its own emergency busbar at all times
Switched off, and will not come online until the load shedding circuits are operated during an inflight generator failure
The output from a three-phase transformer rectifier unit featuring a star and delta secondary winding arrangement fluctuates with DC load changes. A possible fault would be:
a) overheating and breakdown of the bridge diodes
b) an open phase in the delta connection
c) excessive applied DC loads
An open phase in the delta connection
Reactive power (kVAR) of an AC generator can be measured by supplying:
a) the current signal of one phase to one coil of a wattmeter and the same phase voltage to the other coil
b) the current signal of one phase to one coil of a wattmeter and the line voltage of the other two phases to the other coil
c) the line current to one coil of a wattmeter and the phase voltage to the other
The current signal of one phase to one coil of a wattmeter and the line voltage of the other two phases to the other coil
Over frequency in an AC generator system:
a) is normally caused by incorrect oil level in the IDG and would damage capacitive loads
b) is normally caused by a voltage regulator fault and would damage resistive loads
c) is normally caused by any underdrive situation in the IDG and would damage inductive loads
Is normally caused by incorrect oil level in the IDG and would damage capacitive loads
Emergency exit lights power supplies come from:
a) individual nickel cadmium batteries fitted at each exit
b) the aircraft battery
c) the ‘emergency services’ battery which also supplies power for the emergency pathway lights
Individual nickel cadmium batteries fitted at each exit
