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Aptitude > Licence : A thermal circuit breaker ?

Question 25-1 : Protects the system in the event of overload/overheating uses electromagnetic trip system to prevent over heating limits any overcurrent can be re engaged without any danger even if the fault remains

exemple 125 protects the system in the event of overload/overheating.protects the system in the event of overload/overheating.

The auxiliary power unit apu has its own ac generator that ?

Question 25-2 : Supplies the aircraft with three phase 115 200 v 400 hz ac is driven at constant speed through a constant speed drive csd in the same way as the main ac generator is excited by its generator control unit gcu as soon as the apu starts up must have the same characteristics as the main ac generator so that it can be easily coupled with the latter

exemple 129 supplies the aircraft with three-phase 115-200 v, 400 hz ac.supplies the aircraft with three-phase 115-200 v, 400 hz ac.

A magnetic circuit breaker is ?

Question 25-3 : A protection system that has a quick tripping response permits an overcurrent limited in time can be reset without any danger even when fault remains is a system with a slow response time

exemple 133 a protection system that has a quick tripping response.a protection system that has a quick tripping response.

The advantages of alternating current on board an aircraft are.1 simple ?

Question 25-4 : 3 4 5 6 1 2 3 4 5 6 1 2 3 5 6 1 4 6

Alternating current ac is extremely versatile and has the following advantages over direct current ac can be simply and efficiently changed from one voltage to another using a transformer ac generators are simpler in construction and lighter for the equivalent power output of a dc machine ac can be easily and efficiently changed into dc using a rectifier exemple 137 3, 4, 5, 6.3, 4, 5, 6.

On board present aircraft the batteries used are mainly cadmium nickel their ?

Question 25-5 : 3 4 5 6 3 4 6 7 2 3 4 5 6 1 2 5 6 7

The terminal voltage remains substantially constant at about 1 2 volts throughout most of the discharge due to its low internal resistance it is also capable of supply high current during its discharge cycle and low current during recharging without violent fluctuations of terminal voltage.nicad batteries have a low thermal capacity the heat generated in certain conditions is faster than it can dissipate so causing rapid increase in temperature.this has the effect of lowering the effective internal resistance thus allowing an ever increasing charging current which unless checked leads to the total destruction of the battery exemple 141 3, 4, 5, 6.3, 4, 5, 6.

A static inverter is powered by ?

Question 25-6 : Direct current on input alternating current output alternating current on input direct current on output alternating current on input alternating current on output direct current on input direct current on output

.an inverter is a unit used to convert dc into ac.dc to ac inverter .ac to dc rectifier exemple 145 direct current on input, alternating current output.direct current on input, alternating current output.

The voltage regulator of a dc generator is connected in ?

Question 25-7 : Series with the shunt field coil series with the armature parallel with the shunt field coil parallel with the armature

On a dc generator voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field the voltage regulator is connected in series with the shunt field coil exemple 149 series with the shunt field coil.series with the shunt field coil.

During start of an engine fitted with a brushless ac generator with no ?

Question 25-8 : A set of permanent magnets the main field winding the stabiliser winding jointly with the voltage regulator the auxiliary winding

exemple 153 a set of permanent magnets.a set of permanent magnets.

The type of windings commonly used in dc starter motors are ?

Question 25-9 : Series wound shunt wound series shunt wound compound wound

Dc motors are classified as to the ways in wich their field excitation circuits are arranged series wound shunt wound compound wound the series wound motors have their field and armature windings in series with each other so the same current flows through both adding them together. these motors have a high starting torque especially as in the initial stages there is little back emf so all the current is used in them they are commonly used as starter motors exemple 157 series wound.series wound.

The power output of a generator is controlled by ?

Question 25-10 : Varying the field strength varying the speed of the engine the reverse current relay circuit breaker varying the length of wire in the armature windings

The only practical method of controlling the output voltage of a generator is to control the strength of the magnetic field by controlling the current flow in a coil wound around the magnetic pole pieces field coil or field winding control of the current flow is achieved by a voltage regulator .the voltage regulator senses the output voltage of the generator or alternator and adjusts the field current to maintain the correct output voltage irrespective of generator speed or electrical load exemple 161 varying the field strength.varying the field strength.

A relay is ?

Question 25-11 : A magnetically operated switch another name for a solenoid valve a unit that is used to convert electrical energy to heat energy a device that is used to increase electrical power

exemple 165 a magnetically operated switch.a magnetically operated switch.

The voltage of a fully charged lead acid battery cell is ?

Question 25-12 : 2 2 volts 1 4 volts 1 8 volts 1 2 volts

exemple 169 2.2 volts.2.2 volts.

The capacity of a battery is given in ?

Question 25-13 : Ampere hours amperes/volts watts ohms

exemple 173 ampere hours.ampere hours.

A relay is ?

Question 25-14 : An electromagnetically operated switch an electrical security switch a switch specially designed for ac circuits an electrical energy conversion unit

exemple 177 an electromagnetically operated switch.an electromagnetically operated switch.

The most widely used electrical frequency in aircraft is ?

Question 25-15 : 400 hz 200 hz 50 hz 60 hz

If the electrical load of an ac generator providing a constant output voltage ?

Question 25-16 : Increase the intensity of the excitation current change the direction of the excitation current maintain the intensity of the excitation current constant decrease the intensity of the excitation current

The output is regulated by varying the current to the field windings the voltage regulator senses the alternator output and adjusts the field current when a voltage rises above a set value typically 115 5 v the current is cut off around 2000 times a second the voltage regulator is there to stop the battery being overcharged or the system being overloaded exemple 185 increase the intensity of the excitation current.increase the intensity of the excitation current.

The so called 'hot buses' or 'direct buses' are ?

Question 25-17 : Directly connected to the battery kept in operating conditions by an electrical resistance in the case of energy failure automatically connected to the battery if generators have failed providing an alternative current

The reason for using inverters in an electrical system is ?

Question 25-18 : To change dc into ac to change the dc voltage to change ac into dc to avoid a short circuit

exemple 193 to change dc into ac.to change dc into ac.

The function of a constant speed drive csd is to ensure ?

Question 25-19 : That the generator produces a constant frequency that the starter motor maintains a constant rpm irrespective of engine acceleration/deceleration that the csd output remains at a constant rpm irrespective of generator rpm an equal ac voltage output from all generators

exemple 197 that the generator produces a constant frequency.that the generator produces a constant frequency.

A bus bar is ?

Question 25-20 : A distribution point for electrical power a device which may only be used in dc circuits the stator of a moving coil instrument a device permitting operation of two or more switches together

exemple 201 a distribution point for electrical power.a distribution point for electrical power.

A csd of an ac generator may be disconnected in flight the primary reason s for ?

Question 25-21 : Low oil pressure and/or high oil temperature of the generator drive slight variation about the normal operating frequency excessive variation of voltage and kvar illumination of the csd disconnect warning light

exemple 205 low oil pressure and/or high oil temperature of the generator drive.low oil pressure and/or high oil temperature of the generator drive.

A csd unit which has been disconnected in flight ?

Question 25-22 : May be reset on the ground only after engine shut down automatically resets at engine shut down automatically resets in flight providing engine rpm is below a given value may be reset in flight using the reset mechanism

exemple 209 may be reset on the ground only, after engine shut-down.may be reset on the ground only, after engine shut-down.

Because of the input/output relationship of an or gate it is often referred to ?

Question 25-23 : 'any' or 'all' gate 'all or nothing' gate 'state indicator' gate 'inhibited' or 'negated' gate

exemple 213 'any' or 'all' gate.'any' or 'all' gate.

Connecting two 12 volt 40 ampere hour capacity batteries in series will result ?

Question 25-24 : 24 volts 40 ampere hours 12 volts 80 ampere hours 12 volts 40 ampere hours 24 volts 80 ampere hours

exemple 217 24 volts, 40 ampere-hours.24 volts, 40 ampere-hours.

When a conductor cuts the flux of a magnetic field ?

Question 25-25 : An electromotive force emf is induced in the conductor there will be no effect on the conductor current will flow in accordance with flemings left hand rule the field will collapse

exemple 221 an electromotive force (emf) is induced in the conductor.an electromotive force (emf) is induced in the conductor.

In order that dc generators will achieve equal load sharing when operating in ?

Question 25-26 : Their voltages are almost equal equal loads are connected to each generator busbar before paralleling adequate voltage differences exist the synchronising bus bar is disconnected from the busbar system

When two dc generators are operating in parallel control of load sharing is achieved by an equalising circuit which in conjunction with the voltage regulators varies the field excitation current of the generators exemple 225 their voltages are almost equal.their voltages are almost equal.

The purpose of a voltage regulator is to control the output voltage of the ?

Question 25-27 : Generator at varying loads and speeds batteries at varying loads generators at varying speeds and the batteries at varying loads tru

For dc generators the voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field this then is the reactive load wasted power that adjusts the energising current the same principle applies in ac generators alternators but they use solid state circuitry exemple 229 generator at varying loads and speeds.generator at varying loads and speeds.

A current limiter fuse in a dc generation system is used to ?

Question 25-28 : Allow a short term overload before rupturing limit the current in the field circuit allow no overload before rupturing limit the current in the armature

A fuse is a deliberately weak part of a circuit that is designed to fail if a problems occurs current limiters are like fuses but with a much higher melting point so that a higher overload current can be carried they allow a short term overload they will limit the current to a predetermined value and are used for heavy duty circuits exemple 233 allow a short term overload before rupturing.allow a short term overload before rupturing.

A 3 phase ac generator has 3 separate stator windings spaced at ?

Question 25-29 : 120° 60° 45° 90°

exemple 237 120°.120°.

A csd unit is normally provided with means of monitoring during flight the ?

Question 25-30 : Oil temperature and pressure oil temperature and synchronous speed output voltage and oil pressure oil temperature and quantity only

The phase relationship between two unparalleled ac generators ?

Question 25-31 : Is unimportant must be synchronous must be in opposition must be 90° out of synchronisation

exemple 245 is unimportant.is unimportant.

Assuming a csd fault is indicated the csd should be disconnected ?

Question 25-32 : Provided the engine is running at flight idle engine rpm on the ground only when the ac generator voltage is outside limits

The function of a constant speed drive csd is to ensure that the ac generator produces a constant frequency in case of csd fault you must disconnect it if the engine is running if not since the ac generator is not rotating you don't need to disconnect it .a csd unit which has been disconnected may be reset on the ground only after engine shut down

Ac generators operated in parallel must have the same ?

Question 25-33 : Voltage and phase voltage and amperage amperage and kvar frequency and amperage

Two ac generators operated in parallel must be not only at the same speed voltage but also the same phase to be paralleled exemple 253 voltage and phase.voltage and phase.

The measured output power components of a constant frequency ac system are ?

Question 25-34 : Kva and kvar volts and amperes volts and kilowatts amperes and kilowatts

exemple 257 kva and kvar.kva and kvar.

'frequency wild' in relation to a ac generation system means the generator ?

Question 25-35 : Output frequency varies with engine speed output frequency is too high output frequency is too low voltage regulator is out of adjustment

exemple 261 output frequency varies with engine speed.output frequency varies with engine speed.

When the ac voltage across a capacitor is kept constant and the frequency is ?

Question 25-36 : Increase remain the same be zero decrease

Capacitive reactance .when frequency tends to zero current magnitude is almost equal to zero .at contrary when fequency is high this is the magnitude of the voltage which tends to zero . 876.we are talking about capacitive reactance xc expresses in ohm exemple 265 increase.increase.

In an aeroplane fitted with a constant frequency ac power supply dc power is ?

Question 25-37 : Transformer rectifier unit tru static inverter 3 phase current transformer unit rotary converter

exemple 269 transformer rectifier unit (tru).transformer rectifier unit (tru).

On an aeroplane using ac as primary power supply the batteries are charged in ?

Question 25-38 : A transformer rectifier unit a static inverter a dc transformer and rectifier the ac bus via current limiters

exemple 273 a transformer rectifier unit.a transformer rectifier unit.

Immediately after starting engine s with no other electrical services switched ?

Question 25-39 : Would be normal and is only cause for concern if the high charge rate persists indicates a generator failure thus requiring the engine to be shut down immediately indicates a faulty reverse current relay indicates a battery failure since there should be no immediate charge

If the engine was started electrically using the battery there would have been a significant drain on the battery .the ammeter shows a charge after start up to replenish the energy just drained from the battery exemple 277 would be normal and is only cause for concern if the high charge rate persists.would be normal and is only cause for concern if the high charge rate persists.

Circuit breakers protecting circuits may be ?

Question 25-40 : Used in ac and dc circuits used only in ac circuits used only in dc circuits reset at any time

exemple 281 used in ac and dc circuits.used in ac and dc circuits.

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