Electrics Part 1

Question 1

An AC generator without a commutator produces?

Answer 1

AC current

Question 2

An AC generator with a commutator will result in a -

Answer 2

DC generator

Question 3

Control of the voltage output in a DC generator is usually accomplished by varying the strength of the magnet field using some of the generated current. Such generators are called -

A feature of this system, which is used in most aircraft DC generators, is that at a constant speed, the voltage output -

Answer 3

self-excited

Falls slightly as the load increases

Question 4

The brush alternator voltage is regulated by -

Answer 4

DC current fed from the aircraft battery

Question 5

The brush alternator is not -

Answer 5

self-excited

Question 6

For use in DC systems, the AC power output is fed to -

Which typically comprises -

Answer 6

a rectifier

6 diodes, 3 positive and 3 negative.

Question 7

Remember that in the alternator, the brush and slip ring arrangement is only required -

Answer 7

to provide DC current from the battery to the exciter field coil

Question 8

In a brushless alternator, the alternator is self-excited via DC current by the use of a -

Answer 8

rectifier

Question 9

If no CSD is used, the varying frequency( in an AC system only) caused by changes in the speed of rotation as a result of engine power changes would not allow several generators to -

Answer 9

operate in parallel

Question 10

To maintain the ________ frequency required for __ systems a method of ensuring that the ________ is driven at a _______ speed is required. The solution to this is the ___.

Answer 10

To maintain the constant frequency required for AC systems a method of ensuring that the generator is driven at a constant speed is required. The solution to this is the CSD.

Question 11

The CSD:

A governor acts through a piston to control the action of the hydraulic pump so that if the engine power is less than that required by the generator a greater pressure is applied to the hydraulic pump which in turn -

If the engine power is greater than that required by the generator the governor reduces the pressure to the hydraulic pump which in turn -

Answer 11

speeds up the generator drive motor.

Slows down the generator drive motor.

Question 12

The CSD:

Electronic sensors are fitted to detect excessive speed changes which may be caused by the failure of the CSD. Should this happen, the generator supply is -

Answer 12

automatically disconnected from the busbar

Question 13

The type of motor:

In this motor the field and armature windings are connected in series with each other and with the power supply. This means that both field and armature currents are the same. The resistance of the field and armature windings is low which allows the motor to draw a large current on starting, thus avoiding a rapid build up of field strength. The result is a high starting torque with good acceleration. The consequent rapid build up of back EMF in the armature limits the current flow through the motor. The heavier the load, the lower speed; in turn this reduces the back EMF and allows the motor to draw more current thus creating a rapid increase in torque. This type of motor is ideal for engine starting.

Answer 13

Series-wound motor

Question 14

The type of motor:

In this case the field winding is arranged in parallel with the armature and has a high resistance which, because it is connected directly across the power supply, ensures a constant current. Generally, the armature windings are of low resistance and to avoid damaging the motor a variable resistance is connected in series with the armature which provides full resistance on start up and gradually reduces as the speed, and thus the back EMF, increases. The low resistance armature ensures that the variation in motor speed from full load to light load is negligible, effectively making it a constant speed motor.

Answer 14

Shunt-wound motor

Question 15

The type of motor:

This motor basically combines the best of the series-wound motor with the best of the shunt-wound motor. This is achieved through two field windings, one of which is series connected and the other shunt connected with the armature. Generally, a motor is biased towards one or other of the forms. If the series field predominates, an increase in load is offset by the influence of the series field which also provides high torque on start-up. If the shunt field predominates, the variation in speed is stabilised as the load increases.

Answer 15

Compound-wound motor

Question 16

The type of AC motor required for work which requires more power, ie operating undercarriage and hydraulic systems.

Answer 16

The induction motor

Question 17

The type of AC motor commonly used in autopilot servomotors, propeller synchronisers and electric clocks.

Answer 17

The synchronous motor

Question 18

For a DC system, protection for reverse current is provided by?

Answer 18

reverse current cut-out relays or reverse current circuit breakers

Question 19

For a AC system, protection for reverse current is provided by?

Answer 19

diodes in the alternator

Question 20

The purpose of the cut-out relay/reverse current cutout:

This device __________ connects and disconnects the ______ and the ________. It connects the battery and generator when the ________ ______ is ___ enough to charge the battery and __________ them when the generator ____ down or ____. This prevents the battery from discharging through the generator.

Answer 20

This device automatically connects and disconnects the battery and the generator. It connects the battery and generator when the generator voltage is high enough to charge the battery and disconnects them when the generator slows down or stops. This prevents the battery from discharging through the generator.

Question 21

The cutout relay is a -

It has a ___ winding and a ____ winding

Answer 21

magnetically operated switch

Question 22

Resistors are used to?

Answer 22

Control the flow of current in an electrical circuit by varying the voltage

Question 23

The term hot “hot”, relevant to the hot battery bus, means?

Answer 23

Even if the battery switch is off certain items will still be powered

Question 24

Static is discharged from the airframe, through a device attached to the trailing edges of control surfaces. This device is?

Answer 24

A static wick