11.6 - Electrical Power

Question 1

What happens when the disconnect solenoid is energised while the engine is stopped

Answer 1

The disconnect device is triggered and the clutch is damaged when the engine is started

Question 2

How is a CSD disconnect reset performed

Answer 2

The reset ring is pulled when the engine is completely stopped

Question 3

What is the function of the voltage regulator in the GCU

Answer 3

To control the voltage at the point of regulation 115V by influencing the ecciter current

Question 4

Which is the voltage for an under voltage condition

Answer 4

100 volts

Question 5

What happens with a generator working in isolated condition when it receives more exciter current than necessary

Answer 5

Voltage will increase

Question 6

When does the differential protection circuit trip the generator

Answer 6

When the current in 1 phase differs

Question 7

What happens when you exchange 2 phase connections at the generators terminals

Answer 7

The generator runs in reverse

Question 8

How can you check the charge level of a ni-cad battery

Answer 8

You must measure the charge current, if it is nearly zero the battery is fully charged

Question 9

What happens when a ni-cad battery overheats during charging

Answer 9

The charging current increases and could/would start a thermal runaway

Question 10

Which of the following methods is used to charge a battery in an electrical power system

Answer 10

The batteries can be charged by a Transformer Rectifier Unit (TRU) using the constant voltage charging method

Question 11

Consider a 2 engine aircraft with a isolated orientation of the main bus bar, what happens in the event of a failure of one of the main engine generators in flight

Answer 11

The remaining engine generator supplies the main AC bus bar on the failed side via the bus-tie breakers and the galley loads are shed

Question 12

Consider a multi-engined aircraft (x4) with parallel generators. What happens if the number 2 bus-tie contactor is opened

Answer 12

Generator 1, 3 and 4 supply main bus bar 1, 3 and 4 in parallel and generator 2 powers main bus 2 seperatly

Question 13

How is an open phase in a generator detected

Answer 13

By comparing the generator load in each phase

Question 14

What does it mean when a Avail light in the external power push button illuminates

Answer 14

The external power source is activated to supply the network and the GND service must be switched to

Question 15

How are the engine driven generators of multi engined aircraft (3 or 4 engines) usually operated

Answer 15

In parallel operation

Question 16

How many resets are permitted after a circuit breaker has tripped

Answer 16

1, to prevent contacts from welding if a short has occurred

Question 17

What does the abbreviation RCCB mean

Answer 17

Remote Control Circuit Breaker

Question 18

Which is the principle of operation of the CSD disconnect

Answer 18

Electronically disconnected and mechanically reconnected

Question 19

Which is the maximum permitted time for operating a CSD disconnect button

Answer 19

3 seconds

Question 20

Which protective functions are built into the aircraft’s transformer rectifier (TR) units

Answer 20

Low current and high temperature protection

Question 21

Why are there 2 short pins in there external power receptacle

Answer 21

They ensure that the external power can only be applied if the plug is located correctly in the power receptacle

Question 22

How can the CSD disconnect be reliably confirmed

Answer 22

Zero volts and zero frequency is indicated

Question 23

Which are the main components of a static inverter

Answer 23

Solid state switches and a transformer

Question 24

What happens if the bus tie switching is set to off during operation with only ground power available

Answer 24

Te power to the main bus bar is lost

Question 25

What is the main advantage of parallel operation of the main AC busses over isolated operation

Answer 25

All engine driven generators are loaded equally and there is no power loss when one generator fails

Question 26

Why are trip free circuit breakers used on aircraft

Answer 26

Because they can open an overloaded circuit even with the control knob jammed in

Question 27

Which statement accurately describes the bus-tie switching operation in a Boeing multi engined aircraft

Answer 27

The bus-tie switching is normally closed. This is known as parallel operation

Question 28

Consider the function of a GCU. Which of the following statements are true

Answer 28

The GCU’sof the engine driven generators are identical and interchangeable

Question 29

How are the engine driven generators of a twin engine aircraft usually operated

Answer 29

In isolated operation

Question 30

What is the purpose of the 2 min delay before resetting a circuit breaker

Answer 30

To allow the bi-metallic strip in the circuit breaker to cool down

Question 31

Which statement is correct concerning the input speed of the generators producing a voltage with a frequency of 400Hz

Answer 31

The speed depends on the amount of pole pairs, 24000 RPM with one pole pair and 8000 RPM with three pole pairs

Question 32

How does the static inverter generate the correct output frequency

Answer 32

With a beat generator

Question 33

Which statement is correct concerning the functions of a circuit breaker

Answer 33

The CB trips when the normal current is exceeded for a certain time even if the control knob is pressed

Question 34

What is the Transformer Rectifier Unit (TRU) used to convert

Answer 34

3 phase 115V AC from the AC power distribution into 28V DC for the DC power distribution

Question 35

On a 3 phase generator what is the angle between phases

Answer 35

120deg

Question 36

What electrolyte solution is used in a Ni-Cd battery

Answer 36

A strong alkaline

Question 37

What is the voltage and frequency required to energise the aircraft electrical system

Answer 37

115V AC and 400Hz

Question 38

How is the aircraft normally electrically powered in flight

Answer 38

Engine driven generators

Question 39

What is the main source of power when the Aircraft is on the ground

Answer 39

External power

Question 40

How is the speed of the motor controlled in the CSD

Answer 40

Hydraulically

Question 41

Which are the main components of a static inverter

Answer 41

Solid state switches and a transformer

Question 42

What is the function of the GCU regulation circuits in generators that can work in parallel

Answer 42

To make sure that all generators share the same load when they are switched into parallel operation

Question 43

What is the function of the voltage regulator in the GCU

Answer 43

To control the voltage at the point of regulation to 115V by influencing the exciter current

Question 44

What is the main advantage of parallel operation of main AC buses over isolated operation

Answer 44

All engine driven generators are loaded equally and there is no power loss when one generator fails

Question 45

Which of the following power source can work in parallel operation

Answer 45

APU and external power

Question 46

Which statement accurately describes the bus tie switching operation in a Multi engine aircraft

Answer 46

The bus tie switching is normally closed. This is known as an isolated operation

Question 47

Which is the maximum current value that can be used in aircraft circuit breakers

Answer 47

125 amperes

Question 48

Which of these protection functions is used in TR units

Answer 48

Over temperature protection

Question 49

Which statement is correct concerning the function of a circuit breaker (CB)

Answer 49

A CB trips when the nominal current is exceeded for a certain time, even if the knob is pressed