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

What 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 openedb

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, will be in GREEN.

When switched on the ON light will illuminate in BLUE

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

Isolates the battery from the main DC busbar under emergency conditions such as failure of the generator supply or main busbar.

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

In DC power, there are 3 pins overall, and one is shorter and thinner then the other 2.

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

What 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, whats important about the engine driven generators?

Answer 28

The GCU’s of 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

What occurs in a CB when normal current is exceeded?

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

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

Answer 41

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

Question 42

What is the function of the voltage regulator in the GCU?

Answer 42

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

Question 43

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

Answer 43

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

Question 44

Which of the following power source can work in parallel operation?

Answer 44

APU and external power

Question 45

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

Answer 45

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

Question 46

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

Answer 46

125 amperes

Question 47

How long should a battery be able to supply power for in the event of an emergency?

Answer 47

30 mins

Question 48

What connector is used to connect the battery to the aircraft?

Answer 48

Elcon connector - quick release ##Footnote Remove negative lead first Install negative lead last

Question 49

What are the three types of batteries used on aircraft?

Answer 49

Lead acid Nickel - cadmium Lithium - ion

Question 50

How do we check a NI-Cad battery is charged?

Answer 50

By monitoring the voltage and current during charging

Question 51

With multiple lead acid battieres, how are they charged?

Answer 51

Connected in parallel, with the constant voltage method. ##Footnote V is kept constant, current reduces to 0 or 1 amp as the batteries charge

Question 52

What method is used to charge a Ni-Cad battery?

Answer 52

Constant current method. V changes to keep current the same. When its fully charged, it switches to constant voltage, to ensure its not over charged. ##Footnote Reduces thermal runaway. Connected in series

Question 53

What is thermal runway?

Answer 53

A major issue with Ni-Cad batteries, Lead-acid are less likely due to the amount of distilled water.

Question 54

How are Lithium-ion batteries charged?

Answer 54

1. Constant current 2. Balanced - ensures all cells are charged to the correct voltage 3. Constant voltage

Question 55

What is the hot battery bus?

Answer 55

Always connected to the positive terminal of the battery. Always live.

Question 56

What is required for a lead-acid battery in terms of venting?

Answer 56

Should have an acid trap, to neutralise the acid and prevent corrosion to the skin. Also a non return valve is required

Question 57

What is one method used to prevent thermal runway during charging?

Answer 57

A battery charge limiter

Question 58

What is a DC start generator?

Answer 58

It works as a starter until it hits a certain RPM, which it then becomes the generator ##Footnote 28 Vdc and 100 to 200A

Question 59

Which is the best method for mounting the DC starter generator

Answer 59

Manacle ring - doesnt require any studs or fasteners ##Footnote Flange mounted is an alternative method

Question 60

Whats a bus tie breaker?

Answer 60

Connects two buses, allows one power source to supply both buses if one fails.

Question 61

What are the three sources of AC power?

Answer 61

AC generators Static inverters Rotary inverters

Question 62

What are some advantages of constant frequency systems?

Answer 62

Significantly lighter Can be operated in parallel Suitable for a wider range of loads

Question 63

What are the two CSD phases?

Answer 63

Straight through - no input from the the geared differential Under/over phase - Control cylinder causes the variable wobbler to move, displacing the pistons in the variable unit

Question 64

Whats the two phases of CSD?

Answer 64

Straight through - no input from geared differential, oil is trapped and cannot return for cooling Under/over phase - control cylinder causes the variable wobbler to move, displacing the pistons in the variable unit.

Question 65

When the engine speed changes, what controls the voltage and frequency in the CSD?

Answer 65

Voltage - GCU Frequency - CSDU

Question 66

In the CSD what is the oil circuit used for?

Answer 66

Hyd fluid for the motor pump Lubrication Cooling ##Footnote Temp is measured at the exit and entry point Rise in temp = oil out temp - oil in temp

Question 67

If an engine is taking less real load, what does the CSD do?

Answer 67

Input torque is increased ##Footnote Reversible, if the engine is taking more real load, the input torque is decreased

Question 68

What is one component NOT mounted on the CSD?

Answer 68

Oil cooler

Question 69

What is an IDG?

Answer 69

Contains both the CSD and the generator

Question 70

What are current transformers used for?

Answer 70

Detect current, to check for correct load balance and short circuit.

Question 71

What is differential protection used for?

Answer 71

To detect short circuits in areas where CB’s are not usable. Compared the generator current with the current in the distribution in each phase.

Question 72

What are four sources of emergency power?

Answer 72

Main battery Inverters DC to AC APU RAT

Question 73

What buses will the battery supply in an emergency?

Answer 73

Hot Bus Battery bus Essential bus

Question 74

What is used to connect different power sources to the same buses?

Answer 74

Split system breakers. Automatically switches to on when the power sources cannot work in parallel?

Question 75

What are the three things that are apart of the triple unit vibrating contactor?

Answer 75

Voltage regulator Current limiter Reverse current cut out

Question 76

What is an example of a large load?

Answer 76

Galleys, they must be switched off before any power is switched on or off on the ground. Called load shedding, improved the reliability of the power relays and prevents an overload of the power source.

Question 77

What is used to ensure there is no loss of power when switching between power sources?

Answer 77

No break power transfer

Question 78

What is the three stages of charging a Lithium-ion battery?

Answer 78

Constant current Balanced stage Constant voltage

Question 79

What method of charging is used for a lead acid battery?

Answer 79

Constant voltage

Question 80

What method of charging is used for Ni-Cad battery?

Answer 80

Constant current method