ELECTRICAL POWER 11.6

Question 1

What could cause an increase of the oil in, and a decrease of, the oil rise temperature?

Answer 1

The cooling oil is not sufficient

Question 2

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

Answer 2

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

Question 3

How is a CSD disconnect reset performed?

Answer 3

The reset ring is pulled when the engine is completely stopped

Question 4

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

Answer 4

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

Question 5

Which is the voltage level for an under voltage condition?

Answer 5

100v

Question 6

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

Answer 6

The output voltage increases

Question 7

When does the differential protection circuit trip the generator?

Answer 7

When the generator current in 1 phase differs from the current that is measured in the same phase at the generator power relay

Question 8

What happens when you exchange 2 phase connections at the generator terminals?

Answer 8

All connected 3 phase AC motors run in the wrong direction, because of wrong phase sequence

Question 9

How can you check the charging level of Ni-Cd battery?

Answer 9

You must measure the charging current. If it is nearly zero, the battery is fully charged

Question 10

What happens when a Ni-Cd battery overheats during charging?

Answer 10

The charging current increases and would start a thermal runway

Question 11

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

Answer 11

The batteries can be recharged by a TR unit using the constant voltage charging method

Question 12

Consider a 2 engine aircraft with isolated operation of the main bus-bars. What happens in the event of a failure of one of the main engine generators in flight?

Answer 12

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 13

Consider a multi-engine aircraft with paralleled generators. What happens if the number 2 bus-tie contactor is opened?

Answer 13

Generator 2 trips and the loads of the 4 main bus-bars are shared between generators 1, 3, and 4

Question 14

How is an open-phase in a generator detected?

Answer 14

By comparing this he generator load current in each phase

Question 15

What does it mean when the AVAIL light in the external power push button illuminates?

Answer 15

The external power source that is connected provides electrical power with the connect parameters

Question 16

What happens when you switch on EXT PWR in an electrical power system?

Answer 16

The complete normal power distribution is supplied

Question 17

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

Answer 17

In parallel operation

Question 18

How many resets are permitted after a circuit breaker has tripped?

Answer 18

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

Question 19

What does the abbreviation RCCB mean?

Answer 19

Remote Controlled Circuit Breaker

Question 20

Which is the operation of the CSD disconnect?

Answer 20

Electrically disconnected and mechanically re-connected

Question 21

What is the maximum permitted time for operating the CSD disconnect button?

Answer 21

3 seconds

Question 22

What is the maximum permitted time for operating the CSD disconnect button?

Answer 22

3 seconds

Question 23

Which protective functions are built into the aircraft’s Transformer Rectifier (TR) units?

Answer 23

Low current and high temperature protection

Question 24

Why are there 2 shorting pins in the external power receptacle?

Answer 24

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

Question 25

How can a CSD disconnect be reliably confirmed?

Answer 25

Zero volt and zero frequency is indicated

Question 26

What are the main components of a static inverter?

Answer 26

Solid state switches and a transformer

Question 27

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

Answer 27

The main bus bars operate, but separate from eachother

Question 28

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

Answer 28

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

Question 29

Why are trip-free CB’s used on aircraft?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Consider the function of the GCU. Which of the following statements is correct?

Answer 31

The GCU’s of the engine driven generators are identical and interchangeable

Question 32

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

Answer 32

In isolated operation

Question 33

What is the purpose of the 2 minute delay before resetting a CB?

Answer 33

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

Question 34

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

Answer 34

The speed depends on the number of pole pairs.
24,000rpm with 1 pole pair
8,000rpm with 3 pole pairs

Question 35

How does the static inverter generate the correct output frequency?

Answer 35

With a beat generator

Question 36

What happens when the disconnect solenoid is energised while the engine is stopping?

Answer 36

The clutch is damaged immediately