ELECTRICAL POWER 11.6 Flashcards
What could cause an increase of the oil in, and a decrease of, the oil rise temperature?
The cooling oil is not sufficient
What happens when the disconnect solenoid is energised while the engine is stopped?
The disconnect device is triggered and the clutch is damaged when the engine is started
How is a CSD disconnect reset performed?
The reset ring is pulled when the engine is completely stopped
What is the function of the voltage regulator in the GCU?
To control the voltage at the point of regulation to 115v by influencing the exciter current
Which is the voltage level for an under voltage condition?
100v
What happens with a generator working in isolated operation when it receives more exciter current than necessary?
The output voltage increases
When does the differential protection circuit trip the generator?
When the generator current in 1 phase differs from the current that is measured in the same phase at the generator power relay
What happens when you exchange 2 phase connections at the generator terminals?
All connected 3 phase AC motors run in the wrong direction, because of wrong phase sequence
How can you check the charging level of Ni-Cd battery?
You must measure the charging current. If it is nearly zero, the battery is fully charged
What happens when a Ni-Cd battery overheats during charging?
The charging current increases and would start a thermal runway
Which of the following methods is used to charge a battery in an electrical power system?
The batteries can be recharged by a TR unit using the constant voltage charging method
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?
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
Consider a multi-engine aircraft with paralleled generators. What happens if the number 2 bus-tie contactor is opened?
Generator 2 trips and the loads of the 4 main bus-bars are shared between generators 1, 3, and 4
How is an open-phase in a generator detected?
By comparing this he generator load current in each phase
What does it mean when the AVAIL light in the external power push button illuminates?
The external power source that is connected provides electrical power with the connect parameters
What happens when you switch on EXT PWR in an electrical power system?
The complete normal power distribution is supplied
How are the engine driven generators of multi engine aircraft (3 or 4 engines) usually operated?
In parallel operation
How many resets are permitted after a circuit breaker has tripped?
1, to prevent the contacts from welding if a short circuit has occurred
What does the abbreviation RCCB mean?
Remote Controlled Circuit Breaker
Which is the operation of the CSD disconnect?
Electrically disconnected and mechanically re-connected
What is the maximum permitted time for operating the CSD disconnect button?
3 seconds
What is the maximum permitted time for operating the CSD disconnect button?
3 seconds
Which protective functions are built into the aircraft’s Transformer Rectifier (TR) units?
Low current and high temperature protection
Why are there 2 shorting pins in the external power receptacle?
They ensure that the external power can only be applied if the plug is located correctly in the power receptacle
How can a CSD disconnect be reliably confirmed?
Zero volt and zero frequency is indicated
What are the main components of a static inverter?
Solid state switches and a transformer
What happens if the bus-tie switching is set to off during operation with only ground power available?
The main bus bars operate, but separate from eachother
What is the main advantage of parallel operation of main AC buses over isolated operation?
All engine driven generators are loaded equally and there is no power loss when one generator fails
Why are trip-free CB’s used on aircraft?
Because they can open an overloaded circuit even with the control knob jammed in
Which statement accurately describes the bus-tie switching operation in a Boeing multi-engined aircraft?
The bus-tie switching is normally closed. This is known as parallel operation
Consider the function of the GCU. Which of the following statements is correct?
The GCU’s of the engine driven generators are identical and interchangeable
How are the engine driven generators of twin engine aircraft usually operated?
In isolated operation
What is the purpose of the 2 minute delay before resetting a CB?
To allow the bi-metallic strip in the circuit breaker to cool down
Which statement is correct concerning the input speed of generators producing a voltage with a frequency of 400Hz?
The speed depends on the number of pole pairs.
24,000rpm with 1 pole pair
8,000rpm with 3 pole pairs
How does the static inverter generate the correct output frequency?
With a beat generator
What happens when the disconnect solenoid is energised while the engine is stopping?
The clutch is damaged immediately
