11.06 Electrical Power Flashcards
What are the usual four main categories that aircraft electrical power systems are required to supply?
- Electrical heating,
- Lighting,
- To produce mechanical power,
- Electronic devices
Approximately, how much power does the average two engine aircraft require?
100kw
What two components are the electrical power system divided up into?
- generation
- distribution
How are power generation and distribution further divided?
- AC subsystem and
- DC subsystem
What are the five different sources of AC on modern jet aircraft?
- engine driven generators
- APU generator
- External power
- Emergency generator
- Static inverter
What is the normal supplied AC voltage and frequency?
- 115V
- 400 Hz
What other function does the AC system have?
Provides the input power for DC generation
How is AC power used for DC generation?
Transformer Rectifier Units (TRU) - Several identical TRU’s convert the 3 phase 115 volts AC power from the AC distribution system into 28 volts DC
What voltage does the aircraft battery normally supply?
24V DC`
On what type of aircraft would DC be the primary power supply?
Propeller aircraft - 28V DC generators
What does the abbreviation VFG stand for?
Variable Frequency Generator - 115V AC
What are the three levels of distribution of the electrical power supply?
- Main power distribution
- Essential power distribution
- Emergency power distribution
In the case of a total power loss of normal sources, what ill supply electrical power?
Emergency generator or battery
Where will the important electrical power system information be displayed?
ECAM or EICAS
- Power distribution pages
What is the purpose of power source switching?
connects the power sources to the busses
On many two engine aircraft (airbus) what is the function of bus tie switching?
provides a connection between the two busses and part
of the power source switching.
What is the purpose of an electrical bus?
A bus connects the power source to all the electrical consumers which use the same type of electrical power.
In reality, how is an AC bus constructed?
A bus consists only of a low resistance electrical connection between all the wires that lead to the different consumers and the wires from the power source and bus tie switching
What are the four AC consumer groups?
- Single phase consumers
• Voltage different from 115 volts
• 3 phase consumers
• Large loads
What consumer group usually consumes the most power?
Large loads
How can the reliability of the power relays be improved during switching operations?
‘Load shedding’ - Large loads must be switched off before any power source switching on/off on the ground.
How can load shedding be achieved?
- manually via a pushbutton or
- automatically
What components perform the power source switching and how are they controlled?
- Generator control units (GCU, generator power sources)
- Ground power control units (GPCU, external power sources)
When does power source switching take place?
Power source switching always occurs when an existing power source is lost or when a new power source becomes available