Electrical systems production

Question 1

Large aircraft normally use AC power, why?

Answer 1

• High demand for electrical power
• Size of the aircraft means lots of wiring
• High voltage/low current AC wiring is a small diameter, thus lighter than low voltage/high current DC wiring
• This saves much weight - AC alternators are lighter than DC

Question 2

Describe the layout of a generator?

Answer 2

• Armature produces AC
• Add split rings (commutator)
• Output is DC
• Aswell as the use of slip rings plus rectifier outputs DC

Question 3

Explain the layout of an Alternator?

Answer 3

• Stator produces AC
• Add rectifier (diodes)
• Output is DC

Question 4

Differences between alternator and generator?

Answer 4

• Alternator load is generated in a stator which is a solid connection
• Generator load current is generated in the armature and has to flow through a commutator and brushes to the load. (this causes arcing and energy loses)
• Generator is heavier and has a greater reliance on permanent magnets

Question 5

What are the principles of the alternator?

Answer 5

• Rotor is an electromagnet with several pole pieces
• DC is required to energize the rotor coil (create magnetic field)
• Provided by the battery
• Once operating some of the current produced is used to keep the coil energized.
• Stator has several loops

Question 6

What is a 3 phase alternator?

Answer 6

• Stator compromises of 3 coil windings
• Each coil produces a single-phase together 3 AC is produced
• Wired like a star
• 120v across any stage
  400hz

Question 7

How is alternator output frequency controlled within limits?

Answer 7

Hydraulically or mechanically operated constant speed generator drive (CSDG), unit between the ending and the alternator, or an electronic device with variable speed, constant frequency output.

Question 8

What is a variable speed constant frequency system?

Answer 8

• A system without a CSD
• Allows alternator to produce wild frequency power
• This is then conditioned by solid-state power electronics to give constant frequency AC
• This eliminates complex moving parts from the system

Question 9

What are to types of VSCF (variable speed constant frequency system)

Answer 9

A system without a CSD
Allows the alternator to produce wild frequency power
This is conditioned by a solid-state power electronics to give constant frequency
Eliminates moving

• Cyclo converter type
• DC link system.

Question 10

What is a transformer rectifier?

Answer 10

Reduces AC voltage down to a required level e.g 28V and rectifies the DC

Question 11

what is an inverter?

Answer 11

• Provides AC power from DC power supply can be used in a standby and emergency systems.

Question 12

What is an inductor?

Answer 12

An AC device often used as a resistor in AC circuts

Used in a DC circuits to help voltage fluctuations.

Question 13

How is AC power distributed?

Answer 13

Through bus systems, usually twin-engine aircraft use a split bus system
3/4 engine aircraft usually use a parallel system
Some larger aircraft employ a modified split/parallel bus sytem.

Question 14

What is the integrate drive generator?

Answer 14

IDG is a unit with the alternator alongside the CSD in the same casing, lighter than the CSD, and oil-cooled generator, electrical generation