Engine Electrical Systems Flashcards
(30 cards)
What is used as the rectifier to produce direct current in a DC generator?
Brushes and a commutator.
What is used as the rectifier to produce direct current in a DC alternator?
Six solid-state diodes.
Why is it not necessary to flash the field of a DC alternator after it has been overhauled?
An alternator field is excited by battery current and residual voltage is not used to start the alternator producing current.
When should the brushes in a starter motor be replaced?
When they have worn to one half of their original length.
Is a starter motor series-wound or shunt-wound?
Series wound for maximum stalled-rotor toque.
What is a starter-generator?
A single, engine-mounted component that serves as a starter for starting the turbine engine. When the engine is running, the circuitry automatically shifts so it acts as a compound-wound generator.
If the installed ammeter gauge is redlined at 100% of generator or alternator rating, and the regulator does not control current, how is maximum current controlled?
Current is controlled by the pilot or operator of the aircraft by not applying loads greater than redline, except for short, intermittent loads.
If placards or monitoring devices are not practical or desired, what practice protects the battery and electrical system?
The generator is sized so that total continuous load of the electrical system does not exceed 80% of the rated capacity.
When determining maximum continuous electrical load of an aircraft, what defines if the load is intermittent or continuous?
The length of time the system is sued. If the component or system is used for less than two minutes, it is considered an intermittent load. If it is used for more than two minutes, it is considered a continuous load.
How is generator output voltage controlled?
By controlling the fuel current strength through the use of a voltage regulator.
How is the direction of rotation of a DC electric motor reversed?
Reverse the polarity of the armature or the field, but not both.
What must be done to a DC generator, after it has been overhauled, before it can produce electricity?
The field must be flashed to restore residual magnetism to the field frame so it can begin to produce current.
How many phases of AC electricity are produced by an alternator?
Three phases.
How many diodes are required to convert three phase AC to DC electricity?
Six diodes.
What factors must be considered when determining wire size?
-System voltage
-If the circuit has an intermittent or continuous load
-Current
-Distance in feet of the wire run
-The temperature rating of the wire to be used
-The ambient temperature of the area where the wire will be installed
-The number of wires in the wire bundle
-The percentage of time the wire bundle will be loaded
-The maximum altitude the wire will see
When paralleling the outputs of two generators or alternators, how close must the output voltage be?
Within a few tenths of a volt. Follow the instructions in the maintenance manual for specified voltages.
Why is it important to parallel the outputs of a dual-generator system?
If the generator output voltages are not the same, one generator will attempt to carry all, or most, of the load, causing the generator to become overloaded.
What is the purpose of a generator CSD (constant speed drive) unit?
A CSD maintains the output frequency of a AC generator by maintaining the speed of the generator through varying engine speeds.
What is an IDG (integrated drive unit)?
An IDG combines the AC generator and CSD into a single unit.
What are two ways wires can be attached to the pins in a cannon plug?
-By soldering the wires into pots on the pins and sockets.
-by crimping tapered pins onto the wires and inserting the pins into tapered holes the pins and sockets.
Why is stranded wire rather than solid wire used in most powerplant electrical systems?
Solid wire is likely to break when it is subjected to vibration.
What two things must be considered in selection of wire size when making an electrical installation in an aircraft?
The current-carrying capability of the wire, and the voltage drop caused by current flowing through the wire.
What is used to protect a wire bundle from chafing where it passes through a hole in a bulkhead or frame?
A grommet around the edges of the hole.
How are electrical wires protected where they pass through an area of high temperature?
Wires passing through these areas are insulated with high-temperature insulation, and the wires are enclosed in some type of protective conduit.
