Electrical Systems Flashcards
3 things that determine the amount of current in a circuit resulting from magnetic induction:
1) Strength of the magnetic field.
2) Number of conductors passing through the field.
3) Speed with which the field is crossed.
Type of electricity produced by magnetism:
AC
The armature coils of a DC generator produce _______ electricity.
AC
A device that allows electrons to flow in one direction while preventing their flow in the opposite direction:
Rectifier
A mechanical rectifier mounted on the armature shaft of a DC generator:
Commutator
AC is rectified in a DC generator by ____ and ____.
Commutator and brushes.
In an AC generator, the brushes ride on __________ to carry current in and out of the rotor coil.
Slip rings.
An electrical current flowing through a coil of wire will produce a/an _______.
Electromagnet.
The field frame of a typical aircraft DC generator has 4 ______ wound in _______.
Field poles.
Field coils.
The _______ controls the amount of current flowing into the field coils.
Voltage regulator.
T/F
The voltage regulator determines the voltage produced by the generator.
True.
Via the strength of the magnetic field produced by the electromagnets.
DC generators are said to be _______ because of the field frame’s residual magnetism that is used when starting.
Self-excited
Residual voltage is a result of _______ and should amount to _______.
Residual magnetism.
2 volts or less.
The process to restore residual magnetism to the field frame:
Flashing the field.
How to flash the field:
A pulse of current from the battery is sent through the field coils in the direction in which current normally flows.
Types of generators:
1) Series-field generator
2) Shunt-field generator
3) Compound generator
The _________ arrangement is used for low output aircraft generators.
Shunt-field
The _______ arrangement is used for high output aircraft generators.
Compound
The coils of a practical generator are wound around a core of __________.
Laminated soft iron.
The point in the rotation at which there is no voltage or current from the ends of the coil is the ______ or _______.
Neutral position.
Neutral plane.
Required basic controls or protection devices for DC generators:
1) Current limiter
2) Voltage regulator
3) Reverse-current cutout and switch.
A type of circuit protection device (current limiter) that allows a momentary flow of excess current, but opens the circuit if the excessive flow is continued:
Slow blow fuse.
Automatic current limiters monitor output current and reduce ______ to prevent excessive generator output voltage.
Field current
What is the result of voltage being supplied to the output terminal of a DC generator?
The generator will act as a motor.
The reverse-current cutout/switch does what?
Disconnects generator from electrical system to prevent battery discharge and generator damage when gen voltage is lower than batt voltage.
T/F
The reverse-current cutout and switch can be manually operated by the pilot.
True.
It can be both automatically and manually operated.
Types of voltage regulators:
1) Carbon pile
2) Vibrating type (three unit electromagnetic)
Which voltage regulator is used for higher output applications?
Carbon pile type.
How does a carbon pile voltage regulator reduce generator voltage?
A voltage increase in the regulator’s coil causes a magnetic pull on the spring that holds pressure on the carbon pile, loosening the stack and increasing its resistance.
Piston engines use ______ power.
DC
Benefit of brushless motors:
No brush arcing at high altitudes caused by the low dielectric strength of low density air.
Ideal generator belt tension:
1/2 inch of deflection
A multimeter reading of “O.L” means ______ and “I” means _______.
Open lead.
Infinite.
The specific gravity of battery electrolyte is ______.
1.27
Higher frequency (Hertz) means less ______ is needed.
Current.
Lower current means smaller components
AC generators on large aircraft are also called _______.
Alternators.
As frequency drops, some components may overheat due to __________.
An increase in current.
AC generators are driven by the turbine engines through ________.
Constant speed drive units. (CSD)
The _______ holds AC generator speed and frequency constant as engine speed varies.
CSD
Constant speed drive
Define hertz.
A unit of frequency equal to one cycle per second.
A component that contains both the generator and the CSD in one unit:
Integrated drive generator.
IDG
Red wire insulation is for _______ gauge wire.
22-18
Blue wire insulation is for _____ gauge wire.
16 and 14.
Yellow wire insulation is for _____ gauge wire.
12 and 10.
____ is the max number of wire terminals that may be stacked in a terminal strip.
4
How does the vibrator type voltage regulator work?
When voltage rises above the regulated value, the relay pulls the contacts open and inserts a resistor in the generator field. It vibrates open and closed to control the amount of voltage produced.
What three things must be synchronized before a three phase AC generator can be connected to a bus that is being served by another generator?
1) Frequency
2) Voltage
3) Phase rotation
T\F
DC motors have a low starting torque.
False.
High torque.
T/F
The starter motor circuit does not normally contain a fuse or circuit breaker.
True.
Two things that receive current for starter generator operation in start mode.
Field and armature windings.
What is done to ensure that each generator shares the load in a multi generator system?
The generators are paralleled.
How is the voltage of a DC generator controlled?
By varying the field current strength.
Most common type of alternator used in aircraft systems:
3 phase
Voltage regulators and current limiters regulate DC generator voltage and limit current by controlling the ______.
Generator field current.
The field coil in a DC alternator is in the _______ element.
(rotating or stationary)
Rotating.
DC alternator benefits over generators:
1) More field poles (produce current at lower speeds).
2) High current is produced in the stationary component.
3) Lighter charging system than a generator
A starter generator has an additional set of ________.
Series motor windings.
The IDG (integrated drive generator) has the ______ and ______ in a single unit.
Generator and CSD
3 basic types of circuit breakers used in aircraft electrical systems:
1) Push to reset
2) Push-pull
3) Toggle type
Purpose of the constant speed drive (CSD).
Hold AC generator speed and frequency constant as the speed of the aircraft varies.
Reason DC power is used in small aircraft.
They require the ability to store electrical energy (battery) for starting the engine.
Conditions that can affect the state of charge of a battery:
1) Damp/dirty surface of battery.
2) Terminal corrosion.
3) Poor ground-to-structure connection.
4) Improper electrolyte level.
5) Low generator output voltage.
6) Acidic residue on top of battery.
Generator inspection consists of:
1) Checking the mounting.
2) Electrical connections.
3) Check commutator for indications of arcing.
4) Blowing out brush dust.
5) Indications of overheating (solder from the commutator)
6) Check output voltage.
