Engine Electrical Systems Flashcards
What is a generator?
A machine that changes mechanical energy into electrical energy
By what means does a generator produce electricity?
Electromagnetic induction
What are 3 ways to change the value of induced voltage?
-Number of magnetic lines of flux (windings)
-Change the rate of movement (speed)
-Number of conductors affected (strength)
What is a commutator?
A mechanical switch, or rectifier, that converts the AC generated within the armature of a DC generator into DC as it leaves the generator.
What is the commutator made of?
Copper
What is commutation?
The system of changing the AC of the armature to DC in the external circuit
How can residual magnetism be restored?
By passing DC from a battery thru the field windings in normal direction of current flow
What is the procedure for restoring residual magnetism known as?
Flashing the Field
What is residual voltage?
A result of residual magnetism in the field poles
Aircraft generator output is normally rated in what?
Volt/Amps
The maximum allowable voltage drop between the generator and the bus bar is:
2% of the regulated voltage of the generator
How are generators classified?
Depending on how the field coils are connected to the armature
What are the 3 classifications of DC generators?
Series Wound
Shunt Wound (most common)
Compound Wound
In a series wound generator, what causes the voltage to increase and decrease?
When the load is increased, the voltage increases
When the load is decreased, the voltage decreases
In a shunt wound generator, what is required?
Must always be used with a voltage regulator
How do you eliminate armature reaction?
-Shifting the position of the brushes
-Interpoles
-Compensating windings
What is the best method for eliminating armature reaction?
Interpoles used with compensating windings
True or False? Compensating windings can be used alone.
FALSE
They are used to increase the interpoles effectiveness
What are the 5 main components of a DC generator?
-Armature assembly
-Field frame assembly
-Brush assembly
-End frames
-Cooling fans/ducts
What is the commutator made up of?
Copper segments insulated with Mica
How much should the mica insulation be undercut?
0.020 in. Or equal to the width of the mica
What causes arcing and bouncing of the brushes?
Weak spring tension
What causes excessive wear to the commutator and/or brushes?
Heavy spring tension
What are the 3 cooling methods for a DC generator?
-Fan
-RAM air
-Compressor bleed air
What is paralleling?
Electrically balancing the current load among the generators in a given system
Generator loads should be within ____ of each other.
+/- 10%
When are starter brushes supposed to be replaced?
When they are worn to about 1/2 of their original length
How can you fix a commutator that is rough or pitted?
With NO. 000 Sandpaper
How can you seat the starter brushes?
Use NO. 000 Sandpaper
OR
Abrasive stick
What do the brushes connect to?
Pigtails
(Pigtails connect to rivet)
What does FAR 23.1351.d state?
A voltmeter and/or ammeter is required to measure electrical power system quantities
Electrical load should not exceed _____ of the generator capacity.
80%
(If greater, it must have a warning placard or monitoring device)
What is an ammeter referred to as?
A Loadmeter
What does the Loadmeter(ammeter) show when placed in the generator output?
Only the charging of the battery
What does the Loadmeter(ammeter) show when connected at the battery?
Shows both charging and discharging of the battery
True or False?
A voltmeter should indicate output of the generator to be higher than battery voltage.
TRUE
14v for 12v system
28v for 24v system
What is the only practical way to regulate the generator voltage?
Vary the strength of the field
The voltage regulator controls the amount of current flowing to the field coils through the use of a ________ or _________ resistor.
Variable
Or
Intermittent
What are the 3 types of voltage regulators?
-Carbon Pile
-Vibrator
-Solid State
How is resistance adjusted with a carbon pile regulator?
Spring Pressure
More compression = Low Resistance
Less compression = Increased Resistance
The vibrator regulator has points that open and close to adjust the voltage. What designates how long the points will remain open?
The Load
What is the most common type of voltage regulator used on light aircraft?
Solid State
What are the 3 Unit Control Systems?
-Voltage Regulator
-Current Limiter
-Reverse Current Cutout Relay
What does the current limiter do?
Reduces the generator voltage whenever the maximum safe current load is exceeded
What unit is designed to protect the generator from current loads that will cause it to overheat and eventually burn the insulation and windings?
Current Limiter
What is the reverse current cutout relay?
An automatic means to disconnect the generator from the battery when the generator voltage is lower than battery voltage
(Water runs down the hill)
What is an advantage of the starter generator?
Reduction in both size and weight
What is a disadvantage of the starter generator?
Unable to maintain full output at low RPM and therefore is only used on turbine aircraft that sustain a high RPM
What are the 2 types of alternators?
AC & DC
What alternator is used most often on light aircraft with a small electrical load?
DC
What are 3 advantages of AC?
-Voltage and current can easily be stepped up or down
-Power may be supplied at a high voltage with low current
-Low current allows the use of small gauge wires which saves weight
What are the differences between alternators and generators?
Generator
Rotating armature
Stationary field
Alternator
Stationary armature
Rotating field
How many phases are produced in an alternator?
3 phase
In an alternator, the stator has _____ separate windings that are ______ degrees apart.
3 separate windings
120 degrees apart
What are the 3 main components of an alternator?
-Three-phase stator (armature windings)
-Rotor (field windings)
-Rectifier assembly
How are alternator rotor windings excited?
By DC from the aircraft battery, through the voltage regulator
What is motoring?
When the battery is discharging through the generator
What DC motor has the highest starting torque of any other type of electric motor?
Series Wound
How many diodes are connected to form the three-phase, full-wave rectifier?
6
What does the 6 diode rectifier assembly do?
Converts all three phases of AC to DC
What do rectifiers in the form of semiconductor diodes do?
Prevents reverse current flow from the battery in the event the alternators output voltage is less than battery voltage
What allows the alternator to produce more power at a lower RPM than a generator?
It has multiple (8 or 12) poles alternately spaced with north and south polarity so it has more and stronger field poles
How are alternators driven?
-Belt & pulley
Or
-Gear-driven & flange mounted
What are AC generators rated in?
Volt/Amps
What frequency do almost all AC powered aircraft electrical systems utilize?
400 Hertz
What do AC power systems require to maintain a constant speed?
A Constant Speed Drive (CSD)
What is the equation for determining frequency?
Number of poles RPM
————————- X ————-
2 60
What is the equation for determining speed?
Frequency x 120
——————————-
Number of poles
What are the 5 classifications of AC generators?
-Voltage
-Amperage
-Phase
-Power Output
-Power Factor
What are the 3 ways of maintaining constant speed or frequency?
CSD
IDG
VSCF
What device is used for converting DC into AC at the frequency and voltage required?
Inverter
What are the 2 different types of inverters?
Rotary & Static
What is the most common inverter?
Static inverter
Also known as Solid-State type
Wires must only be specifically designed for aircraft use. What type is normally used?
Stranded
When copper wire is replaced with aluminum wire, the aluminum wire should be:
Two sizes larger than the copper wire size
(Aluminum wire has more resistance)
What size wire should not be used on aircraft?
AWG size 8
What is the minimum bending radius for wires?
Single wire is 3x the wire diameter
Preferred is 6x diameter
What must be done to prevent excessive stress on wire insulation when installing wire bundles?
Wire bundles must not be less than 10 times the diameter of the largest wire or cable in the bundle
When is double cord lacing used?
On wire bundles of 1 inch diameter or larger
Maintain a minimum clearance of _______ from any control cable.
1/2 inch
True or False? Wires should be routed below fluid lines.
FALSE
Wire should be routed above or on a level with fluid lines and maintain a 6 in separation
If separation from flammable fluid lines is impractical, run the electrical wire a minimum of _______ above the flammable fluid line and secure.
6 in
Wire bundles should be limited in size to:
75 wires or appx 2” diameter
What are the 3 types of connecting devices?
-Quick disconnect (AN/MS)
-Crimp type
-Solder
Describe a quick disconnect connector.
Wires are put inside an insulated plug with pins and sockets that mate with the opposite type of terminal
On a quick disconnect connector, sockets are ______ and Pins are _______.
Sockets are Positive +
Pins are Negative -
How are crimped terminals designated?
According to wire size and size of the terminal stud
What are the terminal insulation colors and sizes?
YELLOW: 10 - 12 AWG
BLUE: 14 - 16 AWG
RED: 18 - 20 -22 AWG
What is the most common crimp type terminal?
Ring type
If several splices are to be made in any wire bundle, splices should be:
Staggered to reduce bundle diameter
How many terminals are permitted to be on a terminal strip?
4
What are 2 things to ensure when dealing with bonding straps?
-Make as short as practical
-Resistance of each connection cannot exceed 0.003 ohms
Where should circuit breakers be located?
As close to the power source as possible
What is a conduit designed to provide?
Mechanical protection
What can conduits be made of?
Metallic or non-metallic
Aluminum
Brass
Fiberglass
Rigid or flexible
What size should a conduit be?
25% larger than maximum bundle size
What is used to lubricate the inside of an electrical conduit to aid electrical wires being pulled through?
Soapstone Talc
What are the 3 high current surge circuits?
-Incandescent Lamps
-Electric Motor
-Inductive Circuits
What is Derating Factor?
A multiplier that is applied to determine the capacity of a switch for a particular installation
How do you find the Derating Factor?
It will be listed in a chart or given to be calculated with Amps x DF
How should switches be installed?
Should always be installed so the lever will be moved up or forward for ON and down or aft for OFF
Electromagnetic Switches are usually called:
-Relays
&
-Solenoids
What is the difference between a relay & a solenoid?
Relay = electromagnetically operated movable contact switch
Solenoid = electromagnetically operated moveable core switch
What are the two duty cycles that solenoids and relays may be designated by?
-Continuous (> 2 Min)
-Intermittent (< 2Min)
What are 3 circuit protection devices?
-Fuses
-Current limiters
-Circuit breakers
What are the 2 variable resistors?
Rheostats
&
Potentiometers
Describe 4 things about Rheostats:
Connects in series
Varies CURRENT
Low resistance
Has 2 terminals
Describe 4 things about Potentiometers:
Connected in parallel
Varies VOLTAGE
High resistance
Has 3 terminals
Capacitance depends on what?
-Area of the plates
-Dielectric thickness
-Dielectric material
What are 2 types of capacitors?
Fixed & Variable
What are the 5 types of materials that can be used as insulation inside capacitors?
-Paper
-Oil
-Mica
-Electrolytic
-Ceramic
What is a transformer?
A device used to increase or decrease the voltage in an AC circuit.
Allows for high voltage with low power loss.
What is inside of a transformer?
A primary winding and a secondary winding on a laminated soft iron core.
What is the purpose of a laminated core?
Reduces the effects of eddy currents
How many diodes are used in a 3 phase rectifier?
6
