Engine Electrical Systems Flashcards
(115 cards)
1
Q
What is a generator?
A
A machine that changes mechanical energy into electrical energy
2
Q
By what means does a generator produce electricity?
A
Electromagnetic induction
3
Q
What are 3 ways to change the value of induced voltage?
A
-Number of magnetic lines of flux (windings)
-Change the rate of movement (speed)
-Number of conductors affected (strength)
4
Q
What is a commutator?
A
A mechanical switch, or rectifier, that converts the AC generated within the armature of a DC generator into DC as it leaves the generator.
5
Q
What is the commutator made of?
A
Copper
6
Q
What is commutation?
A
The system of changing the AC of the armature to DC in the external circuit
7
Q
How can residual magnetism be restored?
A
By passing DC from a battery thru the field windings in normal direction of current flow
8
Q
What is the procedure for restoring residual magnetism known as?
A
Flashing the Field
9
Q
What is residual voltage?
A
A result of residual magnetism in the field poles
10
Q
Aircraft generator output is normally rated in what?
A
Volt/Amps
11
Q
The maximum allowable voltage drop between the generator and the bus bar is:
A
2% of the regulated voltage of the generator
12
Q
How are generators classified?
A
Depending on how the field coils are connected to the armature
13
Q
What are the 3 classifications of DC generators?
A
Series Wound
Shunt Wound (most common)
Compound Wound
14
Q
In a series wound generator, what causes the voltage to increase and decrease?
A
When the load is increased, the voltage increases
When the load is decreased, the voltage decreases
15
Q
In a shunt wound generator, what is required?
A
Must always be used with a voltage regulator
16
Q
How do you eliminate armature reaction?
A
-Shifting the position of the brushes
-Interpoles
-Compensating windings
17
Q
What is the best method for eliminating armature reaction?
A
Interpoles used with compensating windings
18
Q
True or False? Compensating windings can be used alone.
A
FALSE
They are used to increase the interpoles effectiveness
19
Q
What are the 5 main components of a DC generator?
A
-Armature assembly
-Field frame assembly
-Brush assembly
-End frames
-Cooling fans/ducts
20
Q
What is the commutator made up of?
A
Copper segments insulated with Mica
21
Q
How much should the mica insulation be undercut?
A
0.020 in. Or equal to the width of the mica
22
Q
What causes arcing and bouncing of the brushes?
A
Weak spring tension
23
Q
What causes excessive wear to the commutator and/or brushes?
A
Heavy spring tension
24
Q
What are the 3 cooling methods for a DC generator?
A
-Fan
-RAM air
-Compressor bleed air
25
What is paralleling?
Electrically balancing the current load among the generators in a given system
26
Generator loads should be within ____ of each other.
+/- 10%
27
When are starter brushes supposed to be replaced?
When they are worn to about 1/2 of their original length
28
How can you fix a commutator that is rough or pitted?
With NO. 000 Sandpaper
29
How can you seat the starter brushes?
Use NO. 000 Sandpaper
OR
Abrasive stick
30
What do the brushes connect to?
Pigtails
(Pigtails connect to rivet)
31
What does FAR 23.1351.d state?
A voltmeter and/or ammeter is required to measure electrical power system quantities
32
Electrical load should not exceed _____ of the generator capacity.
80%
(If greater, it must have a warning placard or monitoring device)
33
What is an ammeter referred to as?
A Loadmeter
34
What does the Loadmeter(ammeter) show when placed in the generator output?
Only the charging of the battery
35
What does the Loadmeter(ammeter) show when connected at the battery?
Shows both charging and discharging of the battery
36
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
37
What is the only practical way to regulate the generator voltage?
Vary the strength of the field
38
The voltage regulator controls the amount of current flowing to the field coils through the use of a ________ or _________ resistor.
Variable
Or
Intermittent
39
What are the 3 types of voltage regulators?
-Carbon Pile
-Vibrator
-Solid State
40
How is resistance adjusted with a carbon pile regulator?
Spring Pressure
More compression = Low Resistance
Less compression = Increased Resistance
41
The vibrator regulator has points that open and close to adjust the voltage. What designates how long the points will remain open?
The Load
42
What is the most common type of voltage regulator used on light aircraft?
Solid State
43
What are the 3 Unit Control Systems?
-Voltage Regulator
-Current Limiter
-Reverse Current Cutout Relay
44
What does the current limiter do?
Reduces the generator voltage whenever the maximum safe current load is exceeded
45
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
46
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)
47
What is an advantage of the starter generator?
Reduction in both size and weight
48
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
49
What are the 2 types of alternators?
AC & DC
50
What alternator is used most often on light aircraft with a small electrical load?
DC
51
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
52
What are the differences between alternators and generators?
**Generator**
Rotating armature
Stationary field
**Alternator**
Stationary armature
Rotating field
53
How many phases are produced in an alternator?
3 phase
54
In an alternator, the stator has _____ separate windings that are ______ degrees apart.
3 separate windings
120 degrees apart
55
What are the 3 main components of an alternator?
-Three-phase stator (armature windings)
-Rotor (field windings)
-Rectifier assembly
56
How are alternator rotor windings excited?
By DC from the aircraft battery, through the voltage regulator
57
What is motoring?
When the battery is discharging through the generator
58
What DC motor has the highest starting torque of any other type of electric motor?
Series Wound
59
How many diodes are connected to form the three-phase, full-wave rectifier?
6
60
What does the 6 diode rectifier assembly do?
Converts all three phases of AC to DC
61
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
62
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
63
How are alternators driven?
-Belt & pulley
Or
-Gear-driven & flange mounted
64
What are AC generators rated in?
Volt/Amps
65
What frequency do almost all AC powered aircraft electrical systems utilize?
400 Hertz
66
What do AC power systems require to maintain a constant speed?
A Constant Speed Drive (CSD)
67
What is the equation for determining frequency?
Number of poles RPM
————————- X ————-
2 60
68
What is the equation for determining speed?
Frequency **x** 120
——————————-
Number of poles
69
What are the 5 classifications of AC generators?
-Voltage
-Amperage
-Phase
-Power Output
-Power Factor
70
What are the 3 ways of maintaining constant speed or frequency?
CSD
IDG
VSCF
71
What device is used for converting DC into AC at the frequency and voltage required?
Inverter
72
What are the 2 different types of inverters?
Rotary & Static
73
What is the most common inverter?
Static inverter
Also known as Solid-State type
74
Wires must only be specifically designed for aircraft use. What type is normally used?
Stranded
75
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)
76
What size wire should not be used on aircraft?
AWG size 8
77
What is the minimum bending radius for wires?
Single wire is 3x the wire diameter
**Preferred** is 6x diameter
78
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
79
When is double cord lacing used?
On wire bundles of 1 inch diameter or larger
80
Maintain a minimum clearance of _______ from any control cable.
1/2 inch
81
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
82
If separation from flammable fluid lines is impractical, run the electrical wire a minimum of _______ above the flammable fluid line and secure.
6 in
83
Wire bundles should be limited in size to:
75 wires or appx 2” diameter
84
What are the 3 types of connecting devices?
-Quick disconnect (AN/MS)
-Crimp type
-Solder
85
Describe a quick disconnect connector.
Wires are put inside an insulated plug with pins and sockets that mate with the opposite type of terminal
86
On a quick disconnect connector, sockets are ______ and Pins are _______.
Sockets are Positive +
Pins are Negative -
87
How are crimped terminals designated?
According to wire size and size of the terminal stud
88
What are the terminal insulation colors and sizes?
YELLOW: 10 - 12 AWG
BLUE: 14 - 16 AWG
RED: 18 - 20 -22 AWG
89
What is the most common crimp type terminal?
Ring type
90
If several splices are to be made in any wire bundle, splices should be:
**Staggered** to reduce bundle diameter
91
How many terminals are permitted to be on a terminal strip?
4
92
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
93
Where should circuit breakers be located?
As close to the power source as possible
94
What is a conduit designed to provide?
Mechanical protection
95
What can conduits be made of?
Metallic or non-metallic
Aluminum
Brass
Fiberglass
Rigid or flexible
96
What size should a conduit be?
25% larger than maximum bundle size
97
What is used to lubricate the inside of an electrical conduit to aid electrical wires being pulled through?
Soapstone Talc
98
What are the 3 high current surge circuits?
-Incandescent Lamps
-Electric Motor
-Inductive Circuits
99
What is Derating Factor?
A multiplier that is applied to determine the capacity of a switch for a particular installation
100
How do you find the Derating Factor?
It will be listed in a chart or given to be calculated with **Amps x DF**
101
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
102
Electromagnetic Switches are usually called:
-Relays
&
-Solenoids
103
What is the difference between a relay & a solenoid?
Relay = electromagnetically operated movable **contact** switch
Solenoid = electromagnetically operated moveable **core** switch
104
What are the two duty cycles that solenoids and relays may be designated by?
-Continuous (> 2 Min)
-Intermittent (< 2Min)
105
What are 3 circuit protection devices?
-Fuses
-Current limiters
-Circuit breakers
106
What are the 2 variable resistors?
Rheostats
&
Potentiometers
107
Describe 4 things about **Rheostats**:
Connects in series
Varies **CURRENT**
Low resistance
Has 2 terminals
108
Describe 4 things about **Potentiometers**:
Connected in parallel
Varies **VOLTAGE**
High resistance
Has 3 terminals
109
Capacitance depends on what?
-Area of the plates
-Dielectric thickness
-Dielectric material
110
What are 2 types of capacitors?
Fixed & Variable
111
What are the 5 types of materials that can be used as insulation inside capacitors?
-Paper
-Oil
-Mica
-Electrolytic
-Ceramic
112
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.
113
What is inside of a transformer?
A primary winding and a secondary winding on a laminated soft iron core.
114
What is the purpose of a laminated core?
Reduces the effects of eddy currents
115
How many diodes are used in a 3 phase rectifier?
6
