NAA workbook Engine electrical System
Continuous Lacing
1st loop is a clove hitch locked with a double overhand knot continue with over and under loops end with another clove hitch lock with a square knot more referent Ac 43.13-1b 11-158
What percent is the maximum allowable voltage drop between the Generator and the Bus bar
2% of the regulated voltage of the generator
Conduit size
25% larger than the maximum bundle size must be supported and have drain holes at lower point Al edges smooth and end Flared Can not be flattened to less than 75% of nominal tubing size Soapstone talc may be used to lubricate the inside of an electrical conduit to aid electrical wire being pulled through.
AC Generator almost all utilize how many hertz of ac and why?
400 HERTZ BECAUSE AC POWER SYSTEM require a constant speed Drive to maintain a constant frequency
Circuit Breaker
43-13-1b 11-47 all the information installed primary to protect the circuit and should be located ass close to the power source as possible Resettable Push-pull Switch- type automatic resetting circuit breaker are not permitted
Conduit
43.13 1B, 11-248 Designed to provide Mechanical protection can be: Metallic or Non -metallic Aluminum Brass is used for magnetic shielding Rigid or flexible
Commutator ripple Effect can be resolve with.....
A Ripple filter in the generator output circuit is used to remove the ripple (capacitor; Coil circuit)
Transformers
A device used to increase or decrease the voltage in a circuit Main reason why Alternating Current is so Advantageous allows ac to be transmitted at a High voltage with Low power Loss Voltage can be reduced to any value.
Generator
A machine that converts mechanical energy into electrical energy
Aircraft alternator electrical circuit
A three- phase unit rather then single -phase the Stator has three separate winding 120 degreed a part.
Ammeter gauge on the generator system
AC43.13-1B 11-35 The electrical load should not exceed 80% of the generator capacity. If is Greater, then it must have warning placer or monitor device (80% or 20% reserve)
The use of aluminum wire, smaller then_________on aircraft is to be________
AWG size 8 Discouraged
Aircraft wire sizes standard is base on the?
American wire gauge AWG
Dc generator normally rated in
Amp at given (rated) Voltage volt/amp
Armature reaction
Armature reaction is proportional to the current fallowing in the Armature coil
Commutator Ripple effect
Can interfere with radio and amplifier circuits causing them to ''HUM''
Types Of Voltage Regulator
Carbon pile Vibrator Solid-state (most common in Aircraft Systems)
Compound Wound DC Generator
Combination Series and Shunt(parallel)generator one winding in series & one in parallel to the Armature field the generator voltage will rise as load is increased over compounded when the shunt field has greater effect then the series field voltage will decrease as the load is increased=undercompounded
Dc generator are classified according to the manner of?
Connecting the field coil to the Armature
Generator Cooling System
Fan mounted on the generator shaft Pressure from the ran air duct Compressor air bleed
Paralleling Generator
Electrically balancing the current load among the generator in a given system
Monitor Generator output
Far 23.1351.d a Voltmeter and Ammeter is required to measure electrical power system quantities the Ammeter is preferred however most aircraft have both voltmeter and an Ammeter.
formula for determine frequency
# of poles * rpm
Capacitance depends on What?
1. Area of the plate 2. Dielectric thickness 3. Dielectric materials
Terminal Insulation is color coded for size
Yellow 10-12 AWG Blue 12-16 AWG Red 18-20-22 AWG the wire must be carefully stripped using the proper tool so as to approx. .032 of the conductor is visible when the wire installed. Aluminum will nick easily Use the proper crimping tool.
Shunt Wound DC Generator
Field coils are connected in parallel with the armature must have a means of regulations without load, this generator entire output would go thru the field coils causing the generator to burn out without field, current regulation Shunt-type are only good at a constant speed & with constant load
Armature
The armature is the part of an AC generator in which voltage is produced. This component consists of many coils of wire that are large enough to carry the full-load current of the generator.
Current limiter
1.Reduce the generator voltage whenever the maximum safe current load is exceeded 2.Designed to protect the generator from current loads that will cause it to overheat 7 eventually burn the insulation and winding 3.when the load current is excessive, the current coil electromagnetically open the point and adds resistance to the field
Armature components
1.Rotor 2.Slip Rings 3.Brushes
Rauting Basics
1. Maintain a minimum clearance 1/2 inch from any control cable 2. locate wire above or on a level with fluid lines and maintain 6-inch separation every effort should be made to avoid routing electrical wire near a flammable fluid lines IF separation is impractical run the electrical wire a minimum 6 inches above the flammable fluids line and secure insert grommet if wire passes within a 3/8 inch of the hole edge
Classification of AC generator
1.Voltage 2.amperage 3.phase 4.power output 5.power factor and most aircraft utilize three-phase Alternator
Quick-Disconnect Connector(AN/MA)
1. Wire is put inside an insulated plug with pins or sockets that mate with the opposite type of terminal in a similar plug 2.the two halves are held tight with a special nut 3. Socket is positive(+) 4. Pins are negative (-) *Different style 1.quarter turn sometimes referred to as bayonet type or quick Release 2.Full thread
Dc generator construction main components
1.Armature Assembly 2.Field Frame 3.Brush Assembly 4.End Frames 5.Cooling fans / ducting
Generator Maintenance procedure
1.Inspection 2.Disassemble 3.Commutator care 4.Bearings & Brushes 5.Reassembly 6.Testing
Types of capacitors Materials (Fixed and Variable)
1.Paper 2.oil 3.mica 4.electrolytic (polarize and can de used for DC only) 5.Ceramic
commutator care 1. If rough or pitted
1.can be smoothed with N#000 sandpaper 2.can be turned on an armature lathe and the mica undercut approximately 1/2 width of slot or .020
Eliminating Armature reaction
1.shifting the position of the brushes 2.interpoles 3.compensating winding
Name 3 unit of vibrator control system
1.voltage regulator 2.current limiter 3.reverse-current cutout relay
Shifting the Brushes
1.Position the brushes so they are in the neutral plane 2.Work when the generator operates under a fairly constant load 3.The neutral plane shift with load changes 4.When generator produce is normal load current
Connecting Device
1.Quick -disconnect connect (an/MS) 2.Crimp-type terminal 3.Solder connections
2 Major types of alternators
Dc alternator Ac alternator
Crimped terminals
Designated according to wire size of the terminal stud to which the terminal is to be connected terminal will fit 2 or 3 different sizes of wire
Carbon pile Voltage regulator function
Disks compressed = Resistance is Low pressure on the stack is reduced = resistance increase carbon pile is in Series with the generator field A small Manual rheostat is used to parallel the generator
AC generator Magnetic Fileds components
Fiels poles Field coil The field in an AC generator consists of coils of conductors within the generator that receive a voltage from a source (called excitation) and produce a magnetic flux. The magnetic flux in the field cuts the armature to produce a voltage. This voltage is ultimately the output voltage of the AC generator.
How balancing the current load
Follow Manufacturers recommendations 1.check all generator with a voltmeter 2.adjust generator to the exact same voltage output 3.Turn on substantial load & watch Amp-meter (Generator loads should be within +/- 10% of each other) 4.Adjust the generator with the greatest error 1st by small movements of the potentiometer on the voltage regulator (watch ammeter)
Residual magnetism
Found in the Field poles make it possible to start a generator without exciting the field with an outside source of power. Generator is considered to be self-exciting.
Where we can be found information about aircraft Electrical Wiring basic
General information Far 23.1351 & AC43.13 -1b
Alternator vs Generator
Generator has a rotating Armature Alternator has a stationary armature known as stator Generator has stationary fields Alternator as rotary field knows as a rotor
Series Wound DC Generator
Has a field winding that is in series with respect to the armature winding not suitable for aircraft application the greater the current through the field coil to the external circuit, the greater the induced EMF and the greater the output voltage.
Voltmeter gauge on the generator system
Indicated actual voltage produce by the generator should indicate output of the generator to be higher than Battery voltage. 14 volts for a 12 volt2 system 28 volts for 24 volts system
How can be restores the residual magnetism
It can be restored by passing DC from the battery through the field windings in normal direction of the current flow.
Aircraft Alternators
Just like a Generator change Mechanical energy to Electrical energy (the are different, however)
Induction
MAGNETIC lines of flux in movement across a conductor will induce a Voltage into that conductor.
Bonding Jumper
Make as short as practical resistance of each connection cannot exceed .003 ohms
Commutator function 1 (continue)
Mechanical Switch or rectifier that converts alternating current generated within the armature of Dc Generator into Direct Current as it leaves the generator
New brushes
Must b e seated so the face of each brush has maximum surface contact with the commutator
Generator Cooling
Old style used Ram Air for cooling newer systems use Oil as a cooling agent and combination air/oil heat exchanger
COUNTER EMF ADVANTAGES
Only one drive gear reduction in both size and weight
AC Alternator advantage 2
Power may be supplied at the hight voltage with low current the low current allows the use of small gauge wires which saves weight
What is the Different between Relay & Solenoid?
Relay is an Electromagnetically operated Movable contact switch Solenoids are an Electromagnetically operated Movable core switch current flows through the coil of a Solenoid -operated switch as long as the control circuit is complete when the control circuit is opened a Spring separated the contact
Residual magnetism is the result of
Residual magnetism in the filed poles
Commutator functions 2 continue
Reverse the external connection of the Armature at the same time that the current flow reverses in the Armature
Brushes
Seat by using N#000 sandpaper around commutator with brushes riding on the sandpaper or use a special abrasive stick
Classification of DC Generator
Series wound Shunt-wound Compound wound
Installation of switches
Should always be installed so the lever will be moved Up or forward to turn the circuit on Down or aft to turn circuit Off Switches that operate movable parts should be installed so the switches lever is moved in the same direction that the part moves.
Single cord lacing
Single - cord lacing used for wire bundle of 1-inch diameter or less bundle may lace with continuous series of loops around the bundle or can be secure with a single tie when supports are more than 12 inches apart.
Commutator ripple
Slight pulsation of output voltage from the generator doesn't interference with lighting & motor circuit
Duty Cycle Solenoid and Relays
Solenoids & Relays may be designated by their duty cycle Continuous (>2 min) or more Intermittent (<2 min) or Less
(Ac alternator) AC Generator current can easily be
Stepped up or Down
Terminal Insulation is color coded for size (continue)
Terminal that fit wires large than AWG size 10 have wire size stamped Large than 10 gauge use un-insulated terminal Ring-type is most common for aviation use DO NOT USE HOOK OR SLOTTED TYPE
Alternator components
Three face stator (armature winding) Rotor(field winding) Rectifier Assembly)
Cable Lacing
Use only approved lacing cord with the proper MIL-SPEC
Electromagnetic Switches
Usually called Relays & Solenoids
Rheostats
Usually installed in a circuit to change the current flow has low resistance has 2 terminals
Bearings
Usually the sealed type No lubrication necessary If rotation is not smooth, replace bearings
Carbon pile voltage regulator components
Variable resistance stack(pile) of carbon disks leaf springs exert pressure on the stack and electromagnet release the pressure
(Ac alternator) most often called AC Generator are rated in
Volts /Amp or Kilo volts Amp
Counter EMF
a conductor moving across a magnetic field will have an EMF induced within itself counter EMF opposes applied EMF and thus reduce current flow
Constant speed drive (CSV) is?
a type of automatic transmission that maintains a constant output RPM with a variable input RPM
reverse -current cutout relay
automatic means to disconnect the generator from the battery when the generator voltage is lower than battery voltage use both a voltage coil and a current coil on the same core this opposite floe will weaker the field and allow the spring to open the points to disconnect\the generator from the battery if the points fail to open the battery will be discharged through the generator.
Alternator vs Generator Continue
by directly contacting the Alternator output to the bus it eliminates the poor connection at the brushes generator at hugh power levels rotating contacts are too inefficient to be practical.
When a generator can loss the Residual magnetism ?
by shorting, overheating, impact or a long period of inactive
Voltage depend on
change the rate of movement between the lines of flux and the conductor (speed of the Armature) change the number of conductors affected( add more winding) Change the number of magnetic lines of flux (strength of the magnetic field)
Inverters
device for converting direct current into alternating current at the frequency and voltage required two different types Rotary and static.
Vibrator voltage regulator 2 of 2
if the voltage regulator points stick in the close position the electromagnetic pull of the voltage coil cannot open them so the generator output voltage will increase the load designates how long the point will remain open
Vibrator voltage regulator 1 of 2
intermittent resistance type intermittently cuts resistance in & out by means of vibrating contact points in series with the field part of the 3 unit control system
Aircraft wires
must use only wire specifically designed for aircraft use Normally is stranded stranded wire is more flexible and less susceptible to fatigue usually, copper coated with tin-silver or nickel to prevent oxidation
Bending wires ,minimum Bending radius
one and Single wire is 3 times the wire diameter or 6 times preferred wire bundles must not be less 10 times the diameter of the large wire or cable in the bundle
Solid state Voltage regulator
other name is transistorized type(early version had a set of points but the did not carry the main load. a transistor (electric control valve) controls current o the field. intermittent resistance or ground types most common type used today on light aircraft no moving part or point to ''wear out''
Shunt Wound DC Generator (continue)
shunt-wound generators are always used in conjunction with a voltage regulator and are the most common type for general aviation the voltage regulator will hold the generator output voltage constant but the ampere output(current produced by the generator)will increase, as the generator load is increased
Strength of Magnetic Field of generator
the Only practical way to regulated the generator voltage is to Vary the strengths of the Field
Varying the strength of the field
the output voltage of the dc generator is controlled by varying the strength of the generator stationary field the voltage regulator controls the amount of current flowing to the field coil through the use of variable or intermittent resistor.
Commutator functions 3
the system of changing the alternating current of the armature to direct current in the external circuit is called commutator commutation
Series Wound dc generator when the load is increase the voltage____________ ______________ when the load is decrease_________________________
the voltage increase. the voltage decrease.
Capacitor
two conductor that is capable of Holding electric charge & are separated bu an insulating medium (dielectric) measured in Farads, microfarads or picofarads
COUNTER EMF Disadvantages
unable to maintain full output at low rpm used on turbine aircraft that sustain hight rpm
AC alternator advantage 1
used most often on Large commercial airlines because large aircraft require a large amount of electrical power advantage of alternating current over direct current is the voltage and current can easily be speppep up or down
DC Alternators
used most often on light aircraft with a small electrical load
Double cord lacing
used on wire bundles of 1'' inch diameter or larger always start with a Bowline on a bight
Potentiometer
used to vary the value of the voltage in a circuit comparatively Hight resistance normally connect with 3 terminal
