elect iii sem notes

8/10/2019 Elect III Sem Notes

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DDIIFFFFEERREENNCCEEBBEETTEEWWEEEENNPPRRIIMMAARRYYAANNDDSSEECCOONNDDAARRYYCCEELLLLSS::

PPRRIIMMAARRYYCCEELLLLSS SSEECCOONNDDAARRYYCCEELLLLSS

Not rechargeable. Rechargeable.

Irreversible chemical action. Reversible chemical action.

Compact in size. Large in size.

Less weight. More weight.

Low power rate. High power rate.

Less efficient. More efficient.

Low cost. High cost.

Needs no maintenance. Needs maintenance.

Used for intermittent loads Used for continuous loads.

Cant carry large currents Can carry large currents.

PPRREECCAAUUTTIIOONNSSWWHHIILLEEHHAANNDDLLIINNGGAAIIRRCCRRAAFFTTBBAATTTTEERRYY::

Wear safety glasses;

Remove negative lead first and install it last;

Do not cause short circuit between the terminals;

Do not wear wrist watches and other ornaments / jeweler while working with battery;

Never service the battery near open flame or near sparks;

Never jump start the aircraft from another power source when the aircraft battery is

discharged;Charge batteries in a well ventilated area;

Turn OFF the battery charger before making connections between battery and the

charger;

Check the vent caps of each cells.

RREEQQUUIIRREEMMEENNTTSSOOFFAAIIRRCCRRAAFFTTBBAATTTTEERRYYSSYYSSTTEEMM::

High output to weight ratio;

Less in size;

Less in weight;Non-corrosive nature;

Compact installation facility;

Easier maintenance;

Easier ways for troubleshooting;


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CCAARREEAANNDDMMAAIINNTTEENNAANNCCEEOOFFAAIIRRCCRRAAFFTTBBAATTTTEERRIIEESS::

Inspect the battery case for cracks, distortion and other damage;

Inspect the battery case for electrolyte leakage;

Inspect the vent system for any block and clear for free airflow;

Inspect the cells and clean as required;

Inspect the cell connectors for any loose connection, corrosion, cracks etc.

Always store a battery in a well ventilated area and in a fully charged condition;

Store batteries within the recommended temperature levels.

PPRREECCAAUUTTIIOONNSSWWHHIILLEECCHHAARRGGIINNGGAABBAATTTTEERRYY::

Always charge batteries in a well ventilated area. Use of exhaust system for charging

room is recommended;

Always turn OFF the battery charger before making connections between battery and

the charger;

Remove negative lead first and install it last;

Make sure the caps of each cell of the battery is vented and clean;

Ensure there is no spillage of electrolyte.

Remove the battery from the aircraft prior to charging.

BBAATTTTEERRYYCCOOMMPPAARRTTMMEENNTT::Should be easily accessible so that battery can be serviced and inspected regularly;

Should be away from fuel, oil and ignition areas;

Effective ventilation system should be there;

Drain areas should be cleaned well;

Check the strength of battery compartment and security of mounting bolts;

Check the anti-corrosive protective paint film.

The battery compartment to be near to the Bus bars.

IINNSSTTAALLLLAATTIIOONNPPRROOCCEEDDUURREEAANNDDPPRREECCAAUUTTIIOONNSS::

Perform thorough battery inspection prior to installation;

Check the electrolyte level;Inspect the battery quick disconnect plug for corrosion, pitting, looseness etc.;

Perform ventilation checks;

Connect temperature monitors and watch for any abnormal conditions.

Ensure vent caps or screws are tightened.

Fit the battery into the respective compartment and ensure the tightness and security

of mountings and attachments.

Connect the battery connector and push the respective circuit breakers.

Carry out FOD checks in the battery compartment.

Perform load test for 10 mins. With 20% loads and the voltage should not be dropped

less than 22V if it is 24 volt system.

BBAATTTTEERRYYCCAABBLLEE::Should be strong enough to withstand flow of heavy current at anytime and for a

longer period without fail;

Should be well protected and routed away from hot zones (engine areas);

Should be securely clamped to avoid vibration and swinging here and there;

Should be securely attached to the terminals.


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Constant Current charging

It supply a constant current to a battery for the entire charging cycle. This equipment monitors

current flow and varies the applied voltage in order to charge the battery . As the battery begins to

charge, its voltage is lower than when the battery becomes fully charged. The batteries are

connected in series with respect to each other and the charger thus allowing for a constant current

flow through each battery.

Constant voltage charger :

This charging equipment supplies a constant voltages to the battery and allow current to change as

the battery becomes charged. When the battery is fully charged, its voltage will be equal to the

charger voltage hence the current will cease to flow. If more than one batteries are connected to the

charger. The battery and the charger are connected parallel.

Rotary Inverter :

Principle : The rotary inverter is a combination of DC motor and AC alternator. Both are mounted in

the same shaft. When DC is given as a input the motor will drive the AC generator and produces AC

as per the construction.

End Frame : It support the armature bearing and mounted at the end of field frame.

Shaft : Where the armature is accommodated.

Bearing : It helps to get a smooth rotation of armature shaft.

Armature Slots: To protect the armature conductors against the centrifugal force and ensure the

security of the conductors. Also reduces the air gap between the armature and the field frame in

turn reduces the reluctance path.

Armature conductors : It conducts the current and help to set up a magnetic field around armature.

Commutator : It acts as a reversing switch which reverses the polarity of the armature before thearmature aligns to the main field. The process of converting AC into DC is called commutation.

Yoke : Finishing part of a rotary inverter.

Brush assembly : It consists of Brush holder, brushes, brush springs, brush pigtails.

End bearing : The smooth rotation of a shaft.

Slip rings : Collecting point of AC supply from the AC generator.

Static Invertor :

A static or solid state inverter serves the same function as other invertor. However it has no moving

parts and less maintenance when compare to rotary invertor.

The internal Circuit of a static invertor contains standard electric and electronic component, such as

crystal diode, transducer, capacitor and transformer. By means of an oscillator circuit, the invertor

develops the 400 Hz for which it is designed. The current is passed through the transformer and

filtered to produce the proper wave shape and voltage. The unit utilizes an Input voltage of 18-30V

DC and produce an output of 115 V single or three phase AC. Static invertor are easily removed for


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testing. If they require repair they should be sent to an approved agency. Because of

miniaturisation of electronic component static invertor have become relatively small and light in

weight.

Advantages of Static invertor over rotary invertor:

1.

Smaller and compact in size.

2.

Less in weight.

3.

Occupies less space.

4.

More efficient and reliable.

5. Easy installation and access.

6. No moving parts and requires less maintenance.

7.

Easy for trouble shooting.

Inspection & tests of Invertor :

1.

Visual inspection : Brush assembly, Commutator, Cooling system and armature shaft and

armature assembly.

2.

The brush should be checked for frequent intervals. Check for cracks, faces damaged,

condition of pigtails and its length.3.

Brush holder and the spring tension to be checked as per the manufacturer manual.

4. Performance test.

5. Mechanical test.

6.

Insulation resistance test : all the rotary parts and stator parts not less than 20 M ohms.

Series motors :

i)

The field coils are connected in series with armature.

ii)

High starting torque.

iii)

Heavy starting current.iv)

Can be started with load only otherwise it will burn.

v) Used on engine starter motor and landing gear etc.

Shunt Motor :

i)

The field coils are connected parallel to the armature.

ii)

Low starting torque.

iii)

Low starting current.

iv)

Constant speed at fluctuating load.

v)

Used in centrifugal pump, electric fan, and rotary invertor.

Compound Motor :i) It is a combination of series and shunt wound.

ii)

High starting torque.

iii)

Heavy starting torque.

iv)

Constant speed at fluctuating load.

v)

Used in hydraulic pump.


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Induction Motor :

The induction motor has a wide variety of applications because of its operating characteristics. It

does not require special starting devices or excitation from an auxiliary sources and will handle wide

range of loads. It is adaptable to almost all loads when an exact and constant speed is not required.

The stator windings are placed in these slots in a manner similar to the placement of the winding of

a DC armature. The rotor in an induction motor consists of a laminated iron core in which are placed

longitudinal conductors. In a squirrel cage rotor these conductors are usually copper bars connected

together at the ends by rings. When this assembly is placed in the rotating field by the stator, a

current is induced in the conductors. Since the conductors are short circuited there is a flow of

current from those on one side of the rotor through the rings at the ends of the rotor, to t he

conductors on the other side. If the rotor field came into line with the stator field, there would be

no torque. The percentage of difference between the speeds of the stator and rotor fields is called

the Slip.

Heavy Starting current : On starting the rotor is stationary slip is 100%. And max is induced in rotor,

so that resistance of rotor conductor is low. A heavy current flows producing a magnetic flux which

opposes and weakens the stator flux. As in the transformer, the self induced or back emf in statorwinding is reduced and a heavy current is taken from mains.

Poor starting torque: On starting the voltage of rotor same as supply voltage. At this frequency the

reactance of inductive motor is high causing the rotor current to lag behind rotor emf. Which in

phase with the stator flux. Thus the relative position of the instantaneous rotor and the stator field

are such that there is little interaction between them and although the starting current is high the

starting torque is poor. So that induction motor is not started on load.

Speed and Load : When a load is applied the rotor slow down by amount which will allow sufficient

torque to be developed to drive the applied load due to low resistance of rotor a small change in

induced emf causes full speed load current to flow in rotor conductor and by transformer action , a

corresponding greater current to be taken from supply. The fall in speed between no load and fullload is small and speed characteristics similar to DC shunt motor. So that motor is considered as

constant speed machine.

Synchronous Motor: Synchronous motor as the name implies rotate at a speed of syhchronise with

applied AC. A 3 phase synchronous motor has three separate winding in stator and produce a

rotating field like stator of induction motor. The magnet is free to turn and is placed in a rotating

field, it will align itself with the field and rotate at same speed.

Characteristics : When operating with in load limit a synchronous motor will rotate at the same

speed as alternator supplying to the current provided alternator has same no of poles as motor.

Speed of synchronous motor depends on voltage of current supply.

Principles type of motors : Universal motors, Induction motors, and synchronous motors.

Universal motor : As the name implies it works on both AC and DC. Therefore the direction of

current flow and armature change simultaneously when AC is supplied to motor torque continuous

in same direction at all times. For this reason motor will turn steadily in one direction regardless of

type of current applied. Universal motor not used in Aircraft electrical system because the AC has a

frequency of 400 Hz and at this frequency very substantive energy loss occur in motor.


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Counter EMF : The conductor in the armature are cutting across a magnetic field when armature is

moving in it. Hence an emf is induced in the conductor and this emf opposes the current being

applied to armature from outside. This induced voltage is called counter EMF. Produced by the

armature conductors.

Net EMF : It is the difference between the applied EMF and Counter EMF. Due to back emf electric

motor is self governing. The speed and current consumption automatically adjusting to mechanical

load. Counter EMF determines the efficiency of motor as an efficient motor have very high net EMF.

Losses of Motors:

1.

Friction Loss : The power used to overcome the friction of bearing.

2.

Windage Loss : The loss due to wind friction.

3.

Copper or Resistance loss : The power used to overcome the resistance of windings.

4.

Eddy current loss : The current induced in armature core and field pole and are responsible

for los in form of heat.

5.

Hysteresis Loss : When a material is magnetized in one direction and then in other has rapid

succession. The effect of hysteresis is to cause the change in strength of the magnetic flux tolag behind the magnetizing force and is due to friction between molecule of material as they

are shifted in direction by magnetizing force.

General inspection of Motors while installing :

1.

Inspect the terminal connection to see that they are clean and tight.

2.

Inspect the flange mounting for crack or looseness of mounting bolt.

3.

Remove the cap or band that covers the brushes and commutator. Blow out with ram to

remove the carbon dust.

4.

Inspect the commutator for cleanliness, wear and pitting.

5.

Always inspect the mounting of motor to aircraft.6.

See that the mounting area is free from FOD. Install the correct type of gasket if it is

required.

7.

Be careful not to cause damage when moving the motor in to original place.

8.

Tighten screw or hold down bolts evenly and with the correct torque.

9.

See that the electrical routings and connections are clean and tighten them.

Stripping of Motors :

1.

Use the proper tool for each operation.

2.

Mark and lay out the parts in an order that will aid in assembling.

3.

Do not use excessive force in any operation . If parts are struck, determine the cause. If

necessary use a soft method to disengage parts.4. When bearings are pressed on a shaft or when they are struck because of corrosion, use a

bearing pulley for removal.

5.

Use the extractor for the removal and installation of bearing and clean them.

6.

Keep all parts of an assembly clean. The work bench should be free from dirt and grease.


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Testing of Motors :

1.

A growler is used to test armature for shorted or open circuit.

2.

An ohmmeter or continuity tester is used to test for ground between the armature winding

and the core.

3.

Field coils can be tested with an ohmmeter or a continuity tester for open circuit, short circuit

and ground.

4.

Testing of armature is done with a device called growler. This device consist of many turns of

wire wound around a laminated core with two heavy pole shoes extended upward to form a

voltage into to which an armature can be placed.

5. By connecting a test meter between segment of commutator and the armature on the

growler it can be determined whether an open circuit exist in a coil . To test for the ground

between the winding and the core of the armature an ohmmeter can be used. To test for the

field coil for continuity the probes of ohmmeter are connected to the terminal of the coil.

Equalising circuit : When two or more generator are connected parallel to a power system the

generator should share the load equally. If the voltage of one generator is slightly higher that that of

the other generator in parallel that generator will assume the greater part of load. For this reason an

equilising circuit is used that will cause the load to be distributed evenly among the generator. Anequilising circuit include an equalising coil with the voltage coil in each of the voltage regulator. An

equilising bus to which all equilising circuit are connected and a low resistance shunt in the ground

lead of each generator.

Reverse current cut out relay : It consist of a voltage coil around current coil wound on same soft

iron core.. The voltage Coil is connected parallel to generator output of one end of voltage winding

is connected to the positive side of generator output and other end of winding to the ground which

isve side of generator output. The current coil is connected in series with generator output hence

it will be carry the entire load current. A pair of heavy contact point is placed where it will be

controlled by magnetic field of soft iron core. When generator is not operating these pins are heldin open position by spring.

When generator voltage reach a value slight by above battery voltage. The voltage coil in the

relay magnetized the soft iron core to over come the spring tension. The magnetic field closes the

contact points and thus connect the generator to electrical system of air plane. As long as generator

voltage remains higher than battery voltage, the current flow through the current coil will be in a

direction that aids voltage coil in keeping the point closed. This means that the field of current coil

will be in the same direction as the magnetic field of the voltage coil and that the two will

strengthen each other.

When an airplane engine is slow down or stopped, the generator voltage will decrease and

fall below that of the battery. In this case the battery voltage will cause current to start flowing

forward towards the generator through relay current coil. When this happens the direction ofcurrent flow is such that it create a field opposing the field of voltage winding. This result in

weakening of total field of relay and contact points are opened by spring thus disconnecting

generator from battery.


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AARRMMAATTUURREERREEAACCTTIIOONNAANNDDIITTSSEELLIIMMIINNAATTIIOONN::

Since armature consists of coils of wire wound on it, when current flows through these coils a

magnetic field is induced at right angles to the field causing cross-magnetization of armature. This

distorts the generator field and shifts the neutral plane from GNA to MNA. This is called armature

reaction.

This weakens the leading edge of the poles and strenghthens the trailing edge of the polescausing a considerable lossin the production. This can be eliminated by the following methods;

Introducing inter-poles:

Maintains constant neutral plane;

Its windings are in series with the load;

Its polarity is such that it opposes the armature field.

Introducing compensatory windings:

Has conductors embedded within field poles;

Connected in series with inter-pole windings. This increases its effectiveness;

Faces with one coil sorrounding sections of two fields of opposite polarity.

IINNSSPPEECCTTIIOONNPPOOIINNTTSSFFOORRDDCCGGEENNEERRAATTOORRSS::

Inspect the generator terminal for its cleanliness and tightness;

Inspect the flange mounting for cracks, looseness of bolts etc.;

Remove end cap and blow out carbon dust accumulation from brushes;

Check the spring tension;

Check the brush for cracks, broken edges etc.;

Ensure the brush length is within permissible limits;

Inspect the commutator for wear and cleanliness. If carbon sedimentation is there

clean it with sand paper.

Installation procedure :

1.

There are two basic types of installation they are direct g ear and belt driven.

2.

To install a gear driven generator remove the mounting pad cover and install proper gasket

over stud.

3.

Fit the generator spline or gear into place. Connect generator cable to proper terminal. See

that all connection are clean and tight.

4. If the generator employ direct for cooling. It should be connected properly to avoid

possibility of it coming loose during operation.

5.

To install a belt driven generator mount the unit appropriate location and install allhardware. Then place the drive belts over the aircraft and generator drive pulley. Once the

belt is in proper location, position the generator to tighten the drive belt and secure all

hardware and safety equipment.


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CCHHAARREECCTTEERRIISSTTIICCSSOOFFDDIIFFFFEERREENNTTTTYYPPEESSOOFFDDCCGGEENNEERRAATTOORRSS

Shunt Wound Generator :

Field coils in parallel to armature;

Needs some regulation methods;

Always needs a load coupled;

Constant speed and constant Output voltage.

Suitable for aircraft use.

Series Wound :

Field coils in series with armature;

Load controls field current;

Cant maintain constant voltage output;

Can be used where constant rpm and load is applied.

Compound Wound :

Combination of both shunt and series wound field coils;

Output voltage remains constant;

A voltage regulator is used.

AARRMMAATTUURREEAASSSSEEMMBBLLYY::

Has a laminated soft iron core on a steel shaft; this laminated type is used for reducing

Eddy current;

This core has slots through which the armature coils are wound;

Between the core and the coils, an insulating paper is put to avoid contact between

them;

These coils are insulated from each other and are held firmly by a cir-clip at both the

ends; Finally the coils are coated with insulating varnish;Commutator or slip-rings are placed at the end of the assembly;

The ends of the coil loop is connected to the commutator segments, which are at 1800

opposite;

The entire armature assembly is supported by two sealed bearings each at one end

frame.

FFIIEELLDDFFRRAAMMEEAASSSSEEMMBBLLYY::

Heavy iron or steel housing that supports the field poles;

Has field pole shoes, field coils, and compensating poles;

Provides coupling point for end frames;

In brushless alternators, these provide the terminal points for taking the output

power.


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GGEEAARRDDRRIIVVEENNDDCCGGEENNEERRAATTOORRSS::

The gear assembly uses only one driven gear mechanism. This need not to be engaged or

disengaged from engine drive gear while changing the configuration [i.e. Generator to Motor and

vice-versa]. This mechanism is most commonly used in turbo prop engines and wherever starter-

generator is employed.

AADDVVAANNTTAAGGEESSOOFFPPOOLLYY--PPHHAASSEEPPOOWWEERROOVVEERRSSIINNGGLLEE--PPHHAAZZEEPPOOWWEERR::

High output to weight ratio, because one three phase power can provide two different

voltages [phase to neutral and phase to phase].

Easy to maintain;

Less no. of cable requirement;

Reduction in generator number to be used;

Does not require heavy equipment for phase convertion.

DDCCAALLTTEERRNNAATTOORRAANNDDIITTSSOOPPEERRAATTIIOONN::

A DC alternator works on the same principle as of a motor i.e magnetism and the

electromagnetic induction. It provides DC power at the output. Its construction is same as that of an

AC alternator, but the only difference is, it contains six [6] diodes before the output terminal, three

[3] each for one terminal to convert the produced AC power into a DC power.

DDIISSAADDVVAANNTTAAGGEESSOOFFRROOTTAATTIINNGGAARRMMAATTUURREE::

Less efficiency;

Low power output;Higher maintenance;

Considerable loss due to rubbing contact between sliprings and brushes;

Low speed of rotation;

Rotor coils are subjected to heavy centrifugal force.

IINNSSPPEECCTTIIOONNPPOOIINNTTSSFFOORRAACCAALLTTEERRNNAATTOORR::

Check for proper mounting by shaking the alternator;

Check the condition of flange mounting;

Check the QAD coupling for proper tightness;

Check the terminals for clenliness;

Check the terminal connector for corroion, damage, looseness etc.Remove the end caps and remove all carbon dust by blowing dry air into the

alternator.

AADDVVAANNTTAAGGEESSOOFFRROOTTAATTIINNGGFFIIEELLDD::

High efficiency;


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Less maintenance;

High rotating speed;

Greater output power;

No rubbing contacts between sliprings and brushes, so loss is minimised.

VVIIBBRRAATTOORRTTYYPPEEVVOOLLTTAAGGEERREEGGUULLAATTOORR::

A voltage regulator is a device or circuit that maintains a constant output voltage supplydespite changes in input voltage or load.

A resistance that is intermittently cut in and out of the field circuit by means of vibrating

contact points is placed in series with the field circuit. The contact points are controlled by a voltage

coil connected in parallel with the generator output. When the generator voltage rises to a desired

value, the voltage coil produces a magnetic field strong enough to open the contact points. When

the points are open, the field current must pass through the resistance. This causes a substantial

reduction in field current, with the result that the magnetic field in the generator is weakened. The

generator voltage then drops immediately, causing the voltage coil electromagnet to loose its

strength so that a spring can close the contact points. This allows the generator voltage to rise, and

the cycle continues.

The contact points open and close many times a second., but the actual time that they are

open depends on the load being carried by the generator and the generator [engine] rpm. As the

generator load is increased, the time that the contact points remain closed increases, and the time

that they are open decreases. Adjustment of the generator voltage is made by increasing or

decreasing the spring tension that controls the contact points.

CCAARRBBOONNPPIILLEEVVOOLLTTAAGGEERREEGGUULLAATTOORR::


12/16

Derives its name from the point that the regulating element has a stack or pile of Carbon

disks. This usually has a hard carbon disk and a soft carbon disk alternatively, in a ceramic tube with

carbon or metal contact plug at the each end. One end actually has a radically arranged leaf spring to

exert pressure against contact plug.

Works on the principle that when pressure on carbon pile is reduced then the resistance to

flow of current through it will increase and vice-versa. By placing an electromagnet in a position,

where it can release the spring pressure on the disks, whenever voltage rise is there above a normalpreset value, efficient regulation is obtained.

The carbon pile resistance will be in series with the field current and this in turn is connected

parallel to the generator output power. A manually operated rheostat is connected in series with the

voltage coil i.e the electromagnet and in turn these are shunted across the generator output. This

rheostat is to provide a small amount of adjustment, which is necessary when two or more

generators are in parallel operation in the same electrical system.

SSOOLLIIDDSSTTAATTEEVVOOLLTTAAGGEERREEGGUULLAATTOORR[[TTRRAANNSSIISSTTOORRIIZZEEDD]]::


13/16

Solid state voltage regulator consists of a field relay that supplies current to the transistor.

The transistor controls the current to the field. Solid state voltage regulator has no moving parts.

Transistorised voltage Regulator : The two point that take part in the operation of transistor used

voltage regulator are the zener diode operation and control of power transistor by control transistor.The zener diode can be compared to relief valve. Where zener diode conduct current it causes the

control transistor to shut off power transistor. When the emitter collector circuit of control

transistor begin to conduct, there is no appreciable voltage drop across control transistor hence a 1V

reverse bias become effective across the emitter base circuit of power transistor.

Alternator voltage output is adjusted through a variable resistor. A change in resistance of this

resistor will change the voltage level across the zener diode thus raising or lowering the level of

alternator output voltage required to cause diode to conduct.

There is a resistor which is temperature resistance type and it act to increase the alternator voltage

slightly at a lower temperature. Many modern voltage regulator use alternator control unit and it

maintain the system voltage between 28.4 28.9 volts.


14/16

Electrical conduit : It consist of thin walled aluminum tubing braded metal tubing called flexible

conduit and a non metallic tubing. The purpose of conduit is to provide mechanical protection and

metal conduit is often used as a mean of shielding electrical wiring to prevent radio interference.

Aluminum conduit is of two type i.e bare and rubber covered type. The size of conduit should be

such that the inside diameter is about 25%. Larger than the largest diameter of cable bundle. When

conduit is being cut and prepared all edges and holes should be deburred to assure a smooth surface

that will not damage the cable.

It should be securely attached to the structure with metal clamps so there can be no movement or

vibration. Drain point must be provided at the lowest point in any conduit run. Flexible conduit

cannot be bent as sharply as rigid conduit. Before a wire or cable bundle is placed in a conduit the

bundle should be liberally sprinkled with talc.

Typical terminal used in aircraft wire or cable : Usually crimp type terminal are used on aircraft

cables or wire. It consist of two metal sleeve, one sleeve is part of electrical terminal and is crimped

to copper conductor. The second is a thin metal sleeve surrounded by terminals insulation covering.

This sleeve is used to crimp the wires insulation. When the wires insulation is secured with a second

crimped sleeve the vibration stress is transmitted into wire insulation. This reduces the stress andfatigue failure of wires conductor. Ensure that terminal is crimped twice once to secure conductor

and other to secure insulation.

Proper method of soldering :

1.

Component terminal and leads, as well as the ends of and individual jumper lead should be

cleaned and tinned prior to making the final solder joint.

2.

The soldering iron bit should be cleaned by wiping it on a damp joining and fresh solder

should be applied between each joining operation.

3.

The soldering iron bit should be applied to appropriate joint area until that tinning solder

reflow to make the joint.

4.

After joint has been made by initial reflow, the soldering iron b it should be held in position

and additional solder should be applied to the heater member of the joint until it has

sufficiently provides uniform filling filter around the joint members.

5.

Joint should be permitted to cool without relative movement between joint members.

6.

Flex residual should be removed from solder joints and surrounding area after soldering

operation.

Installation wiring of junction Box : Electrical wiring inside a junction box should be laced or

clamped in such a manner that terminals are not hidden the operation of equipment is not

hampered and motion between wire and equipment is permitted. The opening through which wire

bundle enter the box must be provided with clamps or grommet. So that insulation on the wirecannot be become worn or otherwise damage.

Procedure for soldering wires to connector : In a soldered type connector, at the end of pin or socket

there is a small solder pocket. A short section of insulation is removed from wire and the bare

stranded wire is then inserted in the pocket with the wire in the pocket, Rosin care type solder is

applied to the pocket as it is heated with soldering iron or soldering gun. As soon as the solder

moves smoothly in to the pocket and penetrate the wire the soldering should be removed to avoid


15/16

the possibility of burning the insulation of either the wire being soldered or adjacent wire only in a

solder should be applied to full the pocket and all small drop of solder should be removed from

between the pins. After each pin is soldered a plastic sleeve insulator should be pushed down over

the solder joint and metal pin to prevent the possibility of short circuiting. The insulating sleeve

should be lied or clamped to prevent them from slipping of the pin.

Installation of pins and sockets in crimp type connectors :

1.

Install the pin or socket in to the crimp tool with the wire barrel facing up.

2.

Remove the correct length of insulation from the wire using appropriate method.

3. Install the stripped portion of the wire into the connector barrel and compress the connector

by squeezing the tool handle together. The tool will release the contact when the crimping

process has been completed, if the contact not released, the crimp cycle has not been

completed and then contact must compressed further.

4.

Inspect the finished crimp through the inspection hole in the contact. The wire must be

visible, if it is not the crimp must be redone using new contact.

5.

Install the contact in to the connector housing using appropriate tool. Make sure that the

contact is installed completely and reaches the firm slop inside the connector housing .

There are two methods commonly used to install a contact into connector housing. The first one is

front release and the other is rear release.

Procedure for installing bonding jumpers : Care must be taken so that bonding jumper do not

interfere with the operation of any movable parts of the aircraft and so that the normal movement

of such part does not result in damage to the bonding jumper.

When bonding jumper are installed it is important that all insulating coating, such as anodizing,

paint, oxides and grease be removed so that clean bare metal surface come into contact. After the

bonding is secured it is good practice to coat the junction with a sealing coating to prevent the

entrance of moisture, which would produce corrosion at a bonding connection if adequateprecautions are not taken.

A bonding jumper is short length of metal braid or strip with a terminal at each end for attaching to

the structure. The jumper should be as shortest as possible and installed in such a manner

resistance of each connection does not exceed 0.003 ohms. They should be installed in position that

provides reasonably easy access for inspection and maintenance.

Purpose of bonding in aircraft :

1.

It provides low resistance path for electrical equipment there by eliminating ground wire to

reduce radio interference.

2.

To decrease lightning damage to the aircraft.

3.

To prevent the build up of static charges between the parts of structure thus reducing firehazard that could result from spark discharge between these parts.


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Advantage of Crimping over soldering :

Soldered connections :

1.

The flux used for soldering is corrosive in nature and weakens connection with time.

2.

Errors such as too much heat, too much solder, not enough heat and lack of connection

cleanliness or difficult to eliminate.

3.

Gold plated contact can be destroyed by soldering process.

4.

Soldered wicking in to the wire strand can create additional stress in wire.

Crimped connections :

1. The use of appropriate tool eliminate the chance of human error.

2. No corrosive flux is used.

3.

Gold plated contact are completely compatible with crimping process.

4.

The connection is easily inspected prior to pin installation.

5.

Field repair can b e performed more easily, and with less error than the repair of solder

connection.

Wiring and schematic diagram : During design, manufacture and repair of electrical system. It is

imperative to understand various current path and type of wire being used in such system. For thispurpose electrical diagram and schematic diagram are included in the maintenance and installation

data for the aircraft electrical system. The schematics, uses various symbols to represent different

type of wires and connections within a circuit. Schematic can be thought of as road map that helps

technician to find their way around an electric circuit. In some cases wire identification number are

also included on those electrical schematic.

elect iii sem notes

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