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THE KERALA ELECTRICAL AND ALLIED ENGINEERING CO. LTD

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INTRODUCTION The Kerala Electrical and Allied Engineering Co. Ltd, popularly known as KEL was established in 1964 in the state of Kerala, India and is fully owned by the state govt: As a company engaged in multi various activities, they have gradually broadened our manufacturing base strategically to reach domestic and overseas market. With a manpower base of 1500, which includes more than 250 highly qualified and well trained professional engineers, they are one of the biggest public sector companies in the state. The company has four manufacturing units loaded in various districts of the state. KUNDARA UNIT, KOLLAM DISTRICT INCEPTION: 1964 1. Statodyne Alternator Division Manufactures stat dyne brushless alternator The alternator is used for lighting and air-conditioning of Railway coaches. More than 25,000alternators are in service with the Indian railway alone. 2. Foundary Division Manufactures Spherical Graphite iron and Grey iron Castings. The foundry has capacity of 1500 MT per annum. It has fully mechanized moldings lines with sophisticated testing equipment to ensure quality casting. 3. Charging system division Manufactures brushless alternators for automobile charging system. The product has been developed through the company’s own R&D efforts. The alternator caters to the high power needs of modem vehicles and heavy earth moving equipment. It offers long Ve and maintenance free operation.

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FABRICATION FABRICATION OF STATOR FRAME

The alternator stator frame is made of mild steel. The body is not cast because it increases the brittleness. It is constructed by basically rolling steel sheets. The plate sizes are according to requirement . They are dimensioned, cut and welded. The type cut depends on the thickness of the plate. It is cut using a gas cutter, usually using a double V joint, after which a driller is used to punch it. To get perfect circle, before rolling, the sheet is subjected to prebending in hydraulic press. Different tests for checking the quality are then conducted. Some of the tests conducted are . X - Ray test . Radiography . Die- penetrate test The purpose conducting these tests is to check for cavities and cracks. Before doing any test the surface should be made smooth by grinding and finishing. For example, in the Die penetrate test, at first a cleaner is sprayed and the surface is cleaned with cotton. Then a color is sprayed to see the cracks clearly. After this a developer is used to make the cracks, if any, to be seen more clearly. After the test is conducted, the various accessories like the tension lag and lead box are provided the frame. A suspension pin =, which is the hanging unit, is also provided so as to support the alternator. Fines are provided on the outer frame to facilitate air-cooling. There is a regulator rectifier unit by means of which the output of the machines kept constant always even if the speed of the train varies, due to which the input to the machine changes.

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MACHINE SHOP The section deals with the following production processes: 1) Insertion of stator stampings in to fabricated outer frame 2) Assembly of rotor 3) Fabrication of pulleys These processes are explained in detail STATOR FRAME Based on the shelf number, the stator diameter is fixed. the inner diameter corrected to accommodate the windings. Consider a 25 KW alternator. The unite obtained from fabrication is of 249 mm diameter, which is corrected to 255 mm only 52 micron variation is permitted. After this, it goes to stacking and pressing equipment. Here silicon steel laminations are stacked on one another as shown in diagram. Fiber laminations are fixed on to the circular clips to prevent loss of insulation. This is then compressed under a pressure of 6 kg/cm to press it. A guiding ring is used to prevent twisting. Thus the following processes are carried out on the stator frame:  Boring  Drilling  Slotting  Stacking of Laminations  Filling The stator frame is now passed on to the winding section

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TESTING OF COMPONENT 1. TESTING OF COPPER WIRE

A) PEEL TEST A specimen of wire about 600 mm length shall be placed in a key the apparatus consisting of two fixing devices 500 mm apart in the same axis. One of there is able to rotate and other cannot rotate, but can displace axially. The later is loaded according to the table to apply tension to the rotating wire. Nominal diameter of the

Load

No. of revolutions

conductor 1.18

2.85

93

1.25

2.5

88

1.40

2.5

78

1.60

4

68

b) DIMENSIONAL CHECK 1.5 m length of wire shall be taken from the reel 1) Two pieces of 250 mm long wire shall be the cut from both ends. 2) The diameter of enameled conductor shall be measured using a micro meter at three position are 1200 angular displacement around the circumference of wire. The average of 6 measurements shall be reported as over all diameters. The enamel shall be from a length of 60 mm of wire by exposing it to flame till it come red-hot. Then dip is in ethanol. The wire shall be cleaned using a piece of cotton. The diameter of the bare copper wire shall be measured as above the and their average is the bare copper diameter. The difference between the overall diameter and the base

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Conductor diameter shall be found and the overall diameter conductor and increasing diameter shall be according to able. Nominal

Max

overall Base Max

conductor

diameter(mm)

Cu dia Min

Insulator Thickness

Diameter

Max

(mm) 0.417

0.466

0.422

0.412

0.022

0.9

0.989

0.909

0.891

0.060

1.00

1.094

1.010

0.990

0.063

1.18

1.279

1.192

1.168

0.067

1.25

1.349

1.263

1.2370

0.067

1.40

1,502

1.414

1.386

0.069

1.50

1.606

1.515

1.485

0.071

c) SPRINGNES TEST

METHOD OF TEST: A sample of about in shall be wound 5 times around the manned with a diameter as given the table three. TEST APPARATUS: the general arrangements of the apparatus is shown figure. The dial is marked with 72 equally spaced divisions. So that the spring aback for one turn is read directly in degree. The apparatus shall be maintained twit the shaft of the mandrill horizontal. The specified mandrill shall be locked in position so that the hole form fastening the wire and the commencement of a the helical grove is a vertical position to correspond with zero on the dial and shall then be dusted with finally powdered talc to avoid danger of the annealed wire dinging to the surface of the mended. The specified weight is attached to one end of the sample of wire and after unlatching the meandered so that it will rotate freely the other and of the wire is inserted through the transfers hole in the mandrill at the commencement of the helical grove so that sufficient wire project on the other side of the mandrill. This end of the Dept.of.EEE

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wire is hold firmly and the weight is carefully lowed to apply tension the sample. The mandrill is thus aligned with the dial zero vertically downwards.

2) TESTING OF LAMINATION a) CORE LOSS MEASURMENT The core loss shall be measured using lamination tester the value shall be as given below. The tolerance on the measured core loss shale is 0.5 watts. Material Grade CRNGO

Core loss

M-36

3.57

M-43

4.01

M-45

5.31

M-47

8.01

The tested components are passed on to winding section

Nominal dia of the

Mandrel dia(mm)

Tension (kg)

Spring back(max)

0.417

25

0.8

44

0.90

50

1.53

48

0.95

50

1.53

46

1.00

50

1.53

45

1.12

50

1.53

41

1.18

50

1.53

39

1.25

50

1.53

37

conductor

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WINDING

The KEL brushless alternator does not have a rotor winding. However the basic principal of alternator does not change. The emf is produced by change in flux. The difference with the conventional alternator lies in the method in which this alternating flux is produced. The alternator consisting of two winding. Normally AC winding and field winding. Both accommodated in the stator. The AC winding is distributed in the small slots and field windings are concentrated in to slots. Each field span half the total number of stator slots AC coils are connected in star and field coils connected in series. Rotor consisting of stacked stamping resembles a cogged wheel having eights seat of teeth and slots, uniformly distributed on the rotor surface skewing the rotor axis. The core of the stator which is completely embraced by the field coils will retina a residual magnetism is excited by a battery once, the flux produced by the field coils finds its path through the rotor when the rotor is rotated the passenger of rotor teeth and slots alternatively under the fields offers a varying reluctance path for the flux produced by the field coils. CONSTRUCTION AC winding is accommodated is in the slots in the stator. The slots are insulated using imported Nomex paper. It has very high dielectric strength. The stator has 36 slots divided symmetrically in to two about the horizontal axis two diametrically gaps each equal to 6 slots called cut in space, are proved on either side of the stator frame. This is to support the field coils. The core of testator is completely embraced by the field coils. A winding catcher or pole shoe, made of aluminum, is used for supporting the field coils. Aluminum is used because no magnetisms should be produced with the catcher.

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VARNISHING This is a trivial section of the manufacturing process. The stator frame when the winding shop is given to the varnishing section. Here at first the varnish is mixed, and then its viscosity is checked after that preheated stator frames are transferred to a chamber, inside which a vacuum is created. Then the varnish is admitted and pressure is applied. The remaining varnish is return to the tank. The chart below gives the criteria for varnishing different alternator. Capacity

Class

Preheating

Cooling

Curing

25KW

H

4-5Hrs at120

Till temp

8-10 Hrs at 120

degree

reaches 50

degree

degree 4,5,12,18 KW

F

4 hrs at 1200-

Till Temp

130 degree

reaches 50

4-6 Hers at 140

degree

Flowchart for varnishing

Mixing

Checking of viscosity of varnish Transfer of heated frames to vacuum Apply pressure (curing)

Return to varnish Cooling Dept.of.EEE

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REGULATOR RECTIFIER UNIT The regulator rectifier unit has mainly the following functions. 1. Rectifying 3 phase output of alternator to dc using full wave Rectifier Bridge. 2. Regulating the voltage generated by alternator at the set value. 3. Regulating output current at set value. POWER RECTIFIER This consist of 6 numbers of silicon diodes connected in three phase full wave bridge .the three phase ac output of ac alternator is rectified by these diodes to obtain dc output. Each diode is protected against transit surge voltage by capacitor C1. Whole bridged is protected Against high frequency surges by capacitor C3 and DC output is filtered by capacitor C2. VOLTAGE REGULEATION VOLTAGE induced in ac windings of alternator depends on the speed of the rotor excitation current and load current. The absence of voltage regulator, output voltage is rising the indefinitely due to the positive feedback of the field. The voltage regulator monitors voltage and pass a command, this control circuit to reduce excitation current as soon as the output voltage reaches the set value. Control circuit is wired in rack consisting of the following parts. EXCITATION TRANSFORMER This is a single winding transformer with tapping for input and output transformer stepped down the voltage for field coils. Transformer has 5 sets of terminal brought required to a terminals strip.

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2) VOLTAGE DETECTOR

Voltage detector serves the functions of providing necessary error signal for voltage regulation. it consist of in network of zenor diode potential dividers and rheostat . in the output voltage of the load winding aw here by decreasing the field current, maintaining the output voltage of the alternator of the set value. The voltage drop across R1 can be varied by varying the resistance Rh.

MAGNETIC AMPLIFIER

Magnetic amplifier forms of the nuclease of the evaluated circuit. It works on the principle of saturation of magnetic core. It has 6 sets of winding. The load winding is connected in the field circuit & the field current passes through this winding subject from the command from the voltage and current sensing ckts.manifested through control

windings 10-11 and 26-27

respectively. The load winding offers variable impedance to the field circuit there by regulating the voltage and current at set value.

FIELD RECTIFIER UNIT Silicon diodes dD2 and D3 acts as full wave rectifier for the field supply .these diodes conduct alternatively as terminals 18 and 161 becomes positive with respect to the center taping -19. The rectified current from the diodes is taken to the field back winding 20-40 of the magnetic amplifier to terminals 20 and 19 the positive and negative terminal respectively for the field supply.

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Final Assembly

As the name suggests, this is the final section in terms of the alternator manufacture. Here all the components are assemble3d together and readied for dispatch. This receives the following from the preceding areas. o Rotor and axle pulley (machine shop) o Stator with laminations and winding (varnishing) o Regulator unit

The assembly can be briefly explained as follows.  All components are cleaned and scrapped to remove superfluous metal  The bearings are fitted. Either roller bearing or ball bearing is provided, along with bearing lock.  The bearings are sent for greasing.  The end plate is fatted after heating on the bearing side.  The rotor shaft is cleaned and polouished.  The end of the rotor shaft is padded through the end shield.  The symmetry of air gap is checked by mechanical means. The rotor is rotated at low speed inside the stator and checked for contact.  The alternator pulley is mounted on to the rotor shaft.  The axle is sent as two separate pieces.  It is assembled on site by mounting.

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Testing The assembled alternator is subjected to various tests as per RDSO specification before dispatch. They are briefly explained below.

High Voltage Test

This test is performed to find the leakage current. For this all the current carrying parts are shorted and earthed. A supply of 1500V is given to the stator plate. The leakage current can be directly read using a milli ammeter. The maximum limit is 20 mA. This test can be used to check whether the machine has the capacity to withstand such a high voltage.

Insulation Test

Insulation meager is used to perform this test. The current carrying parts are shorted and connected to one of the terminals of the meager. The other terminal is given to the stator frame. The resistance value can be directly reads. The minimum value of insulation resistance is 20 MC2. This test is done both before and after the high voltage tests. Mechanical Over speed Test. The field is separately excited and is run at a high speed in both the directions. The speed range is as given below 4.5 kW

-

3275rpm

18 kW

-

3035rpm

22.75 kW

-

3035rpm.

The induced emf in all three phases in both the directions is noted. The value should be within the specified range.

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CONCLUSION Kerala Electrical and Allied Engineering CO. Ltd is a Kerala Government owned company. It has three other units in addition to Kundara unit. They are located in Mamala, Ernakulum District, Olavakod, Palakkad District and Kasargod District. It is an ISO 9001-2000 Certified Company.

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