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MANUFACTURING PROCESS OF 660 MW TURBO GENERTOR STATOR WINDING BAR

ABHISHEK SINGH12ERDME0049001472384AT BHEL HARIDWAR

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INTRODUCTION

In 1956 India took a major step towards the establishment of its heavy engineering industry when BHEL, the first heavy electrical Manufacturing unit of the country was set up at Bhopal. BHEL's Heavy Electrical Equipment Plant (HEEP) was set up in technical collaboration with USSR, for the manufacturing of power plant equipment.In 1976, BHEL entered into a collaboration agreement with M/s Kraftwerk Union, AG of Germany for design, manufacturing, erection and commissioning of large size steam turbines. More than 40 percent of the country's electrical energy is generated from the power equipment supplied by BHEL, Haridwar.

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MANUFACTURING BLOCKS:.BLOCK I: ELECTRICAL MACHINE BLOCK, IS DESIGNED TO MANUFACTURING OF TURBOGENERATORS BLOCK II: FABRICATION BLOCKBLOCK III: TURBINE BLADE BLOCKBLOCK IV: COIL & INSULATION MANUFACTURING & APPARATUS & CONTROL GEAR MANUFACTURING BLOCK BLOCK V: FEEDER BLOCK AND KNOWN AS FABRICATION AND FORGE BLOCKBLOCK VI: STAMPING AND DIES MANUFACTURING BLOCKBLOCK VII: WOODWORKING BLOCKBLOCK VIII: HEAT EXCHANGER BLOCK, IS DESIGNED TO MANUFACTURE HEAT EXCHANGER UNIT FOR STEAM TURBINES.

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COIL & INSULATION MANUFACTURING SHOP (BLOCK-IV)

Block-4 is designed to manufacture stator winding bars of Turbo & Hydro generator and coil like DC Armature coil ,main pole coil , equalizer coil etc. There are three BAYS in this block each bay manufactures stator bars and coils for different machines

BAY-I: Bar winding shop: manufacturing of stator winding bars of generatorBAY-II: Manufacturing of heavy duty generator stator bars with New CNC M/cBAY-III: Insulation detail shop: Manufacturing of hard insulation & machining of hares insulation part (Glass Textolite) such as packing, washer, insulation box, wedges etcBar Shop: This shop is meant for manufacturing of stator winding coils of turbo-generator and hydro generator

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Layout of CIM, Block-IV

It is quite difficult (rather impossible) to manufacture, handle and wind in the stator slot of generator of higher generation capacity because of its bigger size and heavy weight. That is why we make coil in two parts. One part its bottom part of coil called bottom or lower bar and other part of coil is called top bar or upper bar.

Why do we call it bar?

Manufacturing ProcessFor the manufacturing of stator bars insulated copper conductors are brought from Bangalore, its of two types i.e. solid copper conductor & hollow copper conductors which are used in water cooled stator layer glass insulation. solid bar for 600/660/700 MW volume - 9.5X1.2 Hollow copper for 600/660/700 Volume 8.0x 4.6x1.3

Cutting

This process is done by automatic 3-444CNC machine. In this process the pre insulated copper conductor is cut into number of required length. Insulation is removed from both ends of the conductor cut.

Transposition

Transposition means changing/shifting of position of each conductor in active core (slot) part. After cutting the required number of conductors, the conductors are arranged on the comb in staggered manner and then bends are given to the conductors with the help of bending die at required distance.Then the conductor are taken out from the comb & die and placed with their ends in a line and transposition is carried out.Need of transposition. 1. To reduce eddy current losses. 2. Equalize the voltage generator. 3. To minimize skin effect of ac current

Cross Over Insulation

The pre insulation of the copper conductor may get damaged due to mechanical bending in die during transposition, hence the insulating spacers are provided at the crossover portion of the conductors. A filler material (insulating putty or moulding micanite) is provided along the height of the bar to maintain the rectangular shape and to cover the difference of level of conductors.

Stack Pressing

The core part of bar stack is pressed in under the pressure b/w 70kg to 80 kg and Temperature b/w 90 C to160 C for given period. Four bar is pressed in one time and six to eight plate are used for pressing .after that the consolidated stack is withdraw from the press. Inter Stand Short Test The consolidated stack is tested for the short between any two conductors in the bar, if found then it has to be rectified.This is done to ensure that no local current is flowing due to short circuit between conductors.(300 A/C supply)

Forming

This process of forming is very important as in this process the bars are bending from both the ends of the bar i.e. at exciter side and turbine side at specific angles and shape as per design. This process is done manually. First the former is set according to the design making different angles at different positions. The straight bar stack is formed as per overhang profile (as per design), The overhang portion is consolidated after forming. . Pickling process After the forming and cutting process of the bar and due to the transportation of the bar, there accumulate very minute particles of dust on the ends of the bar. These particles may cause at the time of brazing and may create some air gaps. So, in order to remove these unwanted particles, basically the oil particles pickling process is performed.

Contact Sleeve Mounting

After the pickling process is complete, contact sleeve and water box bottom parts are mounted on both the ends of the bar. it is a rectangular sleeve which is used to make contact between upper and lower bars . All the solid conductors are cut from the ends of the bar after the contact sleeve except the outer solid conductors. The water box is mounted in two halves; first the water box bottom part is mounted after the contact sleeve keeping some distance between them.

Brazing is basically the process of fixation of both the contact sleeve and water box.Brazing is suitable for small parts , when high joint strength is required.In brazing alloy is mixed with water.

Brazing

Nitrogen gas is the main constituent of the test. This test is similar to puncture test that is inflated tube is dipped in water for any leakage, the air bubbles gives us the exact position of the puncture.

Nitrogen test

Thermal Shock Test

Thermal shock test is performed to check whether the bar can withstand extreme conditions i.e. when the generator is working or running at about 3000 Rpm. This is achieved by thermal shock test. Thermal shock test consist of series of hot water & cold water cycles alternatively. So firstly hot water at temperature of about 90C is passed through the bar and then cold water at about room temperature 27C approx. is flowed inside the bar alternatively. This process is repeated again and again.

Helium Leakage Test

After thermal shock test bar is tested for any leakage with help of Helium gas. Helium test is the most important test of all, because helium test is performed to check any minute leakage within the bar and at the brazed portion. because helium is one of the lightest gases.

Reforming

After all the previous processes which had undergone on the bar. That the shape of the bar is deformed from its original shape due to handling of the bar from one place to another for different processes. So to keep the shape of the bar as per design, the bar is checked if it is found distorted then it is reformed in the previous former machine by placing the bar on the former . InsulationThe stator bars are insulated with Micalastic (trade name) insulation.Insulation is basically done to prevent any kind of short circuit between the bar and the stator core when the bar is assembled in the stator of the machine

Impregnation and Baking

Micalastic System : In case of poor resin system the insulated bars are heated under vacuum and the impregnated (dipped) in heated resin so that all the air gaps are filled, layer by layer, with resin.After impregnation the bars are pressed to bring them back to the original dimensions.

HIGH VOLTAGE TEST

When the bar is dried it is wrapped with aluminum sheet to make outer surface of the bar conducting so that H.V. (High voltage test) can be performed. After this tests the coating of red gel is applied at both the ends of the bar.

In this test the bar which is already wrapped with aluminum is used.High voltage is applied to the bar using auto-transformer and it is increased in steps according to the working voltage of the generator. If the insulation is weak the bar will puncture at the place of weaker insulation.If any of the bar fails this test i.e. bar is punctured at any point then the bar is sent back for re-insulation and all the processes are repeated again

Finishing

The baked and dimensionally correct bars are sanded-off to smoothen the edges and the surface is calibrated, if required, for the dimension. Dispatched for winding The bars preserved with polythene sleeves to protect from dust, dirt, oil, rain etc are send to Block-I (Electric Machines Production Block - I, Turbo Generators and Hydro Generators) for winding

Picture Of Bars

THANK YOU

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