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Traction motor manufacturing & Power transformer BHEL

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Traction motor manufacturing & Power transformer BHEL

  1. 1. BHARAT HEAVY ELECTRICALS Ltd. Summer Training Report TRACTION MOTOR MANUFACTURING & POWER TRANSFORMER MANUFACTURING 2016 Submittedby: PrabjeetSingh UCE,RTU,KOTA 13EUCEE060 20/07/2016
  2. 2. Prabjeet Singh Page 2 MAJOR TRAINING REPORT BHARAT HEAVY ELECTRICALS LIMITED BHOPAL A Training report submitted to HRDC, BHEL BHOPAL (M.P) PROJECT REPORT ON TRACTION MOTOR MANUFACTURING & POWER TRANSFORMER Duration of Vocational Training- 23 June 2016 to 20 July 2016 Guided by: Submitted by: Mr. AMITGAUTAM Prabjeet Singh Sr. Engineer VT-867/16 TPTN Planning 13EUCEE060 BHEL, Bhopal UCE, RTU, KOTA
  3. 3. Prabjeet Singh Page 3 BHARAT HEAVY ELECTRICAL LIMITED PIPLANI, BHOPAL MP-462022, INDIA CERTIFICATE This is to certify that Mr. Prabjeet Singh student of 3rd year, Electrical Engineering, Bachelor of Technology, University College of Engineering, Rajasthan Technical University,Kota has undergone his Vocational Training from 23 June 2016 to 20 July 2016 in Traction Motor Manufacturing Department under my guidance. Mr. Prabjeet Singh has successfully completed his training and submitted the training project report. During the period of training he was found sincere, punctual & regular. His conduct and behavior was very good. Amit Gautam Sr. Engineer TPTN Planning BHEL, Bhopal
  4. 4. Prabjeet Singh Page 4 ACKNOWLEDGEMENT Every projectbig or small is successfullargely due to the effort of a number of wonderful people who have always given their valuable advice or lent a helping hand. I sincerely appreciate the inspiration, supportand guidance of all thosepeople who have been there in making this project and our summer training a successfulone. I am extremely gratefulto the “BHARATHEAVY ELECTRICALS Ltd., Bhopal” for the confidence bestowed in me and allowing me to held the summer training during the duration from23 June 2016 to 20 July 2016. At this junctureI feel deeply honored in expressing my sincere thanks to each and every employee for making the resourceavailable at right time and providing the valuable insights leading to the successfulcompletion of my project. I express my gratitude to Mr. VIVEK KHANDELWAL & Mr. SHRAVAN KUMAR ARORA for arranging the summer training in good schedule. I also extend my gratitude to my project guide Mr. AMITGAUTAM, who assisted me in compiling the project and also helped throughoutmy vocationaltraining period to make my learning much better. I would also like to thank all the faculty members of University College of Engineering, Rajasthan Technical University, Kota for their critical advice and guidance without which this projectwould havenot been possible. Last but not the least I place a deep senseof gratitude to my family members and my friends and the employees of the BHEL, Bhopal who have been a constantsourceof inspiration during the preparation of this project. NAME :PRABJEET SINGH DATE :20th JULY 2016 PLACE :BHOPAL
  5. 5. Prabjeet Singh Page 5 TABLE OF CONTENTS CHAPTER 1: INTRODUCTION  BHEL Bhopal 7  BHEL contribution in different sectors 9  Vision, Mission and Values 11 CHAPTER 2: PRODUCTS OF BHEL, BHOPAL  AC Motors and alternators 13  Transportation equipments 14  Hydro generator 14  Excitation control equipment 14  Steam turbine 15  Oil rigs 15  Transformer 15  Switchgear 15  On load tap changer 16  Large currentrectifier 16  Control and relay panel 17  Maintenance of thermal power station 17  Fabrication 18 CHAPTER 3: TRACTION MOTOR MANUFACTURING  Introduction 19  Experience 21  Customer base 22  TXM currently being manufactured 22  Fundamental traction 23  TXM stator machine shop 25  TXM rotor machine shop 26  TXM commutator and core 27  TXM winding 30  TXM Fielding 32  TXM assembly 33
  6. 6. Prabjeet Singh Page 6  TXM testing 37 CHAPTER 4: POWER TRANSFORMER MANUFACTURING  Introduction 39  Main parts of transformer 39  Core and coil assembly 50  Processing of coreand coil assembly 50  Drying out process 50  Tank fabrication and fitting 51  Insulation shop 51  Tests on transformers 52 CHAPTER 5: BUSHING MUNUFACTURING  Introduction 55  Classification of Bushings 55  Bushing Design 56  Insulating material 57  Constructionaldetails and main parts of bushing 58
  7. 7. Prabjeet Singh Page 7 CHAPTER 1: INTRODUCTION BHEL is an integrated power plant equipment manufacturer and one of the largest engineering and manufacturing company in India in terms of turnover. Itwas established in 1956, ushering in the indigenous Heavy Electrical Equipment industry in India - a dream that has been more than realized with a well recognized track record of performance. The company has been earning profits continuously since1971-72 and paying dividends since1976-77. Governmentof India (Ministry of Heavy Industries and Public enterprises) has granted the status of MAHARATNA to Bharat Heavy Electricals Limited on 1stFeb 2013. It has been engaged in the design, engineering, manufacturing, construction, testing, commissioning and servicing of a wide range of products and services for the core sectors of the economy, viz. Power, Transmission,Industry, Transportation (Railway), RenewableEnergy, Oil ,Gas and Defense. BHEL have a shareof 59% in India’s totalinstalled generating capacity contributing 69% (approx.) to the total power generated fromutility sets (excluding non-conventionalcapacity) as of March 31, 2012. BHEL’s greatest strength is the highly skilled and committed workforceof 49,390employees. Every employee is given an equal opportunity to develop himself/herself and grow in his/her career. Continuous training and retraining, career planning, a positivework culture and participative style of management. All these haveengendered development of a committed and motivated workforcesetting new benchmarks in terms of productivity, quality and responsiveness. BHEL, BHOPAL: BharatHeavy Electricals Ltd was set up in 1956 atBhopal. There are around 10,000 employees atthe BHEL plant in Bhopal being a vital part of BHEL on a whole. Bharat Heavy Electricals ltd .Bhopal is situated near Piplani which is a nowadays covers large part of Bhopal. BHEL TOWN, Bhopal is a suburb of Bhopal, Madhya Pradesh. This has developed like other BHEL townships after Indian public sector engineering company BHEL started its operations here. It is spread over an area of around 20 km2 and provides facilities like, parks, community halls, library, shopping centers, banks, post offices etc. The company has been earning profits continuously since 1971-72 and paying dividends uninterruptedly since 1976-77. In recognition of its consistent high performance, BHEL has been conferred with the 'Maharatna'status by the Governmentof India on 1st February 2013. It is now one among seven Maharatna PSUs With a widespread network of 17 manufacturing units, 2 repair units, 4 regional offices, 8 service centers, 8 overseas offices, 15 regional
  8. 8. Prabjeet Singh Page 8 centers, 7 joint ventures, and infrastructure to execute more than 150 project sites across India and abroad, BHEL provides products, systems and services to customers efficiently and at competitive prices. The company has established capability to deliver 20,000 MW p.a. of power equipment to address the growing demand for power generation equipment. With an export presence in more than 76 countries, BHEL is truly India’s industrial ambassador to the world. Figure 1: Aerial view of BHEL, Bhopal The high level of quality & reliability of our products is due to adherence to international standards by acquiring and adapting some of the best technologies from leading companies in the world including General Electric Company, Alston SA, Siemens AG and Mitsubishi Heavy Industries Ltd., together with technologies developed in our own R&D centers. Most of BHEL’s manufacturing units and other entities have been accredited to Quality Management Systems (ISO 9001:2008), Environmental Management Systems (ISO 14001:2004) and Occupational Health & Safety Management Systems (OHSAS 18001:2007). BHEL has:-  Added more than 124000 MW to the country's installed power generating capacity so far.  Supplied over 25000 Motors with Drive Control System to power projects, Petrochemicals Refineries, Steel, Aluminium, Fertilizer, Cement plant, etc.  Supplied Traction electrics and AC/DC locos over 12000 kms Railway network.  Supplied over one million Values to Power Plants and other Industries.  BHEL has retained its market leadership position during 2013-14 with 72% market share in the Power Sector, even while operating in a difficult business environment.
  9. 9. Prabjeet Singh Page 9 Improved focus on project execution enabled BHEL record highest ever commissioning/synchronization of 13,452 MW of power plants in domestic and international markets in 2013-14, marking a 30% increase over 2012-13. BHEL has been exporting our power and industry segment products and services for over 40 years. BHEL's global references are spread across over 76 countries across all the six continents of the world. The cumulative overseas installed capacity of BHEL manufactured power plants exceeds 9,000 MW across 21 countries including Malaysia, Oman, Iraq, the UAE, Bhutan, Egypt and New Zealand. Our physical exports range from turnkey projects to after sales services. In the world power scene BHEL ranks among the top ten manufacturers of power plant equipment, spectrum of products and services offered, it is right on top. BHEL’s greatest strength is its highly skilled and committed workforceof 48,399 employees. Every employee is given an equal opportunity to develop himself/herself and grow in his/her career. Continuous training and retraining, career planning, a positive work culture and participative style of management - all these have engendered development of a committed and motivated workforcesetting new benchmarks in terms of productivity, quality and responsiveness. BHEL business operations cater to core sectors of the Indian Economy like Power, Industry, Transportation, Transmission, and Defense. BHEL BHOPAL is broadly divided in to 8 BLOCKS:  BLOCK-1 Water Turbine Manufacturing  BLOCK-2 Heavy Electrical Machine and IMMand LEM  BLOCK-3 Transformer, Capacitor and Bushing Manufacturing and Ultra High Voltage Testing.  BLOCK-4 SCR(Switchgear, Control Gear and Rectifier)  BLOCK-5 Press shop  BLOCK-6 CIM(Coil & Insulation Manufacturing)  BLOCK-7 RSMG  BLOCK-8 Fabrication  BLOCK-9 Transportation group(Traction Motors And Alternator) BHEL’S CONTRIBUTION IN DIFFERENTSECTORS  POWER SECTOR: Power sector comprises thermal, nuclear, gas & hydro power plant business. Today, BHEL supplied sets account for nearly 56,318 MW or 65% of the total installed capacity of 86636 MW in as against nit till 1969-1970. BHEL has proven turnkey capabilities for executing power projects fromconcept to commissioning. Itpossesses
  10. 10. Prabjeet Singh Page 10 the technology and capability to produce thermal power plant equipments up to 1000MW rating and gas turbine generator sets up to a unit rating of 240MW. Cogeneration and combined cycle plants have been introduced to achieve higher plant efficiencies. To make efficient useof the high ash content coal available in India, BHEL supplies circulating fluidized bed boilers to thermal and combined cycle power plants. BHEL manufacturers 235 MW nuclear turbine generator sets and has commenced production of 500 MW nuclear turbine generator sets. Custom-madehydro sets of Francis, Pelt on and Kaplan types for different head-dischargecombinations are also engineered and manufactured by BHEL is based upon contemporary technology comparableto the best in the world & is also internationally competitive.  Transmission BHEL also supplies a wide rangeof transmission products and systems up to 400 KV Class. These include high voltage power and distribution transformers, instrument transformers, dry typetransformers, SF6switchgear, capacitors,and insulators etc. For economic transmission bulk power over long distances, High Voltage DirectCurrent (HVDC) systems aresupplied. Series and ShuntCompensation Systems havealso been developed and introduced to minimize transmission losses. A strong engineering base enables the Company to undertaketurnkey delivery of electric substances up to 400 kV level series compensation systems (for increasing power transfer capacity of transmission lines and improving systemstability and voltage regulation), shunt compensation systems (for power factor and voltage improvement) and HVDCsystems (for economic transfer of bulk power). BHEL has indigenously developed the state-of- the-art controlled shuntreactor (for reactive power management on long transmission lines). Presently a 400 kV Facts (Flexible AC Transmission System) projectunder execution.  Transportation A high percentage of trains operated by Indian Railways areequipped with BHEL’s Traction and traction controlequipment including the metro at Calcutta. The company supplies broad gauge electrical locomotives to Indian Railways and diesel shunting locomotives to various industries.5000/6000 hp AC/DClocomotives developed and Manufactured by BHEL have been leased to Indian Railways. Battery powered road vehicles are also manufactured by the company.  International Operations BHEL’s products, services and projects havebeen exported to over 50 countries ranging fromUnited States in the westto New Zealand in Far East. The cumulative capacity of power generating equipment supplied by BHEL outside India is over 3000MW. The Company’s overseas presenceincludes projects in various countries. A few notable ones
  11. 11. Prabjeet Singh Page 11 are: 150 MW (ISOI) gas turbineto Germany, utility boilers and open cycle gas turbine plants to Malaysia, Tripoli-west, and power station in Libya executed on turnkey basis, thermal power Plant equipment to Malta and Cyprus, Hydro generators to New Zealand and hydro power Plant equipment to Thailand. BHEL has recently executed major gas- based power projects in Saudi Arabia and Oman, a Boiler contract in Egypt and several Transformer contracts in Malaysia and Greece  Renewable Energy:- Technologies offered by BHEL for non-conventionaland renewablesources of Energy include: wind electric generators, solar photovoltaic system, stand alone and grid- interactive solar power plants, solar heating systems, solar lanterns and battery- powered road vehicles. The company has taken up R&D efforts for development of multi-junction amorphous solar cells and fuel cells based systems.  Industries BHEL is a major contributor of equipment and systems to industries: cement, sugar, fertilizer, refineries, petrochemicals, paper, oil and gas, metallurgical and process industries. The company is a major producer of large-sizethyristor devices. Italso supplies digital distributed controlsystemfor process industries and control & instrumentation systems for power plantand industrial application. The range of system & equipment supplied includes: captive power plants, cogeneration plants DG power plants, industrial steam turbines, industrialboilers and auxiliaries. Water heat recovery boilers, gas turbines, heat exchangers and pressurevessels, centrifugal Compressors, electricalmachines, pumps, valves, seamless steeltubes, electrostatic Precipitators, fabric filters, reactors, fluidized bed combustion boilers, chemical recovery boilers and process controls. The Company is a major producer of large-sizethruster devices. Italso supplies digital distributed controlsystems for process industries, and control & instrumentation systems for power plantand industrial applications. BHEL is the only company in India with the capability to make simulators for power plants, defenseand other applications VISION, MISSION AND VALUES:
  12. 12. Prabjeet Singh Page 12 Vision A Global Engineering Enterprise providing Solutions for better tomorrow. Mission Providing sustainablebusiness solutions in the fields of Energy, Industry& Infrastructure. Values Governance, Respect, Excellence, Loyalty, Integrity, Commitment, Innovation, TeamWork.
  13. 13. Prabjeet Singh Page 13 CHAPTER 2: PRODUCTS OF BHEL, BHOPAL Power Utilization AC Motors & Alternators Transportation Transportation Equipment Power Generation Hydro Turbines Hydro Generators Heat Exchangers Excitation Control Equipment Steam Turbines Miscellaneous Oil Rigs Fabrication Power Transmission Transformer Switchgear On-Load Tap Changer Large Current Rectifiers Control & Relay Panels Renovation & Maintenance Thermal Power Stations  AC Motorsand Alternators: BHEL is a leading AC Machines manufacturer and in the last four decades havesupplied more than 20000 HT& LT A.C. Machines for various applications to Indian as well as Export market. The applications include Power Plants, Nuclear Energy, Petrochemicals, Fertilizers, Refineries, Cement & Steel Industries, Irrigation Projects, Pipelines, etc. The manufacturing plant in Bhopal was established in technical collaboration with AEI UK. Commercial production of A.C. Machines commenced in the year 1963. Technology was upgraded by collaborating with Siemens AG, Germany from 1980-1990and subsequently from1996-2006. Motors areoffered both in standard as well as tailor made designs to meet customer's specific needs. High performanceis achieved through optimum utilization of the active materials and
  14. 14. Prabjeet Singh Page 14 components. BHEL A.C. Machines offer high efficiency, exceptional reliability, quick installation and minimal maintenance costs. Our engineers combine their extensive experience with state-of-the-artanalytical design tools, latest machine tools, Six Sigma methodology and advanced material development to deliver the best product. Installed Capacity: 2250 machines per annum  Transportation Equipments:BHEL's involvementin the transportation sector has been marked with rapid growth. Today over 85% of Indian Railways, one of the largest railway networks in the world is equipped with traction equipment built by BHEL. The range includes traction motors, traction generators/alternators, transformers, sub-station equipment, vacuumcircuit breakers, locomotive bogies, smoothing reactors, exciters, converters, inverters, choppers and associated controlequipment, viz. master controllers, HSCBs, chopper controllers brakeand door equipment, electronic controls including softwarebased controls extending to rolling stock and other transport applications. BHEL has manufactured and supplied large numbers of electric locomotives (upto 5000 hp) to Indian Railways and Diesel Electric Locomotives ranging from350 hp to 2600 hp to cement, steel and fertilizer plants, thermal power stations, coalfields, ports and other medium and large industries. This has established BHEL as a leading locomotive manufacturer in the country. Diesel Multiple Units, underground Metro-rail systemat Calcutta, Electric Multiple Unit (EMU) services at Mumbai, Calcutta, Chennai & Delhi operate on drives and controls supplied by BHEL. BHEL has also started the supply of equipment for Dual Voltage EMUs with 3 phasetechnology. To contain air pollution & to conservemineral oil resources, battery powered road vehicles are in operation in various cities, BHEL is also ready to undertaketurnkey execution of LRT, MRTS & electric trolley bus.  Hydro Generators: Hydro generator is a synchronousalternator driven by a hydraulic turbine. Motor is synchronous motor to drivepump. BHEL Bhopal is a leading supplier of large, medium & small hydro generators, motors, bulb generators and related services. Installed manufacturing capacity : 2500 MW Sophisticated CAD facilities ISO-9001 certification  Excitation ControlEquipment: Excitation Control equipment for Hydro, Thermal Nuclear, Naval and Industrialapplications. Excitation control equipment (automatic voltage regulator (AVR) and static excitation equipment-(SEE) for semi-static, static and brushless typeof excitation system. Complete range of Digital AVR and SEE available to suit all types of systems and generators added to productprofile in the year 2003. More than 35 years of field experience. More than 600 AVRs operating satisfactorily at various
  15. 15. Prabjeet Singh Page 15 Hydro, Thermaland IndustrialPower Plants. A number of captive power plant installed in Sugar, Chemical, Paper and other industries are also equipped with BHEL make AVRs Total systemsolutions on offer Retrofitting of old excitation control systemwith latest state of art digital systems Dedicated shop area with modern manufacturing and testing facilities  Steam Turbines:BHEL has taken its lead role in following fields : Turbines 1) Design, Manufacturing, Erection, Commissioning and Services of: 30 MW, 120 MW Steam Turbines 236 MW Nuclear Turbines. 15000 SHP MarineTurbines 210 MW Steam Turbines. 2) Supply of Spares and Repairs of aboveSteam Turbines. 3) R & M and Life assessmentstudies of BHEL & Non BHEL TG sets. 4) Repair and Supply of Spares of 210 MW and 500 MW KWU Turbines. 5) Repair and supply of Spares for Non BHEL TG Sets. Diversified Projects For IPRand ISRO: Manufacturing of various components.  Oil Rigs: BHEL is the only manufacturer of complete Land Drilling Rig in India. BHEL has supplied 84 Land Rigs to M/s ONGCL and M/s OIL India Ltd. BHEL has proven capability of designing, manufacturing and commissioning of different type of land rig ranging fromE 760, E1400, E2000, E3000, Mobile Rig, DesertRig and TBA Rig (Transportable by air). BHEL built E 3000 Typerig has capability of drilling up to 6 Km to 10 Km depth. BHEL has executed R&U of 20 Nos. BHEL/ Imported Land Rigs, to tailor made customer specification, to rejuvenateold rigs and meet growing customer requirement. R&U of 16 more rigs is in progress Rig Electrics are manufactured and supplied by BHEL Bhopal Unit.  Transformer:A Leading Engineering Enterprise which Supplies wide Spectrum of Power Transmission Systems/Solutions froma single entity. A Leading Transformer Manufacturer Offering widerange of Transformers. Installed manufacturing capacity: 18000 MVA/Annumwith dustproof facility in critical areas. The capacity is augmented by another 12000 MVA/Annumwith totally dust proof facility. Having nearly 5 decades or over 35,000 man-yearsof experience. Dedicated shop area of over 80000 sq. meters and unique Ultra High Voltage testing facility.  Switchgear:A leading Switchgear Group involved in Design, manufacturing, installation, commissioning and services of Switchgear. A wide spectrumof switchgear catering to various applications like power station auxiliaries, power distribution, process industries,
  16. 16. Prabjeet Singh Page 16 ruralelectrification, open cast mines, electric traction and other special applications. Market leaders in India. Experience of 5 decades Thousands of various types of breakers working satisfactorily in India and abroad. Unique distinction of widestrange of medium voltage Switchgear meeting every requirement of the customer in stringentIndian conditions. Strong R & D infrastructure. Dedicated shop and design area of over 50,000 sq meters. Regular facilities updation with new capital investment. Clear room facility for GIS Strengths: - Reliable and problemfree product - Proven productin service - Repeated successfultypetesting and special testing - Largest rangeto suit various application requirements viz Power Stations Distribution, Industrial& Railways. - 100% routinetesting as per IS & IEC. Switchgear design fully type tested as per IEC: 62271  On Load Tap Changer:A leading On Load Tap Changer (OLTC) group involved in Design, manufacturing, commissioning and services of Tap Changers. Market leaders in India Latest Technology incorporating high speed resistor switching of OLTC Capacity to supply 500 numbers OLTC. Experience of morethan 4 decades. Dedicated shop area of over 10,000 sq meters complete systemfor parallel operation of transformers and remote Tap changer controlpanel.  Large CurrentRectifier:LargeCurrent Rectifier SCR Division of BHEL, Bhopal has been supplying wide rangeof Large CurrentRectifier Equipment since year 1969. The large currentrectifier equipment provides DCpower for electrolytic process of electrochemical, aluminum & graphite industries. BHEL have so far supplied more than 60 units of about 1600000 Kilowattrectifiers for caustic soda, aluminumsmelter and graphite furnaces. Someof the special features of the large Current Silicon Power Rectifier Equipment are listed below: 1) Compact and Rugged design 2) PLC controlled Rectifier (Hotstandby option available) 3) HMI for control, annunciation, status display 4) Interfacewith customer SCADA possible 5) Operates in both currentand power controlmodes 6) High Efficiency 7) Accuracy of control+ 1%
  17. 17. Prabjeet Singh Page 17 8) Uniform currentsharing 9) Large safety margins in Design 10) Easy maintenance and monitoring 11) Single rectifier unit up to 60 KA 12) Auto/Rectifier Transformer & IPT 13) Transductors –housed in single tank 14) Externally mounted on-load tap-changer 15) Non magnetic aluminium rectifier structure 16) FRP covers to avoid eddy current losses 17) Steel shields 18) Suitable for tropical conditions 19) Choice of cooling A rectifier equipment comprises an assembly of semiconductor diodes mounted on heat sinks along with series connected fuseand surgevoltage protection components, all suitably enclosed and a separately mounted transformer. Additionalitems, such as interconnections, control cubicles, switchgear, AC/DCmeasuring system; AC/DC bus bars are included in scope of supply when required. For large currentapplications above 25kA, importantadvantages are gained by mounting the rectifier assembly in close association with the transformer known as 'Rectiformer'by combining the two units into an integral equipment (a) The space requirement is considerably reduced (d) Both preparatory & erection work at site is minimized (c) AC. bus bars connections are reduced to minimum.  Controland Relay Panels: Experience in the field for more than 40 years. Morethan 15000 panels supplied to major customers in India and abroad. Capability to develop complete control of protection schemes for generation and transmission systems to suit customer requirements. Applications of latest state of the art numerical relays with communication facility. Design of controlof relay boards based on latest engineering practices, high degree of reliability and aesthetic consideration.  Maintenance of ThermalPower Station:BHEL is the largestproducer of power generating equipment including turbines, generators, boilers and auxiliaries in the country. BHEL has already supplied thermal sets upto 500 MW rating and has the technology to go upto 800 MW. BHEL manufactured 500/236 MW Nuclear sets are also installed in the country. The BHEL manufactured sets accounts for 65% of total installed capacity in India. There is ample scopefor improving the plant availability by cutting
  18. 18. Prabjeet Singh Page 18 down the shutdown period, by Renovation & modernization, Rehabilitation and by timely arranging the spareparts and other services. Based on our more than 35 years experience in the field of Design, manufacturing, erection and operating experience, services in steam turbine, BHEL is undertaking Renovation and modernization of BHEL & NON-BHEL Thermal Power Plants. This includes, Life assessmentstudies recommendation for up-rating / upgradation, also includes retrofitting, repairs, overhauling, with improved efficiency and heat rate and performanceguarantee for a reasonabletime period. Spares for TG sets: For preventive and capital maintenance, these can be planned in advance, but it is difficult to predict and to organizethe samein caseof sudden break-down especially in case of non-BHEL sets due to various constraints. BHEL has taken lead role by providing specialized services, retrofitting renovating and supply of even such spareparts for which complete design information and manufacturing drawings arenot available fromoriginal suppliers.  Fabrication: 483 strong workforces of engineers, supervisors and highly skilled artisans; which include about 200 qualified welders and welding operators. 20,000 tons of diversified fabrication capability. More than 40 years experience in fabrication & welding. Total Engineering solutions & consultancy services for all kinds of fabrication and welding problems. Accredited with ASME ‘U’ stamp by American National Boiler Board to manufactureHeat Exchanger and PressureVessels since1989. Allsystems qualified and maintained to ISO 9001 and ISO14001 standards. Fully developed ancillary industries within 2kms distanceto meet any emergency requirements.
  19. 19. Prabjeet Singh Page 19 CHAPTER 3: TRACTION MOTOR MANUFACTURING 3.1 INTRODUCTION: A traction motor is an electric motor used for propulsion of a vehicle, such as an electric locomotive or electric roadway vehicle. Traction motors are used in electrically powered rail vehicles such as electric multiple units and other electric vehicles such as electric milk floats, elevators, conveyors, and trolleybuses, as wellas vehicles with electrical transmission systems such as diesel-electric, electric hybrid vehicles, and battery electric vehicles. Figure 2: Traction Motor mounted on Wheel  BHEL (Bharat Heavy Electricals Limited- BHEL, India) started its activity in the field of transportation in1962 in collaboration with Associated Electrical Industries, UK.  Presently BHEL, Bhopal is pioneer in design and engineering for supply of electrics to meet the demand of Indian railways and various other railways abroad. BHEL's capability and experience in the transportation field is very wide and electrics are designed and manufactured for following applications:  Diesel electric freight, passenger and shunting locos with DC drive.  25KV AC and 1500 VDC freight and passenger electric locos.  25KV AC and 1500 VDC electrical multiple units (EMU).  Diesel electrical multiple units.
  20. 20. Prabjeet Singh Page 20  Metro systems.  Tram Cars  Battery powered vehicles  Electric trolley bus. Today, BHEL is the largest engineering and manufacturing organization in India. More than 85% of locomotives & EMUs working in India are equipped with electrics supplied by BHEL. Traction machines, as a product was first established in BHEL in the year 1962, when 16 nos. traction motors were supplied for 1500V DC EMUs for Mumbai (then Bombay). Since then more than 72000 nos. traction machines of different types have been manufactured and supplied to the different customer which are working satisfactorily in our country for Indian railways and abroad for railways of Bangladesh, Srilanka , Myanmar, Sudan, Vietnam, Tanzania, Malaysia etc. History of development:  From the modest beginning in early sixties, BHEL undertook developments of new designs of several products i.e. Motors, Generators, M.G. Sets, Alternators to meet the requirements of various types of rolling stocks developed by Indian Railways.
  21. 21. Prabjeet Singh Page 21  Over the years, BHEL has been contributing with traction machines for various systems of Diesel Electric Locomotives, DC & AC electric multiple units, and echo friendly battery operated road vehicles etc.  Besides, specially designed traction machines are supplied to other application like oil rigs, steel plant, fertilizer plants, NTPC etc. BHEL’s product range consists of large variety of Traction Machines:  DC traction motors up to 750 KW.  AC traction alternators upto 3000 KW.  DC traction generators up to 2000 KW.  DC auxiliary machines upto 50 KW.  DC blower motors upto 50 KW.  DC and AC motor generators sets upto 25 KW.  3-Phase AC traction motors up to 1150 KW.  Motor Generator Sets upto 12 KW  Motor Alternator Sets upto 20 KVA  Eddy current Clutches  Axle and tacho generators.  Smoothing Chokes and Field Diverter Inductive shunts All the traction machines manufactured in BHEL confirm to international specification IEC 60349. 3.2 EXPERIENCE  Traction machines (motor, alternator and auxiliaries) are well established products of BHEL.  80% of the trains in India areequipped with BHEL electric.  BHEL traction equipments are also working in Vietnam, Bangladesh, Sri Lanka, Tanzania and Malaysia.
  22. 22. Prabjeet Singh Page 22  Production of Traction Motor started in 1962.  BHEL has been working sincethen as a supplier of electrics as well as a partner of Indian Railways in development of new LOCO’s and EMU’s 6/2/2003. 3.3 CUSTOMER BASE:  Indian Railways  Vietnam Railways  Bangladesh Railways  Malaysia Railways  Sri Lanka Railways  Tanzania Railways  Underground metro rail system  Power corporation steel plants  Kolkata tram  ONGC  Battery powered road vehicles  Oil India Ltd. 3.4 TRACTION MOTORS CURRENTLY BEING MANUFACTURED BHEL, BHOPAL TRACTION MOTORS S.No TYPE kW Voltage Current Poles Rpm Application 1 TM4501 172 324 610 4 490 DE LOCO 2 TM4605 82 155 625 4 220 DE SHUNTER 3 TM4907AZ 280 325 1000 4 430 BGDE LOCO 4 TM5002AZ 282 350 925 4 444 3100 HP BGDELOCO TYPE WDP2 5 TM5002BY 241 295 925 4 424 BGDE LOCO TYPE WDM3BR EXPORTTO BANGLADESH 6 HS15250A 630 750 275 6 895 25 kV AC LOCO 7 TM3701AZ 167 750 340 4 1100 1500 V DC EMU 8 TM4601BX 167 535 600 4 1260 25 kV BG AC EMU 9 TM4603BZ 101 290 600 4 302 MG DE LOCO 10 TM4303AZ 192 535 400 4 1240 BG AC EMU 11 TM4303BY 287 535 425 4 1170 BG-AC EMU/MEMU 12 TM4303DY 212 557 425 4 1160 1400 HP DEMUICF
  23. 23. Prabjeet Singh Page 23 13 TM3801AZ 45 300 170 4 800 MG DEMU RCF 14 TG4302BY 210 300 700 6 2100 MG DEMU RCF 15 TM4903 OIL RIG 750 750 1050 4 2750 HEAVYDUTY DRILL WATER 16 6FRA6068 850 2180 270 6 1283 AC LOCO WAG9 & WAP7 17 6FXA7059 1150 2180 370 6 1585 AC LOCO TYPE WAP5 18 DMKT53/42 297 1716 136 6 1259 DUAL VOLTAGEAC/DCEMU MUMBAI 19 IM4507AZ 425 1520 220 6 600 4000 HP WAG4 20 IM3601AZ 285 1140 175 4 1400 25 kV AC EMU 3.5 FUNDAMENTAL TRACTION  Traction is defined as a physicalprocess in which a tangential force is transmitted across an interface between two bodies through dry friction or an intervening fluid film resulting in motion, stoppage or the transmission of power.  The units of traction are those of force, or if expressed as a coefficient of traction (as with coefficient of friction) a ratio.  The traction produced by a vehicle if expressed as a force is synonymous with tractive effort, or tractive force, and closely related to the term drawbar pull. Types of Traction Systems:  Steam Locomotives  Internal Combustion Engines  Diesel Locomotives  Diesel Electric Locomotives  Battery operated Locomotives  Electric Traction Systems LOCOMOTIVES
  24. 24. Prabjeet Singh Page 24  DIESEL LOCOMOTIVE: Diesel-electric locomotives were introduced in the United States in 1924, and have become the most widely used type of locomotive. The modern diesel- electric locomotive is a self-contained, electrically propelled unit. Like the electric locomotive, it has electric drive, in the form of traction motors driving the axles and controlled with electronic controls. It also has many of the same auxiliary systems for cooling, lighting, heating, and braking. It differs principally in that it has its own generating station instead of being connected to a remote generating station through overhead wires or a third rail. The generating station consists of a large diesel engine coupled to an alternator or generator that provides the power for the traction motors.  ELECTRIC LOCOMOTIVE: An electric locomotive is a locomotive powered by electricity from an external source. Sources include overhead lines, third rail, or an on-board electricity storage device such as a battery, flywheel system, or fuel cell. Electric locomotive receives currentfromoverhead line through pantograph. This high voltage is step down in case of single phase 25 KV supply and then fed through control and stabilizing circuit to the motors. In case of DC supply, it is fed to motor through control equipment.  MULTIPLE UNITS: The term multiple unit or MU is used to describe a self-propelling train unit capable of coupling with other units of the same or similar type and still being controlled fromone cab. The term is commonly used to denote passenger train sets that consist of more than one carriage, but single self- propelling carriages, or rail cars, can be referred to as multiple units if capable of operating with other units. Multiple units are of three main types:  Electric Multiple Units (EMU’s)  Diesel Multiple Units (DMU’s)
  25. 25. Prabjeet Singh Page 25  Diesel Electric Multiple Units (DEMU’s) Most MUs are powered either by a diesel engine driving the wheels through a gearbox or hydraulic transmission (DMU’s),or by traction motors, receiving their power through a live rail or overhead wire (EMU). 3.6 TXM STATOR MACHINE SHOP The stator is the stationary part of the motor which consist of:  The outer cylindrical frame of the motor, which is made either of welded sheet steel, cast iron or cast aluminium alloy. This may include feet or a flange for mounting.  The magnetic path, which comprises a set of slotted steel laminations pressed into a cylindrical space inside the outer frame. The magnetic path is laminated to reduce eddy currents, lower losses and lower heating.  A set of insulated electrical windings, which are placed in inside the slot of the laminated magnetic path. The cross sectional area of these windings must be large enough for the power rating of the motor. For a three phase motor, 3 sets of winding are required, one for each phase. Casting Marking Vertical Boring Marking Drilling Tapping All Round Machining Pole Pad machining Axel Bore Facing Spot Facingor Counter Bore Final Boring Debarring Block Welding Main Poleand Inter Pole Assembly
  26. 26. Prabjeet Singh Page 26 Figure 3: Stator Description 3.7 TXM ROTOR MACHINESHOP This is the rotating part of the motor. As with the stator above, the rotor consistof the set of slotted steel lamination pressed together in the formof a cylindrical magnetic path and the electrical circuit. The electrical circuit of the rotor can be either:  Wound rotor type, which comprises 3 set of insulated windings with connection broughtout to 3 slip rings mounted on the shaft. The external connections to the rotating part are made via brushes onto the slip rings. Consequently, this type of motor is often referred to as a slip ring motor. Raw Material (Mild Steel, high grade) Copying Machine(5 mm material is left out) CNC Machine(0.5 mm material is left out) Central Lathe Drilling Machine Shaft & Armature
  27. 27. Prabjeet Singh Page 27  Squirrel cage rotor type, which comprises a set of copper or aluminium bars installed into the slots, which are connected to an end ring at each end of the rotor. The construction of these rotor windings resembles a ‘squirrelcage’. Aluminium rotor bars are usually die-cast into the rotor slots, which results in a very rugged construction. Even though the aluminium rotor bars arein direct contact with the steel laminations, practically all the rotor current flows through the aluminium bars and not in the laminations. 3.7 TXM COMMUTATOR AND CORE A commutator is a moving part of a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the currentdirection between the rotor and the external circuit. Itconsists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. Two or more electrical contacts called "brushes" made of a softconductive material like carbon press againstthe commutator, making sliding contact with successivesegments of the commutator as it rotates. The windings (coils of wire) on the armature are connected to the commutator segments. Commutators are used in direct current(DC) machines: dynamos (DCgenerators) and many DC motors as well as universalmotors. In a motor the commutator applies electric currentto the windings. By reversing the currentdirection in the rotating windings each half turn, a steady rotating force (torque) is produced. In a generator the commutator picks off the currentgenerated in the windings, reversing the direction of the current with each half turn, serving as a mechanical rectifier to convertthe alternating current fromthe windings to unidirectional direct currentin the external load circuit. The firstdirect currentcommutator- type machine, the dynamo, was built by Hippolyte Pixii in 1832, based on a suggestion by André-MarieAmpère. Commutators are relatively inefficient, and also require periodic maintenance such as brush replacement. Therefore, commutated machines are declining in use, being replaced by alternating current (AC) machines, and in recent years by brushless DCmotors which use semiconductor switches. PRINCIPLEOF MACHINES: A commutator consists of a set of contact bars fixed to the rotating shaftof a machine, and connected to the armaturewindings. As the shaftrotates, the commutator reverses the flow of current in a winding. For a single armaturewinding, when the shafthas made one-half complete turn, the winding is now connected so that current
  28. 28. Prabjeet Singh Page 28 flows through it in the opposite of the initial direction. In a motor, the armaturecurrentcauses the fixed magnetic field to exert a rotational force, or a torque, on the winding to make it turn. In a generator, the mechanical torque applied to the shaftmaintains the motion of the armaturewinding through the stationary magnetic field, inducing a currentin the winding. In both the motor and generator case, the commutator periodically reverses thedirection of currentflow through the winding so that currentflow in the circuit external to the machine continues in only one direction. RING/SEGMENT CONSTRUCTION: A commutator consists of a set of copper segments, fixed around the partof the circumferenceof the rotating machine, or the rotor, and a set of spring- loaded brushes fixed to the stationary frameof the machine. Two or more fixed brushes connect to the external circuit, either a sourceof currentfor a motor or a load for a generator. Commutator segments are connected to the coils of the armature, with the number of coils (and commutator segments) depending on the speed and voltage of the machine. Large motors may have hundreds of segments. Each conducting segment of the commutator is insulated fromadjacent segments. Mica was used on early machines and is still used on large machines. Many other insulating materials are used to insulate smaller machines; plastics allow quick manufacture of an insulator, for example. The segments are held onto the shaft using a dovetail shapeon the edges or undersideof each segment. Insulating wedges around the perimeter of each segment are pressed so that the commutator maintains its mechanical stability throughoutits normal operating range. Commutator is used to collect currentfrom armatureconductor. In small appliance and tool motors the segments are typically crimped permanently in place and cannot be removed. When the motor fails it is discarded and replaced. On large industrial machines (say, fromseveralkilowatts to thousands of kilowatts in rating) it is economical to replace individual damaged segments, and so the end-wedgecan be unscrewed and individual segments removed and replaced. Replacing the copper and mica segments is commonly referred to as "refilling". Refillable dovetailed commutators are the most common construction of larger industrial type commutators, butrefillable commutators may also be constructed using external bands made of fiberglass (glass banded construction) or forged steel rings (external steel shrink ring type construction and internal steel shrink ring type construction). Disposable, molded type commutators commonly found in smaller DC motors are becoming increasingly more common in larger electric motors. Molded type commutators are not repairable and mustbe replaced if damaged. In addition to the commonly used heat,
  29. 29. Prabjeet Singh Page 29 torque, and tonnage methods of seasoning commutators, somehigh performance commutator applications require a more expensive, specific "spin seasoning" process or over- speed spin-testing to guarantee stability of the individual segments and preventpremature wear of the carbon brushes. Such requirements are common with traction, military, aerospace, nuclear, mining, and high speed applications where prematurefailure can lead to serious negative consequences. Friction between the segments and the brushes eventually causes wear to both surfaces. Carbon brushes, being made of a softer material, wear faster and may be designed to be replaced easily without dismantling the machine. Older copper brushes caused morewear to the commutator, causing deep grooving and notching of the surfaceover time. The commutator on small motors (say, less than a kilowatt rating) is not designed to be repaired through the life of the device. On large industrial equipment, the commutator may be re- surfaced with abrasives, or the rotor may be removed fromthe frame, mounted in a large metal lathe , and the commutator resurfaced by cutting it down to a smaller diameter. The largest of equipment can include a lathe turning attachment directly over the commutator. Figure 4: Cross sectional view of commutator The rotating part of the d.c machine is called the armature. The armatureconsists of shaft upon which a laminated cylinder called armature core, is mounted. The armaturecore has grooves or slots on its outer surface. The lamination are insulated from each other and tightly clamped together. In small machine the lamination are keyed directly to the shaft. In large machine they are mounted on a spider. The purposeof the lamination is to reduce eddy currentloss. The insulated conductors are put in the slots of the armature core. The conductors arewedged and bands of steel wire are fastened around the core to prevent them flying under the
  30. 30. Prabjeet Singh Page 30 centrifugal forces. The conductors aresuitably connected. This connected arrangementis called armaturewinding. Figure 5: Armature of motor 3.8 TXM WINDING Windings are the wires that are laid in coils, usually wrapped around a laminated softiron magnetic core so as to form magnetic poles when energized with current. Electric machines come in two basic magnet field pole configuration: salient pole machine and non salient pole machine. In the salient pole machine the poles magnetic field is produced by a winding wound around the pole below the pole face. In the non salient pole, or distributed field or round rotor motor the winding is distributed in pole face slots. A shaded pole motor has a winding around part of the pole that delays the phaseof the magnetic field for that pole. Some motors haveconductors which consistof thicker metal, such as bars or sheet of metal, usually copper, although sometimes aluminium is also used. These arepowered by electromagnetic induction. Armaturecoils can be connected to the commutator to formeither Lap or Wave winding. LAP WINDING: The ends of the armature coil are connected to the adjacent segments on the commutator so that the total number of parallel paths is equal to the total numbers of poles. That is, for LAP WINDING A=P. This winding is necessarily required for large current applications as it has more number of parallel paths. This may be remembered by the letters A and P in LAP. The disadvantageof lap winding is that it gives less emf as compared to wave winding. This winding requires more number of conductors for giving the same emf, it results in high winding cost. WAVEWINDING: the ends of each armaturecoil are connected to commutator segments some distanceapart, so that only two parallel paths are provided between the positive and the negative brushes. Thatis, for WAVEWINDING A=2.
  31. 31. Prabjeet Singh Page 31  In general lap winding is used in low voltage, high current machines, and the wave winding is used in high voltage, low current machines. WINDING MATERIAL: Coils are typically wound with enameled copper wire, sometimes termed magnet wire. The winding material must havea low resistance, to reduce the power consumed by the field coil, but more importantly to reducethe wasteheat produced by ohmic heating. Excess heat in the windings is a common causeof failure. Owing to the increasing cost of copper, aluminium windings are increasingly used. An even better material than copper, except for its high cost, would be silver as this has even lower resistivity. Silver has been used in rare cases. PROCESS CHART: Core from Commutator & Core Equaliser Winding Armature Winding Oven for 5-6 hrs at 160˚- 165˚C Temporary Banding Wedging and Packing First turningTIG Welding Oven for 5-6 hrs at 160˚- 165˚C Permenant Banding Oven for 5-6 hrs at 160˚- 165˚C Vacuum Pressure Impregnation Oven for 10-12 hrs at 190˚- 195˚C Secondary and Final Turning Mica under cutting & PTFE FITTMENT Shipment to Assembly
  32. 32. Prabjeet Singh Page 32 3.9 TXM FIELDING A field coil is an electromagnet used to generate a magnetic field in an electro-magnetic machine, typically a rotating electrical machine such as a motor or generator. Itconsists of a coil of wire through which a currentflows. In a rotating machine, the field coils are wound on an iron magnetic core which guides the magnetic field lines. The magnetic core is in two parts; a stator which is stationary, and a rotor, which rotates within it. The magnetic field lines pass in a continuous loop or magnetic circuit fromthe stator through the rotor and back through the stator again. The field coils may be on the stator or on the rotor. The magnetic path is characterized by poles, locations at equal angles around the rotor at which the magnetic field lines pass fromstator to rotor or vice versa. Thestator (and rotor) is classified by the number of poles they have. Mostarrangements use one field coil per pole. Some older or simpler arrangements usea single field coil with a pole at each end. Although field coils are most commonly found in rotating machines, they are also used, although not always with the same terminology, in many other electromagnetic machines. These include simple electromagnets through to complex lab instruments such as mass spectrometers and NMR machines. Field coils were once widely used in loudspeakers before the general availability of lightweight permanent magnets. The magnetic field systemis the stationary partof the machine. It produces the main flux. The outer frame or yokeis a hollow cylinder of cast steel or rolled steel. And even number of pole cores is bolted to the yoke. The yokeserves the following two purposes:  Itsupports the pole cores and acts as the protective cover to the machine.  Itforms a part of the magnetic circuit. Since the poles projected inwards they are called salient poles. Each pole core has a pole shoe having a curved surface. The pole shoeserves two purposes:  Itsupports the field coils.  Itincreases the cross sectionalarea of the magnetic circuit and reduces its reluctance. The pole cores are made of sheet steel laminations that are insulated fromeach other and riveted together. The poles are laminated to reduce eddy currentloss.
  33. 33. Prabjeet Singh Page 33 Each pole core has one or more field coils (windings) placed over it to producea magnetic field. The field coils are connected in series with one other such that when the current flows through the coils, alternate north and south poles are produced in the direction of rotation. 3.10 TXM ASSEMBLY Currentis collected fromthe armaturewinding by means of two or more carbon brushes mounted on the commutator. Each brush is supported in a metal box called a brush box or brush holder. Thepressureexerted by the brushes on the commutator can be adjusted and is maintained at a constant value by means of springs. Current produced in the armature windings is passed on the commutator and then to the external circuit by means of brushes.
  34. 34. Prabjeet Singh Page 34 BRUSH CONSTRUCTION: Early machines used brushes madefromstrands of copper wireto contact the surfaceof the commutator. However, thesehard metal brushes tended to scratch and groovethe smooth commutator segments, eventually requiring resurfacing of the commutator. As the copper brushes woreaway, the dustand pieces of the brush could wedge between commutator segments, shorting them and reducing the efficiency of the device. Fine copper wire mesh or gauze provided better surfacecontact with less segment wear, but gauze brushes weremore expensivethan strip or wire copper brushes. Modern rotating machines with commutators almostexclusively use carbon brushes, which may havecopper powder mixed in to improveconductivity. Metallic copper brushes can be found in toy or very small motors, such as the one illustrated above, and somemotors which only operate very intermittently, such as automotive starter motors. Motors and generators suffer froma phenomenon known as 'armaturereaction', one of the effects of which is to change the position at which the current reversalthrough the windings should ideally take place as the loading varies. Early machines had the brushes mounted on a ring that was provided with a handle. During operation, it was necessary to adjustthe position of the brush ring to adjustthe commutation to minimize the sparking atthe brushes. This process was known as 'rocking the brushes'. Various developments took place to automate the process of adjusting the commutation and minimizing the sparking atthe brushes. Oneof these was the development of 'high resistance brushes', or brushes madefroma mixture of copper powder and carbon. Although described as high resistance brushes, theresistanceof such a brush was of the order of milliohms, the exact value dependent on the sizeand function of the machine. Also, the high resistance brush was not constructed like a brush but in the formof a carbon block with a curved face to match the shapeof the commutator. The high resistanceor carbon brush is made large enough that it is significantly wider than the insulating segment that it spans (and on large machines may often span two insulating segments). The result of this is that as the commutator segment passes fromunder the brush, the currentpassing to it ramps down more smoothly than had been the casewith pure copper brushes wherethe contact brokesuddenly. Similarly the segment coming into contact with the brush has a similar ramping up of the current. Thus, although the current passing through the brush was moreor less constant, the instantaneous currentpassing to the two commutator segments was proportionalto the relative area in contact with the brush.
  35. 35. Prabjeet Singh Page 35 The introduction of the carbon brush had convenient side effects. Carbon brushes tend to wear more evenly than copper brushes, and the soft carbon causes far less damage to the commutator segments. There is less sparking with carbon as compared to copper, and as the carbon wears away, the higher resistanceof carbon results in fewer problems fromthe dust collecting on the commutator segments. The ratio of copper to carbon can be changed for a particular purpose. Brushes with higher copper content performbetter with very low voltages and high current, while brushes with higher carbon content are better for high voltage and low current. High copper content brushes typically carry 150 to 200 amperes per squareinch of contact surface, while higher carbon content only carries 40 to 70 amperes per squareinch. The higher resistanceof carbon also results in a greater voltage drop of 0.8 to 1.0 volts per contact, or 1.6 to 2.0 volts across the commutator. BRUSH HOLDERS: A spring is typically used with the brush, to maintain constantcontact with the commutator. As the brush and commutator wear down, the spring steadily pushes the brush downwardstowards thecommutator. Eventually the brush wears smalland thin enough that steady contact is no longer possible or it is no longer securely held in the brush holder, and so the brush mustbe replaced. Itis common for a flexible power cable to be directly attached to the brush, becausecurrent flowing through the supportspring would causeheating, which may lead to a loss of metal temper and a loss of the spring tension. When a commutated motor or generator uses morepower than a single brush is capable of conducting, an assembly of several brush holders is mounted in parallel across the surfaceof
  36. 36. Prabjeet Singh Page 36 the very large commutator. This parallel holder distributes currentevenly across all the brushes, and permits a careful operator to removea bad brush and replace it with a new one, even as the machine continues to spin fully powered and under load. High power, high current commutated equipment is now uncommon, due to the less complex design of alternating currentgenerators that permits a low current, high voltage spinning field coil to energize high currentfixed-position stator coils. This permits the use of very small singular brushes in the alternator design. In this instance, the rotating contacts are continuous rings, called slip rings, and no switching happens. Modern devices using carbon brushes usually havea maintenance-free design that requires no adjustmentthroughoutthe life of the device, using a fixed-position brush holder slot and a combined brush-spring-cableassembly thatfits into the slot. The worn brush is pulled out and a new brush inserted. Figure 6: Brush holder BRUSH CONTACT ANGLE: Commutator and brush assembly of a traction motor; the copper bars can be seen with lighter insulation strips between the bars. Each dark grey carbon brush has a shortflexible copper jumper lead attached. Parts of the motor field winding, in red, can be seen to the right of the commutator. The different brush types make contact with the commutator in different ways. Because copper brushes havethe samehardness as the commutator segments, the rotor cannotbe spun backwards againsttheends of copper brushes withoutthe copper digging into the
  37. 37. Prabjeet Singh Page 37 segments and causing severedamage. Consequently, strip/laminate copper brushes only make tangential contact with the commutator, while copper mesh and wirebrushes usean inclined contact angle touching their edge across the segments of a commutator that can spin in only one direction. The softness of carbon brushes permits direct radial end-contact with the commutator without damage to the segments, permitting easy reversalof rotor direction, without the need to reorient the brush holders for operation in the oppositedirection. Although never reversed, common appliance motors that use wound rotors, commutators and brushes haveradial- contact brushes. In thecase of a reaction-typecarbon brush holder, carbon brushes may be reversely inclined with the commutator so that the commutator tends to push against the carbon for firm contact. Figure 7: Brush angle contact 3.11 TXM TESTING In commutator and core area there are two type of testing’s:  Bar to bar testing: This is the testing in which shortcircuit between the copper bars of COMMchecked. If there is any breakage in mica sheet then shortcircuit will occur.  FT testing: This testing is between COMM hub and COMM BAR. If there is any breakage in mica sheet between COMM hub and COMM bar siren sound will heard. The process of testing is that one end of the testing (positive) is placed on copper wiresurround COMMbar and other end is placed at COMM hub. Tests on Motor:
  38. 38. Prabjeet Singh Page 38  LR testing- it is a light reader testing used to test vibration, temperature, sound, rpm. For measuring rpm optical tachometer is used. In this process of testing radium placed on armatureshaft and optical tachometer is placed in frontof it.  Overall testing: in this AC and DCmotor testing is done. in this testing generator and motor are coupled. In this area vibration, temperature, sound is checked by mechanical mean.  ROUTINE TEST: Cold resistancemeasurement->OneHour run test->over Speed Test- >Commutation Test->Characteristics Test->Dielectric->Hot Internalresistancetest->H.V Test ->Hot InternalTest->Ovality test
  39. 39. Prabjeet Singh Page 39 CHAPTER 4: POWER TRANSFORMER MANUFACTURING 4.1 INTRODUCTION A Transformer is static device used for transforming power fromonecircuit to another without changing frequency. The rangeof power transformers in B.H.E.L. covers fromlow voltage medium power transformer to extra large power transformer of 1500 MVA bank in 765 kV class & HVDC converter transformers of 1500 MVA banks in ± 500 kV DC . Productrangealso includes Shunt Reactor upto 150 MVARin 400 kV class and 330 MVAR in 765 kV class. 4.2 MAIN PARTS OF TRANSFORMER CORE: BHEL maketransformers having Coretype configuration. Coreis built up fromcold rolled grain oriented silicon alloy steel of the best magnetic properties. CNC machine is used for slitting; cropping / mitering operations with perfect controlun burr level. A computer programdetermines number of steps, position of the oil ducts and the sizes of the laminations for optimum cross section of core and yokes. In order to achieve a further reduction of iron
  40. 40. Prabjeet Singh Page 40 loss laminations are mitered and core bolts for clamping are kept to a minimum. Bolts in core legs are completely eliminated by using resin bonded glass tape for binding or by using skin stressed cylinder.  Magnetic circuits are of generally 3 limb construction in single phasetransformer in which only center limb is wound and the outer limbs providereturn path for main flux.  In three phase transformer 5 limb construction is used which has 2 vertical return limbs and 3 main cores. CONSTRUCTIONAL FEATURES: The type of transformer coreconstruction depends on the technical particulars of the transformer and transport considerations. In generalit is preferable to accommodate the windings of all the three phases in a single coreframe. Three phasetransformers areeconomical over a bank of three single-phasetransformers. Another important advantageof three-phasetransformer cores is that componentof the third and its multiple harmonics of mmf cancel each other, consequently the secondary voltagewave shapeare free from distortions dueto the third harmonics in mmf. However, if the three- phaseratings arelarge enough and difficult to transport, one has no choice but to go for single-phasetransformer units. For single-phaseand three-phasetransformers, thecores can be broadly classed as:  Single-phasethree-limbed core  Single-phase two-limbed core  Three-phase three-limb core  Three-phase five-limbed core Figure 8: Stepped core construction
  41. 41. Prabjeet Singh Page 41 (a) Single-phase Three-limbed Core The windings are placed around the central limb, also known as main limb. The main magnetic flux generated in the central limb gets divided into two parallel return paths provided by the yokes and auxiliary limbs. For the same magnetic flux density as that in the main limb, the auxiliary limbs and the yokes need to have the cross section only half of the main limb. This type of transformer core is generally preferred for single-phase transformer, as this is more economical than two limbed construction discussed below (b) Single-phaseTwo-limbed core Sometimes the single-phasepower ratings of transformers are so large that if the windings of full power ratings were to be placed on the central limb, its width would become too largeto be transported. To mitigate such difficulties the windings aresplit into two parts and placed around two separatelimbs. Here the cross-sectionalarea of the legs (limbs) and the yokes are identical. Consequently these cores are bulkier than the single phasethree-limbed arrangements. Also the percentage leakage reactance for this type of core construction is comparatively higher due to distributed nature of the windings in the two limbs separately.
  42. 42. Prabjeet Singh Page 42 (c)Three-phase Three-limbed cores This type of coreis generally used for three-phasepower transformer of small and medium power ratings. Each phaseof the winding is placed around one leg. For each phaseof magnetic flux appearing in a limb, the yokes and the remaining two limbs providethe return path. If the phasefluxes are denoted as ØA, ØB, ØC, their summation at any instant of time is identically zero, which can be mathematically stated as ØA + ØB + ØC = 0. In this type of construction, all the legs and the yokes haveidentical cross section. (d) Three-phaseFive-limbed cores For large rating power transformers, cores have to be built in large diameters. In case of three- phase three-limbed cores, the yokes have the same diameter as the limbs. In case of large diameter cores, the overall core height will go up leading to transport problem. For such cases the yokecross-sections (and consequently yokeheights) are reduced by approximately 40% or more and auxiliary paths for the magnetic flux are provided through auxiliary yokes and limbs. The cross-section and the height of the auxiliary yokes and limbs are lower than that of the main yokes.
  43. 43. Prabjeet Singh Page 43 CORE MANUFACTURING PROCESS: CRGO (cold rolledgrainoriented) Importedfrom: 1) Nippon Steel Corporation, Yawata Works (Japan) 2) VIZ-SteelLtd., Yekaterinburg (Russia) 3) POSCO Slitting Machine (Sequenceof operation): - Drawing / Q plan - Size / Grade CRGO - Burr Level 20 micron - Steel width within tolerance - Every 500mwidth check Burr Gauge - Scrap and Buckling Cropping Machine (Sequence of operation): - Revised drawing / QA Plan checked - Every 100 sheet parameter check After completion of assembly of core including curing of resin glass tape, 10 KV AC test between - Core and End-Frame - Core and Yoke-Bolts - End-Frameand Yoke-Bolts CRGO Imported SlittingMachine CroppingMachine Stacking/Arranging Setting(Jobs) Core Building Clamping Lifting Tapping Curing Test (2kV/10kV) Shift to Assembly/Tank
  44. 44. Prabjeet Singh Page 44 FLOW CHART FOR CORE FORMATION: WINDING: Windings form the electrical circuit of a transformer. Their construction should ensure safety under normal and faulty conditions. The windings must be electrically and mechanically strong to withstand both over-voltages under transientsurges, mechanical stress during short circuit and should not attain temperatures beyond the limit under rated and overload conditions. For core-type transformers, the windings are cylindrical, and are arranged concentrically. Circular coils offer the greatest resistance to the radial component of electromagnetic forces, since this is the shape which any coil will tend to assume under short circuit stresses. WINDING CONDUCTOR: The shape of the winding conductor in power transformers is usually rectangular in order to utilize the available space effectively. Even in smaller transformers for distribution purposes where the necessary conductor cross section easily can be obtained by means of a small circular wire, this wire is often flattened on two sides to increase the space factor in the core window. With increasing conductor area, the conductor must be divided into two or more parallel conductor elements in order to reduce the eddy current losses in the winding and ease the winding work. Strands may be insulated either by paper lapping or by an enamel lacquer. The matter is mechanically soft. In order to withstand the short circuit forces it is sometimes necessary to increase the strength of the material by means of a cold working. In large power transformers the mechanical forces during short circuit current have often Slittingof core steel rolls to required width on slittingmachines. Croppingand mitringto the required dimensions. Hole punchingin the laminationswhere required. Assembly of insulation between clamp plate/end frame & core laminations. Lying of clamp plates and end frame and its levelling. Stackingof laminations of different sizeto the required thickness. Preparation of oil duct in core,Core building. Clampingof core after assembly of the top end frame and Tightening of core. Lifting of core by use of a cradle,and carryingout isolation checks after treatment of insulation items.
  45. 45. Prabjeet Singh Page 45 more influence on the winding dimensions then thermal aspects and loss considerations. Generally two types of conductors are used for winding. PAPER INSULATED COPPERCONDUCTOR (PICC): In PICCs thestrands (Copper conductors) have a lapping of paper insulation. The paper lapping is built up of thin paper strips, a few centimeters wide, wound around and along the strand as indicated in figure. The paper is lapped in several layers to obtain the necessary total thickness set by the electrical and mechanical stresses. CONTINUOUSLY TRANSPOSED COPPER CONDUCTOR: Special kind of winding conductor is the ‘Continuously Transposed Cable (CTC)’. This cable is built up of two layers of enamel lacquer insulated strands arranged axially upon each other as shown in figure. By transposing the outer strain of one layer to the next layer with a regular pitch and applying common outer insulation a continuous transposed cable is achieved. When traversing the same flux for a whole transposition cycle, all strands loops receive the same induced voltage, and circulating currents between the strands are avoided. Transposition of strands mustalso be made in windings with conventional conductors to avoid circulating currents. If necessary for increased mechanical strength, the strands are covered
  46. 46. Prabjeet Singh Page 46 with the epoxy glue, which cures during processing the winding. For lower voltages a netting around the transposed cable is used to keep the strands together. For higher voltages insulation paper covers the cable. DISTRIBUTED CROSS OVER WINDINGS: Thesewindings are suitable for currents not exceeding about 20A. They comprise wires of circular cross-section and areused for HV windings in small transformers in the distribution range. A number of such coils are joined in series, spaced with blocks which provideinsulation as well as duct for cooling. SPIRAL WINDING: This type of winding is normally used up to 33 kV and low current ratings. Strip conductors are wound closely in the axial direction without any radial ducts between turns. Spiral coils are normally wound on a Bakelite or pressboard cylinder. Though normally the conductors are wound on the flat side, sometimes they are wound on the edge. However, the thickness of the conductor should be sufficient compared to its width, so that the winding remains twist-free. HELICAL WINDING: This type of winding is used in low-voltage and high-current ratings. A number of conductors are used in parallel to form one turn. The turns are wound in a helix along the axial direction and each turn is separated from the next by a duct. Helical coils may be single-layer or double layer or multi-layer, if the number of turns are more. Unless transposed, the conductors within a coil do not have the same length and same flux embracing and therefore have unequal impedance, resulting in eddy losses due to circulating current between the conductors in parallel. To reduce these eddy losses, the helical windings
  47. 47. Prabjeet Singh Page 47 are provided with transposition of the conductors which equalize the impedances of the parallel conductors. INTERLEAVED DISCWINDING A disadvantagewith the continuous disc winding is that their strength against impulse voltages is not adequate for voltages above, say, 145 kV class. The impulse voltage withstand behavior of disc coils can be increased if the turns areinterleaved in such a fashion that two adjacent conductors belong to two different turns. Figureshows such a winding in which interleaving has been done in each pair of discs. Itwill be noticed that it is necessary to have 2n conductors in hand for winding when n in the number of conductors in parallel. Conductors of turns 8 and 9 are joined by brazing. A cross-over is given at the bottom of the disc. High Voltage Winding Disk type Large no. of turns Low current density Comparatively small conductor cross section Connected to core Low Voltage Winding Single layer helical type Less no. of turns High current density Large conductor cross section Nearest to the core Tap Winding Interleaved helical type Generally connected in series with High Voltage Winding (Except in GTs) Various coils are provided for tapings to regulate voltage to ± 10 % or more Helical coil (Single layer) Helical coil (Double Layer) Layer LLayer Layer layer)
  48. 48. Prabjeet Singh Page 48 PROCESSING OF WINDINGS AS PERTR10214P: Oil tank cleaning every 3 month. Coil to be pressed again at adjustmentload as specified in drawings. Adjustment forceto be maintained for 1-2 min CD to be measured under pressed condition. Forceto be removed completely. Allow restof 3-4 min. Coil compacting as per load given in drawings/ES. Compacting forceto be maintained for 1 min. Oil impregnation under vacuum. Oil soaking for 3 hrs or moreoften. Heating+Vacuum 100-120˚Cat 0.4 torr 50gm/hr or less for 48 hrs. Sample also to be prepared as per TR10095P. Sample property to be checked. Voltage test on winding. Heating at 120-125˚Cfor minimum 24 hrs. Difference in the top and bottom temperature to be ±5˚C. Samples to be send along with job. Cold compacting after completion of winding manufacturing. (for glued/epoxy coated conductors)
  49. 49. Prabjeet Singh Page 49
  50. 50. Prabjeet Singh Page 50 4.3 CORE AND COIL ASSEMBLY A part of the transformer manufacturing process, thecoreand coil assembly aspectplays a significant role wherethe core assembly is vertically placed where the foot plate touches the ground and the top yoke is removed. The limbs of the core are tightly wrapped with cotton tape and then varnished during the manufacturing and even repairing process.  First, the individual windings are assembled one over the other to formthe entire phase assembly.  The radial gaps between the windings are subdivided by means of solid transformer board barriers.  Stress rings and angle rings areplaced on top and bottom of the windings to achieve a contoured end insulation design for optimal controlof the oil gaps and creepage stresses.  The complete phase assemblies are then carefully lowered over the separatecore legs and solidly packed towards the core to assureoptimal shortcircuit capability.  The top coreyoke is then repacked and the complete core and coil assembly is clamped.  The lead exits (if applicable) and the lead supports and beams are installed. All winding connections and tap lead connections to the tap changer(s) aremade before drying the complete core and coil assembly in the vapor phase oven. 4.4 PROCESSING OF COREAND COIL ASSEMBLY The completed core and coil assembly is thoroughly dried to pre-determined power factor readings by the vapor phasedrying process, providing thefastest, most efficient and most effective drying of the transformer insulation available. The vapor phaseprocess uses the standard kerosenecycle method. In this system, keroseneis vaporized and drawn by vacuum into a heated autoclave where the transformer has been placed. Condensation of the vapor on the coreand coil assembly rapidly causes the temperature to rise and allows moistureto be drawn out of the insulation by the vacuum. High temperature and pressureareused to accelerate the drying process. When the power factor measurements and the removalrate of moisture have reached the required levels, the flow of kerosenevapor is stopped and a high vacuumis used to boil off the remaining moistureand kerosene. Because so much water is removed in this process, the insulation physically shrinks in size. Following removal fromthe autoclave, the transformer is repacked as required and then undergoes its final hydraulic clamping to ensuremaximum short-circuitstrength in the finished product. 4.5 DRYING OUT PROCESS In order to ensure power supply is completely reliable it depends on high performance
  51. 51. Prabjeet Singh Page 51 transformers and in order to achieve that the drying out process is extremely important. Under this process, thepaper insulation and pressboard material, which make up a significant proportion by volume of transformer winding, havethe capacity to absorb large amounts of moisturefrom atmosphere. The presenceof this moisture brings aboutthe reduction in the dielectric strength of the material and also an increasein its noise. 4.6 TANKFABRICATION AND FITTINGS The tanks are made of high quality steel and can withstand vacuum and pressure test as specified in IS as well as by the customers. All welds are checked ensuring 100 % leak proof seems and mechanical strength. All tanks are pressure tested before tanking the active part. The Pressed steel radiators are used to dissipate heat generated at rated load. The fin height and length are calculated according to the rating of transformers as well as customers' specifications. The fins can be plain or embossed. The radiators are fitted variably according to the rating of transformer. For smaller rating radiators are directed welded to the main tank while for higher rating detachable type radiators are provided with valves to facilitate during transportation and handling at site. The tanks are fabricated fromMS plates and are welded construction. They are tested at a pressureof 0.35 Kg./Sq. cm. for oil leakage output and they are normally welded directly to the tank. However, transformerscan be supplied with detachable radiators. 4.7 INSULATION SHOP:insulating materials used for the transformer protection are given below: Sr. No. Material Applications 1. Transformer Oil (Mineral Oil, PXE) Liquid dielectric and coolant 2. Craft paper Layer winding Insulation Covering copper conductor and transposed copper conductor 3. Creep Kraft paper Insulation of winding lead and shield 4. Press Paper Backing paper for axial cooling duct 5. Press Board Angle ring, Cap, lead out, insulating end of winding , Cylinder, Barrier, Washer, Yoke, top and bottom coil clamping ring 6. Wood and laminated wood Cleat , core/ yoke clamp, Wedge block 7. Insulation Tap Tapping and bending of transformer cores
  52. 52. Prabjeet Singh Page 52 8. Phenolic laminated paper base sheet Terminal gear support and cleat, gap filter in reactor, tap changer components 9. Phenolic laminated cotton fabric sheet Terminal board, for making core duct, support and cleat 4.8 TESTS ON TRANSFORMER: Thefollowing tests aregenerally performed on the transformer REFERENCE STANDARD: IEC 60076 Routine tests  Measurement of winding resistance  Measurement of voltage ratio, polarity and check of voltage vector relationship  Measurement of no-load loss and excitation current  Measurement of short-circuitimpedance and load loss  Measurement of insulation resistance  Switching impulse voltage withstand test  Lightning impulse voltage withstand test  Separate-sourcevoltagewithstand test  Induced ac over voltage withstand test with partial dischargemeasurement  Magnetic circuit (isolation) test Type tests  Temperature rise test  Measurement of power taken by water pumps  Dissolved gas analysis (DGA) of oil filled in the transformer Special tests  Measurement of acoustic sound level
  53. 53. Prabjeet Singh Page 53  Determination of capacitances and tan delta between winding-to-earth and between windings Mechanical tests  Vacuumtest on transformer tank  Oil pressuretest on completely assembled transformer
  54. 54. Prabjeet Singh Page 54 CHAPTER 5: BUSHING MANUFACTURING
  55. 55. Prabjeet Singh Page 55 5.1 INTRODUCTION In electrical power, a bushing is an insulated device that allows an electrical conductor to pass safely through a (usually) earthed conducting barrier such as the wall of a transformer or a circuit breaker. In its simplest form, a bushing consists of a central conductor embedded in a cylindrical insulation material having a radial thickness enough to withstand the high voltage. A bushing has to: (a) Carry the full load current. (b) Provide electrical insulation to the conductor for working voltage and for various over- voltages that occur during service. (c) Provide support against various mechanical forces. (d) Acts as an external safety device. 5.2 CLASSIFICATION OF BUSHINGS Bushings are classified according to the following factors:  APPLICATION OR UTILITY (A) ALTERNATOR BUSHING: AC generators require bushings up to 33 kV, but 22 kV, is more usual. With modern alternators, current ratings up to 20,000 Amp are required. (B) BUSHINGS FOR SWITCHGEAR: In the switchgear, bushings are to carry the conductors through the tank wall, and support the switch contacts. (C) TRANSFORMER BUSHINGS: Transformers require terminal bushings for both primary and secondary windings. In some cases, a high voltage cable is directly connected to the transformer via an oil filled cable box. A bushing then provides the connection between the cable box and transformer winding. (D) WALL OR ROOF BUSHING: In recent years, many sub-stations for 132 kV and above, in unfavorable situations have been put inside a building. For such applications wall/roof bushings are used. (E) LOCO BUSHINGS: These bushings are used in freight loco and AC EMU transformers for the traction application.  NON-CONDENSER AND CONDENSER BUSHINGS (A) NON-CONDENSER BUSHING: In its simplest form, a bushing would be a cylinder of insulating material, porcelain, glass resin, etc. with the radial clearance and axial clearance to suit the electric strengths. The voltage is not distributed evenly through the material, or along its length. As the rated voltage increases, the dimensions required become so large that this formof bushing is not a practical proposition. The concentration of stress in the insulation and
  56. 56. Prabjeet Singh Page 56 on its surfacemay give rise to partial discharge. This type of bushing is commonly used as low- voltage bushings for large generator transformers. (B) CONDENSER BUSHING: The condenser bushings are made by inserting very fine layers of metallic foil into the paper during the winding process. Theinserted conductive foils produce a capacitive effect which dissipates the electrical energy more evenly through the insulated paper and reduces the electrical field stress between the energized conductor and any earthed material. 5.3 BUSHING DESIGN All materials carrying an electric charge generate an electric field. When an energized conductor is near any material at earth potential it can cause very high field strengths to be formed. As the strength of the electric field increases, leakage paths may develop within the insulation. If the energy of the leakage path overcomes the dielectric strength of the insulation, it may puncture the insulation and allow the leakage current to flow through the shortest path through the earthed material toward the earth causing burning and arcing. The design of bushing must involve following considerations: (A) AIR-END CLEARANCE: The air-end clearance has to be sufficient to meet the specified over- voltage tests. It is also determined by the creep age distance, and the proportion of it that is protected from the rain. Having determined the air-end length, the air-end dimension of the
  57. 57. Prabjeet Singh Page 57 internal condenser can be determined. It is not necessary to grade 100%. Internal grading of 70% or less will give adequate surface grading for large bushings. (B) OIL-END CLEARANCE: As internal breakdown unlike air flashover, is more severe, specifications, therefore, demand an internal breakdown with a sufficient margin (about 15%) above the air withstand value. Both power frequency, and impulse voltage withstand tests have been used to specify this characteristic. (C) NUMBER OF CONDENSER LAYERS: The number of partial condensers is so chosen that the test voltage of each partial condenser should be between 10 kV to 15 kV. If more foils are introduced, it will cause too many folds and weaken the bushing. Also, will be air introduced in the folds, complicating the manufacture of bushing of high voltage class. (D) LENGTH OF EARTH LAYER: The length of the earth layer of a bushing is usually determined by the accommodation required for current-transformers, or by mounting considerations, though in some cases it may be allowed to assume its optimum dimension in relation to the radial dimensions. The ratio of Length of first foil (L1) and Length of nth foil (Ln) may be taken between 3 to 4. This ratio is denoted by a. (E) RADIAL GRADIENTS AND DIAMETERS: The radial gradient is limited for avoiding damage by discharges at the power-frequency test voltages, whether one minute or instantaneous. If the ratio of the earth layer diameter to that of the conductor 𝑟𝑛 𝑟𝑜⁄ is denoted by 𝛽, the stresses at the HV end and the earth voltage end will be equal, if the product of 𝛼and 𝛽is unity. However, it is not always possible to achieve this value. Hence 𝛼and 𝛽can vary from 0.8 to 1.2 if 𝛼, 𝛽=1, then Ln.Dn = L1.D0 (F) EQUIPOTENTIAL LAYER POSITION: After determining the dimensions of the inner and outer layers of the condenser, the position of the other layers can be calculate. The basis of the design of the condenser bushing is generally equal partial capacitances, which mean equal voltage on them and equal axial spacing between the ends of layers. 5.4 INSULATING MATERIAL Porcelain insulation: A basic porcelain bushing is a hollow porcelain shape that fits through a hole in a wall or metal case, allowing a conductor to pass through its center, and connect at both ends to the other equipments. The inside of these bushings is often filled with oil to provide additional insulation and used up to 36 kV
  58. 58. Prabjeet Singh Page 58 Paper insulation: The insulating material of bushing windings is usually paper-based with the following most common types: (A) SYNTHETIC RESIN BONDED PAPER (SRBP) In SRBP bushings, one side of the paper is film coated with synthetic resin which is cylindrically wound under heat and pressureinserting conducting layers at appropriate intervals. However, use of SRBP bushings is limited to voltages around 72.5 kV There is also the danger of thermal instability of insulation produced by the dielectric loss of the resins. The SRBP insulation is essentially a laminate of resin and paper which is prone to cracking. Moreover, paper itself will include air which will cause partial discharges even at low levels of electrical stress. (B) OIL IMPREGNATED PAPER (OIP) OIP insulation is widely used in bushing and instrument transformers up to the highest service voltages. In the manufacturing process, the Kraft paper tape or sheet is wound onto the conductor. Aluminum layers are inserted in predetermined positions to build up a stress- controlling condenser insulator. The condenser layer may be closer together, allowing higher radial stress to be used. The bushing is fully assembled before being vacuum impregnated in order to contain the oil. (C) RESIN IMPREGNATED PAPER (RIP) RIP bushings are wound in a similar manner as OIP. The raw paper insulation is then kept in a casting tool inside an auto-clave. A strictly controlled process of heat and vacuum is used to dry the paper prior to impregnation with epoxy resin. 5.5 CONSTRUCTIONAL DETAILS AND MAIN PARTS OF BUSHING CORE The core of bushing consists of a hollow or solid metallic tube, over which high grade electrical Kraft paper is wound. For condenser cores, conducting layers of metallic foil are introduced at predetermined diameters to make uniform distribution of electrical stress. The winding of the condenser core is done in a dust-free chamber. The core is then processed; this comprises of
  59. 59. Prabjeet Singh Page 59 drying in a high degree of vacuum (0.005mm), and then impregnating with high quality, filtered and de-gassed transformer oil. PORCELAIN Bushings for outdoor applications are fitted with hollow porcelain insulators. The OIP bushings are provide with insulators, both at air and oil ends, thus forming an insulating envelope, and the intervening space may be filled with an insulating liquid or another insulating medium. The function of an insulator is to resist flash over in adverse conditions. This is determined by.  The profile of the dielectric.  The mounting arrangement of the insulator, i.e., vertical, horizontal, or inclined.  The properties of the surface, i.e., hydrophobic nature, toughness etc. TOP CAP This is a metallic housing for the spring pack. It serves as an in-built oil conservator to cater for oil expansion, and has an oil level indicator. In many cases, it also serves the purpose of a corona shield. MOUNTING FLANGE This is used for mounting the bushing on an earth barrier, such as a transformer tank or a wall. It may have the provisions for following:  CT accommodation length  Rating plate giving the rating and identification details of bushing.  Test tap  Oil drain plug for sampling of oil  Air release plug The design of the flange and top cap is such as to minimize the loss due to hysteresis and eddy current effects. When heavy currents are being carried, this loss raises the temperature of the flange and top cap to a noticeable extent. For heavy currents, ordinary cast iron material cannot be used; hence non-magnetic materials such as stainless steel or aluminum are used. TEST TAP The test tap is provided for measurement of the power factor and capacitance of the bushing during testing and service
  60. 60. Prabjeet Singh Page 60 e. The test tap is connected via a tapping lead to the last condenser foil of the core within the bushing. During normal service, this tapping is electrically connected to the mounting flange through a self-grounding arrangement. REFERENCES  www.wikipedia.org  www.electrical4u.com  www.bhelbhopal.co.in  Daily Report Diary.  Electrical Machines by P.S. Bimbhra  Power System by J.B. Gupta and Power system by V.K. Mehta  Electric Machines by Ashfaq Husain

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