BHEL OVERVIEW BHEL was established more than 50 years ago when its first plant was setup in Bhopal ushering in the indigenous Heavy Electrical Equipment Industry in India. BHEL is largest engineering and manufacturing enterprise in India in the energy related/infrastructure sector. BHEL was established more than four decades ago ushering in the indigenous Heavy Electrical Equipment industry in India. BHEL has built over the years, a robust domestic market position by becoming the largest supplier of power plant equipment in India, and by developing strong market presence in select segment of the industry sector and the Railway. Currently, 80% of the Nuclear power generation in the country is through BHEL sets. A dream which has been more than realized with a well recognized track record of performance it has been earning profits continuously since 1971-72 and achieved a turnover of Rs 2,658 crore for the year 2007-08, showing a growth of 17 per cent . Bharat Heavy Electricals Limited is country’s ‘Navratna’ company and has earned its place among very prestigious national and international companies. It finds place among the top class companies of the world for manufacture of electrical equipments. BHEL caters to core sectors of the Indian Economy viz., Power Generation's & Transmission, Industry, Transportation, Telecommunication, Renewable Energy, Defense, etc. BHEL has already attained ISO 9000 certification for quality management, and ISO 14001 certification for environment management and OHSAS – 18001 certification for Occupational Health and Safety Management Systems. The Company today enjoys national and international presence featuring in the “Fortune International -500” and is ranked among the top 10 companies in the world, manufacturing power generation equipment. BHEL is the only PSU among the 12 Indian companies to figure in “Forbes Asia Fabulous 50” list. Probably the most significant aspect of BHEL’s growth has been its diversification .The constant reorientation of the organization to meet the varied needs in time with a philosophy that has led to total development of a total capability from concepts to commissioning not only in the field of energy but also in industry and transportation. In the world power scene BHEL ranks among the top ten manufacturers of power plant equipments not only in spectrum of products and services offered, it is right on top. BHEL‘s technological excellence and turnkey capabilities have won it worldwide recognition. Over 40 countries in world over have placed orders with BHEL covering individual equipment to complete power stations on turnkey basis 1
BHEL has Installed equipment for over 90000MW of power generation-for utilities, captive and industrial users. Supplied over 225000MW a transformer capacity and other equipment operating in transmission and distribution network up to 400Kv (AC& DC). Supplied over 25000 motors with drive control system to power projects, petro chemicals, refineries, steel, aluminum, fertilizers, cement plants etc. Supplied traction electrics and AC/DC locos to power over 12000kms railway network. Supplied over one million valves to power plants and other industries. BHEL manufactures over 180 products under 30 major product groups and caters to core sectors of the Indian Economy viz., Power Generation & Transmission, Industry, Transportation, Telecommunication, Renewable Energy, etc. The wide network of BHEL's 14 manufacturing divisions, four Power Sector regional centers, over 100 project sites, eight service centers and 18 regional offices, enables the Company to promptly serve its customers and provide them with suitable products, systems and services -- efficiently and at competitive prices. The high level of quality & reliability of its products is due to the emphasis on design, engineering and manufacturing to international standards by acquiring and adapting some of the best technologies from leading companies in the world, together with technologies developed in its own R&D centers. BHEL has acquired certifications to Quality Management Systems (ISO 9001), Environmental Management Systems (ISO 14001) and Occupational Health & Safety Management Systems (OHSAS 18001) and is also well on its journey towards Total Quality Management. BHEL vision is to become a world class engineering enterprise, committed to enhancing stakeholder value. The company is striving to give shape to its aspiration and fulfill the expectations of the country to become a global presence:Vision: “A world class engineering enterprise committed to enhance stakeholder values.” 2
Mission: “To be an Indian multinational engineering providing total business solution through quality product system and services in the field of energy, transportation, industry, infrastructure and other potential area. Values: Ensure speed of response. Foster learning, creativity and team work. Respect for dignity and potential of individuals Loyalty and pride in company Zeal for the change. Zeal to excel. Integrity and fairness in all matters. Strict adherence to commitments.
BUSINESS MISSION To maintain a leading position as supplier of quality equipments, system and services in the field of conversion, transmission, utilization, and conversation of energy for application in the area of electric power, transportation oil and gas exploration and industries. To utilize company’s capability and resources to expand busyness in to allied area an priority sector of economy like defense, communication and electronics.
BHEL OBJECTIVES A dynamic organization is one which keeps its aim high, adopts itself quickly to changing environment, so we are in BHEL. The objectives of the company have been redefined in the corporate plane for 90’s. Growth 3
To ensure a steady growth by enhancing the competitive edge of BHEL in existing busyness, new area and international market so as to fulfill national expectation from BHEL. Profitability To ensure a reasonable and adequate return on capital employed, primarily through improvements in operation, efficiency, capacity utilization & productivity and to generate adequate internal resources to finance the company’s growth. Focus To built a high degree of customer confidence by providing increased value of his money through international standards of product quality performance and superior customer service. People Orientation To enable each employee to achieve his potential, improve his capabilities, understand is role and responsibilities and participate and contribute to the growth and success of the company.
Technology To achieve technological excellence in operation of indigenous technologies and efficient absorption and adoption of imparted technologies to suit business. Image To fulfill the expectations, which stack holders like government as owner employee, customer and the country at large have from BHEL.
BHEL BHOPAL PROFILE
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Heavy Electrical Plant , Bhopal is the mother plant of Bharat Heavy Electricals Limited, the largest engineering and manufacturing enterprise inIndia in the energy-related and infrastructure sector, today. It is located at about 7 kms. from Bhopal Railway station, about 5 kms. from Habibganj Railway station and about 18 kms. From Raja Bhoj Airport. With technical assistance from Associated Electricals (India) Ltd., a UK based company, it came into existence on 29th of August, 1956. Pt. Jawaharlal Nehru, first Prime minister of India dedicated this plant to the nation on 6th of November, 1960. BHEL, Bhopal with state-of-the-art facilities, manufactures wide range of electrical equipments. It’s product range includes Hydro, Steam, Marine & Nuclear Turbines, Heat Exchangers, Hydro & Turbo Generators, Transformers, Switchgears, Control gears, Transportation Equipment, Capacitors, Bushings, Electrical Motors, Rectifiers, Oil Drilling Rig Equipments and Diesel Generating sets. BHEL, Bhopal certified to ISO: 9001, ISO 14001 and OHSAS 18001, is moving towards excellence by adopting TQM as per EFQM / CII model of Business Excellence. Heat Exchanger Division is accredited with ASME ‘U’ Stamp. With the slogan of “ Kadam kadam milana hai, grahak safal banana hai”, it is committed to the customers. BHEL Bhopal has its own Laboratories for material testing and instrument calibration which are accredited with ISO 17025 by NABL. The Hydro Laboratory, Ultra High Voltage laboratory and Centre for Electric Transportation are the only laboratories of its in this part of theworld. BHEL Bhopal's strength is it's employees. The company continuously invests in Human Resources and pays utmost attention to their needs. The plant's Township, well known for its greenery is spread over an area of around 20 sq kms. and provides all facilities to the residents like, parks, community halls, library, shopping centers, banks, post offices etc. Besides, free health services is extended to all the employees through 350 bedded (inclusive of 50 floating beds) Kasturba Hospital and chain of dispensaries. 5
BHEL – BUSINESS AREAS BHEL today is the largest Engineering Enterprise of its kind in India with excellent track record of performance, making profits continuously since 1971-72. BHEL's operations are organised around three business sectors, namely Power, Industry - including Transmission, Transportation, Telecommunication & Renewable Energy - and Overseas Business. This enables BHEL to have a strong customer orientation, to be sensitive to his needs and respond quickly to the changes in the market.
Power Industry Transportation Transmission Defenses etc. The greatest strength of BHEL is its highly skilled and committed 42,600 employees. Every employee is given an equal opportunity to develop himself and grow in his 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 workforce setting new benchmarks in terms of productivity, quality and responsiveness. POWER SECTOR Power is the core sector of BHEL and comprises of thermal, nuclear gas, diesel and hydro business. Today BHEL supplied sets, accounts for nearly 66 % of the total installed capacity in the country as against nil till 1969-70. BHEL manufactures boilers auxiliaries, TG sets and associate controls, piping and station C & I up to 500 MW rating with technology and capability to go up to 6
1000 MW range. The auxiliary products high value capital equipment like bowl and tube mills, pumps and heaters, electrostatic precipitators, gravimetric feeders, fans, valves etc. BHEL has contracted so far around 240 thermal sets of various ratings, which includes 14 power plants set up on turnkey basis. Nearly 85 % of World Bank tenders for thermal sets floated in India have been won by the company against international competition. BHEL has adopted the technology to the needs of the country and local conditions. This has led to the development of several technologies in house. The fluidized bed boiler that uses low graded high-ash abrasive Indian coal is an outcome of such an effort. With large-scale availability of natural gas and the sudden increase in demand, BHEL began to manufacture gas turbines and now possesses two streams of gas turbine technology. It has the capability to manufacture gas turbines up to 200 MW rating and custom built combined cycle power plants. Nuclear steams generators, turbine generators, sets and related equipment of 235 MW rating have been supplied to most of the nuclear power plants in India. Production of 500 MW nuclear sets, for which orders have been received. BHEL has developed expertise in renovation and maintenance of power plant equipment besides specialized know how of residual life assessment, health diagnostic and life extensions of plants. The four power sectors regional centers at New Delhi, Chennai, Kolkata and Nagpur will play a major role in giving a thrust to this business and focus BHEL's efforts in this area. As part of India’s largest Solar Power-based Island Electrification Project in India, Bharat Heavy Electricals Limited (BHEL) has successfully commissioned two Grid-Interactive Solar Power Plants of 100 KW each in Lakshadweep. With this, the company has commissioned a total of eleven Solar Power Plants in the Lakshadweep islands, adding over 1 MW of Solar Power to the power generating capacity of the coral islands in the Arabian Sea. BHEL has proven turnkey capabilities for executing power projects from concept to commissioning and manufactures boilers, thermal turbine generator sets and auxiliaries up to 500MW. It possesses the technology and capability to procure thermal power generation up to 1000MW. Co- generation and combined cycle plants have also been 7
introduced. For the efficient use of high ash content coal BHEL supplies circulating fluidized boiler. BHEL manufacturers 235MW nuclear sets and has also commenced production of 500MW nuclear turbine generator sets.
Custom made hydro sets of Francis, pelton and kepian types for different head discharge combination are also engineering and manufactured by BHEL. In, all 700 utility sets of thermal, hydro, gas and nuclear have been placed on the company as on date. The power plant equipment manufactured by BHEL is based on contemporary technology comparable to the best in the world and is also internationally competitive. The Company has proven expertise in Plant Performance Improvement through renovation modernization and up rating of variety of power plant equipment besides specialized know how of residual life assessment, health diagnostics and life extension of plants. POWER TRANSMISSION AND DISTRIBUTION (T&D) BHEL offer wide-ranging products and systems for T & D applications Products. manufactured include power transformers, instrument transformers, dry type transformers, series – and shunt reactor, capacitor tanks, vacuum – and SF circuit breakers gas insulated switch gears and insulators. A strong engineering base enables the Company to undertake turnkey delivery of electric substances up to 400 kV level series compensation systems (for increasing power transfer capacity of transmission lines and improving system stability and voltage regulation), shunt compensation systems (for power factor and voltage improvement) and HVDC systems (for economic transfer of bulk power). BHEL has indigenously developed the state-of-the-art controlled shunt reactor (for reactive power management on long transmission lines). Presently a 400 kV Facts (Flexible AC Transmission System) project under execution. A wide range of transmission products and systems are produced by BHEL to 8
meet the needs of power transmission and distribution sector. These include: • • • • •
Dry Type Transformers SF6 Switch Gears 400 KW Transmission Equipment High Voltage Direct Current System Series and Shunt Compensation Systems
In anticipation of the need for improved substations, a 33 KV gas insulated sub station with micro processors base control and protection system has been done.
INDUSTRY SECTOR BHEL is a major contributor of equipment and system to important industries like
Cement Petrochemicals Fertilizers Steel papers Refineries Mining and telecommunication
BHEL has indigenously developed the state-of-the-art controlled shunt reactor (for reactive power management on long transmission lines). Presently a 400 kV FACTS (Flexible AC Transmission System) projects is under execution. The range of system and equipment supplied includes:
Captive power plants High speed industrial drive turbines Industrial boilers and auxiliaries Waste heat recovery boilers Gas turbine pump, valves, seamless steel tubes Heat exchangers Process control etc. 9
The Company is a major producer of large-size thruster devices. It also supplies digital distributed control systems for process industries, and control & instrumentation systems for power plant and industrial applications. BHEL is the only company in India with the capability to make simulators for power plants, defense and other applications. The Company has commenced manufacture of large desalination plants to help augment the supply of drinking water to people. TRANSPORTATION BHEL is involved in the development design, engineering, marketing, production, installation, and maintenance and after-sales service of Rolling Stock and traction propulsion systems. In the area of rolling stock, BHEL manufactures electric locomotives up to 5000 HP, diesel-electric locomotives from 350 HP to 3100 HP, both for mainline and shunting duly applications. BHEL is also producing rolling stock for special applications viz., overhead equipment cars, Special well wagons, Rail-cum-road vehicle etc., Besides traction propulsion systems for in-house use, BHEL manufactures traction propulsion systems for other rolling stock producers of electric locomotives, diesel-electric locomotives, electrical multiple units and metro cars. The electric and diesel traction equipment on India Railways are largely powered by electrical propulsion systems produced by BHEL. The company also undertakes retooling and overhauling of rolling stock in the area of urban transportation systems. BHEL is geared up to turnkey execution of electric trolley bus systems, light rail systems etc. BHEL is also diversifying in the area of port handing equipment and pipelines transportation systems. 65 % of trains in Indian Railways are equipped with BHEL's traction and traction control equipment. These include: • Broad Gauge 3900 HP AC / DC locomotives • Diesel Shunting Locomotives up to 2600 HP • 5000 HP AC Loco with thyristor control • Battery Powered Road Vehicles and Locomotives TELECOMMUNICATION BHEL also caters to telecommunication sector by way of small, medium and large switching system. Renewable energy Technologies that can be offered by BHEL for exploiting non-conventional 10
and renewable resources of energy includes: wind electric generators, solar power based water pumps, lighting and heating systems. The company manufactures wind electric generators of unit size up to 250 KW for wind farms, to meet the growing demand for harnessing wind energy. International operations BHEL has, over the years established its references in over 50 countries of the world, ranging from the united-states in the west to new-Zealand in the far-east. These references encompass almost the entire product range of BHEL, covering turnkey power projects of thermal, hydro and gas based type sub-station projects, rehabilitation projects, besides a wide variety of products, like switch gear, transformer, heat exchangers, insulators, castings and forgings. Apart from over 1100MW of boiler capacity contributed in Malaysia, some of the other major successes achieved by the company have been in Oman, Saudi Arabia, Libya, Greece, Cyprus, Malta, Egypt, Bangladesh, Azerbaijan, Sri lanka, Iraq etc. execution of overseas projects has also provided BHEL the experience of working with world renowned consulting organizations and inspection agencies.
RESEARCH AND DEVELOPMENT(R&D) To remain competitive and meet customers’ expectations, BHEL lays great emphasis on the continuous up gradation of products and related technologies, and development of new products. The company has upgraded its products to contemporary levels through continuous in house efforts as well as through acquisitions of new technologies from leading engineering organizations of the world. Research and product development centers at each of the manufacturing divisions play a complementary role. BHEL’s investment in R&D is amongst the largest in the corporate sector in India. BHEL's vision is to become a world-class engineering enterprise, committed to enhancing stakeholder value. The company is striving to give shape to its aspirations and fulfill the expectations of the country to become a global player. The greatest strength of BHEL is its highly skilled and committed 42,600 employees. Every employee is given an equal opportunity to develop himself and grow in his 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 workforce setting new benchmarks in 11
terms of productivity, quality and responsiveness. BHEL has a corporate R & D center supported by R & D groups at each of the manufacturing divisions. The dedicated effort of BHEL's R & D engineers have produced several new products like automated storage retrieval system automated guide vehicles for material transportation etc. Establishment of Asia's largest fuel evaluation test facility at Tiruchi was high light of the year. This facility will enable evaluation of combustion, heat transfer and pollution parameters in boilers. Major R & D achievement include: • Design manufacture and supply of countries first 17.2 MW industrial steam turbines. • Development of 4700 HP AC / DC loco for Indian Railways. • Development of largest capacitor voltage transformers of 8800 PF 400 KV rating. • Development and application low cost ROBOTS for job loading/unloading. According to ex- CMD Mr. R.K.D. Shah, "BHEL is spending Rs. 60 Crores on Research and Development. Earning from product which has been commercialized has gone up 26 % to Rs. 760 Crores."
PRODUCTS Thermal Power Plants • Steam turbines, boilers and generators of up to 800 MW capacity for utility and combined-cycle applications ; Capacity to manufacture boilers and steam turbines with supercritical system cycle parameter and matching generator up to 1000 MW unit size. •
Steam turbines, boilers and generators of CPP applications; capacity to manufacture condensing, extraction, back pressure, injection or any combination of these types of steam turbines.
Nuclear Power Plants • Steam generator & Turbine generator up to 700 MW capacity. Gas-Based Power Plants • Gas turbines of up to 280 MW (ISO) advance class rating. • Gas turbine-based co-generation and combined-cycle systems of industry and utility applications. There are other products given as follows Hydro Power Plants, DG Power Plants, Industrial Sets, Boiler, Boiler Auxiliaries, 12
Piping System, Heat Exchangers and Pressure Vessels Pumps, Power Station Control Equipment, Switchgear, Bus Ducts, Transformers, Insulators, Industrial and Special Ceramics, Capacitors, Electrical Machines, Compressors, Control Gear, Silicon Rectifiers, Thyristor GTO/IGBT Equipment , Power Devices, Transportation Equipment Oil Field Equipment, Casting and Forgings, Seamless Steel Tubes, Distributed Power Generation and Small Hydro Plants.
TECHNICAL COLLABORATIONS PRODUCT
COLLABORATIONS
# Thermal Sets, Hydro Sets, Motors & Control Gears.
Prommashexport RUSSIA
# Bypass & Pressure Reducing Systems
Sulzer Brother Ltd. SWITZERLAND
# Electronic Automation System for Steam Turbine & Generators
Siemens AG. GERMANY
# Francis Type Hydro Turbines
General Electric CANADA
# Moisture Separator Reheaters
Baloke Duerr GERMANY
# Christmas Trees & Conventional Well
National Oil Well Head Assemblies, USA
# Steam Turbines , Generators and Axial Condensers
Siemens AG. GERMANY
# Cam Shaft Controllers and Tractions Current Control Units
Siemens AG. GERMANY
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MAJOR CUSTOMERS OF B.H.E.L
Supplied to all major utilities in India : National Thermal Power Corporation (NTPC) PGCIL NJPC NHPC NLC NPCIL NEEPCO APTRANSCO APGENCO JPPCL ALL State Electricity Boards (SEBs)
Abroad: TNB,Malaysia PPC,Greece MEW,Oman OCC,Oman GECOL,Libya Trinidad & Tobago New Zealand Tanzania etc
MAJOR COMPETITORS OF BHEL 1. Ansaldo 2. Asea Brown Boueri 3. Beehtel 4. Block & Neatch
Italy Switzerland USA USA 14
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
CNMI & EC Costain Electrim Energostio Electro Consult Franco Tosi Fuji GEC Alsthom General Electric Hitachi LMZ Mitsubishi Mitsui NEI Raytheon Rolls Royce Sanghai Electric Co.
China U.K. Poland Russia Italy France Japan U.K. USA Japan Russia Japan Japan U.K. USA Germany China
DIVISIONS OF BHEL There are 20 Divisions of BHEL, they are as follows:
HEEP, Haridwar HPEP, Hyderabad HPBP, Tiruchi SSTP & MHD, Tiruchi CFFP, Haridwar BHEL, Jhansi BHEL, Bhopal EPD, Bangalore ISG, Bangalore ED, Bangalore BAP, Ranipet IP, Jagdishpur IOD, New Delhi COTT, Hyderabad IS, New Delhi CFP, Rudrapur 15
HERP, Varanasi Regional Operations Division ARP, New Delhi TPG, Bhopal Power Group (Four Regions and PEM)
MANUFACTURING UNIT OF BHEL First Generation Units BHOPAL
Heavy Electrical Plant
HARDWAR
Heavy Electrical Equipment Plant
HYDERABAD
Heavy Electrical Power Equipment Plant
TIRUCHY
High Pressure Boiler Plant
Second Generation Units JHANSI
Transformer and Locomotive Plant
HARDWAR
Central Foundry and Forge Plant
TIRUCHY
Seamless Steel Tube Plant
Unit Through Acquisition and Merger BANGALORE
Electronic Division
Electro Porcelain Division
New Manufacturing Units 16
RANIPAT
Boiler Auxiliaries Plant
JAGDISHPUR
Insulator Plant
RUDRAPUR
Component and Fabrication Plant
BANGALORE
Industrial System Group
TRANSFORMERS A transformer is a device that transfers electrical energyfrom one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling. If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np. The windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions ofpower grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the 17
need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical.
BASIC PRINCIPLES
An ideal transformer. The secondary current arises from the action of the secondary EMF on the (not shown) load impedance. The transformer is based on two principles: first, that an electric current can produce a magnetic field(electromagnetism) and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil. An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates amagnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils. If a load is connected to the secondary winding, the load current and voltage will be in the directions indicated, given the primary current and voltage in the directions indicated (each will be alternating current in practice).
Induction law The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:
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where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and Φ is the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals
Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up or stepping down the voltage
Np/Ns is known as the turns ratio, and is the primary functional characteristic of any transformer. In the case of step-up transformers, this may sometimes be stated as the reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for example, a transformer with primary and secondary windings of, respectively, 100 and 150 turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150. Ideal power equation
The ideal transformer as a circuit element If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the 19
transformer is perfectly efficient. All the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the input electric power must equal the output power: giving the ideal transformer equation
This formula is a reasonable approximation for most commercial built transformers today. If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turns ratio.For example, if an impedance Zs is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the primary circuit appears to the secondary to be (Ns/Np)2Zp.
Detailed operation The simplified description above neglects several practical factors, in particular, the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit. Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance. When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core.: The current required to create the flux is termed the magnetizing current. Since the ideal core has been assumed to have near-zero reluctance, the magnetizing current is negligible, although still required, to create the magnetic field. The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VSmeasured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back EMF". This is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field.
PRACTICAL CONSIDERATIONS: 20
Leakage flux
Leakage flux of a transformer The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termedleakage flux, and results in leakage inductance in series with the mutually coupled transformer windings. Leakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss (see "Stray losses" below), but results in inferior voltage regulation, causing the secondary voltage to not be directly proportional to the primary voltage, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance. Nevertheless, it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary. In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply.Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads that become periodically shortcircuited such as electric arc welders. Air gaps are also used to keep a transformer from saturating, especially audiofrequency transformers in circuits that have a direct current component flowing through the windings. Leakage inductance is also helpful when transformers are operated in parallel. It can be shown that if the "per-unit" inductance of two transformers is the same (a typical value is 5%), they will automatically split power "correctly" (e.g. 500 kVA unit in parallel with 1,000 kVA unit, the larger one will carry twice the 21
current) Effect of frequency The time-derivative term in Faraday's Lawshows that the flux in the core is the integral with respect to time of the applied voltage. Hypothetically an ideal transformer would work with direct-current excitation, with the core flux increasing linearly with time. In practice, the flux rises to the point where magnetic saturationof the core occurs, causing a large increase in the magnetizing current and overheating the transformer. All practical transformers must therefore operate with alternating (or pulsed direct) current. The EMF of a transformer at a given flux density increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance. However, properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and winding weight. Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors. As such, the transformers used to step down the high over-head line voltages (e.g. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of a transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers may need to be equipped with "volts per hertz" over-excitation relays to protect the transformer from overvoltage at higher than rated frequency. One example of state-of-the-art design is transformers used for electric multiple unit high speed trains, particularly those required to operate across the borders of countries using different electrical standards. The position of such transformers is restricted to being hung below the passenger compartment. They have to function at different frequencies (down to 16.7 Hz) and voltages (up to 25 kV) whilst handling the enhanced power requirements needed for operating the trains at high speed. Knowledge of natural frequencies of transformer windings is necessary for the determination of winding transient response and switching surge voltages. Transformer universal EMF equation 22
If the flux in the core is purely sinusoidal, the relationship for either winding between its rms voltage Erms of the winding, and the supply frequencyf, number of turns N, core cross-sectional area a and peak magnetic flux density B is given by the universal EMF equation:
If the flux does not contain even harmonics the following equation can be used for half-cycle average voltage Eavg of any waveshape:
ENERGY LOSSES An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%. Experimental transformers using superconducting windings achieve efficiencies of 99.85%. The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design. Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed as "no-load" or "full-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a tradeoff between initial cost and running cost (also see energy efficient transformer). Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic circuit, termed iron loss. Losses in the transformer arise from: Winding resistance Current flowing through the windings causes resistive heating of the conductors. At higher frequencies,skin effect and proximity effect create additional winding resistance and losses. Hysteresis losses 23
Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected. Eddy currents Ferromagnetic materials are also good conductors and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness. Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies use laminated or similar cores. Magnetostriction Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers that can cause losses due to frictional heating. This buzzing is particularly familiar from low-frequency (50 Hz or 60 Hz) mains hum, and high-frequency (15,734 Hz (NTSC) or 15,625 Hz (PAL)) CRT noise. Mechanical losses In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise and consuming a small amount of power. Stray losses Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat. There are also radiative losses due to the oscillating magnetic field but these are usually small.
Core form and shell form transformers
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Core form = core type; shell form = shell type
As first mentioned in regard to earliest ZBD closed-core transformers, transformers are generally considered to be either core form or shell form in design depending on the type of magnetic circuit used in winding construction (see image). That is, when winding coils are wound around the core, transformers are termed as being of core form design; when winding coils are surrounded by the core, transformers are termed as being of shell form design. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent. Shell form design tends to be preferred for extra high voltage and higher MVA applications because, though more labor intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage.
EQUIVALENT CIRCUIT
Transformer equivalent circuit, with secondary impedances referred to the primary
25
side
The parameters of equivalent circuit of a transformer can be calculated from the results of two transformer tests: open-circuit test and short-circuit test.
TRANSFORMER RATINGS Transformers are rated at their kilovolt-ampere (kVA) outputs. If the load to be supplied by a transformer is at 100 percent power factor (pf), the kilowatt (kW) output will be the same as the kilovolt-ampere (kVA) output. If the load has a lesser power factor, the kW output will be less than the kVA output proportionally as the load power factor is less than 100 percent.
CLASSIFICATION OF TRANSFORMERS 1. According to method of cooling a. b. c. d.
Self-air–cooled (dry type) Air-blast–cooled (dry type) Liquid-immersed, self-cooled Oil-immersed, combination self-cooled and air-blast
e. Oil-immersed, water-cooled f. Oil-immersed, forced-oil–cooled g. Oil-immersed, combination self-cooled and water-cooled 2. According to insulation between windings a. Windings insulated from each other b. Autotransformers 3. According to number of phases 26
a. Single-phase b. Polyphase 4. According to method of mounting a. b. c. d.
Pole and platform Subway Vault Special
5. According to purpose a. b. c. d.
Constant-voltage Variable-voltage Current Constant-current
6. According to service a. Large power b. Distribution c. Small power d. Sign lighting e. Control and signaling
TRANSFORMER CORES Until recently, all transformer cores were made up of stacks of sheet-steel punchings firmly clamped together.Sometimes the laminations are coated with a thin varnish to reduce eddy-current losses. When the laminations are not coated with varnish, a sheet of insulating paper is inserted between laminations at regular intervals. A new type of core construction consists of a continuous strip of silicon steel which is wound in a tight spiral around the insulated coils and firmly held by spot welding at the end. This type of construction reduces the cost of manufacture and reduces the power loss in the core due to eddy currents.
OIL USED IN TRANSFORMERS
27
It performs two important functions. It serves to insulate the various coils from each other and from the core, and it conducts the heat from the coils and core to some cooler surfaces, where it is either dissipated in the surrounding air or transferred to some cooling medium. It is evident that the oil should be free from any conducting material, it should be suffi-ciently thin to circulate rapidly when subjected to differences of temperatures at different places, and it should not be ignitable until its temperature has been raised to a very high value. Although numerous kinds of oils have been tried in transformers, at the present time mineral oil is used almost exclusively. This oil is obtained by fractional distillation of petroleum unmixed with any other substances and without subsequent chemical treat-ment. A good grade of transformer oil should show very little evaporation at 100 oC, and it should not give off gases at such a rate as to produce an explosive mixture with the surrounding air at a temperature below 180oC. It should not contain moisture, acid, alkali, or sulfur compounds. It has been shown that the deteriorating effect of moisture on the insu-lating qualities of an oil is very marked; moisture to the extent of 0.06 percent reduces the dielectric strength of the oil to about 50 percent of the value when it is free from moisture, but there is very little further decrease in the dielectric strength with an increase in the amount of moisture in the oil. Dry oil will stand an emf of 25,000 V between two 0.5-in (12.7-mm) knobs separated by 0.15 in (3.8 mm). The presence of moisture can be detected by thrusting a red-hot nail in the oil; if the oil “crackles,” water is present. Moisture can be removed by raising the temperature slightly above the boiling point of water, but the time consumed (several days) is excessive. The oil is subsequently passed through a dry-sand filter to remove any traces of lime or other foreign materials.
OIL PRESERVATION SYSTEM We use a conservator oil preservation system as a standard. Many publications have stated the technical advantages of this system over both sealed tank and automatic positive pressure oil preservation systems, these being: 1. high dielectric integrity, 2. positive static pressure on unit at all times, 3. reduced maintenance, 4. possibility to use a buchholz relay & to collect gasses The conservator oil preservation system uses an expansion tank to and from which the transformer oil may flow freely as it expands or contracts due to oil temperature changes. This system always provides a head of oil above the main tank and keeps it completely filled. An oil level gauge is mounted on the conservator and indicates the change in liquid level. 28
Due to the heating of the oil in the transformer, oil expands and flows freely towards the conservator. The oil expansion of the On-Load Tap Changer diverter is completely separate from the transformer oil. A separate compartment is mounted to the main conservator. Both conservator compartments are equipped with an oil level gauge with a minimum alarm contact, pipes for oil draining, air inlet from the breather and connection to the transformer or OLTC. The oil level gauge is tilted downwards for the ease of reading when standing at the base of the transformer. The breather is filled with silica gel (Caldigel Orange) that removes all moisture and dust particles from the air that is inhaled by the conservator. To reduce maintenance and to save the environment, the standard silica gel breather can be replaced by an automatic breather with repetitive heating cycle on request. Atmoseal The main conservator can be fitted with a nitrile membrane to avoid all contact of ambient air with the transformer oil. This eliminates the possibility of moisture entering the transformer oil and oxidation of the oil in the conservator. On request, a leakage detector can be mounted on the conservator to signal a rupture of the membrane. A nitrile membrane in the load tap changer compartment is not possible due to the gasses produced at each tap change operation. For the same reason, a buchholz relay cannot be fitted on the load tap changer compartment; a special protective relay is designed for this purpose with an oil-surge sensitive damper system that cannot be tested with gas pressure or a spring operated pressure relay
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COOLING OF TRANSFORMER
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electrical breakdown under load. Oil-filled transformers may be equipped with Buchholz relays, which detect gas evolved during internal arcing and rapidly deenergize the transformer to avert catastrophic failure. Oil-filled transformers may fail, rupture, and burn, causing power outages and losses. Installations of oil-filled transformers usually includes fire protection measures such as walls, oil containment, and fire-suppression sprinkler systems. Polychlorinated biphenyls have properties that once favored their use as a dielectic coolant, though concerns over their environmental persistence led to a widespread ban on their use. Today, non-toxic, stable silicone-based oils, or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault.Before 1977, even transformers that were nominally filled only with mineral oils may also have been contaminated with polychlorinated biphenyls at 10-20 ppm. Since mineral oil and PCB fluid mix, maintenance equipment used for both PCB and oil-filled transformers could carry over small amounts of PCB, contaminating oil-filled transformers. Some "dry" transformers (containing no liquid) are enclosed in sealed, pressurized tanks and cooled by nitrogen or sulfur hexafluoride gas. Experimental power transformers in the 2 MVA range have been built with superconducting windings which eliminates the copper losses, but not the core steel loss. These are cooled by liquid nitrogen orhelium Though it is not uncommon for oil-filled transformers to have today been in operation for over fifty years high temperature damages winding insulation, the accepted rule of thumb being that transformer life expectancy is halved for every 8 degree C increase in operating temperature. At the lower end of the power rating range, dry and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation. As power ratings increase, transformers are often cooled by such other means as forced-air cooling, force-oil cooling, watercooling, or a combinations of these. The dielectic coolant used in many outdoor utility and industrial service transformers is transformer oil that both cools and insulates the windings. Transformer oil is a highly refined mineral oil that inherently helps thermally stabilize winding conductor insulation, typically paper, within acceptable insulation temperature rating limitations. However, the heat removal problem is central to all electrical apparatus such that in the case of high value transfomer assets, this often translates in a need to monitor, model, forecast and manage oil and winding conductor insulation temperature conditions under varying, possibly difficult, power loading conditions. Indoor liquid-filled transformers are required by building regulations in many jurisdictions to either use a non-flammable liquid or to be located in fire-resistant rooms. Air-cooled dry transformers are preferred for indoor applications even at capacity ratings where oil-cooled construction would be more economical, because their cost is offset by the reduced building construction cost. 31
INSULATION DRYING Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried before the oil is introduced. There are several different methods of drying. Common for all is that they are carried out in vacuum environment. The vacuum makes it difficult to transfer energy (heat) to the insulation. For this there are several different methods. The traditional drying is done by circulating hot air over the active part and cycle this with periods of hot-air vacuum (HAV) drying. More common for larger transformers is to use evaporated solvent which condenses on the colder active part. The benefit is that the entire process can be carried out at lower pressure and without influence of added oxygen. This process is commonly called vapour-phase drying (VPD). For distribution transformers, which are smaller and have a smaller insulation weight, resistance heating can be used. This is a method where current is injected in the windings to heat the insulation. The benefit is that the heating can be controlled very well and it is energy efficient. The method is called low-frequency heating (LFH) since the current is injected at a much lower frequency than the nominal of the grid, which is normally 50 or 60 Hz. A lower frequency reduces the effect of the inductance in the transformer, so the voltage needed to induce the current can be reduced. The LFH drying method is also used for service of older transformers.
TERMINALS Very small transformers will have wire leads connected directly to the ends of the coils, and brought out to the base of the unit for circuit connections. Larger transformers may have heavy bolted terminals, bus bars or high-voltage insulated bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil.
BUSHINGS
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A bushing is a hollow electrical insulator through which a conductor may pass. Bushings are used where high voltage lines must pass through a wall or other surface, on switchgear, transformers, circuit breakers and other high voltage equipment. DISCRIPTION
The bushing is a hollow insulating liner that fits through a hole in a wall or metal case, allowing a conductor to pass along its centre and connect at both ends to other equipment. The purpose of the bushing is to keep the conductor insulated from the surface it is passing through. Bushings are often made of wet-process fired porcelain, and may be coated with a semi-conducting glaze to assist in equalizing the electrical stress along the length of the bushing. The inside of the bushing may contain paper insulation and the bushing is often filled with oil to provide additional insulation. Bushings for medium-voltage and low-voltage apparatus may be made of resins reinforced with paper. The use of polymer bushings for high voltage applications is becoming more common. The largest high-voltage bushings made are usually associated with high-voltage directcurrent converters. Capacitor types Some of the higher voltage types (layers of conductive paper, film, ink or aluminum foil are used with an insulating medium) are called capacitor bushings because they form a low value capacitor between the conductor and the wall. This is done to disperse the electrical field stress and thus reduce the peak stress that could cause breakdown.
BUSHING FAILURE 33
Bushings sometimes fail due to partial discharge degradation in the insulation. There is at present great interest in the electricity supply industry in monitoring the condition of high voltage bushings.
METHODS OF MOUNTING Transformers are constructed with different types of metal enclosing structures to meet the requirements of different conditions of installation. One type of enclosure is designed for mounting on poles, either directly or with hanger irons, for use in overhead distribution work. Another type of enclosure, called the platform type, is suitable for installations in which the transformer stands upon its own base. It can be mounted on any flat horizontal surface having sufficient mechanical strength, such as a floor or a platform between poles. Subway transformers have watertight tanks which are designed primarily for underground installa-tions when the transformer may be completely submerged in water. Vault transformers also have watertight enclosures so that they will not be injured by total submersion, but they are not designed to operate satisfactorily under such conditions. The vault transformers are intended for operation in underground vaults in which the transformer would not be required to operate for any considerable length of time while submerged. Small transform-ers for power and special application are designed with special types of mounting to meet the requirements of installation for these types of service.
APPLICATIONS
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electrical substation showing 220kV/66kV transformers, each with a capacity of 185MVA
A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage (and therefore lowcurrent) form for transmission and back again afterward, transformers enable economical transmission of power over long distances. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand. All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer. Transformers are also used extensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage. Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers. Audio transformers allowed telephone circuits to carry on a two-way conversation over a single pair of wires. A balun transformer converts a signal that is referenced to ground to a signal that has balanced voltages to ground, such as between external cables and internal circuits. The principle of open-circuit (unloaded) transformer is widely used for characterisation of soft magnetic materials, for example in the internationally standardized Epstein frame method.
MANUFACTURING SECTIONS
INVENTORY It is the section of storage of raw material. FABRICATION Fabrication is nothing but production.It is basically a machine / preparation shop. This section has following machines: 35
• •
• • • • • • •
Pacific Hydraulic Shear & pressure: Hydraulically operated machine to cut to sheet of different thickness. It contain pressure holder which is used to flatten the sheet. CNC (Computerized Numerical control) Flame cutting machine: Used to cut complicated shaft item using OXY-ACETYLENE flame. Maximum 6 torches are used in it. Cutting is done on the basis of computer programming. Rolling Machine: used for making cylindrical shape from a sheet. Bending Machine: Hydraulically operated machine used to bend the job. Hydraulic power press: Has the capacity of 100 tons used to flatten the object. Nibbling Machine: used to do various tasks like straight cutting, circle cutting, nibbling, slot cutting, circular and square punching. Hydraulic Guillotine Shear: It is to cut the sheet which has maximum cross section area of (3200*13 sq.mm). Butler machine: used for facing, tapering, & slot cutting. Plasma Cutting Machine: used for non ferrous metal.
ASSEMBLY SHOP: It is an assembly shop where different part of tank comes . Hear welding processes are used for assembly, after which a rough surface is obtained and is eliminated by grinding. Grinding operates at 1200 RPM. It is assembly shop dealing with making different objects like. • • • • • •
Tank Assembly Tank cover assembly End frame assembly Cross feed assembly Core Clamp assembly Pin & pad assembly
Before assembly, short blasting is done on different part of jobs to clean the surface before painting. After assembly some tests are done as non-destructive tests like. 1. Ultrasonic Test: To detect the winding fault on CRO. At the fault place high amplitude waves are obtain. 2. Die Penetration Test: Red solution is put at the welding and then cleaned. After some time white solution is put. Appearance of red spot indicates a fault at the welding. 36
3. Magnetic crack detection: magnetic field is created and then iron powder is put on the welding. Sticking of the iron powder in the welding indicates the fault. 4. X-Ray Test: It is same as human testing and a fault is seen in X-ray. 5. Air / Vacuum Test: the air is filled inside the body of transformer, than soap solution is produced outside the body. If the holes appear, it is indicate the fault. MACHINE SECTION: To operation to form small components of power and traction transformer are done is this section. The shop consists of following machines. CENTRAL LATHE: It consist one tail stock, head stock. Lower part of tail stock is fixed and tail stock spindle is moving. On this machine is facing, turning and threading is done. TURRET LATHE: Its function is same as central lathe machine but it is used for mass production. Here turret head is used in presence of tail stock because turret head contains many tailstocks around six. CAPSTAN LATHE: It is belt driven. RADIAL ARM DRILLING MACHINE: Used for drilling and boring. HORIZONTAL BORING MACHINE: It is computerized and used for making bore, facing etc. MILLING MACHINE: a. HORIZONTAL MILLING MACHINE: Used for making gear and cutting operations. b. VERTICAL MILLING MACHINE: The machine does facing, slot cutting and T-slot cutting. COPPER SECTION: o Tube slitting Machine: used for cutting the tube along its length and across the diameter. o HYDRAULIC SHEARING MACHINE: It is hydraulically operated and its blade has V-shape and a thickness 15 mm. 37
o WATER COOLED BRAZING MACHINE: It contains two carbon brushes. The sheet is put along with sulfas sheet and the carbon brushes are heated. A lap joint is formed between the sheets as the sulfas sheets melts. o LINCING BELT MACHINE: It creates a smooth surface. o SOLDER POT MACHINE: It has a pot that contains solder. Solder has composition of 60 % Zn and 40 % Pb. TOOLING MACHING: In this section the servicing of tools is done. • • • •
Blade sharp machine Mini surface grinding Machine(used for grinding purpose) Tool and surface grinding Machine(used to grind the tool) Drill grinding Machine (to grid the drills)
WINDING , COIL AND MOULDS SECTION TYPES OF WINDING • Reverse section winding • Helical winding • Spiral winding • Interleaved winding • Half section winding The type of winding depends upon the job requirement. Also, the width and thickness of conductors designed and decided by design department. TYPES OF COIL 1. 2. 3. 4.
Low voltage coil High voltage coil Tertiary coil Tap coil
THE MOULDS ARE OF FOLLING TYPES 1. Belly type 2. Link type 3. Cone type
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LAMINATION AND PUNCHING SHOP The lamination used in power, dry and ESP transformer etc. for making core is cut in this section. CRGO (cold rolled grain oriented) silicon steel is used for lamination, which is imported in India from Japan, U.K and Germany. It is available in 0.27&0.28 mm. For the purpose of cutting and punching the core three machines are installed in the shop. • Slitting machine (used to cut CRGO sheets in different width) • CNC cropping line pneumatic • CNC cropping line hydraulic INSULATION SHOP Various type of insulation are: • • • • • • •
AWWW: all wood water washed press paper. The paper is 0.2-0.5 mm thick cellulose paper is bound on conductor for insulation. Pre-Compressed Board: this is widely used for general insulation and separation of conductors in the form of blocks. Press Board: this is used for separation of coil e.g. LV from HV. It is up to 38 mm thick. Fiber Glass: this is resin material and is used in fire prone area. Bakelite Gasket: used for protection against leakage. Silicon Rubber Sheet: It is used for dry type transformer.
Insulation between windings The great majority of transformers are constructed with two or more windings which are electrically insulated from each other. In some cases a single winding is employed, parts of the winding functioning as both primary and secondary. These transformers are called autotransformers. They are frequently used when the voltage ratio is small. Autotransformers should never be used for high voltage ratios, as the low-voltage winding is not insulated from the high-voltage one, so that in case of trouble it would be dangerous to both life and equipment. Machine used for shaping the insulation material are: 1. Cylindrical machine 2. Circular cutting machine 39
3. Bending machine 4. Punching press machine 5. Drilling machine 6. Guillotine machine 7. Bench saw 8. Jig saw 9. Circular saw 10. Lansing machine
MANUFACTURING PROCESS
CORE ASSEMBLY
40
•
Power Systems transformers are of the “Core Form” design. All cores are stacked, using high-quality grain-oriented silicon steel laminations, purchased slit-to-width and coated with carlite to increase the interlamination resistance and to reduce eddy current losses. Where loss evaluations justify its use, laser or mechanically scribed or plasma treated silicon steel will be used.
•
All cores utilize the step lap principle in the corner joints to reduce losses, magnetizing current and sound level. The cores are fullymitered on all joints in order to improve the flux distribution.
•
Ultra modern computerized core shears supply fully-mitered, highefficiency cores. These machines are able to shear the maximum width of core steel currently available.
•
Some machines automatically stack the legs and yokes to minimize steel handling and mechanical stresses, helping to guarantee the designed loss level.
•
The laminations are stacked in steps, resulting in a circular core shape which gives the windings optimum radial support, especially during short-circuit conditions.
•
The exposed edges of all finished cores are bonded with low viscosity, high-strength epoxy resin on the legs and bottom yoke to help lower the sound level. The temperature rise of the core is designed to be low and is controlled, if necessary, by careful placement of vertical oil ducts within the core packets.
•
The core is clamped using structural steel clamps which provide high strength under both static (lifting and clamping) and dynamic (shortcircuit) mechanical loads. The clamps are very lightweight for their strength and provide a smooth surface facing the winding ends, eliminating regions of high local electrical stress. 41
Under this process bonded core design is used to eliminate hold notching clamp and to minimize fixed losses and magnetizing current. The clamping frames for top and bottom yokes are incorporated into the still age but this must also provide support rigidity for the limbs until the core has been lifted in the vertical positions for assembling of the winding.
COIL WINDINGS AND INSULATION ASSEMBLE Coil windings is of two Types: The precise details of the winding arrangements will be varied according to the rating of the transformers. The general principles remain the same throughout most the range of transformer. The copper or Alluminium strips/wires used in winding are meticulously selected for its quality to give the best output. 1. L.V.Coil 2. H. V. Coil 1. L. V. COIL WINDING: The Low Voltage coil is designed to approximately match the current rating of the available low-voltage (LV). The L.V. coil is normally wound on robust tube of insulation material and this is almost invariably of synthetic resin-bonded paper. This material has high mechanical strength and is capable of withstanding the high loading. Electrically it will probably have sufficient dielectric strength to withstand the relatively modest test voltage applied to the L.V. winding during the repairing without any additional insulation. 2. H. V. COIL COIL WINDING: The second process is H.V. Coil Winding, which are wound with strip conductor and it usually consists of continuous disc type. The coils are usually created in layers and ideally all the joints are extremely well brazen and insulated in order to withstand difficult service conditions and tests.
42
The LV windings are made from Paper covered Copper Strip and placed nearest to the core. The HV winding are wound with Super Enamelled Copper Wire or Alluminium wire or Paper covered Round wire or paper covered Strip depending upon the reting of the transformers. The cross section of the conductor is also chosen to keep the thermal gradiet in the winding to a minium and thus increase the life of transformer. The coils are assembled with the best insulating material avail and they are adequately clamped by the use of permawood rings where necessary to give required mechanical strength. The tappings are provided o the external HV windings. The off circuit tapping swich is gang operated type and good contact is maintained by means of floating spring pressure. Teh tapping swich can be looked in ay desired position. The transformer preferably off capacity 2000 KVA and above can be supplied with on load tap changer alongwith the desired controls as per the requirement.
CORE AND COIL ASSEMBLY A part of the transformer manufacturing process, the core and coil assembly aspect plays a significant role where the 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 form the entire phase assembly. The radial gaps between the windings are subdivided by means of solid transformer board barriers. Stress rings and angle rings are placed on top and bottom of the windings to achieve a contoured end insulation design for optimal control of the oil gaps and creepage stresses. The complete phase assemblies are then carefully lowered over the separate core legs and solidly packed towards the core to assure optimal short circuit capability. The top core yoke is then repacked and the complete core and coil assembly is clamped. 43
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) are made before drying the complete core and coil assembly in the vapor phase oven.
PROCESSING OF CORE AND COIL ASSEMBLY The completed core and coil assembly is thoroughly dried to pre-determined power factor readings by the vapor phase drying process , providing the fastest, most efficient and most effective drying of the transformer insulation available. The vapor phase process uses the standard kerosene cycle method. In this system, kerosene is vaporized and drawn by vacuum into a heated autoclave where the transformer has been placed. Condensation of the vapor on the core and coil assembly rapidly causes the temperature to rise and allows moisture to be drawn out of the insulation by the vacuum. High temperature and pressure are used to accelerate the drying process. When the power factor measurements and the removal rate of moisture have reached the required levels, the flow of kerosene vapor is stopped and a high vacuum is used to boil off the remaining moisture and kerosene. Because so much water is removed in this process, the insulation physically shrinks in size. Following removal from the autoclave, the transformer is repacked as required and then undergoes its final hydraulic clamping to ensure maximum short-circuit strength in the finished product
TAP CHANGING Power Systems transformers can be equipped with either a de-energised tap changer or a load tap changer or with both.Should load tap changing be required, BHEL can provide a resistive bridging type or reactor type LTC. Both types offer up to 500,000 operations between contact replacement and substantially reduce maintenance intervals. The LTC can be installed in the transformer tank with the diverter switch in its own oil compartment, so that no contamination of the transformer oil occurs due to arcing during switching, or can be mounted on the main tank. To prevent voltage surges on the tap changer during switching MOV surge suppressors can be installed. DRYING OUT PROCESS In order to ensure power supply is completely reliable it depends on high performance transformers and in order to achieve that the drying out process is extremely 44
important. Under this process, the paper insulation and pressboard material, which make up a significant proportion by volume of transformer winding, have the capacity to absorb large amounts of moisture from atmosphere. The presence of this moisture brings about the reduction in the dielectric strength of the material and also an increase in its noise. TANK FABRICATION 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 from MS plates and is weldwd construction. They are tested at a pressure of 0.35 Kg./Sq. cm. for oil leakage output and they are normally welded directly to the tank. How ever, transformers, can be supplied with detachable radiators. TANKING After vaccum drying process the active part is removed from the Oven and all components subject to the shrinkage are tightened again. The core & coil assembly is then placed into the tank and properly lacked up during the transformer manufacturing process. The temperature and exposure time is monitored during this time to ensure that the transformer is not too cool by the time it is get off from the oven. While in higher rating transformer, the vacuum is drawn for a period of time dependent on the voltage of the unit and time for which the active part was exposed to the atmosphere and the humidity at the time. The vacuum period is between 12 to 35 hours. Meanwhile the external wiring and termination work to be completed as per customer requirements. PAINTING The outside surface of tank including all fittings and accessories are cleaned properly. Necessary chipping and grinding applied for smooth surface and finishing. After 45
cleaning of the tank, one coat of hoi oil resistance pint is applied on the internal surface of the tank during the transformer manufacturing process. The outside surface is painted with one coat of Red Oxide Primer and subsequently one coat of enamel paint as per customer's requirement. The transformers are fitted with Bare Porcelain Bushings and metal parts conforming to IS specification 3347 "Dimension for Procelain transformer Bushings." The electricals characteristics of the bushings conform to IS 2099 "Specification for High Voltage Porcelain Bushings". Alternatively transformers are supplied, fitted with Cable Box either with Wiping type of glands suitable for PVC/XLP cables. Paintings : The inside of the transformer tank and frame parts are given a coating of Oil and heat resistance paint. The transformer is given an external anticorrosive primer coat and two fiising coats usually of admirally grey. TESTING
The testing room is climatically controlled and is fully equipped with facilities for conducting all routine tests and temperature- rise tests. The transformers are tested at various stages of manufacture and various rating transformers are tested at independent institution to establish short circuit and insulating capacity of the transformers and also the impluse withstanding withstanding capacity. Prior to shipment, all transformers manufactured BHEL are tested in accordance with the latest applicable standards according to customer specifications. All industry standard and optional tests with the exception of short-circuit tests, can be performed in-house by trained personnel using accurate and modern test equipment.
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Impulse Testing
A state-of-the-art digital impulse recording system, the Haefely HIAS system, provides the most accurate analysis of impulse results available today. Electronic recording of the impulse current and voltage waveforms allows quick mathematical comparisons to be made, including the difference between the two waveforms under scrutiny. Accurate printed and plotted final results are quickly available. If required, photographic transparencies from the impulse oscilloscope can be supplied. The construction of the test area incorporates a complete copper mesh ground mat system, with extensive grounding points provided. This eliminates high impedance grounds and provides exceptionally clean test records. The impulse generator is rated at 200 kV per stage for a total of 2.8 MV, with 210 kJ total stored energy. For precise triggering, this generator is equipped with a pressurized polytrigatron gap in each stage. For chopped wave tests, a Haefely multiple chopping gap is used. Our plants are fully capable of performing lightning impulse, switching impulse and front-ofwave tests as required.
Induced Testing
For induced testing, a variable voltage alternator, rated 1500/1000 kVA, 3/1-phase, 170/240 Hz, is used. Voltage control is by solid state automatic voltage regulator, and solid state speed control of the 1000 kW DC driving motor. During the induced test, partial discharge measurements both in pC and μV are taken and equipment is available to locate internal partial discharges by the triangulation method.
Loss Measurement
Power is provided to the loss measuring system by a 5/10 MVA regulating transformer feeding three single-phase 10 MVA variable ratio transformers and a 110 MVAR capacitor bank. Losses are measured by an automated system using CTs for current and gas capacitors for voltage. This system has a fully automated digital readout and printer.
AC Testing
A test supply with an output voltage infinitely adjustable from 3-350 kV is available for high voltage AC testing. To measure the applied voltage level, a digital peakresponding RMS calibrated voltmeter capable of measuring up to 1600 kV is used.
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SHIPING AND INSTALLATION Depending on transportation considerations, BHEL Power Systems transformers may be shipped either with or without bushings, radiators, fans, conservator and oil. BHEL experience in delivering power transformers to over countries throughout the world guarantees fast and reliable transportation.
Installation of the transformer can either be done by the customer or by an experienced BHEL Field Service Crew.
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