BHEL training report

July 10, 2017 | Author: raghuramguda8 | Category: Turbine, Electric Arc, Mechanical Engineering, Machines, Technology
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A brief review about Generator manufacture...


Introduction BHEL is the largest engineering and manufacturing enterprise in India in the energyrelated/infrastructure sector, today. BHEL was established more than 40 years ago, 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 since 1971-72 and paying dividends since 1976-77. 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 centres, over 100 project sites, eight service centres 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 centres BHEL has •

Installed equipment for over 90,000 MW of power generation -- for Utilities, Captive and Industrial users.

Supplied over 2,25,000 MVA transformer capacity and other equipment operating in Transmission & Distribution network up to 400 kV (AC & DC).

Supplied over 25,000 Motors with Drive Control System to Power projects, Petrochemicals, Refineries, Steel, Aluminum, Fertilizer, Cement plants, etc.

Supplied Traction electrics and AC/DC locos to power over 12,000 kms Railway network.

Supplied over one million Valves to Power Plants and other Industries.

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. The fourteen manufacturing Divisions are located at •

Bhopal(Madhya Pradesh)

Bharat Heavy Electrical Limited, Ranipur, Haridwar (Uttarakhand) [4]

Hyderabad (Andhra Pradesh)

Jhansi (Uttar Pradesh)

Tiruchirapalli(Tamil Nadu)

Ranipet (Tamil Nadu)

Bangalore (Karnataka)

Jagdishpur (Uttar Pradesh)

Rudrapur (Uttrakhand)

Goindwal (Punjab)

Bharat Heavy Plates and Vessels Limited (Vizag)

Besides these manufacturing units there are four power sectors which undertake EPC contract from various customers. The Research and Development arm of BHEL is situated in Hyderabad and two repair shops are at HERP(Heavy Equipment Repair Plant),Varanasi and EMRP(Electric machines repair plant) Mumbai.

BHEL-Hyderabad As a member of the prestigious 'BHEL family', BHEL-Hyderabad has earned a reputation as one of its most important manufacturing units, contributing its lion's share in BHEL Corporation's overall business operations. The Hyderabad unit was set up in 1963 and started its operations with manufacture of Turbo-generator sets and auxiliaries for 60 and 110 MW thermal utility sets.

Over the years it has increased its capacity range and diversified its operations to many other areas. To day, a wide range of products are manufactured in this unit, catering to the needs of variety of industries like Fertilisers & Chemicals, Petrochemicals & Refineries , Paper, sugar, steel , etc. BHEL-Hyderabad unit has collaborations with world renowned MNCs like M/S General Electric, USA, M/S Siemens,Germany, M/S Nuovo Pignone, etc. Major products of this unit's manufacture include the following. •

Gas turbines

Steam turbines


Turbo generators

Heat Exchangers



Switch Gears

Gear Boxes

Oil Rigs

Project Engineering

Steam Turbines Operation The expansion of steam through numerous stages in the turbine causes the turbine rotor to rotate. Steam expands through impulse stage or reaction stage. •

Impulse steam turbine stage consists as usual from stator which known as the nozzle and rotor or moving blades

Impulse turbine are characterized by the that most or all enthalpy and hence pressure drop occurs in the nozzle.

The rotor blades can be recognized by their shape, which is symmetrical and have entrance and exit angles around 20o. They are short and have constant cross sections

At BHEL-Hyderabad, compounded turbines are made as they are the most used by plants

Compounded steam turbine means multistage turbine.

Compounding is needed when large enthalpy drop is available.

Since optimum blade speed is related to the exit nozzle speed. It will be higher as the enthalpy drop is higher.

The blade speed is limited by the centrifugal force as well as needs of bulky reduction gear

Compounding can be achieved either by velocity compounded turbine or pressure compounded turbine.

Velocity Compounded Turbine •

It is composed of one stage of nozzles, as the single stage turbine, followed by two rows of moving blades instead of one.

These two rows are separated by one row of fixed blades which has the function of redirecting the steam leaving the first row of the moving blades to the second row of moving blades.

Pressure Compounded Impulse Turbine •

Pressure compounding impulse turbine is a multistage impulse turbine where expansion in the fixed blades (nozzles) is achieved equally among the stages.

Accordingly the inlet steam velocity to each stage is essentially equal, due to equal drop in enthalpy.

This equal enthalpy drop does not mean equal pressure drop

The Manufacture and Parts Casing

The typical casing for an Elliott turbine consists of a cast high-pressure steam chest, an intermediate barrel section, and a separate exhaust casing. The barrel section is generally integral with the steam chest so that the vertical bolting joint is at one of the latter stages where internal pressures are very much reduced. The steam end, exhaust casing, nozzle ring, reversing blades and diaphragms are all split on the horizontal center line which allows for easy removal of the upper half of the turbine for internal inspection. The diaphragms are machined on the outside diameter and assembled into grooves accurately machined in the casing. Cap screws, secured by locking, fasten the nozzle ring to the steam chest, while the diaphragm halves are locked in position by stops located at the horizontal split in the casing. Steam chest passages, nozzle block partitions and the valve opening sequence are all carefully designed to ensure even and rapid heating of the casing after steam is first admitted to the turbine. The high-pressure end of the turbine is supported by the steam end bearing housing which is flexibly mounted to allow for axial expansion caused by temperature changes. The exhaust casing is centerline supported on pedestals that maintain perfect unit alignment while permitting lateral expansion. Covers on both the steam end and exhaust end bearing housings and seal housings may be lifted independently of the main casing to provide ready access to such items as the bearings, control components and seals.

Rotors Rotors are precisely machined from solid alloy steel forgings. An integrally forged rotor provides increased reliability particularly for high speed applications. The complete rotor assembly is dynamically balanced at operating speed and overspeed tested in a vacuum bunker to ensure safety in operation. High speed balancing can also reduce residual stresses and the effects of blade seating. Elliott also offers remote monitoring of the high speed balance testing, allowing customers to witness the testing from their offices or at any other location. Blades

Blades are milled from stainless steel stock purchased within strict specifications for proper strength, damping and corrosion resistant properties. Disk profiles are designed to minimize centrifugal stresses, thermal gradient and blade loading at the disk rims. The blades have various shapes to achieve maximum performance and withstand any mechanical stresses.

Stationary Components Nozzle rings and diaphragms are specifically designed and fabricated to handle the pressure, temperature and volume of the steam, the size of the turbine and the required pressure drop across the stage. The nozzles used in the first stage nozzle ring are cut from stainless steel. Steam passages are then precision milled into these nozzle blocks before they are welded together to form the nozzle ring. The nozzles in the intermediate pressure stages are formed from profiled stainless steel nozzle sections and inner and outer bands. These are then welded to a circular center section and to an outer ring then precision machined. The low-pressure diaphragms in condensing turbines are made by casting the stainless nozzle sections directly into high-strength cast iron. This design includes a moisture catching provision around the circumference which collects released moisture and removes it from the steam passage. Additional features such as windage shields and inter-stage drains are used as required by stage conditions to minimize erosion. All diaphragms are horizontally split for easy removal and alignment adjustment. Labyrinth seals are utilized as end gland seals and also interstage seals. Stationary labyrinth seals are standard for all multistage turbines and grooves are machined on the rotating part to improve the sealing effect. The leakage steam from the outer glands is generally condensed by the gland condenser. Some leakage steam from the intermediate section of the steam end gland seals can be withdrawn and utilized by re-injecting it into the low-pressure stage or low- pressure steam line. Replaceable journal bearings are steel-backed and babbitt-lined with five-shoe tilting pad design. Thrust bearings are double-acting and self-equalizing. Center pivots are

typically used to make assembly easier and provide maximum protection if reverse for high oil temperature applications.

Turbo Generators The turbo-generator is common-shaft excitation AC synchronous generator with 3 phases, 2 poles or with 3 phases, 4 poles. BHEL-Hyderabad makes turbo generators that have the brushless excitation mechanism which has been explained in the NTPC report. BHEL presently has manufactured Turbo-Generators of ratings upto 560 MW and is in the process of going upto 660 MW. It has also the capability to take up the manufacture of ratings upto 1000 MW suitable for thermal power generation, gas based and combined cycle power generation as-well-as for diverse industrial applications like Paper, Sugar, Cement, Petrochemical, Fertilizers, Rayon Industries, etc.

The Manufacture of the Turbo Generator Stator The stator is assembled as six parts. It is made up of steel with 4.5% of silica. Silica decreases hysteresis loss. The sheets are cut at 30 degree angles. The sheets then are punched with man drill holes, support rod slots and slots for the conductors. This process is called notching and the cutting part as shearing. The sheets are then varnished after blanking or smoothening of the surface. This is to increase the insulation. A bunch of these sheets are stacked together and compressed onto each other so that air gaps are eliminated. These stacks are then assembled with a small air gap differentiating each stack. This ventilates the machine and keeps it cool. After the assembly of the stator shell, the inside of the slots are varnished. The sheets of the core are varnished with xylor, at a temperature of 30-400 degrees Celsius. It is heated, coated then cooled. After the core is assembled , the winding is placed in the stator. The winding type depends upon the power required and the current required to be produced. The core and the winding are separated by an insulation called HGL. This prevents the shorting of the core and winding The winding in the front and back are also separated by this material and they are joined as per the winding required (lap or wave) using glass-o-flex, a pink ribbon like material. The windings are insulated. These windings are then painted to obtain a the stator, where the power is generated. The windings are always inserted from the exciter end, one is clockwise and the other anti-clockwise.

The Rotor

The rotor is carved out with the slots into a cylindrical shape from a large block of metal using Lathe heavy machines. The rotor consists of 2 ends – •

The turbine coupling end

The exciter end

The turbine end has a coupling shaft which is circular in shape and has slots. The exciter end has an input lead and an output lead which are used to give the rotor DC input for the excitation of the rotating field. The ends of each rotor consist of bearings. These bearings are placed so as to support the shaft. The bearing consists of oil which is used to support a thin film over the surface. This lubricates and decreases friction and losses. The bearing has top end and bottom end and is stationary. The top end is used to supply the oil. After the construction, the w inding is fitted into the slots. The slots and windings are separated by HGL or hard glass lamination which insulates the core from the cable. The rotor is constructed so as to obtain brushless excitation. The complete rotor along with the excitation mechanism is mounted on the shaft and is balanced for synchronous speed. For better balancing weight removal is done as that is a better option to adding weight to the system. The rotor ends are provided with induction motor fans which are used for cooling of the rotor winding. The winding is mad eup of 99.99 % copper.

Cooling of the Alternator The machine needs to be cooled to avoid damage and for greater life. Heating causes insulation failure. Hence, cooling is a very important factor that needs to be taken care of. For cooling, the stator and rotor are provided with a ventilation to cool it down. Air gaps are provided throughout the machine. But for very high power machines natural

cooling is insufficient so a cooling system is provided. For collection of hot air, a large chamber is provided. This air is cooled and recycled into the generator. The rotor of the alternator consists of fans powered by induction motors. They suck in the air and push it through to the cooling chamber. Another method is also used which is called hydrogen cooling. Hydrogen acts as a coolant and the chamber is shut completely is filled with hydrogen. Hydrogen cools itself. The chamber is emptied each time the machine is stopped.

Circuit -Breakers Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in a medium, such as SF6, having excellent dielectric and arc quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity. Gas blast applied on the arc must be able to cool it rapidly so that gas temperature between the contacts is reduced from 20,000 K to less than 2000 K in a few hundred microseconds, so that it is able to withstand the transient recovery voltage that is applied across the contacts after current interruption. Sulphur hexafluoride is generally used in present high-voltage circuit-breakers (of rated voltage higher than 52 kV) In arc assisted opening interruption principle arc energy is used, on the one hand to generate the blast by thermal expansion and, on the other hand, to accelerate the moving part of the circuit breaker when interrupting high currents. The overpressure produced by the arc energy downstream of the interruption zone is applied on an auxiliary piston linked with the moving part. The resulting force accelerates the moving part, thus increasing the energy available for tripping.

With this interrupting principle it is possible, during high-current interruptions, to increase by about 30% the tripping energy delivered by the operating mechanism and to maintain the opening speed independently of the current. It is obviously better suited to circuit-breakers with high breaking currents such as Generator circuitbreakers.

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