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BHEL: AN OVERVIEW
Bharat Heavy Electricals Ltd. has emerged as the largest engineering and manufacturing enterprise of its own kind in India with an excellent track record of performance. The Company is engaged in engineering, development and manufacturing of a wide variety of electrical and mechanical equipment for generation, transmission and utilization of energy and electrical power. 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 has now thirteen manufacturing divisions, eight service centers and four power sector regional centers, besides a large number of projects sites spread all over India and abroad. This enables prompt service to the customers with state-of-art products, systems and services that meet the needs of energy, industry, transportation and other key sectors.
HEAVY ELECTRICAL EQUIPMENT PLANT
BHEL's Heavy Electrical Equipment Plant (HEEP) was set up in technical collaboration with USSR, for the manufacturing of power plant equipment, AC/DC motors of various with associated control equipment and started production in January 1967. In 1976, BHEL entered into a collaboration agreement with M/s Kraftwerk Union, AG of Germany for design, manufacturing, erection and commissioning of large size steam turbines. More than 40 percent of the country's electrical energy is generated from the power equipment supplied by BHEL, Haridwar.
The products, which are manufactured in HEEP, are: - Steam Turbines, Turbo Generators, hydro turbines, Gas turbines, etc..
COIL & INSULATION MANUFACTURING SHOP (BLOCK-IV)
BAY-I: Bar winding shop manufacturing of stator winding bars of generator.
BAY-II: Manufacturing of heavy duty generator stator bars with New CNC M/c No. 3-464 i.e. Robol bar centre.
BAY-III Insulation detail shop. Manufacturing of hard insulation & machining of hard insulation part (Glass textolite) such as packing, washer,
insulation box, wedges etc.
Bar Shop: This shop is meant for manufacturing of stator winding coils of
turbo-generator
Why do we call it bar: it is quite difficult to manufacture, handle and wind in the stator slot of generator of higher generation capacity because of its bigger size and heavy weight. That is why we make coil in two parts. One part its bottom part of coil called bottom or lower bar and other part of coil is called top bar or upper bar.
Turbo-Generators: The manufacturing of bars of standard capacity such as 100MW, 130MW, 150MW, 210/235MW, 210/250MW, 500MW.
Type of generators: The generator may be classified based upon the cooling system used in the generators such as: THRI, TARI, THDI, THDD, THDF, THFF, THW.
T = First alphabet signifies the type of generator i.e. turbo- generator or Hydro-generator
H/A = Second alphabet stands for the cooling media used for the cooling of rotor i.e. hydrogen gas or air.
R/D/F/I = Third alphabet signifies the type of cooling of rotor e.g. radial, indirect,
forced, direct etc.
I/D/F = Last alphabet stands for the type of cooling of stator e.g. indirect cooling, direct cooling, forced cooling.
W = Cooling media used for cooling of stator coil e.g. water.
Resin System:
a) Rich resin or Thermo reactive insulation system: In this type of insulation system the bond content in resin is 35-37%. The raw materials are ready to use and require preservation and working on temperature 20-250C. Its shelf life is one year when kept at temperature 200C which could be increased when kept at temperature of 50C.
b) Poor resin or Micalastic insulation system: In this type of insulation the bond content in the resin is 5-7% and insulating material is prepared with accelerator treatment. The temperature control need not required. The insulating material is applied on job and then the same is impregnated (fully dipped) in the resin.
Manufacturing process of Bars:
Some points of mfg. process are in brief as below ---
1. Conductor cutting: This process is done by automatic CNC machine. In this process the pre-insulated copper conductor is cut into number of pieces of required length (length given in drawing as per design) insulation is removed from both ends of the copper conductor out.
2. Transposition: Transposition means changing/shifting of position of each conductor in active core (slot) part. After cutting the required number of conductors, the conductors are arranged on the comb in staggered manner and then bends are given to the conductors with the help of bending die at required distance. Then the conductors are taken out from the comb and die and placed with their ends in a line and transposition is carried out. This process is repeated for making another half of the bar which would be mirror image of the first half. The two halves of the bar are overlapped over each other and a spacer is placed between the two halves.
3. Crossover insulation: The pre insulation of the copper conductor may get damaged due to mechanical bending in die during transposition, hence the insulating spacers are provided at the crossover portion of the conductors. A filler material (insulating putty of moulding micanite) is provided along the height of the bar to maintain the rectangular shape and to cover the difference of level of conductors.
4. Stack Consolidation: The core part of the bar stack is pressed in press (closed box) under pressure (varies from product to product) and temperature of 1600 C for a given period. The consolidated stack is withdrawn from the press and the dimensions are checked.
5. Inter Strand Short test :- The consolidation bar stack is tested for the short between any two conductors in the bar, if found then it has to be rectified.
6. Forming :- The straight bar stack is formed as per overhang profile (as per design). The overhang portion is consolidated after forming.
7. Brazing of coil lugs:- for water cooled generator bars, the electrical connection contact and water box for inlet and outlet of water are brazed.
8. Nitrogen leak test:- The bar is tested for water flow test, nitrogen leak test and pressure test for given duration.
9. Thermal shock Test:- The cycles of hot (800C) and cold (300C) water are flew through the bar to ensure the thermal expansion and contraction of the joints.
10. Helium leakage test:- After thermal shock test bar is tested for any leakage with the help of helium gas.
11. Insulation :- The bar is insulated with the given number of layers to build the wall thickness of insulation subjected to the generating voltage of the machine.
12. Impregnation and baking :
a) Thermo reactive System: In case of rich resin insulation the bar is pressed in closed box in heated condition and baked under pressure and temperature as per requirement for a given period.
b) Micalastic System : In case of poor resin system the insulated bars are heated under vacuum and the impregnated (dipped) in heated resin so that all the air gaps are filled, layer by layer, with resin. Then extra resin is drained out and bars are heated and baked under pressed condition in closed box fixture.
VPI Micalastic System :- The bars already laid in closed fixture and full fixture is impregnated (dipped) in resin and then fixture with box is baked under given temperature for given duration.
VIP Micalastic System :- The individual (Separate) bar is heated in vacuum and impregnated in resin. Then bar is taken out and pressed in closed box fixture and then baked at given temperature for given duration.
13. Finishing :- The baked and dimensionally correct bars are sanded - off to smoothen the edges and the surface is calibrated, if required, for the dimension.
14. Conducting varnish coating:
(i) OCP (Outer Corona Protection) Coating :- The black semi-conducting varnish coating is applied on the bar surface on the core length.
(ii) ECP (End Corona Protection) Coating: The grey semi-conducting varnish is applied at the bend outside core end of bars in gradient to prevent from discharge and minimize the end corona.
15. Testing:
(a) Tano Test :- This test is carried out to ensure the healthiness of dielectric (Insulation) i.e. dense or rare and measured the capacitance loss.
(b) H.V.Test:- The each bar is tested momentarily at high voltage increased gradually to three times higher than rated voltage.
