Each and every component of the HT transformer is manufactured and assembled with precision and utmost care. The main process lines of the transformers are:
Core: The core is made with laminated and low loss electrical steel sheets that are imported, grain oriented, cold rolled and sheets of high-grade steel. The cores are assembled in a manner that they reduce the noise caused by vibration; individual stamping is coated with insulation varnish which is resistant to heat and oil on both sides. The core is connected to the clamp which ensures that it is effectually earthed. The core legs are bounded with heavy duty insulating tape. The yokes are rigidly and securely clamped between the folded steel channels. Clamps on top and bottom are firmly attached to each other by the means of tie rods. Tie rods serves the duel purpose of transferring the load from the bottom to the top clamps and securing the winding in place. This prevents tensile stress being setup in the core legs, which could adversely affect the iron losses.
Winding: Transformer windings also known as 'Coils' are precisely designed to meet three basic requirements: thermal, mechanical and electrical. These windings wound concentrically and are cylinder shaped. Both H.V. L.V. type windings are wound with adequate securing and brazing tapes in order to get a sturdy, robust and self-supporting structure. It is provided with inter layer ducts which ensure low-temperature gradient between windings and oil so the hot spot temperature is kept to the minimum. This guarantees that the rate of insulation deterioration is lowered to attain high life expectancy.
Winding Connections: Tapping and phase lead run in paper covered conductors. Adequate barriers are used to separate the phase leads from the tapping. Rigidly brazed tubes are used to maintain the required clearance from the coil to tank.
LV Leads, larger in cross-section, are usually sturdy and robust, where necessary supports are provided.
INSULATION AND IMPREGNATION
The principal component of insulation is insulating pre-compressed pressboard. The component like ring ducts dovetailed spacer; blocks etc. are put under compressing along with the coil assembly for preshrinking. The slight recovery in dimension after the preshrinking is compensated by providing additional insulation. This reduced the probability if coils getting loose during operation and also minimize the failure due to short circuit forces.
SHORT CIRCUIT CAPABILITY
In the order to prevent deformation under short-circuit forces; solid insulation end block and ring are used. Winding are compressed under top and bottom clamping members with the help of tie rods. The axial end thrust under fault conditions is minimized by the suitable balance of the ampere-turns over the length of windings. In a case of the bigger transformer, the HV tapping leads are taken out from two positions to balance the short-circuit forces in a much better way.
All tank are made from mild steel sheet of adequate thickness with corrugated wall panel type radiators of pressed steel fin/cooling tube for heat dissipation.
All tanks are checked by magma flux, ultraviolet ray dies penetrating system to ensure that there is absolutely no leakage from any part of the tank.
QUALITY FINISH THROUGH USE OF SHOTBLASTING TECHNOLOGY
Tanks are shot blasted to remove mill and welding scale and then a primer coat is immediately applied to the exterior to eliminate rust formation.
After priming, all tanks receive a coat of intermediate paint and after pressure testing; they receive a final coat of high gloss paint applied by spray. This ensures high coverage helping to combat corrosion in an inaccessible place.