Each and every component of the OLTC Transformer is manufactured and assembled with precision and utmost care.
The main process lines of the transformers are:
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.
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.
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:Â
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.
Quality Finish Through Use Of Shot blasting Technology: