Transformer windings are designed to meet three fundamental requirements, viz. mechanical, thermal and electrical. They are cylindrical in shape and are assembled concentrically. Paper insulated conductors of high conductivity and soft drawn Electrolytic grade copper is used which comply with the latest Indian as well as international standards.
Windings are made with great care by well experienced skilled Disc Winding workers in dust free & temperature controlled environment.
Insulation between layers and turns is based upon the electrical and mechanical strength level. Inter layer cooling ducts (Axial & Radial) are provided to minimize the temperature gradient between windings and oil, and hence the hot spot temperature is kept to a minimum. This also ensures that the rate of insulation deterioration is minimized and high life expectancy is achieved.
Transpositions are made in multiple conductor windings, to ensure uniform current distributions, minimize circulating currents, decrease eddy current loss and improve the lamination factor.
Multiple conductor layer wound coils are most suitable for low voltage windings of large power transformers to mitigate high current designs requirement. For High voltage windings the disc coils with excellent mechanical strength are used to take the stresses due to voltage level. Special interleaved or shielded construction offers most uniform voltage distribution despite system transient. Specialized disc winding and inter-leaved disc windings are used having very high series capacitance giving a very good impulse voltage performance.
For better short circuit withstand ability under fault conditions, would coils are pressed, clamped and dried in oven prior to impregnation in oil. Cooling ducts formed with rigid, high density spacers and horizontal and vertical ducts are provided to save hot spots.