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 & soft drawn E.C. Grade copper is used which comply with the latest Indian Standards. Both HV & LV windings are wound with adequate bracing with high strength securing tapes in order to achieve a strong & self supporting structure.

Insulation between layers and turns is based upon the electrical and mechanical strength level. Interlayer cooling ducts 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 a high life expectancy is achieved.

LV winding is usually of the two layer helical type, comprising of a number of strips wound in parallel. For larger transformers, a single layer helical winding and in some cases, multiple conductors continuous disc coils may be used.

HV windings with strip conductors, is generally of continuous disc type. All joints are brazed and insulated to withstand test and service conditions. For HV windings of relatively low current, Cross - over type coils of round conductor are used. With this type of multilayer round wire coil, the method of interleaving the interlayer paper and fastening tapes provide adequate mechanical strength for handling during assembly and added electrical insulation between layers.

Transpositions are made in multiple conductor windings, to ensure uniform current distribution and to minimize circulating currents.
Completed windings are processed in drying oven prior to impregnation with transformer oil.

Core is built from best quality, low loss, Cold Rolled Grain Oriented Silicon Steel, with mited/ interleaved construction. To get best results, annealing after cutting is insisted to relieve all stresses. Bonded core design/ technique is used to eliminate hole ounching and to minimize fixed losses and Magnetizing Current. Rigid clamps are provided to reduce vibrations and noise level. Cooling ducts are provided in large transformers for efficient circulation of oil to keep temperature of core well within limit without affecting the flux distortion.

Generally Taps are provided on HV Windings for HV Variation or LV Variation as specified by customer. These are brought up to a gang operated switch, suitable for external manual operation and can be locked in any desired position to avoid unauthorized operation.

All the moving contacts are spring loaded to ensure proper pressure and good contacts.

Higher capacity transformers, specially above 3000 KVA ratings, can be supplied with On Load Tap Changer along with necessary controls to make it suitable for manual, local electrical or remote Electrical operation.

Tapping windings are carefully designed to keep unbalance to minimum. For large tapping range, separate regulating windings are used to maintain Ampere-Turn balance at all tap position.

In order to prevent deformation when subjected to short circuit forces, the windings are axially and radially supported. Solid block end insulation, adequate number of spacer rows and anchoring and bracing tapes, backed-up by substantial supporting frames are utilized. The axial end thrust under fault conditions is minimized by the suitable distribution of ampere turns over the length of the windings, abd by ensuring that the design dimensions are closely adhered to during manufacture.

The transformers designed and constructed in this way are capable of withstanding the effects of short circuit testing as set out in IS : 2026.

For transformers up to 33 KV, drying is carried out in well ventilated, electrically heated oven for a period determined by electrical tests. The transformers are then immersed in freshly filtered oil and allowed to stand for a period until all trapped air is escaped.

For transformers with voltages of 66 KV and above, drying out treatment takes place in a vacuum drying oven. The core and windings assembly is placed in oven and initially heated at 80°C for a period During this period, heated air is circulated rapidly and the moisture laden air is bled off at frequent intervals. Vacuum is then applied, and heating of the core and windings assembly is continued simultaneously. The mixture of air and moisture that is extracted is passed through a condenser and collected in the form of water which is measured and recorded. The end point of drying process is decided by the measurement of dispersion factor, insulation resistance, tan-delta, and the collection of water.

For bigger transformers, 25 MVA and above, Core coil assembly along with tank are in the oven and after completion of heating cycle, hot, degassed oil is then allowed into the transormer tank under vacuum. This oil is then circulated through the transformer and the oil deggassing plant until all gas trapped in the core, windings, and the insulation is removed. This ensures a high degree of stability in the insulation structure and early attainment of its mature condition, which would not otherwise be achieved until the transformer had been in service for some time.

Tanks are fabricated from M.S. Sheet of best quality by electric welding. The tank is designed to withstand vacuum and pressure test as per CBIP. A robust skid under base is provided, and guide bars are located inside the tank to securely fix the core and windings assembly in position, and to prevent any movement during transportation.

All tanks are pressure tested before leaving the fabrication department as per CBIP guidelines.

All the joints are casketed to avoid leakage with the help of rubberized cork sheets, which can withstand high oil temperature and do not deteriorate nor contaminate oil in its contact.

Pressed steel radiators are used to dissipate heat generated at rated load. For smaller ratings, radiators are directly welded to main tank, while for the bigger ratings detachable type radiators sre provided to facilitate transport and handling at site.

Terminals to suit Customer's requirements can be provided. Outdoor bushings are normally provided for the HV & LV terminals. HV outdoor bushings are supplied with arcing horns as standard. Air insulated and compound filled cable boxes, with or without disconnecting chambers, can be provided to suit customer's specification. The terminals of our transformers can be made suitable for heat shrinkable cable termination system.

Metal which has been pre-treated by means of shot/sand blasting to remove rust and welding scale, is throughly cleaned, and then a coat of zinc chromate primer paint is imediately applied to all external surfaces. This anticorrosive primer has rust inhibitive properties and excellent chemical resistance. Two coats of grey, weather enamel finish paint, which is highly resistant to chemicals and oil, are then applied.

All the Transformers are supplied with first filling of oil conforming to IS 335. Before filling, oil is heated, filtered and vacuum treated in filter machine to remove any foreign particles, moisture and air.

Before dispatch each & every transformer is subjected to all routine test as specified by IS. We have fully equipped test laboratory for conducting all routine tests and temperature rise test in accordance with IS-2026.

Arrangement can also be made to carry out relevant type tests, if required, at recognized laboratories. Our transformers up to 20MVA, 66kV class is fully type tested and 50MVA, 132/66kV Transformer is impulse tested