The magnetic core of the transformers is built up of cold rolled grain oriented magnetic stee! laminations. Hi-B grade and laser scribed lamination is used to reduce the no load losses and noise. Laminations are cut at an angle of 45°. Core leg and yoke laminations are interleaved in mitred Joints in order to facilitate the passage of the magnetic flux, to avoid hot spots and to reduce no load losses and sound level.

By using gauges and jigs the lamination are assembled into a core, taking much care to reduce the air gaps between the lamination to a minimum. The lamination of the upper yoke are interleaved after fitting the windings.

For single phase wound core transformer, the slit coils are wrapped in the form of coil on core wrapper machine of Atlanta Grontes, U.S.A.

The windings are designed to optimize Dynamic, Thermal, Mechanical & Electrical stresses depending upon the current & voltage requirements.

Depending on the specific design criteria, spiral, cross over Helical, continuous disc, partly interleaved or fully interleaved windings are used.

Steel winding mandrels are used to ensure tight tolerances. The winding machines are equipped with hydraulic braking devices which ensure that the proper tension is maintained on the winding.

Dovetailed Key spaces are employed to give the winding extra strength. Axial and radial cooling ducts in and between sections of the windings allow the free flow of oil around the conductor. Individual coils are dried and hydraulically pressed to size in accordance with the calculated short circuit forces to obtain the design height and to guarantee full short circuit resistance.

The magnetic core with the windings and some accessories are the active part of the transformer. The windings are slipped over the legs of the core and the lamination of the upper yoke are interleaved. All connections between windings and bushings and the connections between the high voltage lappings and the tap changer are made. The Tap changer allows the increase or decrease of a certain number of turns in the high voltage winding in order to compensate for a voltage drop or to adapt the transformer to an unstable supply, so that the rated low voltage can be maintained. Subsequently, the top cover on which the bushings for high voltage and low voltage are already fixed, is fitted.

A transformer may contain no trace of humidity, otherwise there will be a danger of flash over within the windings. The active part of the transformer is completely dried before the transformer is filled with oil vacuum. The tcink with the active part in it, is connected to an oil supply and placed inside a vacuum chamber. A vacuum is applied and when ihe required vacuum is reached, the oil is admitted into the tank. The rising oil drives out any remaining air and the active part is completely immersed.