The Core

All d’rona rohitra transformers are the core type with vertical limbs of multi-section. The core is built up of crgo low loss non-ageing type silicon steel laminations. The core are held together with staut webbing or stiffening plates and insulated bolts. Joints between core and yolk are carefully interleaved. The individual packets of laminations are further insulated by division into sections, separated by sheets of insulating paper. The yolks are held between clamps made of steel channels, upperand lower being connected with tie rods. The clamps and the tie rods also keep the windings in positions and are rigid enough to take short circuit stresses.

Windings and insulations

Generally the low tension windings are placed next to core with an insulation barrier in between. These windings are of helical type, single or multi layeror continous copper disc type using flat copper strips, depending upon the size and current rating of the transformer. The isolation between the lv and hv windings consists of vertical elephantide wedges with elephantide or presspan barriers so as to give most effective thermo-syphonic action of transformer oil for efficient cooling.
The ht winding consists of cross over coils meant for units upto 1500kva where round wires are used. In round wire coilo manila or kraft paper is used as interlayer insulation. The paper used between the layers is so inerted that it gives the winding an addequate electricals and mechanical strength which sustains short – circuit conditions.
The windings are rigidly supported by elephantide washers and spacers. Sufficient oil ducts are provided by us between the coils and also between the windings and properly dimensuioned for efficient cooling and low electrical stresses. Proper clearance to earth are maintained through washers and spacers. The clearances are in accordance with relevant indian standard specifications. Close attention is given to good mechanical bracing of the windings for equal distribution of stresses resulting under short circuit conditions.


The tappings are generally brought out from the ht windings but can be provided on the lt windings also, if required by the customers the off circuit switch are manufactured by ourselves for mounting inside the transformer and externally operated. They can be locked in any selected position.

On load tap changer: Tank and fittings

The transformer tanks are made up of mild steels plates electrically welded together. Cooling is provided through pressed stell radiators.
The tanks are provided with an oil conservator, which is of the welded drum type, to make the expansion of the transformer oil under working conditions without its coming to the direct contact with atmosphere to eliminate moisture. Breathing of the transformer takes place through a dehydrating breather usually ‘silica gel’ type. The entire transformer assembly is lowered into the tanks with guided rails and botton and tap channels to ensure correct locations of the transformer in the tank to take care of the same transit.
The drona rohitra transformers are provided with standard fittings according to indian standard specification. Any additional requirements of the customers can be incorporated. Procelain bushings of good quality and charactestics are used on distribution transformer , cable boxes can be used to supply any type of cable arrangement.