The active part assemblies are dried by heating under vacuum, in a PLC (Programmable Logic Controller) driven drying oven. This ensures effective removal of moisture. This is followed by vacuum process, either in special chambers with heating or directly on the tank, for very big transformers. Upon drying of the active part assemblies, the clamping and connections are rechecked and tightened. The completely dried and clamped active part assembly is then lowered into the tank.
It is subsequently filled with de-gasified and filtered oil, under vacuum – to ensure the entire core-coil assembly and the insulating materials are totally in oil. Cooling medium is conventional mineral oil, but depending upon customer requirement specialty liquids like Midel, Silicone or R-temp can be used. Upon fixing of the fittings and accessories, the transformer is offered for final testing.