Transformer Warm Up and Drying

The main purpose of the transformer’s warm-up  is to define the insulation characteristics of its active part.  The test warm-up of oil is carried out at 40-60°C / 104 – 140°F but it is not enough to warm up only the dielectric liquid.  The temperature of oil should be 7-10°С / 44.6- 50 F higher than the value, specified in the test report in order to warm up the transformer’s active part.  Oil must be soaked a few hours under specified conditions.  Then the temperature is lowered and all necessary measurements are taken. The special heaters with an open coil should be placed under the transformer tank to equal the temperature of  lower and upper layers.  The test warm-up  may be realized by alternate as well as by direct current powwer.  It depends on the operating conditions.  The test drying is performed in the following cases: (1) the winding insulation and/or oil is moistened; (2) the transformers are kept without oil for a long time; and (3) the active part of the transformer is unsealed. The drying of the transformer is performed in the same way as its warm up.  The drying is preceded by loading a technological tank with the electric-grade cardboard samples from the insulation model. When the main works are done, the moisture content of the insulation samples is measured and the result is compared with the previous one.  The drying is considered to be satisfactory if the moisture content of the samples is no more than 1 %.   If such a result has not been achieved, the drying is repeated. Sometimes a method of freezing of the condensate vapor in a cold trap is applied to carry out a test drying.  The oil must be discharged from the transformers and residual pressure must be maintained in order to realize this method. The test drying is performed by the equipment designated as ‘Iney‘.  The operational principle of this equipment is that it removes vapours from the solid insulation in a cold trap when there is high vacuum. Heat, stored in magnetic conductors and metallic parts, is used to maintain a drying rate at a desirable level.  The drying may be finished if a daily condensate separation is no less than 0.5 kg when under the pressure of 26 Pa (pascal). GlоbeCоre equipment designated as ‘Iney‘ allows the companies to reduce energy and labor costs and eliminate the risk of fire