Determination of Effective Oil Temperature in a Transformer

It has shown in this paper that: 1. The effective oil temperature and the thermal time constant of each winding, as well as the winding temperature at instant of shutdown, can be determined from the resistance-time data taken immediately after the shutdown of a heat run on a transformer. 2. The average oil temperature as determined in accordance with the Test Code checks, within limits of test accuracy, the effective oil temperature determined by the resistance-time data methods described in this paper. 3. The effective oil temperature for each individual winding may not necessarily be the same value. This indicates that such factors as size of ventilation ducts, relative position of the windings to each other and to the core, and the division of loss in the transformner, may affect the temperature of the oil which effectively cools each individual winding.