An investigation of the temperature distribution in cast-resin transformer windings

A comprehensive thermal test program was conducted on a 2000 kVA cast-resin dry type transformer with 300 embedded thermocouples to determine the hottest spot temperature allowance and to obtain data to develop mathematical models. Nineteen thermal test runs were performed at different loads, tap positions, and core excitations under natural and forced air operating conditions. The test data indicated that the hottest spot temperature allowance used in the IEC standard was too low. In the IEEE standard the hottest spot temperature allowance appears conservative up to about 115°C average winding temperature rise. The locations of the hottest spot for the primary and secondary winding were determined. Conclusions about thermal testing and loading are presented