The prototype has six thermocouples placed at locations internal to the
transformer per Fig. 6. Cross-sections AA’ and BB’ depicted in this figure are used later in Section VII to compare results. The transformer was fed from a constant voltage source while the load power was kept constant. The input power, output power, and the temperatures were recorded at intervals of 30 min until steady state was achieved per IEEE C57 [12]: the temperature does not change more than 2 C in three hours. The
difference in input and output power is the power dissipated in the transformer and is responsible for the temperature rise.