Temperature Rise Test for Top Oil of Transformer
First the LV winding of the transformer is short circuited.
Then one thermometer is placed in a pocket in transformer top cover. Other two thermometers are placed at the inlet and outlet of the cooler bank respectively.
The voltage of such value is applied to the HV winding that power input is equal to no load losses plus load losses corrected to a reference temperature of 75°C.
The total losses are measured by three watt-meters method.
During the test, hourly readings of top oil temperature are taken from the thermometer already placed in the pocket of top cover.
Hourly readings of the thermometers placed at inlet and outlet of the cooler bank are also noted to calculate the mean temperature of the oil.