• Transformer winding resistance measurement
• Transformer Ratio Test
• Vector Group Test of Transformer
• Dielectric Test of Transformer
• Temperature Rise Test of Transformer
• Transformer Impulse Test
• Sweep Frequency Response Analysis
• Tan Delta or Dissipation Factor Test
Over Fluxing in Transformer
Earthing or Grounding Transformer
External & Internal Faults in Transformer
Backup Protection of Transformer
Differential Protection of Transformer
Restricted Earth Fault Protection
Maintenance of Transformer
Air Core Transformer
High Voltage Transformer
Temperature rise test of Transformer is included in type test of transformer. In this test we check whether the temperature rising limit of transformer winding and oil as per specification or not.
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.
- Ambient temperature is measured by means of thermometer placed around the transformer at three or four points situated at a distance of 1 to 2 meter from and half-way up the cooling surface of the transformer.
- Temperature rise test for top oil of transformer should be continued until the top oil temperature has reached an approximate steady value that means testing would be continued until the temperature increment of the top oil becomes less than 3°C in one hour. This steady value of top oil is determined as final temperature rise of transformer insulating oil.
- There is another method of determination of oil temperature. Here the test in allowed to be continued until the top oil temperature rise does not vary more than 1°C per hour for four consecutive hours. The least reading is taken as final temperature rise of the oil.
During temperature rise test for top oil of transformer we make the LV winding short circuited and apply voltage to the HV winding. So for full load rated electric current flows in the transformer, the supply voltage required will much less than rated transformer voltage. We know that core loss of a transformer depends upon voltage. So there will not be any considerable core loss occurs in the transformer during test. But for getting actual temperature rise of the oil in a transformer, we have to compensate the lack of core losses by additional copper loss in the transformer. For supplying this total losses, transformer draws electric current from the source much more than its rated value for transformer.