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List of Tests Required for Dual Wound Transformers

Below is the list of some important transformer tests which are conducted on site before final testing and commissioning is planned.

Insulation resistance test

In  this  test  the  insulation   resistance  is measured  by applying  appropriate  voltage  across the terminals as mentioned below:

  • HV to Earth+LV and ground is measured with 5kV test voltage
  • LV to Earth+HV and ground is measured by applying 1kV test voltage
  • HV to LV is measured by applying 5kV test voltage

Winding resistance test

Using a  winding  resistance  meter the HV and LV winding resistance  are  measured  and recorded,  the ambient temperature at the time of test is noted for temperature  corrections. The test is repeated for all taps on HV winding.

Transformer turns ratio

Test and vector group is verified using Megger TTR

Magnetic Core Balance test

For magnetic  balance test apply the two phase voltage  between the 1U & 1V and the tap position is kept at service tap. Then measured voltage on HV & LV in all combinations as tabulated in the test format and lock that applied voltage between 1U & 1W, 1W&1V and measured the voltage

Magnetizing Current

The magnetizing current drawn by the transformer at the LT mains supply Current measured for the HV winding for all phases at all the taps keeping the LV terminals open circuited

Vector group test

For Dyn11 vector group, Keep the terminals 1U (HV R phase) & 2U (LV R phase) shorted, a 3 phase, 415V, supply  is applied  on the  HV side  of the  transformer, the tap  position  is kept at service tap. The voltages on HV & LV are measured in all combinations as tabulated in the test format and it is verified that the voltage 1V-2V is equal to 1V-2W and 1W-2V is greater than 1W-2W. This could be seen in the vector diagram.

Vector group test for transformer

Protective device operation

The  transformer protective  devices  are  operated/simulated as  described  in the project specifications.

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