Transformer oil test

Transformer oil test

1. OBJECTIVE: 

To verify dielectric strength of transformer oil from both tank and OLTC. 

2. TEST INSTRUMENTS REQUIRED: 

- Oil sample bottle 

- BDV tester 

3. TEST PROCEDURE: 

3.1. OIL SAMPLING: 

• A clean, dry GLASS container is to be used. The size of the container should be at least three times the size of the test cell. (A container of approximately 1 litre is

sufficient) 

• During sampling, rinse the glass container with little quantity of oil and drain. 

• Fill the container with oil until the container over flows. 

• Do not allow free air space inside the container. 

• Do not allow air bubbles inside the container. 

• Sampled Container should be closed airtight with cork or any other nonreactive material. 

• (Optional). In case the oil is to be transported to a larger distances, ensure that oil is stored in a clean and dry place and transported with utmost 

care. 

• Before filling the oil in the test cell, gently agitate the container without creating air bubbles. 

• Rinse the walls of the test cells with little of oil and drain it. 

• Ensure that the electrodes of the test cell are clean. 

• Fill the oil sample until overflow, into the test cell without formation of air bubbles. 

• Do not start the test for at least for 5 min. after filling the test sample (oil). 

3.2. BREAK DOWN VOLTAGE TEST: 

• The oil sampling to be carried out as per the procedure explained in the sampling instructions. 

• The BDV test to be started after at least 5 minutes from the filling of the sample oil in the test cell. 

• Ensure that the gap between the electrodes is maintained at 2.5mm. 

• Ensure that the electrodes are clean. 

• The rate of rise of the test voltage to be adjusted at 2kV per second. 

• Conduct the BDV test for 5 to 6 times for the same sample with a time interval of at least 3 - 4 minutes between tests. 

• Ensure that between tests, stirring of the test sample is carried out. 

• Record the test results and obtain the average of the test results to obtain 

the Breakdown voltage of the test sample. (Ignore the odd values).