The solution to prevent transformer failure is to regularly test the insulating oil used in the transformer. The oil acts as a coolant and dielectric material, and its condition is vital for the transformer to operate optimally. One of the most important tests for transformer oil is the Break Down Voltage (BDV) Test. The BDV Test measures the voltage at which insulation breaks down in a transformer oil sample, rendering it ineffective for its intended use. During the test, an oil sample is subjected to an increasing voltage and the voltage at which a spark jumps is recorded. The voltage reading is typically expressed in kilovolts (kV). How to perform the transformer oil test?
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 liter is sufficient)
• During sampling, rinse the glass container with a small quantity of oil and drain.
• Fill the container with oil until the container overflows.
• 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 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 a little oil and drain it.
• Ensure that the electrodes of the test cell are clean.
• Fill the oil sample until overflows, into the test cell without the formation of air bubbles.
• Do not start the test for at least 5 min. after filling the test sample (oil).
BREAK DOWN VOLTAGE TEST:
• The oil sampling is to be carried out as per the procedure explained in the sampling instructions.
• The BDV test is 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 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)