Sampling of Transformer Oil

Sampling of Transformer Oil

In this article, you will learn about preparing of ‘Electrodes and Test Vessel’ before performing breakdown voltage (BDV) test on insulating oil in service in transformers and switchgear. Below are the steps as defined in IS 6792 that needs to be followed.

  1. Between tests, the oil shall be poured away and the cell left in an inverted position to exclude dirt and moisture, alternatively, the cell shall be filled with oil having high electric strength, and suitably covered.
  2. If the cell has not been used for some time, it should be thoroughly cleaned; the electrodes shall be removed, cleaned and finally rinsed with dry, clean new oil. Replacement of the electrodes should be carried out with the greatest care, avoiding all direct contact with the fingers.
  3. Immediately before use, the cell shall be cleaned by rinsing with the test oil (at least twice) before proceeding to the final filling.
  4. The sampling vessel containing the test oil shall be gently agitated and turned over several times in such a way as to ensure as far as possible a homogeneous distribution of the impurities contained in the oil without causing the formation of air bubbles.
  5. Immediately after this, the sample should be poured down into the test cell, slowly in order to avoid air bubbles forming. The operation is carried out in a dry place free from dust.
  6. The oil temperature at the time of the test shall be the same as that of the ambient air, preferably in the neighborhood of 27ºC (15 to 35ºC) and noted.

Dielectric breakdown voltage test

This is one of the significant tests to determine the withstanding capacity of insulating oil. It is necessary to test the insulating oils periodically as it degrades due to ingress of moisture.

BDV test is one of the most regular tests done on all insulating fluids, but a very critical one.