Dissolved Gas-In-Oil Testing

This test, which is performed in accordance with ASTM D3612, is used by many utilities as a part of their maintenance program. Dissolved gas-in-oil analysis is a valuable tool in the preventative maintenance of transformers. Internal transformer faults (three types are corona, hot spots, and arcing) generate gases at an early stage and a portion of these gases dissolve and remain in the transformer oil. Each type of fault will generate gases in quantity and proportion that may be recognizably different than those generated by the other fault types. This "uniqueness" in gas generation for each fault type is the basis for transformer fault diagnosis. By sampling the transformer oil and measuring the dissolved gases, an indication is obtained as to the possible source of a gas generation. This in turn aids in performing preventative maintenance on the transformer.

Follow this easy procedure for fast, accurate results:

  1. All that is required is your name, address, phone number and number of samples to be tested.
  2. T&R Service will send you the number of sample bottles you need. You then fill them with the oil to be tested and return them to T&R Service.
  3. T&R Service will then mail you the test results and recommendations in a convenient form that can be used to record future periodic test results.

This test is easily obtained. First, we provide you with a special stainless steel sampling cyclinder along with instructions. This allows you to remove the oil from the transformer while avoiding contact between the oil and the atmosphere. Then, after we receive the sample from you, the oil is vacum degassed and the gases are injected into a Hewlett Packard gas chromatograph. The gas chromatograph provides parts per million levels of the measured gases and this information is reported to you.

Using a stainless steel cylinder to take a dissolved gas-in-oil sample

  1. Flush the valve. Allow approximately 1qt. of oil to drain to the waste oil container.
  2. Connect a short length of plastic tubing to each valve of the sample cylinder.
  3. Attach one tube to the transformer sample valve and place the other tube in the waste oil container.The sample cyclinder must be held vertical. The end attached to the sampling valve must be pointed down.
  4. Open both valves of the sample cyclinder.
  5. Very carefully open the oil sampling valve of the transformer. This should gradually fill the oil sample cyclinder from the bottom. The overflow should go through the top tube into the waste oil container. Continue over-flowing the oil until no more bubbles can be seen through the plastic tubing and until at least 2 qts. of oil have flushed through the cylinder.
  6. Close the top, or outlet valve, of the cylinder.
  7. Close the bottom, or inlet valve, of the sampling cylinder.
  8. Close the transformer sampling valve.
  9. Disconnect the plastic tubing.
  10. Reuse the cartons and packing materials to ship the cylinders to T&R Service Company.