Transformer oil condition monitoring

Since transformer oils are a vital part of the insulation system, they require regular checking. Oil condition monitoring plays a vital role in assessing plant status and integrity and also in estimating remanent life of the units. It needs to be carried out on a regular basis so that oil deterioration can be detected at an early stage. Yearly intervals are the most common test period. Trends can then be monitored and corrective actions taken at the optimum time. Guidelines for the maintenance of transformer oil in service are published in IEC 422. Whilst some of the oil testing equipment seems expensive, the cost is small in comparison with that associated with insulation failure. Regardless of what test is specified, it is imperative that it be run on a representative liquid sample since accurate sampling is the prerequisite to any standard test. Oil may change appreciably in storage so samples should be tested as soon as possible after removal and dates of sampling and testing recorded. Oil tests performed on site can be the most representative and informative providing cleanliness and quality control are maintained.