As transformers age, gaseous and liquid contaminants become dissolved in the dielectric fluid and can lead to failures or shortened useful lives unless detected and treated early. Sampling and analysis of dielectric fluid is the cornerstone of transformer preventive maintenance. Transformer oil is sampled at least annually and analyzed using gas chromatographs, spectrometers, and other sophisticated test equipment. The results of these tests show the types and amounts of contaminants in the oil and how they have changed from year to year. The contaminants occur as a result of aging, overheating, leaks or other performance problems.

A complete visual inspection of the transformer is performed at the time the samples are drawn. Leaks, inoperative gauges, cracked bushings, low oil level and other defects are identified and described. Nameplate and other operational data is recorded to assist in developing maintenance recommendations. A transformer engineer reviews the sample test results and inspection reports taking into account prior history, the usage and age of the transformer, IEEE Standards and prepares a complete report and trend analysis of the sample results, visual inspection and maintenance recommendations that is sent to the customer.

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