Dielectric testing commonly refers to breakdown voltage testing using a standardized test cell with specified electrode geometry and gap. The sample is placed in the cell, air bubbles are removed, and voltage is increased at a controlled rate until breakdown occurs. Multiple breakdowns are performed to obtain an average value. Proper sampling, temperature control, and clean test equipment are essential to avoid false low results. The test indicates oil cleanliness and moisture condition but should be combined with moisture, acidity, and DGA for diagnosis.
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