A BDV tester applies an increasing AC voltage across a standardized electrode gap immersed in the oil sample until electrical breakdown occurs. The instrument records the breakdown voltage, then typically repeats the test several times on the same sample to produce an average and assess repeatability. Proper preparation is critical: the test cell must be clean and dry, the sample must be free of visible bubbles, and the oil must be handled to avoid moisture pickup. Higher BDV generally indicates better dielectric cleanliness, while low BDV often signals moisture or particulate contamination.
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