How is transformer insulation oil evaluated for dielectric breakdown strength?

Dielectric breakdown strength is evaluated using a Breakdown Voltage (BDV) test. In this test, oil is placed between two standardized electrodes and voltage is gradually increased until electrical breakdown occurs. The result, measured in kilovolts, indicates the oil’s insulating capability. Multiple tests are averaged to ensure accuracy. Low BDV values typically indicate contamination by moisture, particles, or degradation products, signaling the need for filtration or oil replacement.