How is the dielectric strength of transformer oil measured per mm?

The dielectric strength of transformer oil is measured using a device called a dielectric strength tester, which applies a high voltage across two electrodes immersed in the oil. The measurement is typically conducted in accordance with standardized testing methods, such as ASTM D877 or IEC 60156. During the test, the voltage is gradually increased until breakdown occurs, and the dielectric strength is calculated by dividing the breakdown voltage by the distance between the electrodes, usually expressed in kilovolts per millimeter (kV/mm). This measurement is crucial for assessing the insulation properties and overall performance of transformer oil, ensuring that it can effectively prevent electrical breakdown in high-voltage applications. The dielectric strength of transformer oil is key to its reliability and safety in electrical equipment.