OIL BDV TEST The BDV of transformer oil is the breakdown voltage of transformer oil. The BDV or dielectric strength of oil is the maximum voltage withstand capacity of the oil without breakdown. BDV test of transformer oil is very important for the trouble-free operation of the transformer. Therefore, periodic testing of the transformer oil BDV is compulsory to ensure its health. As per IEC, the minimum BDV of transformer oil should be 30 KV as per transformer oil BDV test standard. The transformer oil is used in the transformer for insulation and cooling purposes. The different insulating materials have different dielectric strengths. The insulating material should sustain the voltage up to its dielectric strength. If the voltage is increased above the specified dielectric strength of the insulating material, the current starts flowing through it, and eventually, the material gets permanently punctured. The transformer oil is hygroscopic, i.e., it tends to absorb moisture quickly. The dielectric strength of the oil deteriorates with the absorption of the moisture. That is why the breather filled with silica gel (Moisture absorbent material) is used in the transformer to trap external moisture during breathing in silica gel. Transformer Oil- Testing, Types, And Properties. The core and winding of the power transformer are submerged in transformer oil. The heat generated inside the transformer due to Iron Loss and copper loss needs to be dissipated outside the transformer to limit the temperature to its safe limit. The heat generated inside the transformer is transferred to oil, and the oil transfers the heat to the outer tank body, and the temperature is dissipated in the atmospheric air. The quality of the transformer oil is of the utmost importance for the reliable operation of a filled transformer.