Transformer Oil BDV Test

The BDV of transformer oil is 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 oil is very important for trouble free operation of transformer. Therefore, periodical testing of the transformer oil BDV is compulsory for ensuring healthiness  of the transformer oil. 

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 as well as for cooling purpose. The different insulating materials have different dielectric strength. 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 get permanently punctured. 

The transformer oil is hygroscopic in nature i.e it tends to absorb the moisture quickly. The dielectric strength of the oil gets deteriorated with the absorption of the moisture. That is why the breather filled with silica gel (Moisture absorbent material) is used in transformer so that external moisture during breathing can be trapped in silica gel. 

Core and winding of the power transformer is submerged in transformer oil. The heat generated inside the transformer due to iron loss and copper loss needs to be dissipated outside of 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 has utmost importance for reliable operation of oil filled transformer. 

The reliability of the transformer can be ensured if all the parameters of the transformer oil are as per the standard. 

The dielectric breakdown voltage test is a quick and easy way of determining the contamination in the transformer oil. The water is the major contaminant however, other contaminants like conductive particles,dirt,debris,insulating particles and by product of oxidation and aging of the transformer oil can deteriorate the dielectric strength of the mineral insulating transformer oil.