Oil Testing
BVD Oil Transformer
- Dielectric strength of transformer oil is also known as the breakdown voltage (BDV) of transformer oil.
- Measured by observing at what voltage, sparking strands between two electrodes immersed in the oil, separated by a specific gap.
- Low value of BDV indicates presence of moisture content and conducting substances in the oil.
Oil Viscosity Test
- Viscosity is the resistance of flow, in normal condition. Resistance to flow of transformer oil means obstruction of convection circulation of oil inside the transformer.
- Good oil should have a low viscosity so that it offers less resistance to the conventional flow of oil thereby not affecting the cooling of a transformer.
Interfacial Tension Test
- Interfacial tension between the water and oil interface is the way to measure the attractive molecular force between water and oil.
- Determine the presence of polar contaminants and oil decay products. Good new oil generally exhibits high interfacial tension. Oil oxidation contaminants lower the IFT.
Total Acid Number (TAN) Test
- Acidity test of transformer oil can be used to measure the acidic constituents of contaminants.
- Water content in oil becomes more soluble when oil acidic. The acidity of oil deteriorates the insulation property of paper insulation of winding.
- Acidity accelerates the oxidation process in the oil and includes rusting of iron in the presence of moisture.
Moisture Test
- Moisture or water content in transformer oil is highly undesirable as it affects the dielectric properties of the oil adversely.
- The water content in oil also affects the paper insulation of the core and winding of a transformer. Paper is highly hygroscopic. Paper absorbs the maximum amount of water from oil which affects paper insulation property as well as reduced its life. But in a loaded transformer, oil becomes hotter, hence the solubility of water in oil increases.
- Acid coupled with water decompose the oil forming acid and water. This rate of degradation of oil increases.
