Investigation of the Effect of High Voltage Impulse Stress on Transformer Oil by Infrared Spectroscopy

With the aging of transformers, degradation of internal condition occurs and as a result, they become more susceptible to failures. Extreme conditions like lightning strikes, switching transients, short circuits or other incidents cause failures in transformers. Among these, lightning strikes and switching transients are impulsive in nature and have a degrading effect on transformer insulation. The most widely used insulating liquid for high voltage transformers is mineral oil because it performs the functions of cooling as well as electrical insulation. Due to lightning strikes and switching impulses, transformers are subjected to massive electrical as well as thermal stresses, causing degradation of the insulating oil present inside the transformer. Hence, impulse testing of transformer oil is of utmost importance. All the three characteristics of transformer oil viz. electrical, physical and chemical were examined. The breakdown voltage (BDV) test was carried out to evaluate the electrical characteristics. The refractive index test was done to assess the physical characteristics and the Fourier transform infrared spectroscopy (FTIR) was performed to evaluate the chemical characteristics of the transformer oil.