Study of spectral response of Transformer Oil under Low Electrical Discharge and Thermal Stress

Abstract

Knowing that electric insulating liquid is a weak link in a composite or impregnated dielectric system, many investigators have devoted great efforts to enhance our basic knowledge of the behaviour or aging characteristics of insulating oil under different stresses. Understanding the process of insulating oil degradation is of utmost importance for both manufacturers of electrical equipment and maintenance planners. The process of degradation may alter the physical and chemical structure of the insulating liquid and may lead to the creation of new products or to an increase and decrease in the concentration of existing functional groups. Optical techniques such as ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy are powerful non-destructive techniques to assess the degree of degradation and the shift in atomic or molecular concentration and structure. An in-depth lecture of the optical spectroscopy responses may be used to enhance diagnostic techniques such as DGA method. The aim of this contribution is to use different spectroscopy measurements for studying the influence of low electrical discharge and the local overheating fault on transformer oil properties and investigate the correlation between the different methods. In this regard, various scenarios were considered; the study was carried on mineral oil and the gassing behaviour, as well as turbidity (ASTM D6181), dissolved decay products (ASTM D6802) and infrared spectres have been monitored. The results show that mineral oil is highly susceptible to local overheating and generates further decay products, and the correlation of FTIR spectral responses with DDP and turbidity measurements provides initial knowledge that transformer states can be recognized by using spectroscopic techniques as a non-destructive diagnostic technique