Health assessment of converter transformer pressboard insulation based on FDS and digital image processing

The stable operation of the converter transformer is an essential task for power system operation reliability and security. Nowadays, Frequency domain spectroscopy (FDS) technology is prominently utilized for assessing oil-impregnated pressboard insulation. The present study examines the effect of the pressboard insulation material as a function of frequency and elevated temperature. The experimental analysis on oil-impregnated pressboard insulation is carried out at temperatures from 30 °C to 130 °C with an incremental rise of 20 °C intervals with frequency variation from 1 Hz to 10 MHz. The frequency-dependent permittivity, conductivity and loss tangent angle studies also confirm the deterioration of oil-impregnated pressboard insulation. The surface morphological changes inside the pressboard insulation are recorded with the help of scanning electron microscopy (SEM). The synergistic effect generated on pressboard insulation is examined by fiber width changeand image processing approach by randomly selecting the average of three local areas of SEM image. A canny operator is selected to extract the exact boundaries of images and more change is recorded in the edge detection count after 90 °C.The porosity and pore size distribution can be increased with elevated temperatures. A single-phase, 315 MVA valve side star winding with 60 discs of single-phase converter transformers model is developed in MATLAB Simulink. An impulse of 100 kV, 1.2/50μsec is applied across the star winding to identify the pressboard insulation degradation derived from FDS data with the help of mathematical morphology and wavelet transform technique. The energy of the wavelet coefficient on the neutral current capture during the impulse test adds a significant contribution to analyzing pressboard insulation degradation. The results presented are in good agreement with the published work