SSRG International Journal of Electrical and Electronics Engineering Volume 10 Issue 8, 9-22, August 2023 ISSN: 2348-8379/ https://doi.org/10.14445/23488379/IJEEE-V10I8P102 © 2023 Seventh Sense Research Group ® This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Original Article Degradation Assessment of Oil-Impregnated Paper Insulation for Converter Transformer Based on FDS using Digital Image Processing Shrikant S. Mopari 1 , D. S. More 2 , A. S. Bhalchandra 3 , Pannala Krishna Murthy 4 , K. M. Jadhav 5 1,2 Department of Electrical Engineering, Walchand College of Engineering, Sangli, India. 3 Department of Electronics Engineering, Government College of Engineering, Aurangabad, India 4 Department of Electrical Engineering, Sri Chaitanya Institute of Technology & Research, Khammam, India. 5 University Department of Basic and Applied Sciences, MGM University, Aurangabad, Maharashtra, India. 1 Corresponding Author : mopari1977@gmail.com Received: 02 June 2023 Revised: 06 July 2023 Accepted: 04 August 2023 Published: 31 August 2023 Abstract - The Oil-Impregnated Paper (OIP) insulation is commonly utilized as the foremost insulation type in the case of a converter transformer, which is constantly and unavoidably affected by elevated temperature and different stresses arising during the mode of operation. It causes a safety risk to the insulation system of the converter transformer. Because of this, the present study examines the effect on OIP insulation using the FDS technique as a function of frequency and elevated temperature. The Frequency Domain Spectroscopy (FDS) and Atomic Force Microscopy (AFM) techniques were carried out for condition evaluation and surface morphological changes of OIP insulation. The experimental results show that elevated temperature viz 30°C, 50°C, 70°C, 90°C, 110°C and 130°C produces irreversible damage to the surface of OIP, which can lead to morphological changes. The frequency-dependent permittivity studies also confirm the deterioration of OIP insulation as permittivity decreases with increased frequency. However, the synergistic effect generated on the OIP insulation can also be analyzed by image processing-based evaluation methods dependent on the average of four local areas of AFM images. One disk of a valve side star winding single phase converter transformer is developed in MATLAB Simulink. An impulse of 20kV, 1.2/50μsec is applied to study the correlation among insulation degradation across the turn by considering elevated temperature and frequency dependence of OIP insulating material by wavelet transform. The energy of the wavelet coefficient is utilized to analyze the insulation degradation of insulation of the converter transformer. Thus the effectiveness of the FDS study revealed the condition monitoring of converter transformer insulation, and the presented results agree with the published work. Keywords - Atomic Force Microscopy, Converter transformer, Elevated temperature, Frequency Domain Spectroscopy, Oil Impregnated Paper, Wavelet transform. 1. Introduction The converter transformer performs a dynamic task in an electrical power system's transmission and distribution network. The converter transformer insulation weakens when subjected to harsh operating conditions. The transformer insulating system mainly consists of Oil-Impregnated Paper (OIP). The transformer oil acts as insulation as well as coolant. The primary constituent OIP insulation is a polymer of glucose and Cellulose which degrades because of the stresses and elevated temperature during the operation. The reliable performance and avoiding the transformer outage depends upon the insulating material's character. Thus, insulation degradation due to thermal ageing is recognized as a prime cause of transformer failure. Hence to ensure reliable and safe operation performance, there is a need to test transformer insulation regularly. Thus, DGA analysis is regularly used to diagnose oil and thermally degraded insulating paper [1, 29], but methods produce certain limitations for the actual status of insulating cellulose paper. Due to the above reasons, utility engineers are more interested in non-invasive methods to examine transformer cellulose insulation. During the 1990s, Return Voltage Measurement (RVM) [3, 34] and Polarization and Depolarization Current (PDC) techniques [4-5] were the most widely popular to measure insulation conditions. RVM is a non-destructive technique with certain limitations for separately assessing oil and paper