EFFECT OF AGING ON TRANSFORMER INSULATION MATERIALS

Abstract

In recent years, there has been a significant increase in the interest of researchers and practicing engineers in the field of monitoring and diagnostics of transformers. The primary cause of power transformer failure is attributed to insulation degradation resulting from the aging process. Hence, it is important to monitor the insulation health with aging. Apart from experimental, numerical techniques have been proven to be quite useful in the monitoring in sulation performance. The Finite Element Method (FEM) is considered to be one of the very effective numerical approaches. The primary objective of this study is to investigate the im pact of aging on the performance characteristics of transformer insulation materials through the utilization of FEM analysis. Motivated by the desire to confront novel challenges, this thesis presents a research endeavor that is structured into distinct components. These com ponents encompass the identification of appropriate computational models for the analysis of insulation aging, the examination of the impact of aging on the distribution of space charge and electric field, and the formulation of a comprehensive model capable of analyzing the cumulative effects of insulation aging and oil convection on insulation degradation. Each one of these is briefly discussed below. A model based on plasma dynamics is formulated to examine the discharge phenomena occurring within air-filled voids of various geometries commonly found in power transform ers. The model employs a modified drift-diffusion technique and considers voids with cylin drical, spherical, and ellipsoidal shapes, which are enclosed by different insulating materials employed in power transformers, and the effect of void shape distortion on the discharge dynamics were observed. Hence, an improved model has been developed, and a compara tive assessment has been conducted to analyze the discharge dynamics in different insulating materials containing air-filled voids. The presence of an electric field force at the interface be tween the void and insulation has been observed, leading to the distortion of the void shape. Consequently, the electric field stress intensifies in specific regions, thereby creating sites where partial discharge initiation occurs. The insulation material within the power transformer experiences non-uniform aging as a result of a radial temperature gradient. Under non-uniform aging, transformer insulation is subjected to distinct aging conditions in the direction from the iron core to the tank due to i different temperature gradients. In order to accommodate the non-uniform aging of the insu lation, an enhanced model is formulated by incorporating XY and FEM models. This refined model is employed to examine the cumulative losses in the insulation, taking into consid eration both uniform and non-uniform aging. Additionally, alterations in various electrical parameters are analyzed. The phenomenon of non-uniform aging is found to be associated with increased losses, particularly at medium and higher frequencies, which consequently leads to more severe degradation of the insulation material.