The Method for Aging Condition Prediction of Transformer Oil-immersed Cellulose Insulation Based upon the Aging Kinetic Equation

Abstract

The service life of the transformer is determined by its solid insulation performance. However, it is a rather difficult job to quantitatively evaluate the aging conditions of cellulose insulation materials of the transformer by traditional methods. The existing researches show that the cellulose aging kinetics model of cellulose can establish the functional relationship between the degree of polymerization (DP) and moisture content, aging temperature and aging duration. Therefore, based on the simultaneous considering Arrhenius equation and Ekenstam equation, the purpose of this work is to report an approach that can quantitatively evaluate the aging condition of cellulose insulation of transformer. Furthermore, the present finding of this paper can provide a novel idea for evaluating the aging state of transformer solid insulation. Introduction Cellulose insulation materials have been widely used in oil-immersed insulation systems, such as power transformers, high voltage bushings and cable lines. Transformer oil-immersed cellulose insulation system is often subjected to various thermal, electrical, mechanical, chemical and other stresses during operation, which not only gradually degrades its insulation state, but also leads to the deterioration of transformer insulation [1]. During the operation of the transformer, the performance of liquid insulating oil can be improved by oil filtering and oil changing operations, while the solid insulation materials dominate the service life of the transformer main insulation system due to its irreversible and non-replaceable characteristics [2]. Therefore, the evaluation of the aging degree of cellulose materials has received widespread attention and research from scholars in the industry. In recent decades, the evaluation method of the aging state of cellulose insulation has been developed into two types, which is based upon the electrical characteristic parameters [3] and chemical characteristic parameters [4]. In traditional methods utilized the electrical characteristic parameters, scholars have preliminarily realized the qualitative analysis of aging state by testing dielectric loss, time/frequency domain dielectric response spectrum and other parameters. In contrast, in traditional chemical methods, scholars have also preliminarily realized the qualitative (quantitative) analysis of cellulose insulation materials by analyzing the chemical characteristics such as tensile strength, DP value, dissolved furan in oil, alcohol compounds and acid value. The above work provides a lot of theoretical basis and technical support for cellulose insulation evaluation research, but it cannot be popularized in this field due to various limitations. Specifically, the traditional chemical method cannot accurately establish the quantitative relationship between the aging degree and the characteristic parameters due to the difficulty of sampling and the influence of oil change and oil filtering. However, the traditional electrical method is not reliable because it cannot distinguish the influence of aging and moisture on the dielectric response curve from the spectrum curve. Therefore, how to accurately realize the quantitative evaluation of transformer cellulose insulation materials has become an urgent problem to be solved. The research points out that the aging degradation of cellulose insulation material leads to the destruction of its cellulose microstructure and significant decrease of its mechanical performances, which is directly reflected in the decrease of DP value. Therefore, the DP value has become the key criterion to judge the aging degree of cellulose materials. A large number of the literature show that 2nd International Conference on Electrical and Electronic Engineering (EEE 2019) Copyright © 2019, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Engineering Research, volume 185