Review of Physicochemical-Based Diagnostic Techniques for Assessing Insulation Condition in Aged Transformers

Abstract

Abstract:A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. The service reliability of this important asset largely depends upon the condition of the oil-paper insulation. Therefore, by keeping the qualities of oil-paper insulation system in pristine condition, the maintenance planners can reduce the decline rate of internal faults. Accurate diagnostic methods for analyzing the condition of transformers are therefore essential. Currently, there are various electrical and physicochemical diagnostic techniques available for insulation condition monitoring of power transformers. This paper is aimed at the description, analysis and interpretation of modern physicochemical diagnostics techniques for assessing insulation condition in aged transformers. Since fields and laboratory experiences have shown that transformer oil contains about 70% of diagnostic information, the physicochemical analyses of oil samples can therefore be extremely useful in monitoring the condition of power transformers.

Study on Correlation Among Oil Dielectric Characteristics, Dissolved Gases, and Operating Life of 150 kV Power Transformer

“…Acidity is proven to have a high correlation to increasing operating time of transformer in previous experiments [10] [25]. Oxygen attacked the oil insulation producing acids through oxidation process [10][16] [25].…”

“…[10] [16]. Oxidation and hydrolysis of insulation system that accelerated by temperature continuously happen during operating time of transformers and generate acid even more [25]. It is clearly explained that the increasing operating time of transformer will lead to the increasing of acidity level of oil insulation.…”

“…Oxygen attacked the oil insulation producing acids through oxidation process [10][16] [25]. The presence of acid is detrimental to solid insulation because it obviously will increases the probability of hydrolysis occurrence in cellulose.…”

“…On the other hand, some dielectric characteristics of oil insulation indicates ageing pattern with its strong correlation to transformer operating time. Acidity, IFT and color found to be potential parameters to indicate ageing in transformers [10] [11][18] [20][21][22][23][24][25][26]. It could be concluded since acidity, IFT and color tend to be increased as transformer operating time getting longer [10] [18][26] [27].…”

A New Method for Evaluating Moisture Content and Aging Degree of Transformer Oil-Paper Insulation Based on Frequency Domain Spectroscopy

“…The safety and stability of such transformers are both important and necessary in operating power systems [3]. Oil-paper insulation is an important form of power transformer insulation system; the remaining life of the transformer largely depends on the insulation status of oil-paper which is affected by thermal, mechanical, partial discharge and other aging factors in the long-running process [4][5][6].…”