Effect of Oil Regeneration on Improving Paper Conditions in a Distribution Transformer

Abstract

Managing a large fleet of ageing assets has become a technical challenge faced by many electricity utilities in developed countries. Asset managers are increasingly interested in techniques that can help extend the useful lifetime of a transformer. Oil regeneration is one of such techniques. In this paper, oil regeneration experiments were performed on a 6.4/0.4 kV retired distribution transformer to investigate the effect of oil regeneration on improving paper conditions. Oil regeneration was conducted in two stages, with the first stage aimed at ‘cleaning the oil’ and the second stage targeted at ‘cleaning the paper’. Oil samples were collected at regular intervals throughout the process and paper samples were obtained from the transformer before and after each oil regeneration stage. It was found that oil regeneration restores oil parameters, including moisture and acidity, similar to those of new oils at the end of stage 1. Analysis of paper samples indicated a reduction in paper moisture at the end of stage 2 by nearly 40%, while low molecular weight acids (LMA) in paper exhibited a reduction by around 30% on average. It is found that the extended oil regeneration period, i.e., stage 2, is necessary to improve the paper condition and hence to reduce the paper ageing rate.

Application of Synthetic Ester for Drying Distribution Transformer Insulation—The Influence of Cellulose Thickness on Drying Efficiency

“…Generally, the on-site methods of transformer drying can be divided into two basic types: Liquid (1)-(2) and vacuum (3)- (7). The most commonly used are:…”

“…The main reasons for the increase in moisture content in transformer insulation are tank leakages and cellulose chemical decomposition, which is accompanied by water formation. In the case of sealed transformers, the largest contribution to the growth of water content in cellulose is made by its chemical decomposition [6,7]. Water is one of the products of cellulose aging, and because water accelerates the process, the dynamics of water increase in transformer insulation with years of use is observed [8].…”

“…The efficiency of this method is often improved by the use of vacuum. Method (7) is similar to (6), but the cellulose insulation of the transformer is heated by hot oil rather than hot air. After heating the insulation, the vacuum drying process is practically similar.…”

On Approaching Relevant Cost-Effective Sustainable Maintenance of Mineral Oil-Filled Electrical Transformers

“…The disadvantages of this oil are the low electrical resistivity, which reduces the insulation capability of the oil, and the high investment costs comparing with mineral oil [28]. The last method [30] is the waste oil recycle process to remove the hazard contamination. One of the vital techniques in this process is using the reduction procedure to remove the toxic chemical, such as polychlorinated biphenyl (PCB) from oil waste, which has negative impacts on human and environmental health [31].…”

“…One of the vital techniques in this process is using the reduction procedure to remove the toxic chemical, such as polychlorinated biphenyl (PCB) from oil waste, which has negative impacts on human and environmental health [31]. In general, the most critical challenge for achieving sustainable maintenance is the investment costs of these available technical methods and the return on investment [25,27,30]. Therefore, it is crucial and necessary to establish a relevant sustainable maintenance with regard to minimized costs, i.e., relevant cost-effective sustainable maintenance.…”