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.
Highlights
Most of transformers in service today are of the oil-immersed type, with mineral oil and cellulosic paper/pressboard being used as the main liquid and solid insulation, respectively
This paper investigates the effect of oil regeneration on improving paper condition in terms of removal of ageing accelerator such as moisture and low molecular weight acids (LMA) by performing optimised oil regeneration process on a 6.4/0.4 kV retired distribution transformer
In addition to the expected reductions of moisture and total acid number (TAN) in oil, reductions of LMA and moisture in paper were observed though paper sampling during the process
Summary
Most of transformers in service today are of the oil-immersed type, with mineral oil and cellulosic paper/pressboard being used as the main liquid and solid insulation, respectively. It is imperative that these ageing by-products are identified and removed from the system at an appropriate stage in order to slow down the ageing process. This is mainly achieved through oil regeneration, a process which removes the ageing by-products through physical and/or chemical processes [2,3,4]. CIGRE brochure 413 [6] defines reclamation as “the elimination of soluble and insoluble contaminants from an insulating liquid by chemical absorption means, in addition to mechanical means, in order to restore the properties as close as possible to the original values”. The term ‘regeneration’ shall be used to describe the process involving circulation of oil at elevated temperatures accompanied by adsorbent-based reclamation cycles
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