Abstract

Distribution transformer (DT) is a crucial component in power systems as it exchanges energies between different voltage levels or between utility grid and DC microgrids. Nevertheless, the operation of an oil-immersed DT is limited by the thermal and electrical capabilities of the internal insulating liquid. This paper aims to raise the efficiency of distribution transformers and preserve the environment by using a biodegradable insulating liquid instead of the conventional mineral insulating oil (MIO). This work examines the Egyptian case, where a real distribution network located in middle Egypt is selected as a pilot project. Study and analysis of the status que of the insulation system inside DTs are done with the aid of fault-tree analysis. The deficiency of the insulation system is confirmed by conducting an electronic survey of 100 expert participants. The most appropriate solution among three different alternatives is confirmed using the weighting and ranking method. The best choice suitable for the selected area is the substitution of MIO by synthetic ester (SE). The technical and environmental advantages achieved by the presented solution are discussed. The feasibility studies have proven that the solution is positively acceptable in all aspects. An execution plan is established for the application of proposed solution on the selected Egyptian distribution network.

Highlights

  • For more than a hundred years, mineral insulating oils (MIOs) have been used inside distribution transformers (DTs) to guarantee electrical insulation, suppress arcing in case of a fault and keep thermal stability

  • The periodic tests constantly affirmed the degradation of MIO properties by time even after following the maintenance guidance of IEC 60422 [3]

  • Solution can achieve economic savings of up to 80%

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Summary

Introduction

For more than a hundred years, mineral insulating oils (MIOs) have been used inside distribution transformers (DTs) to guarantee electrical insulation, suppress arcing in case of a fault and keep thermal stability. In order for the oil to fulfill these purposes, its appearance must remain clear, free from sediment or any suspended matters. New MIOs have to comply the international electrotechnical commission standard IEC 60296 especially in the requirement of lower viscosity, higher flash point and good resistance to oxidation [1,2]. Since its discovery by Eliu Thomson, MIOs were widely used due to availability, good dielectric properties and reasonable price. MIOs are non-renewable fossil liquid with low biodegradable nature. The periodic tests constantly affirmed the degradation of MIO properties by time even after following the maintenance guidance of IEC 60422 [3]

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