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This paper presents the investigation of the surface tracking on pressboard surface immersed in MIDEL eN oil.  In this work, the development of surface discharge was analyzed by correlating the visual records of surface tracking on impregnated pressboard and the partial discharge (PD) activities.  The PD activities during the surface tracking process were analyzed in terms of Phase Resolved Partial Discharge (PRPD) patterns.  Throughout the experiment, surface discharge is found as the development of tree-like patterns in the form of white marks occurring on the oil-pressboard interface.  This phenomenon is generally accepted as the drying out process that involves evaporation and decomposition of the oil molecules in the pressboard pores due to the surface discharge activities on the pressboard surface layer.  The development of surface discharge on the pressboard surface can continue from minutes to months or even years until failure.  Thus, condition monitoring system is important to characterize this type of faulty condition.  The experimental results show that there is the decreasing trend of PD magnitude during the development of white mark hallway of a gap distance which is eventually suffered from an unexpected fault.

Power transformers use mineral oil as an insulating liquid due to its outstanding dielectric properties. The poor biodegradability and toxicity of mineral oil have increased the interest in the use of a more environmentally friendly product such as ester-based oil. Generally, natural ester insulating oils (NEI) have a higher flash point and breakdown voltage compared to existing mineral oils. However, the higher price of NEI is the main obstacle to widely applied in power transformers. Therefore, alternative cheaper feedstock processing is required. This paper proposed waste cooking oil (WCO) as a potential alternative to the existing transformer insulating oil. The used of WCO promotes the optimal consumption of plant-based resources and more efficient waste management. Transesterification method is performed to remove the free fatty acids in the WCO and reduce the viscosity. The transesterification process is based on the chemical modification reaction between WCO, methyl alcohol (methanol) and sodium hydroxide (NaOH) catalyst lye that produces waste cooking oil methyl ester (WCOME). Chemical and electrical properties i.e. water content, acidity and breakdown voltage of the developed WCOME are compared with the existing WCO according to IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers (IEEE C57.147).

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