Reclaiming of in-service natural ester-based insulating fluids

The degradation of in-service natural ester-based insulating fluid could result in oil viscosity, acidity and dissipation factor increases. In this work, natural ester-based insulating fluid samples aged in the laboratory and in-service (collected from a Recloser) were reclaimed with different adsorbent materials. All the tested samples showed some properties above the provisional limit for triggering prompt additional investigation suggested by the IEEE guide for in-service natural ester fluids, such as viscosity increase >; 10% from value at time of initial energization, acid number >; 0.3 mg KOH/g or dissipation factor at 25°C >; 3%. The reclamation process was accomplished by the use of two methods: 1) by mechanical agitation of the aged oil in the presence of several adsorbents and 2) by percolation of the aged oil through the adsorbent material. The reclaimed fluids were monitored by evaluation of viscosity, acid number and dissipation factor and the results were compared with unused oil. The results showed that viscosity is the main criterion to evaluate whether or not in-service natural ester-based insulating fluid can be reclaimed.