Article in CIGRE India Journal - Transformer Bushings: Current Technology Trends, Developments & it's relevance in Monitoring of Bushings in Service

Transformer Bushings are expected to be highly reliable components of Transformers. In the event of Failure of Transformer Bushings, usually the result is downtime of several weeks of a power transformer accompanied by financial losses & urgency to restore the system at the earliest. Majority of the Bushings in service (for past many years) are Bushings with OIP (Oil Impregnated Paper) Insulation System. In India, major usage of RIP (Resin Impregnated Paper) Insulated Bushings commenced in 2011-12 & recently in 2018 RIS (Resin Impregnated Synthetics) Insulated Bushings have been also introduced in Indian Grid. OIP Bushings are well established up to 800kV & RIP Bushings are now in use up to 420kV and RIS Bushings are reported to be available up to 245kV. This paper reviews the Current Technology Trends.

In view of Various Insulation Technologies in use , it is essential to understand technical aspects of Insulation Degradation Mechanism and their effects on Service Behaviour of Bushings. This paper describes these aspects in detail. Tan Delta has been considered as a vital health monitoring parameter for OIP Bushings & different utilities have adopted stringent limits for Tan Delta (when compared with IEC Limits of 0.007). Data based evaluation & trend analysis of increase in Tan Delta gives a preliminary clue about Bushing Health, however this needs to be supplemented by DGA Analysis of Oil Sample. This paper describes it in detail.

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