RIP Bushing Service Experience & Replacement Strategy

Bushings

Failure statistics show that bushings are one of the main contributors to transformer failure and can have a catastrophic impact on reliability and safety of a power system as well as on operators managing the asset. Indeed, in the case of one south-east Asian country, failures of high voltage bushings have contributed to almost 30% of total failures in the grid between 2001 and 2022 and translated to almost 0.1% per tx-service years over the past 20 years. While relatively low and despite the fact that there has been a downward trend in their incidence (see Fig. 1 below), failures of bushings, especially of the high voltage oil-filled type, still impact safety and risk of explosions in the field. In fact, it has been estimated that 75% of bushing failures in this system lead to major fire risk. Moreover, the cost of such events translates into to about 10,000 USD/MVA or 1.5 to 2 times the cost of the equipment itself.

Fig. 1: Cumulative bushing major failure rate per tx-service year in Malaysian grid.

Proactively implementing maintenance paradigms toward more condition-based techniques is seen as an effective tool to detect impending failures and Grid efforts have therefore been devoted in this direction. Still, considering the safety and environmental impact of bushing failures in combination with the high associated costs, the company decided to migrate completely, in stages, toward dry bushing technology with polymeric housings. This bushing design is seen as a viable option for risk mitigation. Fig. 2 illustrates the migration strategy to dry bushings since 2015 and over the coming years.

Fig. 2: % Replacement ratio over total population of OIP bushings in Grid systems (2015-2026).

Attend the 2022 INMR WORLD CONGRESS in Berlin to listen to a presentation by bushings expert, Gobi Kannan Supramaniam of Tenaga Nasional Berhad in Malaysia. He will share the Grid’s practical experience and lessons learned during this migration to dry bushing technology and also recommend immediate improvements that can be applied in specifications and procedures.