Online monitoring of RIP Bushings for early failure detection

Several recent field events in the French nuclear and hydro generation fleet highlighted the need for early detection of internal capacitive-layer degradation in RIP (Resin Impregnated Paper) and OIP (Oil Impregnated Paper) bushings.

This paper presents a robust, field-validated algorithm to detect early precursors of bushing failure based solely on online leakage current measurements. Contrary to some conventional monitoring systems, whose alarms were insufficient in several real cases, the proposed method detects the loss of a single capacitive layer as soon as physically possible.

The algorithm is based on leakage current online measurement and two innovations:

• attenuation of network‑voltage noise by applying a deviation analysis comparing each phase with the average of the three phases, • Z-score logic to eliminate false positives due to unexplained current drops. The method has already prevented major transformer failures in operation. Avoided production losses are estimated in the order of hundreds of millions of euros.