Inter-foil electrical breakdown in high voltage ERIP condenser bushings

Accelerated electrical breakdown in ERIP (epoxy resin impregnated paper) condenser bushings has been investigated. Inter-foil breakdown of the grading foils, via electrical treeing, occurred over several 10s of hours when the applied electrical stress was ~6 times the normal working stress. The progress of inter-foil breakdown could be monitored using a simple capacitance measurement technique. The bushing breakdown times were reproducible and decreased with increasing temperature. Many bushings operate at temperatures in excess of 90°C and so the breakdown times would be expected to decrease further. However, the service life for bushings at service stress and service temperature is in excess of 40 years