Introduction
During RBP bushing manufacture, the insulating paper is first coated with a phenolic or epoxy resin and then wound into a cylindrical form whilst inserting conducting layers at suitable intervals; this process occurs whilst the parts are subjected to heat and pressure. RBP insulation is essentially a laminate of resin and paper.
RBP bushings are designed for service operations with maximum radial stresses of approximately 20 kV/cm (50.8 kV/inch). RBP bushings have poor partial discharge characteristics. At values greater than 100 pC (pico-coulombs), premature bushing failure may occur. The RBP condenser body always contains some air between the fibres of the paper and at the edges of the grading layers, this is the reason for its poor partial discharge characteristics. Due to the RBP bushings limitations, this type of bushing is now considered obsolete.
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How Electrical Bushings Work
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Additional Resources
https://en.wikipedia.org/wiki/Bushing_(electrical)
https://www.inmr.com/ris-bushing-technology-reliability-testing-field-experience