Development of non-filled EPR insulation system for power lead of 66 kV-class superconducting fault current limiter

Development of ethylene-propylene rubber (EPR) insulation system has been advanced for a compact power lead of 66 kV-class high temperature superconducting fault current limiter (SCFCL). It is well known that insulation layers of superconducting cables are molded by extruding EPR containing inorganic filler. The power leads are not as long as the superconducting cables, making it difficult to mold their insulation layers by extrusion. When molding EPR by heat treatment, voids tend to remain in the insulation layer because of the low viscosity of filler-containing EPR. Partial discharge will occur and insulation deteriorates if voids exist in the insulation layer. Fluidity of EPR without filler (non-filled) was experimentally investigated to be used for insulating power leads. It was found that the viscosity of non-filled EPR is sufficiently low. It was also found that non-filled EPR has excellent crack resistance. An insulation model was easily constructed with simple dies. No voids were found in the insulation layer of this model, and no cracks occurred by thermal cycling between 333 K and 77 K. Consequently, it was confirmed that non-filled EPR is a suitable material for insulating power leads.