For the optimization of electrical insulation design for High Temperature Superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN, impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN, plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN, impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN, and cable model with short length with polypropylene laminated paper (PPLP"), Nomex" paper and cellulose paper. PD current pulse was found to have a steep rise time ofns and amplitude oftens FA at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be -5 mm under PD-free condition from viewpoint of long-term reliability.Index Terms -Partial discharge, breakdown, high temperature superconducting cable, liquid nitrogen, butt gap, cold dielectric, wrapped tape insulation, PPLP, Nomex" paper, cellulose paper, insulation design.
Long range optical fiber sensors for power cable maintenance have been incorporated into a newly developed 500 kV DC submarine power cable. Optical fibers are used for a distributed temperature sensor and a mechanical damage sensor. The distributed temperature sensor provides data on temperature at distances up to 30 km, and the mechanical damage sensor locates extemal damage points on the submarine cable. After each characteristic was investigated, optical fiber sensors were incorporated on the submarine power cable. This composite cable was evaluated by various mechanical tests. The results were satisfactory and showed the composite cable to be of practical use. This new approach of incorporating optical fiber sensors in the cable structure brings a new sophistication and reliability to cable maintenance.
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