Long-term reliability testing of 500 kV DC PPLP-insulated oil-filled cable and accessories

This paper describes the results of a long-term reliability test of a newly developed 500 kV DC oil-filled cable and accessories that transmit up to 2800 MW. This is the largest capacity ever used for submarine cables. The test line was 500 m and consist of submarine cables, land cables and several kinds of accessories. An optical fiber sensor was first installed in the oil duct of the cable to measure the conductor temperature directly under application of DC voltage. From 1994 to 1996, the authors carried out an accelerated electrical and thermal aging test equivalent to 40 years, a load cycle test, a polarity reversal test and a transient overloading current test. Satisfactory breakdown strength was confirmed in the residual test which followed the long-term test. These results have been instrumental to the decision to construct 500 kV DC commercial submarine cable lines.