Development of 500 kV DC PPLP-insulated oil-filled submarine cable

Abstract

Plans are under way for 500 kV dc submarine cable project to establish a 2800MW dc link between Honshu and Shikoku islands in Japan, as shown in Table 1 and Figure 1. As a result of a feasibility study to develop a cable having a bulk ampacity of 2800A to transmit 2800MW at ±500 kV bipole, an oil-filled type cable was selected for the development in terms of the higher permissible conductor temperature and reliability. In addition, because it was evaluated that such a large size of cable would be critical when manufactured using conventional kraft paper insulation. Polypropylene Laminated Paper (PPLP) insulation was selected because of its higher dc and impulse breakdown strengths than conventional kraft paper in order to decrease the insulation thickness, which would reduce the total thermal resistance of the cable and enable downsizing of the cable. Through fundamental tests on PPLP, breakdown tests on the prototype cables, and mechanical and electrical tests on the final designed cable according to the relevant CIGRE Recommendations, PPLP proved to be superior to kraft paper as the insulation material for dc oil-filled cables as well as for ac oil-filled cables. The construction of the submarine cable is shown in Figure 2, and its features a re summarized as follows: • The conductor size is 3000 mm2, which is the largest size for submarine cables ever put into practical use. • PPLP insulation is the first application to dc cables. • Optical fibers, each of which is stored in a stainless steel tube with a polyethylene jacket, are incorporated into the single-core power cable. This paper describes various properties of PPLP, the test results of cable and the insulation design.