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Newsletter "SEI NEWS" 2014

Home > Company Information > SEI WORLD > Back number > Vol.441

[Newsletter "SEI WORLD" Vol.441]

PPLP™-MI DC Submarine Power Cable

Sumitomo Electric developed the innovative PPLP™-MI DC submarine power cable that uses polypropylene laminated paper (PPLP) as its insulator. This cable provides higher performance and capacity than the MI submarine cable.


What submarine cables have been in use previously?

The distances of submarine power transmission needed in Japan are relatively short, up to some 50 km in many cases. In such applications, oil-filled (OF) submarine cables have been used. The insulating paper in the OF submarine cable is impregnated with low-viscosity insulating oil. When in use, pressure is applied to the insulating oil so as to prevent the paper from losing the oil due to elevation differences and heat shrinkage, which might result in electrical performance degradation. The insulating paper has improved in performance since the conventional insulating kraft paper was replaced with PPLP™, or a laminated sheet of kraft paper and polypropylene developed and commercialized by Sumitomo Electric in the 1970s.

Meanwhile, in Europe, Kraft MI DC submarine power cables are widely used in long-distance interstate grids. In comparison with OF submarine cables, which are subject to the limitation that the pressure on the insulating oil extends only up to some 50 km, no distance limits are imposed on Kraft MI DC submarine power cables. This is due to the insulation formed by impregnating kraft paper with high-viscosity insulating oil, which stays in the paper without pressure.


What are excellent features of the PPLP™-MI DC submarine power cable?

Sumitomo Electric developed the PPLP™-MI DC submarine power cable incorporating PPLP™ in place of the insulating kraft paper used in Kraft MI DC submarine power cables in order to enable higher voltage and capacity operations than possible with conventional cables.

The use of PPLP™ has improved the cable in electrical insulation performance. Moreover, higher temperatures are allowed in operation since the polypropylene layer serves as a barrier to keep the paper from losing the insulating oil. Thanks to this, the PPLP™-MI DC submarine power cable is approximately 30% higher in power transmission capacity than the conventional Kraft MI DC submarine power cable. This enables interstate grids, currently operating at 500 kV, to operate at a higher voltage and capacity.

■Interview with engineer in charge
What are the difficulties in developing the PPLP™-MI DC submarine power cable?

Fu Vincent Development and Engineering Group Power Cable Div.

The cable is similar in structure to the proven PPLP™-OF submarine cable. However, it was necessary to investigate breakdown mechanisms to select manufacturing conditions and insulation materials since in the PPLP™-MI DC submarine power cable the insulating oil is not under pressure. Moreover, to explore one set of prototype conditions, it took about six months, three for the fabrication of a prototype cable and three for testing. We spent a long period of time to find the best mix of manufacturing conditions and materials.

What are future plans for the PPLP™-MI DC submarine power cable?

Sumitomo Electric has had no experience in supplying long-distance MI submarine cables due to the sole need for short-distance submarine cables in Asia including Japan. For PPLP™-MI to be selected by power companies that put reliance on proven products, we needed experience in manufacturing kraft MI DC submarine power cables. This year we have worked on prototype making and evaluation of a 500 kV kraft MI DC submarine power cable for the submarine power cable project planning to connect between Italy and Montenegro, and won a contract for cable production. This opens a way to commercializing the PPLP™-MI DC submarine power cable.

2014 Index
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