500,000 Volt Submarine Cable Shipped

Hitachi Cable has completed manufacture of a 500,000-volt DC submarine cable for The Kansai Electric Power Co., and Electric Power Development Co.,Ltd. The two companies will use the composite electric-optical cable for their Anan-Kihoku DC trunk line. The completed cable was shipped from Hitachi Cable's Minato Works in Hitachi City, Ibaraki Prefecture on November 9 aboard a cable-laying vessel.

The project's four cables are being manufactured and installed by a joint venture comprising Sumitomo Electric Industries, Ltd.,The Furukawa Electric Co., Ltd., Fujikura Ltd. and Hitachi Cable, Ltd. Installation of the November 9 shipment will mark the final phase of this world-class submarine cable project.

To improve the insulation properties of this high-voltage electric-optical fiber cable, the joint venture used two layers of insulating paper with a layer of polypropylene in between. This is the first time Polypropylene Laminated Paper(PPLP) has been used for a DC cable. The technique permits thinner insulation, reducing the cable diameter by 7 percent and its weight by 14 percent.

The cross-section of the conductor is 3,000 mm2, considerably greater than the previous record of 1,600 mm2 in the Baltic Sea submarine DC line between Germany and Sweden. The designed operating voltage of 500,000 V is also the world's highest for a submarine cable.

In addition,12 optical fibers are placed under the wire armor layer. Of these, two are used as temperature sensors to monitor the cable's temperature. This enables efficient and effective maintenance procedures to ensure greater reliability. The temperature sensor measuring devices were newly developed. The optical signals that perform the sensor function use low-loss wave length zones that halve the losses of conventional equipment. In addition, the signal processing section incorporates proprietary technology to enable monitoring 30 km of cable, the longest in the world. This revolutionary system means that temperature can be monitored over the entire length of all four cables by placing one signal processor at each end and switching back and forth between the two optical fibers used as sensors.

The Anan-Kihoku DC trunk line will carry some of the electric power to be generated by Electric Power Development Co.,Ltd.'s 210,000 kW Tachibanawan Thermal Power Station, now under construction in Tokushima Prefecture's Anan City. The power will be supplied to the Kansai area. Operations are slated to commence in July 2000. From the Anan Converter Station, the cable will cross the Kii Channel over a distance of 50.7 km to its terminus in Wakayama Prefecture's Yura Town. The length of the underwater segment is 48 km.

The four cables comprising the trunk line are divided into two for positive and negative DC poles, and two neutral cables without polarity. This trunk line has a capacity of 1,400,000kW at an initial 250,000V, to be upgraded in future to 500,000 V.

Installation of the cable shipped by Hitachi Cable will begin on November 15, with completion scheduled for the end of that month. That will mark the fourth and final segment of the submarine cable project. The remaining work involves connection of landlines and installation of protective surveillance systems, including temperature-monitoring devices. The entire system is slated for completion in September 1999.

For reference:

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First cable: 18 April/ 25 April-10 May/Fujikura
Second cable: 29 May/ 7 June-20 June/Sumitomo
Third cable: 3 July/ 3 October-12 October/Furukawa