Power Cables: Tracking Technology InnovationsPosted On: 01-09-2017 By: Katherine Eveland
Power cables are an essential element in the transportation and distribution of electricity in all modern economies. Medium-voltage (MV) and high-voltage (HV) AC power cables are the workhorses transporting bulk power across the electrical grid. Historically, there have been two types of MV power cable: Paper Insulated Lead Covered (PILC) and Polyethylene cables. The cable design can typically be a single-core able or a three-core cable. If we go back more than 50 years to the 1960s, paper insulation was the dominant technology used in copper and aluminum distribution power cables.
Through the 1970s, the superior polymeric (EPR-Ethylene propylene rubber, XLPE) insulations displaced paper insulated cables. Polyethylene has a wide number of advantages, but its relatively low melting point (105°C-115°C) meant it initially found limited application. However, by converting thermoplastic polyethylene into a cross-linked thermoset, the melting point increased significantly, and this meant these cables could surpass the thermal capabilities of PILC.
Irradiation could be one method of cross linking, but the most common method has been thermal cross linking polyethylene by continuous catenary vulcanization (CCV line). There has been a significant progression from very poor quality steam curing XLPE in the 1980s, to the high-quality dry curing in a nitrogen atmosphere used today. Vertical catenary vulcanization (VCV line) is a similar process, but with a vertical tube. The construction of the vertical tower to house equipment has a much higher capital cost that for the CCV line. Historically, only VCV lines could produce high quality, low-eccentricity EHV power cable. An alternative technology that we need to mention is MDCV (Mitsubishi Dainichi Continuous Vulcanization). The MDCV process is a continuous dry curing process developed by Mitsubishi Cable Industries Ltd. and Mitsubishi Petrochemical Co. Ltd. (gormerly the Dainichi Chemical Company of Japan). Despite some technological advantages, MDCV did not take off commercially across the industry.
Successive improvements to the CCV process and its relative lower cost has made it the process of choice for cable manufacturers. Further development in new generations of compound materials and equipment have reduced the constraints for CCV lines to produce higher-voltage HV and EHV power cable. New techniques such as caterpillar systems help keep the central axis of the core concentric. The leading suppliers of HV and EHV extrusion equipment and CCV and VCV lines include Troester, Maillefer and Royle Systems Group. Globally, Troester and Maillefer have the high market share into the HV and EHV cable companies. Leading suppliers of CCV line in Asia include Baicheng Fujia Technology, based in China and Indian-based Supermac Industries (India) Ltd. Baicheng has supplied hundreds of CCV lines in China, and more recently into the USA.
We are currently updating all our data in a Power Cable report, which will track these CCV and VCV lines across the global cable sector including a plant by plant analysis of capabilities by company, at each cable plant and location. The report will list all the leading HV and EHV power cable producers worldwide. One of the main issues is what is going to happen to all the capacity that has been installed in China. There are more than 60 VCV lines in China alone, and more than 600 CCV lines. A change on the horizon for CCV lines and cross linking is the rise of higher rated thermoplastics. Prysmian has developed and patented its HPTE (High Performance Thermoplastic Elastomer) “P-Laser” technology. Prysmian argues that since there is no cross linking, there is no degassing required in the production process. This allows longer cable runs can be produced for both AC and DC cables in an uninterrupted, single line process.
Written by Philip Radbourne, Director of Wire & Cable at Integer Research
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