InnoPower

Innopower's HTS Cable Installed and Operating 2004-8-24
China’s first High Temperature Superconducting(HTS) power cable project, led by Innopower Superconductor Cable Co.,Ltd. has been put into operation at Puji substation. The 30m, 35kV /2kArms, 3-phase cable uses a warm dielectric, closed-cycle cryogenic system. Innopower reported that, since the cable was commissioned for live grid operation on April 19,2004, it has had no major faults or break downs, and has demonstrated satisfactory performance according to all design parameters. As lead developer for the project, Innopower undertook system design, conductor design and fabrication, cable assembling, system installation, field-testing, and supervision of the project as a whole. The company developed a warm XLPE dielectric cable with the following key specifications: length of 33.5m(flange to flange); rated voltage of 35kV; rated current of 2kA rms; short current of 20kA /2S. Cable has an outer diameter of 112mm, and satisfies the requirement for installation bending angle of 90 degrees. Funding for the project was shared across four major contributors. The Department of Science and Technology provided 7.2 million Chinese Yuan($.89million), the Beijing Municipal Government contributed 8.25 million Yuan($1million),the Yunnan Provincial Government gave 1.8 million Yuan($.22million), and YEPG contributed 18 million Yuan($2.17 million). The HTS wire for the cable was developed by Innova Superconductor Technology Co.,Ltd., and the Applied Superconductivity Research Center, at Tsinghua University. Innova manufactured a multi-filamentary Bi-2223 wire with engineering critical current density (Je) of 8500A/cm2(77K,self-field),critical current (Ic) of 85A(77K,self-field),maximum tensile stress of 100MPa (5% Ic degradation), and minimum bending redius of 30mm (5% Ic degradation). Innova stated that it has an HTS wire production capability of 200 kilometers per year. Conductor winding and cable assembling was performed by Shanghai Cable Works. The Institute of Plasma Physics, Academia Sinica developed the termination design and fabrication. The institute conducts research and development in the areas of high temperature plasma physics, magnetic plasma confinement, ion beams, high field magnets, plasma applications, and solar cells. The cable’s cryostat and the cryogenic couplings were provided by NEXANS, which has a corporate agreement with Innopower to collaborate in developing HTS cable technology. The cryogenic sleeve developed by NEXANS consists of two flexible and concentric corrugated tubes made of stainless steel. The outer part of the inner tube is covered with layers of superinsulation. A spacer with low thermal loss centers the inner tube inside the outer tube and prevents any contact between the two. A molecular sieve provides a long-term vacuum. The flexibility of the cryogenic envelope enables it to be handled like a cable. The cryogenic system design and assembly was performed by the 16th Research Institute of China Electronics Technology Corporation. The institute’s solution is a closed-cycle LN2 system that employs seven sets of Cryomech AL300 refrigerators operating in parallel, and a Barber Nickels BNCP-30-000 liquid nitrogen pump. It has a 2000W cooling capacity at 75K, with a LN2 flow rate of 600-900L/h. Utility Company plays central roles. The cable was installed in the China Southern Power Grid by Yunnan Electric Power Group, Co.(YEPG), in the Kunming, Yunnna province. The utility company also provided technical requirements for designing the cable, including the rated voltage, rated current, short current, length, and installation bending angle specifications. YEPG performed the site preparation, as well as the construction of all infrastructure required to operate the cable, including the refrigeration station building and cable corridor. YEPG also conducted field-testing for the system, and is now is responsible for day-to-day operations. Operations and maintenance of the HTS cable are performed by YEPG substation workers as a part of their daily duty. All operational parameters of the system-both mechanical and electrical-as well as the scene of site itself, are monitored at the substation’s control center via a real time monitoring and protection system, which was developed by Huazhong University of Science and Technology. However, operation also calls for the worker on duty to visit the cable site three times a day. The worker conducts a visual inspection of all machines and meters in the refrigeration station, and completes a daily log. Each visit takes 10 to 20 minutes. Before building the system, Innopower carried out a series of experiments to investigate various aspects of cable design and manufacturing, including winding angles and layer configurations of the cable’s Bi-2223 tape conductor, LN2 cooling mechanisms, termination configurations, and fabrication techniques. Innopower then built and tested a 4m superconductor cable and terminations. Ying Xin, General manager for Innopower Superconductor Cable described one specific example of the significant challenges involved in developing an HTS cable for live grid installation. “Since the cable was to be installed as a part of the 35kV bus line for the substation, a 20kA/2S short circuit capability was required by the substation. To assure a design that met our requirements, we conducted a lot experiments on the short cable models at different current overflow levels. We then finalized the quantity of HTS tape needed- beyond the rate current capacity- in order to satisfy operating short circuit requirements. This was one of the most challenging things we undertook.” Innopower reported that it is working with the State Grid, Co.(formerly, the Department of Electric Power) and the Department of Science and Technology to develop a plan for building a 300-400 meter transmission line. The project could start in 2005, and would be completed by 2008. As before a utility company will contribute financially to the project. Details of the project, as well as the final decision, remain to be worked out. Innopower is investigating the possible commercial applications for HTS cables as high capacity bus lines for power plants and metallurgical refineries. The company said it has also started to develop a HTS fault current limiter. Innopower is the first HTS power cable manufacturer in China. ------“Superconductor Week” August 4,2004,Vol.18,No.8