Introduction

As the electricity consumption of commercial, residential, and electric vehicles rapidly increases, the peak power demand in large and medium-sized cities around the world is approaching the limits of urban power supply capacity. The proliferation of overhead lines and crowded underground cables have made it a challenge for the development of power grids in various countries to provide stable and efficient power transmission to city centers. The development of HTS materials has extended the application of superconducting technology into the power industry, offering new solutions to some of the drawbacks of existing power equipment. The applications of superconducting technology in power mainly include superconducting cables, superconducting current limiters, superconducting energy storage devices, and superconducting motors.

Superconducting cables, leveraging the properties of HTS tapes, offer significant advantages such as high transmission capacity, low losses, high reliability, small corridor footprint, and environmental friendliness. The current-carrying capacity of superconducting materials is 50-500 times that of copper wires of the same size, and their engineering current capacity is 5-10 times higher, making them highly advantageous for capacity expansion and high-current transmission in densely populated urban commercial areas, residential zones, industrial districts and super-large high-rise buildings.

HTS current limiters are currently considered the most effective devices for limiting short-circuit fault currents in power systems. These devices have minimal impedance during normal operation but automatically increase impedance during faults, with response times in the microsecond range and automatic current-limiting capabilities, allowing for long-term, repeated use. The application of SFCLs can significantly enhance power grid stability and improve the reliability and safety of power supply.

In recent years, the application of superconducting power technology has accelerated in China. Both the State Grid Corporation of China and China Southern Power Grid are focusing on developing various HTS power devices. China has already commissioned two commercially operational HTS cable demonstration lines in Shanghai and Shenzhen. Additionally, 220 kV AC, 500 kV AC, and 160 kV DC superconducting current limiters have been successfully developed. During the 14th Five-Year Plan period, China Southern Power Grid has prioritized the development of 10 Mvar-class superconducting synchronous condensers and 10 MJ-class superconducting energy storage devices. Several HTS cable transmission projects with longer transmission distances, higher current capacities, or voltage levels are also being intensively prepared in Guangdong, Shanghai, Zhejiang, and other regions. The race for superconducting power applications is expected to rapidly expand in the coming years.

Project Cases

| Domestic First 35kV Kilometer-Scale HTS Cable Demonstration Project — State Grid/Shanghai Cable Research Institute/Shanghai International Superconductor Technology Co.,Ltd.

The demonstration project is located between the Changchun Substation and the Caoxi Substation, two 220kV substations in Xuhui District, Shanghai. The total line length is 1.2km with a design current of 2200A. It is currently the world's largest capacity, longest line, fully commercialized 35kV HTS cable, and was officially put into operation in Shanghai on December 22, 2021.

SST provided nearly 170 kilometers of ST-05-L high-performance HTS tapes for the conductor layer of this cable project. Additionally, SST supplied approximately 10 kilometers of ST-04-E high-performance HTS tapes for the cable's shielding layer.

| Domestic First 10kV Three-Phase Coaxial High-Temperature AC Superconducting Cable — China Southern Power Grid/Zhongtian Technology Group Co.,Ltd.

This three-phase coaxial HTS cable was put into operation on September 28, 2021, providing high-reliability power supply to the Ping An Finance Center in Shenzhen. It is also the world's first superconducting cable applied in the central area of a mega-city, expected to comprehensively address numerous issues and challenges such as the difficulty of securing land for urban grid construction, continuous growth in grid load demand, and the saturation of urban transmission and distribution corridors.

All superconducting materials for this project were supplied by SST. Remarkably, from January to March 2021, SST successfully delivered over 110 kilometers of ST-05-L high-performance HTS tapes for the project within a production cycle of only about two months.

| 160kV DC Resistive Superconducting Current Limiter — Guangdong Power Grid

This project is a national key R&D program led by China Southern Power Grid. It is the world's highest voltage level and largest capacity superconducting DC current limiter, effectively enhancing the security and protection of DC power transmission. It has already passed third-party test in January 2019 and began trial operation on the grid in August 2020.

SST specially developed and supplied double-layer laminated superconducting tapes for this project. The tapes offer both high room-temperature resistivity (improving current limiting effect) and superior impact stability (enhancing equipment reliability). In 2019, SST completed the timely delivery of tens of kilometers of 10mm wide double-layer laminated tapes for the project (equivalent to nearly 200km of 4mm wide superconducting cable tape), contributing to the successful implementation of the project.

| 220kV AC Resistive Superconducting Current Limiter — Zhongtian Technology/CAS Institute of Electrical Engineering/Beijing Jiaotong University

This project is a significant superconducting project during China's 13th Five-Year Plan, part of the National 863 Program. It passed acceptance in January 2018. The project's success has laid a solid foundation for the future grid application of resistive superconducting current limiters.

All superconducting materials for this project were provided by SST, which supplied nearly 20 kilometers of 12mm wide stainless steel laminated HTS tapes.

| 500kV AC Saturated Iron Core Superconducting Current Limiter — Guangdong Power Grid

This project is the first self-developed 500kV superconducting current limiter in China with the highest voltage level internationally. It overcame key technological bottlenecks in designing and manufacturing large-sized HTS magnets and realized stable operation, passing acceptance in July 2017. 

During the development phase of the project in 2016, SST had just broken the international monopoly on tape products and achieved small-scale supply capability. Thanks to the trust and support of China Southern Power Grid for domestically produced core materials, SST 's materials were used in the high magnetic field regions at the ends of the coils (with the rest of the materials still imported from Japan). This project marked the first application of domestic 2G-HTS tape products in large-scale superconducting power equipment in China.

| China's First HTS Synchronous Condenser Prototype — Guangdong Power Grid

This prototype, led by Guangdong Power Grid Co., Ltd., was designed and developed to verify the feasibility of large HTS synchronous condenser technology. A successful phase trial was conducted in October 2020, marking a significant step in exploring new avenues for dynamic reactive power compensation in power grids.

SST has a long-term collaboration with Guangdong Power Grid and provided approximately 18 kilometers of ST-12-L and ST-06-L high-performance HTS tapes for this prototype project.