High temperature superconducting (HTS) cable, with significant low dissipation and massive current carrying capability, is a promising solution for the shortage of transmission capacity in mega-cities. China Southern Grid launched a HTS cable project in 2017 to develop a medium voltage concentric HTS cable system for installation in the distribution grid at urban area in Shenzhen City. It is the first time that concentric HTS cable system is developed and will be the first HTS cable installed in urban grid in China. The cable core mainly consists of three concentric phases winded by YBCO tapes and cold dielectric insulations in between phase-to-phase, phase-to-former, and phase-to-screen. The cable has a rated voltage of 10 kV and a rated current of 2.5 kArms. The critical current ( I _c ) is at least 6 kA per phase. The outline diameter of the cable core is 76 mm and the cryogenic pipe is 175 mm. As a middle step, we designed and manufactured a 30 m long prototype cable system and it was tested generally according to IEC 63075. For improvement of the manufacture processes, several short cable core samples were made, tested, and dismantled. The ultimate goal of the 30 m prototype is to verify the design and accumulate experience for the installation of the 400 m fully functional cable system in the grid. The test results of the 30 m cable prototype are presented and discussed. The 400 m class HTS concentric cable demonstration project has already started and it is expected to energize in grid in late September, 2021.

High-temperature superconducting (HTS) cable can transmit massive power with little dissipation in a limited corridor, which is an attractive solution for future power transmission. Shenzhen Power Supply energized a 400 m/10 kV/2.5 kA concentric HTS cable system on 28 September 2021 to power Ping’an Financial Centre, a Shenzhen’s landmark building, which was the debut of concentric HTS cable made of YBCO in the urban area of a megacity. For more than 1 year, the HTS cable system has been operating well and will continue to operate for a long time. This paper systematically reviews the system specification, cable and its accessories design, cryogenic cooling system design, type and exploratory test, project construction, pre-commissioning test, and operation of the demonstration cable system. Based on our R&D practice, we identify that cost, long-term reliability, and operational simplicity are the main hinders factors that need to be addressed to advance the large-scale application and we propose a set of solution ideas meanwhile.

Energy conservation and emission reduction is a critical task for China’s aluminum industry. During the last decade, the high temperature superconducting (HTS) technology has been successfully demonstrated to have great potential for energy conservation in this field. Different from the present AC induction heater, this HTS direct current (DC) induction heater is expected to significantly improve the energy efficiency of preheating aluminium billets before extrusion process. This paper thoroughly presents the development of the world’s first commercial megawatt HTS DC inducting heater based on 2nd generation HTS tapes. Firstly, the commercial design of this 1MW HTS DC induction heater including design specifications, energy efficiency and commercial potential are analyzed carefully. Subsequently, the manufacture and operation of three core parts including HTS magnet with extra-large diameter, iron core structure and electrical driving system, are introduced. A low cost and practical driving system consisting of motors and gearboxes is developed to solve the problem of peak electromagnetic torque at low rotation. Meanwhile, the heating quality of aluminium billets (i.e., temperature distribution along the radial and axial direction) can be accurately controlled by an adjustable air gap structure. Finally, the present technique challenges and corresponding solutions of this commercial HTS DC induction heaters are summarized and proposed. Compared with an energy efficiency of 45-60% in the MW-class conventional heater, the energy efficiency of this HTS DC induction heater can achieve up to 80.6% based on test results. This work can also provide guidance for the design and optimization of HTS DC induction heaters.

High-temperature superconducting (HTS) cable has the merits of high capacity and small volume in the normal operation condition. However, the fault current, which could be 10–30 times of the nominal current, gives a great challenge to its thermal stability. Due to the overcurrent, the HTS tapes will quench to resistive state and result in generating large amount of heat, which may degrade or even damage the HTS tapes. Therefore, it is of great significance to study the thermal stability of superconducting tapes. This article studies the thermal characteristics of different HTS tapes under dc overcurrent. The testing tapes are made of YBCO produced by Shanghai Superconductor (SHSC) and Samri advanced material (SAM). The thermal stability is defined as the maximum overcurrent and impact duration that a tape can withstand before getting its properties degraded. According to the testing results, the thermal stability of the HTS tape with copper reinforced layer is better than brass and stainless steel. The thicker the thickness of the tape, the better the stability. But the thermal stability of 25 $\mu \text{m}$ copper reinforced YBCO is close to 50 $\mu \text{m}$ . Owing to the resistivity and specific heat capacity, with the same pulse lengths, the 150 $\mu \text{m}$ copper reinforced YBCO can be pulsed to twice the current of 25 $\mu \text{m}$ .