In recent years, wireless power tranfer technology has become a hot technology. Compared with traditional power tranfer mode, wireless power transfer is more convinient and safer, and it has been applied to many fields. Because the efficiency of wireless power transfer system is dominated by the resistive losses of the coils, and the smaller the resistances of the coils, the higher the transfer efficiencyis. With the characteristics of zero DC resistance and low AC loss, supercondcuting materials have significant efficiency advantage for use in wireless power transfer. In this paper, the research status on supercondcuting wireless power transfer technology is introduced, especially our complete and ongoing research works in the Key Lab of Applied Superconductivity on superconducting wireless power transfer, and the potential application prospects of superconducting wireless power transfer technology are also presented.

Superconducting DC power transmission (SDCPT) technology is a potential alternative solution for large power transmission over long distance. In this paper, the advantage of superconducting technology is introduced. Some typical projects of high-temperature superconducting cable worldwide carried out in recent years are reviewed. The R&D status and the possible development trend of SDCPT in the future are discussed, and then some proposals for the future R&D of SDCPT is offered.

With the development of high temperature superconducting (HTS) materials, HTS technology has been used to develop superconducting cables which have practical applications in power transmission systems. Compared with the traditional cables, HTS power transmission has various advantages: large capacity, low loss, small volume, light weight, high reliability, saving resources, environment friendly and so on. It is expected to play an important role in the development of power grids in the future. This paper introduces the structure and characteristics of the HTS cables, design principle, current distribution in conductor layers and AC loss; discusses the main technical issues of the HTS cables; and introduces the application of the HTS cables in AC and DC transmission systems including current HTS cable projects and their performances worldwide.

The research history and current status of high temperature superconducting (HTS) cable in the world are summarized, and the basic structure and insulation requirements of HTS cable body are introduced. Then, the structure and problem of the main insulation for HTS cable are analyzed. For liquid nitrogen ( LN₂ ) and several solid insulation materials under low temperature applied in HTS cables, related researches are put forward separately on their dielectric property under low temperature. It can be concluded that, in LN₂, the breakdown strength of insulation material is higher in DC field than that in ac field; the breakdown strength of polyimide is higher than that of polypropylene laminated paper (PPLP) in both ac and dc field; low temperature can suppress the growth of the electrical tree in epoxy resin.

A powerful and efficient power transmission network is urgently required to support offshore renewable energy harvesting. To promote the development of submarine superconducting power cables, it is essential to investigate the influence of partial dysfunctions on the supercondncting power cable, especially to its AC loss characteristics. It is possible that the partial dysfunctions can cause fast and massive increase of losses in the form of heat, and consequently break the cryogenic thermal stability and drive cables out of superconducting state. Based on underground cables, numerical models are developed to simulate monolayer and multilayer submarine superconducting cables. Currernt and magnetic field distributions and AC losses are analyzed via Finite Element Method(FEM). Results show that AC losses of monolayer and two-layer cables increase dramatically with a single superconductor tape damaged, while AC loss of six-layer cables exhibits an increase of less than 5%. This makes six-layer superconducting cables more suitable for developing superconducting power networks within marine environments.

Superconducting magnetic energy storage (SMES) technologies have significant application prospects in fast, efficient and intelligent energy management of future smart grids. A novel SMES energy interaction model and its mutual experimental device are presented by using the circuit-field-superconductor coupled analysis principle, which friendly links the applied superconductivity field and the electrical engineering field by one SMES device. For the feasibility studies of SMES frontier applications based on the advanced SMES development and application status, SMES-based liquid hydrogen powered fuel cell electric vehicle and SMES-based low-voltage direct-current micro grid are fulfilled,practical system scheme design and feasibility analysis of smart grid application are presented, and integrated application prospects in the power generation, transmission, distribution and utilization subsystems of future smart grids are forecasted.

Due to its characteristics of quick response and high power density, superconducting magnetic energy storage (SMES) system has bright future of applications in power system. The principle, components and key technology of SMES are discussed in this paper. The development trend of SMES is analyzed from three aspects of apparatus, application and control, it is pointed out that SMES will develop toward modularization and decentralization, and SMES can also form hybrid energy storage system with other energy storage system. Based on the influence of the magnet current and thermal stability of superconducting magnet on the power response characteristic of SMES, it is proposed to conduct SMES status evaluation and control strategy optimization during SMES operation. At last, factors restricting the development of SMES are summarized.

Superconducting magnet is the core of a superconducting magnetic energy storage (SMES) system, and its optimal design can improve the economical efficiency and the operating performance of SMES. This paper proposes a design method of high temperature superconducting (HTS) magnet considering the magnet dynamic characteristics. The finite element method and genetic algorithm are used in the design. Optimal variables are the inner radius of the magnet, the turns of a single pancake and the numbers of the double pancake. The optimization procedure is divided into two parts. The first part is optimizing the length of the HTS tapes, and the second part is optimizing the AC loss based on the results of the first part. Last, a 150 kJ HTS magnet is optimizd with this method, and the final magnet scheme has the advantages of less usage of the HTS tapes and low AC loss.

Superconducting generator provides an effective way to reduce the size, weight and cost of large-scale wind genertors. This paper presents the design of an offshore direct-drive superconducting wind generator (SCWG). It has a stator with low temperature superconducting (LTS) field winding and a rotor with normal copper armature winding. First, the main design specifications and topology of the generator are introduced, and some design considerations on SCWGs are discussed. Then the stator and rotor design of the generator are presented, including electromagnetic design, mechanical design, the rotor forced-air cooling system design and cryogenic and refrigeration system design for the superconducting stator, etc. Finally the weight and cost of the proposed SCWG are estimated and compared with that of a direct-drive permanent-magnet wind generator (PMWG) of the same power. It is found that the proposed SCWG is 46% lighter than the PMWG, while the initial material cost is only about 71% of that of the PMWG.

Since superconductor can carry carrying direcet current with zero resistance, its application in superconducting equipments such as superconduting cable, fault current limiter (FCL), transformer,supercondducting magnetic storage (SMES),generatot/motor has attactive worldwide interetst, among of which the high-temperature superconducting (HTS) transformer has some adavntageous characteristics, that is, small volume, light weightness, low loss, no fire hazard and environmental pollution as well as low leakage reactance. With a brief description on the basic structure of the HTS transformer, this paper focuses on several key issues in its research and development, including insulation characteristics of liquid nitrogen (LN₂) and gas nitrogen (GN₂), analyzing methods of alternative current (AC) losses of the superconducting windings and designs of current leads and non-metallic cryostat, and thus provides useful reference for resaerch and development of HTS transformer.

Comparing with the conventional transformer, high temperature superconducting (HTS) transformer has more advantages, such as small volume, light weight and low loss without pollution or fire hazard. In past decades, great progress on the development of high temperature superconducting (HTS) wires has been made, research and development of HTS transformer have be progressed worldwide. At present, three HTS transformer prototypes successfully operated in grid.This paper briefly introduces the research and development of both the HTS power transformer and the transaction transformer in domestic and abroad in recent years, as well as several recent projects of HTS transformers based on 2G HTS wires, pointing out that as HTS wires developing, the research in limiting current transformers is worthy of attention.

As the most typical appliction of superconducting technology, superconducting fault current limiter (SFCL) can alleviate the serious situation that the short circuit current grows quickly with the expansion of power system, and ensure the stability of power grid as well as the safety of electric equipment. However, the normal operation of power system relay protection devices would be affected by the impedance characteristics of SFCL. For these problems, firstly the structure and the woking principle of saturated iron-core SFCL are introduced briefly. Then the influences of SFCL on circuit protection, distance protection, zero-phase circuit protection and longitudinal differential protection are analyzed. Finally, some corresponding solutions are proposed by modifying the setting value of protections and improving the design requirements of SFCL, These solutions provide a reference for the practical applications of SFCL.