Glass Fiber Reinforced Plastic (GFRP) is usually employed as the insulator material of superconducting cable terminal, owing to its excellent mechanical properties and insulation strength at low temperature. However, in the presence of the long-term of surface discharge, GFRP often shows a poor insulation performance, which severely restricts its application on superconducting application. At present, the research on surface discharge and electrical aging of GFRP generally focuses on room temperature and high temperature, and there are few researches on low temperature. This paper designs surface discharge and electrical aging electrode models according to the actual working conditions of the AC superconducting cable terminal. To provide a stable cryogenic temperature environment and high voltage conditions, a cryogenic temperature experiment chamber is employed and builds a low temperature test platform. Based on the established experimental platform, by comparing the related surface discharge characteristics of GFRP at 278.7K, 223K and 153K, the influence mechanism was analysed. Compared with normal temperature, the partial discharge initiation voltage (PDIV) and breakdown voltage (BDV) of GFRP at low temperature are increased, and the average PD charges and PD repetition rate are reduced, indicating that the surface discharge is suppressed at low temperatures. However, for electrical aging at low temperature, the statistical life of the sample at low temperature is greatly reduced, and surface discharge increases in the later stage of aging. The low temperature accelerates the surface discharge and shortens the insulation life of the material. This may be related to the accumulation of space charge and the change of material surface morphology at low temperature. © 2021 The Institution of Engineering and Technology.

The insulation design of superconducting power equipment requires liquid dielectric with excellent electrical and thermal characteristics at cryogenic temperatures. Many liquid dielectrics have been used for cooling the superconducting materials, a potential choice being chlorotetrafluoroethane (R124), due to its good thermal conductivity. However, its electrical characteristics at low temperatures are yet to be investigated. In this paper, devices for measuring the volume resistivity and electrical intensity of R124 are designed and the prototypes are built. The changes in the volume resistivity and breakdown with respect to the parameters such as temperature and electric field are measured. It is observed that at low temperatures and with low strength electric fields, the volume resistivity of the R124 decreases rapidly with increase in the temperature. Conversely, its value increases with the increase of electric field strength. Also, it is observed that the breakdown field strength increases with the decrease of temperature. However, when R124 breaks down at high voltages, carbon deposition takes place, and thus, it cannot be used for cryogenic liquid insulation. © 2021, Beijing Oriental Sun Cult. Comm. CO Ltd.

Offshore wind power generation system needs large capacity synchronous generator with high power density, so the lightweight and small size of the superconducting synchronous generator (SCSG) have a broad prospect in the field of offshore wind power generation. To apply superconducting synchronous generator to offshore wind power generation, designing the corresponding grid-connection system is required. In this paper, a 3.6 MW class offshore SCSG is designed and its performance is simulated using the finite element method (FEM). A cooperative control strategy combining the superconducting field c oil and the converter is proposed. A Simulink model of the superconducting wind power system (SCWPS) is built to evaluate the system operation under variable wind speed and Low-voltage ride-through (LVRT) performance. © 2021 IEEE

DC electric field analysis should be carried out for the insulation design of dc high-temperature superconducting (HTS) equipment. For that purpose, the conductivity of PPLP was measured under room temperature and liquid-nitrogen temperature. The testing results show that the conductivity of single PPLP is 2.02 × 10-15 S/m at liquid-nitrogen temperature and 2.86 × 10-15 S/m at room temperature. The threshold electric field of PPLP insulation at liquid-nitrogen temperature and room temperature is 17.5 kV/mm. When the applied electric field is lower than 17.5 kV/mm, the conductivity of PPLP does not change with the electric field strength. When the applied electric field is higher than 17.5 kV/mm, the conductivity of PPLP increases with the electric field strength. Different layers of PPLP have the same electric field threshold, but the conductivity is not the same. © 2021 IEEE.

High-temperature superconducting (HTS) linear motors adopt HTS magnets with high current density and strong magnetic density to substitute copper winding coils or permanent magnets in traditional linear motors, which can effectively reduce the weight of linear motors and improve the efficiency of linear motors under the same output power level. In order to better meet the requirements of high thrust density and strong equilibrium stability of the future ultra-high speed magnetic levitation train driving device, a neo-structure of a new type of bilateral multi-air gap HTS linear motor is proposed in this paper, and its stator structure, rotor structure, air gap and other key parts are designed. The corresponding electromagnetic transient model is established by ansys finite element method, which verifies its better normal stability during operation. The influences of superconducting coil loop current and coil turns on the maximum thrust of the motor are studied, and the causes of the results are analyzed. In order to further improve the thrust density of the motor, the electromagnetic thrust output characteristics of the motor are compared between the structure without a core and the structure with a core, and it is concluded that the coreless structure of the superconducting linear synchronous motor is more suitable for the operation of high thrust and ultra-high speed. © 2020 IEEE.

Epoxy resin has been widely used in the cable terminations and current lead insulation of a HVDC high temperature superconducting (HTS) power transmission system. The electrical tree is one of the main reasons for the long-term degradation of electrical insulations. This paper presents the DC electrical tree characteristics and partial discharge patterns during the growth of the trees of the pure epoxy resin at room and cryogenic temperatures. The results show that the inception probability and tree lengths under positive voltages are higher than negative voltages at both temperatures. The cryogenic temperature inhibits the initiation and growth of the electrical tree in the epoxy resin. The partial discharge measurement is performed using similar test conditions as that of the electrical tree measurement. Significantly higher partial discharges are observed during the voltage-rise and voltage-drop stages. Moreover, the higher amplitude partial discharges with lower repetition rate occur at the cryogenic temperature than the room temperature. In addition, the tree shape of the DC trees is also affected under the cryogenic temperature. During the electrical tree propagation at the room temperature, more number of lateral branches could be observed than in LN2. © 2020 IEEE.

With the in-depth application of superconducting technology in the field of electrical engineering, low-temperature insulation has become one of the key technologies in the practical application of low-temperature electrical equipment. Under the combined effect of temperature difference close to 200K and multiple physical fields, the electrical aging phenomenon of Glass Fiber Reinforced Plastic as the main insulating material is very obvious. Therefore, it is very important to study the low temperature partial discharge characteristics of Glass Fiber Reinforced Plastic. In this paper, a low temperature electrical experiment platform is designed to conduct low temperature partial discharge experiments of GFRP. The experimental results show that low temperature has little effect on the acceleration of material aging in the early stage of material aging, but it will accelerate the material aging sharply in the later stage of insulation life. © 2020 IEEE.

This paper aims at studying the partial discharge (PD) characteristics of the LN2/PPLP insulation system under DC superimposed AC voltage for high temperature superconducting (HTS) cables. The pulse current method was adopted to measure the PD characteristics under the superimposed voltage with different DC components. The voltage virtual value (Vrms) of AC-DC superimposed voltage is set as 7 kV to analyze the effects of the DC component on the phase distribution of discharges times and amplitude. The experimental results show that: the number of discharges and the discharge amplitude decreases with the increases of DC component. According to the distribution characteristics of the phase spectrum of discharges times, the discharges with different ratio of DC components can be divided into three stages. The partial discharge pulse repetition rate is highest when AC voltage was applied. With the increase of DC components of the superimposed voltage, the total discharge times and the maximum discharge amplitude decrease, together with the widening of the PD phase distribution in stage I and II. When the DC component is up to 6 kV, the discharge times is minimized, and the PD is concentrated in the first quadrant in stage III. As a result, with the increase of the proportion of positive DC in the AC-DC superimposed voltage, the total discharge times and discharge amplitude decrease throughout the process of the PD. As the positive DC proportion increases, the discharge pulse in the positive period gradually exceeds that in the negative one. © 2020 IEEE.

High Tc Superconducting (HTS) DC cable is a promising solution for large-scale power transmission over long distance. However, the indispensable refrigeration system for HTS cable might be undesirable. Considering that LNG (liquid natural gas) now is one kind of clean energy that is used more widely and widely, it is possible to integrate the HTS cable and LNG transportation into an energy pipeline, resulting an acceptable new energy transportation system. In this paper, the principle and structure of the energy pipeline are discussed firstly, and then the basic physical properties of HTS tapes and liquid insulation media in LNG temperature range are analyzed. On the base as above, the general design of +/- 100 kV/1kA energy pipeline is made.

Epoxy resin is a kind of material used as electrical insulation in superconducting magnetic devices. The dielectric properties of the epoxy resin directly affect the safety and stable operation of the whole magnet. While operating, the epoxy resin faces the challenges of complex electric field and strong magnetic field. Researches on the effects of harmonic superimposed dc voltage and magnetic field on the electrical treeing behaviour in epoxy resin were carried out. Experimental results show that low-order harmonics are more likely to lead to the extension of electrical tree branches, which mainly results from the higher energy generated by partial discharge under low-order harmonic voltages. Meanwhile, the addition of dc voltage can result in more sever partial discharge because of the asymmetric charge accumulation, and eventually accelerates the degradation process. Zeeman effects were taken into account while considering the effect of magnetic field. More shallow traps are generated under strong magnetic field, thus charges are more easily to migrate under the action of magnetic field and gain enough energy to break the molecular chain. Besides, Lorenz force leads charges to hit the molecular chain more frequently. The above results in the more serious damage in epoxy resin under electro-magnetic coupled field. © Published under licence by IOP Publishing Ltd.