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Medium voltage direct current (MVDC) shipboard power system (SPS) is the development trend of future ships. With the characteristics of compact structure and high-power density, the short circuit is much more serious than land-based power system, which seriously restricts the development of MVDC SPS. Therefore, there is an urgent need for prospective research on fault-protection. According to the fault characteristics of MVDC SPS, a DC superconducting current-limiting switch (SCLS) is proposed, so as to realize the current limiting protection of MVDC SPS. In this paper, a small-scale SCLS superconducting coil is wound, and a current limiting experiment of the prototype is completed. The results show that SCLS has a fast current-limiting response speed and a good current-limiting effect. The experiment summarizes the characteristics of the two current limiting modes of SCLS and it is concluded that R-type current limiting mode is more suitable for MVDC SPS.

At present, superconducting power technology has been applied more and more in the ac field, such as ac superconducting current limiter, ac superconducting cable, and so on. Critical current is the key parameter in the design, manufacture, and operation process of superconducting devices, but few studies were carried out on the ac critical current of superconductors now. In this article, a method for measuring the ac critic al current of the HTS coil based on the thermal stability was proposed, the ac critical current measurement experiment of the superconducting coil is carried out, and the electromagnetic–thermal coupling model is built to analyze the quench principle of the superconducting coil. This article explains the principle of ac critical current from the balance of heating and cooling and gives the rule that the value of ac critical current changes with frequency.

With regard to the state-of-the-art technologies in the fields of applied superconductivity and electromagnetic devices, research and development highlights are presented. The recent progress and achievement described with principle and technical details include mainly i) applied superconducting materials; ii) superconducting magnets and their applications such as in ITER and Tokamaks; iii) high T c superconducting (HTS) magnetic levitation and applications; iv) HTS smart grids; v) superconducting and electromagnetic material modelling and characterization; and vi) advanced electromagnetic devices. The applied superconductivity technology and availability are especially focused and verified with the trend of development prospection.

The high temperature superconducting (HTS) cable can be used as a low-voltage tie line between substations for its characteristic of high currentdensity. In this way, the remaining capacity on the low-voltage side of the transformer can be fully utilized. Moreover, The HTS cable can run in parallel with the original tie line, forming an electromagnetic ring network, to ensure the power supply of important loads. However, the short circuit current of the distribution network is large, and the electromagnetic ring network operation results in the quench of HTS cable when the short circuit fault is outside the HTS cable. It is important to ensure the safety of HTS cable under various short circuit faults. To ensure the safe operation of HTS cable in Shenzhen Power Grid, this paper built a distribution network model with HTS cable in Matlab/Simulink. The fault current and thermal process in different fault situation were analyzed. The design of fault current limiter (FCL) which is composed of the resistive superconducting fault current limiter (R-SFCL) and a shunt reactor was completed. The model of R-SFCL using R - Q method is build, and the effectiveness of the R-SFCL design is verified.

A simplified two-dimensional (2D) model, which takes the helical structure of the conductor on round core (CORC) cable into consideration, is utilized to analyze the electromagnetic and thermal properties of the cable. The model couples multi-physical fields through the J cBT( B , T ) properties of the superconducting tape. We first introduced the modeling strategy and verified the validity of the 2D model. Then, considering the influence of thermal on the critical current of the tape, the cable loss under different conditions has been calculated. By changing the relative positions of the inner and outer conductor layers of the 2D model, the influence of the magnetic field on CORC cable loss can be obtained, and it can be extended to the periodic three-dimensional (3D) structure.

The medium voltage direct current (MVDC) is a promising direction of future shipboard power system (SPS). However, one of the main limitations encountered in its development is the fault isolation of DC side. This paper reveals the evolution process of short-circuit fault in typical MVDC SPS through equivalent circuit and transient simulation. Based on the analysis of protection needs, a superconducting current-limiting switch (SCLS) topology is proposed, which includes one superconducting coupled coil and two DC circuit breakers (DCCBs). The models of SCLS is built on MATLAB/Simulink and the current limiting principle and current sharing principle of SCLS are verified. The results show that the SCLS has effective current limiting performance and fault clearing effect.

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types.

As medium voltage dc-based (MVDC) technology is widely considered in the shipboard integrated power system (IPS), the short fault protection of shipboard IPS is urgent. This paper suggests resistive type superconducting fault current limiter (R-SFCL), flux-coupling type SFCL (FC-SFCL), and a hybrid type SFCL (H-SFCL) alleviate fault current and improve the transient behaviors of shipboard MVDC IPS. All of these SFCLs are installed at the DC line. When pole to pole short fault occurs, resistive and inductive components play roles in current limiting. To evaluate these SFCLs and choose one for the system, theoretical analysis, simulation verification and experiments are done. According to the current limiting and economic cost index, H-SFCL is preferable in these SFCLs.

The development of power system has increased the level of short-circuit fault current, and flux-coupling-type superconducting fault current limiter can effectively limit short-circuit current by the increased impedance after decoupling of windings. In this paper, two prototypes of pancake-winding and layer-winding were manufactured and experiments were conducted. The results show that the current-limiting ratio of two prototypes reached more than 40%. Analysis of the control strategy indicates that two breakers of the limiter could operate at the same time or at different times, and when two breakers operated asynchronously, there would be a damping direct current in the windings. When decoupled, two prototypes had coil voltage distributions of increase and then fall off, and pancake-winding had a intercoil voltage distribution of sawtooth.

Compared with insulated superconducting magnet, no-insulation magnet can obtain higher magnetic field with smaller volume, but the existence of radial current complicates the transient analysis of NI magnet. In this paper, a 2-dimensional (2D) method was introduced into the thermal-electrical analysis of NI magnet, we discussed the current distribution and power generation during charging process at different working status. The result confirmed 2D method could greatly simplify the modeling process and reduce the number of meshes, which can enhance the convergence of calculation process, and speed up the analysis process.

In the future, superconducting magnetic energy storage (SMES) technology will be developed toward large capacity. Among them, a single magnet is expensive and technically challenging. The integration of multiple SMES (M-SMES) is a feasible technical route. But there is coordination among multimodule energy storage magnets, so the formulation of its control strategy is very important. In this article, based on the toroidal magnet, a state evaluation method of toroidal magnet considering the withstand voltage and temperature of the magnet is proposed. To solve the problem of power distribution caused by the difference in initial capacity, initial temperature, and maximum output power during the cooperative control of multiple SMES, a temperature equilibrium control strategy for energy storage magnets combined with state assessment is proposed. System simulation results showed that this strategy could effectively balance the working state of each module and maximize the power output capability of the energy storage magnet by ensuring the safety of the magnet.

Superconducting coils may suffer from electromagnetic vibration due to changing electromagnetic fields under AC conditions. In the long term, this vibration may cause performance degradation of superconducting tapes. In order to study the influence of electromagnetic vibration between superconducting tapes on their performance, the study can be started from the simplest form of electromagnetic vibration, that is, the electromagnetic vibration between two superconducting tapes. The degree of electromagnetic vibration under different AC currents were analyzed by simulation, and the variation of critical current ( I c) and the n-value of Y-Ba-Cu-O (YBCO) tapes after undergoing long-term electromagnetic vibration through experiments were measured. The results show that two YBCO tapes does not show obvious performance degradation under tens of hours the electromagnetic vibration caused by the AC current amplitude of 1.2 to 1.4 times Ic .

The performance degradation of High Temperature Superconducting (HTS) tape, which may be influenced by various heat exchange conditions due to different cooling methods, is of significant for HTS devices under repeated overcurrent. In this article, considering different heat exchange conditions, a series of repeated overcurrent experiments were carried on YBCO tapes under 50Hz sinusoidal alternating current. The degradation of critical current of YBCO tapes after repeated overcurrent was recorded. the resistance characteristics of YBCO tapes under different cooling conditions were analyzed. Through finite element simulation, the temperature and current distribution of YBCO tape under different heat exchange conditions were simulated. The experimental results show that the overcurrent capability of the conductor under conduction cooling is far inferior to the liquid nitrogen immersion method.

High temperature superconducting (HTS) cables have advantages of low loss and large capacity transmission. In order to analyze and protect the HTS cable, especially in the transient process, this paper develops a new method to analyze its thermal properties. Based on the structure parameters and actual working conditions of three-phase coaxial (tri-axial) HTS cable a two-dimensional (2-D) axisymmetric finite element simulation model along the axis was built in COMSOL. By coupling first and then decoupling, the temperature distribution was studied under the conditions of cooling, rated current, cryogenic system failure, local hot spot and short circuit fault. This method solves the problem that non-isothermal flow (nitf) is hard to converge under transient conditions, and has the advantages of simple and accurate.

High-temperature superconducting (HTS) potential solution of solving the urban demand of large load and high-density power. However, the ac loss within the cable body is one of the primary factors limiting the large-scale HTS cable application. Due to the complex spiral structure of CORC (conductor on round core) cable and the high aspect ratio of conductors, modeling and calculation of CORC cable are pretty challenging. To better assess the cable loss, this article illustrates an improved model based on T-A formulation. Combined with a low-dimensional thermal model, the J cBT( B , T ) characteristics of HTS tape are applied in simulation. With a global parameter control equation, the current redistribution of the tape can be analyzed by the model. The loss of a three-phase coaxial (tri-axial) HTS cable under different electric and thermal conditions has been calculated. This article provides a method based on T-A formulation to study the current redistribution and quench process.

The power industry is changing rapidly. One approach to accommodate a part of the change is the use of energy storage, in particular superconducting magnetic storage systems (SMES). Both solenoidal and toroidal magnets storing a few megajoules have been designed and valuated for this application. Solenoidal magnets have extensive stray fields, which are one of the serious limitations. Toroidal magnets require more conductor and are more complicated in terms of construction and insulation. The existing power systems require 100 s of megawatts of power from energy storage systems, whereas the power capacity of a single SMES installation will be quite limited. Modular SMES may provide a solution to this limitation. This article describes a 3 MJ/2 MW modular toroidal SMES using YBCO tape. The design approach is aimed at the reduction of the insulation requirement; and a slit structure of the cooling plate is designed to reduce the eddy current loss. The cooling process and losses of the magnet are analyzed.

In the process of power compensation of the superconducting magnetic energy storage system (SMES) in the power grid, the existence of ac loss and eddy current loss will cause the magnet to heat up, and temperature rise is the main factor limiting the power output capability of SMES. This article proposes a state assessment method (SAM) that considers the temperature rise of the magnet. This method comprehensively considers the effects of the initial operating current ( I 0), initial temperature ( T 0), power response time ( t ), and output voltage ( U ) of the magnet on the temperature rise. Before SMES responds to the system power command, a magnet temperature estimation link is added to adjust the power command according to the magnet's possible temperature rise so as to ensure the magnet's safety. By simulating the operating conditions of 150 kJ/100 kW SMES in the microgrid, it is proved that the magnet's thermal stability is significantly improved after adding SAM, and the system operating parameters still meet the requirements within a particular response time. This method helps to maximize the power response potential of SMES under the premise of protecting the safety of the magnet.

Superconducting energy pipeline is a novel type of cotransmission system of electric power and fuel. As an indispensable part of the energy pipeline, the heat leakage and thermal performance of current leads are critical for the efficiency and safety of the system. In this article, a design method of current leads with given heat flux was proposed and used, which provides a new idea of lead optimization. Based on the working principles and design parameters of the terminal, the lead was optimized in a structure consisting of three different leads instead of a uniform one by the finite element model. Considering thermal and mechanical properties, the lead materials were compared and determined. Underrated current, steady-state overcurrent and fault conditions, the heat leakage, temperature distribution, and dynamic process were calculated and analyzed, which offers a reference for the lead performance evaluation and design parameter correction. The designed lead can meet the requirements for the energy pipeline, and it verifies that the lead of multisection structure can realize the balance between the minimum heat leakage and different operation requirements under complex terminal structure.

Superconducting cables or fault current limiters may encounter short-circuit currents during operation. When experiencing multiple overcurrent cycles, the critical current degradation of yttrium barium copper oxide (YBCO) tapes may occur. The performance degradation of YBCO tapes under overcurrent is a gradual process. It may take dozens or hundreds of overcurrent or overheating pulses. To get a better understanding of this process, we explored the performance change of YBCO tapes under repeated overcurrent. A life characteristics test platform was established. The electromagnetic performance degradation of YBCO tape under 50 Hz sinusoidal ac operating conditions was investigated, taking the effect of the overcurrent amplitude and duration into account. Meanwhile, the relationship between the number of overcurrent cycles and the I c degradation is proposed. The reason for this performance change is analyzed by comparing the 2-D current density distribution of the YBCO film before and after experiencing overcurrent. In addition, the U-I property and resistance variations of these tapes are presented. It is inferred that the cracking of the superconducting layer is the main cause of I c degradation. The experimental results provide meaningful references for the performance degradation of the YBCO tapes and related devices.

To solve the low-voltage ride-through (LVRT) issue of a virtual synchronous generator (VSG) under severe grid fault, our research group proposes to use a modified flux-coupling-type superconducting fault current limiter (SFCL). In this study, the configuration structure of the VSG with the SFCL at the point of common coupling (PCC) is designed. The fault analytical circuit of the VSG is presented, and the functions of the SFCL are stated from the aspects of current restraint, voltage compensation, and energy dissipation. Using MATLAB/Simulink, symmetrical and asymmetrical faults are both simulated to assess the transient behaviors of the VSG, and the SFCL parameters are changed to clarify the quantitative effects. From the comparison results, the SFCL parameters are properly determined to provide favorable performance. The SFCL can visibly decrease the fault current of each phase within the permissible level, and facilitate the VSG to have a preferable voltage profile. Furthermore, the SFCL can positively stabilize the VSG by enhancing the power delivery, mitigating the frequency fluctuation and consuming the excess energy. A satisfactory LVRT operation is gained, and the efficacy of the SFCL on reinforcing the VSG robustness is validated.

The performance degradation of superconducting equipment under repeat fault is a key issue for the operation of superconducting equipment in grid operation. The mechanism of the High Temperature Superconducting (HTS) tape performance degradation behavior is an important issue that need to be figured out. Therefore, it's necessary to carry out the performance degradation study of HTS tape under repeat overcurrent. In this paper, considering overcurrent duration, a series of repeated overcurrent experiments were carried on YBCO tapes under 50 Hz sinusoidal alternating current. The degradation of critical current of YBCO tapes after repeat overcurrent was recorded. The critical current density of the YBCO tape was scanned to track sample's structural change during experiment. The mechanism of the degradation development of YBCO tapes after their first degradation was described. The research could provide a reference for the design of fault protection and life assessment of HTS devices.

With the rapid development of the integrated power system (IPS) on shipboard, the medium voltage DC (MVDC) power distribution system has received widely attention. At present, one of the bottlenecks restricting the development of MVDC IPS for ships is the occurrence of short circuit faults. Short circuit faults not only cause extensive damage to the line hardware, but also cause a lot of losses. Therefore, how to protect system from high-amplitude short circuit fault current has become a hot research topic. In order to ensure that the MVDC IPS of the ship can still operate safely in the event of typical faults, a flux-coupling-type superconducting fault current limiter (SFCL) is applied to shipboard MVDC IPS under two typical short circuit faults. In this paper, a flux-coupling-type SFCL is conceptual and electromagnetic designed, with working principle analyzed and mathematical model established. Two typical types of short-circuit fault are selected in the shipboard MVDC IPS, and the flux-coupling-type SFCL is installed at different positions on two fault short platforms to evaluate its performance. The results show that the flux-coupling-type SFCL has effective current limiting performance on protection of shipboard MVDC IPS.

For the high temperature superconducting magnetic energy storage (HTS SMES) magnet with large capacity, in order to reduce the leakage magnetic field and the vertical magnetic field component on the wire, it mostly adopts the toroidal magnet structure. However, this structure has imposed new challenges in calculating the AC loss of the magnet. Due to the particularity structure of the toroidal magnet, that is, its magnetic field is not distributed in the 2D axisymmetric manner, it is impossible to calculate the AC loss in the toroidal magnet with a traditional 2D computation model. At the same time, the 3D model has its problems, such as the modeling is complicated; the calculation efficiency is low; the demand for computation is enormous, and so on. In order to provide a solution for calculating the AC loss in the magnet with a non-2D axisymmetric distributed magnetic field, a method of “dimensionality reduction and inversion” is proposed. In this method, the magnetic field distribution in the toroidal magnet is calculated by using a 3D model intended for uniform flow, and the AC loss is calculated by using a 2D model. The practical application shows that this method can provide a solution for calculating the AC loss in the magnet with a non-2D axisymmetric distribute magnetic field, and the calculated results meet the requirements of engineering calculation.

Directing at the robustness increase of a high voltage direct current (HVDC) system with line commutated converter (LCC) and voltage source converter (VSC), this paper proposes to coordinate resistive superconducting fault current limiters (SFCLs) and hybrid-type DC circuit breakers (HDCBs) for dealing with the DC line fault. The theoretical modeling of the SFCLs is presented, and the DC fault current characteristics are analyzed. Considering that the fault interruption involves multi-stages, the coordination of the SFCL and the HDCB in the LCC/VSC station is elaborated. Using PSCAD/EMTDC, the simulation model of a 320 kV HVDC system is built. Changing the SFCL size and the HDCB operation delay is simulated, and the performance indexes such as the fault current level, breaking time and dissipated energy are compared. The proposed coordination is verified to be very effective in handling the fault. Especially for the VSC station, it enables to visibly limit the fault current rising, shorten the transient voltage duration, and facilitate a significant decrease in the dissipated energy of the HDCB. For the LCC station, the proposed coordination can serve as a competitive backup to ensure a timely fault breaking. Consequently, the DC line fault is removed more rapidly and reliably.

Yttrium Barium Copper Oxide (YBCO) tape has a superconducting layer with a thickness of 1 μm. In the actual operation of YBCO superconducting devices, they may be subjected to mechanical strains produced by electromagnetic and thermal forces. In some cases, these forces may repeat tens of thousands times during their lifetime. We designed and built a cyclic strain test apparatus for HTS tapes, and tested the critical current degradation characteristics of YBCO tapes with two different stabilizing layers. Most of the test samples show extremely small critical current degradation even after 60000 cyclic mechanical strains. But the tapes with stainless steel layer are more likely to suffer from thermal stability problems. Increased current density was observed in the lateral direction when magnetizing the degraded samples.

The level of short circuit current in power system is increasing rapidly, and flux-coupling superconducting fault current limiter based on paralleled superconducting windings can effectively limit short-circuit current by the increased impedance after decoupling of the windings. The superconducting winding with high coupling factor is the core component of this SFCL, and the voltage distribution of windings may be uneven depending on the winding type and operating condition. This could affect the quenching of superconducting windings, and even endanger the insulation. In this paper, the voltage distribution of pancake-winding and layer-winding is theoretically analyzed, then simulations considering different operating conditions were carried out, and two prototypes were processed and the experiment results are in accordance with simulation to some degree.

The resistive superconducting fault current limiter (R-SFCL) is considered as a promising protection device to restrict the DC fault current in modular multilevel converter based high voltage direct current (MMC-HVDC) system. One bottleneck of R-SFCL is that it needs to withstand an overcurrent impact during fault, which results in temperature rise and may damage superconducting coils. A shunt resistor connected in parallel with R-SFCL can reduce temperature and protect superconducting coils. However, there are few studies to quantitatively analyze the influence of shunt resistor. This paper applies a novel R-Q method to calculate the quenching resistance of R-SFCL. By combining the R-Q method and finite element method, the system simulation and electromagnetic field analysis are separated, and the calculation feasibility is greatly improved. Then, the effect of shunt resistor in reducing the temperature of R-SFCL is studied. The influence of shunt resistance to the economic and current-limiting performance of R-SFCL is discussed.

Superconducting energy pipeline is a new type of hybrid energy transmission cable. Current leads are an indispensable part of the superconducting device, and their heat leakage accounts for more than 50% of the total heat load of the system. In this paper, the process of optimal design, simulation analysis, and heat leakage test of current leads in superconducting energy pipeline are presented. Based on the quasi-analytical numerical method, four current leads with different structures and heat transfer area have been fabricated. To verify the design, a heat leakage measurement platform was built based on the temperature gradient method. The temperature profile of the current leads was measured to calculate their heat leakage. The experimental results verify the validity of the design method, and prove that the thermal performance of current leads cooled by liquid nitrogen bath can be optimized by increasing the heat transfer area.