Due to their excellent current-carrying capacity and mechanical properties, layer-wound high temperature superconducting (HTS) cables are promising candidates for large-scale applications in high-performance superconducting power devices and long-distance power transmission. However, AC losses induced by operating currents, background magnetic fields, or sudden quenches lead to heat accumulation within the superconducting tapes, posing a threat to the stable operation of the system. Therefore, it is essential to conduct an electromagnetic-thermal coupled analysis to investigate the AC loss characteristics of HTS cables. This paper proposes a two-dimensional (2D) model based on the H formulation using the finite element method. By utilizing cross-sectional parameters to represent the global geometry, the model complexity is drastically reduced, resulting in a significant improvement in computational efficiency. The validity of the proposed model is verified by comparing the simulation results with analytical solutions. Furthermore, the AC loss, temperature rise, and current distribution of the HTS cable under various operating conditions are calculated and analyzed using the developed 2D model.

In multi-terminal flexible DC transmission systems, using the DC breakers for fault isolation is the technologically superior solution at present. The hybrid DC breaker is well-suit for the construction of DC grids because of its low on-state losses of mechanical switches and rapid breaking capability of power electronic devices. The modular HVDC breaker has greater flexibility by partial inserting the arrester modules, however, the large number of the breaker’s sub-modules leads to cumbersome model-building process and low simulation efficiency while applying it to different systems. Based on the topological structure of this DC breaker, this paper analyzes its operation processes and principles form the practical working characteristics, and then this paper proposes a simplified resistance-equivalent model which effectively reduces the structural complexity of the DC breaker. Simulation results demonstrate that this simplified model essentially achieves an equivalent substitution of the original modular HVDC breaker. It not only significantly enhances simulation efficiency but also has the advantage of convenient parameter modification, making it highly useful in engineering practice analysis of multiple DC breakers working in cooperation.

During the energy exchange process with the grid, the losses of superconducting magnetic energy storage (SMES) magnets are unavoidable and will cause temperature rise, which may lead to serious consequences such as quench. In recent years, many literatures have studied the AC losses and thermal characteristics of SMES under specific operating conditions, but there has been little research into the factors that influence AC losses and temperature rise. In this paper, a reduced dimensional finite element simulation model based on T-A equation is established to investigate the influence of different response speed, energy and initial temperature of the magnet on the AC loss and temperature rise of a 3 MJ magnet, which provides a theoretical basis for the optimization of SMES control and state evaluation.

High-temperature superconducting (HTS) bulk-based magnetic bearings possess the advantages of self-stability and are well-suited for high-speed rotary systems. However, they suffer from levitation force decay issues and lack of controllability, which restrict their practical applications. To address these limitations, this paper presents the design and experimental validation of self-stable and actively controllable rotary superconducting magnetic bearings (SMBs) based on flux-pumped closed-loop HTS coils. The closed-loop HTS coils provide self-stability, and the integrated self-rectifier flux pumps wirelessly provide real-time magnetic flux modulation, allowing active adjustment of the levitation status. Experimental results show that the proposed system can: (i) eliminate levitation height decay, maintaining the rotor height within +0.1 mm up to 3600 rpm; (ii) provide 10-mm dynamic levitation height control with high tracking accuracy; and (iii) actively counteract external axial loads of +15 N, improving the effective axial stiffness. Furthermore, the influence of active flux modulation on axial self-stability is experimentally investigated. As the flux modulation intensity increases, the axial restoring force is progressively weakened, and the self-stability region correspondingly shrinks. These results demonstrate that flux-pumped closed-loop HTS coils enable actively controllable SMBs while preserving self-stability, offering a potentially feasible approach for applications such as flywheel energy storage systems and maglev motors.

This paper presents research progress on a 10 MJ-class hybrid high-temperature superconducting magnetic energy storage (SMES) module. The magnet employs a toroidal D-shaped coil configuration, combining the advantages of YBCO and MgB2 materials. Internally, YBCO coils are arranged in the high-field region to enhance critical performance, while compact and cost-effective MgB2 coils are utilized externally in the low-field region. System design parameters include a maximum stored energy of 11.9 MJ, effective output energy of 10 MJ, operating current of 1600 A, and operating temperature <= 20 K. The MgB2 magnet cable employs a multi-stage twisted structure, with a critical current exceeding 3 kA at 20 K/3 T; the YBCO magnet cable utilizes a stacked design, and bend tests reveal a critical bending radius of approximately 85 mm for the cable. Based on the design, a 1:1 verification coil was developed. Cryogenic tests indicate: when the YBCO coil is ramped to 1400 A, its temperature rise is <0.8 K; under equivalent current, the MgB2 coil exhibits a temperature rise of <0.1 K, demonstrating excellent stability; during rapid current ramping (to 1800 A in 30 min), temperature rise differences are negligible. Testing confirms this hybrid magnet meets the 10 MJ energy storage target, laying the foundation for the engineering implementation of large-capacity SMES cooled by liquid hydrogen.

Superconducting cables, due to their advantages of low losses, large transmission capacity, and environmental friendliness, have become one of the most competitive technological options for large-scale power transmission in the future. However, a series of fundamental challenges remain for their long-distance applications, among which the configuration of cryogenic refrigeration stations along the cable length is a critical issue. In this study, we take the 35 kV/2.2 kA kilometer-scale superconducting cable prototype in Shanghai as the research object. Focusing on the commonly adopted co-flow refrigeration scheme in engineering practice, and considering factors such as internal-external flow heat transfer and frictional heat generation in the coolant, we establish a mathematical model of the corresponding refrigeration system. Analytical solutions for the temperature distribution under different refrigeration schemes are obtained via numerical analysis, in order to reveal the underlying patterns. Finally, in view of the characteristics of longdistance superconducting power transmission, we investigate the relationship between the dimensional parameters of the liquid nitrogen channels and the maximum achievable refrigeration length, and further analyze the interaction mechanisms among these parameters. The results indicate that, under the coflow refrigeration scheme, appropriately increasing the inner dewar radius within a certain range can extend the refrigeration distance, but exceeding this range may in-stead lead to a reduction in refrigeration length. Moreover, the theoretical maxi-mum refrigeration length is derived.

Controlled nuclear fusion is regarded as a promising solution to the global energy crisis, and its realization depends strongly on superconducting magnetic confinement technology. High temperature superconducting tokamak magnets are considered key candidates for future fusion devices because of their high critical field and low operational energy consumption. However, alternating current losses in superconducting conductors can induce local temperature rise and trigger magnet quench, thereby threatening operational safety. Accurate modeling of such complex magnet systems remains challenging for conventional finite element methods because of large geometric scales, strong electromagnetic coupling, and nonlinear superconducting behavior. In this study, a three dimensional to two dimensional multiscale coupling method is proposed for AC loss evaluation. The toroidal field, poloidal field, and central solenoid magnets are first analyzed independently at the three dimensional scale, and an interaction matrix is constructed from their magnetic field distributions. This matrix is then imposed as time dependent boundary conditions on a two dimensional cross sectional model, where local AC losses are calculated using the homogenized H formulation. Compared with the conventional homogenized H formulation model, the proposed method improves the computational speed by at least three times, and the acceleration factor increases with model complexity, while the deviations in boundary magnetic field and AC loss are both controlled within 1%. The proposed framework provides an efficient reduced dimensional approach for thermo electromagnetic design and system level simulation of large scale high temperature superconducting fusion magnets.

The current carrying capacity of high temperature superconducting (HTS) cable is related to the operating temperature, and its thermal characteristics are directly related to the safe and stable operation of the cable. Overheating will lead to the serious consequences of loss of superconductivity and even cable burning. The HTS cable is coupled by electromagnetic thermal fluid in actual operation, and the flow field will affect the temperature distribution of the cable. The coupling relationship between temperature and fluid should be fully considered when studying the thermal characteristics. However, the existing analytical methods are difficult consider the characteristics of the flow field, and the finite element method usually simplifies the model by 2D reduction, which is not suitable for the three-in-one high temperature superconducting cable with non axisymmetric structure. Therefore, based on the scaling system, a 3D finite element thermal model of HTS cable is proposed through the one-way thermal-fluid coupling. This method can significantly save computational resources and ensure reliable calculation accuracy. Firstly, a 2D axisymmetric and 3D model of HTS cable with oneway thermal-fluid coupling is proposed by scaling system. Secondly, based on the full load operation experiment of HTS cable in Shanghai, the effectiveness of the method is verified. Compared with the original thermal-fluid coupling model, the calculation time of this model is reduced to 1/17 of the original while keeping the error within the range of 0.28%. The method proposed in this paper can provide a scheme for the thermal characteristics analysis of long-distance HTS cable, and has reference value for the setting strategy of relay protection system.

Superconducting Magnetic Energy Storage (SMES) systems are power type energy storage for grid stability control. Advantages such as millisecond scale response and very low operational loss are offered. Nonperiodic charging and discharging currents generate significant AC loss that constrains thermal stability, so rapid and reliable assessment is required. A physics based, system level real time evaluation framework for high temperature superconducting tapes is presented. Current history is respected by identifying the critical state and reconstructing the current density distribution. A penetration depth loss map of the target wound magnet is produced by a finite element algorithm, which separates electromagnetic states during charge and discharge. Local loss of micro elements at different penetration depths is evaluated through a superposition scheme, and then aggregated into the total loss. The method is applied to solenoid magnets with energy from 150 kJ to 10 MJ using practical operating conditions of SMES. Agreement with a finite element model is achieved. The interval error is 1.75%. For three solenoid magnets the errors are 2.49, 3.04, and 8.63%. Evaluation time is reduced from 2 h 4 min and 5 h 8 min to 0.17 and 0.20 s. AC loss assessment for SMES is therefore fast, reproducible, and suitable for engineering application when current history from the critical state is considered. The method supports thermal margin design and the co design of control for grid services. A consistent benchmark for future comparative studies is also provided.

The Photovoltaic-Energy storage-Direct-Flexible system (PEDF) is an innovative distribution system in buildings. This study theoretically derives the transient fault characteristics of the PEDF system and analyzes the fault current limiting mechanism of superconducting fault current limiters (SFCLs) in this context. It is proposed to install a hybrid SFCL at the converter outlet of the battery, where the fault impact is most severe. A comprehensive assessment of the current-limiting effects and economic viability of the SFCL led to the identification of the optimal configuration scheme. Finally, a simulation model o f the PEDF distribution system was established using PSCAD/EMTDC software, integrating the SFCL optimization model at the designated location. Simulation results validate the proposed scheme's feasibility, providing a basis for the fault protection strateg y of the PEDF system.

High-temperature superconducting (HTS) synchronous machines have promising application prospects due to their high power-to-mass ratio and high efficiency. The driven mode is commonly used for the excitation of HTS synchronous machines, which relies on thick current leads to connect ambient temperature power supplies and cryogenic temperature superconducting magnets, incurring considerable heat load. Existing travelling wave flux pumped based wireless excitation technique, such as HTS dynamo, is an alternative to the driven mode excitation, but it has the intrinsic drawback of excitation-rotation coupling. In this article, we propose a novel wireless excitation method for the rotor magnet in HTS synchronous machines using a transformer-self-rectifier circuit topology. Experimental results show that the proposed wireless excitation approach manages to decouple excitation from rotation. Based on the new excitation technique, a proof-of-concept HTS synchronous generator is designed, fabricated, and tested in liquid nitrogen. This article may help solve the excitation problem of HTS synchronous machines and facilitate their wider applications.

Due to the limited current carrying capacity of a single superconducting tape, high temperature superconducting composite conductors must be used for hundred MJ level High Temperature Superconducting Magnetic Energy Storage (HT-SMES). Conductor on Round Core (CORC (R)) wires are a highly promising high-temperature superconducting composite conductor. The time-varying loss is the critical electromagnetic performance of CORC (R) wires. When CORC (R) wires are wound into a coil to supply a large current, the bending configuration increases the risk of overload of refrigeration system due to AC loss. This paper presents a modeling and numerical simulation method for bent CORC (R) wires and investigates its transport and magnetization loss subsequently. First, a three-dimensional (3D) model of a straight CORC (R) wire was modeled and bent to different bending radii based on SolidWorks. Then, on the basis of published studies, the AC loss was calculated for various bending radii of CORC (R) wires. Finally, the variation of magnetization loss of bent CORC (R) wires under various background magnetic fields was investigated in a detailed parametric study. The simulation results show that for the CORC (R) wires with the parameters presented in this paper, there is a specific bending radius that minimizes the AC loss for CORC (R) wires, while it has almost no effect to magnetization loss. Furthermore, reducing this angle between background magnetic field and the plane where the bent CORC (R) wires is located can significantly suppress the magnetization loss. In conclusion, in comparison with winding superconducting tapes directly on a circular former, the modeling method proposed in this paper not only guarantees the accuracy of the winding parameters, but also provides a geometry basis for the electromagnetic-thermo-mechanical analysis of the bent CORC (R) wires.

The thermal load on high-temperature superconducting (HTS) tapes during quenching poses a threat to the stable operation of superconducting magnets. To protect superconducting coils and cables, this paper investigates the quench characteristics of HTS tapes as a basis. First, coupled with a reduced-dimensional thermal model and current redistribution model, a finite element method (FEM) model based on the 3D T-A formulation for a single HTS tape was built. Taking into account the terminal resistances and circuit inductances, the quench characteristics of parallel HTS tapes can be further analyzed by the field-circuit model. Then, a platform for detecting local quenches was constructed to verify the simulation results, and the experimental procedure was explained in detail, along with the test samples. Finally, we present the quench characteristics of single HTS tape, parallel HTS tapes, and stacked HTS tapes, which were found to be consistent with the simulation results. The parallel structure significantly reduces the risk of local quench compared to a single HTS tape. Due to contact resistances, the quench time of parallel tapes is longer than stacked tapes.

After connected to the grid, the tri-axial coaxial high temperature superconducting cable would be affected by the short-circuit fault current and generate massive heat and may be damaged. In this paper, the effects of fault parameters and cable structure parameters on operation stability after high current impact are studied by establishing a calculation model of electrothermal coupling, and the operating and transient response characteristics of tri-axial superconducting cables are obtained. By studying the effect of each phase fault on the temperature distribution, impedance characteristics, loss and recovery characteristics of the cable, the comprehensive influence law of various factors affecting the recovery process of loss is expounded. When a three-phase short circuit occurs, the temperature of the A phase conductor rises the highest and its temperature recovery speed is the fastest. When same short-circuit faults occur in each of the three phases, the temperature of the A phase rises the highest and the temperature of the C phase rises the least. The results can provide a basis for judging the safety of tri-axial superconducting cable and improving its stability.

The advancement of high-voltage direct current (HVDC) transmission is crucial for future smart grids, but it brings challenges like high short-circuit fault currents with rapid rise rates. Saturated iron-core superconducting fault current limiters (SISFCLs), effective in AC systems, also show promise in DC systems. However, they can affect fault location techniques based on traveling waves (TWs) due to their impedance characteristics. This study investigates the impact of SISFCLs on TW-based fault location in DC systems. We analyze this influence analytically and simulate a +/- 320 kV modular multilevel converter (MMC) DC system in PSCAD/EMTDC, incorporating the SISFCL model computed in COMSOL Multiphysics. Simulations of positive-pole-to-ground faults reveal that SISFCLs reduce the accuracy of TW-based fault location. The paper also outlines future research directions for integrating SISFCLs into DC systems.

Medium voltage direct current shipboard power system (MVDC SPS) is the development trend of navy in the future. At present, one of the bottlenecks restricting the development of MVDC SPS is that the short fault. This paper presents a method of applying a hybrid type superconducting fault current limiter (H-SFCL) to MVDC SPS protection. The topology and working principle of H-SFCL are introduced, and current limiting performance is evaluated. The small-scale prototype experiment is done to analyze the current limiting process of common SFCLs and H-SFCLs. The optimal allocation of H-SFCL in MVDC SPS is studied. A novel three-objectives optimal method is proposed to cope with the optimal allocation problems considering both inductive, resistive components and break time of the CBs. The three objective optimization configuration evaluation model for current limiters with both resistive and inductive current limiting components is proposed, which can also optimize the breaking time of external circuit breakers with good convergence.

In order to enhance the stability and reliability of the Photovoltaic-Energy storage-Direct-Flexible (PEDF) system, a novel line-compensation superconducting magnetic energy storage-fault current limiter (SMES-FCL) was designed to address voltage fluctuations and fault current limiting issues. The operating principle of the proposed SMES-FCL is explained in detail. By analyzing the transient characteristics of the PEDF system under power variations and transmission cable short-circuit faults, the effectiveness of the SMES-FCL in voltage fluctuation suppression and fault current limitation was thoroughly investigated. Finally, a model was built in PSCAD/EMTDC to validate the accuracy and effectiveness of the analysis.

Ambiguity Resolution (AR) is regarded as an effective technique for enhancing positioning accuracy and reducing convergence time in Precise Point Positioning (PPP). However, the Wide-Lane Fractional Cycle Bias (WL FCB) and Narrow-Lane Fractional Cycle Bias (NL FCB) needed for AR are generated from network solutions based on numerous globally distributed stations, leading to considerable computational load and processing time. A prediction model for FCB is proposed using the Genetic Algorithm Optimized Backpropagation Neural Network (GA-BPNN), and high-precision predictions of WL and NL FCB for Day of Year (DOY) 321 in 2023 are successfully achieved. Comparisons with iGMAS products show that predicted WL FCB deviations are within 0.01 cycles, and predicted NL FCB over 12 h deviates within 0.1 cycles (excluding satellite C20). The performance of three PPP schemes, Float, Fixed (based on FCB from iGMAS), and BP-Fixed (based on FCB predicted by GA-BPNN), is compared through experiments. For GPS + BDS-3, the accuracies of the BP-Fixed scheme are 0.0034 m, 0.0039 m, and 0.0100 m in the east, north, and up directions, respectively. The ambiguity fixed rates reach 98.62% for BP-Fixed. These outcomes confirm that the positioning performance using the predicted FCB of GA-BPNN is highly consistent with that using FCB products.

As an important part of superconducting devices, the heat leakage of current leads directly affects the overall heat load of the cryogenic system. Therefore, the design of low heat leakage current leads is one of the most important issues in system design of superconducting devices. Vapor-cooled current leads (VCCL) are widely used in various superconducting devices because they have lower heat leakage compared with conduction-cooled current leads, and smaller consumption of cooling gas and higher economy compared with gas-cooled current leads. In this paper, an improved thermal analysis method for solving the heat leakage, temperature distribution and heat transfer efficiency of VCCL is proposed, which has a great advantage in terms of time-consumption and convergence while guaranteeing accuracy in comparison to conventional finite element method. Firstly, based on the heat balance equation of VCCL, the relationship of the heat transfer efficiency and convective heat transfer coefficient between VCCL and cooling gas is clarified. Subsequently, the formula to calculate the heat transfer efficiency of VCCL is derived according to heat transfer and fluid dynamics. Then, a thermal analysis method for VCCL based on iterative algorithm is put forward. Finally, the feasibility of the thermal analysis method is verified by finite element model based on COMSOL, which has been proved to be correct by experimental results in existing literature. The results indicate that for several VCCLs with typical structures, the calculation differences of heat leakage between the thermal analysis method proposed in this paper and COMSOL are all within 5 % and the calculation differences of temperature distribution are all within 10 K. However, in terms of timeconsumption and convergence, the thermal analysis method proposed in this paper has a significant advantage, especially for VCCLs with complex structures.

The round-core conductor cable (CORC) possess advantages of low AC losses and high current-carrying capacity, making it a promising candidate for applications in superconducting magnetic energy storage technology. The High Temperature Superconducting (HTS) tapes in CORC cables are helically wound around a core to form a conductive layer, which inevitably subjects the tapes to certain mechanical stresses. These stresses can cause deformations that compromise the structure of the superconducting layer, thereby affecting the current-carrying capacity of the tapes and, consequently, the overall current-carrying capacity of the superconducting cable. To better assess the degradation of the critical current in HTS tapes under such mechanical behavior, this paper first conducts experiments to measure the current-carrying capacity of the tapes under helical deformation. The critical current degradation is evaluated under various winding angles and radii. Based on these experimental results, a mechanical simulation model using ABAQUS is developed to simulate the actual helical winding process. By incorporating composite materials and the actual structure of the tapes, the model solves for the stress and strain along the tape's length. This allows for the derivation of a function that describes the relationship between the mechanical deformation and the electro-mechanical characteristics of the HTS tapes under different helical deformations. Using this function, the current-carrying capacity degradation caused by the winding process in the manufacturing of superconducting cables can be evaluated.