X. Deng

Design of Superconductivity Windings of a 35-kV/3.5-MVA Single-Phase HTS-Controllable Reactor

In order to compensate flexibly reactive power, it is necessary to develop a controllable reactor in long-distance and ultrahigh-voltage system. High-temperature superconductivity-controllable reactor (HTS-CR) is a potential equipment in power system. A 35-kV/3.5-MVA single-phase HTS-CR is being developed. The HTS windings of the HTS-CR are made of double pancakes that are wound with HTS tapes connected in parallel. The relationship between the number of double pancakes and the number of HTS tapes, which has great effect on the current of each HTS tape, is studied. Furthermore, the solution that reduces the ac loss of the HTS winding is also investigated, which discloses the optimized design parameters and the calculation results of the HTS windings. The study here is believed to provide some references for developing HTS-CR with larger capacity in the future.

The Effect of Flux Diverters on Energy Storage Capacity and Heat Losses in a HTS SMES

Energy storage capacity and the heat losses are key factors in superconducting magnetic energy storage (SMES). In this paper, the use of flux diverters to increase the energy storage capacity and reduce the heat losses is analyzed in a HTS SMES magnet. The analysis is carried out using a 100 kJ SMES model based on FEM. The location, the geometry shape and the material configuration of flux diverters are investigated. To get an accurate loss reduction, magnetic losses of flux diverters are considered in heat loss calculation. The results show flux diverters are effective in the rated condition. Because the flux distribution is affected by the saturation level of flux diverters, the effect is related to the operating current.

Test and Analysis of an YBCO Toroidal Magnet

In this paper, we designed and fabricated a conduction-cooled laboratory-scale YBCO toroidal magnet to explore the feasibility of applying YBCO tape in tokamaks. The tested magnet includes 14 double-pancake coils and works at a current of 200 A; the stored energy is 5 kJ at 20 K. We conducted a series of experiments to investigate the properties of each coil and the magnet as a whole, including current carrying ability, V-I characteristic, and thermal stability. In this paper, the test results and analysis of the magnet are presented.

An Experimental and Numerical Study on the Inductance Variation of HTS Magnets

Inductance is an essential parameter of a high-temperature superconducting (HTS) magnet. We have found that the inductance of HTS magnets would vary with temperatures and transport currents. The input and output properties of a magnet will change due to the variation of inductance. In this paper, an electromagnetic model has been built according to the characteristics of HTS tapes to analyze the inductance variation characteristic of HTS magnets. Four HTS coils have been made to verify this model. The result of coil and magnet experiments basically agrees with the simulation results. According to this study, the inductance variation in an HTS magnet can be attributed to the change of current density distribution in the magnet.

A Coupling Simulation and Modeling Method for High Temperature Superconducting Magnets

Under transient operating conditions, especially in the case of alternating current or pulse current, the high temperature superconducting (HTS) magnet will suffer ac losses leading to changes in the temperature and critical current distribution throughout the magnet. A magneto-thermal model is needed to simulate this process. In fact, the state change of the magnet will lead to a nonlinear performance of the HTS magnet in the power system. This paper introduces a coupling simulation and modeling method for the HTS magnet based on a cosimulation model built in MATLAB and COMSOL. The HTS magnet element is a customized module created via the self-code S-Function in MATLAB. A magneto-thermal finite element model based on the PDE and Heat Transfer modules of COMSOL is built into the S-Function. This model allows the state of the HTS magnet to be monitored during the operating process. A small-scale HTS magnet including three single pancake coils with a dc excitation system is illustrated to verify the nonlinear characteristic of the HTS magnet and the effectiveness of this coupling simulation and modeling method.

Design and Simulation of HTS Coils With a New Structure for an Inductive Pulsed Power Generator

Inductive pulsed power supplies (PPS) attract attention from several research institutions and scholars since the energy density of inductors is approximately one order of magnitude higher than that of capacitors. To effectively improve the output current of high-temperature superconductor (HTS) PPS and lower requirements for the switch, research studies have been done on STRETCH meat grinder circuit with HTS coils as an inductive module of XRAM. This paper mainly discusses the possibility of HTS coils applying to the STRETCH meat grinder as one of the fundamental research for PPS. With the characteristics of strong mechanical properties, high Ic, and low loss, HTS wire has become sufficiently available to build prototypes and practical instruments. This paper proposes a new coil winding structure that makes HTS coils applicable to the STRETCH meat grinder. Simulation results show that the transposition method can obtain a relative even current distribution in HTS parallel coils. By using the HTS magnet in the STRETCH meat grinder, maximum pulse current amplitude of 625 A can be obtained with a current multiplication factor of 5.2. Compared with the simulation results, experiments will be taken in the near future to verify the feasibility of the proposed coil structure and will be described in detail in further research work.

Design and Experimental Demonstration of a YBCO Toroidal Magnet

A laboratory-scale toroidal magnet was designed and tested in this paper to explore the feasibility of YBCO tapes applied to tokamak technology. The magnet consists of 12 D-shaped double-pancake subcoils arranged in the circumference of 80 mm; the outer radius is 280 mm. The magnet is conduction-cooled by two cryocoolers. We conducted a series of experiments on the prototype to investigate the properties of the magnet at 20 K, and the results show that the maximum current capacity is 200 A and the storage energy is 6.4 kJ.

Current and Voltage Distribution Analysis of Control Winding in a 35-kV HTS-CR Considering AC Losses

A 35-kV/100-A high-temperature superconducting controllable reactor (HTS-CR) is under development based on the principle of adjusting the main magnetic flux density and the length of magnetic circuit. The control winding of the HTS-CR is made up of double pancakes (DPCs) that are wound with HTS tapes. In order to increase the current margin of HTS winding, a four-tape bundle conductor is adopted in DPCs. Although tape transportation is utilized to balance the inductance, the current of each parallel conductor should be calculated to get the critical current. In particular, the ac losses caused by the high leakage of flux density on HTS tapes may aggravate imbalance of current and voltage distribution. This paper builds the equivalent circuit model of the parallel conductor and calculates the distribution characteristic of ac losses. Current redistribution has been analyzed by importing the equivalent resistance. Meanwhile, voltages of parallel inductance have been detected to acquire a more intuitive reference, which will provide a basis and support for quench detection and protection.