Jiahui Zhu

The Quench Detection System for YBCO Superconducting Magnets

Quench detection is a key issue for the practical application of superconducting electrical power equipments. In this paper, a quench detection system has been developed for a YBCO superconducting magnets. It detects a set of quench input signals, such as magnet voltages and current, which are isolated, amplified and filtered by the quench detection system. It can also manage a standard set of output control signals to activate the dump and to control the magnet current to ramp down in the event of a quench. According to the experimental results, this quench detection system can fulfill the function effectively.

Magnetic-Thermal Coupling Analysis of the Cold Dielectric High Temperature Superconducting Cable

A finite element analysis model of the cold dielectric high-temperature superconducting (HTS) cable was built considering the feature of current and heat transfer boundary condition, based on which the magnetic-thermal coupled field was studied and simulated. Then the boundary conditions in the finite element analysis model, such as temperature, magnetic field and the current distribution in HTS cable conductor, were iteratively renewed based on the results of the simulation. Also, the magnetic-thermal coupled field in HTS cable was simulated again using the fixed boundary conditions. The change regularity of the magnetic-thermal coupled field in HTS cable was obtained through the cycle of dynamic simulation of the magnetic-thermal coupled field.

Design and cost estimation of superconducting magnetic energy storage (SMES) systems for power grids

This paper presents a preliminary study of Superconducting Magnetic Energy Storage (SMES) system design and cost analysis for power grid application. A brief introduction of SMES systems is presented in three aspects, history of development, structure and application. Several SMES systems are designed using the state of art superconductors and have taken into account their electromagnetic properties. The magnets of the SMES systems are designed using a global optimization algorithm. Both solenoid and toroid configurations are designed and compared. The capacities of SMES systems are designed on different scales including kJ-, MJ- and GJ-class for different applications. Finally the costs are calculated based on the commercial price of superconductors. The result indicates that the solenoid configuration is suitable for kJ-scale SMES, while the toroid configuration is suitable for GJ-scale SMES.

AC loss comparison between multifilament and nonstriated YBCO coils designed for HTS propulsion motors

In this paper, the properties of current capacity and ac transport loss of striated high temperature superconductor (HTS) coil is compared with ordinary HTS coil by using both experimental and simulation methods. The measurements were carried out by transporting a sinusoidal varying current at 77 K, with an amplitude range of 10–50 A in frequency from 70 up to 300 Hz. Measurement facilities and methods are explained in more detail in the paper. The critical current of the 4-mm width multifilament coil made with four filaments at a spacing 0.03 mm was found to be lower than that of the nonstriated coil. The frequency dependent characteristics agreed well in both experimental and simulated results. Reducing ac loss of HTS is one enabling factor for widespread adoption of the technology, and therefore, understanding its characteristics is important and discussed in this paper. Future plans based on this preliminary work are the testing of multifilament tapes in an axial flux motor field environment.

Experimental test of two types of non-inductive solenoidal coils for superconducting fault current limiters use

Growing electricity demand from a range of sources and the changes of the power grid structures open the possibility of more frequent and much higher fault current. Traditional solutions to the fault are difficult to satisfy the requirement of the new power grid due to many factors, such as high cost, additional impact to power grid in normal loading condition, which leads to the research for an efficient alternative solution of interest to both academia and industry: Superconducting fault current limiter (SFCL). In this paper, two types of low-inductance solenoidal coils, the braid type and the nonintersecting type, are built with 2G high-temperature superconductors. The current limiting performance, the recovery characteristics, and the ac losses of both types of coils are tested and compared in detail. Experimental results show that both types of coils can effectively limit fault current and recover in several seconds. Furthermore, comparison between the ac losses of both types of SFCLs shows that the ac loss of the braid type coil is lower than that of the single tape by about an order of magnitude in low-current regions.

Comparison of Liquid Nitrogen Flow Resistance in Corrugated Pipe With Smooth Pipe for HTS Cable

In the high-temperature superconducting (HTS) cable system, liquid nitrogen is usually chosen to be the coolant because of its low saturation temperature and large latent heat of vaporization. The liquid nitrogen should be forced to flow in the cryostat, which is usually made of flexible corrugated pipes. Compared with smooth pipes, the surface of corrugated pipes is more complicated and rough. Thus, the characteristics (e.g., wave pitch and wave depth) of corrugated pipes have more effects on the flow resistance coefficient between corrugated pipes and liquid nitrogen. In this paper, an original model was referenced to analyze the effect of corrugated characteristics on the flow resistance of liquid nitrogen. In addition, an experimental apparatus was set up to measure the flow resistance of liquid nitrogen in the corrugated and smooth pipes, respectively. The flow resistance of liquid nitrogen gradually increases as the wave pitch of the corrugated tube decreases and the wave depth increases. The flow resistance coefficient in corrugated pipes is three times as large as that in smooth pipes at least.

A Novel AC Loss Measurement Technology for High Temperature Superconducting Cable With Large Current Capacity Using a Compensation Coil

High temperature superconducting (HTS) cable is a new development of applying superconducting technology in power system. AC loss measurement technology is a key factor in designing HTS cable as it decides the stability and operating cost of the cable. In this paper, a novel AC loss measurement technology for HTS cable is proposed based on LabVIEW. A compensation coil with large current carrying capacity and a stepping motor are used to test the variation of AC losses of HTS cable. A closed loop system is developed to obtain AC losses measured using modules of high-precision Data Acquisition (DAQ) and motion controller of National Instruments (NI). Finally, AC losses of a 0.2 m, 110 kV/1.5 kA prototype HTS cable are measured at 49.9 Hz and 60 Hz frequency considering compensation coil and lock-in amplifier. Obtained results show that AC losses linearly increase with the transport current in logarithmic coordinates. The comparison results applying with compensation coil and lock-in amplifier prove that the proposed measurement system is effective in measuring AC loss of HTS cable with large current capacity in different frequency.

Strain Characteristic of a Toroidal HTS-SMES Fabricated by YBCO Stacked-Tape Cables

In need of high current carrying capacity, tapes are usually assembled in a cable. There are several cable options and one of them is the YBCO stacked-tape cable. In this paper, four YBCO tapes were stacked and pancake coils were constructed, which are the components of a toroidal superconducting magnetic energy storage system. The stacked-tape cable could improve the operating current of the toroidal magnet, and, therefore, increase the stored energy. However, the stress experienced by the conductor will also be very high. In this paper, numerical simulation analyses of stress and strain combining electromagnetic fields and mechanical behaviors were performed to investigate the effect of the electromagnetic forces on the coil and the support structure.

Inductance and current distribution analysis of a prototype HTS cable

This project is partly supported by NSFC Grant 51207146, RAEng Research Exchange scheme of UK and EPSRC EP/K01496X/1. Superconducting cable is an emerging technology for electricity power transmission. Since the high power capacity HTS transmission cables are manufactured using a multi-layer conductor structure, the current distribution among the multilayer structure would be nonuniform without proper optimization and hence lead to large transmission losses. Therefore a novel optimization method has been developed to achieve evenly distributed current among different layers considering the HTS cable structure parameters: radius, pitch angle and winding direction which determine the self and mutual inductance. A prototype HTS cable has been built using BSCCO tape and tested to validate the design the optimal design method. A superconductor characterization system has been developed using the Labview and NI data acquisition system. It can be used to measure the AC loss and current distribution of short HTS cables.

Experimental research on power fluctuation compensation in different scenarios using a hybrid HTS SMES

A hybrid HTS SMES using two different kinds of superconducting coils, BSCCO and YBCO coil, is optimized to achieve the maximum energy storage taking the influence of the magnetic field into account. The cooling system with sub-cooled LN2 maintains the cryogenic operating environment at 69K. A LCL filtered voltage source power converter (VSC) is designed for the HTS SMES. A dual processor combined with DSP and MCU is applied in the dual-core controller and a digital closed loop algorithm based on the SVPWM pulse modulation is programmed for the VSC-based SMES. The dynamic simulation experiment is achieved with the hybrid HTS-SMES in different scenarios for the power fluctuation compensation. The experimental results validate that the SMES can output the required compensation power and restrain the power fluctuation in milliseconds.