Jingye Zhang

The superconducting fault current limiter (SFCL) improves the power grid safety by restricting the drastically increased current when the circuit fault occurs. However, the SFCL suffers from a long recovery time and can hardly recover to the superconducting state before the breaker attempts to reclose, which hinders its practical application. This paper presents the implementation of the rapid-recovery SFCL with efficient heat dissipation even if encountering a large fault current. This is enabled by thermal performance regulation of the working coolant through adding tetrafluoromethane (CF₄) into the liquid nitrogen (LN₂). The proposed mixed coolant features a high critical heat flux that suppresses the onset of film boiling. Controlled experiments were performed with the fabricated current-limiting coil immersed in the N₂/CF₄ mixed coolants containing 0, 20 and 40 mol% of CF₄. Measured results regarding both quenching and recovery processes are reported, demonstrating an 85.4% reduction in recovery time for the 40 mol% composition compared to the conventionally used pure LN₂. Analyses of the electrical parameters of the coil verify its effective quenching performance in the proposed immersion cooling system with an overall current limiting rate of over 55%. These findings lay a foundation for designing the rapid-recovery-type SFCL and facilitating its application in power systems.

A novel superconducting DC induction heater which can heat more than two aluminum billets at a time is proposed. The workpiece can rotate on its axis and move around the center cylinder of the iron core. In order to evaluate the effect of the movement speed and the rotation speed on the heating the aluminum billet, a 2D simulation model has been built by the finite element software. And the magnetic flux density distribution and the temperature distribution under different movement speed for different rotation speed has also been evaluated. Results show that the movement can improve the temperature uniformity of the aluminum billet at the cost of increasing the heating time. What is more, the new superconducting DC induction heating structure is feasible.

In this paper, a general scheme of a 40 kV/2 kA resistive type DC superconducting fault current limiter (SFCL) is suggested, which could be utilized to suppress the surge current caused by short-circuit faults in voltage-source-converter HVDC (VSC-HVDC) power grids. This DC SFCL is designed and fabricated with 6 coil modules in parallel and 4 in series. In order to investigate the current-limiting performance of the DC SFCL under the rapidly rising fault current, the SFCL is tested on the platform with a pulsed DC impact generator. Besides the property of current limitation, the current capacity, insulation and quench recovery performance of such SFCL are also tested. Results indicate that the critical current of SFCL is larger than 2050 A at 69 K, and the DC withstand voltage is larger than 74 kV in 2 hours. During the 9kV DC impact test, the short-circuit current could be limited to 8842 A, and the quench recovery time is less than 200ms.

We develop an electric internal heating method based on a Ni-foam structured catalyst for CO₂ methanation, in which the Joule heat generated by electric current passing through the catalyst drives the reaction.