To meet the ultra-fast, selective, and reliable requirements of the DC fault protection, a protection scheme for modular multilevel converter based HVDC grids is proposed in this paper. The protection scheme is consisted of main protection, directional pilot protection, and faulty pole identification. The new fault directional criterion is achieved by employing the surge arriving time difference of line-mode backward traveling wave and line-mode forward traveling wave. This criterion is valid even when the fault current limiting reactors(FCLRs) are installed at the converter side of DC bus. The main protection without communication and complex computation relies on co-operation of the derivative of line-mode forward traveling wave and the directional criterion. The directional pilot protection by comparing the double end directional criteria can be used as a backup protection. The accumulation of zero-mode component is adopted to discriminate the faulty pole. Simulations have demonstrated that the proposed scheme is capable of identifying various types of faults with different fault resistances at different positions. The robustness analysis shows that the protection scheme presented is not sensitive to the FCLR size, noise environment, sampling frequency, and the operation of hybrid DC circuit breakers.

High temperature superconducting (HTS) generator was promising in the wind power applications for its advantages in the weight, size and thermal stability against load fluctuations, especially in the “direct-driven” design. A 100 kW generator was proposed for the demonstration of the feasibility of using HTS in 10 MW wind turbine generators. The electromagnetic design and optimization of the rotor were done using finite element method (FEM). The excitation coil of the rotor was designed considering variable working conditions. According to the numerical results, a number of suggestions in the design and winding techniques of the superconducting rotor were proposed.

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.

A 1MVA/1MJ superconducting fault current limiter-magnetic energy storage system (SFCL-MES) has been developed. The SFCL-MES utilizes one superconducting coil to both enhance low voltage ride through capability of wind turbine and smooth wind power output. The developed SFCL-MES was installed and put into operation in a wind farm northwest of China. This paper presents final design and test of the four major components of SFCL-MES: power conditioning system, cryogenic system, superconducting coil and monitoring system. Test results of the SFCL-MES are also presented. Test results show that the SFCL-MES has good performance and improves the power quality and reliability of wind power generation successfully.

SMES is a potential solution for power quality issues. The development of a 1 MJ/0.5 MVA SMES is now at its final stage and the device will be put into operation in a live power grid of 10 kV in late of 2006 at a substation in the suburb of Beijing, China. The design and analysis of the SMES coil has been completed and magnetic flux density distribution of and electromagnetic force on the coil has been analysed by means of FEM. The cryogenic system adopts bath cooling method and employs four cryo-coolers to re-liquefy the evaporated helium. And HTS current leads are utilized to reduce heat loss.

High temperature superconducting (HTS) power cable is an effective power transmission utility with large capacity, high efficiency, and low loss, especially in DC power transmission. This paper describes the design of a 380 m HTS power cable with rated current of 10 kA for an aluminum electrolysis enterprise. The power cable connects the rectifier at a substation at one end with the bus bar of an aluminum electrolysis plant at the other end at Henan Zhongfu Industrial Co. LTD. The power cable will be energized in late of 2010. The design of the cable conductor, cryogenic envelope, termination, refrigeration, and online monitoring system of the 380 m HTS power cable are discussed in this paper.