| Wind energy exploitation is an important means to ease the world’s energy and environmental crisis, but difficulty of cost reduction and limited resources of onshore wind energy hinder the development of wind power. Researching large capacity offshore wind turbines is an effective way to solve the two problems. Owing to the outstanding advantages of high efficiency, light weight and small volume, high temperature superconducting (HTS) generators is one of the important direction to develop large capacity offshore wind turbines. With the support of the national863program, a direct drive12MW HTS wind turbine generator has been designed. This paper foucs on the design of superconducting field winding, including electromagnetic design, dynamic stability analysis, quench protection and refrigeration system design.Electromagnetic design is the key point of HTS field winding design. Based on the characteristics analysis data of HTS tape and overall parameters of the12MW HTS generators, HTS field winding parameters is proposed which satisfy the requirement of magnetic density. By means of genetic algorithm and software COMSOL, the electromagnetical and structural parameters of superconducting field winding are optimized to decrease the dosage of HTS tape. In order to reduce heat leakage and to ensure the reliability of the HTS field winding, the optimization design of current lead is carried out and the heat leakage parameters of single current lead is calculated.Dynamic stability is a significant topic of HTS field winding. Based on the operation characteristics and the design parameters, the stability of the HTS field winding in two operating conditions which are armature winding three-phase short circuit fault and the wind speed fluctuations is studied by theoretical analysis and simulation. The peak current of superconducting field winding after three-phase short circuit fault is lower than the critical current of superconductor tape, but the excitation current caused by short circuit rising too fast and may result in quench of superconducting field winding. The analysis results show that the fluctuation of wind speed will increase AC loss of the superconducting field winding and affect the stable operation of the superconducting wind turbine generator. In order to guarantee the reliability of the superconducting generators, adjustable cooling power of the refrigeration system and high shielding rate screen are used to improve the dynamic stability of the field winding.Based on the results of electromagnetic design parameters, dynamic stability analysis and the structure characteristics of HTS wind turbine generator, a new refrigeration system is designed to meet the requirements of excitation winding operation by comparative study of different cooling methods in this paper. The refrigeration system uses new structure of torque tube, multi-layer insulation material, half double radiation screen and other measures to reduce the heat load to improve the overall efficiency of superconducting generators. According to the design of refrigeration system and the result of heat load calculation, the selection of refrigerating machine and the calculation of flow parameters of helium are accomplished in this paper.Quench protection is important to ensure the safe of the superconducting field winding. The quench mechanism of HTS generators is studied in this paper. The combination of active power method and optical fiber temperature measurement method is chosen for quench detection after the analysis of different quench detection methods. Due to the high value inductance and energy storage, the paper adopts the active quench protection which use the release energy resistance and heating wire to restrict the part peak voltage and the highest temperature of superconducting field winding.The research results are summarized, and the work of future is prospected at the end of this paper. |
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