Transient Stability Analysis Of High-Temperature Superconducting Fault Current Transformer

High-temperature superconducting fault current limiting transformer(SFCLT)based on the second generation(2G)high-temperature superconducting(HTS)tape so called coated conductors(CCs)is promising in power grid,since it not only has transformation function of power but also ability of fault current limiting.In this thesis,the winding design of a single-phase 125kVA(6kV/400V)SFCLT is proposed based on the 2G HTS tape,and the short-circuit impact resistance of the superconducting tape is tested.Based on the analyzing methods of electro-magnetic-thermal-force coupling models,the electromagnetic distribution,stress,thermodynamic characteristics,quench and recovery,current limiting ability of the SFCLT are numerically simulated during the fault current occasion and lightning impulse occasion,and the safety of glass fiber reinforced plastics(FRP)Dewar container of transformer is checked.It has important reference value for practical application of SFCLT.In this thesis,the short-circuit impact resistance of the 2G HTS tape is studied firstly.The critical current and the maximum alternating current which can resist the short-circuit impact are measured by effectively simulating the operation environment of the winding.Then,based on the short-circuit impedance engineering algorithm of the 2G HTS tape YBCO and referring to the common transformer design method,a power transformer with fault current limiting rate greater than 50%is obtained The design scheme of superconducting transformer winding provides reference for the following transient simulation.The transient process of the proposed SFCLT is simulated in the case of short circuit fault and lightning impulse.Based on the thermo mechanical coupling analysis method,the calculation model of quench resistance and temperature distribution of HTS coil is established.The short-circuit current of superconducting transformer is simulated under the condition of short-circuit fault,and its current limiting characteristics are verified by comparing with ordinary transformer with the same capacity.The finite element model of superconducting transformer is established,and the nonlinear E-J characteristic curve of HTS is loaded into the model,and the short-circuit current is obtained The magnetic field distribution characteristics,stress distribution and temperature change curve of the whole process of quench recovery were analyzed.The energy heating diagram of high and low voltage winding coil in the process of transformer short circuit fault is obtained by simulation,and the vaporization volume of liquid nitrogen and the maximum instantaneous pressure of Dewar are calculated.The results show that the strength and thermal load of the design meet the requirements of safe operation of the transformer.Based on Matlab simulation software,the calculation program of transformer winding wave process is compiled to complete the calculation of transformer winding overvoltage under standard lightning impulse full wave and cut-off wave,and the wave distribution law on high voltage winding is obtained.Referring to the corresponding national standard of 10kV distribution voltage impulse for phase voltage,75kV impulse voltage is applied to the HTS current limiting transformer,and the distribution of potential and electric field on the winding is obtained.It can be seen that the 125kVA HTS current limiting transformer meets the requirements of lightning impulse insulation and operates safely,which can provide reference for the design of reliable and economical winding insulation structure and transformer operation in the future.