Research On A Superconducting Conductor And Its Electromagnetic Properties For Superconducting Fault Current Limiting Transformer

With the rapid growth of population and economy,the ever-increasing grid capacity and voltage level will generate large fault currents that exceed the capacity of the circuit breaker,which in turn will have a great impact on the economy and the safety of the power system in the region.Therefore,the development of power equipment with limited fault current is very necessary to improve the safety and reliability of the power system.The superconducting fault current limiting transformer(SFCLT)has the dual functions of a transformer and a fault current limiter,and has huge potential in the field of electrical engineering applications.Aiming at SFCLT,this thesis proposes a high-temperature superconducting(HTS)conductor with the ability to limit fault current.The conductor with fault current limiting function adopts the structure of a traditional superconducting cable,which is composed of a former,conductor layers and an insulating layer.Considering that the resistivity of stainless steel is higher than that of copper,to better limit the fault current,the former of the conductor is made of stainless steel,and the superconducting tapes of the conductor layer are made of stainless steel reinforced REBCO superconducting tapes.This thesis presents the structure of fault current limiting conductor and its design method,and gives the specific parameters of its structure.The structure of the proposed conductor is a three-dimensional asymmetric structure in space.This thesis introduces the three-dimensional T-A formulation which is more efficient when solving the electromagnetic field problem of three-dimensional complex structure,and obtains the critical current of the conductor.According to the conductor design plan,a fault current limiting conductor sample was prepared,and the critical current measurement experiment of the conductor sample was carried out.The simulation results are consistent with the experiment,which verifies the rationality of the design and the effectiveness of the simulation.The core performance of the fault current limiting conductor for SFCLT is its current limiting characteristics.In order to study whether the conductor has a fault current limiting ability and its electromagnetic characteristics under AC impulse current,this thesis builds an AC impulse experimental measurement platform.The AC impulse experiment obtains its fault current limiting characteristics by simulating a short circuit fault and measuring the voltage at both ends of the conductor sample and the current flowing through it.The experimental results show that the quenching resistance of the fault current limiting conductor is two orders of magnitude higher than that of the conventional underground cable XLPE cable and overhead line.The proposed conductor has a good ability to limit fault current,which is of great significance to the winding of the superconducting fault current limiting transformer.