Analysis And Research Of Leakage Magnetic Field For Saturated Iron-core Superconducting Fault Current Limiter

Due to the rapid expansion of China’s power system as well as the increasing interconnection, excessive short current is one of the major problems facing the power system, which immensely affects its safety and reliability. Fault current limiters are used in power system in order to reduce fault currents and weaken influence on online equipment. However, there are limits with traditional methods used to constrain the current, which can not be applied for power system for large power losses and voltage drop. Due to its low-loss nature in superconducting condition during non-fault operating, Saturated Iron-core Superconducting Fault Current Limiter(SISFCL) offers a good solution to current limiting. In the event of a fault, SISFCL inserts impedance into the circuit and limits the fault currents to safe level. During current limit, current density is large, superconducting coil does not quench, they make SISFCL an ideal and a potential short current limiting device for power grids.Superconductor bias coil of SISFCL is made by high temperature superconducting tapes whose current carrying capacity is strong, and there is huge magnetic field since SISFCL operating normally, so leakage magnetic field is produced around it, leakage magnetic field is increased sharply due to iron cores in a deep saturated state during normal operation in power transmission, simultaneously, magnetic flux leakage which caused by loose coupling windings structure is more serious. It is very necessary to have research on magnetic flux leakage of SISFCL because huge magnetic flux leakage not only bring adverse effect on current limiter, but also electronic equipment and staff.This dissertation mainly aims at the study on the leakage magnetic field of SISFCL and the influence of different structure on the leakage magnetic field. Firstly, the composition and working principle of SISFCL are introduced, the major parts of the SISFCL are given, and then, the present situation of the development and research status of SISFCL are summarized.Secondly, on the basis of the theory foundation of electromagnetic field analysis of the SISFCL, iron core magnetic field and leakage magnetic field are simulated and analyzed with Ansys Maxwell when current imposed, and then, spatial distribution regularities of the core, winding and leakage flux are obtained. The significance to calculate current limiter leakage inductance accurately with finite element method is proposed, magnetic flux leakage energy and winding leakage inductance of the SISFCL is got by using energy method. The equivalent magnetic circuit model is built with magnetic field division method which combined with electromagnetic field simulation results.Finally, the structures of the superconductor bias coil are introduced in detail, and leakage magnetic field of SISFCL is analyzed of three different superconducting winding structures and three pillar type iron core and toroidal core with same capacity, it gets the advantages of superconducting winding in parallel and toroidal core, the simulation results provide a reference basis for the optimization of design, taking of shielding measures of the leakage magnetic field produced in the work. The nonlinear inductance is computed by energy perturbation method, and the current limiting effect of transient performance of the SISFCL with different superconducting winding and iron core is simulated by the method combining Finite Element Analysis and circuit differential equation.