Study On The Inductive Fault Current Limiter Based On High Temperature Superconducting Non-insulated Coils

With the development of the power grid in China,the capacity of the power grid continues to expand,resulting in the increasing level of short-circuit current,which greatly affects the operation of the power system and the electrical equipment.As the short-circuit current is approaching the breaker capacity limit,the problem of short-circuit current exceeding limit is imminent.Short-circuit current limiter is one of the most effective methods to solve this problem.Among all the current limiters,high temperature superconducting(HTS)fault current limiter(FCL)has the advantages of self-triggering,fast response and high reliability due to the superconducting material characteristics,which has a wide application prospect.In this paper,for the first time,the HTS non-insulated(NI)coil is used as the secondary winding of the inductive HTS FCL,which absorbs the advantages of compact structure,strong mechanical performance and good heat dissipation capability of the HTS NI coil,so as to improve the quench recovery capability and the electric stability under short-circuit impulse current of the FCL.Firstly,in order to verify the technical feasibility of HTS NI coil as the inductive FCL secondary winding,this paper compares the AC magnetic field shielding characteristics of the insulated coil and non-insulated coil through experiments.Combining simulation analysis,it is verified that the NI coil to completely shield external magnetic flux in a certain range.Then,through the DC magnetic field shielding experiment,the magnetic field shielding capability of superconducting NI coils is quantitatively analyzed,and the internal mechanism of magnetic field shielding capability decline under large external magnetic field is revealed.Secondly,the working characteristics of the inductive superconducting FCL in normal operation and current limiting process are studied by simulation model.The transient simulation model for simulating the current limiting characteristics of the inductive FCL proposed in this paper is introduced.The model is based on the coupling of multi-physics finite element simulation and circuit model.It can simulate the macroscopic characteristics of current limiting process,such as voltage/current curve,winding temperature rise,etc.;as well as its microscopic characteristics,such as current distribution and winding temperature distribution,etc.Thirdly,through the experimental study on the inductive FCL prototype,the current limiting capability of the inductive FCL with HTS NI coil as the secondary winding is verified,and the steady-state and transient-state simulation model validity is also verified.Then,in order to study the influence of different iron core structures on the current limiting characteristics,the short circuit tests are carried out on the prototype with air core,semi iron core and full iron core respectively.The impedance variation characteristics under different short circuit currents are studied.Considering volume,weight and current limiting capacity,it is concluded that air core and semi iron core are more applicable to the inductive FCL.Finally,aiming at a 10 kV transformer sudden short-circuit test system,through analyzing the need of the test system to suppress the fault short circuit current,it can be concluded that the test capacity of the system can be effectively improved after importing the inductive FCL.Then,the preliminary design of the air core inductive HTS FCL for the test system is given,and the validity and rationality of the FCL design are verified by the simulation model.