Research On Key Problems Of Fault Current Limitater Based On The Control Of Magnetic Circuit

As a industrial power,China also has huge electricity consumption.However the regional imbalance of energy distribution and economic development prompted China to propose " three vertical three horizontal " high-voltage supergrid plan in the 12 th Five Year Plan,confirmming the goal of building a strong supergrid.However,the high-voltage and large-capacity transmission lines will not only reduce the line loss,but also increase the short-circuit current.Excessive short-circuit current will inevitably cause damage to the power equipment on the lines.Replacement of the higher capacity breakers and transformers will greatly improve the construction cost of the grid.Therefore,the magnetic control fault current limiter(MCFCL)have gradually attracted the attention of power grid workers around the world due to their good capabilities of current-limiting and low losses during normal system operation.Firstly this dissertation introduces the current development of MCFCL and points out that it still has the disadvantages of high demand for DC power,poor dynamic performance,and excessive consumption of ferromagnetic materials.Then,A finite element simulation model was established according to the working principle of MCFCL.This dissertation proposes a novel type of tightly-coupled structure.By winding AC coils and DC coil on the same core,the coupling degree of AC coil and DC coil is increased,and the the requirement of DC excitation power for the saturation of the core is reduced.The influence of four kinds of air-gaps on current limiting reactance is analyzed.Based on the tightly coupled and loosely coupled structures,the finite element simulation model is built in Jmag,and a 10 kV prototype is manufactured to verify the rationality of the structure proposed in this dissertation.This dissertation proposes a novel winding method of AC coils,which reduces the demand of ferromagnetic materials in traditional structure.Changing the way the permanent magnets are embedded which not only reduces the demand of DC excitation power,but also wide the difference between the currentlimiting reactance and saturated reactance.The theoretical analysis and simulation modeling of the novel structure under different short circuit conditions are performed to verify the superiority of the novel structure.The influence of tightly-coupled structure on the voltage across the DC coil in DC control system is analyzed.At the same time,a novel DC released circuit is proposed,which can accelerate releasing energy in the DC coil by increasing the reverse DC excitation voltage,optimize the dynamic characteristics of the MCFCL,and accelerate converting intocurrent-limiting in case of system fails.The electrical parameters of the finite element simulation model are introduced into the electromagnetic transient simulation in MATLAB.In addition,the results of 10 kV dynamic model prototype test also verify the superiority of the topology.According to different fault types,this dissertation analyzes the influence of MCFCL on the transient stability and relay protection of the system,and verifies the analysis results through the digital-analog hybrid simulatio of RTDS.A new setting scheme of distance protection is proposed,which makes up for the influence of MCFCL on distance protection.