Research On A Novel Magnetic-Controlled Switcher Type Fault Current Limiter

With the development of modern industries of our country, power system scale is expanding in recent years, which set request for safe, stable and reliable demands for the grid. Fast current limiting technology as one of the important measures to ensure the grid's safety and reliable, has become the hotspot for power system research.A novel magnetic-controlled switcher type fault current limiter is proposed in this paper. The topology and current limiting key technology of the FCL have been studied, and a 220V/50A FCL has been manufactured.The conclusions are as follows:The topology of a novel magnetic-controlled switcher type FCL is presented in this paper. The FCL is composed of a magnetic core with three columns which has the effect of magnetic-controlled switcher, current limiting inductance and controllable dc bias source. Under normal operation state, by using magnetic saturate principle, the dc bias current is adjusted to drive the side columns core in deep saturated state, and the impedance of the FCL is very low. When a fault occurs, the current limiting inductance in the bias current circuit is converted into the ac circuit to limit the fault current automatically due to magnetic circuit coupling. By bias current adjusting, the FCL can limit the fault current to desired level speedily. The magnetic-controlled switcher type FCL has the advantages of fault current fast scouting, automatically current limiting inductance inserting, low voltage loss under steady state, no harmonic generating, flexible control strategy, and simplicity and reliability. The FCL meet the demands of selectivity, quick operation, sensitivity and reliability for the power system protections. It can be used as an effective apparatus for the power safety protection.In this paper, the FCL system parameters design method, magnetic field distribution, loss and temperature rise has been studied theoretically. Software of FCL system parameters designation, simulation and ANSYS magnetic field distribution have been programmed. Theoretic analysis and simulation results show that the FCL can limit the fault current effectively. The equivalent impedance of the FCL can be adjusted by bias current, so that it can limit the fault current to desired level. The magnetic-controlled switcher type FCL use current limiting inductance to join equivalent inductance of AC windings, and bias winding to limit the fault current, which has the effect of decreasing voltage loss ratio and enhancing current limiting ability. The theoretic analysis laid theory base for FCL test model manufacture and high voltage, high capacity FCL research.Control system of the novel magnetic-controlled switcher type FCL has been developed. The FCL control system has the complex nonlinear and parameter variations characteristics, so fuzzy PID control strategy is brought forward in the third chapter. It has the merit of precisely online control without accurate mathematical model. Based on the FCL control system characteristic analysis, a hardware platform of the bias current controller with DSP and FPGA as its core processors has been designed, and software design scheme has also been layout. The hardware platform of the bias current controller is composed of three phase bias current sampling system with DSP and the digital phase transfer and trigger system with FPGA, the other components of the controller is the communication system which send message between the controller and supervisor system. The FCL control system fulfills the functions of thyristors trigger, signal sampling, samples analysis and filtering, and communicating with the supervisor system. The control system construction made technology preparation for the FCL test model manufacturing.The 220V/50A magnetic-controlled switcher type FCL has been manufactured. Experimental study has been done on the FCL test model. The experiments include FCL control system test, static test and dynamic test, loss analysis and temperature rise test. FCL test results show that the FCL has the ability of fast fault current limiting, high recovering speed when the fault be cleared, and will not influence the normal operation of the fast reclosing relay. The harmonics introduced by the FCL is negligible. FCL loss analysis indicated that the FCL temperature rise is under normal level and need no additional heat dispersion apparatus. The FCL satisfies the desired design demands. FCL experiment verified the feasibility and validity of the test model, and provided experimental basis for the large-scale FCL research and designing.Application technology of magnetic-controlled switcher type FCL is investigated in the fifth chapter. When FCL is installed into the grid, its influence on the stability of power system should be analyzed, and high voltage FCL realization technology has also been investigated. The FCL can enhance the power system transient stability due to its fast current limiting effect, which will decrease the unbalanced power in the system under fault state. The simulated results of 220kV and 500kV FCL show that high voltage FCL has large bias current, so that the design of exitation system is the key for the high voltage level FCL realization.A novel magnetic-controlled switcher type FCL has been proposed in this paper, which has the advantages of low voltage loss under steady state, adjustable current limiting ability, fast dynamic response, satisfied current limiting effect and no harmonics. It is a promising apparatus as the power system protection. FCL theoretic analysis and simulations laid theory base for FCL test model manufacture and high voltage, high capacity FCL research. Experimental study on the low voltage limiter validated the current limiting principle and the model construction, which make a ready for large-scale current limiter research and designing.