Study Of Fault Signal Identification And Protection Co-operation Of Fault Current Limiter In 500kV Power Grid

With the fast development of grid, short-circuit current will be a serious problem. A reasonable network structure is the most effective and the most fundamental solution. Alternatively the fault current limiter (FCL) can limit the short-circuit current without changing the normal power flow. It is prospective.Based on the fault current limiter demonstration project in East China 500kV power grid, the fast identification of fault signal of FCL and co-operation of FCL protection and system protection are studied. BOD triggering thyristor bypass as back-up protection was proposed in the dissertation and applied for a patent. The co-operation between the slope set value and the instantaneous set value of the line current was proposed, which is the supplement to line current slope criterion. Based on a new approach improving the effect of FCL on system protection, several reasonable proposals of co-operation between FCL protection and system protection were given. All the works provide reference for the fault current limiter demonstration project in East China 500kV power grid. The main works of the dissertation are as follows:First, the equivalent system of the fault current limiter demonstration project in East China 500kV power grid is established using PSCAD-EMTDC. The existing fast identification method which can be used in FCL and other two new fast identification methods were simulated in the equivalent system. The identification criteria of fault signal based on the line current, the line current slope, the MOV current and the MOV energy are studied in details. The co-operation between the slope set value and the instantaneous set value of the line current are detailed with the aid of PSCAD simulation results. Simulation results show the best co-operation, i.e. the line current slope and the instantaneous value of the line current reach the setting values successively(without regard to sequence), and the interval is 5ms. After that, the criterion based on the line current slope is examined with the transient fault recorder data from Yimin-Fengtun series compensation project and Dongming-SanBao series compensation project.Then, the effect of FCL on the zero-sequence current protection, the effect of circuit re-switching on FCL and the co-operation between FCL protection and line protection are studied theoretically and simulated on the equivalent system. Simulation results show that, the insert of FCL will reduce the sensitivity of zero-sequence current protection even make the protection fail to operate. The problem can be solved by switching the protection fixed value freely. Re-switching of circuit breaker will impact on the capacitor bank, and the FCL by-pass breaker must be closed when the circuit breaker re-switched. The FCL breaker closing failure protection can reclose the by-pass breaker and open the line breaker at the same time to protect the thyristors and other main equipments of FCL when the by-pass breaker fails to close. The line coupled protection can close the by-pass breaker to protect the capacitor banks when a remote fault occurs and other protections fail to operate. Finally, the dynamic simulation experiments of FCL protections were conducted in the Digital Dynamic Simulation Room of East China Electric Power Test Research Institute to inspect the operation characteristics of the FCL breaker failure protection and the line coupled protection in various operating conditions.