Research On Adaptive Reclosing Of AC And DC Interconnected Power Grid

With the rapid development of China's energy construction and the reverse distribution of primary energy and load demand,the development of long distance and large capacity UHV AC/DC transmission mode has become a necessary means.China's power grid is bound to become an interconnected large power grid that interconnects power grids and DC power grids,which also provides a solid foundation for the development of energy Internet.For this purpose,the influence of commutation failure on AC side relay protection equipment caused by AC side fault and adaptive reclosure after commutation failure are studied.The main contents and results of the paper are as follows:The influence of commutation failure on AC side relay protection under the condition of AC side failure is studied.First,we use dynamic vector method to establish the voltage and current switching function model in normal state.Then we decompose the switching waveform of single commutation failure on this basis,and establish a three phase current switching function model under single commutation failure.Next,the control characteristics of the DC system are analyzed,based on which,the DC side current of the inverter side is obtained,and the fault analysis model of AC and DC system is established.Changes in phase change failure occurred when the current finally analyzes the DC into AC side using the phasor method,slight failure due to commutation failure case,AC power frequency variation of the current lags behind the DC side equivalent current of power frequency variation,which coincides with the pure AC system instead,let the imaginary part of equivalent power frequency variation the amount of impedance measured by AC grid is less than zero is the capacitive impedance,is likely to determine the direction of error fault resulting in protection action.In order to solve the problem of incorrect operation of traditional relay protection equipment in commutation failure of AC/DC interconnected system,a new line protection method based on parameter identification is proposed.First,the transmission line with shunt reactor is analyzed,and the system model of internal fault and external fault is established.Then the model is unified and the fault identification is carried out based on the parameter theory of shunt reactor.Then,the DC system is analyzed,and the equivalent power frequency variation impedance model of DC system is established.The maximum value of the equivalent power frequency variation impedance of the DC system is calculated based on the single-phase ground fault,and the criterion is put forward accordingly.After locating the fault accurately,a permanent fault identification method for transmission line with double ended shunt reactors is proposed.First,commutation failure is classified into single commutation failure,continuous commutation failure and discontinuous commutation failure,and their switching function models are established respectively by waveform superposition method.Then the double end with shunt reactor circuit analysis,circuit diagram of transient fault and permanent fault occurs in the line on the line were established by the fault current path two fault is different from that of the current relationship with the second chapter calculate the commutation failure by the DC infeed AC side,the coupling current can be obtained non fault phase in the fault phase,the fault transient fault and permanent fault phase current by solving method to distinguish between permanent and transient fault is proposed by comparing the two kinds of current,so as to put forward a new method of adaptive reclosing.The simulation results show that the above analysis and conclusion are correct,and the new method can determine the instantaneous and permanent faults.