Research For Intelligent Reclosure Of Transmission Lines Based On Natural Frequency Characteristics

It is well known that autoreclosure technique is one of the most economic and effective measures to improve the power supply reliability for transmission network,while three-phase reclosure have more application advantages than single-phase reclosure in the closely linked network line,as its action logic is simple,does not exist the problems such as open-phase running.As the present three-phase reclosure may aggravate secondary short circuit to the system for blind reclosing in the case of an arcing transient fault or a permanent fault,even threaten the system security and the power supply reliability.At the same time,operating overvoltage is produced in the process of tripping,which may bring a serious threat to the safe and stable operation of the important equipment in power system even than that caused by unsuccessful single-phase reclosing.Thus,it is significant to study on autoreclosure aiming to detect non-fault for extra high voltage(EHV)and ultra high voltage(UHV)transmission lines.Detecting non-fault before three-phase reclosing has practical application value to improve reclosing success rate.This paper proposes a method capturing the natural frequency of the currents from shunt reactors to identify the non-fault state before three-phase reclosing.In the primary arc,secondary arc and recovery voltage periods in the case of a transient fault,the three free oscillation circuits are formed by the energy storage elements in the different periods,which will produce different inherent oscillation frequency components based on the different network.Using difference natural frequency components in different physical phases propose methods for fault identification and the time of extinguished arc.But existing FFT algorithm is not fast and not accurately extracts frequency and low frequency,Prony algorithm of short data window can be used to quickly extract the frequency components of the frequency,which closer to natural low frequency component information.Therefore,the characteristics of inherent oscillation frequency components are used to recognize the condition of a transient,and then to detect non-fault before three-phase reclosing.After phase-mode transformation,the free oscillation circuits in mode components are obtained and the inherent frequencies are captured,thus the non-fault detection scheme for three-phase reclosure is presented.Analysis closing overvoltage particularly coincide overvoltage,and thus determine a reasonable time,and coincide coincidence mode.In order to verify the validity and correctness of the criterion referred to in this article,using PSCAD software to simulate and analyze combined with MATLAB.PSCAD simulation using real transmission line parameter to build simulation models,a variety of simulations under different fault conditions and fault nature etc.verify the correctness and effectiveness of criterions,which lays a good foundation for engineering application of smart three-phase reclosure in the future.