Study On Electric Power Transient Signal Based On Nonlinear Dynamics

With the rapid development of social economy and increasing number of users,users put forward higher requirements on power grid stability.To have further improvement of stability and reliability,it's urgent to improve the power grid protection rapidity and sensitivity.Traditional power frequency protection is due to the influence of power frequency oscillation and transition resistance,leading to its slow response and low detection accuracy,which can't identify transmission line small current fault and internal transient fault of power equipment effectively.However,transient protection based on fault information can solve the above problems well,which also makes it a new research direction of power system relay protection.The electric power transient signal contains large information,including fault type,fault location,duration such information data,so it can achieve power grid fault location and selection such function.It's known that extracting characteristic information from power transient signal effectively is the premise of transient protection,however,the detection and its analysis of power transient signals are also difficulties to disturb the development of transient protection.The study finds that the root is in a lack of complete transient signal analysis theory,especially detection,denoising and recognition theory,which doesn't constitute theory system,while lack practical application.The key problems of power grid transient protection are studied in this paper,such as characteristic analysis,detection and extraction,fault identification such key technology of power transient signals,and nonlinear dynamics theory for signal research is proposed,the feasibility and effectiveness of dynamics in study of power transient signal is verified.Based on nonlinear dynamics theory,it presents a series of new methods,such using Duffing chaotic oscillator to detect transient signals,combining dynamic with Huang transform to research traveling wave signal,using improved method EEMD-HHT to lacate traveling wave position,and this paper presents many new ideas about using dynamic method to study lightning transient signal and substation lightning protection strategy.Finally,a series of new theories and methods for the study of power transient signals based on nonlinear dynamics are presented.The main research contents and innovations are as follows:(1)Based on identification of line fault trip mode based on wavelet energy,this paper put forward a new method to study power transient signal based on nonlinear dynamics.It has a profound study on the correspondent relationship between dynamic characteristics of transient signal and ground distance,grounding resistance,phase difference under the situation of different ground fault type,and analyze dynamic character of different ground fault type.Finally,dynamic characteristics of transient signals are obtained.(2)This paper proposes a new method to identify grounding fault type by using Duffing chaotic oscillator combined with wavelet edge detection technique,whose method is simple and straight with high accuracy,and simulation and field verification results are the same.This paper analyzes nonlinear dynamic characteristics and distribution law of lightning transient signal.Alternatively,it proposes a new strategy of lightning protection scheme selection based on nonlinear dynamics,which provides new idea for the strategy research of substation lightning protection.(3)This paper proposes a new method to study the characteristics of transient traveling wave using nonlinear dynamics,and explores the distribution law of transient traveling wave nonlinear dynamic characteristic index in power grid.Aiming at traveling wave distortion in power grid transportation,this paper analyzes transmission characteristics and traveling wave decay law through simulation.It deeply analyzes the time-frequency characteristics for traveling wave of different station,and studies the relationship between arrival time and propagation path for wave traveling,it makes use of EMD-HHT to solve the time of wave reaching to measure point.Based on nonlinear dynamics theory,it calculates the kolmogorov entropy and fractal dimension F of traveling wave.The study finds out that the distance adding is in the decreasing tendency of kolmogorov entropy and fractal dimension F of traveling wave and the index of the adjacent line or the ring network node is close.The law can be used to identify appropriate position of traveling wave.(4)This paper studies detection technology of weak traveling wave signal,and provides improvement method.Aiming at the possible white noise,pulse interference and narrowband interference under strong noise background,this paper proposes a integrated denoising method by using median filter to filter white noise,mathematical morphology filter to filter pulse interference,and Duffing chaotic oscillator to filter narrow band interference.Aiming at limitation of traditional EMD-HHT method that there may be mixing,this paper proposes a improved technique EEMD-HHT to locate traveling wave position,through investigation,it's shown that EEMD-HHT method improves traveling wave location accuracy.In this paper,the common grounding transient signal and lightning transient signal in power system are taken as examples,it provides a series of new methods and new techniques for studing electric power transient signal based on nonlinear dynamics,which provides new thought for analysis and research of power system transient signal,and further enriches transient protection research based on transient information.The paper's theory study,simulation analysis and field detection results show that analysis and application of power transient signal based on nonlinear dynamics has broad development space and bright application prospects extremely.