Research On Single-phase Grounding Fault Line Selection Method For Resonant Grounding System

Among the three neutral point grounding methods used in domestic distribution networks,the current single-phase grounding fault mechanism and line selection theory for neutral point ungrounded systems and high-resistance grounded neutral systems are relatively mature,and relevant units have developed Developed a variety of line selection devices based on different line selection principles with high accuracy.However,the faulty electrical characteristics of the neutral point via the arc suppression coil grounding system are weak,and the line selection effect cannot meet the production needs.Therefore,the single-phase ground fault line selection of the resonant grounding system has become the focus and difficulty of current line selection research.Weak periodic signal detection methods such as chaos detection theory and stochastic resonance technology based on modern signal processing technology can detect weak periodic signals under the background of strong noise,and have been widely used in many fields in recent years.This paper focuses on the mathematical models and non-linear dynamic behavior of these two methods;and time scale transformation is performed to make the large-frequency signals to be detected fit the system’s natural frequency range.Thus paving the way for the practical integration of the two weak signal detection theories and the traditional resonant grounding system line selection method.The use of the fifth-order harmonic mutation of the zero-sequence current can effectively reduce the effect of the fifth-order harmonic content in the normal operating current of the system;the chaotic system has a high initial value sensitivity,and any additional sinusoidal periodic signal with the same driving force frequency as the chaotic system The addition of can cause changes in the state of motion of the system.Based on the above analysis,a new detection method is proposed which combines the theory of the 5th harmonic abrupt change of the capacitor current with the detection theory of the Duffing oscillator.The fault line can be identified by using the different phase trajectory changes of the chaotic system caused by the signals of the fault line and the non-fault line.Compared with the traditional 5th harmonic line selection method,the accuracy has been greatly improved.When the traditional signal injection method is applied to the single-phase ground fault line selection of the resonant grounding system,the injected current signal to be measured is weak and difficult to detect,which seriously affects the line selection accuracy.Stochastic resonance can transfer part of the energy of the noise to the weak periodic signal,so that the amplitude of the specific frequency signal in the power spectrum of the output signal is increased,and it is easier to be detected and extracted.A new line selection method based on the combination of traditional signal injection method and variable-scale stochastic resonance theory is proposed,so that the specific frequency signal injected by the fault line reaches random resonance,and its relative value and absolute value are greatly increased;instead of the original injection signal of the fault line The amplitude is unchanged,and the accuracy of line selection has been greatly improved.Matlab simulation verifies the feasibility and anti-interference of these two different fusion line selection methods.