Research on fault line selection method for distribution network in small current grounding system

The probability of two-point same-phase ground fault (TPSPGF) is low in small current grounding system (SCGS), but the harm of TPSPGF can not be ignored. However, there is no effective fault line selection method for TPSFGF at present. A fault line selection scheme for TPSPGF is proposed in this paper. Firstly, the simplified equivalent circuit model of TPSPGF in SCGS is established, and the steady and transient fault characteristics of TPSPGF are analyzed. Secondly, two common line selection methods for single point ground fault are introduced, and their applicability for TPSPGF is analyzed. Finally, based on the fault component of phase current, the line selection procedure for TPSPGF is given. The correctness of the analysis results and the effectiveness of selection scheme is verified by simulation.

This paper investigates fault line selection in small current grounding systems, focusing on the zero sequence current phase characteristics. Small current grounding systems, prevalent in medium voltage distribution networks, face challenges in fault detection due to minimal fault currents during single status phase grounding faults. Traditional methods relying on manual line switching and zero sequence voltage monitoring are inefficient and can induce overvoltage. This study categorizes fault line selection techniques into three approaches: steady-state fault information, transient information, and modern signal processing technology. The analysis of zero sequence currents in non-grounded systems reveals that fault line zero sequence currents equal the sum of system capacitive currents, flowing opposite to those in non-fault lines. Additionally, transient signal analysis shows that these signals provide more robust information for fault detection. MATLAB simulations validate the theoretical models, demonstrating that zero sequence current direction and amplitude effectively identify fault lines. The results confirm the efficacy of combining steady-state and transient signal analyses for accurate fault line selection, contributing to enhanced safety and reliability in power distribution networks. This research offers practical insights and tools for engineers, improving fault management and reducing potential economic losses in small current grounding systems.

When single-phase to ground fault occurs in small current grounding system, the zero-sequence transient current contains a lot of complex fault information. In order to extract characteristic from the zero-sequence current accurately as the criterion of fault line selection, this paper puts forward a method of fault line selection based on VMD energy entropy and optimized K-means clustering. Firstly, the zero-sequence current of each line is decomposed by VMD (variational mode decomposition, VMD), and each sub mode of the original current is obtained. Secondly, the energy entropy of each sub mode is calculated as the characteristic quantity of each line state. Finally, the optimized K-means clustering algorithm is used to cluster the fault feature to realize fault line selection. In this paper, Simulink is used to simulate the single-phase to ground fault in resonant grounded system and the results show that the method that has high accuracy can provide reference for practical engineering application.

Because of line parameters, running types, fault grounding impedances and other factors, the veracity of current fault line selection (FLS) method is not high enough and may contain some dead areas for FLS device of non-utility grounding system (NUGS). To overcome this shortage, a novel FLS method is proposed in this paper based on analyzing the fault characters of distribution network, combining merits of prevalent FLS methods, constructing these methods' subjection functions and then synthesizing them based on the fuzzy theory. Experiments show this method can achieve high sensitivity, adjustability and veracity. The dynamic simulation experiment shows in the neutral un-grounding system(NUS), the method which is made of the zero sequence inactive power (ZSIP) method, the base-wave virtual value (BV) method and the base-wave phase (BP) method of zero sequence current (ZSC) can achieve high accuracy; in the neutral resonant grounding system (NES), the method that combines zero sequence active power (ZSAP) method, 5-harmonic phase (HP) method and remaining current increment (RCI) method can even achieve 100% accuracy. Based on the PC104 industry control computer, a new FLS device of NUGS according to this new FLS shows very high accuracy in dynamic simulation experiments, and it should be widely used in China.

Based on the detailed analysis of single-phase grounding fault characteristics in the small current grounding system, an adaptive multi-criteria fusion method of fault-line selection based on transient signal is proposed in this paper. This method introduces fault membership and criterion confidence to achieve the fusion of multiple fault-line selection criteria. At the same time, each criterion adaptively determines whether to participate in the selection according to its confidence level. MATLAB/Simulink simulation results indicate that this fault-line selection method is not influenced by such factors as the transient characteristics of the fault, fault resistance, length of the faulty line, etc.

In order to improve the line selection accuracy of the fault line selection device for small current grounding systems, a line selection method based on information fusion is proposed, that is, several complementary single line selection methods based on transient and steady state characteristics are used for comprehensive line selection. Firstly, wavelet method, zero-sequence active component method, and fifth harmonic method are used according to the characteristic definition of transient and steady-state fault characteristics, and then the rough set theory algorithm model is used to fuse the faults with various fault characteristics to select the fault line. In Matlab, a distribution network model was built and a program of fusion algorithm was written for simulation analysis and verification of route selection methods. The simulation results show that the line selection method based on rough set theory and information fusion has high accuracy and good application value.

At present, the MVDC distribution grid is developing rapidly and relay protection is the key technology to ensure stable operation. Therefore, this paper focuses on the fault line selection method. Firstly, the fault characteristics are analysed when a fault occurs in the line, and a novel single‐pole fault line selection method is proposed based on 0‐mode power. The polarity of current fault component measured at the terminal of each line is used to identify the internal and external faults. And the 0‐mode power is used to select the faulty line. Finally, to verify the correctness of the proposed method, a radial MVDC distribution grid is built in PSCAD to output fault data in different fault conditions, and the fault line selection algorithm is implemented in MATLAB. The simulation results show that the proposed method is fast, effective, reliable and it has a certain degree of tolerance to transition resistance with a strong anti‐data delay and anti‐interference ability. Moreover, the fault line selection method proposed in this paper can still correctly select the fault line in the case of serious faults such as multiple line faults, sudden removal of lines, and sudden changes in photovoltaic output power.

Using wavelet to achieve fault line selection, traditional methods are all in accordance with the principles of the largest energy to determine the characteristic band. However, this square sum operation overlooks the detailed band features, so when the fault characteristics are not obvious, it will cause wrong judgment. For transient quantity mutations are the basis of wavelet fault line selection, a new perspective that ¿the frequency band with the maximum absolute value of adjacent wavelet packet decomposition coefficients difference¿ should be chosen as the line selection frequency band is first proposed in this paper after the wavelet packet decomposition of the complex transient mutational quantity. The paper expounds on the detailed fault line selection steps and practical criterion, and also analyzes the selection of mother wavelet, sampling frequency and scale of the decomposition. Theoretical analysis and simulation results show that the method can accurately select fault line, with high reliability.

This paper proposes a method of intelligent protection and location integration for single-phase grounding fault in small current grounding system, which can quickly transfer the grounding current at the grounding fault point and make the current at the grounding fault point tend to zero. The arc cannot maintain and extinguish, thereby protecting the personal safety of the staff. At the same time, the fault location is carried out according to the principle that the zero sequence electrical parameters on different lines and the zero sequence electrical parameters of each line after the active grounding of the fault phase bus before and after the single-phase grounding fault. Finally, through PSCAD/EMTDC and Matlab simulation, the feasibility and effectiveness of this method are verified from different ground resistance, initial phase angle, and fault distance in small current grounding system.

Small current grounding system is mainly used in China’s distribution network. When single-phase grounding fault occurs in the distribution network, it is important to quickly and accurately select the fault line and locate the fault section to ensure the safe and stable operation of the system. In this paper, the fault location methods for the small current grounding system are described in detail, the advantages and disadvantages of various methods are compared, the main problems existing in the low-current grounding system are pointed out, and the future development direction is prospected.

Transient analysis is carried out for the single-phase grounding fault in small current grounding system, the transient grounding current expression is derived, and the influence factors are analyzed. Introduces a method for non-stationary and non-linear signal analysis method-Hilbert Huang transform (HHT) to analyze the single phase grounding fault in small current grounding system, HHT can be better used to extract the abundant transient time frequency information from the non-stationary and nonlinear fault current signals. The empirical mode decomposition (EMD) process and the normalized Hilbert Huang transform (NHHT) algorithm are presented, NHHT is used to analyze and verify an example of the nonlinear and non-stationary amplitude modulation signals. Build a small current grounding system in the EMTP_ATP environment, by selecting the appropriate time window to extract the transient signals, NHHT is used to analyze the transient current signals, and the Hilbert amplitude spectrum and the Hilbert marginal spectrum of the zero sequence transient current signals are obtained.

Accurate and fast identification of the fault types and the fault feeders can improve the distribution networks’ power supply reliability. This article focuses on two issues of classifiers in performing fault identification and line selection of the distribution networks, namely, the low utilization rate of fault information and the insufficient accuracy. We propose to use multilabel and multiclassification and build a fast-multibranch residual network (Fa-Mb-ResNet) to accomplish the identification and line selection of the distribution network grounding fault simultaneously. Our work has the following contributions. First, we propose a method of frequency division and time division for learning the features of the time–frequency matrix based on wavelet transformation. Second, we propose an improved residual unit (IRU) structure, which employs different small branches and convolution kernels to achieve the fusion of abstract fault feature information in different dimensions and enhance learning efficiency. Finally, the IRU structure is connected end to end. The new approach fully exploits the side fault information. Our extensive experiments show that the Fa-Mb-ResNet is faster, more adaptable, and has better anti-interference than the state-of-the-art methods in fault identification and line selection of the distribution network.

In this paper, an adaptive fault line selection method based on the wavelet packet comprehensive singular value for small current grounding system is presented. First of all, wavelet packet decomposition is utilized to decompose transient zero sequence current (TZSC) of 2 cycles, then the comprehensive singular values are introduced to describe the fault information. Secondly, normalize the comprehensive singular values to compute the fault membership values. At last, according to the difference between the maximum membership value and the second maximum membership value, the selected fault line can be output. The simulation results show that the proposed method cannot be affected by fault line type, fault resistance and fault initial phase angle, and also has good anti-noise capability.

Due to the effect of the arc suppression coil and the large grounding resistance, the electrical quantity of the high-resistance grounding fault of the neutral point through the arc suppression coil grounding system is relatively weak, which makes fault detection and line selection difficult. This article starts with the transient characteristics of high impedance faults, analyzes the instantaneous or permanent changes caused by the fault to the system's ground parameters, and proposes effective identification methods based. According to the different transient fault characteristics of the faulted line and the non-faulty line, the transient energy characterizing the change of structural parameters is constructed and used to design the transient fault line selection method. The method improves the detection range of high resistance ground faults while ensuring the correct line selection. The simulation results verify the accuracy and reliability of this method.KeywordsArc suppression coilHigh impedance faultParameter identificationTransient energyFaulty feeder identification

The single phase grounding fault line selection has the following problems for small-current grounding system, including low reliability, large computational amount and complicated algorithm implementation. To solve these problems, a method based on VMD-DTW transient energy ratio is presented in this paper. Firstly, the variational mode decomposition (VMD) is used to decompose the transient zero-sequence current within 1/4 cycle after the fault and get different frequency band modes. Then, the dynamic time warping (DTW) is introduced to calculate the transient similarity measure of corresponding mode of different lines. Finally, the transient energy of each line is calculated with the similarity measure as the weight, and the line with the energy ratio of 1 is the fault line. To test the reliability of this method, a typical model of 10kV distribution network is built in MATLAB/SIMULINK. The simulation results verifies that the method has a good fault line identification rate, and is not susceptible to fault location, fault closing angle and transition resistance.