Single-line-to-ground Fault Research Articles

Identification of Ground–fault Current in Various Transformer Connection and Generator Grounding using Symmetrical Components Method

Single line to ground-fault (SLG) fault is the record frequent fault probable to occur in an electric power system. The effect of ground-fault is determined by using grounding method and transformer connections. In this study, the simulation showed the performance of a simple power system within the SLG fault in the system at various transformer connection and generator grounding method. New approach the application of ground fault current calculation using symmetrical components method on unit generator transformers. A symmetrical components method applied with simulation was conducted in Matlab software. The results were then analyzed, presenting a comparison with the fault impact at various transformer connection and generator grounding method. The models of transformer connection for each side (primary and secondary) used were wye (Y), wye-grounded (Yn) and delta (Δ). It was clearly shown that the ground-fault currents at the generator bus had significantly an effect on the type of the transformer connections used during the ground-fault at the secondary side of the transformer.

Single Line-to-Ground Faulted Line Detection of Distribution Systems With Resonant Grounding Based on Feature Fusion Framework

Faulted line detection is a key step of intelligent fault diagnosis of distribution systems, laying the foundation for the further fault location and service restoration. A novel single line-to-ground (SLG) faulted line detection method based on the feature fusion framework is proposed. In the proposed framework, one-dimensional convolutional neural network is employed as a powerful tool to extract more effective features. In addition, there is an imbalance phenomenon between data of the faulted line and healthy lines when a data-driven model is used in the faulted line detection. The proposed framework offers an avenue for overcoming it and improves the accuracy of detection. Considering the limited data of SLG faults in actual power systems, prior knowledge of SLG fault detection is integrated into the data-driven model, which proves useful in reducing dependence on the training data quantity. The experiments verified the superior performance of the proposed feature fusion framework-based method.

A traveling-wave-based line protection strategy against single-line-to-ground faults in active distribution networks

Electricity networks are in the era of major transition from stable passive distribution networks with unidirectional electricity transportation to active distribution, and the fault on the distribution lines should be cleared from both sides accordingly. This paper proposes a traveling-wave-based line protection scheme which can isolate the Single-Line-to-Ground (SLG) fault from both sides of the faulted line in neutral non-effectively grounded distribution network including Distributed Generation (DG) sources. In the proposed scheme, when a SLG fault occurs, first, relays distinguish the fault direction by comparing the polarities of the initial voltage and current traveling waves; and then the relays that detect the fault on the downstream and upstream sides operate based on the conventional time grading coordination, and the electrical changes of three-phase in a specified time window, respectively; finally, after operation of the relay upstream of the fault on the faulted line with the fastest time setting, the relay downstream of the fault operates by detecting the tripping of the opposite circuit breaker. In order to validate the efficiency of the proposed scheme, extensive simulations have been performed on a typical active distribution system using ATP-EMTP software. The simulation results indicate that the proposed line protection scheme can accurately and quickly isolate the SLG fault from both sides.

Single Line to Ground Fault Detection in a Non-Effectively Grounded Distribution Network

In the event of a single line to ground (SLG) fault in a non-effectively grounded distribution network, the faulted current is weak (only a few amperes or less) and the existing devices cannot accurately judge the faulted feeder. In this paper, we proposed algorithms that combine complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and Hilbert transform to construct a multi-criteria comprehensive voting method. First, CEEMDAN algorithm is used to decompose the zero-sequence current to obtain the IMF1 (the first intrinsic mode function) component and the Hilbert transform is used to calculate the instantaneous amplitude and instantaneous phase. Then, according to the three largest instantaneous amplitudes information, we constructed the characteristic instantaneous phase, characteristic instantaneous energy relative entropy and characteristic instantaneous zero sequence current polarity criteria from the phase, energy and polarity, respectively. Finally, we proposed a comprehensive voting method, which is specifically shown as follows: when two or more criteria show that one feeder or the bus has an SLG fault, it is voted that the feeder or the bus has an SLG fault. In contrast, if the judgment results of the three criteria are inconsistent, then we would return to recalculation and then vote. Compared with existing method, simulation tests and field experiments show that the method proposed in this paper has higher accuracy and a faster calculation speed.

A Comprehensive AC-Side Single-Line-to-Ground Fault Ride Through Strategy of an MMC-Based HVDC System

When a single-line-to-ground (SLG) fault occurs on the ac side of the modular multilevel converter (MMC) in an high-voltage direct-current transmission (HVDC) system, it results in the ac-side voltage sag and leads to an instantaneous reduction of the MMC power capacity. Thus, it calls for the fault ride through (FRT) strategy to coordinate two MMC stations in the HVDC system to protect the MMCs against the submodule (SM) capacitor overvoltage in case of the SLG fault. In the meantime, the HVDC system is expected to track the prefault active power as much as possible during the FRT to secure the power system stability. In this paper, a comprehensive FRT strategy is proposed, which is free of interstation communication. The proposed FRT strategy presents fast dynamic response, and it can prevent effectively the MMC SM-capacitor overvoltage and HVDC transmission line overvoltage. Moreover, the second-order voltage and current fluctuations in the HVDC transmission line caused by the grid unbalance are inherently avoided. Validity of the proposed strategy and its superiority over existing methods are demonstrated by simulation of a 200-kV, 400-MW cable-based HVDC system.

Setting Zero-Sequence Compensation Factor in Distance Relays Protecting Distribution Systems

Reliable protection of modern distribution systems is challenging due to various technical difficulties, mainly related to the need for more efficient use of existing networks (e.g., shorter interruption durations and fewer affected customers, integration of distributed generation, meshed network operation, etc.). Such challenges require, among others, the reconsideration of conventional protection techniques. A potential solution under examination concerns the adoption of distance protection for distribution feeders, due to its advantages compared to overcurrent protection. However, as distance relays are mainly designed for transmission networks, there are several issues to deal with in distribution applications, such as the proper setting of the zero-sequence compensation factor ( K 0). The latter issue is critical in order to guarantee correct relay operation during single-line ground faults. This paper examines the effect of K 0 on the operation accuracy of distance relays protecting inhomogeneous distribution feeders. Theoretical analysis, as well as investigation of various influencing factors, result in the determination of a pattern, which relates relay accuracy to K 0. Based on this analysis, a simple methodology for setting K 0 properly is proposed, which is implementable with commercially available relays. The methodology is applied on a test distribution feeder and meaningful conclusions are derived.

Zero-sequence voltage trajectory analysis for unbalanced distribution networks on single-line-to-ground fault condition

Faulty phase recognition under single-line-to-ground (SLG) fault condition is critical for some arc suppression methods in medium voltage (MV) networks. Traditional methods usually assume that the distributed parameters of the network are symmetrical, thus are unsuitable for the asymmetrical networks, especially when the ground-fault resistance is relatively high. In this paper, the trajectory of the zero-sequence voltage with the change of ground-fault conductance is analyzed in detail. The magnitude and phase angle variation rules of the voltage under different asymmetry ratios are presented. Then, the ranges of their unique variation rules on SLG fault for each phases are separately and strictly discussed both for the under-compensated and over-compensated grounding conditions. Furthermore, a faulty phase recognition method is proposed based on the variation rules of zero-sequence voltage on faulty condition. Simulation results verify the concluded variation rules and validate the effectiveness of the proposed fault phase recognition method, which ensures exact recognition of faulty phase in asymmetrical network and high-resistance ground fault condition.

SLG(Single-Line-to-Ground) Fault Location in NUGS(Neutral Un-effectively Grounded System)

This paper reviews the SLG(Single-Line-to-Ground) fault location methods in NUGS(Neutral Un-effectively Grounded System), including ungrounded system, resonant grounded system and high-resistance grounded system which are widely used in Northern Europe and China. This type of fault is hard to detect and location because fault current is the sum of capacitance current of the system which is always small(about tens of amperes). The characteristics of SLG fault in NUGS and the fault location methods are introduced in the paper.

Statistical Feature Extraction for Fault Locations in Nonintrusive Fault Detection of Low Voltage Distribution Systems

This paper proposes statistical feature extraction methods combined with artificial intelligence (AI) approaches for fault locations in non-intrusive single-line-to-ground fault (SLGF) detection of low voltage distribution systems. The input features of the AI algorithms are extracted using statistical moment transformation for reducing the dimensions of the power signature inputs measured by using non-intrusive fault monitoring (NIFM) techniques. The data required to develop the network are generated by simulating SLGF using the Electromagnetic Transient Program (EMTP) in a test system. To enhance the identification accuracy, these features after normalization are given to AI algorithms for presenting and evaluating in this paper. Different AI techniques are then utilized to compare which identification algorithms are suitable to diagnose the SLGF for various power signatures in a NIFM system. The simulation results show that the proposed method is effective and can identify the fault locations by using non-intrusive monitoring techniques for low voltage distribution systems.

Currents Distribution During a Fault in an MV Network: Methods and Measurements

When a single line to ground fault (SLGF) happens on the MV side of an HV/MV system, only a small portion of the fault current is injected into the ground by the ground grid of the faulty substation. In fact, the fault current is distributed between grounding electrodes and MV cables sheaths. In systems with isolated neutral or with resonant earthing, this may be sufficient to provide safety from electric shock. Experimental measurements were performed on a real MV distribution network: a real SLGF was made and fault currents were measured in the faulty substation and in four neighboring substations. In this paper, the problem of fault current distribution is introduced, the test system is described and the measurements results are presented.

A Novel Protection Method for Single Line-to-Ground Faults in Ungrounded Low-Inertia Microgrids

This paper proposes a novel protection method for single line-to-ground (SLG) faults in ungrounded low-inertia microgrids. The proposed method includes microgrid interface protection and unit protection. The microgrid interface protection is based on the difference between the zero-sequence voltage angle and the zero-sequence current angle at the microgrid interconnection transformer for fast selection of the faulty feeder. The microgrid unit protection is based on a comparison of the three zero-sequence current phase directions at each junction point of load or distributed energy resources. Methods are also included to locate the minimum fault section. The fault section location technology operates according to the coordination of microgrid unit protection. The proposed method responds to SLG faults that may occur in both the grid and the microgrid. Simulations of an ungrounded low-inertia microgrid with a relay model were carried out using Power System Computer Aided Design (PSCAD)/Electromagnetic Transients including DC (EMTDC).

Yg-Yg 3상 내철형 변압기의 영상분 임피던스 분석

In this paper, zero sequence equivalent circuit of Yg-Yg three phase core-type transformer is analyzed. Many problems by iron core structure of the three phase transformer due to asymmetric three phase lines, which includes line disconnection, ground fault, COS OFF, and unbalanced load are reported in the distribution system. To verify a feasibility of zero sequence impedance of Yg-Yg type three phase transformer, fault current generation in the three phase core and shell-type Yg-Yg transformer is compared by PSCAD/EMTDC when single line ground fault is occurred. As a result, shell-type transformer does not affect the flow of fault current, but core-type transformer generate an adverse effect by the zero sequence impedance. The adverse effect is explained by the zero sequence equivalent circuit of core-type transformer and Yg-Yg type three phase core-type transformer supplies a zero sequence fault current to the distribution system.

Application of signal processing and analysis in detecting single line‐to‐ground (SLG) fault location in high‐impedance grounded distribution network

In high-impedance grounded distribution networks which are common in many countries, single line-to-ground (SLG) fault diagnosis is difficult due to weak fault characteristics, noise interference, three-phase unbalanced operation's influence and so on. Upon thorough analysis on the space-time characteristics of SLG fault, this study applies signal processing and analysis techniques to do SLG fault location detection. First, finite impulse response (FIR) filter is applied to effectively strain out interference factors and extract pure fault characteristics for each line. Afterwards, hierarchical clustering is used to classify lines based on the extracted fault characteristics. According to the clustering result, the fault line could be determined. If there are monitoring terminals distributed in the fault line, the fault section could also be further identified. Simulation shows that the proposed method works well under various fault conditions and has a higher reliability compared with wavelet analysis. Besides, this method makes full use of the existing hardware conditions in the grid and the cost is low, hence it has high practical value.

루프화 배전계통에 초전도 한류기 적용에 따른 Recloser-Fuse 보호협조 분석

Recently, protection coordination issues can occur due to increased fault current in power system when power system being changed radial power system to grid system such as loop power system, micro grid and smart grid. This paper analyzed Recloser-Fuse coordination in loop power distribution system with Superconducting Fault Current Limiters(SFCLs) when single line ground fault occur in loop power distribution system with SFCLs. We analyzed Recloser-Fuse Coordination in radial power distribution system and changed coordination caused by increased Fault current because of loop system when single line ground fault occur in power distribution system. This paper simulated to improve changed coordination using SFCLs in loop power distribution system. Power distribution system, SFCLs and protective devices are modeled using PSCAD/EMTDC.

Investigation of Earth Fault Characteristics Under Different Neutral Grounding Methods

Medium voltage (MV) distribution systems use different methods for grounding the neutral point. Influences of these grounding methods on the single line to ground (SLG) fault characteristics are discussed in this paper. Jordanian MV network is used as a case study. The network has both underground cables and overhead lines. Simulation models are implemented in both MATLAB®/SIMULINK® and DigSilent/Power Factory®softwares. The models allow detailed investigation of the different fault factors and grounding methods. Results are obtained to evaluate the impact of each grounding method on the SLG fault features. Isolated neutral, solid grounding, resistance grounding and Petersen coil (Arc suppression coil) grounding are compared for different fault locations, fault incidence angles, and fault resistances. Current and voltage waveforms, as well as symmetrical components are used to describe the fault case.

The Identification of Single-Line-to-Ground Fault in Neutral Un-Effectively Earthed System

The correct and reliable identification of SLG(single-line-to-ground) fault is the foundation of starting the fault line selection and location device in neutral un-effectively earthed system. The traditional method based on the zero sequence voltage is invalid when the fault happens with high impedance, because the zero sequence voltage in bus is small. So a new algorithm based on the variation of voltage including the zero sequence voltage and phase voltages is proposed. The algorithm is not affected by the unbalance of system, and the sensitivity and the reliability of the algorithm are considered simultaneously. The algorithm is proved effectively by the large numbers of simulations using PSCAD/EMTDC program.

Detecting the single line to ground short circuit fault in the submarine’s power system using the artificial neural network

The electric marine instruments are newly inserted in the trade and industry, for which the existence of an equipped and reliable power system is necessitated. One of the features of such a power system is that it cannot have an earth system causing the protection relays not to be able to detect the single line to ground short circuit fault. While on the other hand, the occurrence of another similar fault at the same time can lead to the double line fault and thereby the tripping of relays and shortening of vital loads. This in turn endangers the personals' security and causes the loss of military plans. From the above considerations, it is inferred that detecting the single line to ground fault in the marine instruments is of a special importance. In this way, this paper intends to detect the single line to ground fault in the power systems of the marine instruments using the wavelet transform and Multi-Layer Perceptron (MLP) neural network. In the numerical analysis, several different types of short circuit faults are simulated on several marine power systems and the proposed approach is applied to detect the single line to ground fault. The results are of a high quality and preciseness and perfectly demonstrate the effectiveness of the proposed approach.

Single-Line-to-Ground Fault Location in the Compensated Distribution Network

One of the most difficult problems in compensated distribution networks is the grounded fault location. This paper proposes a new method for locating single-line-to-ground (SLG) faults in compensated distribution networks. The grounded fault location system is made up of the host, the controller, the signal generator and the grounded fault indicator (GFI). When a SLG fault occurs, the fault phase is identified firstly, and then a signal generator paralleled with the arc suppression coil injects a special current into the system. Subsequently, GFIs along the fault phase are activated to sample the fault phase current and send it back. The fault phase current is computed by the host with a fast Fourier transform algorithm. By comparing these frequency components of the fault phase current, the fault section is identified based on the significant difference of the second harmonic of two adjacent GFIs. Due to the short length of feeders, the distance between two adjacent GFIs is short enough for line patrol personnel to find and repair the fault easily. Finally, a modified IEEE 13-node feeder test is constructed in PSCAD/EMTDC to evaluate this method. The simulations results confirm the validity of the proposed approach.

풍력발전(DFIG)의 고압배전선로의 사고특성 해석에 관한 연구

2008년도 지식경제부의 전망에 의하면 신재생에너지전원 중 풍력발전의 보급전망은 2020년 37%, 2030년 42%에 달하고, 2012년부터 시행 예정인 신재생에너지 의무할당제(Renewable Portfolio Standard-RPS)의 도입으로 태양광 및 풍력 등의 신재생에너지가 향후 지속적으로 배전계통에 연계 운용될 것으로 예상된다. 현재 풍력은 배전계통에 전용선로로 연계되어 계통에 미치는 영향은 미미하지만, 3[MW] 이상의 대규모 풍력발전이 일반 배전선로로 확대 운용되면, 풍력발전 연계용 변압기 및 풍력발전기의 %임피던스에 의한 사고전류 변동으로 보호계전기(OCR, OCGR)의 오 부동작을 야기할 수 있다. 따라서 본 논문에서는 대표적인 풍력발전기인 이중여자유도발전기(Double-Fed Induction Generator-DFIG)가 고압 배전선로에 연계되어 운전되는 경우, 3상단락, 2선단락 및 1선지락의 사고특성을 분석하기 위하여, 전력계통 상용소프트웨어인 PSCAD/EMTDC를 이용하여 풍력발전기의 모델링과 시뮬레이션을 수행하고, 대칭좌표법을 통한 이론적인 수치해석의 결과치를 비교/분석하여, 제안한 수법의 유용성을 확인하였다. Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.

Single line-to-ground fault location based on unsynchronized phasors in automated ungrounded distribution systems

This paper proposes a new method for locating single line-to-ground (SLG) faults in ungrounded distribution systems. A distribution automation system is required to obtain all the required information from feeder remote terminal units via a communication channel with unpredictable time delays. Before locating a SLG fault, the faulted section is identified based on the absolute difference between the approximate zero-sequence angles of two adjacent nodes. Fault location starts by obtaining the synchronized zero-sequence voltage and current at the faulted node. This is achieved by forward calculation from the zero-sequence voltage and current at the substation. Because the zero-sequence current at the faulted node is calculated in synchronization with the substation, the other phasors at the faulted node are synchronized by phase compensation based on the phase difference between the synchronized and measured phasors corresponding to the zero-sequence current. Using the synchronized phasors, the fault location is identified through application of an orthogonal operator to the voltage equation at the faulted node. The performance of the proposed algorithm was evaluated using fault signals generated by the EMTP. The simulation results confirmed the validity and efficiency of the proposed algorithm for locating SLG faults in ungrounded distribution systems.