High Resistance Ground Faults Research Articles

A Simple Magnetic-Flux-Based Method for Localizing High-Resistance Stator Ground Faults in Synchronous Machines

This paper presents a new offline method based on the analysis of the magnetic flux to determine the location of stator ground faults in synchronous machines. First, the defective phase is identified via the insulation resistance (Megger) test, and then the longitudinal axis of the rotor is aligned with the faulty phase winding. During two measuring modes, a voltage is applied separately to each end of the faulty phase while the other end is floating and the core is grounded. The application of the voltage between each terminal of the faulty phase and ground will lead to the circulation of a current through the stator winding to the fault point, being its path closed by the grounded core. A magnetic flux will then be created, which can be sensed indirectly by measuring the induced voltage in the rotor field winding. The fault point can be identified by measuring the applied current or voltage and the magnetic flux created in both measuring modes. Since stator ground faults usually occur via high resistances, the method is extended for the detection of such faults by processing the data using the stationary wavelet transform. The experimental results show that the proposed method is very sensitive and is able to identify the ground fault location for fault resistances up to a few hundred of k-Ohms.

Fault Identification of UHVDC Transmission Based on DF-AD and Ensemble Learning

High-resistance ground faults are difficult to detect with existing ultrahigh voltage direct current (UHVDC) transmission fault detection systems because of their low sensitivity. To address this challenge, a straightforward mathematical method has been proposed for fault detection in UHVDC system based on the downsampling factor (DF) and approximation derivatives (AD). The signals at multiple sampling frequencies were analysed using the DF, and the AD approach was used to generate various levels of detail and approximation coefficients. Initially, the signals were processed with different DF values. The first, second, and third order derivatives of the generated signals were calculated by the AD method. Next, the entropy features of these signals were computed, and the Random Forest-Recursive feature elimination with cross-validation (RF-RFECV) algorithm was used to select a high-quality feature subset. Finally, an ensemble classifier consisting of Light Gradient Boosting Machine (LightGBM), K Nearest Neighbor (KNN), and Naive Bayes (NB) classifiers was utilized to identify UHVDC faults. The MATLAB/Simulink simulation software was used to develop a ±800 kV UHVDC transmission line model and perform simulation experiments with various fault locations and types. Based on the experiments, it has been established that the suggested approach is highly precise in detecting several faults on UHVDC transmission lines. The method is capable of accurately identifying low or high resistance faults, irrespective of their incidence, and is remarkably resistant to transitional resistance. Furthermore, it exhibits excellent performance in identifying faults using a small sample size and is highly reliable.

Arc Suppression Control With Adaptive Parameters of Active Grounding Device Considering Ground Fault Resistance Uncertainty

Active grounding device (AGD) is an effective device to eliminate grounding arcs and prevent disasters caused by ground faults in distribution networks. However, due to the uncertainty of the ground fault resistance, the traditional arc suppression control cannot guarantee the suppression effect and the control stability simultaneously under the fixed control parameters. In this paper, an arc suppression control method based on adaptive parameters is proposed. According to the dual-loop control model of the AGD connected to the fault distribution network, the relationship between the model input and the fault voltage is derived. Then in two extreme cases of the ground fault resistance, the suppression effect and the system stability are analyzed using the amplitude-frequency curve and the root locus, respectively. Further, a control method is proposed to make control parameters self-adaptive through the feedback information of the residual fault voltage. Finally, the effectiveness of the proposed control method is verified by the simulation model of MATLAB/Simulink and the low-voltage experiment of the prototype, which can realize arc suppression with high, low or dynamic resistance ground fault.

Fault current constrained impedance-based method for high resistance ground fault location in distribution grid

Fault locating technology is crucial to the safe operation of a distribution grid. Impedance-based method is quite promising in fault locating due to its low cost and easy implementation. However, this method suffers from low precision when locating high resistance ground fault. This paper proposes a fault current constrained impedance-based fault location method. This method establishes location equations via the assumption that fault resistance consumes zero reactive power. First, this method adds the Thevenin equivalent to the downstream network after the fault. Second, the increment of fault current caused by distributed generations is quantified. These efforts provide an exact estimation of fault current, leading to a higher locating precision when encountering a high resistance ground fault. Simulations based on IEEE-34 node network show that the proposed method outperforms the traditional impedance-based method in precision significantly. Moreover, the proposed method does not need to distinguish fault type in advance, and is compatible to different fault scenarios.

High-Resistance Grounding Fault Detection and Line Selection in Resonant Grounding Distribution Network

The detection and selection of fault lines in resonant grounding distribution networks pose challenges due to the lack of sufficient state parameters and data. This paper proposes an approach to overcome these limitations by reconstructing the initial criterion for fault occurrence and fault line selection. Firstly, a combination of 15% of the traditional phase voltage and the sum of the zero-sequence voltage gradient is suggested as the initial criterion for fault occurrence. This improves the speed of the line selection device. Additionally, the transient process of high-resistance grounding in a resonant grounding system is analyzed based on the impedance characteristics of high- and low-frequency lines. The line selection criterion is then established by comparing the current and voltage derivative waveforms on high- and low-frequency lines. To verify the effectiveness of the proposed method, simulations are conducted. The results demonstrate that this method can effectively handle high-resistance grounding faults under complex conditions while meeting the required speed for line selection.

Research on the identification of high-resistance ground faults in the flexible DC distribution network based on VMD–inception–CNN

With the rapid development of flexible DC distribution networks, fault detection and identification have also attracted people’s attention. High-resistance grounding fault poses a great challenge to the distribution network. The fault current is very small and random, which makes its detection and identification difficult. The traditional overcurrent protection device cannot identify and act on the fault current. Therefore, this paper proposes a fault detection method based on variational mode decomposition (VMD) combined with the convolutional neural network (CNN) of the inception module. This method first uses VMD to decompose the positive transient voltage. Second, it inputs the decomposed signal into CNN for training to obtain the optimal parameters of the model. Finally, the model performance is tested based on the PSCAD/EMTDC simulation platform. Experiments show that the detection method is accurate and effective. It can realize the accurate identification of seven different fault types.

A new method for single‐phase high resistance grounding fault protection in low resistance grounded distribution networks

AbstractThe neutral point of the distribution network is grounded with low resistance, which can quickly remove single‐phase grounding fault and effectively suppress overvoltage. However, the existing zero‐sequence overcurrent protection has a high setting value. In the case of large fault resistance and weak fault current, the existing protection methods may refuse to operate. Based on the waveform characteristics of the zero‐sequence current of each outgoing line in the distribution network, this article proposes a new method for single‐phase high resistance grounding fault protection in low resistance grounded distribution network, which combines cosine distance and improved K‐means algorithm. First, the cosine distance between zero‐sequence current of every two outgoing lines is obtained, and the cosine distance matrix used to describe the fault characteristics is constructed. Then the improved K‐means algorithm is used to cluster the row vectors of the cosine distance matrix to obtain the convergent cluster center and cluster label, so that the fault line can be determined. This protection method does not need to set the threshold value manually, and has strong ability to handle large fault resistance. It can effectively deal with noise interference and intermittent arc grounding fault, and still has good adaptability in scenarios such as change of fault initial phase angle, change of fault location, access of distributed generations and occurrence of two outgoing lines in phase to grounding fault. Finally, a model is built, and the effectiveness of the proposed method is proved by the simulation of grounding fault.

Enhanced sensitive phase alpha plane scheme against high resistance ground faults

Abstract Phase-based Alpha (α) Plane Relaying (APR) scheme has numerous advantages over the Current Differential Relay (CDR) for transmission line protection. Since the large Restraining Region (RR) in the APR makes high security against CT saturation, channel delay, line charging current and synchronization error. However, the APR loses its sensitivity for high resistance ground faults, especially single line to ground faults under outfeed conditions. Also, losing its dependability under close-in low resistance three-phase faults. Thereby, the sequence-based APR provides enhanced sensitivity with the cost of computational burden and complexity. Hence, in this paper, the concept of the average value (I Avg) of both end instantaneous currents is used as an auxiliary logic. In which, the polarity of I Avg is incorporated as an add-on logic to the conventional APR to confirm high resistance internal faults. Thereby, the requirement of sequence components can be avoided (negative and zero). To validate the proposed auxiliary logic, it is tested for the WSCC (Western System Coordinating Council) 9-bus, 110 kV, 50 Hz. System. The simulated results under various fault cases found authenticated results. In addition, the comparative assessment and validation with real-world data reveal the enhanced sensitivity of the proposed logic under high-resistance ground faults.

분산전원이 있는 배전계통에서 딥러닝을 통한 고저항 지락사고 판별

This paper proposes a method to detect a high-resistance ground fault in a distribution system with complicated configuration such as installation of a distributed generation. A method to detect high-resistance ground fault accidents by converting the fault current into visual data and applying the CNN technique to this is presented and verified. The data for learning the CNN technique was generated through simulation of the model system. Simulations were performed for data generation by changing the fault resistance, the size, location of faults and amount of distributed power generation, in the case of a high-resistance ground fault and an increase in load in the model system. The generated data was transformed into graphic data by applying Morlett wavelet transform, and then learning was performed by applying CNN. As a result of the learning, high-resistance ground faults were identified with 98.29% accuracy, and a protective algorithm including this result that can respond to high-resistance ground faults occurring in the distribution system was proposed.

A novel distance protection scheme using single‐ended transient voltage based on generalized S transform

Concerning the distance protection steady-state over-reach or under-reach caused by the transition resistance, a novel distance protection scheme based on transient information is proposed. First, multiple fault features are extracted using the Generalized Stockwell Transform (GST), and a criterion for identifying low-resistance and high-resistance ground faults is constructed. Then, a GST coefficient matrix is established for the single-ended transient voltage of the line, the attenuation coefficient and delay coefficient are derived by the least-squares method and the beat phenomenon, and the transition resistance is calculated. On this basis, adjust the operation boundary in the +R axis direction of the operation zone according to the transition resistance value. Finally, test results on real-time digital simulation system (RTDS) demonstrate that the protection scheme operates reliably in different fault cases and is highly immune to fault resistance. Compared with the traditional distance protection scheme, this scheme performs better when the transition resistance is large.

Faulty Section Location Method Based on Dynamic Time Warping Distance in a Resonant Grounding System

When a single-phase grounding fault occurs in a resonant grounding system, the determination of the fault location remains a significant challenge due to the small fault current and the instability of the grounding arc. In order to solve the problem of low protection sensitivity when a high-resistance grounding fault occurs in a resonant grounding system, this paper proposes a fault location method based on the combination of dynamic time warping (DTW) distance and fuzzy C-means (FCM) clustering. By analyzing the characteristics of the zero-sequence current upstream and downstream of the fault point when a single-phase grounding fault occurs in the resonant grounding system, it is concluded that the waveform similarity on both sides of the fault point is low. DTW distance can be used to measure the similarity of two time series, and has the characteristics of good fault tolerance and synchronization error tolerance. According to the rule that the DTW value of faulty section is much larger than that of nonfaulty sections, FCM clustering is used to classify the DTW value of each section. The membership degree matrix and cluster centers are obtained. In the membership degree matrix, the section corresponding to the data in a class of their own is the faulty section, and all other data correspond to the nonfaulty section; otherwise, it is a fault occurring at the end of the line. The simulation results of MATLAB/Simulink and the field data test show that the method can accurately locate the faulty section.

A Single-Phase High-Impedance Ground Faulty Feeder Detection Method for Small Resistance to Ground Systems Based on Current-Voltage Phase Difference

At present, the small resistance to ground system (SRGS) is mainly protected by fixed-time zero-sequence overcurrent protection, but its ability to detect transition resistance is only about 100 Ω, which is unable to detect single-phase high resistance grounding fault (SPHIF). This paper analyzes the zero-sequence characteristics of SPHIF for SRGS and proposes a SPHIF feeder detection method that uses the current–voltage phase difference. The proposed method is as follows: first, the zero-sequence current phase of each feeder is calculated. Second, the phase voltage root mean square (RMS) value is used to determine the fault phase and obtain its initial phase as the reference value. The introduction of the initial phase of the fault phase voltage can highlight the fault characteristics and improve the sensitivity and reliability of feeder detection, and then CVPD is the difference between each feeder ZSC phase and the reference value. Finally, the magnitude of CVPD is judged. If the CVPD of a particular feeder meets the condition, the feeder is detected as the faulted feeder. Combining the theoretical and practical constraints, the specific adjustment principle and feeder detection logic are given. A large number of simulations show that the proposed method can be successfully detected under the conditions of 5000 Ω transition resistance, –1 dB noise interference, and 40% data missing. Compared with existing methods, the proposed method uses phase voltages that are easy to measure to construct SPHIF feeder detection criteria, without adding additional measurement and communication devices, and can quickly achieve local isolation of SPHIF with better sensitivity, reliability, and immunity to interference.

Flexible Grounding System for Single-Phase to Ground Faults in Distribution Networks: A Systematic Review of Developments

The neutral grounding method is one of the crucial technologies used to ensure the safe and stable operation of distribution networks. With the development of power electronics-based devices, the application of highly controllable inverters to grounding systems has become a new research direction. In this review paper, based on the summary and analysis for the research status, the flexible grounding system is systematically classified according to its control strategy and structure. And then, the following core technologies are summarized: faulted line selection, current component detection, high-resistance ground identification, ground parameter measurement, neutral point voltage control, and fault location. Subsequently, deficiencies of flexible grounding systems are summarized from the following four perspectives: reliability, accuracy, speed, and stability. Finally, some discussions and recommendations for future development and research direction are presented. Especially, the reliability-enhanced hybrid grounding system that combines active inverters and low resistance for high-resistance ground faults is recommended. This paper provides a systematic literature review of the crucial technologies for flexible grounding systems and can be used as a technical reference for future research.

Faulty feeder detection of single phase-to-ground fault for distribution networks based on improved K-means power angle clustering analysis

High-resistance ground faults often occur in distribution networks, and the fault current can be as low as 0.1A, making it extremely difficult to realize faulty feeder detection. The application of traditional faulty feeder detection methods based on single fault characteristic is limited. Thus, a method of single-phase grounding fault feeder detection based on improved K-means power angle clustering analysis was proposed. First, collect various fault characteristic quantities of each feeder under different operation and fault conditions, and establish a historical sample database. Then, the improved K-means clustering algorithm is used to quickly classify the historical sample database, and the cluster center is optimized through the spatial density and maximum neighbor distance principle. Finally, the power angle similarity is calculated according to the relative position of the real-time feature sample and the cluster center in the fault space, so as to realize the sensitive detection of the fault feeder. The PSCAD simulation and the 10 kV distribution network test field showed that the proposed method effectively eliminates the misjudgment of a single fault characteristic caused by external interference. And without a fixed setting value, the accurate fault feeder detection of intermittent arc grounding, high resistance grounding and other fault conditions can be realized.

Discussion of Third Harmonic Voltage Characteristics of Large Hydro Generator Stator Winding and Improvement of Ground Protection

Large hydro-generators require a 100% protected area for stator ground protection. Because the fundamental voltage criterion has low sensitivity near the neutral point, a high sensitivity third harmonic voltage criterion is needed to ensure that the generator can accurately respond to stator ground fault. This paper analyzes the third harmonic voltage characteristics of two large hydro-generators, calculates the sensitivity of the existing third harmonic criterion, and points out that the impedance parameters of the grounding transformer should be considered. In view of the lack of sensitivity of the third harmonic criterion for large hydro-generators, this paper proposes a stator ground protection criterion based on the third harmonic voltage variation, which has zero action quantity under the generator non-fault conditions and zero braking quantity after a ground fault occurs, and thus has high sensitivity and can effectively respond to high-resistance ground faults. PSCAD/EMTDC simulation results show that the proposed method has high sensitivity at different fault locations and transition resistances, which can provide theoretical support for the improvement of stator grounding protection in practical engineering.

Wavelet packet coefficient of transient first half wave line selection method for single-phase grounding fault

Overvoltage will occur after single-phase grounding fault in distribution network, endangering system insulation. It is of great significance to find out the fault line as soon as possible to ensure the safe operation of the system. Wavelet modulus maxima can be used to detect the sudden change singularity of transient current. However, the judgement of single mode maximum value is easily influenced by the form of fault and interference, leading to misjudgement. In this paper, the transient characteristics of single-phase grounding fault are analyzed, and the magnitude and phase characteristics of the first half wave are given; Based on wavelet packet algorithm, several key problems such as boundary effect, wavelet selection and decomposition scale are explored; Taking the zero sequence voltage as the reference to determine the fault interval, the zero sequence current of each line is decomposed by three-scale wavelet packet using db6 wavelet, and the wavelet coefficients of the characteristic frequency band are extracted for comparison. The fault line is the one with the largest amplitude and different phase from others. The distribution system model of neutral grounding through arc suppression coil is built. Simulation is carried out for several cases with great difficulty in line selection, such as short circuit when phase voltage crosses zero, high resistance grounding and long line fault. The experimental results prove the reliability of this method.

Faulty Line Selection Method Based on Comprehensive Dynamic Time Warping Distance in a Flexible Grounding System

A flexible grounding system is a system in which the neutral point of the power supply is grounded via the arc suppression coil in parallel with a low-resistance resistor. When operating normally or a temporary ground fault occurs, the arc suppression coil is used for grounding, whereas the small resistance is switched on when a permanent ground fault occurs. At present, the problem of low protection sensitivity when a high-resistance ground fault occurs in a flexible grounding system has not been solved yet. According to the characteristics of low waveform similarity between the faulty line and the non-faulty line when a single-phase grounding fault occurred, a new faulty line selection method based on a combination of Dynamic Time Warping (DTW) distance and the transient projection method is proposed in this paper. Firstly, the fault transient signal is extracted by a digital filter as a basis for faulty line selection. Secondly, the transient zero-sequence current of each line is projected onto the busbar transient zero-sequence voltage, and the projected DTW distance of each line is calculated. Finally, according to the calculation formula of waveform comprehensive similarity coefficient, the Comprehensive DTW (CDTW) distance is obtained, and the top three CDTW distance values are selected to determine the faulty line. If the maximum value is greater than the sum of the other two CDTW distance values, the line corresponding to the maximum value is judged as the faulty line; otherwise, it is judged as a busbar fault. The simulation results based on MATLAB/Simulink and field data test show that the method can accurately determine the faulty line under diverse fault conditions.

Fault Current Constrained Impedance-Based Method for High Resistance Ground Fault Location in Distribution Grid

Fault Current Constrained Impedance-Based Method for High Resistance Ground Fault Location in Distribution Grid

High-Resistance Grounding Fault Detection and Line Selection in Resonant Grounding Distribution Network

High-Resistance Grounding Fault Detection and Line Selection in Resonant Grounding Distribution Network

Double-K Differential Protection Principle of Regional Power Grid Based on Voltage Vector Compensation

In the regional active distribution network where the Distributed Generation (DG) penetration rate is getting higher and higher. When a high-resistance ground fault occurs in a heavy-load line, the traditional current differential protection has very low sensitivity, the protection may refuse to act. And the power differential protection has the voltage dead zone. In addition, the T-type branch will further reduce the sensitivity of the traditional differential protection. In order to solve the problems, this paper proposes a new principle of double-K differential protection with voltage vector compensation. The principle can flexibly adjust the braking zone range by setting two parameters, and then introduce the voltage vector to compensate the operating point, which effectively improves the protection sensitivity in the case of high-resistance ground fault occurs in a heavy-load line, and there is no voltage dead zone. Simulation shows that the principle can greatly improve the reliability of protection.