Grounded Distribution Systems Research Articles

Fault section location in resonant grounding distribution systems based on feature subset optimization of phase current variation

SummaryThe existing single‐phase grounding (SPG) fault section location methods typically suffer from difficulty in feature selection, limited feeder terminal units (FTUs) configuration, and excessive dependence on communication, which weaken their generalization and robustness. To overcome these challenges, an SPG fault section location approach based on feature subset optimization is proposed. First, the relation between the position of FTU and its three‐phase current variation is analyzed, and its fault features are extracted to construct the candidate feature sets as feature subset optimization objects. Then, genetic algorithm and support vector machine (SVM) are combined to select the optimal feature subset with small dimensions and recognition error, which avoids the empirical errors of artificial feature selection. To reduce the cumulative errors, the SVM hyperparameters are simultaneously optimized. Finally, the SVM model is trained based on the optimal feature subset and hyperparameters. In the absence of zero‐sequence current measurement, three‐phase currents measured by FTU are locally processed to locate the fault section by the trained SVM. The experimental results verified the effectiveness and feasibility of the proposed method.

An adaptive faulty phase detection method based on wavelet packet reconstruction energy of three-phase voltage signals in resonant grounded distribution systems

An adaptive faulty phase detection method based on wavelet packet reconstruction energy of three-phase voltage signals in resonant grounded distribution systems

Faulty Feeder Detection Based on Grey Correlation Degree of Adaptive Frequency Band in Resonant Grounding Distribution System

Due to the particularity of their process, petrochemical enterprises have high requirements for the reliability of power supply. If a large-scale blackout occurs due to a grounding fault, it will pose a huge threat to safe production. When the resonant grounding system of petrochemical enterprises faults, due to the complex fault process and weak fault signal, it is difficult to accurately detect the faulty feeder by traditional methods. This paper presents a new method of grey correlation degree based on adaptive frequency band. Firstly, the transient zero-sequence current of each feeder is decomposed by coif5 wavelet, and the low frequency band a5 (power frequency component) and high frequency band d1, d2 (noise signal) are removed. By stacking all of the remaining frequency band signals to construct the wavelet area matrix, the faulty feeder detection characteristic scale and the first faulty feeder detection result are obtained. Secondly, based on the faulty feeder detection characteristic scale, the second faulty feeder detection result is obtained by the average grey correlation degree matrix, which detects the faulty feeder according to the waveform correlation degree. Finally, the final faulty feeder detection result is obtained by equal weight voting. In MATLAB/Simulink, the 10 kV resonant grounding system of petrochemical enterprises is modeled. A large number of simulation results show that the faulty feeder detection method is not affected by the initial phase angle (0°, 45° and 90°), transition resistance (10 Ω, 100 Ω and 1000 Ω), fault distance (1 km, 8 km and 15 km) and overcompensation degree (5%, 8% and 10%), and has good sensitivity.

Research on eigenparameters and detection methods for single‐phase‐to‐ground faults in non‐effectively grounded distribution systems

AbstractNon‐effectively grounded power distribution systems (NGDS) are widely used in China and other countries. However, over a long time, single‐phase‐to‐ground faults (SGF) have been misjudged or omitted by the monitoring system, threatening the security of the power supply system and human safety. Based on the reason analysis for the omitted and misjudged SGFs in NGDS, the concept of NGDS fault eigenparameters to correctly reflect fault characteristics and a method of SGF detection based on fault eigenparameters are proposed. Then, the detection mechanism of phase voltage and fault current resistive elements for SGF is revealed. The variation characteristics of typical fault parameters changing with distribution system scale (parameter) and fault transition resistance, such as residual voltage and Zero‐sequence current (iA‐iO), are analysed. The eigenparameters of SGF in certain NGDS with specific scales/parameters are also proposed, which can correctly reflect the fault characteristics under different transition resistances.

Faulty Feeder Detection Under High Impedance Faults for Resonant Grounding Distribution Systems

The problem of high impedance fault (HIF) detection in resonant grounding distribution systems has not been well solved. In practical applications, the existing detection methods either have complex calculation processes and low accuracy or have a weak ability to adapt to complex fault conditions, which limits the adaptability of the existing methods. Based on a theoretical analysis, a novel faulty feeder detection method based on the inner product transformation of extreme values is proposed in this paper. First, to eliminate the interference of high-frequency components, the low-frequency characteristic modes of zero-sequence current of each feeder are extracted by the variational mode decomposition (VMD) algorithm. On this basis, the low-frequency intrinsic mode functions (IMFs) are processed by the first-order difference to obtain the current waveform after the difference. Second, the zero crossing point of the differential current waveform is obtained, and then the extreme value point of the original zero-sequence current is calibrated, including the maximum and minimum. Third, at the extreme value point, the comprehensive inner product values (CIPV) of each feeder are calculated. Then, when the values are positive, it is judged as a bus fault, when the value has at least one negative value, it is judged as a feeder fault, and the feeder with the minimum value is judged as a faulty feeder. A large number of simulations and field tests show that this method has better fault detection accuracy in practical applications and is suitable for strong noise interference and asynchronous sampling.

Ground Fault Detection Based on Fault Data Stitching and Image Generation of Resonant Grounding Distribution Systems

Fast and accurate fault detection is important for the long term, stable operation of the distribution network. For the resonant grounding system, the fault signal features extraction difficulties, and the existing detection method’s accuracy is not high. A ground fault detection method based on fault data stitching and image generation of resonant grounding distribution systems is proposed. Firstly, considering the correlation between the transient zero-sequence current (TZSC) of faulty and healthy feeders under the same operating conditions, a fault data stitching method is proposed, which splices the transient zero-sequence current signals of each feeder into system fault data, and then converts the system fault data into grayscale images by combining the signal-to-image conversion method. Then, an improved convolutional neural network (CNN) is used to train the grayscale images and then implement fault detection. The simulation results show that the proposed method has high accuracy and strong robustness compared with existing fault detection methods.

Fault location of flexible grounding distribution system based on multivariate modes and kurtosis calibration

Aiming at the problems of large fault location errors when the traditional traveling wave fault location is applied to flexible ground distribution systems. This paper proposed the fault location of flexible grounding distribution system based on multivariate modes and kurtosis calibration. Firstly, a disturbance signal is generated by putting a small resistor in parallel. This signal reaches the fault point and undergoes a sudden change, generating an aerial mode traveling wave signal. Secondly, it used the multivariate variational mode decomposition algorithm to decompose the aerial mode current and extracts the fault features. Then, the discrete kurtosis value is calculated for the highest frequency intrinsic mode function component. The moment of maximum kurtosis is the arrival time of the aerial mode current. Finally, it adopted the head-end detection device to calculate the fault distance. For the complex topology of the flexible ground distribution systems, the localization equation of the overhead line, cable line, and hybrid lines are studied, and the pseudo-fault points are excluded by adding auxiliary devices at the branch end. The simulation results demonstrate that the proposed method can accurately locate faults and is not affected by the fault's initial phase angle, transition resistance, and location.

A Decentralized Fault Section Location Method Using Autoencoder and Feature Fusion in Resonant Grounding Distribution Systems

In industrial applications, the existing fault location methods of resonant grounding distribution systems suffer from low accuracy due to excessive dependence on communication, lack of field data, difficulty in artificial feature extraction and threshold setting, etc. To address these problems, this study proposes a decentralized fault section location method, which is implemented by the primary and secondary fusion intelligent switch (PSFIS) with two preloaded algorithms: autoencoder (AE) and backpropagation neural network. The relation between the transient zero-sequence current and the derivative of the transient zero-sequence voltage in each section is analyzed, and its features are extracted adaptively by using AE, without acquiring network parameters or setting thresholds. The current and voltage data are processed locally at PSFISs throughout the whole procedure, making it is insusceptible to communication failure or delay. The feasibility and effectiveness of the approach are investigated in PSCAD/EMTDC and real-time digital simulation system, which is then validated by field data. Compared with other methods, the experiment results indicate that the proposed method performs well in various scenarios with strong robustness to harsh on-site environment and roughness of data.

A comprehensive review of control techniques for compensating the fault current in resonant grounded distribution networks: From the perspective of mitigating powerline bushfires

Powerline faults are responsible for major bushfires around the world where arcs provoked from ground faults are common causes for igniting such fires. The grounding techniques (mainly resonant grounding) used in distribution substations and arc suppression devices play a crucial role for compensating fault currents in order to extinguish arcs so that the likelihoods of powerline bushfires are significantly reduced. Though passive arc suppression devices (e.g. Petersen coils) are extensively used for compensating the reactive component of the fault current, the active component of this current is still large enough to ignite the fire in bushfire prone areas for which active arc suppression devices are recently used. These active arc suppression devices incorporate residual current compensation inverters and the full compensation of the fault current rely on the control scheme of these inverters. This paper comprehensively reviews different control schemes that are used for compensating the fault current in resonant grounded power distribution systems. The existing control schemes are discussed in terms of the model used during the controller design process, loop structures, control block diagrams, and performance analysis frameworks (i.e. the type of fault impedances). It is worth mentioning that faults on resonant grounded power distribution networks exhibit the characteristics of high impedance faults and it important to consider this aspect for performance analysis of the control scheme. This paper also covers a brief overview of different grounding techniques used for mitigating fault currents and finally, the challenges with the existing controllers are identified in terms of extinguishing powerline bushfires. The comprehensive review motivates and guides future research activities on developing more efficient fault compensation techniques.

A discrete sliding mode control scheme for arc suppression devices in resonant grounded power distribution systems to mitigate powerline bushfires

In this paper, a discrete sliding mode control scheme is developed for the residual current compensator (RCC) inverter in a arc suppression coil (ASC) which is used for eliminating the fault current in resonant grounded power distribution networks to eliminate the impacts of powerline bushfires. The proposed discrete sliding mode controller (D-SMC) is designed based on the dynamical model of the ASC where the model is first represented in the dq-frame and then discretized. The D-SMC ensures the injection of the desired current through the RCC inverter so that the current flowing through the neutral reduces to zero which in turn reduces the phase-to-ground voltage of the faulty phase and hence, mitigates the adverse effects of powerline bushfires. A discrete sliding surface is selected to determine the switching control inputs for the RCC inverter and the stability of the proposed D-SMC is also analyzed to ensure the injection of the desired current to the neutral point under any operating conditions while satisfying operational standards. The effectiveness of the proposed D-SMC is evaluated through simulation results in terms of minimizing the fault current through the injection of the current to the neutral point and comparisons are made with existing proportional integral (PI) controller through simulations as well as other control strategies.

Identification of Single Phase to Ground Faults in Power Distribution Systems with RG Technique

Fault in a power system is an irregular condition that interrupts the stability of the system and causes a high fault current to flow through the power systems and its devices. Single phase to ground fault is an unsymmetrical fault that takes place between any phase of the system and ground. It is the most frequently occurring fault (70%-80%) that happens in the power system. Resonant Grounding (RG) is the proposed approach that reduces a fault current of a single phase to ground fault to a minimum level that is often independent of fault impedance. In this case, the single phase to ground fault current is too small and the typical overcurrent relay does not respond in this circumstance. As a result, a new and improved approach for detecting single phase to ground fault failures in arc suppression coil grounding distribution system with very low fault currents, though the fault impedance is low, is required. The faults are initially detected based on the neutral voltage displacement by a regionalized fault detection technique. The statement is validated by simulating a single phase to ground fault on an IEEE thirteen node test system and the results are presented. Since it employs local voltage and current information to detect power system fault condition, the suggested technique does not require communication between circuit breaker, relays, transformer, transmission lines etc. This approach can be used to a variety of different forms of unsymmetrical faults.

A Nonlinear Backstepping Control Scheme for Rapid Earth Fault Current Limiters in Resonant Grounded Power Distribution Systems: Applications for Mitigating Powerline Bushfires

This article presents a nonlinear backstepping control scheme for rapid earth fault current limiters (REFCLs) in resonant grounded power distribution systems to mitigate the severity of powerline bushfires. The main feature of the proposed control scheme is that it quickly eliminates both active and reactive components of the fault current to make it zero for reducing the chance of igniting bushfires. The nonlinear backstepping control scheme is employed on the dynamical model of a REFCL equipped with a T-type inverter. The desired tracking of the fault current is ensured with the proposed scheme by appropriately injecting the current to the neutral point. The performance of the controller is evaluated in terms of the fault current and faulty phase-to-ground voltage under different fault conditions while following the standard criteria for the practical operation. The fault current compensation capability of the proposed scheme is evaluated for both low and high impedance faults. Simulation results in software and processor-in-loop platforms clearly demonstrate the fault current is limited to a value much lower than its desired value of 0.5 A in less than 1 s, which means that the chance of igniting bushfires will be reduced with the proposed controller.

Active arc suppression device based on voltage‐source convertor with consideration of line impedance in distribution networks

In the non-effectively grounding distribution system, residual current under single-line-to-ground (SLG) fault threatens the safety of human being and power supply equipment. Active arc suppression device has been proved to be effective for SLG fault arc suppression when the line impedance is ignored. However, in practice, line impedance varies with the fault location and the load current flowing through the impedance brings about additional voltage drop, which increases the fault current and is not dealt with by the conventional methods. To achieve accurate SLG fault arc suppression with the existence of line impedance, the neutral-to-ground voltage reference for full ground-fault current compensation is firstly derived and a detection method is then proposed. The pre-fault and post-fault line currents are used to eliminate the influence of load current on the line impedance voltage drop. A dual-loop voltage and current controller is then designed. The prototype of active arc suppression device was developed. The results of simulation and prototype experiment validate the effectiveness of the proposed method.

Fault current compensations in resonant grounded distribution systems to mitigate powerline bushfires using a nonsingular terminal sliding model controller

A fault current compensation technique is proposed in this paper for resonant grounded power distribution systems in bushfire prone areas. Arc suppression devices with residual current compensation inverters are used to compensate fault currents due to single line-to-ground faults in order to mitigate powerline bushfires. The main contribution of this paper is the design of a compensation technique for the T-type residual current compensation inverter using a non-singular terminal sliding mode control scheme. The main objective of the proposed scheme is to reduce the fault current and bring its value to a level so that it cannot ignite fires. The proposed controller is designed based on the selection of a sliding surface in a way the singularity problem can be avoided and chattering effects in existing sliding mode controllers can be eliminated. The desired current injection through the residual current compensation inverter is ensured by enforcing the control law into the terminal sliding surface where the control law is determined by satisfying the Lyapunov stability criteria. The performance of the non-singular terminal sliding mode controller is compared with an integral sliding mode controller by considering different values of fault currents where these values are varied by changing fault resistances. Results for simulation in the software and processor-in-loop simulations are verified against operational standards which are essential for mitigating powerline bushfires. This work focuses to design a non-singular terminal sliding mode controller for the residual current compensation inverter which is used in an arc suppression device to compensate both active and reactive components of the fault current and keeps its value below 0.5 A within 2 s after activating the residual current compensation inverter which is a requirement as per the operational standard. This controller is designed based on the selection of a terminal sliding surface while satisfying the condition for avoiding the singularity problem.

Control of arc suppression devices in compensated power distribution systems using an integral sliding mode controller for mitigating powerline bushfires

An integral sliding model controller (I-SMC) is proposed in the work for arc suppression devices (ASDs) in resonant grounded power distribution systems which generally experience single line-to-ground faults and arcs from such faults are responsible for power line bushfires in remote areas.The proposed I-SMC is designed for the residual current compensation (RCC) inverter that is used with ADSs and the current is injected in a way that the risk of powerline bushfires are completely eliminated by reducing the fault current. In this work, a T-type inverter is employed and the control law is derived by considering the model uncertainties while the reference value of the current injected by the RCC inverter is calculated based on the fundamental analysis of ASDs. The sliding surface for the switching control input is derived in such a way that the system becomes stable. Finally, simulation studies are carried out to demonstrate the performance of the proposed scheme in terms of the desired tracking of the fault current and phase to neutral voltage with different fault impedances. Furthermore, the performance is compared with traditional proportional-integral (PI) controller in the time-domain to demonstrate its high performance and robustness.

A Novel Faulty Phase Selection Method for Single-Phase-to-Ground Fault in Distribution System Based on Transient Current Similarity Measurement

In modern electrical power distribution systems, the effective operation of inverter-based arc suppression devices relies on the accuracy of faulty phase selection. In the traditional methods of faulty phase selection for single-phase-to-ground faults (SPGs), power frequency-based amplitude and phase characteristics are used to identify the faulty phase. In the field, when a high-resistance SPG occurs in the system, traditional methods are difficult for accurately identifying the faulty phase because of the weak fault components and complicated process. A novel realizable and effective method of faulty phase selection based on transient current similarity measurements is presented when SPGs occur in resonantly grounded distribution systems in this paper. An optimized Hausdorff distance matrix (MOHD) is proposed and constructed by the transient currents of three phases’ similarity measurements within a certain time window of our method. This MOHD is used to select the sampling time window adaptively, which allows the proposed method to be applied to any scale of distribution systems. Firstly, when a SPG occurs, the expressions for the transient phase current mutation in the faulty and sound phases are analyzed. Then, the sampling process is segmented into several selection units (SUs) to form the MOHD-based faulty phase selection method. Additionally, the Hausdorff distance algorithm (HD) is used to calculate the waveform similarities of the transient phase current mutation among the three phases to form the HD-based faulty phase selection method. Finally, a practical resonant grounded distribution system is modeled in PSCAD/EMTDC, and the effectiveness and performance of the proposed method is compared and verified under different fault resistances, fault inception angles, system topologies, sampling time windows and rates of data missing.

Determination of Proper Angle Settings in Resistance Grounded Distribution Systems for Directional Earth Fault Relays

Determination of Proper Angle Settings in Resistance Grounded Distribution Systems for Directional Earth Fault Relays

A Novel Linear Optimization Method for Section Location of Single-Phase Ground Faults in Neutral Noneffectively Grounded Systems

The existing four linear section location methods are all established based on the three-phase fault current direction. When a single-phase grounding fault occurs in a neutral noneffectively grounded system, these methods are no longer applicable. This study proposes a linear optimization method for section location suitable for single-phase ground fault in the neutral noneffectively grounded system. It presents an improved transient zero-sequence current direction identification algorithm based on line voltage to accurately determine a transient zero-sequence current direction under single-phase grounding faults without zero-sequence voltage information. Second, it proposes a suitable linear section location model for single-phase ground faults as per the transient zero-sequence current direction’s distribution characteristics after the single-phase ground fault. Finally, it is verified in different feeders that the proposed method can quickly and accurately locate the fault section after the single-phase ground fault occurs in the neutral-point ineffectively grounded distribution system.

Feature‐clustering‐based single‐line‐to‐ground fault section location using auto‐encoder and fuzzy C‐means clustering in resonant grounding distribution systems

Many sensors like digital fault indicators (DFIs) have been applied and promoted in distribution systems. The sensors can provide a technical mean for single-line-to-ground (SLG) fault section location, but there are still some feature extraction and fault diagnosis problems. A novel SLG fault section location method utilizing auto-encoder (AE) and fuzzy C-means (FCM) clustering is presented in this work. Taking advantage of abundant information provided by DFIs, striking features can be extracted by the AE network, which is different from the artificially designed features that rely on prior knowledge. Compared with the learning-based methods requiring massive training data, the proposed method only requires the data from one SLG fault. By applying the AE network to the zero-sequence current measured by DFIs, the SLG fault section location's striking features could be obtained. Through feature classification by FCM clustering without setting threshold, the positional relationship between each detection node and the fault point would be distinguished to locate the fault section. Considering the abnormal communication of DFIs, the experiment proves that the proposed method can work effectively under various fault conditions.

Automatic network capacitive balancing technique for resonant grounded power distribution systems

This study presents an automatic network balancing technique to limit the capacitive unbalance in resonant grounded power distribution systems (RGPDSs). The aim of this capacitive balancing technique is to minimise the unbalance current through the line to ground (which is the current through the neutral of the system) in order to automatically limit the neutral voltage. The proposed technique is designed by combining the weighted-sum technique and genetic algorithm (GA), where distributed switched capacitor banks (SCBs) are used for balancing RGPDSs. The proposed technique is employed to optimise available SCBs for limiting the network unbalance at the substation under a pre-defined threshold considering all possible network configurations. The unbalances at different locations of the network are also minimised to limit the system unbalance within the threshold due to minor changes in network parameters. Since the lifetime of capacitor banks relies on the switching, the proposed technique is designed in such a way that the system balance is achieved with the minimum switching. The performance of the proposed technique is evaluated through simulation studies in MATLAB/SimpowerSystems environment. Simulation results show that the proposed technique works well and capable to maintain the capacitive balance of the system with changes in network configurations.