Faulty Segment Research Articles

Converter non‐blocking DC fault ride‐through and system fast restoration arrangements in R‐L SFCL‐equipped MMC‐M2TDC system

AbstractEquipping a DC‐type superconducting fault current limiter (SFCL) in a modular multilevel converter‐based multi‐terminal DC (MMC‐M2TDC) system has the potential to reorganize the protection control arrangements during the DC‐side short‐circuit fault. This paper introduces the converter non‐blocking operation and system fast restoration control of the SFCL MMC‐M2TDC with the DC‐side bipolar fault condition, as well as their feasibility verifications. Considering the characteristics of overdamping oscillation of DC voltage and the additional impedance effect of the new resistor‐inductor SFCL (R‐L SFCL), the unfaulty converter non‐blocking protection enables faulty segment isolation and DC fault ride through without unwanted active power interruption. The restoration control for smooth reconnection and fast recovery of the off‐grid converter station ensures the DC voltage rebuilding process and reduces the required period. To validate the above arrangements, the simulation is conducted upon the PSCAD/EMTDC corresponding to the three‐terminal R‐L SFCL MMC‐M2TDC system. Finally, the research routes for novel superconducting coil design, SFCL scheme design, and multi‐device cooperative strategy are discussed, all of which contribute to promoting the high‐quality development of SFCL in MMC‐M2TDC scenarios.

A fault segment location method for distribution networks based on spiking neural P systems and Bayesian estimation

With the increasing scale of distribution networks and the mass access of distributed generation, traditional centralized fault location methods can no longer meet the performance requirements of speed and high accuracy. Therefore, this paper proposes a fault segment location method based on spiking neural P systems and Bayesian estimation for distribution networks with distributed generation. First, the distribution network system topology is decoupled into single-branch networks. A spiking neural P system with excitatory and inhibitory synapses is then proposed to model the suspected faulty segment, and its matrix reasoning algorithm is executed to obtain a preliminary set of location results. Finally, the Bayesian estimation and contradiction principle are applied to verify and correct the initial results to obtain the final location results. Simulation results based on the IEEE 33-node system validate the feasibility and effectiveness of the proposed method.

Fault location in hybrid transmission lines on the basis of VMD energy entropy and SVM

Finding the head of a traveling wave is challenging because an overhead line-cable hybrid transmission line’s wave impedance is not constant. Because of this, it is difficult to measure the hybrid transmission line precisely. This leads to the proposal of a hybrid transmission line fault location algorithm, which combines VMD energy entropy for training support vector machines and traveling wave law graphs. The VMD energy entropy is first used to train SVM to identify the faulty section. The method of traveling waves with a single end is utilized to precisely fix the fault distance within the faulty segment when the type of traveling wave has been identified. The simulation results demonstrate that the method provides precise measurements and is effective for hybrid transmission lines with a range of fault distances and grounding resistances.

Fault Detecting and Isolating Schemes in a Low-Voltage DC Microgrid Network from a Remote Village

Fault detection and isolation are important tasks to improve the protection system of low voltage direct current (LVDC) networks. Nowadays, there are challenges related to the protection strategies in the LVDC systems. In this paper, two proposed methods for fault detection and isolation of the faulty segment through the line and bus voltage measurement were discussed. The impacts of grid fault current and the characteristics of protective devices under pre-fault normal, under-fault, and post-fault conditions were also discussed. It was found that within a short time after fault occurrence in the network, this fault was quickly detected and the faulty line segment was efficiently isolated from the grid, where this grid was restored to its normal operating conditions. For analysing the fault occurrence and its isolation, two algorithms with their corresponding MATLAB/SIMULINK platforms were developed. The findings of this paper showed that the proposed methods would be used for microgrid protection by successfully resolving the fault detection and grid restoration problems in the LVDC microgrids, especially in rural villages.

Multi-Source Data-Cooperated Neutral Low-Resistance Grounding Cable Grid Faulty Segment Identification

The multi-source data-driven faulted segment identification methodology has spurred research interest recently. Based on analyzing the post-fault physical features of the three-core cable earthed strap current, this study develops an approach to identify the faulty cable segment(s) of neutral low-resistance grounding distribution grids with distributed generators. To eliminate the potential uncertainty of recorded data, introducing Mixed Integer Linear Programming to construct the fault diagnosis model. The model employs traditional fault indications, including alarms from remote fault indicators and metering signals of zero-sequence current, to promote the validity of identifications. Under the causal logic constraint of events, employing the expected fault scenario with the minimum discrepancy to available data to determine the true faulty cable segment(s). Additionally, the model decision variables can be used as the reference for anomalous data determination. The effectiveness and robustness of the proposed methodology are validated by applying it to a simulation model based on a real-life three-core cable utility feeder.

Multiple Heterogeneous Information Source

Today, this fault location analysis is completed within the digital signal processing method. Scenario packet transmission source of some of the attacks and intruders get data packets, and route alters identity problem before cumulative. Reduces processing time can find significant speed advantage and the accuracy of the classical method of calculation failure and presents a simple analog implementation. Back-propagation time is modeled as a fault location estimation of each repeated signature and the switches along with the network. Rapid Packet Transmission Algorithm (RPTA) by a certain load distribution, which leads to restrictions to avoid packet loss. Due to increased packet transmission, improving technology to limit non-destructive testing costs is in great demand. Our algorithm means that each candidate seriously and error detection mechanisms and can provide any fault tolerance of the routing path assessment. Simulation results with different fault resistance indicate that these methods are robust, fault-type, and the initial angle of the disorder. To find the faulty segment, use the transient to the common connection point. Good accuracy for complex network topologies also reduces the overhead generation region by implication checking logic; thus, compared to the typical failure locations of the techniques developed to reduce the total number of required effects, this solution charm.

Accurate Location of Faults in Transmission Lines by Compensating for the Electrical Distance

Accurately locating faults is quite important, especially when the geographical environment is complicated. If the exact location of the fault is not given, wrong route would be chosen, which will greatly slow down repair. This paper proposes an improved traveling wave method by compensating the electrical distance of transmission lines. The catenary model is constructed that considers parameters of the tower and the actual temperature. The actual line length is also derived by the catenary model. A 500 kV transmission line model is established by PSCAD/EMTDC. Various fault simulations are conducted and the results demonstrate that the presented method effectively reduces the error ratio of faulty segment positioning and locates faults with high accuracy.

A Reliable Protection Scheme for Fast DC Fault Clearance in a VSC-Based Meshed MTDC Grid

A multi-terminal high voltage DC (MTDC) grid, is an optimum and cost-effective transmission network to minimize the energy crisis worldwide largely. However, the core demand for a fast DC protection scheme with an extraordinary strict fault clearance time of a few milliseconds, is a key research gap in this network, holding back its development and scalability. To bridge this gap, this paper proposes a novel protection scheme for a meshed MTDC grid. The main goals of the scheme include accurate discrimination of a faulty line, rapid fault detection, fault location estimation, significant fault current reduction, and fully selective isolation of only the faulted line, while continuing normal power flow in the healthy grid zones. Reliability of the scheme for long and extra-long-distance power transmission is increased by aiding the differential protection and Type-D traveling wave (TW)-based algorithms utilizing the distributed optical current sensing technology with the other auxiliary methods and backup plans. These auxiliary methods include independent discrete wavelet transform (DWT), current derivative polarity principles with a minimum sample (short time) window, overcurrent relays, and AC circuit breakers (ACCBs). A faulty segment of a transmission line is accurately discriminated from the healthy ones by measuring a series of multi-point differential currents on it. A faulty line at a particular DC node is accurately discriminated using the differential protection by measuring the current flowing into or out of each line from each side at every node to obtain the algebraic sum. The current sum of a real-time local transient data and a delayed remote data is compared to a preset threshold level. DC fault current is significantly reduced below the breakable levels by coordinating bidirectional hybrid DC circuit breakers (HDCCBs) with the active and passive fault current limiters (FCLs) and the half bridge-VSC-based modular multilevel converters (MMCs). The proposed concepts are successfully verified by the simulation results under a variety of fault scenarios and are found to be accurate.

Faulty feeder selection and segment location method for SPTG fault in radial MMC‐MVDC distribution grid

As a modular multilevel converter-based medium-voltage direct current (MMC-MVDC) distribution grid mostly utilises small current grounding modes, the weak fault current for single-pole-to-ground (SPTG) fault is very difficult to detect especially in the case of noises and fault resistance. Therefore, this study proposes a fast and accurate faulty feeder selection and segment location method. For SPTG fault, the transient current fault component is the charge-discharge current of distributed capacitance on the DC feeder. Analysis indicates that the waveforms of current fault component of positive and negative poles are negatively correlated for a faulty feeder; while they are positively correlated for a non-faulty feeder. According to these characteristics, a faulty feeder selection criterion using Pearson correlation coefficient (PCC) is constructed. Then, utilising the energies difference between the current fault components of two poles, the faulty pole can be verified. In addition, the faulty segment is located by the PCC of the current fault component on both sides of each segment. Finally, simulation results confirm the validity of the proposed faulty feeder selection and segment location method.

A novel fault location algorithm for mixed overhead‐cable transmission system using unsynchronized current data

The characteristic impedance value of the overhead line is different from that of the underground cable. Existing traveling wave‐based fault location methods for mixed power transmission systems have setbacks including location error caused by wave velocity and difficulty in detecting wave arrival time. In order to solve these problems, the increase of available information from different locations by installing wire‐based sensors along the power line is a feasible solution. In this paper, a traveling wave‐based fault location system, which is based on the current data measured at the midpoint of the overhead line and the joint point, is introduced. The data at these two locations are measured by the wire‐based current sensor we designed. The whole transmission line system is divided by these two sensors into three segments. The first step of this proposed method is to record the postfault current data at the two measuring devices. Second, by comparing the amplitudes and polarities of the current at these two measurement points, the faulty segment can be identified. Finally, postfault wave propagation paths are ascertained; the accurate velocity values of the waves in the overhead line and underground cable are obtained; and then, the fault point is located without the need of time synchronization. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A New Location Method of Faulty Segment for Hybrid Transmission Lines Based on Transient Travelling Wave Analysis

The paper proposes a new location method of faulty segment for hybrid transmission lines combined with overhead line and cable. Conventional location method of faulty segment identify faulty segment through position calculation of fault point. However, affected by error, the fault at cable-overhead line joint is hard to be identified. In this approach, faulty segment is identified through characteristics comparison of transient travelling wave under different condition. Compared with situation that fault occurs on overhead line, if fault occurs in cable, there is an additional impedance discontinuity in cable. Thus, the amplitude and wave of various reflected wave will change significantly. The proposed method extracts various reflected waves based on time windows and polarity. It makes use of the relative amplitude and time difference between first travelling wave and secondary reflected wave of cable-overhead line joint as criterion of faulty segment location. To verify its effectiveness, fault simulations based on EMTDC are performed; the simulation results reveal that the proposed method can correctly identify the faulty segment for hybrid transmission lines.

Hierarchical distributed model scheme implementation in DC μgrid for numerous ground faults condition

This article presents a new protection scheme for the µgrid structure is implemented on low voltage side as DC system’s protection methods are quite new when compared to the AC systems. The protection system designed in AC system faces many difficulties like frequency matching, reactive power violation, and instability. The main objective of the proposed system is to eliminate the faulty segment promptly while keeping the healthy segments functioning unaltered. In the proposed method, a unitwise controller is designed and is connected in feedback so as to maintain stability under all conditions. The unitwise controller comprises primary and secondary controllers which continually monitor all the units of DC grid comprising semiconductor bidirectional switches and snubber circuits. A primary controller is used for monitoring the complete variation in the parameters in all the units. If the observed parameter value is greater than the acceptable range, the secondary controllers receive the command so as to take the required action to eliminate the faulty segment. Both lines and ground faults are tested on all the sections separately and also simultaneously. The tested results are analyzed in all aspects and the results of the states that the designed protection scheme competent in isolating the defective segment within a short period of time. Once the defective segment is isolated, the other segments retain the stabilized voltage and current limits. The protection scheme is designed and verified using MATLAB/Simulink.

Decentralized Cooperative Control for Smart DC Home With DC Fault Handling Capability

This paper presents a decentralized cooperative control (DCC) method along with a fault segment identification (FSI) scheme to achieve the control and protection objectives for a smart dc home by using only local measurements. The dc home is interfaced with the utility grid via a new modular multilevel converter configuration. Distributed generators are also integrated into the dc home via power converters to guarantee sufficient energy capacity and to support ac and dc loads consumption in the off-grid mode. The proposed DCC method ensures accurate current sharing, dc bus voltage regulation, and fast restoration after the fault clearance. On the other hand, the main objective of the proposed FSI scheme is to quickly identify and isolate the faulty segment to protect the sensitive power electronic components in the dc home from the high fault current. The FSI technique identifies the faulty segment by using only the information extracted from the local current sensor. Time-domain simulation studies using detailed nonlinear models confirm the effectiveness of the proposed control and protection schemes under various normal and faulted operating scenarios. Hardware-in-the-loop studies demonstrate the feasibility of hardware implementation and verify the proposed system performance.

A Novel Protection and Location Scheme for Pole-to-Pole Fault in MMC-MVDC Distribution Grid

Nowadays, the efficient and reliable protection and location schemes for MMC-MVDC (Modular Multilevel Converter-Medium Voltage Direct Current) grid are few. This paper is the first to propose a scheme to not only protect the feeders and the busbar, but locate the segments in MMC-MVDC grid. To improve the reliability, this paper analyzes the transient characteristics of the pole-to-pole fault and then obtains the characteristic frequency band. Based on S-transform, STCFB (S-transform characteristic frequency band) Phase of fault component is utilized to construct the identification criterion for faulty feeder and faulty segment. The whole scheme can be divided into three steps, namely, protection starting criterion, faulty feeder and busbar protection criterion, and faulty segment location criterion. Firstly, the current gradient method is utilized to quickly detect the fault and start the protection device. Secondly, the non-unit protection criterion on busbar and feeders is proposed according to STCFB Phase of the voltage and current fault component. Thirdly, according to the STCFB Phase on both sides of the feeder segment, the faulty segment can be located. A radial MMC-MVDC distribution network model was built in PSCAD/EMTDC software to evaluate the performance of the protection and location method. Simulation results for different cases demonstrate that the proposed scheme has high accuracy, good adaptability and reliability.

Pilot Protection Based on Amplitude of Directional Travelling Wave for Voltage Source Converter-High Voltage Direct Current (VSC-HVDC) Transmission Lines

This paper presents a novel pilot protection scheme of DC cable line in voltage-source-converter (VSC) based multi-terminal DC (MTDC) grids, which utilizes a novel phase-mode transformation to decouple the bipolar DC cable current into six mode and it uses the stationary wavelet transform to extract the modulus maxima of fault initial traveling waves current (FITWC). With accurate amplitude and polarities of the FITWC being collected from the fault-detection devices located at each terminal, the proposed scheme can correctly determine the faulty segment and the faulty pole. In this paper, the ratio of amplitudes between sixth mode forward and backward travelling wave currents is used to judge the faulty segment and the polarity of fifth mode forward travelling wave current is used to identify the faulty pole. A four-terminal VSC-based MTDC grid was built in PSCAD/EMTDC to evaluate the performance of the fault-protection scheme. Simulation results for different cases demonstrate that the proposed protection scheme is robust against noise, and has been tested successfully for fault resistance of up to 400 Ω. Since the scheme merely needs the characteristics of FITWCs, the practical difficulties of detecting subsequent travelling waves are avoided. Moreover, only the state signal is needed to send to the other side in proposed scheme, so low communication speed can satisfy the requirement of relay protection and it does not need the data synchronization seriously.

Two-terminal AF location scheme for multi-segment combined transmission lines using unsynchronized measurements

Arcing faults (AFs) have probabilistic and nonlinear nature which is related to environmental parameters. Thus, the conventional fault location methods can not locate the AFs, accurately. This article puts forward a novel and precise AF location technique for multi-segment combined transmission lines which uses unsynchronized measurements from two terminals of the line. The method consists of stages; the number of them is equal to the number of segments plus one. This scheme does not need to employ a selector to identify the faulty segment of the line. Finally, the case studies are carried out using MATLAB/Simulink with variations of fault conditions including fault distance, type, incidence angle and faulty segment of the line, and also with variations of synchronization angle which show that the presented method provides a high accuracy in AF location under various situations.

Switching High Voltage DC Power in Branching Units of Large-scale Cabled Seafloor Observatories

Cabled Seafloor Observatories(CSOs) are powered by shore stations with DC voltage levels up to -10kV. When a backbone or spur cable fault occurs, the power system must isolate the fault by disconnecting the faulty segment quickly. So the BUs installed in the backbone cable need to carry out the switching operation under high voltages(HV). However, DC circuits have no zero-current points and the fault currents will rise rapidly, bringing a big challenge to the switching on/off operation. In this paper, we have purposed an HVDC circuit breaker based on series-connected IGBTs with voltage balance. Under the backbone voltage of -10kV and a peak current of around 14A, the simulation results show that the proposed design is feasible, with the switching-off time about 1ms.

A Traveling-Wave-Based Fault Location Scheme for MMC-Based Multi-Terminal DC Grids

This paper presents a novel fault location scheme of DC line in modular multilevel converter (MMC)-based multi-terminal DC (MTDC) grids. Considering the low-inertia characteristics and the meshed topology, the scheme, based on traveling-wave principle, is divided into three steps, namely, faulty pole identification, faulty segment determination and fault-distance calculation. With accurate amplitude, polarities and arrival times of the first arrival current traveling waves (FACTWs) collected from time-synchronized measurements taken just at the converter stations, the proposed scheme can correctly determine the faulty pole, the faulty segment and the precise fault location. The continuous wavelet transform (CWT) is deployed to extract the required features of the input signals at the DC lines. Since the scheme merely needs the features of FACTWs, the practical difficulties of detecting subsequent traveling waves are avoided. A four-terminal MMC-based high voltage direct current (HVDC) grid was built in PSCAD/EMTDC software to evaluate the performance of the fault-location scheme. Simulation results for different cases demonstrate that the proposed fault-location scheme has high accuracy, good adaptability and reliability. Furthermore, the algorithm can be used for a MMC-MTDC grid with any number of meshes.

Transient selectivity for enhancing autonomous fault management in unearthed distribution networks with DFIG-based distributed generations

This paper proposes a method for identifying the faulty section in unearthed distribution networks connected with Doubly-Fed Induction Generator (DFIG)-based distributed generation. The proposed method depends on a dedicated transient-based selectivity function that is incorporated in an autonomous fault management procedure. Faulty section discrimination is performed by extracting the relative polarities of the front slopes at the terminals of each section generated by the fault current. The integration procedure of the protection selectivity function with the autonomous control is designed for the unearthed MV networks. Both earth and phase faults are considered in order to realize a broad, versatile and practical classification for such networks. Simulation cases are prepared using the ATP-EMTP package for testing purposes. The results corroborate the efficacy of the proposed method for classifying the faulty segment in distribution networks even for high impedance arcing faults as well as with considerable amounts of distributed wind turbines.

The Design of Location System for Single-Phase Grounded Fault in Distribution Network Based on Zero-Sequence Current

In this paper, A location system for single phase grounded fault in distribution network is proposed and it is based on the phase of zero-sequence current. The system is composed of central station and nodes installed on the power line, and their functions are illustrated in this paper. The principle of the method is shown and experiments are carried out. The results show that the feasibility of the method. The advantage of this method is it’s short time to detect. The method is Applicable to detect the faulty segment for neutral point non-grounded system with grounded resistance less than 1kΩ.