Fault Current Research Articles

A Period Energy Method for Demagnetization Detection in Surface Permanent Magnet Motors with Search Coils

Irreversible demagnetization of permanent magnets (PMs) in PM synchronous motors (PMSMs) degrades the performance and efficiency of a machine and its drive system. There are numerous fault diagnosis methods for detecting demagnetization under steady-state conditions. However, only a few works could be found on fault diagnosis under dynamic conditions, whereas the dynamic operation of a motor is a very common scenario, e.g., electric vehicles. The voltage and current signal-based traditional fault detection method is not only affected by the structure of the motor, but it also becomes complicated to extract signals involving fault characteristics. Hence, this paper proposes a search coil-based online method for detecting demagnetization faults in PMSMs under dynamic conditions, which are not affected by the motor structure. To gather the flux of the stator tooth, flexible Printed circuit board (FPCB) search coils are positioned at the stator slot. The search coil is made up of two branches that are one pole apart and arranged in reverse sequence. In this installation option, the output signal in the fault state cannot be eliminated, and the output signal in the health state is zero. This paper defines only that characteristic value related to the position angle of the rotor. Further, the aim was to simultaneously eliminate the influence of elements like the search coil installation error and the inherent dispersion of the permanent magnet on the detection results. To characterize the fault degree, the measurement differential between the health state and the fault state is further integrated according to a predetermined angle range. Last but not least, speed-independent detection of individual permanent magnet demagnetization faults is possible using rotor position and stator tooth flux. A six-phase PMSM was used in experiments to show the efficiency of the suggested approach. The findings of the experiment demonstrate that the suggested strategy may precisely ascertain when a defect will occur.

Estimating distance to transient and restriking earth faults in high-impedance grounded, ring-operated distribution networks using current ratios

Earth faults occur frequently in distribution networks, and in resonant grounded networks they are challenging to locate precisely due to their naturally low fault current. Transient and restriking faults are more challenging still due to the short time available for the fault location logic, as well as the absence of steady-state conditions. This paper investigates the performance of three fault location methods utilizing the ratios of various current components in a network operated in a closed-ring configuration. A frequency dependent model of a distribution network is used to simulate transient and restriking faults, and both isolated grounding and resonance grounding are considered. The results show that fault location based on negative-sequence currents is able to locate transient faults, and its accuracy of a few hundred metres is comparable to what has been observed during permanent faults. A zero-sequence method is observed to be less accurate, particularly in resonant grounded networks. A transient method is also proposed, and while it is fast, it is ultimately limited by the presence of loads and branches in the network. It is concluded that the negative sequence method is best suited for transient and restriking faults.

An active pole-to-ground fault location scheme for FB-MMC-MTDC system using the short-time blocking of sub-modules

The pole-to-ground (PTG) fault current is small in the multi-terminal direct current (MTDC) system, which cannot be used to locate the fault. This paper proposes a PTG fault location scheme for MTDC based on full bridge modular multilevel converter (FB-MMC), by actively blocking the sub-modules (SMs). The SMs blocking generates a voltage pulse wave which travels between the MMC and the fault point. By using the wave polarity analysis method, the reflected wave from fault point can be identified. The improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) is used to detect the reflected wave arrival time. The time difference between pulse start time and reflection arrival time is processed for fault location. A four-terminal MMC-MTDC simulation model established in PSCAD/EMTDC validates the proposed method have not affected the power transmission. Afterwards, the fault location accuracy under the influences of fault type, fault location and fault impedance issues are also confirmed.

Adaptive Leakage Protection for Low-Voltage Distribution Systems Based on SSA-BP Neural Network

The fluctuation of normal leakage current has a great influence on the fixed-threshold leakage protector. To address this issue, this paper proposes an adaptive leakage protection method based on the sparrow search algorithm (SSA)-backpropagation (BP) neural network. Based on the analysis of the normal leakage current generation mechanism, this method uses the SSA optimized BP neural network to construct a prediction model of normal leakage current. By dividing the normal leakage range into several intervals and setting the corresponding action threshold, the action threshold of the interval is automatically selected in advance, based on the predicted value of the model, so as to realize the adaptive protection of the leakage current faults. Experiments have proved that the leakage protector can identify the leakage fault more sensitively and increase the ratio of the protector put into operation by predicting the development of normal leakage current and adjusting the protection action threshold in advance.

Highly sensitive multifunction protection coordination scheme for improved reliability of power systems with distributed generation (PVs)

AbstractThe high penetration of distribution generators (DGs), such as photovoltaic (PV), has made optimal overcurrent coordination a major concern for power protection. In the literature, the conventional single or multi‐objective function (OF) for phase overcurrent relays (OCRs) scheme faces challenges in terms of stability, sensitivity, and selectivity to handle the integration of DGs and ground fault scenarios. In this work, a new optimal OCR coordination scheme has been developed as a multifunction scheme for phase and ground events using standard and non‐standard tripping characteristics. This research introduces and validates a coordinated optimum strategy based on two new optimization approaches, the Tug of War Optimization algorithm (TWO) and the Charged System Search algorithm (CSS), to mitigate the effects of DGs on fault currents and locations across the power network. Industrial software is used to create a case study of a CIGRE power network equipped with two 10 MW PV systems, and the results of the proposed new optimum coordination scheme are compared to traditional schemes. The findings show that the proposed multifunction OCR scheme is able to reduce the tripping time of OCRs over different fault and grid operation scenarios and increase the sensitivity of the relays in islanding operation mode.

Rolling bearing fault diagnosis based on multi-scale weighted visibility graph and multi-channel graph convolution network

Current data-driven fault diagnosis methods are prone to overfitting and a decrease in accuracy when working with only a limited number of labeled samples. Additionally, existing graph neural network-based fault diagnosis methods often fail to comprehensively utilize both global and local features. To address these challenges, we propose a rolling bearing fault diagnosis method based on multi-scale weighted visibility graph and a multi-channel graph convolutional network (MCGCN). Our approach converts vibration signals into multiple weighted graphs from the perspective of geometric meaning and extracts local node feature information and global topology information of graphs using MCGCN. Experimental results demonstrate that our method achieves excellent performance under both sufficient and limited data conditions, providing a promising approach for real-world industrial bearing fault diagnosis.

Analysis on Protection Coordination of OCRs Using Index for Impedance Compensation Considering Unsymmetrical Ground Fault in a Power Distribution System With SFCL

The superconducting fault current limiter (SFCL) has been spotlighted as the effective device to limit the fault current because it has no effect on a power distribution system in a normal time due to its zero resistance. However, the SFCL causes the trip of the overcurrent relays (OCRs) to be delayed due to the reduc-tion of the fault current, which causes a negative impact on the protection coordination of power distribution system. The delayed trip of OCR makes the exposure time's increase of the neighboring power facilities from the fault current at fault line. In this paper, the OCR's index for the impedance compensation of the SFCL in case of the unsymmetrical ground fault was suggested. The sug-gested OCR's index consists of all sequence components for the impedance, calculated from the voltages and the currents meas-ured from both the power distribution system and the SFCL. To prove the effectiveness of algorithm, the protection coordination between OCRs in a power distribution system with the SFCL were analyzed for the unsymmetrical ground fault as well as the sym-metrical ground fault through the simulation using PSCAD/ EMTDC.

Current Limiting Simulation of Magneto-biased Superconducting Fault Current Limiter (SFCL)Applied in 66 kV/10 kV Power Substation in China

The short-circuit fault currents in the large capacity transmission lines pose a challenge to the stability and safety of power system. Magneto-biased superconducting fault current limiter (MBSFCL) is with the advantages of two-stage current limiting, self-triggering and fast recovery so that it can effectively reduce the short-circuit fault current when applied to the urban power system. This paper analyzes the operation principle of MBSFCL and establishes a package type magneto-thermal coupled simulation model of MBSFCL based on MATLAB/SIMULINK. A power system model of a 66 kV/10 kV Zhang Tai Zi power substation which is in Liaoning province in China has been established and the grid-connected simulation applied MBSFCL has been achieved. Moreover, the grid-connected test is carried out, and the results of fault current, quench resistance and temperature change are obtained. The comparison of results between simulation and test verifies the accuracy of the simulation model and the application feasibility of MBSFCL.

Operation Characteristics of a Mechanical DC Circuit Breaker With a Resistive Superconducting Element for High-Reliability HVDC Applications

The issue of DC transmission and distribution systems is increasing due to the increase in DC supply and demand. The fu-ture MTDC (Multi-Terminal HVDC) system is becoming a big issue beyond the general PTP (Point to Point) HVDC system. We live in an era where the super grid is gradually expanding. However, the protection device is required to protect the grid conversion equip-ment from fault currents during line transients to progress from the HVDC stage to the MTDC stage in PTP. The DC fault current, about ten times higher than AC, occurs at a very high speed because of the lack of zero-crossings. We propose a resistive-mechanical DC circuit breaker with a resistive superconducting element is a com-bined model of a resistance-type superconducting element and a me-chanical DC circuit breaker. In detail, it limits the initial fault cur-rent by quenching the resistive superconducting element. Also, it creates an artificial zero-crossing through the LC divergence oscil-lation circuit of the mechanical DC circuit breaker to perform safe fault protection. In this paper, the fault protection of the resistive-mechanical DC circuit breaker with a resistive superconducting el-ement was tested to confirm the current limiting rate of the initial fault current, the artificial zero-crossing, and the total cutoff time. As a result, the initial fault current was limited by about 17.3% by quenching the resistive-superconducting element.

A Novel Fault Current Full Compensation Method in Active Flexible Grounding Distribution Networks

As the power equipment represented by the inverter is gradually increasing in the power systems, the residual capacitive component of the grounding fault current cannot be ignored. To solve the problem of insufficient compensation for capacitive components in the traditional arc suppression coil grounding mode, a grounding fault current full compensation method based on the active flexible grounding mode was proposed. First, the principle of full compensation in the active flexible grounding mode was analyzed to provide a reference for the injected current of voltage arc suppression full compensation. Then, the inverter control system was designed, and a closed-loop control method was proposed, both of which can ensure the stable target current of the system. Finally, the simulation results compare the fault current compensation difference between the two grounding modes, and the practicability of the proposed compensation method was verified.

Applicability Analysis of a Multi-Filar Meander R-SFCL and an RSC-DCCB in an MMC-MTDC Grid

modular multilevel converters (MMC)-based high voltage direct current (HVDC) topology is an effective solution to solve the power transmission demand between countries. However, the initial fault current can rise to several tens of kA within a few ms by capacitor discharge during a fault. This fault current can permanently damage the converter components and cables. Therefore, to increase the stability of the system, the protection of the DC system is very important. DC system protection methods include circuit breaker technologies and current limiting technologies. We have selected a circuit breaker with combined resonant current source (RCS) and a resistive superconducting fault current limiter (SFCL) as protection methods for the DC system. The RSC-DC circuit breaker has no conduction power losses by on-state voltage drop. Therefore, it can provide stable interruption compared to a solid-state DC circuit breaker. Since the resistive SFCL has a very fast response time, it can effectively limit the rapidly rising initial fault current. We wound the superconducting tape by the multi-filar meander method. This method can increase the length of the superconducting tape used and speed up the bubble diffusion during quenching. We modeled an MMC-HVDC grid, resistive SFCL, and RCS DC circuit breaker using PSCAD/EMTDC. In this paper, the interrupting and current limiting characteristics are discussed when the resistive SFCL and the RCS-DC circuit breaker proposed by us are connected to the MMC-based MTDC grid. In the simulation, the current limiting factor of resistive SFCL was up to about 58%. In addition, the combination of resistive SFCL and RCS-DC circuit breaker can shorten the interruption time when the fault occurs.

A Study on Increasing the Capacity of Transformer-Type Superconducting DC Circuit Breaker

Superconducting Fault Current Limiter (SFCL) can increasethefaultcurrent-limitingratethroughtheseriesconnection of superconducting elements, and through this, it can be applied to systems with high capacity. However, when multiple superconduct-ing elements are connected in series, unbalanced quench character-istics may occur continuously due to problems of critical character-istics andpartialquenching.Wehaveproposedaquenching method ofbalancedSFCLusingthe neutrallinetosolvethisproblem.Inthis paper, we applied several superconducting elements with the neu-trallinetoincreasethecurrent-limitingrateofthetransformer-type superconducting current limiter module (T-SFCL module). Inaddi-tion, when the T-SFCL module was combined with the DC circuit breaker, the operating characteristics of the superconducting DC circuit breaker were confirmed. As a result, power consumption of superconducting elements was balanced due tothe balanced quench of superconducting element, and fault current was reduced due to the highcurrentlimitingcharacteristics of superconducting element.

A Fast and Robust Local-Based Protection Algorithm Based on the High-Frequency Transient for HVDC Grid

With the expansion of HVDC grids, short-circuit faults and their protection issues are among the main challenges of these networks, which should be given more attention. This study presents an investigation of the DC side fault current in HVDC grids during the transient period. Also, a fast and robust protection algorithm is introduced that is essential for secure and appropriate HVDC grids operation. The Short-Time Fourier Transform (STFT) is applied to extract the frequency components of the fault current, and the time features of these components are utilized as the basis of the proposed algorithm. A four-terminal cable-based HVDC grid with bipolar configuration is modeled via EMTP, and a wide range of simulation scenarios are applied for various fault locations, fault impedances, and operation points. Furthermore, the algorithm thresholds are determined with the explicit procedure. Simulation results indicate that the proposed method is fast, selective, sensitive, and robust against AC-side fault, operating condition variations, fault distance, and fault direction. Also, it has an appropriate performance during high impedance faults.

A Bidirectional Efficient Circuit Breaker With Automatic and Controllable Shutoff Functions for DC Distribution Network

Compared with the solid-state circuit breakers based on IGBT and MOSFET, circuit breakers based on thyristor have higher capacity and lower cost, which have been extensively studied. However, the existing circuit breakers based on thyristor cannot achieve fast and reliable shutoff of the fault current. Therefore, a novel efficient bidirectional circuit breaker is proposed in this paper, which has the functions of automatic and controllable shutoff. In any current direction, only one thyristor is conductive, which eliminates the unnecessary power losses. The automatic shutoff function can cut off the fault current independently without detection delay. The controllable shutoff function can isolate the fault reliably without being affected by the line inductance. The proposed topology integrates the advantages of high efficiency, fast reaction and high reliability. Although the existing bidirectional circuit breakers based on thyristor may have one of these advantages, no circuit breaker integrates all of them. Finally, the proposed circuit breaker is verified through simulation and experiment of 1.2kW.

Prevention of Oil-Immersed Equipment Rupture Due to Arcing Faults Based on Metal Foam

Oil-immersed power equipment, even when equipped with complete relay protection devices, is still exposed to a risk of rupture and explosion. During an internal arcing fault, such equipment will suffer from overpressure before the fault current is interrupted by circuit breakers. In this letter, a novel approach based on metal foam is proposed for preventing oil-filled equipment rupture. Specifically, density-layered aluminum foam sandwich panels are designed for use as sacrificial claddings to promptly mitigate arc-induced overpressure by absorbing energy through deformation. An actual arcing fault test platform with two limited closed tanks was established, and a multicharacteristic measurement system with pressure sensors and laser displacement sensors was used. Field arcing test results under various fault levels demonstrate the effectiveness of the presented method. Furthermore, the detailed morphology of metal foam, observed by a scanning electron microscope (SEM), indicates that the impact energy was partially absorbed through microscopic deformation. The proposed method provides new insight into fast overpressure mitigation and serves as a potential countermeasure to the challenging problem of equipment rupture.

Operational failure mechanisms of electromagnetic potential transformer

In response to the problem of transformers blowing up or even burning up together with detuning devices in recent years, an assessment method based on the equivalent of transformer winding currents is proposed for potential transformers (Potential Transformer, PT) in low and medium voltage distribution networks. Firstly, the damage mechanism of potential transformers is analyzed and the thermal breakdown is identified as the main cause of damage to the winding insulation. At the same time, the winding currents under different faults are analyzed theoretically to identify the characteristics of various fault currents. Secondly, an operational failure indicator based on thermal equivalence, i.e. the fault current threshold indicator, is proposed in conjunction with the general voltage transformer specification. Finally, the proposed indicator is verified by means of ATP simulation software and combined with simulation tests. The results show that the proposed index can accurately reflect the winding failure of potential transformers, and the research results can provide a reference for the selection of potential transformers and the prevention of insulation breakdown.

Mechanism of Recovery Performance Improvement With Porous-Stabilized REBCO Tape for Resistive-Type Superconducting Fault Current Limiters

Resistive-type superconducting fault current limiters (R-SFCLs) utilizing rare-earth barium copper oxide (REBCO) tapes have been developed to limit fault currents. To balance recovery and current-limiting performances, a porous-stabilized REBCO tape was proposed. The experimental results showed that using a porous stabilizer with the REBCO tape and insulating epoxy reduced recovery time to 25%. However, the underlying mechanisms of this improvement in recovery performance are not yet clear. The aim of the present study is to understand these mechanisms. To do so, a vapor-film-collapse model was proposed to clarify the impact of the insulating epoxy on vapor film collapse. This model suggests that when liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) comes into contact with the insulating epoxy, it causes a rapid decrease in the temperature of the insulating epoxy surface, leading to the collapse of the vapor film. Additionally, a liquid-retention model was proposed to investigate the effect of the porous stabilizer. This model indicates that if the porous stabilizer can retain LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the equivalent heat flux observed in experiments can be achieved through evaporation of the retained LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Experimental investigation of a real-time singularity-based fault diagnosis method for five-phase PMSG-based tidal current applications

This paper presents a novel real-time singularity-based fault diagnosis method for tidal current applications, specifically utilizing a five-phase permanent magnet synchronous generator with trapezoidal back electromotive forces. The proposed method incorporates an innovative orthogonal signal generator through a second-order filter, enabling the extraction of detectable singularity signatures from phase current signals. The principle of the method is elucidated through step-by-step design procedures, outlining the indicator enhancement approach and adaptive thresholds employed for enhanced robustness and adaptability. Fault detection is performed based on the improved fault indicators and an adaptive threshold law, followed by immediate fault localization that is achieved via twice average operations of the phase currents. To demonstrate the effectiveness and efficiency of the proposed method, a comparative study is carried out with a classical mean current vector-based fault diagnosis method. A small-scale experimental platform emulating a tidal current application is established for a comprehensive evaluation of both methods. The experimental results highlight the superior fault diagnosis performance of the proposed method, particularly in detecting single and multiple open circuit faults in phases or switches, while exhibiting enhanced robustness against variations in torque and speed. The simplicity of implementation and rapid detection mechanism are principal merits for the proposed method.

Single-phase broken-line fault of a 10 kV ungrounded distribution Line

In recent years, a great many applications of overhead insulated lines in distribution networks have reduced the occurrence of single-phase ground faults, and at the same time made broken-line faults a problem that cannot be ignored. Timely fault detection and fault location are of great help to reduce power outages and improve the quality of power supply for users. Aiming at the ungrounded system, this article designs a single-phase broken-line model, considers the influence of abort situation and others, analyses the fault characteristics such as sequence current and neutral point offset voltage, and then advances a fault model according to negative sequence current and neutral point offset voltage fault detection method. Lastly, the validity of the suggested way is confirmed by MTALAB.

Automatic fault location method for power communication network based on a machine learning algorithm

The current conventional automatic fault location method of power communication network mainly realizes the identification of faulty branches by calculating node power parameters, which leads to poor location effects due to the lack of effective analysis of fault signal data. In this regard, the automatic fault location method of the store head communication network based on a machine learning algorithm is proposed. Firstly, the fault signal data are collected and pre-processed, specifically including data cleaning and data format conversion, and then the individual fault signal is used as the basis to differentiate the weight parameters of different abnormal degrees and combine with the state threshold to realize the judgment of the fault node interval location. In the experiments, the fault location performance of the proposed method is verified. The experimental results show that when the proposed method is used for fault location, the relative positioning error value of the method is small and has a high fault location accuracy.