Fault Moment Research Articles

Adaptive feature fusion and disturbance correction for accurate remaining useful life prediction of rolling bearings

As a key component in the transmission system of high-speed trains, bearings need to withstand certain loads while rotating at high speeds. Once a failure occurs, it can directly affect the safety of train operations. Therefore, it is of great significance to establish a reliable remaining useful life model to ensure train operation safety. Addressing the problems of redundant features in the existing multi-feature fusion process, which affects diagnostic performance, and the spurious fluctuations in the fusion features, which cause inaccurate determination of the start fault time and lead to low prediction accuracy of remaining useful life, we propose a method based on adaptive feature fusion and the autoregressive integrated moving average model for rolling bearing prediction. Firstly, features from the time domain, frequency domain, and entropy are extracted. A feature selection mechanism with minimum redundancy is constructed to screen the optimal sensitive feature set. Secondly, based on adaptive feature fusion, the optimal sensitive feature set is dynamically fused, and the spurious fluctuations of the health index are corrected using linear regression and the 3σ principle. Next, a bottom-up time series segmentation method is employed to divide the health status of the Improved Health Indicators. Finally, a remaining useful life prediction model based on the autoregressive integrated moving average model is established. This study demonstrates that the proposed method effectively identifies features that are most sensitive to degradation trends, accurately determines the initial fault moment of bearings, and achieves effective prediction of the remaining useful life of bearings.

Research on single-phase grounding detection method in small-current grounding systems based on image recognition

In small-current grounding systems, the fault current during a single-phase grounding fault is small, and the transient process is complex, leading to challenges in line selection accuracy and reliability. This paper proposes a single-phase grounding line selection method based on transfer learning using the ResNet-50 model. Zero-sequence voltage and current waveforms at the fault moment are preprocessed and combined to generate training data for the model. Simulation results using PSCAD demonstrate that the proposed method achieves 99.77% validation accuracy, even under noisy conditions. These results confirm the method’s feasibility and reliability in identifying grounding faults in various conditions.

Ground fault protection algorithm of active distribution network based on energy extremum direction

AbstractAfter large‐scale distributed power sources are connected to the distribution network, the fault current undergoes noticeable changes, affecting the accuracy of traditional single‐phase grounding fault algorithms. Therefore, the objective of this paper is to address the impact of distributed power integration on the grounding algorithms of distribution networks. The main contribution is: by establishing an electrical system structure and model for distribution network grounding faults that include distributed generation (DG), theoretically deriving and calculating the transient zero‐sequence current frequency changes at the moment of fault, analysing the directional characteristics of zero‐sequence currents under DG connection conditions, designing a local grounding fault judgment algorithm based on energy extremum direction, and providing a fault judgment and isolation process for grounding fault monitoring devices. The results show: through simulation and experimentation, the algorithm was tested, and the method can reliably judge grounding faults under various transition resistances, different numbers and capacities of connected distributed power sources, and different grounding switch‐on angles. The applicability of the algorithm covers both methods of neutral grounding through an arc suppression coil and ungrounded neutrals, adapting to scenarios with or without DG connections.

Transparent Grid Visualization Surveillance and Fault Warning in High Density Distributed Power Access Areas

Abstract Transparent grid, as an advanced form of “Internet + smart energy”, is of great value in supporting energy transformation and promoting the development of new power systems. Based on the grid connection requirements of high-density distributed power supply, this paper provides specific grid connection methods and trend calculations and explores the impact of grid connection on high-density distributed power supply. Subsequently, the technical framework and blueprint of the transparent grid are proposed, combined with the grid visualization system to monitor the grid state visually, and based on the random matrix single-loop theory and ARIMA algorithm to realize fault identification and early warning of the transparent grid. The analysis of the algorithm shows that the fault identification has good rapidity, feasibility, and practicability, and while ensuring that no fault alarm is issued in the case of normal disturbance of distributed power supply, it is able to issue fault alarms for all locations and types of short-circuit faults in the system and determine the fault moment within 0.1s. It is “fast”, “accurate,” and “stable” in the research and judgment of active distribution network faults, and it is more intuitive in the assignment of risk levels, and it can identify the categories and levels of faults and realize the following Visualization of early warning.

Nearest neighbor convex hull for health indicator construction

Developing a suitable and monotonous health index (HI) that can be used to represent a whole degradation process is a key step for continuous machine health monitoring during its life cycle. It is expected that the potential HI is able to inform incipient fault moment and then track machine degradation trajectories effectively and monotonically. Previously, nearest neighbor convex hull classification (NNCHC) has been widely applied for fault classification. In this paper, a HI construction methodology for machine life cycle health monitoring based on NNCHC is proposed. Firstly, a normal convex hull is modeled based on normal vibration data to fully characterize machine health conditions. Afterward, two HIs are constructed based on ℓ 1 norm and ℓ 2 norm distances between the normal convex hull and test points. The superiority of the developed approach in this study lies in the flexible and efficient development of a HI for fault progress tracking. Moreover, the only usage of a normal dataset in the proposed methodology is closer to real application.

Fault characteristics analysis of DFIGWT in whole LVRT process considering control strategy switching between RSC and Crowbar

In order to address the relaying protection issues of the full renewable energy grid, the fault characteristics of the DFIGWT in whole LVRT process should be studied. Currently, researches on fault characteristics of DFIGWT considering crowbar generally assume that crowbar is activated at the moment of fault. However, in fact, the DFIGWT’s fault current characteristics are mainly affected by both (rotor-side converter) RSC and crowbar. The crowbar does not act instantaneously at the moment of fault due to the control system. The DFIGWT is mainly controlled by the RSC before the crowbar is activated. In this paper, the fault process was divided into two stages, namely RSC control stage and crowbar activating stage. The fault characteristics of DFIGWT were analyzed at RSC control stage. Then, the activation time of crowbar was obtained, especially the activation of crowbar due to over-voltage of DC bus was considered. The last values of stator and rotor flux linkages at the first stage were calculated and used as the initial values of the stator and rotor flux linkages at the second stage. Then, the analytical expressions of rotor flux linkage were deduced by Laplace and inverse Laplace transformations. Based on this, the fault mechanism of DFIGWT is resolved and analytical expression of DFIGWT’s short circuit characteristics considering whole LVRT process was proposed. The expression of DFIGWT’s fault current characteristics was verified by the simulation results.The research results are helpful to the construction of relaying protection system for a full-renewable-based system.

Creep Rate Models for the 2023 US National Seismic Hazard Model: Physically Constrained Inversions for the Distribution of Creep on California Faults

Abstract Widespread surface creep is observed across a number of active faults included in the United States (US) National Seismic Hazard Model (NSHM). In northern California, creep occurs on the central section of the San Andreas fault, along the Hayward and Calaveras faults through the San Francisco Bay Area, and to the north coast region along the Maacama and Bartlett Springs faults. In southern California, creep is observed across the Coachella segment of the San Andreas fault, through the Brawley Seismic Zone, and along the Imperial and Superstition Hills faults. Seismic hazard assessments for California have accounted for creep using various data and methods, including the most recent Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3) in 2013. The purpose of this study is to expand and update the UCERF3 creep rate data set for the 2023 release of the US NSHM and to invert geodetic data and the surface creep rate data for the spatial distribution of interseismic fault creep on California faults using an elastic model with physical creep constraints. The updated surface creep rate compilation consists of a variety of data types including alignment arrays, offset cultural markers, creepmeters, Interferometric Synthetic Aperture Radar, and Global Positioning System data. We compile a total of 497 surface creep rate measurements, 400 of which are new and 97 of which appear in the UCERF3 compilation. We compute creep rate distributions for each of the five 2023 NSHM geodetic-based and geologic-based deformation models. Computed creep rates are used to reduce the total fault moment rate available for earthquake sequences in the NSHM model. We find that, despite relatively large variability in model long-term slip rates across all five deformation models, the variability in depth-averaged creep rate across all models is relatively small, typically 5–10 mm/yr along the creeping San Andreas fault section and only 2–4 mm/yr along the Maacama and Rodgers Creek-Hayward faults.

A new approach to improving the sensitivity of earthing relay and reducing the over-voltage in 6 kV grid of open-pit mines

Purpose. Earthing relays are utilized very commonly in open-pit mines for disconnecting the failure part of 6 kV electric system from earthing incident. Much previous research is mentioned on searching either an optimal method for improving the effect of relays or improvements of reducing the overvoltage caused by grounding separately. The paper presents a new approach to not only improving the relays sensitivity but also to limiting the over-voltage. A new algorithm is also proposed to control automatic connection of an additional resistor in order to achieve both above mentioned purposes of 6 kV earthing relay. Methodology. The propose controlling diagram is implemented on PROTEUS to get 3U0 signals. The main components appeared when 6 kV feeders were faulted to earth. Afterward, the detecting signal is utilized as input for simulation diagram in MATLAB to get and analyze the wave forms of responded zero sequence voltage. Findings. The paper presents a new algorithm utilizing a resistor that is auto-controlled to auto-connect the open-triangle coil of 6 kV measurement transformer at the moment of earth fault. This automatic connection aims to increase the relay sensitivity as well as reduce the overvoltage. The finding results are sensitivity factors of relay and voltage magnitudes of healthy phases, which will be compared with corresponding values when there is no connection of resistor to prove the effectiveness of the method. Originality. A useful method is proposed for increasing the earthing current to enhance the sensitivity of earthing relay. Practical value. The proposed control diagram could be used to design a device aiming to improve the safety of 6 kV grid in open pit mines when earth faults occur.

Space-time evolution of Longmenshan fault coupling and moment deficit inverted by multi-source geodetic data

Space-time evolution of Longmenshan fault coupling and moment deficit inverted by multi-source geodetic data

Application of an ensemble earthquake rate model in Italy, considering seismic catalogs and fault moment release

We develop an ensemble earthquake rate model that provides spatially variable time-independent (Poisson) long-term annual occurrence rates of seismic events throughout Italy, for magnitude bin of 0.1 units from Mw ≥ 4.5 in spatial cells of 0.1° × 0.1°. We weighed seismic activity rates of smoothed seismicity and fault-based inputs to build our earthquake rupture forecast model, merging it into a single ensemble model. Both inputs adopt a tapered Gutenberg-Richter relation with a single b-value and a single corner magnitude estimated by earthquakes catalog. The spatial smoothed seismicity was obtained using the classical kernel smoothing method with the inclusion of magnitude dependent completeness periods applied to the Historical (CPTI15) and Instrumental seismic catalogs. For each seismogenic source provided by the Database of the Individual Seismogenic Sources (DISS), we computed the annual rate of the events above Mw 4.5, assuming that the seismic moments of the earthquakes generated by each fault are distributed according to the tapered Gutenberg-Richter relation with the same parameters of the smoothed seismicity models. Comparing seismic annual rates of the catalogs with those of the seismogenic sources, we realized that there is a good agreement between these rates in Central Apennines zones, whereas the seismogenic rates are higher than those of the catalogs in the north east and south of Italy. We also tested our model against the strong Italian earthquakes (Mw 5.5+), in order to check if the total number (N-test) and the spatial distribution (S-test) of these events was compatible with our model, obtaining good results, i.e. high p-values in the test. The final model will be a branch of the new Italian seismic hazard map.

Faulty Feeder Detection Based on Space Relative Distance for Compensated Distribution Network With IIDG Injections

To improve the accuracy of faulty feeder selection based on zero sequence current mutation, distribution networks with inverter-interfaced distributed generators (IIDGs) are analyzed in detail. It is found that the IIDGs cannot be completely equivalent to a positive sequence current source due to their boosting increments. Thereby, a more accurate IIDG current estimation model based on the Gauss-Seidel method that considers the control strategy at the moment of fault is established. Moreover, a real-time estimation algorithm is introduced for faulty feeder detection to adjust the compensation degree of the Petersen coil. On this basis, this paper proposes a novel faulty feeder detection approach using the zero-sequence current space relative distance between the increments of each feeder and an estimation of the faulty path generated by Kalman filtering (KAF). The feasibility of the proposed approach is demonstrated in both a PSCAD/EMTDC simulation and a MATLAB experimental laboratory. The test results indicate that the proposed approach can achieve a high speed when employed for different fault conditions.

Characteristics and restraining strategy of fault current in VSG

With the increase of distributed generation (DG), DG is needed to provide inertia for the grid to maintain the security and stability of the grid. Therefore, the virtual synchronous generator (VSG) technology is proposed to compensate for the loss of inertia and reserve capacity. Similar to SGs, the large transient inrush fault current will flow into VSG at the moment of fault, which may lead to the damage of inverters and the instability of the power grid. Therefore, the characteristics of the inrush fault current of the VSG are studied. On the basis of this, a fault current limitation strategy based on adaptive virtual impedance is proposed, and its effectiveness is verified by simulation.

Influence of transition resistance and fault moment on DC system commutation process caused by two‐phase fault of AC system

Commutation failure caused by the fault of AC system at inverter side seriously affects the safety and stability of high-voltage direct current (HVDC) system. Although two-phase fault is a typical asymmetrical fault, the studies on commutation failure caused by two-phase fault are few compared with the studies on commutation failure caused by three-phase fault or single-phase fault. In this study, the features of two-phase fault occurring on commutation bus is analysed theoretically. The analysis shows that the transition resistance will affect the amplitude and phase of the commutation voltage at Y-Y and Y-D1 transformer valve sides. Furthermore, the change regularity of the commutation voltage along with the change of transition resistance is given. Taking interphase short circuit as an example, the influence of different fault moments on commutation process is studied. For the first commutation process before the fault, the possible cases of commutation failure are given for fault moments in one cycle. For the first commutation process after the fault, a calculation method of critical voltage drop is given. Simulation results verify the correctness of the analysis.

TOV in SMs during MMC riding through zero DC voltage fault: analysis and suppression

A comprehensive analysis and a suppression method of sub-modules’ (SMs’) transient over-voltage (TOV) in a hybrid modular multilevel converter are presented, consisting of half half-bridge SMs and half full-bridge SMs, during riding through zero DC voltage faults. Analytical expressions of SMs’ TOV are initially explored. The relations among transient voltages of SMs in six arms with the same fault moment and those in a fixed arm with different fault moments are deduced. Furthermore, the maximum value of SMs’ transient voltages dependent on the fault moment is also presented. A suppression method using common-mode voltage injection is proposed without sacrificing the performance of the converter on riding through zero DC voltage faults. Simulated results are provided to demonstrate the validity of the analytical results and the feasibility of the proposed suppression scheme.

Threshold selector for fault detection on closed-loop predictor-based recursive system identification

In this research, a technique is developed to separate an additive fault from a multiplicative fault by using recursive update of predictor-based system identification. If additive fault occurs at the same moment of multiplicative fault in a system, the recursively updated system model can take away the effect of multiplicative fault from residual. Thus, purely additive fault affects on residual of which threshold is calculated based on Chi-squared distribution. In this research, the Chi-squared residual is computed as whitened-residual and its whitening covariance matrix is derived from residual itself in order to accommodate identification error. To detect multiplicative fault, the norm to measure the distance between the original system matrices and the changed is recursively checked with user-defined parameter. The benefit of this approach is illustrated with an adopted system.

Determining the efficiency of the compensation of single-phase capacitive earth currents using arc-suppression coils of different designs implemented in an experimental workbench

Results of the experimental comparison of the compensation of single-phase capacitive earth currents using arc-suppression coils of two cardinally different designs, i.e., plunger-type coils and coils controlled by magnetic bias, are presented. It was previously shown using the simple formula and the calculation grid model that the response time of the reactors determined through the time required to compensate the power component of the earth current depended on the phase angle of the voltage at the moment of earth fault [1]. If the earth fault occurs not at the moment of the maximum voltage, an aperiodic component appears in the coil current, which makes it impossible to compensate instantaneously the capacitive earth current. An experimental workbench with a voltage of 6 kV used to carry out the measurements is described. The measurement results show that the coils of both designs have similar response times, which are on average of the order of a few hundreds of milliseconds; these values substantially exceed the implied values of the response time of the coils. It is shown that the response time of the coils cannot be the criterion for their efficient operation. Therefore, to compensate for an intermittent arc capacitive earth fault, a comparative criterion for assessing the efficiency of the operation of the coil is proposed, which is based on the average value of the energy dissipated the site of fault.

Short Circuit Fault Classification and Lo cation in Transmission Lines Using A Combination of Wavelet Transform and Support Vector Machines

In this paper, a modern synthetic framework which has the capability to rap- idly Classify and locate short circuit faults over transmission lines is presented. The proposed algorithm singles out short circuit faults based on the measured voltage wave- form and three-phase current when fault events occur in power transmission lines. The values resulting from the three-phase currents and the three-phase voltages wavelet transform are used to fault classification algorithm. Then, fault location algorithm is ac- tivated as the result of fault classification. Different kinds of methods such as multilevel wavelet transform and support vector machine have been combined in a set to determine fault classification and location at every time. This paper lays out the fundamental con- cept of the proposed framework and introduces a pattern recognition approach via wavelet transform, statistical processing techniques, neural network (NN) and a joint decision-making mechanism. Voltage and the recorded current values in measurement devices from the fault moment to a quarter of post-fault have been used for pre- processing and training in the support vectors machines.

Power System Fault Diagnosis Based on Wavelet Transform and Neural Networks

Using the principle of wavelet transform in the aspect of signal singularity detection analyzes and detects the electric power system fault signal. Then we extract signal feature near the fault moment and sent the feature vectors into the neural network. The simulation results fully prove the effectiveness and superiority of combining wavelet transform and neural network in electric power system fault recognition.

Focal mechanism and rupture process of the 2012 M w 7.0 Santa Isabel, Mexico earthquake inverted by teleseismic data

The point source parameters of the April 12, 2012 Mw 7.0 Santa Isabel, Mexico, earthquake indicated by teleseismic P and SH waveforms obtained by a means of traditional cut and paste (CAP) method show that the best double-couple solution of this event is: 37°/127°, 90°/81° and −9°/−180° for strike, dip and rake, respectively. Its centroid depth is 13 km. Global teleseismic waveform data exhibit that the rupture of the earthquake initiated at a focal depth of 13 km and propagated southeastward with a relatively slow rupture velocity (about 1.8 km/s on average). The maximum slip occurred at 30 km southeast of the hypocenter, with the peak slip of 3.57 m and total seismic moment of whole fault up to 3.98×1019 N·m. These observations provide some insight into properties, co- or post-seismic deformation and coulomb stress changes of future earthquake in this area.

Fault Current Management Using Inverter-Based Distributed Generators in Smart Grids

This paper presents a novel fault current management (FCM) technique for radial distribution systems with embedded inverter-based distributed generators (IB-DGs). At the point of connection to a power system, many distributed generators (DGs) require power electronic (PE) interfaces, which are normally idle during faults. The proposed FCM method employs these PE interfaces for control of the fault current. For this purpose, operation of IB-DGs is modified to FCM mode at the moment of fault and new current references are applied. Of the two controllable parameters of the IB-DG output current-current magnitude and current phase angle-the current phase angle is chosen as the means of controlling the fault current magnitude. The reference current phase angle is calculated based on the relation between the fault current elements and their phase angles. As a result of this novel operation, IB-DGs with larger capacity can be connected at different locations of the system without affecting the fault current magnitude. Also, implementing this technique in smart grids is economically proven, since the asset of power system which have been designed for normal operation are employed to manage the fault current magnitude. Moreover, possibilities of synchronization problems are reduced by keeping IB-DGs connected to the system at all the time. The evaluation of the proposed FCM technique using the standard IEEE 33-bus distribution system demonstrates the effectiveness of the proposed method for managing the fault current magnitude.