Fault Period Research Articles

Surrounding rock control technology for the fault passing of mining face by removing gangue in advance from excavation roadways

This study presents a new technology for passing through faults quickly by removing gangue in advance from driving roadways of working faces; this technology has the advantages of short moving time and good coal quality during fault passing. However, in practice, driving roadways are affected by mining pressure during the driving and mining period; thus, roadway support is difficult. This study aims to develop appropriate support for driving roadways, not only to ensure the stability of the roadway and satisfy the space requirements for the working face when it passes through the fault but also to reduce the strength of the rock pillars in the roadway. In this manner, the shearer can directly reduce the working strength during the period of fault passing. In this study, UDEC numerical simulation software is used to explore the size of rock pillars and the parameters of bolt support. In addition, the supporting effect of ordinary, high-strength prestressed, and high-strength prestressed yielding bolts is compared. On the basis of the simulation results, a reasonable control scheme of surrounding rock in advanced driving roadways is proposed. Moreover, the successful application of the technology in field practice shows the remarkable effect of this scheme on the surrounding rock control when passing faults. Thus, this study provides some references for surrounding rock control during the fault passing of the mining face.

Augmentation of DC-Link Protection System of PMSG Based Wind Turbine Using Fuzzy Logic Controlled Buck Controller System

Recently, permanent magnet synchronous generator (PMSG) is one of the most familiar type of generator for wind power plant (WPP). Generally, PMSG is connected to gird using back to back converter. During fault period, power imbalance situation is happened between machine side and gird converter. As a result, the DC-link voltage can be rise significantly which can damage the whole converter system. In this paper, a novel DC-Link protection system of buck converter based on fuzzy logic is designed in order to augment the transient stability of the PMSG system. The new buck converter along with its control system is designed to manage the supplied voltage of the braking resistor during fault period. For investigating the performance of the proposed system, fault analysis is performed on different case scenarios PSCAD/EMTDC software.

Non-Unit Protection for HVDC Grids: An Analytical Approach for Wavelet Transform-Based Schemes

Speed and selectivity of DC fault protection are critical for High-Voltage DC (HVDC) grids and present significant technical and economic challenges. Therefore, this paper proposes a non-unit protection solution that detects and discriminates DC faults based on frequency domain analysis of the transient period of DC faults. The representation of a generic HVDC grid section and the corresponding DC-side fault signatures in the frequency domain form the basis of a generalized approach for analytically designing a protection scheme based on Wavelet Transform (WT). The proposed solution is adaptive within its design stage and offers general applicability and immunity to system changes, while the protection settings are configured for optimized performance. The scheme is validated through offline simulations in PSCAD/EMTDC and the technical feasibility of the algorithm in the real world is demonstrated through the use of real-time digital simulation (using RTDS) and Hardware-in-the-Loop (HIL) testing. Both offline and real-time simulations demonstrate that the scheme is able to detect and discriminate between internal and external faults at a significantly high speed, while remaining sensitive to high impedance faults and robust to external disturbances and outside noise.

Investigation of diode dynamic effect on fault detection of photovoltaic systems

Abstract This study proposes a new fault diagnosis algorithm for a photovoltaic (PV) solar system implemented on the bases of diode distribution and two classifiers based on ensemble bagged trees and neural pattern recognition techniques. The proposed approach is designed by adding two diodes connected to the upper and lower terminals of each PV string. The two diodes are connected to prevent the reverse direction of faulted string currents, thereby preventing high injecting fault currents. Given that the string fault current is prevented owing to diode interaction, this dynamic interaction provides new states during the fault periods considered to detect string faults. Owing to the distributed diodes, system voltage is not reduced during fault disturbances and voltage is not considered an input to the proposed detection techniques. Monitoring currents at the upper and lower ends of each string is required as input for the proposed approaches to detect string fault types. The proposed approaches are used to detect string fault types, such as cell-to-string negative terminal, cell-to-cell in the same string, and string-to-string faults. The proposed model is applied for 400 kW, and the PV system consists of 4 arrays interconnected with 1200 V AC grid built-in MATLAB/Simulink. Experimental results validate the newly suggested approaches.

Phasor-based fault location challenges and solutions for transmission lines equipped with high-speed time-domain protective relays

This paper presents a study on the performance of phasor-based fault location methods under reduced fault period conditions. Such a scenario can arise in lines equipped with high-speed circuit breakers (CBs) and time-domain protective relays, so that the fault can be eliminated even before it reaches its steady-state. Considering this context, challenging scenarios that may arise during phasor-based fault location procedures are firstly addressed, and then statistical approaches for fault location estimation sample processing are investigated, evaluating their advantages and limitations. Initially, Alternative Transients Program (ATP) fault simulations are carried out to generate realistic fault records, which are played back into actual micro-processed relays equipped with both high-speed time-domain protection functions and phasor-based fault location algorithms. Finally, by means of tests using a Real-Time Digital Simulator (RTDSTM) and an actual Digital Fault Recorder (DFR), different procedures to analyze phasor-based fault location data are assessed. The obtained results show the statistical processing of fault location estimations can improve existing fault location procedures in some cases, but not completely solving the problem if CBs come to be faster than those in the present technology.

Ground fault protection for DC-filter high voltage capacitors based on virtual capacitance

DC filter is an important electrical apparatus to restrain harmonics in a line-commutated converter based HVDC (LCC-HVDC) system. The used differential protection for DC filters has poor selectivity and insufficient sensitivity to identify ground faults of DC-filter high voltage capacitors (DFHVCs). Based on virtual capacitance, a novel ground-fault protection for DFHVCs is proposed in this paper. According to the equivalent circuit of DC filter in a LCC-HVDC system, virtual capacitance characteristics are analyzed under different ground faults of DFHVC. Then, these characteristics are used for constructing protection scheme to identify DFHVC ground faults from external faults. A ±500 kV HVDC system built in PSCAD/EMTDC is used to verify the performance of the proposed protection. Comprehensive simulations show that the proposed protection can reliably identify DFHVC ground fault in time domain and is immune to fault resistance, fault location, measurement error and DC filter structure. Moreover, it is noted that the protection can identify a ground fault of DFHVC during the whole fault period and is of high reliability, making it valuable and prospective for applications in LCC-HVDC system.

A Novel Fault Let-Through Energy Based Fault Location for LVDC Distribution Networks

Low Voltage Direct Current (LVDC) distribution systems have recently been considered as an alternative approach to electrical system infrastructure as they provide the additional flexibility and controllability required to facilitate the integration of more low carbon technologies (LCTs). However, DC protection systems and, more specifically high accuracy DC fault location, have been recognised as a key challenge to facilitating post-fault network maintenance. Most of the existing fault location techniques rely on current derivative or communications-based methods that are either very sensitive to noise or require a high level of data synchronisation. Fault energy has been recognized as a reliable indicator of more accurate fault location estimations. Therefore, this paper develops a mathematical model for describing fault energy during the transient period of DC faults. The method subsequently proposes a new fault let-through energy based DC fault location working strategy to facilitate post-fault network maintenance. The proposed method does not require data synchronisation regardless of the voltage, current, and the size of the converters connected to the LVDC feeder. The capabilities of the proposed fault location strategy are validated against different faults applied on an LVDC test network in PSCAD/EMTDC and shown to be more reliable and accurate than existing methods.

Coordinated LVRT Control for a Permanent Magnet Synchronous Generator Wind Turbine with Energy Storage System

This study introduces a coordinated low-voltage ride through (LVRT) control method for permanent magnet synchronous generator (PMSG) wind turbines (WT) interconnected with an energy storage system (ESS). In the proposed method, both the WT pitch and power converters are controlled to enhance the LVRT response. Moreover, the ESS helps in regulating the dc link voltage during a grid fault. Previous LVRT methods can be categorized into strategies with or without an additional device for the LVRT. The latter scheme is advantageous from the perspective of no additional installation cost; in this case, pitch and converter controllers are used. Meanwhile, the former method uses an additional device for LVRT operation and hence, involves additional expense. However, it can effectively enhance the LVRT response by reducing the LVRT burden on the WT. Moreover, the additional device can be used for various WT power control applications and it is common that the ESS is interconnected to the WT for multiple objectives. Previous studies focused on these two aspects separately; hence, a method of coordinated control for an ESS and a WT is needed as more ESSs are required to connect to WTs for flexible wind power operation. The proposed method introduces a control method with different LVRT modes considering the ESS state of charge (SoC). When the WT does not have a sufficient inertial response operation range, the ESS reserve energy capacity is required for LVRT operation. This coordinated LVRT method employs both the WT and ESS controls when it is hard to handle the LVRT using the WT control alone at high wind speeds. In this case, power curve analysis is used to obtain the appropriate power reference during the fault period. In addition, a power reference is also used to ensure a safe operation. Using the proposed method, an ESS can be operated in a manner that is appropriate for WT operation, especially at high wind speeds. To validate the effectiveness of the proposed method, we considered two case studies. One study compares the LVRT response between the WT itself and the proposed method. The other research work compares the response of the conventional LVRT method that uses a WT and an ESS and with that of the proposed method. From these case studies, we concluded that the proposed method achieved a better performance while operating within the constraints of the WT rotor speed and ESS SoC limits.

Magnetizing Characteristics of Bridge Type Superconducting Fault Current Limiter (SFCL) with Simultaneous Quench Using Flux-Coupling

A bridge type superconducting fault current limiter (SFCL) with simultaneous quench using two high-temperature superconducting (HTSC) elements and two coils was fabricated to analyze the fault current limiting characteristics. Before and after the fault occurrence, the current limiting operation and the voltage waveforms of each device were compared according to the change of the input voltage. We also analyzed flux linkages and instantaneous powers of the bridge type SFCL with simultaneous quench using flux-coupling composed of HTSC elements with different critical currents. During the fault period, the magnetization power area and the flux linkage’s operating range variation due to the magnetizing current were compared with each other.

Blind deconvolution assisted with periodicity detection techniques and its application to bearing fault feature enhancement

Abstract Maximum correlated kurtosis deconvolution (MCKD), multipoint optimal minimum entropy deconvolution adjusted (MOMEDA) and maximum second-order cyclostationarity blind deconvolution (CYCBD) have remarkable performances in extracting periodic impulses. However, these deconvolution methods highly rely on the prior period of measured signal and can only enhance the specific periodic impulses. Aiming at these limitations, six kinds of periodicity detection techniques (PDTs) are introduced to adaptively identify the period of repetitive impulses. Further, PDTs-assisted MCKD, MOMEDA and CYCBD are proposed for bearing fault feature enhancement. The improved deconvolution methods have two characteristics: first, the fault period is automatically identified by PDTs according to the characteristics of the measured signal; second, the impulses of different faults can be enhanced adaptively. The analysis results of simulated and experimental datasets demonstrated the better capability of the proposed methods in enhancing bearing fault features with respect to original deconvolution methods and the fast kurtogram method.

Design of alternating current voltage–regulating circuit based on thyristor: Comparison of single phase and three phase

The voltage sag problem in a power grid can be solved by a voltage regulator. In this study, the voltage regulator based on thyristor was used to compensate the single-phase and three-phase voltage of voltage sag fault, so as to recover the normal level of voltage. The simulation analysis was carried out on MATLAB. The results showed that voltage sag faults mainly affected the amplitude of voltage, but not the frequency of voltage. After voltage regulation, the single-phase and three-phase voltage waveforms in the fault period had a certain recovery, but the voltage regulator had a certain hysteresis effect.

Enhancement of dynamic phasor estimation‐based fault location algorithms for AC transmission lines

A new technique to improve fault location methods in AC transmission lines is introduced in this study. The identification of fault location is carried out using one-end fault location algorithms based on impedance through dynamic phasors. This timely approach relies upon the fact that a fault resistance may introduce errors in the distance estimation when a fault takes place. Therefore, active power variations caused by the fault are used to enhance the fault location algorithms, i.e. power losses increase during the fault period for non-zero fault resistances. The present approach is extensively evaluated, using ATP-EMPT software, which relies upon the computation of a compensation factor associated with the rate of change in the resistance during pre-fault and fault conditions. This is achieved through the estimated phasors for voltage and current. Furthermore, the dynamic phasor estimation technique Taylor-Kalman-Fourier Filter is compared against a static phasor method. The proposed approach is validated using three fault location algorithms which are evaluated under different fault conditions, such as fault inception, location, and fault resistance. Results show that this proposed technique improves the fault location including fault resistances by 3% with respect to existing approaches.

Protection Coordination of Radial Distribution Networks Connected with Distributed Generation Considering Auto-reclosing Schemes by Resistive Superconducting Fault Current Limiters

AbstractRadial distribution networks are normally protected against fault currents by fuses and reclosers. This protection is coordinated in a way that reclosers clear temporary faults before the melting of fuses and fuses melt to clear permanent faults. Distribution networks, which are recently connected with distributed generations (DGs), incur a variety of issues that are certainly worthy of closer considerations. One of these issues is the operation of protection devices. Recloser-fuse coordination may be lost when DGs are integrated with distribution networks due to the effect of current flowing from DGs during fault period and the breaking of the radiality nature of these networks. The impact of DGs on recloser-fuse coordination depends on penetration level, location, and type of DG. Recloser-fuse coordination of radial distribution networks connected with DGs can be kept by connecting resistive superconducting fault current limiter (R-SFCL) in series with the DG to limit the fault current contribution of DG during the fault period. However, when considering the auto-reclosing scheme of the recloser, recloser-fuse coordination may be lost even if R-SFCL is connected. This paper shows the effectiveness of R-SFCL to restore recloser-fuse coordination without considering auto-reclosing scheme. It also proposes solution methods based on three different configurations of R-SFCL to maintain recloser-fuse coordination when auto-reclosing scheme is considered. Simulation results illustrate the effectiveness of the proposed configurations of R-SFCL to keep recloser-fuse coordination. All simulations are performed using MATLAB/Simulink package.

Distribution system protection by coordinated fault current limiters

The protection of distribution networks is one of the most substantial issues, which needs special attention. Using appropriate protective equipment enhances the safety of the power distribution network during the fault conditions. Fault current limiter (FCL) is a kind of modern preserving system being used for protecting power networks and equipment. One of the main concerns of power networks is the voltage restoration of buses during faulty conditions. In this study, a group of coordinated DC reactor type faults current limiters are designed and tested to protect the network and restore its buses voltage within the fault period. To coordinate FCLs and measurement devices during the fault sequences, a wireless communication system and decision-making computer are used. The proposed FCLs coordination strategy is modelled and simulated in MATLAB platform and the results are validated by the developed laboratory test setup.

Parallel resonance type fault current limiting circuit breaker

The main goal of this study is introducing a novel fault current limiter based on parallel resonance structure (PRFCL) for high voltage application. During normal mode, the PRFCL reactor is short-circuited via a rectifier bridge DC output voltage and LC resonance tank shows negligible impedance in the line. During a fault, the rectifier bridge switches are turned off, so that the parallel resonance LC tank connects to the line with high impedance. This impedance of the resonance structure can limit the fault current, successfully. It is shown that the suggested PRFCL can act as a breaker and opens the line during the fault period. In order to show the suggested PRFCL abilities, MATLAB software is used to simulate the normal and fault cases. In addition, a scale-down prototype is implemented to confirm the simulation results. The comparative study shows that PRFCL has acceptable performance in normal and current limiting operation modes.

Real-Time Calculation Method of DC Voltage and Current to Eliminate the Influence of Signal Delay

In this study, the influences of the signal delay duration between rectifier and inverter in ultra-high voltage direct current (U-HVDC) transmission systems have been analyzed. The simulation results with different signal delay time under the same fault condition show that the signal delay time has a significant influence on the control system response during the fault and recovery periods. In the worst condition, it may lead to a commutation failure in the inverter. To eliminate the influence of the signal delay time on the DC control system, a fast calculation method for computing the voltage and current has been proposed by establishing the equivalent capacitance and inductance of the DC line. A voltage dependent current order limiter is added in the rectifier control system, which can calculate the DC current order value. Based on this concept, this paper proposes an improved control strategy to eliminate the influence of signal delay. The analysis and simulation results show that the calculation method can effectively improve the response speed and shorten the fault recovery time of the HVDC systems.

Impulse Feature Extraction of Bearing Faults Based on Convolutive Nonnegative Matrix Factorization

The detection of bearing faults is of great significance for the stable operation of rotating machinery. Apart from detection by analysing the vibration response, another powerful strategy is to extract the periodic impulse excitation directly induced by faults, which efficiently eliminates the influence of the transmission path and noise. Typical methods of this strategy include maximum correlated kurtosis deconvolution (MCKD) and multipoint optimal minimum entropy deconvolution (MOMEDA). However, these deconvolution methods based on maximizing a certain measurement index are still insufficient at finding the correct fault period directly because of the interference of noise components. To effectively extract the periodic impulse excitation from the vibration response, a new impulse feature extraction method from the vibration spectrogram based on convex hull convolutive nonnegative matrix factorization (CH-CNMF) is proposed. As the spectrogram intuitively reveals the time and frequency information of the impulse response generated by the fault excitation, according to the decomposition characteristics of CH-CNMF, the time-frequency structure of the impulse response is represented by the basis tensor, while the weight matrix corresponds to the impulse excitation. Meanwhile, autocorrelation is adopted to enhance the periodic impulse excitation. Finally, based on power spectral entropy and first-order correlated kurtosis, the optimal periodic pulse can be selected from the autocorrelation curves of the weight matrix. Both numerical simulation and experimental verifications on bearings indicate that the proposed method can eliminate the influence of random shock excitations and directly attain the periodic impulse for the source of the bearing fault, and that its extraction effectiveness outperforms MOMEDA.

Design method for strengthening high-proportion renewable energy regional power grid using VSC-HVDC technology

This paper proposes a general design method for strengthening regional power grids with high proportion of renewable energy using voltage source converter based high voltage direct current (VSC-HVDC) technology. First, three main security and stability problems of regional power grids with high proportion of renewable energy are pointed out, which implies the necessity of the VSC-HVDC reinforcement scheme. Second, two VSC-HVDC reinforcement schemes are designed to strengthen a real high-proportion renewable energy regional power grid in China, with emphases on the determination of location and capacity of VSC stations. Third, three evaluation indexes that related to the security and stability of power grids are put forward, namely line load rate, bus voltage level and system strength of the VSC-connected terminal. Finally, the two alternative reinforcement schemes are analyzed in detail. The results show that, the two VSC-HVDC schemes can well solve the line overload problem of electromagnetic loop networks with high generation of renewable energy, and can effectively increase the voltage level of the system during the fault period. After a comprehensive evaluation, scheme 2 is slightly superior to scheme 1.

An integrated reactive power control strategy for improving low voltage ride-through capability

Among all renewable energies, wind power is rapidly growing, whereby it has the most participation to supply power. Doubly fed induction generator (DFIG) is the most popular wind turbine, as it can play a very significant role to enhance low voltage ride through (LVRT) capability. Ancillary services such as voltage control and reactive power capability are the main topics in wind power control systems that should be handled profoundly and carefully. The lack of reactive power during fault period can result in instability in generators and/or disconnection of the wind turbine from the power system. The main aims of this study are to illustrate the most effective approaches subject to improve the efficiency, stability, and reliability of wind power plant associated with LVRT capability enhancement. This effectiveness and efficiency are demonstrated by, firstly, comparison between all types of wind turbines, focusing on the ancillary services, after the existing advanced control strategies. According to the literature, there is a consensus that modifying converter-based control topology is the most effective approach to enhance LVRT capability in DFIG-based wind turbine (WT). Therefore, an advanced integrated control strategy is designed by considering the effect of the rotor side converter (RSC) and the grid side converter (GSC). A model of the wind power plant is presented based on the control objectives. MATLAB/Simulink is also used to illustrate the effectiveness of the designed algorithm.

Fault Ride-Through Enhancement of Grid Supporting Inverter-Based Microgrid Using Delayed Signal Cancellation Algorithm Secondary Control

The growing level of grid-connected renewable energy sources in the form of microgrids has made it highly imperative for grid-connected microgrids to contribute to the overall system stability. Consequently, secondary services which include the fault ride-through (FRT) capability are expected to be possessed characteristics by inverter-based microgrids. This enhances the stable operation of the main grid and sustained microgrid grid interconnection during grid faults in conformity with the emerging national grid codes. This paper proposes an effective FRT secondary control strategy to coordinate power injection during balanced and unbalanced fault conditions. This complements the primary control to form a two-layer hierarchical control structure in the microgrids. The primary level is comprised of voltage/power and current inner loops fed by a droop control. The droop control coordinates grid power-sharing amongst the voltage source inverters. When a fault occurs, the participating inverters operate to support the grid voltage, by injecting supplementary reactive power based on their droop gains. Similarly, under unbalanced voltage condition due to asymmetrical faults in the grid, the proposed secondary control ensures the positive sequence component compensation and negative and zero sequence components clearance using a delayed signal cancellation (DSC) algorithm and power electronic switched series impedance placed in-between the point of common coupling (PCC) and the main grid. While ensuring that FRT ancillary service is rendered to the main utility, the strategy proposed ensures relatively interrupted quality power is supplied to the microgrid load. Consequently, this strategy ensures the microgrid ride-through the voltage sag and supports the grid utility voltage during the period of the main utility grid fault. Results of the study are presented and discussed.