Low Voltage Fault Research Articles

中山配网故障定位分析快速复电系统的设计与实现

快速复电系统对低压故障定位一直以来缺乏足够的技术手段支撑，本文基于营配信息集成平台的电网模型数据、配网自动化系统故障信息和配变终端实时信息设计并实现配网故障定位分析快速复电系统。根据用户报障信息、电网故障信息和配变数据实现低压故障自动定位，为客户服务人员掌握第一手停电范围信息提供技术支持，有效指导抢修人员快速复电。研究成果在中山供电局进行示范应用，效果良好。 Rapid restoration system has lacked adequate technical support to low voltage fault location ever since. This paper designs and realizes a fault location technology analysis and rapid restoration system, based on data which are provided by grid model of information integration platform and fault information from distribution network automation system, and variable terminal real-time information. According to the user alarm information, fault information and terminal data, this system can automatically find out low-voltage fault location, offer technical support to customer service’s first-hand blackout range information, and also support effective guide to salvage crews restoring electricity. Research results set an example and are applied in Zhongshan power supply bureau, having a good effect.

Application of Fault Location Method Based on Multi-Source Fault Information in Repair of Distribution Network

Fault location method based on multi-source fault information in repair of distribution network is proposed to make the precision and speed of fault location higher. Firstly a topology description and storage method which is appropriate to distribution network fault location is proposed. Then, based on the topological structure of distribution network, fault information on the distribution network is integrated processed. Fault information grouped and priorities are identified using the association of distribution equipment. Low-voltage fault location is achieved by applying fuzzy set theory in fault message omissions and misstatements situations. Finally, an example demonstrates the effectiveness of this method.

A Novel Method of Ground Fault Phase Selection in Weak-Infeed Side

The sequence current-based fault phase selector and traditional low-voltage fault phase selector have difficulties in being applied to the weak-infeed side. This study proposes a new method of ground fault phase selection for high-voltage/extra-high-voltage transmission-line protection under weak-infeed conditions. The method utilizes the relative phase-angle relationship between negative- and zero-sequence voltages and a relative phase relationship between superimposed positive-sequence voltage and superimposed negative-sequence voltage to identify the fault phase under weak-infeed conditions. Theory analysis and simulation have proven that the proposed method has high immunity against fault resistance as well as impedance phase-angle inequality and overload.

Control Design of a Dynamic Voltage Restorer for Wind-Driven Induction Generators during a Low Voltage Fault at Grid Bus

To reduce the parallel transient and resume the power balance immediately after fault clearing, many countries have included the low voltage ride through (LVRT) requirements in the grid codes for grid-connected wind turbines (WTs). Although the removal of the WT from the power grid in the conventional approach is beneficial to alleviate severe mechanical stress incurred by the low voltage fault, remaining the WT to be connected to the grid during the low voltage fault becomes obligate to reduce the risk of voltage collapse for the power system associated with the ever-increasing WT installation. This article presents a control strategy to which the LVRT capability enhancement of a wind-driven squirrel cage induction generator (IG) by the use of a dynamic voltage restorer (DVR). The DVR, with the flexibility of changing output voltage polarity in series with the power source, can sustain the excitation of IG subjected to the low voltage fault and the random change in load and wind speed. A DC voltage regulator is employed to support the DC-link voltage of the DVR for generating appropriate AC voltage level required for the IG. The AC output voltage of the DVR is controlled by an AC voltage regulator according to the IG terminal voltage deviation from the desired value. To achieve voltage and current decoupling control between distinct coordinate axes in the stationary reference frame, a proportional-resonant (PR) controller is adopted. The DVR output voltage can be instantaneously tracked by the PR controller according to the sinusoidal command comes from the DC and AC regulators. To fully utilize the compensation capacity for the DVR, the dynamic estimation of grid voltage lower limit for recasting the AC voltage command (ACC) of the DVR in response to the low voltage fault is proposed to prevent DVR from malfunction due to controller saturation. The experimental results confirm the effectiveness of the proposed strategy.

Research on Low-Voltage Arc Fault Detection Based on BP Neural Network

In electrical fires, arc fault is one of the important reasons. In virtue of cross talk, randomness and weakness of arc faults in low-voltage circuits, very few of techniques have been well used to protect loads from all arc faults. Thus, a novel detection method based on BP neural network was developed in this paper. When arc faults occur in circuits, current integrations of cycles were variable and erratic. However, current integrations of cycles would also vary while the working conditions of circuits change. To better discriminate the current integrations, four characteristics were extracted to represent their differences through chain code. Based on these characteristics, BP neural network was used to distinguish arc faults from normal operations. The validity of the developed method was verified via an experimental platform set up. The results show that arc faults are well detected based on the developed method.

An advanced control strategy of PV system for low-voltage ride-through capability enhancement

This paper presents a novel control strategy of the two-stage three-phase photovoltaic (PV) system to improve the low-voltage ride-through (LVRT) capability according to the grid connection requirement. With the help of the new strategy, the PV array can generate active power as much as possible according to the depth of the grid voltage dip and the power rating of the grid inverter to keep power balance between the two sides of the inverter by operating in different modes. It is worthy of special mention that the proposed strategy can ensure the reactive power support when a low voltage fault occurs at the point of common coupling (PCC) without additional device. Besides, the new control method introduces a feed forward compensation reflecting the instantaneous current injecting into the DC-link from the PV array to smooth the DC-link voltage fluctuations during the grid fault. The effectiveness of the proposed control strategy has been demonstrated through various simulation scenarios. Compared with the conventional protection, the proposed control strategy can not only enhance the LVRT capability of the PV system, but also provide grid support through the active and reactive power control.

Instability of Wind Turbine Converters During Current Injection to Low Voltage Grid Faults and PLL Frequency Based Stability Solution

In recent grid codes for wind power integration, wind turbines are required to stay connected during grid faults even when the grid voltage drops down to zero; and also to inject reactive current in proportion to the voltage drop. However, a physical fact, instability of grid-connected converters during current injection to very low (close to zero) voltage faults, has been omitted, i.e., failed to be noticed in the previous wind power studies and grid code revisions. In this paper, the instability of grid side converters of wind turbines defined as loss of synchronism (LOS), where the wind turbines lose synchronism with the grid fundamental frequency (e.g., 50 Hz) during very deep voltage sags, is explored with its theory, analyzed and a novel stability solution based on PLL frequency is proposed; and both are verified with power system simulations and by experiments on a grid-connected converter setup.

Rotor Current Analysis on Transient Performance of Low Voltage Ride-Through of Doubly Fed Induction Generator

From a theoretical perspective, this paper develops a systematic approach to analyze the transient characteristics of the low voltage ride through in three-phase short-circuit rotor current. Firstly, the steady state current mathematical model of the system is described. And then, the short-circuit rotor current dynamic characteristic during the low voltage fault is analyzed, the resistance value and switching strategy of crowbar are discussed. Finally, the simulation results and the theoretical analysis manifest that appropriate crowbar reactance value and switching time can improve LVRT control characteristic and grid stability.

A Combined Design-Time/Test-Time Study of the Vulnerability of Sub-Threshold Devices to Low Voltage Fault Attacks

The continuous scaling of VLSI technology and the possibility to run circuits in subthreshold voltage range make it possible to implement standard cryptographic primitives within the very limited circuit and power budget of radio frequency identification (RFID) devices. However, such cryptographic implementations raise concerns regarding their vulnerability to both active and passive side-channel attacks. In particular, when focusing on RFID targeted designs, it is important to evaluate their resistance against low-cost physical attacks. A low-cost fault injection attack can be mounted, for example, by lowering the supply voltage of the chip with the goal of causing setup time violations. In this paper, we provide an in-depth characterization of a chip implementation of the AES cipher. The chip has been designed using a 65-nm low-power standard cell library and operates in a subthreshold voltage range. We first show that it is possible to inject faults (through lowering the supply voltage) compliant with the fault models required to perform attacks against the AES cipher. We then investigate the possibility of predicting, at design time, which parts of the chip are more likely to be sensitive to such fault injection attacks and produce the desirable (from the point of view of the attacker) faulty behavior. Identifying such sensitive logic signals allows us to suggest to the designer a tailored countermeasure strategy for thwarting these attacks, with a minimal impact on the circuit's performance.

Research on Low-Voltage Series Arc Fault Detection Based on Higher-Order Cumulants

Arc faults are one of the main reasons of electrical fires. For the difficulty of series arc fault detection, very few of techniques have successfully protected loads from arc faults in low-voltage circuits, especially in China. When series arc faults occur, shoulders will appear in load currents. The shoulder widths of non-arc faults such as normal load arcs are stable, while those of arc faults are variable because the appearance of arc faults is erratic. Therefore, a novel detection method based on shoulder characteristics was proposed. To better capture shoulder widths, original currents were firstly converted into pulses. Then, the pulse widths were used to detect arcs and the fourth-order cumulants of their differential were used to distinguish arc faults from normal operations. Finally, an arc fault detection device (AFDD) prototype was developed for test. The results show this prototype can discriminate arc faults effectively from normal operations.

Asymmetrical Low-Voltage Ride Through of Brushless Doubly Fed Induction Generators for the Wind Power Generation

Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction generator (BDFIG) has a commercial potential for wind power generation due to its lower cost and higher reliability. In the most recent grid codes, wind generators are required to be capable of riding through low voltage faults. As a result of the negative sequence, induction generators response differently in asymmetrical voltage dips compared with the symmetrical dip. This paper gave a full behavior analysis of the BDFIG under different types of the asymmetrical fault and proposed a novel control strategy for the BDFIG to ride through asymmetrical low voltage dips without any extra hardware such as crowbars. The proposed control strategies are experimentally verified by a 250-kW BDFIG.

Identification Method of Low-Voltage Series Arc Fault Based on Harmonic Component Relative Change Coefficient

Low voltage series arc fault is one of the main reasons caused the accident of electrical fire, so it is necessary to detect and identify the fault arc. The low voltage series arc fault is researched in this paper, current waves of some typical electric equipment under arc fault and normal operation are measured, and DFT transform of current waveforms are done by Matlab software, so that an identification method of low-voltage series arc fault based on the harmonic component relative change coefficient is presented in this paper. The simulation results show that this method can effectively identify whether the arc fault occur.

Crowbarless Fault Ride-Through of the Brushless Doubly Fed Induction Generator in a Wind Turbine Under Symmetrical Voltage Dips

The brushless doubly fed induction generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional DFIG. In the most recent grid codes, wind generators are required to be able to ride through a low-voltage fault and meet the reactive current demand from the grid. A low-voltage ride-through (LVRT) capability is therefore important for wind generators which are integrated into the grid. In this paper, the authors propose a control strategy enabling the BDFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250-kW BDFIG, and the experimental results indicate that the LVRT is possible without a crowbar.

Using Dynamic Reactive Power Compensation Equipments to Enhance Low Voltage Ride-Through Capability of Fixed Speed Asynchronous Wind Farms

This paper presents wind energy conversion model, drive shaft’s dual-mass model and generator’s transient mathematical model for the transient analysis of fixed speed asynchronous wind generators, and analyzes the transient characteristics of the wind generators under the condition of low voltage fault. The control principles of two dynamic reactive power compensation equipments as static var compensator (SVC) and static synchronous compensator (STATCOM) are introduced. Take a wind farm consists of fixed speed asynchronous wind generators as an example, the two compensation equipments are simulated in PowerFactory/DIgSILENT to compare the effort of them on enhancing the low voltage ride-through capability of the wind farm.

A doubly-fed induction generator test facility for grid fault ride-through analysis

This paper has described a laboratory-scale DFIG test facility commissioned to investigate the low voltage fault behavior of a DFIG wind turbine generator. In this DFIG test facility, a dc motor driven by a four-quadrant dc drive is used as a prime mover to replicate the torque input from a wind turbine's drive shaft. A mechanical model created in Simulink is executed by the dSpace controller. The IGBT power converter and dc-link capacitors are over-rated to withstand various grid faults. The fault emulator permits a flexible approach to the application of grid faults and also provides an opportunity to mimic the typical grid connection impedance of a wind turbine.

Dynamic Characteristic Analysis of Doubly-fed Induction Generator Low Voltage Ride-through

For studying the impacts of wind turbines integrated into grid, the relation between the protection of doubly-fed induction generator (DFIG) during low voltage fault and the dynamic characteristic of grid is established from the points of generator operation constrains and district grid voltage stability. Then the resistance value and switching strategy of crowbar are discussed. Based on analyzing the electric characteristic of the voltage or current during the short-circuit fault in wind turbines with crowbar switching, the equation to estimate peak current of stator and rotor of DFIG with crowbar switching and the value range of crowbar resistance are derived. The numeric test analyzes the impacts of crowbar switching on district grid voltage stability with different fault types, crowbar switching time and crowbar resistance values. Also the interaction impact of crowbar switching on multi-wind farms is analyzed. The results show that reasonable crowbar resistance value and switching strategy can improve low voltage ride through (LVRT) ability of wind turbines and reduce bad impacts on district grid voltage stability with large-scale crowbar switching of wind farms.

Classification of severity of low-voltage motor coil arcing fault using statistical techniques

Developments spanning a major portion of the previous decade have witnessed the emergence of high/medium/low-voltage arcing fault as one of the more prominent issues confronting the power industry and associated researchers alike. Research over the past decade has been dedicated to the modelling, detection and/or monitoring of arcing faults at various voltage levels and power system apparatuses. The performance of statistical methodologies utilised to classify the severity of low-voltage arcing in a motor coil is presented and compared. The approaches revolve around the utilisation of statistical techniques such as spectral angle mapper, spectral information divergence and linear discriminant analysis to classify the severity of the motor coil arcing fault. Dedicated test-benches are utilised to simulate the arcing phenomenon of varying severity in a motor coil within laboratory environment. Hall-effect sensors in conjunction with the data acquisition module of LabVIEW provide an able means for data collection which is then subjected to offline analysis. The conceptual approach preceding the classification process revolves around the extraction of pre-decided features associated with the current signal gathered during the arcing process. These features are associated with the higher-order harmonic content of the current signal. Comparative analysis of the higher-order harmonic content in the arcing current as obtained from the test-bench and that from contemporary mathematical models for low-voltage arcing faults is presented to validate the choice of parameters for the spectral signature. The extracted features are utilised for classifying the severity of the motor coil arcing fault using the approaches mentioned above. The performance of the classification approaches has been evaluated based on the accuracy of classification, robustness and feasibility of implementation of the approach. The classification results seem very promising in terms of accuracy and feasibility of approach for real-time implementation.

Fault Ride-through Testing of Wind Turbines

Grid codes concerning low-voltage fault ride-through capabilities of wind turbines are not (yet) harmonized, varying from country to country. Full-scale field testing of wind turbines with respect to all such codes may therefore not be practical. IEC 61400-21 is currently under revision, and the last committee draft (CD 2006) presents a standardized physical test for characterizing a wind turbine's response to a voltage-dip. The results of such physical tests may be used to validate numerical models of the turbine, which in turn can be used for modelling grid code compliance assessment of particular country codes. Success with such modelled validation will provide confidence in numerical simulations. The hypothesis of this paper is that the use of numerical models, that have been validated against the standardized tests, can reduce the number of physical full-scale tests needed. This paper assesses to what degree a validated simulation model is capable of predicting the fault ride-through capabilities of a fixed speed induction generator. This is done by comparing measurements on a wind-turbine emulator in a laboratory with predictions from a validated simulation model of the laboratory emulator. Simulations and laboratory measurements show excellent agreement. The validated simulation model accurately predicts the fault ride-through capability of the direct grid connected induction generator. It is concluded that the proposed methodology is promising and thus has the potential to increase the efficiency of grid code assessments. Full-scale field tests will still be required to validate the modelling completely, but using numerical models reduces the number of field tests needed.

Test of a 1 kA Superconducting Fault Current Limiter for DC Applications

A low voltage fault current limiter (FCL) having a nominal current of 1 kA has been set up using switching elements based on YBCO thin films fabricated by reactive thermal co-evaporation. The films showed critical current densities exceeding 1 MA/cm/sup 2/ @ 77 K. After patterning and contacting the films, the elements have been assembled in a closed cryostat for operation in a liquid nitrogen bath. The FCL model was successfully tested using prospective fault currents from 25 kA to 150 kA. The electric data show a peak current of 2.7 kA within 1 ms and a limitation to approximately nominal current within 5 ms. Due to this fast response of the YBCO switching elements, FCL coupled grids can be instantaneously decoupled during a fault, leaving the faultless part of the grid practically unimpaired.

A Complete Field Analysis of a Substation Ground Grid by Applying Continuous Low Voltage Fault

A Complete Field Analysis of a Substation Ground Grid by Applying Continuous Low Voltage Fault