High impedance fault arcing on sandy soil in 15 kV distributionfeeders: contributions to the evaluation of the low frequency spectrum

The measured values of current harmonics at a staged high-impedance ground fault on sandy soil are presented. The measured low-frequency spectrum is compared with current harmonics recorded continuously for one week at the substation. This comparison was carried out to determine to what extent 120 Hz and 180 Hz components can be used to help detect a high-impedance fault. The field measurements are supported by a simple theoretical model and laboratory measurements. It is concluded that, for the studied feeder, detection of high-impedance arcing faults may be possible by monitoring of the second-harmonic current     

Analysis of high-impedance fault generated signals using a Kalmanfiltering approach

High-impedance faults are accompanied by variations in the 60 Hz and harmonic components. An approach that accounts for the time-varying nature of the fundamental and harmonic components is developed. This approach is based on Kalman-filtering theory to obtain the best estimation of the time variations of the fundamental and harmonic components. Four actual recorded data sets for staged arcing fault on different types of soil are investigated by the proposed Kalman-filtering technique. The time variations of fundamental and low-order harmonic components significantly contribute to high-impedance fault detection using the features presented     

Verification of the Wavelet-Based HIF Detecting Algorithm Performance in Solidly Grounded MV Networks

The application of the wavelet-based algorithm for arcing high-impedance fault detection medium-voltage (MV) distribution networks is presented in this paper. This paper describes continuation of research on HIF detection with particular reference to algorithm application in solidly grounded MV networks. The results obtained by use of the improved version of the algorithm are presented. The algorithm performance was tested using data obtained from staged HIGFET in a real MV network as well as from EMTP-ATP simulations. Satisfactory results of the algorithm performance were observed for all examined HIF cases in which the ground fault current was greater than 3 A root mean square. The improved algorithm also proved to be more immune to transients generated during switching operations in protected feeders and to capacitor bank switching.     

Detection of Distribution High Impedance Faults Using Burst Noise Signals near 60 HZ

Previous papers have described a method for the detection of arcing fallen distribution primiary conductor faults using the electrical noise in feeder current above 2kHz. While this method provided improved detection of such faults, this high frequency signal often would not propagate past capacitor banks. In the present paper, we describe a technique for the identification of arcing high impedance faults using burst noise signals at frequencies near the power system fundamental and low order harmonics. Arcing generates non-synchronous burst noise signals which approximate white noise, providing a signal which can be differentiated from synchronous power system signals in the frequency bands of interest. The primary advantage of monitoring frequencies near the fundamental is that this arcing fault signal at low frequencies will exhibit little attenuation from capacitor banks or other sources. This paper provides preliminary results that arcing faults can be detected effectively using frequency components below 60 Hz or between low order harmonics of 60 Hz. The technique is demonstrated through analysis of analog signals recorded during numerouis staged utility downed conductor tests.     

Classification of faults and switching events by inductivereasoning and expert system methodology

Under certain conditions, one electrical parameter (independent variable) is not enough to detect high-impedance faults on certain surface conditions. These faults do not draw sufficient current for detection and may draw less current than similar faults on other soil surfaces. Moreover, because every electrical detection parameter displays characteristics of randomness, it is difficult to assign a probability that a given event is a high-impedance fault, rather than a switching event. It has been shown that detection by induction laws can improve the classification of faults and switching events. The second and third laws of induction are utilized with a minimum entropy method. Setting detection threshold values using induction methods is also proposed. The methods presented are taken from ongoing research in high-impedance fault detection. While the techniques have not been reduced to practice or field-tested, they hold promise for future improvements in the relaying of high-impedance faults     

Fault location in power networks with mixed feeders using the complex space-phasor and Hilbert–Huang transform

The paper introduces a practical approach to power system fault location in power networks using advanced fault signal processing. The three-phase fault voltages are converted to the vector of absolute values of its complex space-phasor. This vector represents fault traveling wave and it is further processed for fault location finding with the Hilbert–Huang transform. The simulation results, including single line to ground faults, faults in mixed feeders and high-impedance arcing faults, confirm the accuracy and practical applicability of the proposed approach.     

高压线路单相弧光接地对数仿真模型数据修正算法

受污闪、山火等因素影响,中性点接地高压输电线路易发生单相弧光高阻接地故障,但总体来讲现场获取的故障数据仍然严重不足,制约了弧光接地故障检测及保护技术的研究。人工弧光高阻接地故障实验成本较高,也难以普及应用。针对该问题,文中基于可直接表征电弧燃弧V-I特征的对数电弧模型,详细分析了该模型仿真数据和录波数据的差异性,针对该模型所表征出的电弧V-I特征未能反映实测录波数据中V-I相角差的问题,提出了一种对该模型仿真数据进行修正的数据处理算法,修正后的数据波形具有和真实录波V-I曲线更为接近的外特征,为后续弧光高阻接地故障的研究提供了数据支撑。     

基于谐波能量和波形畸变的配电网弧光接地故障辨识

配电网弧光接地故障会产生严重的弧光过电压并释放大量热能,从而造成设备损坏,引发火灾并危害人员生命安全。针对传统电弧模型无法正确描述电弧不稳定燃烧过程中的间歇性燃熄弧和随机波动等问题,提出了基于随机控制变量的改进Mayr电弧模型;通过对故障特征的分析,提出归一化谐波能量描述方法,实现了包括高阻故障在内的不同接地故障情况下谐波含量的一致性描述和整定,并根据归一化谐波能量在时间尺度上的随机分布特性以及故障波形畸变特征,实现对弧光接地故障的准确辨识。最后,结合配电网新型智能测量终端的发展应用,提出基于三相电压和零序电流录波数据的弧光接地故障综合辨识算法,并通过PSCAD仿真算例和某10 kV配电网的实测故障试验数据对算法的可靠性和安全性进行验证。     

New insight into the detection of high-impedance arcing faults onDC trolley systems

High-impedance arcing faults are difficult to detect with conventional switchgear, and the presence of these faults in coal mine power systems represents a significant fire hazard. Research was performed to identify plausible techniques that would discriminate between the high-impedance arcing faults and legitimate load currents on the DC trolley system. This paper briefly summarizes that effort and focuses on the frequency characteristics of the arc current. After the arc was modeled as a stochastic process, good agreement was obtained between experimental observations and mathematical predictions     

电压电流能量信息融合的低压交流电弧故障检测

针对串联电弧故障检测判据选择难、阈值设置难的问题,本文在传统基于电流检测方法的基础上融合使用电压信息,提出了一种电压电流能量信息融合的交流电弧故障检测方法。以分析开关电源和非开关电源类负荷下的各自故障特征为基础,提出了利用电压半波总能量的开关电源类电弧故障直接判定方法,并融合使用电压电流特征能量波形相关性实现故障线路的选择;提出了基于敏感域电压电流最大瞬时特征能量相位匹配的适用于非开关电源类负荷下的故障检测方法,以特征能量相位信息构建判据,克服了传统检测方法的阈值设定困难问题。本文检测方法判据虽利用了负荷分类思想,但由于开关电源类负荷下的故障检测可利用电压半波总能量幅值实现故障直接判定,因此实际应用中无需辨识负荷类型。相较传统利用电流特征的检测方法,本文方法具有判据简单、易于阈值设定的优势。试验结果表明,本文方法可有效用于多种类型负荷的电弧故障检测,检测时间满足相关标准规定。     

小电阻接地配电网零序保护的改进研究

中性点经小电阻接地系统发生高阻接地故障时,由于传统零序过流保护达不到定值而无法跳闸,导致故障长时间存在,而且此时无故障告警信号,因此存在危害系统可靠运行及人身安全的隐患。对中性点经小电阻接地系统发生接地故障时的零序电流电压特征进行了分析,提出了利用阻容比闭锁条件改进零序保护的方案。阻容比闭锁条件的本质在于通过分析零序电流阻性部分和容性部分的不同组成进行故障线路的识别。阻容比闭锁条件不受电压互感器和电流互感器极性的影响,因此能够可靠使用专用零序电流互感器。加入阻容比闭锁条件后不改变原有的保护配置,易于实施,能够提升零序保护的高阻接地故障检测能力,及时切除故障,保证系统的可靠运行以及人身安全。     

Ground resistance-revisited

The nature of ground resistance is examined to explain the high impedance of faults directly to ground as contrasted to conventionally assumed low-impedance ground faults to neutral conductors or to towers with low footing resistance. High-impedance faults are shown to be inherently nonlinear due to the characteristics of soil. This nonlinearity is shown to be different from that of the arcing between conductor and ground. The harmonic content of the resulting current is used to distinguish such faults from normal load variations. Specifically, the magnitudes of the resulting harmonic currents appear sufficiently predictable to be utilized in a high-impedance fault detector     

High-impedance fault detection in distribution networks with use of wavelet-based algorithm

A new simple and effective algorithm of arcing fault detection in distribution networks with the application of a wavelet transform technique is presented in this paper. The protection algorithm developed observes the phase displacement between wavelet coefficients calculated for zero-sequence voltage and current signals at a chosen high-level frequency. The final decision in regards to feeder switching off (or alarm issuing) is met either with a deterministic logic scheme or with the use of a neural net trained especially for that purpose. The developed wavelet-based high-impedance fault (HIF) detector has been tested with Electromagnetic Transients Program-Alternative Transients Program (ATP)-generated signals, exhibiting better performance than traditionally used algorithms and methods. The protection method proposed may be used for HIF detection independent of the network neutral-point grounding mode. The scheme proved to be robust against transients generated during normal events such as feeder energizing and de-energizing as well as capacitor bank switching.     

Algorithm comparison for high impedance fault detection based onstaged fault test

Four high-impedance fault-detection algorithms-proportional relaying, ratio ground relaying, second-order harmonic current relaying, and third-order harmonic current relaying-were simulated by mathematical models. Relaying performances using staged fault data were then compared. Results of the fault data processing were used to distinguish the detection characteristics: fault identification, stability, threshold setting adaptability, transient recovery characteristic, and availability. The operations of a ground overcurrent relay and a ratio ground relay were also checked in the test. The results can be used as a reference for the development of a reliable high-impedance fault detector     

配电网单相电弧接地故障选线暂态分析法

小电流接地系统发生最多的故障是单相接地故障，现有的基于稳态零序电流的故障选线方法，受弧光接地，运行方式因素的影响较大，选线精度并不理想，文中在充分研究电弧故障暂态零序电流变化的基础上，指出电弧因素对故障选线准确性的影响，由于对称分量法对接地故障进行暂态分析十分不便，文中采用Clarke变换，并运用小波变换技术建立新的基于暂态电气量的选线方法，应用EMTP对电弧接地故障进行了仿真，在不同采样频率以及不同的A／D分辨率情况下进行了大量的仿真试验，结果表明该方法是正确，有效的，而且具有较强的鲁棒性。     

一种城市配电网自适应全线电流保护方法

针对现有电流速断保护无法保护线路全长且可能失去保护范围的问题,提出一种双层判据的自适应全线电流保护方法。该保护方法先通过第一层判据中可自适应调整的低整定值,实现不受系统运行方式与故障类型影响的全线故障监测,再利用第二层判据实现线路故障区段定位,确保保护正确动作。考虑到电流保护难以准确辨识高阻接地故障,通过分析系统零序网络,提出一种基于复合功率的高阻接地故障辨识方法。仿真结果表明,所提保护方法不受系统负荷变化及故障类型影响,可有效提升配电网线路保护范围及高阻接地故障辨识能力,保障保护动作的可靠性及灵敏性。     

基于虚拟能量变化率的谐振接地系统高阻接地故障选线方法

谐振接地系统的高阻接地故障由于消弧线圈和接地阻抗作用,故障电气量较微弱,故障检测与选线困难。通过对高阻故障的暂稳态特征以及故障线路对地支路的瞬时和永久性改变的分析,总结出健全线路和故障线路对地电容参数的瞬时变化规律及特征。进而构造表征故障前后各线路对地电容参数变化的虚拟能量分量,并分析虚拟能量变化率的变化规律。最后,提出了利用线路虚拟能量变化率峰值占比来确定故障线路的判据,并用于设计故障选线方法。所述方法在保证选线正确的同时,扩大了检测范围并增强了抗三相不平衡干扰的能力,仿真结果和现场实测数据验证了方法的准确性与可靠性。     

一种断路器开断燃弧时间检测新方法

准确测量断路器燃弧时间的关键是确定电弧的起弧时刻.根据断路器开断时开断电弧的模型,详细分析了断路器开断前后电流的变化过程和开断相角等因素对燃弧时间的影响,提出了一种基于暂态电流的燃弧时间检测方法.通过对线路发生故障后的部分故障线路的三相电流录波数据滤波后进行拟合,预测之后的电流变化,并与实际电流数据比较,求得电流畸变量.当畸变量大于设定阈值时,即可认为该时间点为断路器的触头始分点;断路器首开相的触头始分点即起弧时刻.开断完成的时间点即熄弧点为相电流小于设定阈值的时间点,末开相的熄弧点为熄弧时刻.起弧时刻与熄弧时刻之间的时间差为断路器的燃弧时间.利用电磁暂态分析程序EMTP仿真证明了该方法的可行性和较高的可靠性.     

Practical high-impedance fault detection on distribution feeders

Distribution protection systems must balance dependability with security considerations to be practical. This is quite difficult for high-impedance faults. Only highly sensitive algorithms can achieve absolute dependability in detecting very low current faults. This high sensitivity results in a propensity for false tripping, creating a less secure, system and resulting in the potential for decreased service continuity and lower reliability. Researchers at Texas A&M University have balanced fault detection with fault discrimination, resulting in a practical combination of detection algorithms in a commercially viable system. This device has many “intelligent” features, including the ability to analyze and correlate numerous fault characteristics in real time, so that a correct determination of the status of the feeder can be made with a high probability of accuracy. This paper describes the use of multiple algorithms to detect various types of faults and the use of an expert decision maker to decipher incoming data, to determine the status and health of a distribution feeder. Requirements for a practical, secure high-impedance fault relay are also discussed. Finally, Texas A&M has licensed this technology to a commercial partner, which manufactures a device that detects high-impedance faults, in addition to performing numerous other monitoring and protection functions     

New ANN-Based Algorithms for Detecting HIFs in Multigrounded MV Networks

Application of two new ANN-based algorithms for arcing high impedance fault (HIF) detection in multigrounded medium-voltage (MV) distribution networks is presented in this paper. The paper provides an evaluation of two new structures of artificial neural networks (ANNs) that may be used for reliable HIF detection in multigrounded as well as isolated, compensated, and grounded via small resistance distribution grids. The results obtained by use of both neural nets are presented. The performance was tested using data obtained from staged HIFs in real MV network as well as from electromagnetic transients program-alternative transients program simulations. A small number of necessary neurons in developed ANNs, short measuring sliding data window, and easy interpretation of obtained output signals are the main advantages of the proposed approach. Satisfactory results of ANN performance were observed for all examined HIF cases in which the ground fault current was greater than 16 A. The selected ANNs of best performance show high reliability and immunity to transients resulting from switching operations in protected feeders and from capacitor bank switching.