Analysis of shunt faults in the laterals of overhead power distribution feeders using superimposed components

In this study, a digital fault location and monitoring technique for overhead power distribution lines with laterals is presented. The technique is based on utilising the fault voltage and current samples obtained at a single location. In the implementation of the algorithm, the superimposed voltage and current components rather than total values are used to minimise the effects of preloading on the accuracy. The effectiveness of the method is verified through electro-magnetic transients program simulations.     

利用矩阵变换求解电力系统短路故障的残压变换法

参数不对称元件的出现为对称分量法处理不对称故障的序网联接处理方法设置了障碍.该文针对之以相分量法故障处理方法为依据,建立了相分量坐标下适用于各种短路故障公式化的残压变换法,并以矩阵变换的方式完成不对称短路故障的处理：通过公式变换将该方法应用于对称分量坐标.使用矩阵运算代替对称分量法的传统序网故障变换,以实现不对称短路故障计算,并给出常见故障对应的参数矩阵.对于多重短路故障和含不对称元件的网络都能够直接处理,而计算量却不会明显增大.文中用实例证明了该方法简单实用,而且便于程序实现.     

A new iterative method for fault currents calculation which models arc resistance at the fault location

In order to calculate fault currents in distribution systems accurately, the fault model must also include the electrical arc existing at the fault point and playing an important role in the fault currents calculation. In the existing approaches the value of the arc resistance at the fault location must be known in advance. Since fault current depends on the arc resistance, which is itself a non-linear function of the fault current, the fundamental question here is how to calculate the arc resistance and the fault current at the fault location simultaneously and accurately. In this paper, a new solution for the above-defined problem by using an iterative procedure is given and thoroughly tested. A new method for calculating short circuit currents in medium voltage distribution networks based on the iterative hybrid compensation short circuit method and a new formula for arc resistance are presented. The new method calculates short circuit currents and arc resistance simultaneously. Results of fault analysis and arc resistance calculation in the IEEE-34 distribution network with/without distributed generator are presented and discussed.     

Hybrid classifier for fault location in active distribution networks

This paper presents a fast hybrid fault location method for active distribution networks with distributed generation (DG) and microgrids. The method uses the voltage and current data from the measurement points at the main substation, and the connection points of DG and microgrids. The data is used in a single feedforward artificial neural network (ANN) to estimate the distances to fault from all the measuring points. A k-nearest neighbors (KNN) classifier then interprets the ANN outputs and estimates a single fault location. Simulation results validate the accuracy of the fault location method under different fault conditions including fault types, fault points, and fault resistances. The performance is also validated for non-synchronized measurements and measurement errors.     

Fast isolation of faults in transmission systems using current transients

This paper presents a protection scheme that is capable of very fast isolation of faults in high voltage transmission systems. Proposed scheme comprises set of relays connected through a telecommunication network, located at different nodes of the system. Relays use wavelet coefficients of current signals to identify the fault directions relative to their location. Fault directions identified at different locations in the system can be combined to determine the faulted line (or busbar) and isolate it. A robust single ended traveling wave based fault distance estimation approach is proposed as a backup in case of communication failure. Investigations were carried out using time domain simulations in PSCAD/EMTDC for a high voltage transmission system.     

Location of faults in power distribution laterals using superimposed components and programmable logic controllers

In this study, a digital fault location and monitoring technique using programmable logic controller (PLC) for primary overhead power distribution networks is presented. This technique employs pre- and post-fault current and voltage information along with data from the laterals. By using lateral current data transferred through shielded coaxial cables to the substation, the possibility of multiple fault point locations are eliminated. The effectiveness of this method is verified through Electromagnetic Transients Program (EMTP) simulations.     

间谐波相序特性的研究

相序是三相电力系统中电压和电流的重要特性。为了认识间谐波的相序特性，文中以两种典型的间谐波源(变频驱动装置和电动机)为例，通过理论分析和实验探讨了它们产生的间谐波的相序。研究表明间谐波可以表现为正序或负序。但是间谐波的相序特性不同于谐波，同一频率的间谐波可以具有不同的相序。一般规律是：间谐波的相序与被调制的系统基波(或谐波)分量的相序相同。如果调制后得到的频率为负值，则间谐波信号的相序将变反，即由正序变负序或由负序变正序。文中的研究成果有助于深入认识间谐波的特性和发展间谐波仿真软件。     

Fault location in active distribution networks using non-synchronized measurements

Fault location is a necessity to realize the self-healing concept of modern distribution networks. This paper presents a novel fault location method for distribution networks with distributed generation (DG) using measurements recorded at the main substation and at the DG terminals. The proposed method is based on an iterative load flow algorithm, which considers the synchronization angle as an unknown variable to be estimated. Therefore, it obviates the need of synchronized measurements. A new fault location equation is also proposed which is valid for all different fault types, hence the fault type information is not required. The developed method can be simply implemented by minor modifications in any distribution load flow algorithm and it is applicable to different distribution network configurations. The accuracy of the method is verified by simulation studies on a practical 98-node test feeder with several DG units.     

Non-linear representation of voltage sag profiles for fault location in distribution networks

Fault location for distribution networks with multiple laterals would requires additional information such as from fault indicators and protective devices. As SCADA systems to provide such information are limited in 11 kV or lower voltage distribution networks, effective fault location method that only use information from a measurement at primary substation is needed. This paper presents the application of calculated non-linear voltage sag profiles and voltage sag measurement at primary substation to locate a fault in distribution networks. The proposed method firstly identifies the faulted section. From the indentified section, fault distance is calculated. The method has been tested under different fault scenarios that include various fault resistance, loading variation and data measurement errors. The results indicate the possibility of using this method to support automatic fault management system.     

Improved fault location algorithm for radial distribution systems with discrete and continuous wavelet analysis

This paper presents a novel wavelet based approach for fault location using voltage transient waveforms in power distribution systems. The proposed method includes two main stages. Firstly, the approximate location of the fault or fault section is determined using a new algorithm with discrete wavelet transform. The difference between arriving times of transient components in different measurement units is used for this purpose. The accurate location of the fault is determined in the second stage. Depending on the determined fault section, the difference between arriving times of transient components in different measurement units or the frequency content of the voltage transients are used. The time difference and frequency content are calculated using discrete and continuous wavelet transform (DWT and CWT) respectively. The proposed technique is implemented on an unbalanced 34 bus distribution system with two distributed generation units which is simulated in ATP–EMTP. The comparison of the results of the proposed method with previous works verifies its better accuracy and more robustness to fault conditions including fault inception angle and fault resistance.     

Study of optimal combination between SFCL location and PSS type to improve power system transient stability

In this paper, authors present a method to select the optimal combination between the type of the power system stabilizer (PSS) and the location of a Superconducting Fault Current Limiter (SFCL) in an Electrical Power Grid (EPG) to improve the transient stability in case of fault. The angular separation between generators rotors when different types of short-circuit appears in the EPG is used as the main criterion of the proposed method to select this optimal combination. To complete the study, the optimal resistive value of the SFCL is evaluated to improve the global stability of the EPG. Results show that an optimal combination between the type of PSS, the location of SFCL in the EPG and the resistive value of SFCL exists in order to obtain the smallest variation of the angular separation of generators rotors, i.e. the best stability of the power system in case of fault.     

A new fault location method for distribution networks using sparse measurements

In response to the growing demand to improve reliability and quality of power supply, distributed monitoring devices are gradually being implemented in distribution networks. On the other hand, utilities are demanding more accurate and reliable fault location systems to reduce the economic impact of power outages. This paper presents a novel method that takes full advantage of all available measurements to provide an accurate fault location. The developed method first uses an iterative state estimation based algorithm to find the nearest node to the fault location. It then examines all lines connected to the selected node and locates the fault. The performance of the proposed method is studied by simulation tests on a real 13.8 kV, 134-node distribution system under different fault scenarios. The results verify the accuracy of the algorithm and its robustness even under uncertain measured data. The method robustly handles measurement errors, and is applicable to any distribution network with laterals, load taps and heterogeneous lines.     

On the application of wavelet transform for symmetrical components computations in the presence of stationary and non-stationary power quality disturbances

Symmetrical components method allows systematic analysis of unbalanced three-phase systems. This method represents the backbone for many applications in an electric power system (EPS) such as fault analysis, power system protection, power and energy measurements. Moreover, with the increased penetration of plug-in hybrid electric vehicles (PHEVs), studying and evaluating the distribution system unbalance considering power quality disturbance pronounced by fleet of these vehicles, becomes a necessity. In time-invariant polluted environment, the measurements of the symmetrical components for the fundamental and harmonic components could be performed using Fourier basics. However Fourier-based techniques are unsuitable in the presence of any time-variant power quality disturbance which is typically the case when considering PHEVs and other nonlinear industrial process such as computer numerical control (CNC) machines. In this paper, time-frequency expressions for the symmetrical components are developed using different wavelet transforms: Discrete Wavelet Transform (DWT), Wavelet Packet Transform (WPT) and Stationary Wavelet Transform (SWT). The paper also includes a comparative study of the results obtained when applying the developed approach using different wavelet basis functions, such as Daubechies, Coiflets and Symlets into three case studies (two synthetic and one real) including unbalanced three-phase system under different operating conditions while considering different kind of disturbances. The results are analyzed and conclusions are presented. The outcomes of this study lay the ground for further studies in unbalanced distribution system with high penetration of PHEVs, two-way protection devices for smart grid and power quality evaluation.     

同杆双回线复杂故障的精确计算

介绍同杆双回线复杂故障的精确计算方法.采用了精确的分布参数模型和多次叠加的算法,将分布电容和线路换位的影响计算在内从而精确地计算同杆双回线复杂故障下的工频电量.文中以单线接地后故障线的一侧断路器断开后的复杂故障为例阐明了该算法的原理.     

Application of neural networks to the management of voltage constraints in the Spanish market

The security criteria of a power system require that branch power flows and bus voltages are within their limits, not only in normal operating conditions but also when any credible contingency occurs. In the Spanish electricity market, voltage constraints are solved by connecting a set of off-line generators located in the areas where they occur. Thus, for a market participant it is necessary to predict approximately when its generating units are connected in order to prepare the annual budget and/or decide the time and location of new plants. The authors have presented in a former paper a methodology based on decision trees to estimate the daily load pattern of units, which have not been cleared in the daily energy market and can be connected to alleviate voltage constraints. In this paper, considering a set of potential explanatory variables, a different methodology based on neural networks is proposed to forecast if a non-connected unit will be committed by the System Operator to remove voltage violations. The performance of neural networks is illustrated with a study case. In addition, a thorough comparison with the methodology based on decision trees is carried out.     

Comparison of impedance based fault location methods for power distribution systems

Performance of 10 fault location methods for power distribution systems has been compared. The analyzed methods use only measurements of voltage and current at the substation. Fundamental component during pre-fault and fault are used in these methods to estimate the apparent impedance viewed from the measurement point. Deviation between pre-fault and fault impedance together with the system parameters are used to estimate the distance to the fault point.     

面向对象的实用复杂故障计算

文章首先说明了基于多口网络理论的电力系统复杂故障计算模型。然后说明了面向对象的概念 ,并用面向对象的思想实现了复杂故障计算。详细分析了复杂故障类的层次关系和实现。     

A new method for comparing the transfer function of transformers in order to detect the location and amount of winding faults

Since the transfer function (TF) is an acknowledged method for detecting power transformer faults, introduction of a proper manner to compare these TFs is necessary. Although a lot of effort has been made, proposed methods are not reliable. This paper presents a new approach based on weight functions, compared with all other methods. This comparison shows that the weight function method is much more effective than the others.     

Detection,classification, and location of faults in power transmission lines

This paper presents a pattern recognition approach for current differential relaying of power transmission lines. The current differential method uses spectral energy information provided through a new Fast Discrete S-Transform (FDST). Unlike the conventional S-Transform (ST) technique the new one uses different types of frequency scaling, band pass filtering, and interpolation techniques to reduce the computational cost and remove redundant information. Further due to its low computational complexity, the new algorithm is suitable for real-time implementation. The proposed scheme is evaluated for current differential protection of a transmission line fed from both ends for a variety of faults, fault resistance, inception angles, and significant noise in the signal using computer simulation studies. Also the fundamental amplitude and phase angle of the two end currents and one end voltage are computed with the help of the new formulation to provide fault location with significant accuracy. The results obtained from the exhaustive computation show the feasibility of the new approach.     

A novel fault location method for distribution networks with distributed generations based on the time matrix of traveling-waves

To improve location speed, accuracy and reliability, this paper proposes a fault location method for distribution networks based on the time matrix of fault traveling waves. First, an inherent time matrix is established according to the normalized topology of the target distribution network, and a post-fault time matrix is obtained by extracting the head data of initial waves from traveling wave detection devices. A time determination matrix is then obtained using the difference operation between the two matrices. The features of the time determination matrix are used for fault section identification and fault distance calculation, to accurately locate faults. The method is modified by considering economic benefits, through the optimal configuration of detection devices of traveling waves when calculating fault distances. Simulation results show that the proposed method has good adaptation with higher fault location accuracy than two other typical ones. It can deal with faults on invalid branches, and the error rate is under 0.5% even with connected DGs.