Transmission line distance protection based on wavelet transform

Wavelet transform (WT) has the ability to decompose signals into different frequency bands using multiresolution analysis (MRA). It can be utilized in detecting faults and to estimate the phasors of the voltage and current signals, which are essential for transmission line distance protection. A digital distance-protection scheme for transmission lines based on analyzing the measured voltage and current signals at the relay location using WT with MRA is presented in this paper. The scheme has been tested by both computer simulation and experimentally. The tests presented include solid ground faults, phase faults, high impedance and nonlinear ground faults, and line charging.     

Two-stage numerical algorithm for distance protection, fault location and arcing faults recognition

In this paper, a novel two-stage numerical algorithm devoted to fault distance calculation and arcing faults recognition is presented. The first algorithm stage serves for the fault distance calculation. The fault distance is calculated from the fundamental frequency phase voltages and current phasors, thus utilizing the positive- and the zero-sequence impedances of the line as input parameters. The second algorithm stage serves for the arc voltage amplitude calculation. It utilizes the fault distance calculated in the first algorithm stage as well as the third harmonics of the terminal phase voltage and line current phasors, respectively. From the calculated value of arc voltage amplitude it can be determined whether the fault is transient arcing fault or permanent arcless fault. The phasors needed for algorithm execution are calculated by using the Discrete Fourier Technique. In this paper, the solution for the most frequent phase-to-ground faults is given. The results of algorithm testing through computer simulation and real field data records processing are given.     

An adaptive PMU based fault detection/location technique fortransmission lines. I. Theory and algorithms

An adaptive fault detection/location technique based on a phasor measurement unit (PMU) for an EHV/UHV transmission line is presented. A fault detection/location index in terms of Clarke components of the synchronized voltage and current phasors is derived. The line parameter estimation algorithm is also developed to solve the uncertainty of parameters caused by aging of transmission lines. This paper also proposes a new discrete Fourier transform (DFT) based algorithm (termed the smart discrete Fourier transform, SDFT) to eliminate system noise and measurement errors such that extremely accurate fundamental frequency components can be extracted for calculation of fault detection/location index. The EMTP was used to simulate a high voltage transmission line with faults at various locations. To simulate errors involved in measurements, Gaussian-type noise has been added to the raw output data generated by EMTP. Results have shown that the new DFT based method can extract exact phasors in the presence of frequency deviation and harmonics. The parameter estimation algorithm can also trace exact parameters very well. The accuracy of both new DFT based method and parameter estimation algorithm can achieve even up to 99.999% and 99.99% respectively, and is presented in Part II. The accuracy of fault location estimation by the proposed technique can achieve even up to 99.9% in the performance evaluation, which is also presented in Part II     

Fast orthogonal search approach for distance protection of transmission lines

A distance protection scheme for transmission lines based on analyzing the measured voltage and current signals at the relay location using fast orthogonal search (FOS) is presented in this paper. FOS has the ability to accurately provide fast estimate of the voltage and current fundamental frequency phasors that are required for a digital distance relay. Compared to the conventional FFT, FOS can estimate the fundamental phasors with higher accuracy and less number of samples. The proposed scheme has been tested on a transmission line model to verify the merit of this approach. The tests presented include solid ground faults, phase faults, and high impedance faults at different fault locations and loading conditions. The proposed scheme can classify all fault cases in less than one cycle after the inception of the faults.     

Modal decoupling of overhead transmission lines using real and constant matrices: Influence of the line length

The Clarke’s matrix is a well-known real and constant transformation matrix used for modal transformation in three-phase transmission lines modeling. Although modal analysis has been widely discussed in the technical literature on power system modeling, a new content is approached in this research proving that the approximation using an exact and constant modal transformation matrix depends on both the frequency-dependent parameters and transmission line’s length. As an important conclusion, the approach using the Clarke’s matrix leads to more accurate results considering long transmission lines. There are two methods for modal decoupling in power systems modeling. The first uses only a single constant and real transformation matrix during the entire modeling/simulation routine. The second uses the frequency-dependent transformation matrix for parameters decoupling into the propagation modes and the Clarke’s matrix for mode-to-phase transformation of voltage and current values during simulations. The accuracy of these two modeling/simulation processes are evaluated, in the time and frequency domains, based on results obtained from a reference routine that employs the exact frequency-dependent matrix in modal transformations and numerical transforms for simulation in the time domain. The proposed analysis proves that the accuracy of both methods varies with the line length during electromagnetic transient simulations that leads to peak errors up to approximately 10%. The influence of the line length in modal analysis techniques was not approached in previous references on power system modeling, which represents the original contribution of this paper.     

含逆变器的微电网动态相量模型

微电网作为一种分布式可再生能源并网的有效途径,是传统电力系统的重要补充。然而,微电网中含有大量的并网逆变器、机端负荷和线路,其电磁暂态过程给微电网的建模、分析和控制带来了巨大的挑战。以并网逆变器、线路和机端负荷的动态相量模型为基础,建立含并网逆变器的微电网动态相量模型。最后,在电磁暂态综合分析程序PSCAD/EMTDC中建立一个含有多台并网逆变器的微电网模型,并在Matlab/Simulink中建立其动态相量模型。仿真试验的结果验证了所提微电网动态相量模型的正确性和有效性,为并网逆变器和微电网的建模、分析和控制提供了一种新方法。     

Protection of parallel transmission lines using wavelet transform

A new scheme to enhance the solution of the problems associated with parallel transmission line protection is presented in this paper. The scheme depends on the three line voltages and the six line currents of the two parallel lines at each end. Fault detection, fault discrimination, and calculation of the phasors of the measured signals are done by using wavelet transform (WT). By comparing the magnitudes of the estimated current phasors of the corresponding phases on both lines, internal faults on the parallel lines can be identified. Also, by calculating the distance element of the phases on which a disturbance is detected and having a very small current difference magnitude can enhance and strengthen the scheme. Studies show that all types of faults at different loading conditions can be correctly identified in less than one cycle of the fundamental frequency.     

Accurate fault location algorithm for double-circuit series compensated lines using a limited number of two-end synchronized measurements

This paper presents a new fault location algorithm for double-circuit series compensated lines based on synchronized phasor measurements. Only the sequence current phasors from both ends of the line and the sequence voltage phasors from one local end are taken as input, limiting thus the amount of data needed to be exchanged between the line terminals. In addition, the proposed algorithm does not utilize the model of the series compensation device, eliminating thus the errors resulting from modeling such devices. The new algorithm consists of three steps. In the first step, the fault type and the circuit(s) involved in the fault are determined using a synchrophasor-based fault type selection method. In the next step, the algorithm applies two subroutines designating for locating faults on particular line sections which are defined according to the series compensation placement along the line. In these subroutines, the sequence voltages and currents at the fault point are expressed with respect to the known sequence voltages and currents at the two measuring ends and the distance to fault. Then, using the fault boundary conditions that exist for a given fault type, the fault location is solved by an iterative method. Finally, in the last step a procedure for selecting the valid subroutine is applied. Due to zero sequence mutual coupling, it is not straightforward to express the zero sequence voltage and current at the fault point as a function of the zero sequence voltages and currents at the measuring ends and the distance to fault. To overcome this problem, a modal transformation matrix is introduced to obtain the modal networks, which are decoupled and can be analyzed independently. Based on distributed parameter line model, the proposed algorithm fully considers the effects of shunt capacitances and thus achieves superior locating accuracy, especially for long lines. Mutual coupling between circuits, source impedances and fault resistance does not influence the locating accuracy of the algorithm. Simulation results using ATP-EMTP and MATLAB demonstrate the effectiveness and accuracy of the proposed algorithm.     

基于电流双反相量的同杆四回线故障选相方法

为了解决同杆四回线故障情况复杂,跨线故障时无法应用单回线故障选相方法的难题,提出了一种基于故障电流双反相量的同杆四回线故障选相方法。同杆四回线发生一回线内或两回线间跨线故障时,对四回线各相电流进行变换,可得故障相电流的双同及双反相量。通过对故障电流边界条件的分析可知,不同类型故障时故障电流的3个双反相量分别具有不同的幅值和相位特点。以此为基础,提出了在一回线内故障和两回线间跨线故障时能够准确识别故障回线和故障相的同杆四回线故障选相方法。仿真表明本方法在不同的负载电流、过渡电阻、故障位置及故障类型下均能进行有效的故障选相。     

复杂电力系统电气故障电磁暂态数字计算方法研究

电力系统电磁暂态的数值仿真研究是一个历久不衰的研究题目，尤其是其时域仿真研究中的Bergeron模型经Dommel实用化改进后，业已成功地应用于著名的EMTP当中，但ENYFP的严重不足在于对各种故障和操作进行暂态仿真前的预处理工作是相当繁杂的。文章针对EMTP使用中的不足，提出了一种普遍适用的电力系统电气故障电磁暂态仿真方法。该方法克服了EMTP由于系统结构或参数改变需要重新计算初始值的缺点，它可以仿真包括串补线路在内的单、双回线路任意点的电弧故障、母线故障、断路器开合和断线故障，并且故障起始角可以设定。新方法可极其方便地对线路故障点序列——系列冲击电流、过电压和谐波分量进行系列数字仿真，亦可极其方便地仿真发展型故障，在线路保护仿真校验和过电压计算等方面极具意义。大量仿真表明，本方法精度高、速度快。     

含统一潮流控制器装置的电力系统动态混合仿真接口算法研究

提出了一种新的含UPFC装置的电力系统动态混合仿真接口算法，算法中对UPFC采用动态相量建模，对电力系统网络则采用成熟的机电暂态仿真。仿真中UPFC并联侧采用定交流母线电压控制和定直流电容电压控制，串联侧采用定线路潮流控制。文中推导了UPFC的动态相量模型，讨论了与网络机电暂态模型的接口算法。研究分析和算例仿真表明：使用动态相量建模可精确地仿真UPFC的电磁暂态（EMT）过程，且仿真速度快；文中所提混合仿真方案能保证较快的仿真速度和优良的仿真精度，具有较好的收敛性，且可用于含UPFC等FACTS装置的系统发生不对称故障时的暂态稳定分析。     

Tools for dynamic analysis of the general large power system using time-varying phasors

This paper extends the applicable range of phasors for transient analysis from the traditional slow quasi-stationary range to accommodate fast speeds up to the carrier frequency. Rigorous phasor calculus is developed for time varying low pass phasor signals whose bandwidths are less than the 60 Hz carrier frequency. Symmetrical components technique for analysing quasi-stationary unbalanced power system transients is extended to cover the low pass time-varying phasors. It is also proved that the time varying phasors can be used for computing the fast electromagnetic transients within the linear RLC lumped parameter representation of the transmission network irrespective of the transient speeds. In linear networks, this time-varying phasor concept unifies two classical approaches: (1) transient analysis using instantaneous currents and voltages, and (2) steady state analysis using traditional phasors, into analysing both behaviours precisely using the time-varying phasors.     

一种新的电力系统短路故障测距方法

本文提出一种新的精确测定电力系统短路故障距离的计算方法，该方法只需线 路单端电压及电流测量值，不受系统电源阻抗、故障类型及接地电阻等因素的 影响；同时该方法建立在电力线路精确的分布参数模型的基础上，因此为提高 测距精度奠定了理论基础。     

A novel adaptive PMU-based transmission-line relay-design and EMTP simulation results

This paper proposes a novel adaptive relaying scheme based on phasor-measurement units (PMUs) for transmission lines. The proposed adaptive relaying scheme can provide an extremely accurate discrimination between in-zone and out-of-zone faults. Two novel and composite fault discrimination indices in terms of Clarke components of synchronized voltage and current phasors at two ends of a line are derived. A line parameter estimation algorithm is developed and built in the newly designed relay to solve the uncertainty problem of line parameters. The proposed relaying scheme is independent of fault types, fault locations, fault path resistance, fault inception angles, and the variations of source impedance. The tripping decision time of the designed relay is very fast and almost held well within 6 ms for most fault events. All of the EMTP simulation results show that the proposed adaptive relaying scheme provides a high level of dependability and security.     

基于双频法的树形配电线路单相断线兼接地故障诊断

针对树形配电线路特点，建立分布参数电路模型，利用故障后线路起始端的电压，电流相量，提出了树形配电线路单相断线兼接地故障定位新算法。本方法将始端相量逐分支向后传递故障点逐分支探索的方法实现故障测距，并利用双频法识别真伪故障。     

Hybrid Traveling Wave/Boundary Protection for Monopolar HVDC Line

A novel hybrid protection algorithm, based on traveling wave protection principle and boundary protection principle for a monopolar HVDC line is proposed. Stationary wavelet transform (SWT) is adopted in the traveling wave protection to process the dc signal and then wavelet modulus maxima are used to further represent the useful traveling wave signal. The boundary protection principle based on SWT is used jointly with traveling wave protection to distinguish internal faults from external faults. The effect of border distortion, noise, high ground fault resistance, close-up faults, transients caused by lightning strokes and different dc line terminations are considered in the paper.      

Fast and accurate parameter estimation algorithm for digital distance relaying

Response of digital distance relaying depends on the fast and accurate calculation of parameters such as voltage and current phasors and fault impedance. This paper describes a new apparent impedance estimation algorithm that is based on modal components theory. It is shown in the paper that the proposed algorithm has several advantageous features in terms of speed and accuracy over previously suggested symmetrical and modal components based algorithms. The paper discusses a procedure for deriving a fault impedance estimation algorithm that can be used for protecting power transmission lines. The proposed algorithm was evaluated using an alternative transient program (ATP). The program models a power system, simulates many fault conditions on a selected transmission line and generates fault data. The relay software then obtains filtered, scaled and sampled data and calculates fault impedance using the proposed algorithm. The relay characteristic makes trip decisions based on the fault impedance estimates. The paper shows the feasibility of the proposed algorithm for first zone distance protection. Some results of these studies are presented and discussed in the paper.     

A new PMU based power swing detector to prevent mal-operation of distance relay

In conventional transmission line protection, a distance relay is used to provide the primary as well as remote backup protection. The voltage and current phasors measurement needed by the distance relay for determining the impedance may be affected by the power disturbances such as power swing. Consequently, this power swing may cause mal-operation of Zone three distance relays which in turn may affect on the reliability of the whole protective scheme. To mitigate these effects and hence improve the relay reliability, this work proposes a new real-time power swing detector using phasor measurement units for blinding the distance relay only during this transient disturbance. However, this developed detector will not block relay when the power swing accompanied with faults. To validate the present work, the performance of developed enhanced distance relay is tested by signals generated by Simulink/MATLAB simulator under different conditions. The test results show that this proposed scheme provides good discrimination between the transient currents and the fault current which in turn it may contribute in enhancing the reliability of Distance relay.     

An adaptive approach for three zone operation of digital distance relay with Static Var Compensator using PMU

Modern energy transmission systems suffer from great voltage dropping due to enormous loads. Therefore appropriate schemes should be devised to regulate the voltage. FACTS devices such as Static Var Compensator are often used for this purpose. However, SVC at mid-point of transmission line may leads to deteriorate of distance relay operation, resulting in inaccurate estimation of faults locations i.e. over-reach or under reach for different cases. This paper proposed a new algorithm that utilizes synchronized phasors measurement (SPM) to enhance the operation of distance protection zone in many aspects. The proposed method is tested for 230 kV system simulated in EMTDC/PSCAD with Bergeron model of transmission line. The results prevailed for adaptive approach scheme are more accurate, victor and robust in equivalence with usable transmission line distance protection with SVC.