On the modeling of long arc in still air and arc resistance calculation

An important macroscopic arc parameter, describing its complex nature is the arc resistance. It can be easily calculated by using the well-known Warrington formula. Authors investigated the results of Warrington's tests. By taking into account the conditions under which they are obtained (e.g., inaccurate measurement devices), it is unquestionable that these results are today highly empirical and not accurate and general enough. Laboratory testing provided in the high-power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the basis for the research results presented in the paper. Based on the analysis of laboratory-recorded arc voltage and current waveforms, the new arc model is derived. An example of arc computer simulation using the new model is given. Based on the new arc model, a new approach to arc resistance calculation is presented. The new formula for arc resistance is compared with the old Warrington formula.     

Direct estimation of voltage phasor, frequency and its rate of change using Newton''s iterative method

A new approach to the design of a digital algorithm for direct estimation of voltage phasor, frequency and its rate of change is presented. The algorithm derived is based on Newton's iterative method, very commonly used in the field of unconstrained optimization studies. A five-parameter voltage model was assumed, so the result of the estimation was a parameter vector, consisting of the following unknown parameters of the voltage signal processed: its DC component, magnitude, phase angle, frequency and its rate of change. To demonstrate the performance of the algorithm, off-line computer simulation results are presented. The algorithm showed high measurement accuracy over a wide range of frequency changes. The algorithm ‘order two convergence’ provided a very good dynamic response as well as a fast algorithm adaptability. The new algorithm seems to be a particularly useful tool in the field of frequency relaying as well as in various aspects of power engineering applications.     

Distance protection and fault location utilizing only phase currentphasors

Two numerical algorithms for fault location and distance protection which use data from one end of a transmission line are presented. Both algorithms require only current signals as input data. Voltage signals are unnecessary for determining the unknown distance to the fault. The solution for the most frequent phase to ground fault is presented. The algorithms are relatively simple and easy to be implemented in the on-line application. The algorithms allow for accurate calculation of the fault location irrespective of the fault resistance and load. To illustrate the features of the new algorithms, steady-state and dynamic tests are presented     

Measurements get together

EEveryday life relies heavily on the reliable operation and intelligent management of critical infrastructures, such as electric power systems, telecommunication networks, and water distribution networks. Designing, monitoring and controlling such systems is becoming increasingly more challenging as a consequence of the steady growth of their size, complexity, level of uncertainty, unpredictable behavior, and interactions. These critical infrastructures are susceptible to natural disasters, frequent failures, and malicious attacks. At the epicenter of the well-being and prosperity of society lie the electric power systems. The secure and reliable operation of modern power systems is an increasingly challenging task due to the ever-increasing demand for electricity, the growing number of interconnections, penetration of variable renewable energy sources, and deregulated energy market conditions. Power companies in different parts of the world are therefore feeling the need for a real-time wide area monitoring, protection, and control (WAMPAC) system. Synchronized measurement technology (SMT) has the potential of becoming the backbone of this system. The major advantages of using SMT are that 1) the measurements from widely dispersed locations can be synchronized with respect to a global positioning system (GPS) clock, 2) voltage phase angles can be measured directly, which was so far technically infeasible, and 3) the accuracy and speed of energy management system (EMS) applications (e.g., state estimation) increases manifold.     

Numerical algorithm for adaptive autoreclosure and protection of medium-voltage overhead lines

In this paper, a new numerical algorithm for medium-voltage overhead lines, autoreclosure, is described. The subfunction of the autoreclosure scheme that would inhibit the first shot after detecting a solid fault (as compared with an arc fault) is evaluated and presented. It is based on one terminal data processing and it is derived in the time domain. In the algorithm the fault nature (arcing or arcless fault) is estimated using linear least error squares estimation technique. The arc, occurring on the fault point during arcing faults on overhead lines, is included in the problem consideration. In addition, by introducing the prefault load current in the existing model, better algorithm performances and a more reliable adaptive algorithm for autoreclosure are achieved. The algorithm is derived for the case of three-phase symmetrical fault. The results of the algorithm testing through computer simulation are presented. Particularly the algorithm sensitivity to arc elongation effects, supplying network parameters, and processing of the signals in the presence of harmonics are tested and analyzed.     

Dynamische Frequenzmessung durch ein verbessertes rekursives Newton-Raphson-Parameterschätzverfahren

Contents In spite of existing modern estimating techniques, the parameter estimation of non-linear and time-variant processes with noisy measuring signals is difficult. This is the case with frequency measurement in power engineering. In order to achieve good results under these conditions, a recursive parameter estimation method is derived from the non-recursive Newton Raphson method. Additionally, the forgetting factor adaptation procedure is suggested in the new method, which improved both the algorithm convergency and accuracy. By computer simulation results of applying the new improved method for the purpose of frequency measurement in power system protection are obtained. For numerous input signals the new improved method was successfully applied and shows better results in comparison with the basic method.

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Dynamische Frequenzmessung durch ein verbessertes rekursives Newton-Raphson-Parameterschätzverfahren

Übersicht Trotz moderner Schätzverfahren ist die Parameterschätzung nichtlinearer und zeitvarianter Prozesse bei gestörten Meßsignalen schwierig. Dies ist auch der Fall bei der Frequenzmessung im elektrischen Energieversorgungsnetz. Um unter diesen Bedingungen gute Resultate zu erhalten, wird ein rekursives Parameterschätzverfahren aus dem ursprünglichen nichtrekursiven Newton-Raphson-Verfahren abgeleitet. Darüberhinaus wird in diesem neuen Verfahren eine Anpassung des Gedächtnisfaktors vorgeschlagen, die sowohl die Konvergenzeigenschaften als auch die Genauigkeit verbessert. Durch Simulationsrechnungen werden Erfahrungen bei der Anwendung des neuen rekursiven Parameterschätzverfahrens für die Frequenzmessung im Netzschutz gewonnen. Bei zahlreichen Eingangssignalen konnte das verbesserte Verfahren mit Erfolg eingesetzt werden, während das ursprüngliche versagte.

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Dieser Aufsatz ist Herrn Prof. Dr.-Ing. D. Nelles gewidmet.     

Wake effect in wind farm performance: Steady-state and dynamic behavior

The aim of this paper is to evaluate the impact of the wake effect on both the steady-state operation and dynamic performance of a wind farm and provide conclusions that can be used as thumb rules in generic assessments where the full details of the wind farms are unknown. A simplified explicit model of the wake effect is presented, which includes: the cumulative impact of multiple shadowing, the effects of wind direction and the wind speed time delay. The model is implemented in MATLAB^® and then integrated into a power system simulation package to describe the wake effect and its impact on a wind farm, particularly in terms of the wake coefficient and overall active power losses. Results for two wind farm layouts are presented to illustrate the importance of wind turbine spacing and the directionality of wind speeds when assessing the wake effect during steady-state operation and dynamic behavior.     

电力系统频率动态行为衍变与分析方法需求综述

低惯量可再生能源发展导致电力系统运行形态发生变化, 频率动态行为愈加复杂, 频率安全稳定面临新的挑战。阐述频率动态响应过程, 综述频率动态行为量化特征和分析方法, 强调基于人工智能分析方法的优势和前景。从可再生能源发电强波动、电源非同步并网低惯量及大功率缺额与连锁故障高风险三个角度, 分析电力系统运行形态变化, 探讨对频率分析与控制的新要求。剖析可再生能源快速发展背景下电力系统等效惯量的内涵, 综述可再生能源虚拟惯量控制方法, 强调多类型虚拟惯量协调控制的优势和前景。总结频率分析与控制领域中亟待研究的重点内容, 给出后续研究建议。     

Effective Two-terminal Numerical Algorithm for Overhead Lines Protection

In the paper an effective numerical algorithm for overhead lines protection, particularly fault location and adaptive autoreclosure, is presented. It is based on the two terminal line currents and voltages acquisition. For this purposes the synchronized sampling of all analogue input variables, i.e. the application of the Global Position System/Phasor Measurement Units, was assumed. The algorithm presented is derived in the spectral domain. By this the set of third harmonics variables and line parameters was also used. The prerequisite for successfully adaptive autoreclosure functionality realization was the suitable modelling of the electrical arc. Arc was considered as a source of higher harmonics, distorting by this other electrical variables. In the arc modelling, results of laboratory testing were used. Algorithm is tested for a typical network configuration, assuming by this that the line considered was short enough to neglect its capacitive nature. Based on the results obtained, it is very realistic that the algorithm presented could be implemented in praxis in modern Intelligent Electronic Devices (IEDs).     

Numerical algorithm for overhead lines protection and disturbance records analysis

A new and very efficient numerical algorithm for overhead lines protection is presented. The algorithm particularly improves up-to-date solutions with regard to fault location, adaptive autoreclosure, detailed disturbance records analysis and fault data management. It is based on the two-terminal line currents and voltages acquisition. For this purpose, the synchronised sampling of all analogue input variables, that is, the application of the global positioning system/phasor measurement units, was assumed. The algorithm presented is derived in the spectral domain and based on the application of the discrete Fourier transform. The prerequisite for the successful adaptive autoreclosure functionality realisation was the suitable modelling of the electrical arc. The electrical arc was considered as a source of higher harmonics. These are included in the complete fault model, which was the starting point for the development of this new algorithm. One of the algorithm's sophisticated features is its ability to determine both the arc and the fault resistance. For the purpose of arc modelling, the results of high current laboratory testing are used. The algorithm is tested through computer-based simulation of a line connected to two active networks. On the basis of the results obtained, it is very realistic that the algorithm presented could be implemented in praxis in modern intelligent electronic devices