Janusz Szafran

Digital Signal Processing in Power System Protection and Control

Digital Signal Processing in Power System Protection and Control bridges the gap between the theory of protection and control and the practical applications of protection equipment. Understanding how protection functions is crucial not only for equipment developers and manufacturers, but also for their users who need to install, set and operate the protection devices in an appropriate manner.After introductory chapters related to protection technology and functions, Digital Signal Processing in Power System Protection and Control presents the digital algorithms for signal filtering, followed by measurement algorithms of the most commonly-used protection criteria values and decision-making methods in protective relays. A large part of the book is devoted to the basic theory and applications of artificial intelligence techniques for protection and control. Fuzzy logic based schemes, artificial neural networks, expert systems and genetic algorithms with their advantages and drawbacks are discussed. AI techniques are compared and it is also shown how they can be combined to eliminate the disadvantages and magnify the useful features of particular techniques.The information provided in Digital Signal Processing in Power System Protection and Control can be useful for protection engineers working in utilities at various levels of the electricity network, as well as for students of electrical engineering, especially electrical power engineering. It may also be helpful for other readers who want to get acquainted with and to apply the filtering, measuring and decision-making algorithms for purposes other than protection and control, everywhere fast and on-line signal analysis is needed for proper functioning of the apparatus.

A new method of voltage stability margin estimation based on local measurements

The paper presents a method of monitoring the local voltage stability of the power system at the receiving node. To estimate the voltage stability margin a simplified equivalent circuit - called the Thevenins equivalent is used. Publication concerns three main issues: creation and updating of the Thevenins circuit model, determination of voltage stability margin and verification of proposed methods. Two methods of Thevenins model parameters calculation are presented: analytical and based on local phasors measurements. To define the Thevenins parameters by using analytical method there is a need to know current configuration of power system. The second method uses only available locally measurements. During the changes of load admittance, actual value of bus voltage, apparent power and derivatives of apparent load power against the node voltage dS/dV are determined. This allows to update continuously parameters of Thevenins circuit and to follow the ongoing changes in the power system. These changes may be caused by normal switching operations or unexpected faults. Thevenins model parameters are used to calculate local voltage stability margin. The paper presents also the performance and accuracy tests of the algorithm used in calculation of Thevenins model parameters and algorithm for determining voltage stability margin.

Adaptive measurement of power system currents, voltages and impedances in off-nominal frequency conditions

The problem of basic power system electric quantities (current, voltage magnitudes, power and impedance) measurement in off-nominal frequency conditions is considered under the assumption that the quantities are calculated from orthogonal components of input current and voltage phasors which are obtained by the use of nonrecursive digital filters. Adaptive algorithms which make the measurement insensitive to wide range frequency changes of the input signals are presented. The adaptive features of the algorithms are obtained by use of the frequency measuring algorithm and modification of orthogonal filter coefficients and data window length. Sample results of simulation studies which show the algorithm performance are presented and discussed.

Fundamentals of System Analysis and Synthesis

Synthesis of digital power system protection systems is possible with application of many advanced and complex mathematical tools. Understanding of digital systems, digital signal processing, analysis and synthesis of digital filters require transformations between time and frequency domain as well as transitions between continuous and discrete data and systems. All of them belong to the family of methods being a part of signal and system theory and use Fourier, Laplace and Z transforms as well as Fourier series as the most important mathematical basis.

Application of Kalman filter technique to stationary and nonstationary state observer design

The paper presents a method of power system current and voltage estimation using the state space signal model approach. Design of stationary and nonstationary state observers based on Kalman filter technique is described. The results of dynamic performance of the state observers are presented for simulated fault currents and voltages obtained from EMTP model of 400 kV transmission line. The advantages and drawbacks of both types of state observers are discussed.

Evolutionary improvement of neural classifiers for generator out-of-step protection

In the paper the results of investigation are presented on application of artificial neural networks to protection of synchronous machines against out-of-step conditions. The new ANN-based protection ensures faster and more secure detection of generator loss of synchronism when compared to traditional solutions. To determine the most suitable network topology for the recognition task a genetic algorithm is proposed. The final ANN structure is found using the rules of evolutionary improvement of the characteristics of individuals by concurrence and heredity. The proposed genetic optimisation principles have been implemented in Matlab programming code. The initial as well as further consecutive network populations were created, trained and graded in a closed loop until the selection criterion was fulfilled. The results of thorough testing of the designed protection scheme with ATP-generated power system signals are described and discussed.

Estimation, control and prediction of voltage level and stability at receiving node

The paper presents issues of receiving node voltage stability. Voltage level is related to voltage stability. However, this value is not always a good indicator of distance to the stability limit. Discrepancies may occur especially when voltage regulation is performed. Such regulation causes changes of voltage level and voltage stability conditions. Thus, it seems reasonable to observe and predict voltage stability margin. In the paper basic information about the voltage stability considered as a local problem and voltage regulation influence on stability conditions are presented. Method of stability conditions calculation using local information and including of this parameter in the regulation processes are proposed. Stability margin calculation is based on on-line local measurements and the range of change of Thevenin model parameters determined in off-line studies. During simulations two models were used: IEEE 14-bus test system (ATP-EMTP) and node model containing voltage regulation (Matlab).

The Double Diploma Project: A New Higher Education Concept in a United Europe

Due to todays highly competitive and unstable job market the educational process of young people is more important than ever. New possibilities to improve both qualifications and the level of education are needed. After the expansion of the European Union the process of exchange and studying abroad in EU countries has become much easier. This increased mobility of students has created a need to standardise the structure of higher education. Student exchange programmes, e.g. SOCRATES-ERASMUS, provide the possibility of studying for one or two semesters at a partner university abroad, after which the student returns to his/her mother university. However, under this type of exchange programme the student can neither write the diploma thesis at the partner university abroad nor receive his/her degree from this university. In 2002, a new concept in educational cooperation began between the Otto-von-Guericke University in Magdeburg, Germany, and the Wroclaw University of Technology — Poland, called the Double Diploma, which offers such possibilities. Prerequisites for participation are good grades during studies at the mother university (Wroclaw University of Technology) and knowledge of the German language. The qualified persons go to the partner university (Otto-von-Guericke University) and study there for two years. After passing all examinations and defending his or her thesis, the student receives a Masters diploma in Engineering from both partner universities.

Adaptive and Intelligent Systems for Generator Monitoring and Protection Purposes

Abstract New adaptive scheme for signal parameter measurement for generator monitoring and protection is presented. The algorithm is based on the orthogonal components of currents and voltages obtained with adaptive orthogonal filters. The filter data window length and coefficients are adapted according to coarsely estimated signal frequency. As a result, the measurements can be performed with high accuracy in wide frequency band conditions, i.e. also for generator start-up, etc. The measured signals are further used for training of artificial neural networks with the aim to design a robust and effective classifier of generator operation mode. The main attention is paid to the phenomena accompanying pole slipping and out-of-step conditions.

Analysis of protection criterion values algorithms in case of distorted signals

Nowadays fast increase of nonlinear elements number in the power system is observed. Besides of nonlinear loads there are also new energy sources that require electronic and power electronic equipment. These elements cause distortion of electrical signals and presence of higher harmonics in currents and voltages. Algorithms of protection criterion values are matched to fundamental components of currents and voltages and can cause errors due to these harmonics. In the paper some signals and load models are considered as well as the most influenced criterion values including a few models of a reactive power. As a complement practical model of nonlinear heating system is described and analysed.