Waldemar Rebizant

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

Correction of Current Transformer Transient Performance

If a current transformer (CT) saturates while transforming the heavy primary current, in each period, there are sections when the magnetic core is unsaturated and transformation is correct, and when it is saturated, it causes enormous errors. The key to correct the errors is to detect instants of saturation and moments when the saturation ends. This paper presents simple and efficient methods of doing that. In addition, it shows the way how to predict up to three samples after saturation with the acceptable degree of accuracy, thus artificially expanding the unsaturated section. It may substantially facilitate operation of protective devices. The ultimate solution of the problem is to estimate the values of the fundamental frequency component amplitude and the decaying DC component in each period. This paper presents the method of doing that on the ground of four consecutive samples taken during the unsaturated section. If the primary current consists of the fundamental and DC exponential components only, the accuracy of the method is excellent. Neglecting contamination of the current signal with harmonics and noise, it is possible to reconstruct the CT primary current based on the measured values of fundamental and DC components.

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.

Fuzzy logic application to out-of-step protection of generators

Efficient protection scheme against out-of-step (OS) conditions based on fuzzy logic (FL) technique is presented. The protection proposed makes use of an adaptive-network-based fuzzy inference system (ANFIS). The FL-based OS protection scheme developed has been thoroughly optimized and tested with ATP-generated case signals. The scheme designed displays almost perfect efficiency and high speed of OS detection. With the scheme designed the OS cases are identified much earlier comparing to standard impedance-based protection schemes. Wide robustness features of the ANFIS-based scheme have also been achieved.

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.

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.

Wavelet transform approach to high impedance fault detection in MV networks

Application of wavelet transform technique to high impedance arcing fault detection in distribution networks is presented. Phase displacement between discrete wavelet coefficients calculated for zero sequence voltage and current signals at natural network frequency is tracked. The developed wavelet based HIF detector has been tested with EMTP-ATP generated signals, proving better performance than traditionally used algorithms and methods. The protection method proposed is efficient, robust and may be used for HIF detection independently of the network neutral point grounding mode.

Ultrasaturation Phenomenon in Power Transformers—Myths and Reality

In this paper, the ultrasaturation phenomenon of power transformers during their energization is studied. It is shown that under special conditions, the currents observed after transformer switching on do not contain enough restraining information (e.g., second harmonic), which may lead to protection maloperation. This paper concentrates on a thorough explanation of the problem and possible causes of ultrasaturation. Theoretical investigations are supported and illustrated with simulation studies performed both with MATLAB and electromagnetic transients program-alternative transients program. The outcomes of this research can further be used as hints for substation operation personnel as well as for the development of new protection stabilization criteria, which is not discussed further in this paper.

Fuzzy Adaptive Transmission-Line Differential Relay Immune to CT Saturation

This paper presents an enhanced current differential protection scheme with fuzzy inference system (FIS) support for high-voltage transmission lines. The proposed adaptive fuzzy scheme combines strengths of current and phase comparison protection criteria. The relay stabilization characteristic is adapted online depending on the output of the fuzzy reasoning scheme supplied with information from the phase comparison unit. The resulting protection is characterized by improved selectivity for external fault cases as well as when nearby transformer inrush currents cause the saturation of current transformers installed in the protected line. The performance of the fuzzy protection scheme has been tested with the signals generated with the use of Alternative Transients Program-Electromagnetic Transients Program and compared to the traditional solutions.

Sensitive protection of power transformers for internal inter-turn faults

In the paper new sensitive algorithms for detection of internal inter-turn faults in power transformers are described. Such faults are extremely difficult to detect since they induce negligible increase of the currents at the transformer terminals, although the currents flowing at the fault place are very high and dangerous for the transformer. The algorithms developed are based on the differential equation of the equivalent circuit of the transformer. In one version additional information from a CT installed inside of the triangle of delta side windings is used, which brings very promising results. Theoretical investigations are supported and illustrated with simulation studies performed with EMTP-ATP.