Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Mirosław ŁUKOWICZ"

Analysis of the synchrophasor estimation problem DOI:10.15199/48.2018.11.20

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An accurate estimation of electrical signal parameters is a fundamental issue as far as the appropriate operation and control of a power system is concerned. The imbalance between power supply and the load leads to dynamic changes in the system state, so that the voltage and current values, waveshapes and system frequency may differ from nominal. Efficient control of an electrical network requires more and more accurate information on signal parameters. This includes accurate measurement of the signal phase, amplitude, frequency, higher harmonics, rate of change of frequency and the amplitude change rate. These parameters can be represented concisely as a complex valued function referred to as a phasor. As a result, in standard C137.118.1- 2011 [1], estimation algorithms have been organized and divided into P (protection) and M (measurement) classes depending on their purpose. M class algorithms are designed for measurement devices with high accuracy requirements and slow response times. P class algorithms are designed for protection purposes with a strict response time and overshoot limits, but higher estimation errors are acceptable. The phasor estimation issue has been approached in various ways and methods. The most popular concept of a phasor estimation is based on Fourier transform algorithms, in particular short time Fourier transform (STFT). This includes the process of the optimal filter design to ensure appropriate noise damping, good dynamical properties and more effective higher harmonic damping [2], [3]. It has been observed that even a proper filter design can be insufficient for processing of abnormal signals. More advanced methods of filter design employ dynamic filtering to enhance phasor estimation for off nominal frequencies [4], [5]. The most accurate estimation method involves polynomial approximation [6], [7], [8]. Least square method (LSM) is used to evaluate polynomial coefficients of the correspondi[...]

Selection of Zone 3 time delay for backup distance protection using probabilistic fault trees with time dependencies

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W pracy analizowany jest system zabezpieczeń odległościowych linii elektroenergetycznej. Badane jest zdarzenie: odległy (rezerwowy) wyłącznik zostaje wyłączony, mimo że może być wyłączony wyłącznik lokalny (podstawowy). Prawdopodobieństwa wystąpienia tego zdarzenia w funkcji czasu opóźnienia Strefy 3 zabezpieczenia rezerwowego wyznaczane są za pomocą probabilistycznych drzew niezdatności z zależnościami czasowymi. (Dobór czasu opóźnienia Strefy 3 rezerwowego zabezpieczenia odległościowego za pomocą probabilistycznych drzew niezdatności z zależnościami czasowymi) Abstract. Distance protection schema of power system is analyzed in the paper. Hazard is the event: remote (backup) circuit breaker tripping provided the local (primary) circuit breaker can be opened. Incorrect values of set time delays can cause the hazard. In the paper, the emphasis is put on selection of Zone 3 time delay of backup distance protection. Hazard probabilities as functions of this time values have been obtained using Probabilistic Fault Trees with Time Dependencies by simulation, and Erlang distribution based approximation. Słowa kluczowe: zabezpieczenie odległościowe, strefa zabezpieczenia, impedancja pętli zwarciowej, probabilistyczne drzewo niezdatności z zależnościami czasowymi. Keywords: distance protection, protection zone, fault loop impedance, Probabilistic Fault Tree with Time Dependencies. Introduction Distance protections are often used in Polish power system. Numerical protection relays use specialized digital signal processors as the computational hardware, together with the associated software tools. Relays convert voltage and current input signals into a digital representation and process according to the appropriate mathematical algorithms. Processing is carried out using specialized microprocessors that are optimized for signal processing applications. Distance protection schema is based on local (primary) and remote (backup) relays. Each sect[...]

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