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Abstract
Impulse Response Coefficients (IRC) of digital filters is an imperative step in the development of transmission line protection relay algorithms. Traditionally, Fourier-based filters are used in real applications, where IRC are fixed values of sine and cosine functions with a data window of one or more cycles. Based on state-of-the-art, Mother Wavelet coefficients used in Multiresolution Analysis, and Structuring Element coefficients used in Mathematical Morphology are usually proposed to develop protection algorithms. However, the proper choice of these coefficients is based on empirical process of trial and error. This paper proposes a novel methodology for optimally determining coefficients that depend on the waveform structure analyzed, which is determined using variance as the metric. Assessment of methodology for three case studies considering requirements of relay manufactures (response time, design, harmonic attenuation and other) is presented. The first assessment is to extract coefficients useful for distinguishing among non-fault conditions, harmonics, and arcing faults. The second one is to extract coefficients to filter harmonic components. The assessment is carried out considering different data windows and sampling rates. Test results highlight the efficiency of the model to determine specific coefficients for each case study analyzed. Interestingly, results also showed that the discovered coefficients can be used in another filtering technique. Thus, the third case study involves developing two fault classifiers, which are developed using mathematical morphology where the structuring elements used correspond to the coefficient vectors determined through the proposed methodology. There is a notable paucity of scientific literature focusing on this topic. Therefore, there are several important areas where this study makes an original contribution regarding protection relays.
Highlights
In contrast to the above mentioned, this paper offers a novel methodology for optimally determining Impulse Response Coefficients (IRC) that can be applied to TL protection relay algorithms
In order to guarantee that the design of a new digital filter will be successful in real applications, it must be examined on different features such as filtering response, harmonic attenuation, transient behavior, and others
In [18], based on the cutting-edge technology developed by many SEL engineers, including technical papers and others, it is presented that currently, in modern protection solutions, automation, and monitoring, microprocessor-based relays must provide many advanced functions and abilities such as faster fault clearing without sacrifying security for high-speed DF and TL protection [19], [20]
Summary
Ds are applied to minimize faults effects and abnormal phenomena on the operation of EPS, especially on TLs which are elements with the highest probability of faults occurring [1]. As regards the Cosine filter, it is a simple filter with unitary filter impulse response that uses fixed IRCs of the cosine function with a data window of one cycle approximately Another filter used by relays is based on LES, which minimizes the mean-square error between the analyzed waveform and the mathematical model coefficients of the waveform used as a reference [28]. All studies based on SPT reviewed here use empirical methods in order to find the best IRCs. Previous studies of digital filters have not dealt with the optimal extraction of IRCs applied to TL relaying. In contrast to the above mentioned, this paper offers a novel methodology for optimally determining IRCs that can be applied to TL protection relay algorithms These coefficients are based on the signal’s variance value (see Section II). Coefficients obtained are considered the most suitable for analyzing said data, and a trial-error procedure is not necessary to determine these coefficients
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