Estimação fasorial: uma abordagem considerando a presença da componente DC, harmônicos e ruídos aleatórios, aplicada à relés numéricos de proteção

Abstract

The increase in demand from the Brazilian electricity sector has made it more complex and prone to failures. In this sense, the current norms referring to the electric sector encourage the development of several techniques that guarantee reliability to the electric energy transmission and distribution systems. Relays are of great importance in protection systems, being responsible for defect identifying and locating as accurately as possible. During a short circuit occurrence, a component with exponential decay (DC) appears, due to instantaneous variation in the state of the system. In addition to this component, harmonic, interharmonic, subharmonic and random noises are present in the network signals. Therefore, this work aims to verify the performance of Half Cycle Fourier Filters (FFMC) and Full Cycle Fourier Filters (FFCC), intended for phasor estimation, associated with the Least Squares Method (MMQ) for the removal of DC component. The research methodology was divided into three stages: the first consists of the fundamental signal modeling, plus the DC component, harmonics and random noises; the second deals with the half-cycle and full-cycle Fourier filters implementation, in addition to the Cosine filter, all associated with the least squares method; and in the third stage, the filters performance indexes were created based on the convergence time, over-elevation, relative error and maximum relative error, with the convergence time found when the percentage relative error is less than 0.1% for two consecutive cycles. The results demonstrate that the association of Fourier filters with the least squares method allows the removal of the signal undesirable components, ensuring the estimation of the fundamental frequency phasor with good precision, regardless of the signal sampling rate.