Uma nova proposta para a remoção da componente DC das correntes de falta usando mínimos quadrados e transformada discreta de Fourier

Abstract

In the event of a short-circuit there are transient components that impair the correct functioning of the protection relays as well as the current transformers. In this context, the DC component, which appears at the first instant of occurrence of the fault and has an exponential character, presents a higher level of difficulty for its removal, since it is a non-periodic signal, whose spectrum includes all frequencies. The algorithms of the numerical relays make use of the data of the digital filters which perform the calculations for estimation of voltage and current phas-ors. To ensure that the relays operate quickly and selectively, without compromising accuracy, these phasors must be free of noise, harmonics and the DC component, and must contain only the desired frequency. This ensures that there is no distortion in the relay reading and that it operates within the range in which it has been configured, sending a shot signal to the circuit breakers, if necessary. In this work, it is proposed to use the least squares method for the re-moval of the DC component, which is estimated and subtracted from the input signal. The result is processed by either the Half Cycle Fourier Filter or the Full Cycle Fourier Filter. Thus, in order to select the most adequate filter for the protection of the electric system, a comparison is made between the performances of said filters, with and without the step of estimating the DC before the signal processing. This comparison is made through the analysis of performance indexes, such as the overshoot of the output response before convergence, the relative error and the convergence time. Finally, it should be pointed out that the selection of the most appropriate algorithm should take into account its performance in the index that is most important for the respective application.