An accurate digital low-pass filter for transmission line protection

Abstract

The paper presents a procedure for designing, testing and evaluating digital low-pass filters for the removal of high-frequency transients from transmission line short-circuit voltage and current waveforms, as is required for certain digital distance relays and may be useful in other similar applications. The procedure is based on the ‘trapezoidal’ type of low-pass digital filter which has characteristics that enable low-order digital filters to be achieved. Criteria for the design and optimization of such filters in the foregoing type of application are also presented.