Fourier-series techniques applied to distance protection

For distance-relay applications, the fundamental system impedance as seen from the relaying point is used as the basis for the decision to give the trip signal. This system impedance can be calculated from knowledge of the fundamental frequency components of the voltage and current waveforms, these, in turn, being determined by processing appropriate waveforms sampled at the relay point. Fourier-series analysis is one method suitable for processing the sampled waveforms and for determining their fundamental components. The analysis is designed for continuous, periodic waveforms and, in these circumstances, separates the various harmonic components of the waveform. Its behaviour under the nonperiodic conditions of fault incidence and transient interference will be demonstrated.