Instantaneous overcurrent element for heavily saturated current in a power system

This invention relates generally to instantaneous overcurrent elements used in microprocessor-based protective relays for power systems and more specifically concerns such an overcurrent element which provides accurate current magnitude information under normal operating conditions and when the current waveform from the current transformer is heavily saturated. The instantaneous overcurrent element, used in a microprocessor-based protective relay for a power system, includes a finite impulse response filter which generally is a cosine filter and is responsive to the current waveform from the current transformer for fault determination unless the distortion in the current reaches a preselected threshold, at which point a peak detector circuit is used to provide the current magnitude values for fault determination.