Importance

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Abstract

Protective relay apparatus and method for determining the faulted phase conductor of a three-phase ac electrical transmission line. The voltage and current on each conductor are measured and the steady-state ac electric power signal removed. The resulting filtered-voltage signals are multiplied by the characteristic admittance of the transmission line and then combined with the filtered-current signals to produce three current signals representative of the current on each conductor caused by an incident traveling wave and three current signals representative of the current on each conductor caused by a forward traveling wave. A comparator compares the six current signals to provide an indication of the direction to the fault and to provide an enable signal when the fault is on the protected line segment. The three incident-wave current signals are filtered to provide a modal signal representing the total current produced on the transmission line by a first propagational mode of the incident traveling wave. A discriminator processes the three incident-wave signals, the modal signal, and the enable signal to provide an indication of the faulted phase conductor.

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First Claim