Patent ID: 8680872

Claim:
A method of identifying false positive indications of high impedance faults in an AC electric power transmission and distribution network, said network including a phase conductor for conducting AC electrical power, the method comprising: using an amplitude monitoring procedure to monitor the phase conductor for amplitude disturbances indicative of specified faults, said procedure generating an initial fault signal indicating one of said specified faults in the conductor; monitoring a phase shift between a voltage and a current of the electric power conducted through the conductor; generating, based upon the monitoring of the phase shift, a correction signal when the phase shift between said voltage and said current is detected over a defined period of time and said detected phase shift meets one or more given conditions, the correction signal indicating that said initial fault signal is a false indication of said one of the specified faults indicated by the amplitude disturbances; and applying the generated correction signal to the initial fault signal to produce a modified fault signal that suppresses an alarm; wherein the phase shift monitoring includes: (a) generating a mean value for said phase shift over a given period of time; (b) comparing a plurality of values for said phase shift at a plurality of particular times to said mean value; and (c) generating a squash curve over the given period of time from said phase shift based on said comparing; wherein the generating the squash curve includes: (a) giving the squash curve a first value when the value for the phase shift at a given time exceeds said mean value by more than a threshold level; (b) giving the squash curve a second value when the value for the phase shift at a given time does not exceed said mean value by said threshold level; and (c) smoothing the squash curve over the given period of time based upon the first and second values given to the squash curve prior to the smoothing; and wherein the generating the correction signal includes generating the correction signal when the smoothed squash curve has a specified value.