Patent ID: 7720619

Claim:
A method for detecting a high-impedance fault in a multi-grounded electrical power distribution system using an intelligent electronic device, said method comprising the steps of: for each cycle: periodically sampling at least one distribution system quantity so that a plurality of samples are taken per cycle using an analog to digital converter, the plurality of samples including at least a first sample, a second sample, a third sample, and a fourth sample; using said intelligent electronic device, calculating a plurality of differences for at least one distribution system quantity with a difference filter, wherein at least first, second, third and fourth differences are calculated wherein said first difference is calculated by calculating an absolute value of a difference of a first sample taken in a most recent cycle with a first sample taken in a previous cycle, and said second difference is calculated by calculating an absolute value of a difference of a second sample taken in the most recent cycle with a second sample taken in the previous cycle, and said third difference is calculated by calculating an absolute value of a difference of a third sample taken in the most recent cycle with a third sample taken in the previous cycle, and said fourth difference is calculated by calculating an absolute value of a difference of a fourth sample taken in the most recent cycle with a fourth sample taken in the previous cycle, wherein said differences collectively form a plurality of sequential differences within each cycle within said intelligent electronic device; using said intelligent electronic device, calculating a sum of differences by summing each of the plurality of sequential differences including at least said first, second, third, and fourth differences, to produce a sum of differences during each cycle; calculating a sum of differences by summing each of the plurality of sequential differences to produce a sum of differences during each cycle; providing a trending with an output; receiving the plurality of sum of differences, receiving the output of the trending, and generating a set threshold; establishing a reference based upon the plurality of sum of differences and the set threshold; using said intelligent electronic device, calculating a difference between the plurality of sum of differences and the reference; forming a trend output if the difference exceeds the set threshold; and determining existence of a high-impedance fault with decision logic based on the trend output.