Demonstration of a low-cost fault detector for sum current measurement of overhead MV lines

We present field test results of a low-cost fault detector for medium voltage power lines. Three devices are clamped on the lines and measure current with induction coils up to 190 A. The sensors harvest energy inductively from the line current. They are synchronized by radio and sum current of three phases is calculated. We compared the measured sum current with a substation reading during earth faults. With fault resistances between 0 - 5000 Ω the full scale error of sum current was between 0.2 - 4.0 %. In a normal state the maximum error was 2.6 %. Earth faults up to 330 Ω were detectable. The energy harvesting provided adequate operating power for the tests, but not yet for continuous operation.