Electric distribution line ground fault prevention systems using dual parameter monitoring with high sensitivity relay devices

Abstract

A system for preventing ground fault in a three-phase electric distribution line system caused by a line break, includes: the transmission lines, a programmable relay protection system, including high sensitivity. The HS relays on each line are programmed to include: preset acceptable operating parameter ranges of at least two electric operating conditions, namely, high sensitivity instantaneous undercurrent and at least one high sensitivity negative sequence overcurrent; monitoring; permitting closed circuit operation when all of the lines show that the two operating conditions are within the preset acceptable operating parameter ranges; tripping a circuit breaking device on a broken line when that line shows that the two operating conditions are outside the preset parameter ranges; and shutting down power to the broken line before it otherwise causes a ground fault or other short circuit. A third parameter monitoring: rate of change in current is preferred.