Electric Distribution Line Ground Fault Prevention Systems Using Dual Parameter High Sensitivity Relay Device, Monitoring Small Current Reduction With Small Increase In Negative Sequence Current

In a system for preventing ground fault or other short circuit in electric distribution line system, caused by a break in a line, utilizing programmable relay protection in a plurality of relay devices programmed to monitor high sensitivity parameters, the improvement of micro-monitoring segments of a distribution line that are significant distances from a relay on a four line distribution circuit, which comprises:

• a broken conductor protection subsystem having sufficient hardware and software that is programmed:
• a) to detect changes in instantaneous undercurrent on said distribution line, to calculate the change in instantaneous undercurrent, to store a preset acceptable range for change of instantaneous undercurrent, to compare said calculated change in instantaneous undercurrent to said preset acceptable range for change of instantaneous undercurrent;
• b) to detect changes in zero sequence overcurrent on said distribution line, to calculate the change in zero sequence overcurrent, to store a preset acceptable range for change of zero sequence overcurrent, to compare said calculated change in zero sequence overcurrent to said preset acceptable range for change of zero sequence overcurrent;
• and,
• c) if the calculated change in instantaneous undercurrent is outside said preset acceptable range for change of instantaneous undercurrent, and if the calculated change in zero sequence overcurrent is outside said preset acceptable range of change of zero sequence overcurrent, then there is a true line break fault and the high sensitivity monitoring proceeds to signal a true line break fault for line shut down of the monitored line.

In a system for preventing ground fault or other short circuit in electric distribution line system, caused by a break in a line, utilizing programmable relay protection in a plurality of relay devices programmed to monitor high sensitivity parameters, the improvement of micro-monitoring segments of a distribution line that are significant distances from a relay on a four-line distribution circuit, which comprises:

• a broken conductor protection subsystem having sufficient hardware and software that is programmed with two Modules, mutually independent of one another, as follows:
• A) Module a:
• a) to detect changes in instantaneous undercurrent on said distribution line, to calculate the change in instantaneous undercurrent, to store a preset acceptable range for change of instantaneous undercurrent, to compare said calculated change in instantaneous undercurrent to said preset acceptable range for change of instantaneous undercurrent;
• b) to detect changes in negative sequence overcurrent on said distribution line, to calculate the change in negative sequence overcurrent, to store a preset acceptable range for change of negative sequence overcurrent, to compare said calculated change in negative sequence overcurrent to said preset acceptable range for change of negative sequence overcurrent;
• and
• B) Module B:
• c) to detect changes in instantaneous undercurrent on said distribution line, to calculate the change in instantaneous undercurrent, to store a preset acceptable range for change of instantaneous undercurrent, to compare said calculated change in instantaneous undercurrent to said preset acceptable range for change of instantaneous undercurrent:
• d) to detect changes in zero sequence overcurrent on said distribution line, to calculate the change in zero sequence overcurrent, to store a preset acceptable range for change of zero sequence overcurrent, to compare said calculated change in zero sequence overcurrent to said preset acceptable range for change of zero sequence overcurrent, and:
• C) OUTPUTS of MODULE a and MODULE B:
• e) if from MODULE A, the calculated change in instantaneous undercurrent is outside said preset acceptable range for change of instantaneous undercurrent, and, if the calculated change in negative sequence overcurrent is outside said preset acceptable range of change of negative sequence overcurrent, then there is a true line break fault and the high sensitivity monitoring proceeds to signal a true line break fault for line shut down of the monitored line;
• or
• f) if from MODULE B, the calculated change in instantaneous undercurrent is outside said preset acceptable range for change of instantaneous undercurrent, and, then there is no blown fuse, and the blown fuse protection subsystem signals to permit said high sensitivity monitoring to proceed to signal a true broken conductor for line shut down of said line;
• and, if the calculated change in zero sequence overcurrent is outside said preset acceptable range of change of zero sequence overcurrent, then there is a true line break fault and the high sensitivity monitoring proceeds to signal a true line break fault for line shut down of the monitored line.