Characterization of distribution systems overcurrents using Expert Systems

Overcurrents on distribution systems include permanent faults, temporary faults and other lower magnitude surges, typically from switching events. The overcurrent environment of the distribution system requires quantification if improvements are to be made in power quality, protection and reliability. New and more complex overcurrent protection products require more exact knowledge of feeder conditions. In the absence of todaypsilas data acquisition equipment and computer simulations, overcurrents were previously characterized by employing broad assumptions and deriving some long-standing ldquorules-of-thumbrdquo. Kinectrics has engaged in a study that built upon those existing characterizations of overcurrents, by monitoring overcurrents in the field and conducting computerized analysis. Over 5000 electronic waveforms were collected by monitoring 9 feeders from 3 distribution stations. Using an Expert System, the waveforms were grouped into several categories (ie permanent and temporary fault currents, inrush currents, emergency overloads or cold load pick-up, and switching events). Pertinent parameters (frequency of occurrence, magnitude, peak current, rms current, duration, 1
²
t and time constant) were measured or computed.