Power Arc-Over on Overhead Distribution Lines and Newly Developed Equipment for Protection Against Conductor Burndown From That Cause

With conventional types of switchgear and customary methods of circuit operation, power arc-overs resulting from transient faults on overhead primary lines cause unnecessary burndown of conductors and undesired operation of fuses. The majority of faults on overhead distribution circuits are of transient nature. Factual data concerning arcing characteristics of covered and bare conductors were established by tests conducted under field conditions. They show that to prevent burndown of covered wire and to hold the arc damage within admissible limits, power arcs must be limited to one-half- to two-cycle (sixty-cycle basis) over-all time, depending upon size of conductor and arc current. Bare conductors are less liable to serious arc damage owing to the phenomenon of arc travel and to the self-extinguishing characteristics of arcs on such conductors. However, the duration of traveling arcs is sufficient to cause undesired operation of sectionalizing fuses unless the line is rapidly de-energized. Speeds of operation required to protect covered wire are also ample to assure against operation of fuses on transient faults. New switching devices capable of meeting the required one-half- to two-cycle initial circuit clearance have been developed as part of this project. They also provide for automatic reclosure and a sequence of timedelay openings and reclosures before lockout. Simplicity of construction, ease of installation, and self-actuating principles which dispense with auxiliary power requirements, make investment sufficiently low to bring these devices within the realm of practicability for low revenue distribution circuits as well as the more important distribution circuits.