Mid-Carolina Electric Cooperative (MCEC) replaced their hydraulic reclosers with solid dielectric reclosers and microprocessor-based recloser controls as part of a program to modernize their distribution system. MCEC was having problems with hydraulic reclosers, including excess maintenance costs and poor repeatability of the time-overcurrent trip characteristic. As part of the replacement, they expected to solve these problems as well as reap the anticipated benefits of adding microprocessor-based relaying, including event reports, sequence of events recording, metering, and communication. What they did not expect to encounter was that, although the settings were the same as those used previously, several of the reclosers tripped on the fast curve due to inrush conditions. Adding the microprocessor-based relays made MCEC aware of this problem, which presumably existed all along. MCEC did not have the capability to detect the problem previously. After this discovery, MCEC engineers gathered event reports to allow them to characterize the inrush. This paper discusses those inrush events and ways to overcome undesired tripping on distribution feeders on inrush conditions using both settings changes and second-harmonic blocking.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.