Voltage Sag Performance of a Distribution System and Its Improvement

The voltage sag performance of a distribution system has been investigated. A Monte-Carlo procedure has been used to construct the sag density table and estimate the number of unacceptable sags per annum at a sensitive load bus. The subtransmission lines and distribution feeders that largely contribute to the unacceptable sags have been identified. It has been shown that proper protective relay coordination and adequate maintenance of the critical lines and feeders result in significant improvement of the voltage sag performance of the distribution system.