Statistically generalized rating for CLR in power transmission systems

Abstract

Current Limiting Reactors (CLR) connected in series with the transmission line, limit system short circuit currents on occurrence of a fault. Cost and size of these current limiting reactors is conventionally attributed to the system specified peak short circuit current and the inductance, as peak short circuit current and the duration of short circuit are the basis for size of the conductor. The conventional designs overlook the fact that peak current flowing through CLR is not constant but changes with the instant of short circuit. The short circuit currents also differ substantially from one short circuit to other. This variation in peak short circuit current, spread over from minimum to maximum, is statistically studied and generalized using PSCAD simulation in this work, for a standard power system (40kA) to study the scatter, highest amplitude and frequency of occurrence. Number of experiments has been conducted utilizing randomly selected short circuit events and for various sample sizes. Authors have co-related results and defined optimal experiments for acceptable prediction accuracy. The work is extended further to develop an empirical relation defining the change. The authors claim that substantial reduction in cost and size of CLR is possible considering statistical rating of CLRs against conventional.