Voltage Sag Assessment Considering Relay Protection Actions

Abstract

The relay protection devices installed on the power grid lines will significantly change certain voltage sag indices. Taking this into account can improve the accuracy and credibility of the existing assessment methods. Based on the characteristics of relay protection configuration scheme, this paper analyzes the influence of stage distance protection and inverse time current protection action on voltage sag amplitude and duration, and derives the calculation formula of the sensible load failure rate. Based on IEEE 30-bus system, the voltage sag amplitude and duration are calculated by MATLAB program, whose results are then compared with the simulation results of PSCAD. The sensitivity load failure rate of a 66-bus isolated network, under the condition of with and without protection device operation, are evaluated and compared.