Modern voltage stability index for prediction of voltage collapse and estimation of maximum load-ability for weak buses and critical lines identification

Abstract

Voltage collapse is a problem that may happen when power systems are overloaded. An accurate estimation of critical operating conditions is necessary to prevent voltage collapses in power grids. Accurately predicting voltage collapse in the network will help the operators take timely rectification by monitoring the system and its closeness to the voltage collapse. This article suggests a more accurate voltage collapse prediction for identifying weak buses and critical lines based on a new proposed index termed Modern Voltage Stability Index (MVSI). The proposed index ignores the line resistance partially, i.e., the method consists of zeroing the resistance of a part and not entirely of the exact formula of the system to develop an approximate and fast collapse prediction index. It indicates that entirely ignoring the line resistance creates an erroneous voltage collapse prediction that may exceed 70%. For verification purposes, this study compared the existing stability indices (Lmn, FVSI, LQP, NLSI, VSLI and NVSI) with the proposed index based on the variables contained in each index, simulation results and percent errors. Determining the influences of the relative directions of real and reactive power-flow in the branches is one of the most important considerations of the proposed index to predict voltage collapse. Different load conditions have been used to examine the feasibility and performance of the proposed index in collapse predictions. Under several load conditions, the performance of MVSI has been compared with the performance of Lmn, FVSI, LQP, NLSI, VSLI and NVSI to determine the highest performance among them in collapse predictions. Usually, the voltage stability is very sensitive to reactive power-flow. Therefore, the maximum reactive power loads in each particular bus have been determined in this article based on a new proposed index (MVSI). The bus which can withstand the lowest maximum reactive power before the collapse is ranked as the highest ranking, and it is considered the weakest bus in the system. The proposed index is examined on IEEE 30-bus to validate its practicability. The weak areas of EPSN have been diagnosed, studied, and evaluated by the smooth method with the help of the MATLAB environment.