Improved method of maximum loadability estimation in power systems by transforming the distorted P-e curve

This paper presents an improved method to estimate the maximum load level for heavily loaded power systems with the load-generation variation vector obtained by ELD (economic load dispatch) and/or short term load forecasting by using the elliptic pattern of the P-e curve. The previous study suggested a simple technique of removing e-f coupling, where only high voltage load flow solutions to calculate transforming angle of system reference is needed. The proposed algorithm is improved to require only one load flow solution at a specific load level in addition to the operating point at the beginning stage, which reduces the computation time and the iteration number of estimation. The proposed method can be efficiently applied to heavily loaded systems with the combination of CPFlow when the reactive power limit and ULTC (under load tap changer) are considered. In this paper, the effect of ULTC on the estimation of maximum loadability index is also investigated. The proposed algorithm is tested on IEEE 14 bus system, New England 39 bus system and IEEE 118 bus system.