PMU based voltage stability indices with intermediate load compensation

Wide area measurement has revolutionized the monitoring of electric power systems (EPS) which are often operated near of their stability limits. Currently, several grid operators make off-line studies of different electric system topologies to determine the voltage stability margins under different fault scenarios (loss of transmission links, loss of generation units, etc.); from these studies several decisions are taken including the disconnection of primary equipment. There are several voltage stability indices for radial electric systems that employ wide area measurement; however their major drawback is that they do not consider the intermediate load scenario in the transmission link. In this paper we propose a method to find the maximum power of a radial link between two nodes with intermediate loads and a general method to compensate loads at the receiving end that can be applied to indices that use that parameter to determine the proximity to the collapse. The performance of the compensated stability indices is evaluated by off-line simulations and it is concluded that the intermediate load compensation improves the accuracy of the indices.