An Improved Direct Method to Compute the Load Margin of Power Systems

The voltage stability margin is an index calculated as the difference between the load level of the nominal operating point of power systems and the load level where a voltage collapse occurs. This index is a valuable safety measure used in power system operation centers. However, this load margin may not be adequate because it does not consider oscillatory instabilities that may eventually arise as the load level increases and also because it does not consider different schemes for active power generation redispatches. This article proposes a unified direct method that determines the load margin of power systems considering voltage and oscillatory instabilities and, in addition, different schemes for active power generation redispatch are considered. Case studies of the application of the proposed method in the IEEE 39-bus power system model are presented and discussed.