Local Voltage Stability Constraint for OPF

Power systems are in constant expansion, their topology is more complex every time, and the growth of electric power demand leads to work the power system near to its operating limits. At this point, the voltage instability begins to get importance into the operative area and power systems operational planning. The voltage instability is a phenomenon related to very loaded systems, associated in general, with the demand of reactive power. Voltage collapse involves all or almost all the system. For this reason, consideration of this phenomenon and its prevention is very important in order to improve the operation of the power system. There is a number of methods to evaluate voltage stability margins, some of which give structural information of the behavior of the system around its voltage stability. Other kinds of methods are based on bus indexes giving local information about the voltage stability of the system. This paper is focused on including the L Index, as a local constraint of voltage stability margin to be used in the computation of the Optimal Power Flow (OPF). The program was implemented in Matlab using the PSAT-GAMS interface. The methodology was tested using a 6 bus system and the IEEE-RTS 24 bus system.