Design of Special Protection System Against Voltage Instability

Nowadays detection of contingencies and performing corrective actions on time for prevention of power system collapse is necessary. It needs to protective plans that addition to original equipments' protections, supervise whole power network in emergency conditions. Therefore protective and preventive actions must perform for preventing power system collapse. These protective plans are named Special Protection System (SPS). SPS supervises over whole power system and decides and performs corrective actions in emergency conditions. In this paper, first of all, a suitable SPS is designed for power system. Next, a mechanism for SPS will design so that SPS can perform corrective actions against short time voltage instability. As short time voltage instability happen in the range of 1-3 seconds, operators do not have enough time to perform the corrective actions. Therefore, most important contingencies which may happen and result in voltage instability are considered off-line. After that, a list of corrective actions for every important events prepare for operators of system. This list uses in contingency conditions. For every important event calculates maximum load-ability of system. Then, the maximum load-ability of system in each important event compare with minimum acceptable loading system. If loading system is less than minimum acceptable loading, some of the load should be shed to prevent voltage instability. Load shedding is executed based on the two purposes: cost of load shedding should be minimum and most effective of load on the voltage instability. Therefore, an objective function defines to consider these two purposes of load shedding. Optimization of the objective function is performed using Genetic Algorithm (GA). At the end, amount of load which is shed for each load bus is presented for every event.