Simulation of load shedding as a corrective action against voltage collapse

The evolution of many voltage collapse scenarios on large power systems can be alleviated by controlled load shedding associated with rearrangement of generator outputs. Dynamic simulation of power system mid-term voltage response is required to adequately determine the impact of load shedding actions and to design appropriate control systems. The dynamic simulation must take into account load-voltage behaviour, transformer tap changer controls and limits, generator over-excitation limiters, automatic generation control and system protective devices. This paper demonstrates the impact of load shedding as a corrective action through simulation of the system dynamic response to a disturbance. Whilst load shedding can stabilise a system, rigorous techniques are required to identify the magnitude and location of shedding. The application of voltage modal analysis in combination with the determination of reactive power margins in resolving this problem is demonstrated.