Emergency Control Power System Separation

Power systems in many countries are stressed towards their stability limit. If these stable systems experience any unexpected contingencies, or disturbances, there is a significant risk of instability, which may lead to wide-spread blackout. Existing methods to minimize the risk of stability and excessive frequency decline; need to be redeveloped to address these new challenges. This research project will develop a new emergency control methodology, which can more effectively prevent power system frequency and voltage instability under emergency conditions. Frequency and voltage instability are two major concerns in power system operation. The primary aim of this project is to develop new optimal load shedding techniques, which are able to better address various voltage and frequency instability issues for power systems emergency control purpose. In this thesis, new approach of load shedding for frequency and voltage stability are presented. For the load shedding to prevent frequency collapse, System Frequency Respond – Under Frequency Load Shedding (SFR-UFLS) from the previous approach has been redeveloped to compute an optimal load shedding scheme. The limitation of previous optimal load shed method is that they only shed load following one particular contingency event. As an improvement of this method, we developed a technique that protects against a range of contingencies. For the load shedding to prevent voltage collapse, The proposed method is then tested on the 39-bus New England test system. Generators are of different importance to the system in terms of voltage stability. It is essential to investigate generators’ impact on system voltage stability. The theory of the normal forms of diffeomorphism is used to analyze the power flow equations, and then nonlinear active participation factor is obtained and is used to determine the influence of generators on voltage stability. By using this method, the nonlinearity of power systems can be taken into consideration while the computational efficiency is maintained. Therefore, the impact of generators can be measured with more accuracy even for the cases in which the system is characterized with strong nonlinearity. In order to show the validity of the proposed method, the IEEE 14-bus test system and the New England 39-bus power system are used as case studies. The steady-state voltage stability index verifies the proposed method. The results show that nonlinear active participation factor can describe the characteristics even when power systems are operating at a highly stressed condition