No abstract

No abstract

Creating defense plans against extreme contingencies requires knowledge of the principal vulnerabilities of power systems. This paper describes the blackout phenomenon as a process with separate phases and distinctive transitions. The paper proposes two indicators that can help to identify vulnerabilities in a specific operating scenario and recommends that the dynamic behavior of a power system after successive faults should be analyzed. This analysis would reveal vulnerabilities connected to high impact low probability contingencies where the system response can change after several successive contingencies. These vulnerabilities cannot be captured by steady state analyses. Analyses of some recent large European blackouts, presented in the paper, indicate that a power system may collapse after only a limited number of contingencies, implying that these power systems are more vulnerable to multiple contingencies than the system operators may be aware of.Index Terms-blackout, cascading failure, N -1 criterion, power system security, power system stability, power transfer capacity

Defining power system security requires knowledge of the dynamic behavior of the system in disturbed conditions. This paper describes the process of identifying vulnerabilities and quantifying the security of a power system by presenting a dynamic simulation study of the Finnish power system. The results show the change of the security of a power system as the amount of power transfer is increased or decreased on the critical corridor. The results also show the variation of system security as the fault frequency varies. The paper presents equal areas of risk when power transfer on critical corridor and fault frequency vary. This clearly illustrates that exceeding N − 1 secure transfer limits lead to highly different system collapse probabilities which depend on the grid fault frequency.