Revealing stability limitations in power system vulnerability analysis

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.