Determining the Vulnerabilities of the Power Transmission System

Determining the vulnerabilities in power transmission systems requires two distinct steps because most large blackouts have two distinct parts, the triggers/initiating event followed by the cascading failure. Finding the important triggers for large blackouts is the first and standard step. Next, the cascading part of the extreme event (which can be long or short) is critically dependent on the "state" of the system, how heavily the lines are loaded, how much generation margin exists, and where the generation exists relative to the load. However, during large cascading events there are some lines whose probability of overloading is higher that the others. Statistical studies of blackouts using the OPA code allow the identification of such lines or groups of line for a given network model, thereby providing a technique for identifying at risk (or critical) clusters. This paper addresses both parts of the vulnerability question.