System vulnerability as a concept to assess power system dynamic security

The concept of system vulnerability is introduced as a new framework for power system dynamic security assessment. This new concept combines information on the level of security and its trend with changing system condition. In this paper the transient energy function (TEF) method is used as a tool of analysis. The energy margin ΔV is used as an indicator of the level of security, and its sensitivity (∂ΔV/∂p) to a changing system parameter p as an indicator of its trend. The thresholds for acceptable levels of the security indicator (ΔV) and its trend (∂ΔV/∂p) are related to the stability limits of a critical system parameter. A method is proposed to determine these thresholds using heuristic techniques derived from operating practices and policies for a change in plant generation. Results from the IEEE 50 generator test system are presented to illustrate the procedure