Analysis of the tap changer related voltage collapse phenomena for the large electric power system

It is shown that nonsmooth events, such as tap changing can be integrated into the framework of a general theory recently presented by the authors (1991,1992) on the dynamics of large power systems modeled by smooth equations. The boundary to the region of feasible operations starting at a stable operating point, the feasibility boundary, is shown to be composed of five types of segments including two types connected with tap changers. These segments are defined as zero sets of explicitly known functions and thus are relatively computable (at roughly the load flow level). These results offer a powerful new approach to system security when tap changers are present. No reference needs to be made to P-V curves of the large power system, an obstacle in more conventional approaches