A metric for quantifying the risk of blackout

This paper addresses the problem of quantifying the risk of blackout and the need to do it fast, in real-time and for multiple off-line simulations. Is there a metric that can tell how far is a given power system state from its stability limit? But then, what is a stability limit? How to quantitatively describe such limit, or perhaps, limits, if more than one, and how to quickly determine how far is the transmission network from a state where a blackout might occur? The concept of steady-state stability reserve, introduced half a century ago to quantify the distance to instability, is also reviewed. Space and presentation time do not allow a detailed analysis, but an extensive list of references is provided to help promote further research. The main theme of this paper is particularly relevant in the aftermath of the wave of blackouts that affected utilities in US, UK and mainland Europe in 2003. The approach presented herein can help system dispatchers and reliability engineers foresee whether the transmission loading progresses, or is projected to progress, beyond the operating reliability limit.