Increasing voltage stability line limits

Constraining the loadings of transmission lines on interconnected grids has increased the operating costs of power systems and yet has not prevented collapses following disturbances that have disrupted system voltage stability. An understanding of the post-disturbance phenomena gained by simulation, has shown that during the initial slow phase, rotating units hold high levels of reactive power reserves which can sustain high transmission line loadings. Automatic measures that respond within the first phase would eliminate the need to constrain transmission line loadings by preventing the second disruptive phase, when reactive power reserves suddenly vanish. This is when voltage stability is lost and the power system collapses