Improving voltage stability line limits

Simulation results of the variables associated with a large power system following a severe disturbance, have 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.