Dealing with system voltage stability

In spite of conservative transmission line loading limits for operational security, interconnected power systems continue to suffer extensive and costly collapses following severe disturbances which disrupt system voltage stability. An approach has been developed which can minimise the danger of system voltage instability and at the same time allow much heavier transmission line loadings. The proposal is based on the development of automatic measures which can respond to the effects of unpredictable multiple contingencies which presently would disrupt the transmission grid and lead to collapse. The foundation of this proposal hinges on the initial slow phase, sometimes lasting minutes, that has been described in reported incidents of collapse. This temporary stability shows that initially the power system has a large margin of reactive reserves which abruptly vanishes in the disruptive second phase. By having adaptive automatic responses during the first phase, it becomes possible to capitalise on these large reactive power reserves in permitting much heavier transmission line loadings. The continuous accessability of higher transmission line loadings would gain large savings under normal conditions and the automatic protection would avoid the multi-million dollar costs incurred by extensive and long duration blackouts of the power system