Wide area voltage regulation and protection: When their co-ordination is simple

A transmission network voltage protection scheme based on an effective co-ordination with an automatic voltage and reactive power control system is the main paper issue. Evidence is given to the practical feasibility and the simplicity of a wide area voltage protecting solution, very effective to eliminate the risk of voltage instability. The main simplification comes by the already existing and correct subdivision of the networks in to areas given by the operating secondary voltage regulation which fixes the areas of the protection scheme intervention and gives, in real time, their control efforts. On this base, a voltage stability index is proposed to operate the area load shedding according with a given control logic. Simulation results of a dynamic analysis related to the North Italy power system shows the effectiveness of the proposed protection scheme which minimizes the operated load shedding to achieve the continuity and stability of the controlled power system, in front of a ramping load increase.