Wide Area Voltage Regulation in Italy and related wide area protection

A very promising Wide Area Voltage Protection (V-WAP) solution to face EHV voltage stability and system security problems is presented. Its unique ability is mainly due to an effective co-ordination with a Wide Area Voltage Regulation (V-WAR) modern system where the Secondary and Tertiary Voltage Regulations (SVR and TVR respectively) operate according with their hierarchy. Both the voltage regulating and protecting controls are here presented. Particular evidence is given to the practical feasibility and the simplicity in defining and developing a very effective V-WAP solution, when operating a V-WAR regulating system. The main simplification comes by the already existing and appropriate network subdivision in to areas given by the operating Secondary Voltage Regulation which also fixes the areas of the protection scheme intervention and provides, in real time, data on area control efforts for voltage support. On this base, an area voltage stability index is proposed to operate the area load shedding according with incontrovertible and simple control logic that leaves the regulating system to operate up to its saturation before becoming active. This very important coordination between V-WAR and V-WAP is the key to understand the relevant stability improve. Dynamic simulation results on the North Italy power system shows the effectiveness of the V-WAR in increasing the system voltage stability margins as well as of the V-WAP in reducing or eliminating the risk of voltage collapse by a very low load shedding amount.