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The hierarchical voltage control system, currently fully exploited in the Italian transmission grid and presented in Part I, improves voltage quality, network security and operation efficiency. This coordinated automatic system, operated by the Italian ISO (GRTN), is subdivided into three hierarchical control levels, requiring unconventional regulation apparatuses. They are the Voltage and Reactive Power Regulator (REPORT) at the power plant level, the Regional Voltage Regulator (RVR) at the regional dispatcher level, and the National Voltage Regulator (NVR) at the ISO control center. This survey paper provides a general description of the characteristics of these new automatic control apparatuses and of the interventions required on existing equipment for their installation, activation and operation. A brief presentation of the main dynamic performance of the hierarchical control system, from the inner to the outer control loops, is also given with reference to laboratory, commissioning and field tests.
Date of Publication: Nov. 2004