The coordinated automatic voltage control of the Italian transmission Grid-part I: reasons of the choice and overview of the consolidated hierarchical system

Transmission network voltage regulation through coordinated automatic control of reactive powers is now becoming a challenging objective for many utilities and system operators (ISO or TSO) to achieve significant improvements in the security, quality, and efficiency of power system operation. This survey paper is concerned with application of Secondary and Tertiary Voltage Regulations (SVR and TVR), already operating in the Italian transmission network. The basic concepts behind SVR and TVR and the related hierarchical control system are first described in terms of system characteristics, main functions and design requirements. Cost/benefit analysis and comparison with alternative voltage control solutions are also provided in relation to the influence of power system restructuring process on the voltage ancillary service. More details about control system apparatuses and their field test results are provided in Part II.