Impact of real losses and operational constraints on the reactive support value in presence of a hierarchical voltage control

The aim of the paper is to assess the impact of the real power losses and of the satisfaction of some operational constraints on the value and the consequent price of the reactive power support in a new competitive electricity market. The evaluation of the marginal costs of the reactive power demand and the marginal benefits of the reactive power production is performed by the use of a suitable optimal reactive power flow program (ORPF) which takes in the due account the hierarchical voltage control (HVC) scheme designed for the Italian EHV transmission system. The marginal costs (benefits) are determined by a linear combination of the real losses gradient and of the active constraints sensitivities with respect to the nodal reactive power injections in the ORPF solution point Therefore the impact of the operational constraints adopted by the transmission system operators (TSO) on the reactive support value is strictly tied to the Lagrange multipliers of the active constraints of the problem. The ORPF procedure has been applied to the analysis of the operation of the EHV Italian system for different voltage control structures. The results show that an adequate HVC scheme is suitable to exploit the local nature of reactive power allowing the introduction of a regional reactive market, obviously related to the control areas of the secondary voltage regulation (SVR).