Coordination between the reactive power scheduling function and the hierarchical voltage control of the EHV ENEL system

The paper presents the control strategies adopted at ENEL (the Italian Electric Power Company) for the automatic voltage regulation and for the short and very short term reactive power scheduling. The advanced project is based upon a three level hierarchical control of voltage and reactive power (primary, secondary and tertiary regulation) and a reactive power dispatch procedure. The three levels are characterized by specific control actions which affect systems of different size and complexity, operating in three steps. In particular, the slowest third level executes the optimal voltage profile defined by the short or very short term reactive power scheduling. The need of an effective co-ordination between the off-line reactive scheduling procedures and the on-line voltage control is pointed out in the work. Besides, the paper presents a computation procedure realized in order to simulate the steady state behaviour of the electric power system submitted to the hierarchical voltage control system and its interaction with the VAr optimisation program