The voltage and reactive power control of ENEL transmission system

The ENEL project for secondary and tertiary voltage regulation requires an effective coordination of the reactive power resources through a composite online automatic control system, to meet the objective of keeping up a suitable voltage profile in the EHV network in the face of the continuously changing reactive power demanded by loads and the possible network perturbations. The chosen control system regulates, in closed loop, the voltage of some EHV busses (pilot nodes), selected among the strongest ones, through controlling the reactive powers of the generators which most influence those busses. The project is based on a hierarchical control structure which provides a network subdivision into areas around the pilot nodes. The areas are controlled by signals of `reactive power level´ (one for each area) supplied by regional secondary voltage regulators. At higher hierarchical level a central tertiary voltage regulator coordinates, in closed loop, the action of the regional controllers, establishing the voltage pattern of the pilot nodes and effecting slow corrections in order to have a better balance of reactive power generation among the areas