Power system operation is based on the constant balance between the electricity demand and supply. Due to the deviations between realized and scheduled values, based on the bilateral supply contracts and electricity trade contracts, there is a need for system balancing. The real time system balancing is responsibility of Croatian Transmission System Operator.
Balancing energy is electricity activated by the Transmission System Operator to cover the difference between electricity delivered or taken over and the contracted amounts of electricity for the purpose of maintaining the frequency of the electricity system within the prescribed range.
Operational implementation of power system balancing is conducted through the provisions of Transmission Grid Code (OJ 67/17), which during normal operation considers use of secondary control, tertiary control and buying/selling of energy. If the electric power system cannot be balanced with aforementioned mechanisms, the emergency state operation occurs. In that moment the following measures for returning to the previous normal state operation are implemented:
- in case of energy surplus in the electric power system or in some of its parts (respecting order), by giving an order for the decrease of production to producers connected to the transmission network that do not have the eligibility status to operational minimum via order of the authorized person of the producers and by giving an order to decrease production of the eligible producers connected to the transmission network, remotely or via order of authorized persons of the producers;
- in case of shortage of energy in the electric power system or some of its parts (respecting order) by giving an order to disconnect from operation pumped storage power plants that take electricity from network, by raising production of production facilities up until maximum production power and implementation of manual demand disconnection procedure within transmission and distribution network.
Following the decision of dispatchers, the production unit can be excluded from previously specified procedures in cases when it could cause further disturbance of secure operation of electric power system and/or there is danger of material damage and/or endanger human lives.