A brief historic introduction
Following the Framework Guidelines on Electricity System Operation, four network codes were initially developed:
Network Code on Operational Security
Network Code on Operational Planning and Scheduling
Network Code on Load-frequency Control and Reserves
Network Code on Emergency and Restoration
During the adoption process led by the European Commission, the Network Codes on Operational Security, Operational Planning and Scheduling and Load-frequency Control and Reserves were merged into the Guideline on Electricity Transmission System Operation.