About SSC

System security is the primary goal of the operation of the interconnected grid. In an interconnected system there exist numerous interdependencies between the grids forming part of the system. In addition, there are impacts attributable to the usage of the system by market players. In an unbundled environment, grid operators are not allowed to interfere with market forces unless system security is at stake.

The operation of the interconnected grid is founded on the principle that each partner is responsible for its own grid. However, because the national electricity systems exert an influence upon one another, more and more coordination between TSOs is needed at the regional level. In order to give practical application to the basic interconnection principle that each TSO is responsible for its own control area, one of the aims is to extend the definition of methods of cooperation to operational situations where factors external to the control area may reduce the ability of a TSO to operate its system within the operating limits laid down by the UCTE/ENTSO-E rules.

TSOs are in charge of managing the security of operation of their own grids. The most relevant rules for the security of interconnected operation are related mainly to the functioning of interconnections. All these coordinating rules complement any other existing national commitments (whether legal or contractual) concerning access to the transmission grids. The performance control of facilities connected to grids will remain the responsibility of TSOs to the extent of their national commitments.

Each control area and each TSO is responsible for procedures to ensure reliable operation over a reasonable future time period, in view of real-time conditions and preparation. For this reason, the N-1 principle has been developed, whereby each TSO must prevent the propagation of any incidents occurring within its control area. This means that there must be no cascading that has an impact outside the borders of the relevant TSO’s control area. The N-1 principle is aimed at preventing an critical situation that arises as a result of a combination of events. Coordination between TSOs contributes to greater solidarity resulting from the operation of interconnected grids. Enhanced coordination will also allow the participating TSOs to prevent disturbances, to provide assistance in the event of failures with a view to reducing their impact, and to provide resetting strategies after a collapse. This coordination has been developed intensively and today also includes new aspects related to market mechanisms.