What are the consequences of the System States for Grid Users?
The first aim of a common definition for System State is to give to TSOs a common understanding of the situation, and of the coordination they must have to undertake. The principles for System State classification aims at differentiating when the system is N- and (N-1) compliant (Normal State), N compliant but not (N-1) compliant (Alert State), or not N- compliant (Emergency State). That means that in both Normal and Alert State, there is no significant violation of the Operational Security Limits.
When the Transmission System is in Alert State, although all Operational Security Limits are respected, there is at least one Contingency which is reasonably probable and which is part of the Contingency List, for which, in case of occurrence, at least one of the operational parameters will not remain within the Operational Security Limits. It's therefore important to mitigate the risk of occurrence of such Contingency, and this is the reason why TSO can ask for stopping actions which can increase the probability of Contingency.
1. In Emergency State, at least one of the operational parameters is outside of the Operational Security Limits, so it affects the quality and security of the electricity supply towards Significant Grid Users. Nevertheless, a precise definition of the impact on Grid Users in case of Emergency State cannot be done in the OS NC, since it varies depending on the sequence of events that have occurred: impact on frequency in case of big imbalance without sufficient amount of active reserves, impact on voltage in case of insufficient of Reactive Power reserves, etc.;
2. In Alert State the system is secure in N- situation, so there is no direct consequence for Grid Users, except for those currently conducting a test;
A precise definition of the impact on Significant Grid Users in case of Emergency State cannot be done in the OS NC, since it varies depending of the sequence of events that have occurred.
(ENTSO-E Supporting Document for the Network Code on Operational Security of 24 September 2013 2nd Edition Final, p. 155)