Alert State is the System State where the system is within Operational Security Limits, but a Contingency from the Contingency List has been detected, for which in case of occurrence, the available Remedial Actions are not sufficient to keep the Normal State (Article 3(2)(17) of the Network Code on System Operation).
Article 18(2) of the Network Code on System Operation
A transmission system shall be in the alert state where:
(a) voltage and power flows are within the operational security limits defined in accordance with Article 25; and
(b) the TSO's reserve capacity is reduced by more than 20 % for longer than 30 minutes and there are no means to compensate for that reduction in real-time system operation; or
(c) frequency meets the following criteria:
(i) the absolute value of the steady state system frequency deviation is not larger than the maximum steady state frequency deviation; and
(ii) the absolute value of the steady state system frequency deviation has continuously exceeded 50 % of the maximum steady state frequency deviation for a time period longer than the alert state trigger time or the standard frequency range for a time period longer than time to restore frequency; or
(d) at least one contingency from the contingency list defined in accordance with Article 33 leads to a violation of the TSO's operational security limits, even after the activation of remedial actions.
The criteria to be used by the Transmission System Operator (TSO) when classifying the System State of its Transmission System as Alert State are as follows:
ii. at least one of the following conditions is fulfilled:
a. Active Power Reserve requirements are not fulfilled with lack of more than 20% of the required amount of any of the following reserves: FCR, FRR and RR according to the dimensioning in the Network Code on System Operation for more than 30 minutes and with no means to replace them;
b. frequency is within the frequency limits for the Alert State as defined in the Network Code on System Operation;
c. at least one Contingency from the Contingency List defined can lead to deviations from Operational Security Limits, even after effects of Remedial Actions.
Network Code on System Operation, Article 18(2), Article 3(2)(17)