CHAPTER 1

A transmission system shall be in the normal state when all of the following conditions are fulfilled: voltage and power flows are within the operational security limits defined in accordance with Article 25; frequency meets the following criteria: the steady state system frequency deviation is within the standard frequency range; or the absolute value of the steady state system frequency deviation is not larger than the maximum steady state frequency deviation and the system frequency limits established for the alert state are not fulfilled; active and reactive power reserves are sufficient to withstand contingencies from the contingency list defined in accordance with Article 33 without violating operational security limits; operation of the concerned TSO's control area is and will remain within operational security limits after the activation of remedial actions following the occurrence of a contingency from the contingency list defined in accordance with Article 33. A transmission system shall be in the alert state when: voltage and power flows are within the operational security limits defined in accordance with Article 25; and 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 frequency meets the following criteria: the absolute value of the steady state system frequency deviation is not larger than the maximum steady state frequency deviation; and 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 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. A transmission system shall be in the emergency state when at least one of the following conditions is fulfilled: there is at least one a violation of a TSO's operational security limits defined in accordance with Article 25; frequency does not meet the criteria for the normal state and for the alert state defined in accordance with paragraphs 1 and 2; at least one measure of the TSO's system defence plan is activated; there is a failure in the functioning of tools, means and facilities defined in accordance with Article 24(1), resulting in the unavailability of those tools, means and facilities for longer than 30 minutes. A transmission system shall be in the blackout state when at least one of the following conditions is fulfilled: loss of more than 50 % of demand in the concerned TSO's control area; total absence of voltage for at least three minutes in the concerned TSO's control area, leading to the triggering of restoration plans. A TSO of GB and IE/NI synchronous areas may develop a proposal specifying the level of demand loss at which the transmission system shall be in the blackout state. The TSOs of GB and IE/NI synchronous areas shall notify this instance to ENTSO for Electricity. A transmission system shall be in the restoration state when a TSO, being in the emergency or blackout state, has started to activate measures of its restoration plan. Each TSO shall, in real-time operation, determine the system state of its transmission system. Each TSO shall monitor the following transmission system parameters in real-time in its control area, based on real-time telemetry measurements or on calculated values from its observability area, taking into account the structural and real-time data in accordance with Article 42: active and reactive power flows; busbar voltages; frequency and frequency restoration control error of its LFC area; active and reactive power reserves; and generation and load. In order to specify the system state, each TSO shall perform contingency analysis at least once every 15 minutes, monitoring the transmission system's parameters defined in accordance with paragraph 2, against the operational security limits defined in accordance with Article 25 and the criteria for system states defined in accordance with Article 18. Each TSO shall also monitor the level of available reserves against the reserve capacity. When carrying out the contingency analysis, each TSO shall take into account the effect of remedial actions and the measures of the system defence plan. If its transmission system is not in normal state and if that system state is qualified as a wide area state the TSO shall: inform all TSOs about the system state of its transmission system via an IT tool for the exchange of real-time data at pan-European level; and provide with additional information on its transmission system elements which are part of the observability area of other TSOs, to those TSOs. Each TSO shall endeavour to ensure that its transmission system remains in the normal state and shall be responsible for managing operational security violations. To achieve that objective, each TSO shall design, prepare and activate remedial actions taking into account their availability, the time and resources needed for their activation and any conditions external to the transmission system which are relevant for each remedial action. The remedial actions used by TSOs in system operation in accordance with paragraph 1 and with Articles 21 to 23 of this Regulation shall be consistent with the remedial actions taken into account in capacity calculation in accordance with Article 25 of Regulation (EU) 2015/1222. Each TSO shall apply the following principles when activating and coordinating remedial actions in accordance with Article 23: for operational security violations which do not need to be managed in a coordinated way, a TSO shall design, prepare and activate remedial actions to restore the system to the normal state and to prevent the propagation of the alert or emergency state outside of the TSO's control area from the categories defined in Article 22; for operational security violations which need to be managed in a coordinated way, a TSO shall design, prepare and activate remedial actions in coordination with other concerned TSOs, following the methodology for the preparation of remedial actions in a coordinated way under Article 76(1)(b) and taking into account the recommendation of a regional security coordinator in accordance with Article 78(4). When selecting the appropriate remedial actions, each TSO shall apply the following criteria: activate the most effective and economically efficient remedial actions; activate remedial actions as close as possible to real-time taking into account the expected time of activation and the urgency of the system operation situation they intend to resolve; consider the risks of failures in applying the available remedial actions and their impact on operational security such as: the risks of failure or short-circuit caused by topology changes; the risks of outages caused by active or reactive power changes on power generating modules or demand facilities; and the risks of malfunction caused by equipment behaviour; give preference to remedial actions which make available the largest cross-zonal capacity for capacity allocation, while satisfying all operational security limits. Each TSO shall use the following categories of remedial actions: modify the duration of a planned outage or return to service transmission system elements to achieve the operational availability of those transmission system elements; actively impact power flows by means of: tap changes of the power transformers; tap changes of the phase-shifting transformers; modifying topologies; control voltage and manage reactive power by means of: tap changes of the power transformers; switching of the capacitors and reactors; switching of the power-electronics-based devices used for voltage and reactive power management; instructing transmission-connected DSOs and significant grid users to block automatic voltage and reactive power control of transformers or to activate on their facilities the remedial actions set out in points (i) to (iii) if voltage deterioration jeopardises operational security or threatens to lead to a voltage collapse in a transmission system; requesting the change of reactive power output or voltage setpoint of the transmission-connected synchronous power generating modules; requesting the change of reactive power output of the converters of transmission-connected non-synchronous power generating modules; re-calculate day-ahead and intraday cross-zonal capacities in accordance with Regulation (EU) 2015/1222; redispatch transmission or distribution-connected system users within the TSO's control area, between two or more TSOs; countertrade between two or more bidding zones; adjust active power flows through HVDC systems; activate frequency deviation management procedures; curtail, pursuant to Article 16(2) of Regulation (EC) No 714/2009, the already allocated cross-zonal capacity in an emergency situation where using that capacity endangers operational security, all TSOs at a given interconnector agree to such adjustment, and re-dispatching or countertrading is not possible; and where applicable, include the normal or alert state, manually controlled load-shedding. Where necessary and justified in order to maintain operational security, each TSO may prepare and activate additional remedial actions. The TSO shall report and justify those instances to the relevant regulatory authority and, where applicable, the Member State, at least once every year, after the activation of the additional remedial actions. The relevant reports and justifications shall also be published. The European Commission or the Agency may request the relevant regulatory authority to provide additional information concerning the activation of additional remedial actions in those instances where they affect a neighbouring transmission system. Each TSO shall prepare and activate remedial actions in accordance with the criteria set out in Article 21(2) to prevent the system state from deteriorating on the basis of the following elements: the monitoring and determination of system states in accordance with Article 19; the contingency analysis in real-time operation in accordance with Article 34; and the contingency analysis in operational planning in accordance with Article 72. When preparing and activating a remedial action, including redispatching or countertrading pursuant to Articles 25 and 35 of Regulation (EU) 2015/1222, or a procedure of a TSO's system defence plan which affects other TSOs, the relevant TSO shall assess, in coordination with the TSOs concerned, the impact of such remedial action or measure within and outside of its control area, in accordance with Article 75(1), Article 76(1)(b) and Article 78(1), (2) and (4) and shall provide the TSOs concerned with the information about this impact. When preparing and activating remedial actions which have an impact on the transmission-connected SGUs and DSOs, each TSO shall, if its transmission system is in normal or alert state, assess the impact of such remedial actions in coordination with the affected SGUs and DSOs and select remedial actions that contribute to maintaining normal state and secure operation of all involved parties. Each affected SGU and DSO shall provide to the TSO all necessary information for this coordination. When preparing and activating remedial actions each TSO shall, if its transmission system is not in normal or alert state, coordinate to the extent possible such remedial actions with the affected transmission-connected SGUs and DSOs to maintain the operational security and the integrity of the transmission system. When a TSO activates a remedial action each impacted transmission-connected significant grid user and DSO shall execute the instructions given by the TSO Where constraints have only consequences on the local state within the TSO's control area and the operational security violation does not need to be managed in a coordinated way, the TSO responsible for its management may decide not to activate remedial actions with costs to relieve them. Each TSO shall ensure the availability, reliability and redundancy of the following items: facilities for monitoring the system state of the transmission system, including state estimation applications and facilities for load-frequency control; means to control the switching of circuit breakers, coupler circuit breakers, transformer tap changers and other equipment which serve to control transmission system elements; means to communicate with the control rooms of other TSOs and RSCs; tools for operational security analysis; and tools and communication means necessary for TSOs to facilitate cross-border market operations. Where the TSO's tools, means and facilities referred to in paragraph 1 affect the transmission-connected DSOs or SGUs involved in supplying balancing services, ancillary services or in system defence or restoration or in delivery of real-time operational data according to Articles 44, 47, 50, 51 and 52, the relevant TSO and those DSOs and SGUs shall cooperate and coordinate to specify and ensure the availability, reliability and redundancy of these tools, means and facilities. Within 18 months from the entry into force of this Regulation each TSO shall adopt a business continuity plan detailing its responses to a loss of critical tools, means and facilities, containing provisions for their maintenance, replacement and development. Each TSO shall review at least annually its business continuity plan and update it as necessary and in any case following any significant change of the critical tools, means and facilities or of the relevant system operation conditions. The TSO shall share parts of the business continuity plan which affect DSOs and SGUs with the DSOs and SGUs concerned. Each TSO shall specify the operational security limits for each element of its transmission system, taking into account at least the following physical characteristics: voltage limits in accordance with Article 27; short-circuit current limits according to Article 30; and current limits in terms of thermal rating including the transitory admissible overloads. When defining the operational security limits, each TSO shall take into account the capabilities of SGUs to prevent that voltage ranges and frequency limits in normal and alert states lead to their disconnection. In case of changes of one of its transmission system elements, each TSO shall validate and where necessary update the operational security limits. For each interconnector each TSO shall agree with the neighbouring TSO on common operational security limits in accordance with paragraph 1. Each TSO shall specify, taking into account Article 5 of Council Directive 2008/114/EC Council Directive 2008/114/EC of 8 December 2008 on the identification and designation of European critical infrastructures and the assessment of the need to improve their protection (OJ L 345, 23.12.2008, p. 75). , a confidential security plan containing a risk assessment of assets owned or operated by the TSO, covering major physical or cyber threat scenarios determined by the Member State. The security plan shall consider potential impacts to the European interconnected transmission systems, and include organizational and physical measures aiming at mitigating the identified risks. Each TSO shall regularly review the security plan to address changes of threat scenarios and reflect the evolution of the transmission system.

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Source: EUR-Lex (Cellar) · retrieved 2026-11-04 · Text as adopted (Official Journal); later amendments are not incorporated in this text.