(N-1) criterion — the rule according to which the elements remaining in operation within a TSO's control area after occurrence of a contingency are capable of accommodating the new operational situation without violating operational security limits (14)

(N-1) situation — the situation in the transmission system in which one contingency from the contingency list occurred (15)

ACE — the sum of the power control error (‘ΔP’), that is the real-time difference between the measured actual real time power interchange value (‘P’) and the control program (‘P0’) of a specific LFC area or LFC block and the frequency control error (‘K*Δf’), that is the product of the K-factor and the frequency deviation of that specific LFC area or LFC block, where the area control error equals ΔP+K*Δf (19)

active power reserve — the balancing reserves available for maintaining the frequency (16)

adequacy — the ability of in-feeds into an area to meet the load in that area (68)

affected TSO — a TSO for which information on the exchange of reserves and/or sharing of reserves and/or imbalance netting process and/or cross-border activation process is needed for the analysis and maintenance of operational security (94)

aggregated netted external schedule — a schedule representing the netted aggregation of all external TSO schedules and external commercial trade schedules between two scheduling areas or between a scheduling area and a group of other scheduling areas (69)

alert state — the system state in which the system is within operational security limits, but a contingency from the contingency list has been detected and in case of its occurrence the available remedial actions are not sufficient to keep the normal state (17)

alert state trigger time — the time before alert state becomes active (98)

automatic FRR — FRR that can be activated by an automatic control device (99)

automatic FRR activation delay — the period of time between the setting of a new setpoint value by the frequency restoration controller and the start of physical automatic FRR delivery (100)

automatic FRR full activation time — the time period between the setting of a new setpoint value by the frequency restoration controller and the corresponding activation or deactivation of automatic FRR (101)

availability plan — the combination of all planned availability statuses of a relevant asset for a given time period (70)

availability status — the capability of a power generating module, grid element or demand facility to provide a service for a given time period, regardless of whether or not it is in operation (71)

average FRCE data — the set of data consisting of the average value of the recorded instantaneous FRCE of a LFC area or a LFC block within a given measured period time (102)

blackout state — the system state in which the operation of part or all of the transmission system is terminated (22)

close to real-time — the time lapse of not more than 15 minutes between the last intraday gate closure and real-time (72)

constraint — a situation in which there is a need to prepare and activate a remedial action in order to respect operational security limits (2)

consumption schedule — a schedule representing the consumption of a demand facility or of a group of demand facilities (73)

contingency analysis — a computer based simulation of contingencies from the contingency list (27)

contingency influence threshold — a numerical limit value against which the influence factors are checked and the occurrence of a contingency located outside of the TSO's control area with an influence factor higher than the contingency influence threshold is considered to have a significant impact on the TSO's control area including interconnectors (26)

contingency list — the list of contingencies to be simulated in order to test the compliance with the operational security limits (4)

control capability providing TSO — the TSO that shall trigger the activation of its reserve capacity for a control capability receiving TSO under the conditions of an agreement for sharing reserves (103)

control capability receiving TSO — the TSO calculating reserve capacity by taking into account reserve capacity which is accessible through a control capability providing TSO under the conditions of an agreement for sharing reserves (104)

control program — a sequence of set-point values for the netted power interchange of a LFC area or LFC block over alternating current (‘AC’) interconnectors (20)

criteria application process — the process of calculating the target parameters for the synchronous area, the LFC block and the LFC area based on the data obtained in the data collection and delivery process (105)

critical fault clearing time — the maximum fault duration for which the transmission system retains stability of operation (28)

cross-border FRR activation process — a process agreed between the TSOs participating in the process that allows for activation of FRR connected in a different LFC area by correcting the input of the involved FRPs accordingly (107)

cross-border RR activation process — a process agreed between the TSOs participating in the process that allows for activation of RR connected in a different LFC area by correcting the input of the involved RRP accordingly (108)

data collection and delivery process — the process of collection of the set of data necessary in order to perform the frequency quality evaluation criteria (106)

dimensioning incident — the highest expected instantaneously occurring active power imbalance within a LFC block in both positive and negative direction (109)

disturbance — an unplanned event that may cause the transmission system to divert from the normal state (31)

dynamic stability — a common term including the rotor angle stability, frequency stability and voltage stability (32)

dynamic stability assessment — the operational security assessment in terms of dynamic stability (33)

electrical time deviation — the time discrepancy between synchronous time and coordinated universal time (‘UTC’) (110)

emergency state — the system state in which one or more operational security limits are violated (37)

ENTSO for Electricity operational planning data environment — the set of application programs and equipment developed in order to allow the storage, exchange and management of the data used for operational planning processes between TSOs (74)

exceptional contingency — the simultaneous occurrence of multiple contingencies with a common cause (39)

exchange of reserves — the possibility of a TSO to access reserve capacity connected to another LFC area, LFC block, or synchronous area to fulfil its reserve requirements resulting from its own reserve dimensioning process of either FCR, FRR or RR and where that reserve capacity is exclusively for that TSO, and is not taken into account by any other TSO to fulfil its reserve requirements resulting from their respective reserve dimensioning processes (96)

external commercial trade schedule — a schedule representing the commercial exchange of electricity between market participants in different scheduling areas (75)

external contingency — a contingency outside the TSO's control area and excluding interconnectors, with an influence factor higher than the contingency influence threshold (24)

external TSO schedule — a schedule representing the exchange of electricity between TSOs in different scheduling areas (76)

FACTS — equipment for the alternating current transmission of electric power, aiming at enhanced controllability and increased active power transfer capability (67)

fault — all types of short-circuits (single-, double- and triple-phase, with and without earth contact), a broken conductor, interrupted circuit, or an intermittent connection, resulting in the permanent non-availability of the affected transmission system element (29)

FCP — a process that aims at stabilising the system frequency by compensating imbalances by means of appropriate reserves (114)

FCR — the active power reserves available to contain system frequency after the occurrence of an imbalance (6)

FCR full activation frequency deviation — the rated value of frequency deviation at which the FCR in a synchronous area is fully activated (111)

FCR full activation time — the time period between the occurrence of the reference incident and the corresponding full activation of the FCR (112)

FCR obligation — the part of all of the FCR that falls under the responsibility of a TSO (113)

forced outage — the unplanned removal from service of a relevant asset for any urgent reason that is not under the operational control of the operator of the concerned relevant asset (77)

FRCE — the control error for the FRP which is equal to the ACE of a LFC area or equal to the frequency deviation where the LFC area geographically corresponds to the synchronous area (43)

FRCE target parameters — the main target LFC block variables on the basis of which the dimensioning criteria for FRR and RR of the LFC block are determined and evaluated and which are used to reflect the LFC block behaviour in normal operation (123)

frequency coupling process — a process agreed between all TSOs of two synchronous areas that allows linking the activation of FCR by an adaptation of HVDC flows between the synchronous areas (115)

frequency deviation — the difference between the actual and the nominal frequency of the synchronous area which can be negative or positive (40)

frequency quality defining parameter — the main system frequency variables that define the principles of frequency quality (116)

frequency quality evaluation criteria — a set of calculations using system frequency measurements that allows the evaluation of the quality of the system frequency against the frequency quality target parameters (118)

frequency quality evaluation data — the set of data that allows the calculation of the frequency quality evaluation criteria (119)

frequency quality target parameter — the main system frequency target on which the behaviour of FCR, FRR and RR activation processes is evaluated in normal state (117)

frequency recovery range — the system frequency range to which the system frequency is expected to return in the GB and IE/NI synchronous areas, after the occurrence of an imbalance equal to or smaller than the reference incident, within the time to recover frequency (120)

frequency restoration power interchange — the power which is interchanged between LFC areas within the cross-border FRR activation process (124)

frequency restoration range — the system frequency range to which the system frequency is expected to return in the GB, IE/NI and Nordic synchronous areas, after the occurrence of an imbalance equal to or smaller than the reference incident within the time to restore frequency (122)

frequency setpoint — the frequency target value used in the FRP, defined as the sum of the nominal system frequency and an offset value needed to reduce an electrical time deviation (125)

frequency stability — the ability of the transmission system to maintain frequency stable in the N-situation and after being subjected to a disturbance (34)

FRP — a process that aims at restoring frequency to the nominal frequency and, for synchronous areas consisting of more than one LFC area, a process that aims at restoring the power balance to the scheduled value (42)

FRR — the active power reserves available to restore system frequency to the nominal frequency and, for a synchronous area consisting of more than one LFC area, to restore power balance to the scheduled value (7)

FRR availability requirements — a set of requirements defined by the TSOs of a LFC block regarding the availability of FRR (126)

FRR dimensioning rules — the specifications of the FRR dimensioning process of a LFC block (127)

generation schedule — a schedule representing the electricity generation of a power generating module or of a group of power generating modules (78)

HVDC — borrowed from another act; this instrument states no meaning of its own 1.

imbalance netting power interchange — the power which is interchanged between LFC areas within the imbalance netting process (129)

imbalance netting process — a process agreed between TSOs that allows avoiding the simultaneous activation of FRR in opposite directions, taking into account the respective FRCEs as well as the activated FRR and by correcting the input of the involved FRPs accordingly (128)

influence factor — the numerical value used to quantify the greatest effect of the outage of a transmission system element located outside of the TSO's control area excluding interconnectors, in terms of a change in power flows or voltage caused by that outage, on any transmission system element. The higher is the value the greater the effect (25)

initial FCR obligation — the amount of FCR allocated to a TSO on the basis of a sharing key (130)

instantaneous FRCE data — a set of data of the FRCE of a LFC block with a measurement period equal to or shorter than 10 seconds used for system frequency quality evaluation purposes (133)

instantaneous frequency data — a set of data measurements of the overall system frequency for the synchronous area with a measurement period equal to or shorter than one second used for system frequency quality evaluation purposes (131)

instantaneous frequency deviation — a set of data measurements of the overall system frequency deviations for the synchronous area with a measurement period equal to or shorter than one second used for system frequency quality evaluation purposes (132)

internal commercial trade schedule — a schedule representing the commercial exchange of electricity within a scheduling area between different market participants (79)

internal contingency — a contingency within the TSO's control area, including interconnectors (23)

internal relevant asset — a relevant asset which is part of a TSO's control area or a relevant asset located in a distribution system, including a closed distribution system, which is connected directly or indirectly to that TSO's control area (80)

K-factor of an LFC area or LFC block — a value expressed in megawatts per hertz (‘MW/Hz’), which is as close as practical to, or greater than the sum of the auto-control of generation, self-regulation of load and of the contribution of frequency containment reserve relative to the maximum steady-state frequency deviation (45)

level 1 FRCE range — the first range used for system frequency quality evaluation purposes on LFC block level within which the FRCE should be kept for a specified percentage of the time (134)

level 2 FRCE range — the second range used for system frequency quality evaluation purposes on LFC block level within which the FRCE should be kept for a specified percentage of the time (135)

LFC area — a part of a synchronous area or an entire synchronous area, physically demarcated by points of measurement at interconnectors to other LFC areas, operated by one or more TSOs fulfilling the obligations of load-frequency control (12)

LFC block — a part of a synchronous area or an entire synchronous area, physically demarcated by points of measurement at interconnectors to other LFC blocks, consisting of one or more LFC areas, operated by one or more TSOs fulfilling the obligations of load-frequency control (18)

LFC block imbalances — the sum of the FRCE, FRR activation and RR activation within the LFC block and the imbalance netting power interchange, the frequency restoration power interchange and the replacement power interchange of this LFC block with other LFC blocks (138)

LFC block monitor — a TSO responsible for collecting the frequency quality evaluation criteria data and applying the frequency quality evaluation criteria for the LFC block (139)

LFC block operational agreement — a multi-party agreement between all TSOs of a LFC block if the LFC block is operated by more than one TSO and means a LFC block operational methodology to be adopted unilaterally by the relevant TSO if the LFC block is operated by only one TSO (136)

load-frequency control structure — the basic structure considering all relevant aspects of load-frequency control in particular concerning respective responsibilities and obligations as well as types and purposes of active power reserves (140)

local state — the qualification of an alert, emergency or blackout state when there is no risk of extension of the consequences outside of the control area including interconnectors connected to this control area (46)

manual FRR full activation time — the time period between the setpoint change and the corresponding activation or deactivation of manual FRR (143)

maximum instantaneous frequency deviation — the maximum expected absolute value of an instantaneous frequency deviation after the occurrence of an imbalance equal to or smaller than the reference incident, beyond which emergency measures are activated (144)

maximum steady-state frequency deviation — the maximum expected frequency deviation after the occurrence of an imbalance equal to or less than the reference incident at which the system frequency is designed to be stabilised (47)

monitoring area — a part of the synchronous area or the entire synchronous area, physically demarcated by points of measurement at interconnectors to other monitoring areas, operated by one or more TSOs fulfilling the obligations of a monitoring area (145)

N-situation — the situation where no transmission system element is unavailable due to occurrence of a contingency (3)

neighbouring TSOs — the TSOs directly connected via at least one AC or DC interconnector (49)

netted area AC position — the netted aggregation of all AC external schedules of an area (81)

normal state — a situation in which the system is within operational security limits in the N-situation and after the occurrence of any contingency from the contingency list, taking into account the effect of the available remedial actions (5)

observability area — a TSO's own transmission system and the relevant parts of distribution systems and neighbouring TSOs' transmission systems, on which the TSO implements real-time monitoring and modelling to maintain operational security in its control area including interconnectors (48)

operational security — the transmission system's capability to retain a normal state or to return to a normal state as soon as possible, and which is characterised by operational security limits (1)

operational security analysis — the entire scope of the computer based, manual and automatic activities performed in order to assess the operational security of the transmission system and to evaluate the remedial actions needed to maintain operational security (50)

operational security indicators — indicators used by TSOs to monitor the operational security in terms of system states as well as faults and disturbances influencing operational security (51)

operational security ranking — the ranking used by TSOs to monitor the operational security on the basis of the operational security indicators (52)

operational tests — the tests carried out by a TSO or DSO for maintenance, development of system operation practices and training and to acquire information on transmission system behaviour under abnormal system conditions and the tests carried out by significant grid users for similar purposes on their facilities (53)

ordinary contingency — the occurrence of a contingency of a single branch or injection (54)

out-of-range contingency — the simultaneous occurrence of multiple contingencies without a common cause, or a loss of power generating modules with a total loss of generation capacity exceeding the reference incident (55)

outage coordination region — a combination of control areas for which TSOs define procedures to monitor and where necessary coordinate the availability status of relevant assets in all time-frames (82)

outage planning agent — an entity with the task of planning the availability status of a relevant power generating module, a relevant demand facility or a relevant grid element (87)

outage planning incompatibility — the state in which a combination of the availability status of one or more relevant grid elements, relevant power generating modules, and/or relevant demand facilities and the best estimate of the forecasted electricity grid situation leads to violation of operational security limits taking into account remedial actions without costs which are at the TSO's disposal (86)

prequalification — the process to verify the compliance of a reserve providing unit or a reserve providing group with the requirements set by the TSO (146)

process activation structure — the structure to categorise the processes concerning the different types of active power reserves in terms of purpose and activation (142)

process responsibility structure — the structure to determine responsibilities and obligations with respect to active power reserves based on the control structure of the synchronous area (141)

ramping period — a period of time defined by a fixed starting point and a length of time during which the input and/or output of active power will be increased or decreased (147)

ramping rate — the rate of change of active power by a power generating module, demand facility or HVDC system (56)

reactive power reserve — the reactive power which is available for maintaining voltage (57)

reference incident — the maximum positive or negative power deviation occurring instantaneously between generation and demand in a synchronous area, considered in the FCR dimensioning (58)

regional security coordinator — the entity or entities, owned or controlled by TSOs, in one or more capacity calculation regions performing tasks related to TSO regional coordination (89)

relevant asset — any relevant demand facility, relevant power generating module, or relevant grid element partaking in the outage coordination (84)

relevant demand facility — a demand facility which participates in the outage coordination and the availability status of which influences cross-border operational security (83)

relevant grid element — any component of a transmission system, including interconnectors, or of a distribution system, including a closed distribution system, such as a single line, a single circuit, a single transformer, a single phase-shifting transformer, or a voltage compensation installation, which participates in the outage coordination and the availability status of which influences cross-border operational security (85)

relevant power generating module — a power generating module which participates in the outage coordination and the availability status of which influences cross-border operational security (88)

replacement power interchange — the power which is interchanged between LFC areas within the cross-border RR activation process (137)

reserve capacity — the amount of FCR, FRR or RR that needs to be available to the TSO (95)

reserve connecting DSO — the DSO responsible for the distribution network to which a reserve providing unit or reserve providing group, providing reserves to a TSO, is connected (149)

reserve connecting TSO — the TSO responsible for the monitoring area to which a reserve providing unit or reserve providing group is connected (150)

reserve instructing TSO — the TSO responsible for the instruction of the reserve providing unit or the reserve providing group to activate FRR and/or RR (148)

reserve provider — a legal entity with a legal or contractual obligation to supply FCR, FRR or RR from at least one reserve providing unit or reserve providing group (9)

reserve providing group — an aggregation of power generating modules, demand units and/or reserve providing units connected to more than one connection point fulfilling the requirements to provide FCR, FRR or RR (11)

reserve providing unit — a single or an aggregation of power generating modules and/or demand units connected to a common connection point fulfilling the requirements to provide FCR, FRR or RR (10)

reserve receiving TSO — the TSO involved in an exchange with a reserve connecting TSO and/or a reserve providing unit or a reserve providing group connected to another monitoring or LFC area (151)

restoration state — the system state in which the objective of all activities in the transmission system is to re-establish the system operation and maintain operational security after the blackout state or the emergency state (38)

rotor angle stability — the ability of synchronous machines to remain in synchronism under N-situation and after being subject to a disturbance (59)

RR — the active power reserves available to restore or support the required level of FRR to be prepared for additional system imbalances, including generation reserves (8)

RR availability requirements — a set of requirements defined by the TSOs of a LFC block regarding the availability of RR (153)

RR dimensioning rules — the specifications of the RR dimensioning process of a LFC block (154)

RRP — a process to restore the activated FRR and, additionally for GB and IE/NI, to restore the activated FCR (152)

schedule — a reference set of values representing the generation, consumption or exchange of electricity for a given time period (44)

scheduling agent — the entity or entities with the task of providing schedules from market participants to TSOs, or where applicable third parties (90)

scheduling area — an area within which the TSOs' obligations regarding scheduling apply due to operational or organisational needs (91)

security plan — the plan containing a risk assessment of critical TSO's assets to major physical- and cyber-threat scenarios with an assessment of the potential impacts (60)

sharing of reserves — a mechanism in which more than one TSO takes the same reserve capacity, being FCR, FRR or RR, into account to fulfil their respective reserve requirements resulting from their reserve dimensioning processes (97)

stability limits — the permitted boundaries for the operation of the transmission system in terms of respecting the limits of voltage stability, rotor angle stability and frequency stability (61)

standard frequency deviation — the absolute value of the frequency deviation that limits the standard frequency range (156)

standard frequency range — a defined symmetrical interval around the nominal frequency within which the system frequency of a synchronous area is supposed to be operated (155)

steady state frequency deviation — the absolute value of frequency deviation after occurrence of an imbalance, once the system frequency has been stabilised (157)

synchronous area monitor — a TSO responsible for collecting the frequency quality evaluation criteria data and applying the frequency quality evaluation criteria for the synchronous area (158)

system defence plan — the technical and organisational measures to be undertaken to prevent the propagation or deterioration of a disturbance in the transmission system, in order to avoid a wide area state disturbance and blackout state (63)

system frequency — the electric frequency of the system that can be measured in all parts of the synchronous area under the assumption of a coherent value for the system in the timeframe of seconds, with only minor differences between different measurement locations (41)

system state — the operational state of the transmission system in relation to the operational security limits which can be normal state, alert state, emergency state, blackout state and restoration state (36)

time control process — a process for time control, where time control is a control action carried out to return the electrical time deviation between synchronous time and UTC time to zero (159)

time to recover frequency — for the synchronous areas GB and IE/NI, the maximum expected time after the occurrence of an imbalance smaller than or equal to the reference incident in which the system frequency returns to the maximum steady state frequency deviation (121)

time to restore frequency — the maximum expected time after the occurrence of an instantaneous power imbalance smaller than or equal to the reference incident in which the system frequency returns to the frequency restoration range for synchronous areas with only one LFC area and in the case of synchronous areas with more than one LFC area, the maximum expected time after the occurrence of an instantaneous power imbalance of an LFC area within which the imbalance is compensated (13)

topology — the data concerning the connectivity of the different transmission system or distribution system elements in a substation and includes the electrical configuration and the position of circuit breakers and isolators (64)

transitory admissible overloads — the temporary overloads of transmission system elements which are allowed for a limited period and which do not cause physical damage to the transmission system elements as long as the defined duration and thresholds are respected (65)

transmission system element — any component of the transmission system (30)

virtual tie-line — an additional input of the controllers of the involved LFC areas that has the same effect as a measuring value of a physical interconnector and allows exchange of electric energy between the respective areas (66)

voltage control — the manual or automatic control actions at the generation node, at the end nodes of the AC lines or HVDC systems, on transformers, or other means, designed to maintain the set voltage level or the set value of reactive power (21)

voltage stability — the ability of a transmission system to maintain acceptable voltages at all nodes in the transmission system in the N-situation and after being subjected to a disturbance (35)

week-ahead — the week prior to the calendar week of operation (92)

wide area state — the qualification of an alert state, emergency state or blackout state when there is a risk of propagation to the interconnected transmission systems (62)

year-ahead — the year prior to the calendar year of operation (93)