'Frequency' means the electric frequency of the system expressed in hertz that can be measured in all parts of the synchronous area under the assumption of a consistent value for the system in the time frame of seconds, with only minor differences between different measurement locations. Its nominal value is 50Hz (Article 2(22) of the Network Code on requirements for grid connection of generators (NC RfG)).
The ENTSO-E Supporting Document for the Network Code on Operational Security of 24 September 2013 (2nd Edition Final) indicates the frequency is the sole parameter in the synchronous area common to all Transmission System Operators (TSOs) and system users, who are all concerned with its quality.
Frequency permanently reflects the balance between supply and demand. Deviations from the nominal value signal either a generation surplus or a generation deficit within the synchronous area.
According to the Network Code on System Operation, "System Frequency" means 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 time frame of seconds, with only minor differences between different measurement locations (Article 3(2)(41)), its nominal value is 50 Hz in all synchronous areas.
System frequency drops whenever there is shortage of generation to supply demand and frequency increases whenever there is excess of energy.
Frequency at its nominal value reflects balance in supply and demand. Sudden loss of supply or demand will result in frequency deviation from equilibrium. Frequency deviations may be caused by critical events such as power plant or load tripping.
With regard to frequency response the speed and scale of the change in power production/absorption or power transfer will be highly dependent on the size of the synchronous system and the largest loss of either power production/absorption that can occur.
Therefore in the context of small synchronous area, such as Ireland or GB, a single loss of a generator or HVDC interconnector can result in a change in system frequency that is markedly greater than what could be in CE synchronous network.
This leads naturally to the need for a faster response and/or larger response to a frequency change in smaller synchronous areas than in Continental Europe to arrest a change in frequency and restore the nominal frequency (Parameters related to frequency stability, ENTSO-E guidance document for national implementation for network codes on grid connection, 16 November 2016, p. 5).
The rate of change in frequency due to imbalance depends partly on the system inertia. Frequency response is defined as the automatic corrective response provided for balancing load and generation.
As ENTSO-E guidance document for national implementation for network codes on grid connection, Selecting national MW boundaries, Draft for consultation 1 July - 15 August 2016, 30 June 2016 underlines, frequency response provided by the generation represents an important service to the electricity system.
The scope of frequency control management is to maintain a continuous balance between generation and demand, ensuring frequency quality and stability within each synchronous area.
Due to its cross-border impact, this Regulation should aim at the same frequency-related requirements for all voltage levels, at least within a synchronous area. That is necessary because, within a synchronous area, a change in frequency in one Member State would immediately impact frequency and could damage equipment in all other Member States.
Recital 14 of the Demand Connection Code (DCC)
Recital 16 of the Network Code on requirements for grid connection of generators (NC RfG)
For this purpose, TSOs procure adequate upward and downward Active Power Reserve and define criteria, according to which the quality of the frequency are assessed.
in line with the Network Code on Electricity Balancing common criteria are set for the dimensioning and establishment of these reserves.
System frequency is important for defining a synchronous area (being an area covered by interconnected Transmission System Operators with a common system frequency in a steady state).
Collaboration on frequency-related requirements is reasonably recommended at synchronous area level (Harmonisation, ENTSO-E guidance document for national implementation for network codes on grid connection, Draft for consultation 1 July - 15 August 2016, 30 June 2016, p. 2).
Frequency response is defined as the automatic corrective response provided for balancing load and generation. Based on the different response time, frequency response can be classified into three different categories: Inertial Frequency Response, Frequency Containment Response and Frequency Restoration Response.
In the last few years, practically all ENTSO-E synchronous areas have been experiencing increasing frequency variations at hour boundaries, multiple times per day, mainly during the ramping periods in the morning and the evening.
Furthermore, lasting frequency deviations (generally high frequency) can more often also be observed not only at boundaries hours: statistics shows an increase of the system frequency variations, in respect to number, duration and size.
Important requirements for defining frequency quality and target parameters are stipulated in Article 127 of the Network Code on System Operation and Annex III thereto (see below tables and box).
Frequency quality defining parameters of the synchronous areas
referred to in Article 127 of the of the Network Code on System Operation and Annex III thereto (Table 1)
|
CE |
GB |
IE/NI |
Nordic |
|
|
standard frequency range |
± 50 mHz |
± 200 mHz |
± 200 mHz |
± 100 mHz |
|
maximum instantaneous frequency deviation |
800 mHz |
800 mHz |
1 000 mHz |
1 000 mHz |
|
maximum steady-state frequency deviation |
200 mHz |
500 mHz |
500 mHz |
500 mHz |
|
time to recover frequency |
not used |
1 minute |
1 minute |
not used |
|
frequency recovery range |
not used |
± 500 mHz |
± 500 mHz |
not used |
|
time to restore frequency |
15 minutes |
15 minutes |
15 minutes |
15 minutes |
|
frequency restoration range |
not used |
± 200 mHz |
± 200 mHz |
± 100 mHz |
|
alert state trigger time |
5 minutes |
10 minutes |
10 minutes |
5 minutes |
Frequency quality target parameters of the synchronous areas
referred to in Article 127 of the Network Code on System Operation and Annex III thereto (Table 2)
|
CE |
GB |
IE/NI |
Nordic |
|
|
maximum number of minutes outside the standard frequency range |
15 000 |
15 000 |
15 000 |
15 000 |
Network Code on System Operation
Article 127
Frequency quality defining and target parameters
1. The frequency quality defining parameters shall be:
(a) the nominal frequency for all synchronous areas;
(b) the standard frequency range for all synchronous areas;
(c) the maximum instantaneous frequency deviation for all synchronous areas;
(d) the maximum steady-state frequency deviation for all synchronous areas;
(e) the time to restore frequency for all synchronous areas;
(f) the time to recover frequency for the GB and IE/NI synchronous areas;
(g) the frequency restoration range for the GB, IE/NI and Nordic synchronous areas;
(h) the frequency recovery range for the GB and IE/NI synchronous areas; and
(i) the alert state trigger time for all synchronous areas.
2. The nominal frequency shall be 50 Hz for all synchronous areas.
3. The default values of the frequency quality defining parameters listed in paragraph 1 are set out in Table 1 of Annex III.
4. The frequency quality target parameter shall be the maximum number of minutes outside the standard frequency range per year per synchronous area and its default value per synchronous area are set out in Table 2 of Annex III.
5. The values of the frequency quality defining parameters in Table 1 of Annex III and of the frequency quality target parameter in Table 2 of Annex III shall apply unless all TSOs of a synchronous area propose different values pursuant to paragraphs 6, 7 and 8.
6. All TSOs of CE and Nordic synchronous areas shall have the right to propose in the synchronous area operational agreement values different from those set out in Tables 1 and 2 of Annex III regarding:
(a) the alert state trigger time;
(b) the maximum number of minutes outside the standard frequency range.
7. All TSOs of the GB and IE/NI synchronous areas shall have the right to propose in the synchronous area operational agreement values different from those set out in Tables 1 and 2 of Annex III regarding:
(a) time to restore frequency;
(b) the alert state trigger time; and
(c) the maximum number of minutes outside the standard frequency range.
8. The proposal for modification of the values pursuant to paragraph 6 and 7 shall be based on an assessment of the recorded values of the system frequency for a period of at least 1 year and the synchronous area development and it shall meet the following conditions:
(a) the proposed modification of the frequency quality defining parameters in Table 1 of Annex III or the frequency quality target parameter in Table 2 of Annex III takes into account:
(i) the system's size, based on the consumption and generation of the synchronous area and the inertia of the synchronous area;
(ii) the reference incident;
(iii) grid structure and/or network topology;
(iv) load and generation behaviour;
(v) the number and response of power generating modules with limited frequency sensitive mode — over frequency and limited frequency sensitive mode — under frequency as defined in Article 13(2) and Article 15(2)(c) of Regulation (EU) 2016/631;
(vi) the number and response of demand units operating with activated demand response system frequency control or demand response very fast active power control as defined in Articles 29 and 30 of Regulation (EU) 2016/1388; and
(vii) the technical capabilities of power generating modules and demand units;
(b) all TSOs of the synchronous area shall conduct a public consultation concerning the impact on stakeholders of the proposed modification of the frequency quality defining parameters in Table 1 of Annex III or the frequency quality target parameter in Table 2 of Annex III.
9. All TSOs shall endeavour to comply with the values for the frequency quality defining parameters or for the frequency quality target parameter. All TSOs shall verify the fulfilment of the frequency quality target parameter at least annually.
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Documentation |
Network Code on requirements for grid connection of generators (NC RfG), Article 2(22)
Network Code on System Operation, Article 3(2)(41), Article 127, Annex III
Network Code on Electricity Balancing
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Links |
