# Commission Regulation (EU) 2017/1485 of 2 August 2017 establishing a guideline on electricity transmission system operation (Text with EEA relevance), Article 127: Frequency quality defining and target parameters

Extent: E+W+S+N.I.

1. The frequency quality defining parameters shall be:
(a) the nominal frequency ...;
(b) the standard frequency range ...;
(c) the maximum instantaneous frequency deviation ...;
(d) the maximum steady-state frequency deviation ...;
(e) the time to restore frequency ...;
(f) the time to recover frequency ...;
(g) the frequency restoration range ...;
(h) the frequency recovery range ...; and
(i) the alert state trigger time ....
2. The nominal frequency shall be 50 Hz ....
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 the GB synchronous area propose different values pursuant to paragraphs ... 7 and 8.
6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7. All TSOs of the GB synchronous area 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 ... 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.

---
Source: https://www.legislation.gov.uk/eur/2017/1485/article/127 (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-1485/article-127
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.