# Commission Regulation (EU) 2017/1485 of 2 August 2017 establishing a guideline on electricity transmission system operation (Text with EEA relevance), Article 131: Frequency quality evaluation criteria

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

1. The frequency quality evaluation criteria shall comprise:
(a) for the synchronous area during operation in normal state or alert state as determined by Article 18(1) and (2), on a monthly basis, for the instantaneous frequency data:
(i)the mean value;
(ii)the standard deviation;
(iii)the 1-,5-,10-, 90-,95- and 99-percentile;
(iv)the total time in which the absolute value of the instantaneous frequency deviation was larger than the standard frequency deviation, distinguishing between negative and positive instantaneous frequency deviations;
(v)the total time in which the absolute value of the instantaneous frequency deviation was larger than the maximum instantaneous frequency deviation, distinguishing between negative and positive instantaneous frequency deviations;
(vi)the number of events in which the absolute value of the instantaneous frequency deviation of the synchronous area exceeded 200 % of the standard frequency deviation and the instantaneous frequency deviation was not returned to ... the frequency restoration range for the GB synchronous area, within the time to restore frequency. The data shall distinguish between negative and positive frequency deviations;
(vii)for the GB synchronous area the number of events for which the absolute value of the instantaneous frequency deviation was outside of the frequency recovery range and was not returned to the frequency recovery range within the time to recover frequency, distinguishing between negative and positive frequency deviations;
(b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(c) for the LFC blocks of the GB ... synchronous area, during operation in normal state or alert state in accordance with Article 18(1) and (2), on a monthly basis and for a data-set containing the average values of the FRCE of the LFC block over time intervals with a length of one minute: the number of events for which the absolute value of the FRCE exceeded the maximum steady-state frequency deviation and the FRCE was not returned to 10 % of the maximum steady-state frequency deviation within the time to restore frequency, distinguishing between negative and positive FRCE.
2. All TSOs of the GB synchronous area shall specify in the synchronous area operational agreement a common methodology to assess the risk and the evolution of the risk of exhaustion of FCR in the synchronous area. That methodology shall be performed at least annually and shall be based at least on historical instantaneous system frequency data for not less than 1 year. All TSOs of the GB synchronous area shall provide the required input data for this assessment.

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Source: https://www.legislation.gov.uk/eur/2017/1485/article/131 (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-1485/article-131
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.