title: RfG Regulation (EU) 2016/631 - Requirements for Generators type: wiki primary_source: sources/legislation/eu-retained/eur-2016-631-rfg.md url: https://www.legislation.gov.uk/eur/2016/631 updated: 2026-04-10 tags: [generators, grid-connection, g98, g99, frt, neso, eu-retained]

RfG Regulation - Requirements for Generators

Commission Regulation (EU) 2016/631 is the network code establishing the technical requirements for connecting generating plant to the GB electricity grid. It is retained EU law, operative in GB since 17 May 2019 and amended at Brexit (31 December 2020) by S.I. 2020/1006.

In practice, generators do not deal directly with the Regulation. The operative instruments are ENA Engineering Recommendations G98 (small plant) and G99 (larger plant), which implement RfG requirements for day-to-day connection applications.

What it covers

RfG applies to all power-generating modules above 0.8 kW that are newly connected to the GB grid. Three technology classes are covered:

• Synchronous power-generating modules - conventional rotating plant (gas, coal, nuclear, large hydro) that maintains synchronism with network frequency
• Power park modules (PPMs) - non-synchronous or power-electronics-connected plant (wind, solar, batteries, small hydro via converter); the dominant category for new generation
• Offshore power park modules - PPMs located offshore, connected by AC cable (those using HVDC are outside RfG scope and fall under the HVDC Network Code)

Storage is excluded except for pump-storage, which must comply in both generating and pumping modes. Back-up generators operating less than 5 minutes per calendar month in parallel with the system are also excluded.

The Type A/B/C/D framework

RfG classifies generating units into four types based on size and connection voltage. Higher types face more demanding requirements.

The thresholds for Types B, C, D are proposed by NESO as TSO subject to Ofgem approval. GB thresholds are currently set at the Table 1 maxima (1/50/75 MW). Type A's 0.8 kW lower bound is fixed in the Regulation itself; it cannot be raised.

Requirements accumulate upward: a Type D generator must meet all Type A, B, C, and D requirements.

Technical requirements summary

Frequency ranges (all types, GB)

Every generator above 0.8 kW must withstand and remain connected across the GB frequency range. The operative table:

Frequency response

• LFSM-O (all types): Above 50.2-50.5 Hz, generators must reduce output in response to overfrequency. Droop 2-12%.
• LFSM-U (Type C+): Below 49.5-49.8 Hz, generators must increase output in response to underfrequency. Droop 2-12%.
• FSM - full frequency sensitive mode (Type C+): Continuous active response to frequency deviations. Full activation within 30 seconds, sustained for 15-30 minutes as specified by NESO. This is the requirement underpinning frequency response ancillary services.

Voltage ranges and fault ride-through (Type D)

Type D generators connected at or above 110 kV must: - Operate continuously at 0.90-1.10 pu voltage (synchronous) or 0.90-1.05 pu unlimited / 1.05-1.10 pu for 15 minutes (PPMs). - Ride through a three-phase fault lasting 0.14-0.25 seconds with voltage dropping to zero (Uret = 0 pu) without disconnecting, and recover to 85-90% of pre-fault voltage within 0.7-1.5 seconds (synchronous) or 1.5-3.0 seconds (PPMs).

FRT for Type B is also required (per Figure 3/Tables 3.1-3.2) but with less demanding parameters than Type D.

Reactive power

• Type C synchronous: must be capable of delivering/absorbing reactive power up to Q/Pmax = 0.95.
• Type C PPMs: up to Q/Pmax = 0.66.
• Offshore PPMs (single connection): no reactive power requirement (Q/Pmax = 0). Meshed offshore: up to Q/Pmax = 0.33.

How G98 and G99 implement RfG

RfG is the legal framework. G98 and G99 are the ENA Engineering Recommendations that translate it into connection process requirements.

G98 covers small generating units connected at single-phase or three-phase supplies below 16A per phase. Its core requirement is loss of mains (LoM) protection and disconnection behaviour. G98 units are Type A under RfG.

G99 covers all other generation. It was first issued in April 2019 to coincide with RfG's requirements application date. G99 incorporates RfG's technical tables, notification requirements (installation document, PGMD, FON/ION/EON/LON), and compliance testing obligations. DNOs apply G99 when assessing new connections. Disputes under G99 are referred to the relevant system operator and ultimately Ofgem.

The practical effect is that connection applicants receive a G99 offer from their DNO specifying compliance requirements derived from RfG. RfG itself is the legal basis if those requirements are challenged.

Type D and transmission-connected plant additionally must comply with NESO's Grid Code, which incorporates and elaborates RfG requirements for large generators. The Grid Code Connection Conditions (CC) are the primary reference for transmission-level connections.

Relationship to the Grid Code

The Grid Code applies RfG requirements for Type D and transmission-connected generating plant. It can impose requirements in addition to RfG's minimum standard, provided they are proportionate, non-discriminatory and approved by Ofgem under Article 7 of RfG.

Article 71 of RfG requires all connection contracts and industry codes (including the Grid Code, DCUSA, and BSC) to be updated to reflect RfG requirements. This is the legal mechanism by which RfG flows through to industry codes.

Brexit changes

Five Articles were omitted on 31 December 2020 (S.I. 2020/1006): Articles 11, 58, 59, 65, 68. These were EU coordination and monitoring provisions (ENTSO-E roles, ACER derogation monitoring, EU classification procedures). The substantive technical requirements were unchanged. GB-specific values were substituted into the Tables (frequency ranges, voltage ranges, FRT profiles). ACER was replaced throughout with 'the regulatory authority' (Ofgem).

The 2024 Energy Act consequential amendments updated the TSO definition to reference NESO's section 10H designation under the Electricity Act 1989.