title: "ER Regulation (Emergency and Restoration) 2017/2196" type: wiki updated: 2026-04-11 tags: [emergency, restoration, black-start, neso, system-states, sogl] primary-source: ../sources/legislation/eu-retained/eur-2017-2196-er.md
ER Regulation - Emergency and Restoration Network Code
Full reference: Commission Regulation (EU) 2017/2196 of 24 November 2017 Status in GB: LIVE. Retained under the EU (Withdrawal) Act 2018. Amended by S.I. 2019/533 and S.I. 2020/1016, effective 31 December 2020. TSO in GB: NESO (National Energy System Operator) Canonical source: eur-2017-2196-er.md
What it is
ER is the GB rulebook for electricity system emergencies. It establishes what NESO and other electricity system parties must do when the system moves from normal operation into emergency, blackout, or restoration states.
It does not stand alone. ER is built on top of SOGL 2017/1485, which defines the five system states. SOGL tells you when a state has been reached; ER tells you what to do about it.
Two core deliverables:
- System Defence Plan (SDP): automatic and manual procedures that activate when the system enters emergency state, aimed at preventing a blackout.
- Restoration Plan (RP): procedures that activate after the system has either stabilised from emergency or suffered a blackout, aimed at restoring supply to normal state.
Both plans were required by 18 December 2018 (design and regulatory notification) and 18 December 2019 (implementation on the transmission system).
The five system states and ER obligations
The five states are defined in SOGL Art 18. ER maps obligations onto them.
| State | Description | Key ER obligation |
|---|---|---|
| Normal | All parameters within limits | No ER obligation; SOGL applies |
| Alert | Frequency or voltage approaching limits but system intact | Frequency deviation procedure (Art 18); frequency leader appointment if frequency exceeds alert limits (Art 29) |
| Emergency | Active constraint violation; system at risk | SDP activation (Art 13); RP activation once stabilised; market suspension possible |
| Blackout | Widespread loss of supply | RP activation (Art 25); market suspension |
| Restoration | Re-energisation underway following blackout or post-SDP stabilisation | Full RP: re-energisation, frequency management, resynchronisation |
System Defence Plan
The SDP contains three automatic protection schemes and five manual procedures.
Automatic schemes: - Under-frequency: automatic low frequency demand disconnection (ALFDD), with parameters set by the GB Annex - Over-frequency: automatic generation reduction (LFSM-O or stepwise shedding) - Anti-voltage collapse: low-voltage demand disconnection or OLTC blocking
Manual procedures: - Frequency deviation: NESO sets active power set-points for generators - Voltage deviation: NESO instructs reactive power/voltage range maintenance - Power flow management: NESO sets active power set-points and may disconnect units - Assistance for active power: NESO requests inter-TSO or BSP support before suspending markets - Manual demand disconnection: NESO instructs DSOs to disconnect specified amounts of load
DSOs, SGUs, and defence service providers must implement SDP measures within 12 months of notification and must execute instructions without undue delay during activation.
Restoration Plan
The RP covers three procedural areas.
Re-energisation (Arts 26-27): The plan must include both top-down and bottom-up strategies. Bottom-up (black start without external assistance) is the primary GB approach given GB's island status post-Brexit. NESO selects the strategy and instructs DSOs on demand reconnection.
Frequency management (Arts 28-31): A frequency leader is appointed among TSOs sharing a synchronised region (highest K-factor rule). The frequency leader takes sole control of FRR/RR activation; other TSOs suspend manual frequency response. If the synchronous area has split, the frequency leader targets the resynchronisation leader's frequency.
Resynchronisation (Arts 32-34): A resynchronisation leader is appointed by the frequency leaders. The leader selects the resynchronisation point (usually a circuit breaker), sets target frequencies, and executes when conditions are met.
Black start in GB
Black start is the ability to restore supply to a section of the grid without drawing power from the wider network. It is the foundation of the bottom-up re-energisation strategy.
Under Art 23(4), NESO's Restoration Plan must identify the number and location of black-start-capable and island-operation-capable power sources. In practice:
- NESO runs competitive procurement tenders for black start services (typically every 3-4 years)
- Selected providers become restoration service providers and are contractually bound to maintain capability
- Black start capability tests are required at least every 3 years (Art 44(1); also Art 46 for HVDC systems)
- NESO's test plan (approved by Ofgem under Art 4(2)(g)) governs the testing schedule
Black start providers in GB have historically included gas-fired plant (open and combined cycle), pumped storage (Dinorwig), and battery storage. The NESO tender specifies geographic distribution requirements to ensure the network can be rebuilt in sections.
ALFDD parameters (GB Annex)
The automatic low frequency demand disconnection scheme disconnects blocks of demand as frequency falls, giving time for generation to recover. The GB parameters from the Annex are:
| Parameter | Value |
|---|---|
| Starting frequency | 48.8 Hz (5% of national load disconnected) |
| Final mandatory level | 48.0 Hz (50% of national load disconnected, cumulative) |
| Range at each step | +/- 10% of national load |
| Minimum steps | 4 |
| Maximum per step | 10% of national load |
Normal GB system frequency is 50 Hz. The scheme engages well below the normal operating range (49.5-50.5 Hz). At 48.8 Hz the grid is in a serious degraded state; at 48.0 Hz, without intervention, collapse is likely. The scheme provides a structured load shedding ladder that buys time for generation to stabilise frequency.
LFDD relays installed in DSO networks carry out the disconnection automatically. DSOs must test these relays at nationally defined intervals (Art 47) and report settings and disconnected percentages to NESO annually (Art 50(1)).
Communication protocols and backup power
ER imposes prescriptive resilience requirements for emergency communications and control room operations.
Voice communication (Art 41): - NESO, identified DSOs and SGUs, and restoration service providers must maintain voice communication systems with 24-hour backup power - NESO must establish interoperability requirements with DSOs/SGUs and with neighbouring TSOs (including Northern Ireland/SONI) - Annual test required
Backup power supply for communications (Art 48(2)): - Full backup power supply test every 5 years
Control rooms (Art 42): - NESO must maintain a geographically separate backup control room with 24-hour backup power - Switchover from main to backup control room must be achievable within 3 hours - Both main and backup power sources tested annually (Art 49(1)) - Transfer procedure tested annually (Art 49(4)) - Critical tools and facilities tested every 3 years (Art 49(2))
Essential substations (Art 42(5)): - Must remain operational for 24 hours without primary power supply - Backup power tested every 5 years
Review cycles
| Obligation | Party | Frequency |
|---|---|---|
| SDP review | NESO | Every 5 years; before substantial grid changes |
| RP review (computer simulation) | NESO | Every 5 years; before substantial grid changes |
| Black start capability test | Restoration service provider | Every 3 years |
| Communication systems test | NESO, DSOs, SGUs, restoration SPs | Every year |
| Backup power for communications | NESO, DSOs, SGUs, restoration SPs | Every 5 years |
| Essential substation backup power | NESO, DSOs | Every 5 years |
| ALFDD settings update to NESO | DSO | Every year |
Brexit omissions
GB retained ER in full except for provisions requiring coordination with EU institutions (ENTSO-E, RSCs, ACER) or with third-country TSOs. The omitted Articles are: 6 (regional coordination), 10 (third-country TSO agreements), 13(4) (RSC coordination during SDP), 25(4) (RSC notification during RP), 36(7)-(8) (EU coordination on market suspension rules), 37(3)-(5) (multi-TSO EU coordination for market restoration), and 52 (ACER monitoring). The core SDP, RP, ALFDD, and testing framework is fully retained and operative.
Related instruments
- SOGL 2017/1485: defines the five system states that trigger ER obligations
- RfG 2016/631: sets generating module type classifications and black start / houseload test methodologies
- DCC 2016/1388: sets OLTC blocking, low-voltage demand disconnection, and ALFDD relay test methodologies
- HVDC NC 2016/1447: covers DC-connected systems in ER context (black start tests, active power control)
- Grid Code: incorporates ER obligations into NESO's licence conditions