New Fault Ride Through compliance arrangements introduced for transmission-connected generators

Ofgem approved Workgroup Alternative Grid Code Modification 1 (WAGCM1) of GC0151 Grid Code Compliance with Fault Ride Through (FRT) Requirements on 5 November. In short, this decision introduces a new, legal process, into the Grid Code – the legal text that governs those connecting to the electricity transmission system – that will allow the Electricity System Operator (ESO) the right to require a user that is suspected of a FRT failure to restrict their output to an agreed level, which could be as low as 0MW.

Fault ride through (FRT) refers to the ability of generation units and High Voltage Direct Current systems to maintain operation during periods of low voltage caused by transmission system faults and disturbances. The Grid Code sets out that assets connected to the onshore transmission network, should remain stable and connected to the system without tripping during short circuit faults and voltage dips at voltage above 200kV (supergrid voltage).

The ESO first made industry aware of its concerns surrounding FRT compliance when it issued an open letter on 6 May 2021 outlining that certain assets had tripped during faults deemed “normal” and within system parameters. From the letter it was clear that the ESO considered that the inability of generation, interconnectors or other transmission-connected plant to ride through such faults was intolerable and a serious risk that should be managed quickly and effectively. On a more factual note, the ESO outlined that between 10 February and 18 April 2021 there were eight transmission faults where generation was unexpectedly lost, which in one case, was more than 1GW. The ESO said that it would consider raising modifications to provide clarity on non-compliances, but in the meantime set out an interim process to manage failures.

In response to the open letter, SSE Generation formally raised the modification GC0151 because it had concerns that the ESO’s interim process was potentially discriminatory, and could result in generators breaching legal requirements. The ESO’s interim process could have resulted in generators reducing their Maximum Export Limit to zero, which SSE considered would risk being deemed to have physically withheld generation capacity, potentially in breach of the EU Regulation on Wholesale Energy Market Integrity and Transparency (REMIT) market manipulation rules. Under SSE’s proposed solution, generators and networks company assets demonstrating fault ride through non-compliance would have initially faced no export limits or be constrained to 70% of Transmission Entry Capacity (TEC) or asset capability, depending on the situation. If after three months the issue was not resolved, this would be reduced to 50% until compliance was achieved.

An alternative developed by the workgroup (WAGCM1) effectively codified the process set out in the ESO’s open letter. This mirrored the interim process where a preliminary report would be required from those failing to comply with the FRT requirements within two hours of an incident, although there is a level of flexibility for longer timescales to be agreed. If those at fault find no evidence of FRT shortcomings in their part they can then self-certify for compliance with FRT prior to their reconnection or re-demonstrate compliance if there are issues found and corrected. Where FRT compliance issues are identified, WAGCM1 provides the ESO with the right to require a user that is suspected of a FRT failure to restrict their output to an agreed level, which could be as low as 0MW, albeit this is likely only to be in the most extreme cases.

The main differences between WAGCM1 and the original were the magnitude and duration of required export restrictions, and the timeframe in which a user is expected to provide an explanation of potential FRT non-compliances. Ofgem approved the alternative akin to the process outlined in the ESO’s open letter, considering that allowing the ESO and those who failed to comply with the FRT requirements to agree a level of output restrictions would mitigate the potential risks of FRT non-compliance. SSE’s proposal would have imposed an inflexible pre-determined export reduction on generators, however, Ofgem was concerned that where they choose to reconnect post-fault, it forces potential FRT risks to remain on the system operating at a level that may not sufficiently reduce the impact of the risk to the transmission system. In addition, while several workgroup members and consultation respondents considered the two hour timeframe proposed under WAGCM1 too short, Ofgem considered generators should respond as quickly as possible in order to return to normal service.

As mentioned before, SSE raised GC0151 to address concerns around commercial implications that could arise from the ESO’s interim solution, including whether reducing output to 0MW would be in breach of EU market transparency obligations. Ofgem noted that from an engineering perspective, it expects export restrictions applied at the request of the ESO as a result of GC0151 to be considered akin to a reduction in the capacity of that unit which was technically available, and thus would not comprise market manipulation.

GC0151 was implemented on 8 November. While the new process could have serious implications for those failing to comply with FRT requirements, material output reductions are likely to only be used as a last resort and in the interests of mitigating impacts on the wider transmission system. In its decision, Ofgem touched on the potential for further modifications with workgroup discussions highlighting a number of deficiencies in the current FRT requirements. The ESO is expected by Ofgem to take these issues into consideration in assessing Grid Code compliance and there is potential for changes to the FRT requirements to be progressed as a separate modification in the future if the industry deems it beneficial.

We will be keeping track of all future FRT changes through our bespoke weekly impact report for generators which sets out the current open energy consultations and industry code modifications you should be aware of. Such changes can impact the technical requirements for assets, costs and revenues, and how parties might trade or participate in balancing services or the balancing mechanism. An impact rating and explanation are provided for each change to help prioritise your resources and understand the effect on the business.

For more information on the Bespoke weekly impact report for generators please contact Tom Faulkner at or by calling 01603 542123.

You may also be interested…

Service | Bespoke weekly impact report

An update on the very latest regulatory and governance changes that are relevant to your business. Tailored to meet the needs of your organisation, you can rest assured that you will receive the latest regulation developments to ensure you are compliant with all your obligations.

Service | Alerts services (electricity or gas)

An overview of industry developments that you and your business should be aware of. You can subscribe to either gas, electricity or both ‘Alert services’. Each alert provides you with a timely update of any changes to regulation, policy, consultations or proposals.

Related thinking

Home supply and services

Reforming Energy Bills: What’s on the Table?

There has been much speculation in the energy industry over what reforms to household energy bills could potentially be introduced, particularly with Ofgem due to announce its Q3 (July – September) 2024 Default Tariff Cap figures on Friday (24th). With so many areas under review, we’ve put together an overview...

Energy storage and flexibility

Revenue Stacking for Flexibility: A Deep Dive into GB Electricity Flexibility Services 

In the ever-evolving landscape of the energy sector, the role of flexibility services in ensuring a stable and resilient electricity grid has become increasingly vital. As the demand for renewable energy sources continues to grow, flexibility service providers play a crucial role in balancing supply and demand, optimising grid performance,...

Low carbon generation

Latest developments in the TPI space

We recently published our 2023 Annual TPI report which provides an independent review and analysis of the market for TPIs, and the services provided by them. The report also looks at the current challenges and opportunities for TPIs, such as regulatory changes, competition with suppliers, and diversification of services. 2023...

Regulation and policy

What’s going on with REGOs?

Renewable Energy Guarantees of Origin, more commonly referred to as REGOs, are certificates issued to accredited renewable generators for every MWh of electricity they produce over a year period. The initial intentions of these certificates were to provide suppliers a means to prove the level of renewable generation they received...

Home supply and services

Ofgem strives to improve consumer experiences across both the domestic and non-domestic sectors

Over the last week, a number of anticipated publications were issued by Ofgem that hold the potential to make a significant change to the requirements on both domestic and non-domestic suppliers. The findings of Ofgem’s non-domestic market review were revealed, alongside a policy consultation on the options available to address...

Energy storage and flexibility

Waiting to connect: the problems and solutions for network connection queues (Part 2)

Network connection queues continue to be a notable topic of interest as many generators face significant delays to project development – an issue that is directly conflicting with net zero ambitions and recent focuses on strengthening domestic energy supplies. In Part 1 of our two-part series on connection queues we...

Home supply and services

Addressing consumer harms in the non-domestic market

In recent months, Ofgem has shone a light on areas across both the domestic and non-domestic market where suppliers could improve their practices for customers and go beyond what they are obligated to do in the licence conditions. In a time of significant and extended volatility, the regulator has brought...

Energy storage and flexibility

Waiting to connect: the problems and solutions for network connection queues

The number of grid applications has risen significantly in recent years, resulting in increased pressure on the electricity networks to facilitate new connections. In its Energy Security Strategy, the UK government set out ambitions for 95% of electricity to be sourced from low carbon generation by 2030, and for the...