Looking for more information about the 9 August power cut?

See our interim technical report and other ESO resources.

Transmission constraint management

Constraint management is required where the electricity transmission system is unable to transmit power to the location of demand, due to congestion at one or more parts of the transmission network. Here you can find out how to provide this service.

Accelerated Loss of Mains Change Programme

Accelerated Loss of Mains Change Programme is an industry led project delivered by National Grid ESO, Distribution Network Operators, and Independent Distribution Network Operators. The projects aims to accelerate compliance with new requirements in the Distribution Code and will be funded by balancing services use of systems charge. 

National Grid ESO and GB Distribution Network Operators (DNOs) / Independent Distribution Network Operators (IDNO) are undertaking electricity transmission and distribution industry led initiative managed on behalf of the Distribution Code Review Panel.

The purpose of the initiative is to consider Loss of Main (LoM) protection and their settings. The aim being to reduce the risk of inadvertent tripping and reduce system balancing issues by giving National Grid ESO greater latitude with regards to system RoCoF limits.

Pending approval by Ofgem, it will be a requirement of the Distribution Code that all owners of generation installed prior to February 2018, and where the generation equipment is not type-tested, to comply with new setting requirements for the interface protection in accordance with EREC G59.  Owners of generation will have to comply with the Distribution Code and have until May 2022 to comply with these modified interface protection requirements.  After that date owners who have not made the change will be the subject of an enforcement programme.

A Request for Feedback outlining how National Grid Electricity System Operator (NGESO) and network operators (including both Distribution Network Operators and Independent Distribution Network Operators) propose to accelerate loss of mains protection changes required by the Distribution Code has just been published on the Energy Network Association website.

We are sharing this draft document and requesting feedback ahead of final publication to ensure that the industry has an opportunity to comment on our approach and highlight potential areas for improvement.

The Request for Feedback is available online at:


Please provide your feedback by Friday 10 May 2019

Feedback and any questions should be submitted via email to [email protected]

Scotland Enhanced Reactive 2019

A tender has been launched for Enhanced Reactive Service in Scotland. The tender is to allow the Electricity System Operator to access reactive power capability beyond Grid Code Obligations. In this tender the focus is on reactive capability available when active power output is less than 20% of the rated active power output of the unit. 

South Wales and Mersey 2019/2020

Request for Information

3rd October 2018 - We have published a Request for Information for the provision of Reactive Power Service in both South Wales and Mersey areas. The Request for Information forms part of our commitment in the Product Roadmap for Reactive Power. Interested reactive power providers are requested to submit information with an outline of their capability by the 5th November as detailed in the Request for Information. Please use the South Wales Proforma or Mersey Proforma in response to the RFI. 

Next steps update

4th December 2018 - The next steps for Request for Information for the provision of Reactive Power Service in South Wales and Mersey are published. Thank you to all providers who responded to the RFI, the information provided helped to shape the next steps of the RFI. The next steps can be found here for South Wales and Mersey


Following the publication of the Request for Information for the provision of reactive power services published on the website on the 3rd October 2018 and the update published on the 4th December 2018, please see below information regarding the next steps for the tenders in South Wales and Mersey

For Information: Vector Shift - Loss of Mains Protection change

FAO: Distributed Generators: Loss of Mains Protection change, away from Vector Shift (VS)

In order to preserve the stability of the electricity system, loss of mains (LoM) protection settings on a limited volume of existing generators fitted with Vector Shift (“VS”) type protection must be changed immediately in targeted locations across the south of England.

In order to encourage your support, the transmission system operator (TSO) and distribution network operators (DNOs) have agreed to a compensation proposal outlined in the open letters on this page, subject to generating units meeting the relevant criteria.

  • Is your site located in the SSE, UKPN or WPD DNO areas?
  • Is your distributed generation scheme sized at >1MW?
  • Is your protection afforded by a discrete G59 relay which utilises Vector Shift as its loss of mains protection?

Context and additional information is outlined in the open letters below.


181 submissions were submitted to the DNOs and assessed by us. These sites accounted for over 1.3GW of Vector Shift capacity. All applications were ranked by their effectiveness at reducing the Vector Shift capacity at risk of trip, accounting for the cost, location, capacity and load factor during risk periods of each.

Two applications with incomplete information were excluded from the assessment.

Submissions from 71 sites, with a combined capacity of 811MW, met the assessment criteria and fulfilled our requirement at least cost to the consumer.