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.

Static Reactive Power - Mersey 2022 - 2031

Note: Please direct all queries and tender submissions to [email protected]

We have launched a long term tender for a Reactive Power service to meet a static need in the Mersey region. The 9-year contract, starting 1 April 2022, is part of a new approach to procuring reactive power to determine whether a third party can deliver a more economic solution compared to the network asset alternative. This tender is open to potential providers embedded within the Distribution network as well as at Transmission level, including those that are not yet connected.

Stability Pathfinder Phase One - GB 2020

The tender closed on 17 January 2020 and results expected by 31 January 2020. This multi-year contract, starting between 1st April 2020 and 1st April 2021, is our first tender for this type of service. This approach has been developed following the stability request for information, part of our network development roadmap. Phase two will follow next year looking to include a broader range of technology solutions to provide stability solutions.

Reactive Power - Mersey 2020/21

A tender has been launched for a Reactive Power service to meet a static need in the Mersey region. The 1-year contract, starting 1st April 2020, is part of a new approach to procuring reactive power including potential new providers. This tender enables embedded assets, for the first time, to participate in a tender to solve a transmission voltage system need.

Accelerated Loss of Mains Change Programme - Update


The Accelerated Loss of Mains Change Programme (ALoMCP) is an industry led project delivered by National Grid ESO, Distribution Network Operators, and Independent Distribution Network Operators on behalf of the Distribution Code Review Panel. The project aims to accelerate compliance with new requirements in the Distribution Code and will be funded by Balancing Services Use of System (BSUoS) charges. 

The purpose of the initiative is to bring Loss of Main (LoM) protection devices and their settings in line with EREC G59 standards. 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 Rate of Change of Frequency (RoCoF) limits. This will ultimately increase the security of the system and reduce balancing costs.

It is 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, comply with new setting requirements for the interface protection in accordance with EREC G59.  Owners of generation sites must comply with the Distribution Code and have until September 2022 to comply with these modified interface protection requirements.  After that date owners who have not made the necessary changes may be subject to an enforcement programme.

Update 1st October 2019:

Eligible owners are invited to apply for funding from programme launch on Wednesday 2nd October 2019. Owners need to register their interest via an Application Portal on the Electricity Network Association’s (ENA) website. Funds are limited, so owners are encouraged to register and apply for funding as soon as possible. To ensure balancing spend is economic, funding will be prioritised and awarded based on a set of criteria described in National Grid ESO’s procurement methodology available below.

Further details concerning the programme including access to the Application Portal are available on the ENA’s website. Any queries regarding applying or the programme overall should in the first instance be raised with owner’s respective DNO/IDNO, details of which can be found here.

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.