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.

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.