A transmission constraint arises where the system is unable to transmit the power supplied to the location of demand due to congestion at one or more parts of the transmission network. In the event that the system is unable to flow electricity in the way required, National Grid will take actions in the market to increase and decrease the amount of electricity at different locations on the network.

The exact way in which a constraint is managed depends on a number of factors including the nature of the flows on the transmission system, the duration of the requirement, the local level of generation output, and the local level of system demand. Therefore the technical requirements will be specific to the location of the constraint and defined in the Commercial Services Agreement.

For more detailed information on Transmission Constraint Agreement principles please view the information in our Balancing Services Contracts Information Pack.

The Constraint Management Service (CMS) is designed to manage price risk during constraints. In exchange for an availability payment, energy prices are required to be within set limits. The CMS is targeted at sites within constrained zones, as this is where the cost risk for the System Operator lies. 

The CMS caters for both import and export constraints and can be provided by generation and demand sites. The service is procured via tender. Details of the tender process can be found below.

The sixth CMS Invitation to Tender was published on Thursday 18^th September August 2008.

Please contact your Account Manager or Ian Pashley of our Contracts & Settlements team (+44 (0)1926 653446, ian.pashley@uk.ngrid.com) at your earliest convenience to discuss the potential to provide this service.