Transmission Constraint Agreement

Who can participate?

  Generation Demand
BMU yes yes
Non-BMU yes yes

Service Description

A 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.

Why is it needed?

National Grid is responsible for ensuring the system remains within safe operating limits and that the pattern of generation and demand is consistent with any system transmission related constraints (for example due to a planned outage of a circuit). 

Whilst National Grid will endeavour to place outages coincident with relevant generation outages in order to minimise constraint costs it may be necessary to take actions (by entering into a Transmission Constraint Agreement, trading or taking actions in Balancing Mechanism with generators, suppliers and large customers) to resolve constraints on the transmission system.

Major Technical Requirements

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 Transmission Constraint Agreement

Procurement Process

Where sufficient competition exists, National Grid will seek to contract via some form of market mechanism. In other circumstances, bilateral contracts will be entered into with the service providers.


Payment Structure will be defined when the contact is entered into.

BSAD: Not applicable.

ABSVD: Not applicable.

Summary of Further Information

Balancing Principles Statement Part D