Transmission constraint management on the National Grid system and the effect upon the commercial market place

This paper explains the major types of transmission constraints which exist on the National Grid transmission system of England and Wales. The three categories of constraints which are considered are thermal, voltage and stability. The paper considers transmission constraints from an economic viewpoint. In accordance with it´s Transmission Licence, National Grid Company (NGC) despatches generation in strict adherence to the merit order, taking due account of the prevailing transmission constraints. The way in which the costs associated with constraints are dealt with in The Electricity Pool of England and Wales is also discussed