Reactive Power

The requirement for reactive power is primarily driven by the interaction of real power flows on the transmission system with the complex impedances of the various elements that make up the network together with the demand at the lower voltage system interfaces. National Grid is required to maintain the real and reactive power balances between sources of generation and points of demand. Unlike system frequency, which is consistent across the network, voltages experienced at points across the system form a 'voltage profile', which is uniquely related to the prevailing real and reactive power supply and demand. Without the appropriate injections of reactive power at correct locations, the voltage profile of the transmission system will exceed statutory planning and operational limits. Further details are in the Introduction to Reactive document below.

Frequency Response

System frequency is a continuously changing variable that is determined and controlled by the balance between system demand and total generation. If demand is greater than generation, the frequency falls while if generation is greater than demand, the frequency rises. National Grid has a statutory obligation to maintain system frequency within 1% of 50Hz.

Further details are in the Introduction to Frequency Response document below, additionally prices and requirement curves are available.

CUSC Amendment CAP46 introduced Power Delivery Data Tables which contain data used to estimate the volume of response delivered when providing the mandatory service of Frequency Response. Some technical information on PDDT's is available which may assist providers if any revisions to their default PDDT's are required. A template for submitting requested revisions to PDDT's is also available. Further information on CAP46 can be found in the CUSC Amendments Area.