National Grid Company
NGC has a statutory duty under the Electricity Act 1989 to develop and maintain an efficient, co-ordinated and economical Transmission System for the supply of electricity. One of NGC’s statutory obligations is the requirement to maintain system frequency within the range 49.5Hz - 50.5Hz. This is achieved through the management of changing generation and/or demand. These services are automatic and can be required at any time to contain frequency deviations and recover it back to normal. To date these services have been provided by Generators, obliged to have a frequency control capability by virtue of their Grid Code connection conditions, and large industrial electricity consumers capable of interrupting firm loads for a required time. Given the limited number of production processes able to offer a firm interruptible load, NGC has been developing a frequency response service through the aggregation of fluctuating electrical loads. By combining a large number of cyclic demands, a relatively firm level of response can be derived and delivered when required.