Delivery of a Robust a Frequency Response Service from Wind Farms for the Great Britain Transmission System

Abstract

Frequency stability refers to the ability of a synchronous a.c. power system to remain in operation following an imbalance between generation and load [1]. With excess generation the frequency will increase, and conversely, with a deficit of generation the frequency will fall. When either happens either all or a selection of plant must increase or decrease output automatically and rapidly to make up for the short fall or excess in power. This ancillary service is known as frequency response. Failure to do this correctly could result in system frequency exceeding permitted limits and automatic disconnection of customers, or in the worst case, system blackout. As the volume of wind turbine generation continues to increase exponentially, particularly in wind rich island countries such as Great Britain and Ireland, there comes a point where the synchronous generation must operate at reduced output or even be disconnected. Services which were once provided by this displaced synchronous generation must logically be taken up by other plant, with the obvious target being the replacement wind generation [2, 3]. Frequency response is one of these key services, particularly in smaller island networks with highly variable system frequency. Wind plant is ideally placed during windy days to provide a high frequency response service (reducing in output when frequency is high), with the remaining connected synchronous generation operating at low load to provide the required low frequency response. However, there are several factors which must be considered before wind plant can provide a robust, reliable and repeatable service to help in maintaining frequency stability in a grid. The major factors are discussed in this paper, together with presentation of a technique for providing frequency response from wind plant. This technique has been adopted by several wind turbine manufacturers, and has been, or is in the process of being implemented in a number of onshore and offshore wind farms in Great Britain.