GC0028: Constant Terminal Voltage

Under CC.6.3.4 of the Grid Code, Generating Units, Power Park Modules, DC Converters and OTSDUW Plant and Apparatus are required to be capable of providing their full reactive capability within the voltage range of ±5% at 400kV, 275kV and 132kV and lower voltages. In addition, CC.6.3.8(a)(i), of the Grid Code requires Generating Units to be installed with a continuously acting automatic excitation control system to provide constant terminal voltage control of the Generating Unit without instability over the entire operating range. A number of Generators have expressed concern over National Grid’s interpretation of these requirements relating to operation at constant terminal voltage and sought further clarification.