Technical Brochure 556 - Power system technical performance issues related to the application of long HVAC cables

This Technical Brochure describes system technical performance study issues important for a power system with (a large share of) long AC cable lines. The study areas are divided into planning studies, system impact studies and equipment design studies. The brochure contains examples and explanations of system technical performance phenomena occurring as a result of various system operations, guidelines for simulation methods, interpretation of the results and possible suggested countermeasures. As some of the presented examples produce overvoltages of significant duration and / or amplitude, consideration is given to the adequacy of cable tests recommended by IEC. The focus of this Technical Brochure is system technical performance issues and modelling of cables and other equipment is not its main topic. Nevertheless, in order to retain the ability to stand on its own, relevant recommendations concerning modelling of cables and other pieces of equipment as well as the required extent of network equivalents are given. Guidelines and recommendations for adequate modelling of AC cable lines for different types of power frequency studies and for studying phenomena that involve other frequencies are presented. Practical methods for gaining confidence in the accuracy of cable line models are described. Calculations of power frequency impedances based on published norms are shown. Available models for transient studies are identified and their selection for various studies is discussed including the required level of detail, accuracy and other implementation details. Sensitivity of study results due to variation of cable input parameters is analysed. Line constant solver results are benchmarked against manual calculations. Also a transient cable model validation procedure is shown. Derivation of basic computer cable line models, setups for measurement of cable impedances and results of real-life measurements performed on 100 km long AC cable of an offshore wind farm are also presented.