Application of differential protection to offshore wind farm for earth fault detection with substantially unbalanced charging current

Abstract

Introduction of renewable resources into the power system has raised significant challenges to the protection system. Conventional ways of working are deemed insufficient and need to be improved. This study will focus on one subject that has often been overlooked – unbalanced charging current. The application of long high voltage submarine cables to connect a large number of wind turbines to offshore substation has resulted in the considerable unbalanced charging current flowing into the system during earth fault. This study will present a real‐life application of differential protection to an offshore wind farm network. It will primarily discuss how the existence of unbalanced charging current affects the sensitivity of the differential protection relays. This discussion is further substantiated with actual fault measurements taken from one of Siemens built offshore wind farms. This study will subsequently recommend ways to improve the sensitivity of differential protection based on Siemens’ experience. As more and larger wind farms are built, this study serves a very valuable experience for offshore wind farm protection.