Design of generation runback scheme for a HVDC-connected wind farm

HVDC systems based on voltage sourced converters are more and more widely used to connect remote generation (especially offshore wind farms) to power grids across the world. These are typically systems with ratings of around 1GW or more. When connecting these systems to networks with voltages lower than extra high-voltage, the current at the point of connection can be so large that it triggers the need to split the power over multiple circuits, especially when using cables for the connection to the network. When one or more such circuits are lost, it is crucial to provide overload protection in case the power production is above the rating of the remaining circuit(s). This can be done via runback schemes that reduce power transmission when a relevant outage occurs. This paper describes the design and implementation of one such runback scheme for a HVDC-connected offshore wind farm currently being constructed. The scheme aims at reducing power efficiently, avoiding unnecessary trips and minimizing loss of production, but at the same time providing the necessary levels of backup and redundancy to ensure the scheme is robust and reliable.