Model based Protection for Export Cables Connecting Off-shore Wind Farms to the Grid

Long export cables help in transfer of the electricity generated from offshore wind farms. Installation and maintenance of such cables are expensive. Reliable protection system which safeguards them during faults is essential. Limited fault currents, unique and non-homogeneous fault response from the wind farm converters, multiple inhomogeneous cable sections, etc. may render traditional protection principles such as distance and differential inadequate. This paper explores the application of an alternate principle, namely model based protection (MBP). It uses the model and measurements related to the export cable in a state estimation framework to detect faults. In addition to detection of faults, MBP can also help identify faulted phases and/or faulted cable section which can be beneficial for other fault management applications. MBP is comprehensive and can potentially minimize the need for complementary protection relays, thereby reducing the overall footprint of protection and control system in offshore platforms. Case studies are done using PSCAD/EMTDC simulations of a typical 220 kV, 160 km long export cable network connecting an offshore wind farm to the main grid.