Protection of Export Cables Connecting Off-shore Wind Farms to the Grid using Model-based State Estimation

Enabled by advancements in large turbine technologies, these installations deliver higher efficiency while minimizing environmental impact. A critical challenge in this domain is the protection of long subsea export cables to prevent irreversible damage during fault conditions.

The distinctive fault behavior of wind farm converters marked by limited and non-uniform fault current contribution compared to the grid renders conventional overcurrent and distance protection schemes inadequate.

Export cables typically consist of multiple sections with varying geometries and configurations, further amplifying network non-homogeneity. Line differential protection faces difficulties in compensating for charging currents that differ across cable sections, while the presence of variable shunt reactors can lead to unintended differential operations if not properly accounted for. Existing improvement strategies primarily address individual limitations of traditional schemes and may serve as good retrofitting solutions for current installations.

This paper explores an alternative approach based on a state-estimation framework that integrates cable models with real-time measurements to detect faults. By leveraging information collectively across the cable network, this methodology enables a comprehensive protection scheme using model-based state estimation (MBSE) scheme. The feasibility of

MBSE is supported by advancements in substation automation, including cost-effective highperformance computing platforms, centralized high-frame-rate time-synchronized measurements via process bus, reliable standards-based communication, and non-intrusive sensor technologies. Compared to conventional protection principles, MBSE offers the potential to eliminate the need for multiple complementary relays and their coordination, thereby reducing the overall footprint of protection and control systems on offshore platforms.