Offshore wind farms are connected to the power grid onshore through power trains commonly known as export paths. The export paths consist of long, typically high voltage submarine cables. These cables are predominantly capacitive in nature as a result of their insulation characteristics. It is common practice to offset the Ferranti effect caused by the cable capacitance by adding shunt reactors at their offshore remote termination ends. Power factor requirements at the onshore Point of Interconnection (POI) can warrant the addition of onshore shunt reactors. The electrical characteristics of the export path such as series impedance and shunt capacitance; thermal ratings of the path; and power factor requirements all play a significant role in the selection of the shunt reactor sizing and location. These shunt reactors are typically permanently connected to the cables as a result of the physical configuration of offshore export path. The export path and hence the submarine cables and reactors are operated through circuit breakers at the onshore substation.

Generally, the breakers operate to energize or de-energize the export path, in this case, a predominantly capacitive circuit with permanently connected shunt reactors. As has been studied in previous literature, this condition can lead to concerns regarding resonance conditions and circuit breaker operating constraints such as switching transient propagation and successful current interruption. These concerns have been observed to deteriorate breaker health, impact insulation coordination, and pose operational risks including fault clear.

This paper includes case studies demonstrating circuit breaker operation strategies to mitigate these concerns such as independent-pole operation, synchronous controlled or targeted switching and pre-insertion resistor inclusion. The paper compares the results to discuss the trade-offs between the strategies on both the power system operation as well as substation equipment operation, including compliance with IEEE standards of device withstand capabilities. The paper also studies other onshore circuit breaker operating concerns such as the impacts of back-to-back energization of multiple parallel unloaded offshore export paths. The paper discusses the modeling techniques and common assumptions in electromagnetic transient domain ranging from ideal device models to realistic model representation and studies their impact on the observed simulation results.

Furthermore, this paper discusses other mitigation strategies and alternate solutions to existing design and operation practices for such export paths.