Offshore wind export circuit switching transient stresses and mitigations

Offshore wind farms are connected to the power grid through export paths that typically consist of high-voltage submarine cables of significant length. Since cables are predominantly capacitive, export paths often require reactive compensation to offset voltage rise (i.e., Ferranti effect) at the offshore remote termination. Additionally, power factor requirements at the point of interconnection (POI) may require reactive compensation at the onshore termination. As such, shunt reactors are typically installed at each end of the cables as permanent components (i.e., no switching device) to compensate the predominantly capacitive circuit. Circuit breakers at the onshore substation used to switch the compensated cable circuits may be exposed to transient stresses and delayed current zeros (DCZ) of potential concern. Excessive arcing times from DCZs have been observed to deteriorate interruption capability, which may lead to equipment damage, failure, or other system related concerns. This paper presents case studies demonstrating circuit breaker switching mitigation strategies for reactive compensated export cables including controlled switching and pre-insertion resistance. The goal of this paper is to demonstrate and discuss trade-offs between switching mitigation strategies with respect to equipment health and system impacts.