A study of switching overvoltages in offshore wind farm

Switching transient as one of the main transient phenomena in power systems have been simulated and measured in many studies. Since offshore wind farms have been integrated to power system only in recent years, the consequences of switching phenomena in offshore wind farms have not yet been thoroughly analyzed. This paper contributes to the topic by a study on overvoltages using a high-frequency model of the wind turbine transformers (WTTs). The WTTs are represented by a black-box high-frequency model obtained from measurements and represented by an equivalent RLC network for inclusion in ATPEMTP. The model represents a 300 kVA 11.0/0.230 kV transformer. The resonance frequencies observed at the Low Voltage (LV) and High Voltage (HV) terminals of the transformer are found by voltage ratio and impedance matrix simulations using the derived high frequency transformer model. The simulation results indicate that the dominant resonance frequency of this transformer in terms of voltage ratio from the HV side to the LV side appears at 2 MHz. In energization of a wind turbine, the critical cable length leading to transformer resonance overvoltages and the impact of surge arresters on LV and HV are investigated. The simulation results indicate that the LV surge arrester have prominent role in limiting the resonance overvoltages although the ground lead inductances some how decrease the effect of surge arresters.