Modeling of high frequency transients of vacuum circuit breaker switching transformers in offshore wind parks

Switching transient as one of the main transient phenomena in power systems has 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. In this paper, the high frequency transient over-voltages of vacuum circuit breaker switching transformers in collection grid of offshore wind parks are studied. Based on the reflection and refraction of traveling waves and vacuum circuit breaker characteristics, the Vacuum circuit breaker has been modeled in PSCAD/EMTDC, which simulates the occurrence of current chopping, re-ignition and pre-strike that will cause high frequency, steep fronted transient voltages and currents. The main reasons for the occurrence of over-voltages in collection grids for offshore wind parks have been analyzed. Finally, the offshore wind farm internal electrical system model has been developed and the case of breaking transformer with VCB in three-phase system has been simulated.