In closing operation of vacuum circuit breaker for no-load transformer in medium-voltage cable power collection grid of offshore wind farm

the prestrike of the vacuum circuit breaker will produce transient over-voltage on the high-voltage side of the generator transformer

and this over-voltage

interacting with the cable

will produce high-frequency oscillation over-voltage to cause damage to the transformer insulation. In order to reveal the producing mechanism of high-frequency transient over-voltage in prestrike of the vacuum circuit breaker

this study employs the transient analysis software PSCAD/EMTDC to build a self-defined model which can reflect the prestrike phenomenon of vacuum circuit breaker. This model is applied to a simplified simulation model of the medium-voltage cable power collection grid of offshore wind farm to analyze the influences of initial phase angle of closing

cable length and generator transformer position on the transient over-voltage. Simulation results show that the over-voltage steepness is the largest when the generator transformer is located in the engine room and the initial phase angle is 15°

and the transient over-voltage steepness is obviously suppressed after the over-voltage protection device including choke and parallel small capacitor is installed on the generator transformer.