Switching transients caused by vacuum circuit breakers in collection grids of offshore wind farms

In this study, transients that can occur in the collection grids of offshore wind farms were investigated. On the basis of the multiple prestrike and reignition model that can reflect the actual operation of a vacuum circuit breaker (VCB), a switching transient simulation model of a typical offshore wind farm was built. The developed model included a VCB, a transformer, a cable, and an arrester. Issues concerning the closing time, length of the feeder, and topology of the collection grid were discussed. Results showed that the relationship between overvoltage amplitude and closing time was approximately sinusoidal and the maximum value was obtained when the closing time was near the peak of the power source. In addition, the overvoltage at the end of a feeder terminal was the largest among all of the transformer overvoltages of the same feeder. The overvoltage of the main transformer and that of the transformer located at the end of a feeder decreased slowly with the increase in feeder length during the closing of VCB. However, these overvoltages were positively related to feeder length during the opening of VCB. The star topology was superior to the other topologies in terms of coping with the overvoltage caused by switching transients. The effectiveness of a suppression measure, namely, installation of a resistance-capacitor filter, was also verified.