Lightning strikes are a major threat to the secure operation of wind turbines. When lightning strikes a wind turbine, the lightning current flows through the blade and the tower and then the induced overvoltage will damage sensors and signal cables. In this study, a comprehensive transient surge impedance model of a wind turbine was built to analyze the causes of the overvoltage in the signal cable. The model that studies the overvoltage caused by both capacitive coupling and electromagnetic induction included the blade, nacelle, tower, signal cable, power cable, and grounding system using π networks. The influences of the cable shielding layer, soil resistivity, and lightning current waveform on the overvoltage were also analyzed. Then, 2 overvoltage suppression measures, ie, grounding at 2 ends of the outer shielding layer and installation of a surge protective device, were tested. Results show that a signal cable with double shielding layers reduced the overvoltage in the signal cable, and higher soil resistivity resulted in increased voltage on the tower base. In addition, the peak and the front time of the lightning current significantly influenced the overvoltage on the tower and the cable. The effectiveness of the 2 suppression measures was also verified. The calculation results will provide guidance for a reasonable lightning protection design.

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.

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