Configuration of suppression schemes against high-frequency transient reignition overvoltages caused by shunt reactor switching-off in offshore wind farms

Abstract

It is crucial to protect offshore wind farms from overvoltages because of bad accessibility and high maintenance costs. During the process of switching-off a shunt reactor with a 40.5 kV vacuum circuit breaker, high-steepness reignition overvoltages may occur. In order to reproduce this reignition overvoltage accurately and further determine a suitable mitigation scheme, this paper proposes a new quantitative evaluation framework, which comprehensively considers its magnitude and steepness. Firstly, main component models of a typical offshore wind farm are developed in PSCAD/EMTDC, which consider their high-frequency transient characteristics. Subsequently, the transient characteristics of reignition overvoltages at the 35 kV side of shunt reactors are analyzed. Then, for the sake of investigating the mitigation performance of different overvoltage protective schemes, a quantitative evaluation is conducted. Simulation results show that switching-off shunt reactors in offshore wind farms can cause high-frequency transient reignition overvoltages characterized by a high amplitude and a high steepness at its terminals. It is found that a resistor-capacitor filter or a new scheme combining a surge arrester with a smart choke can be installed on the terminals of shunt reactors to decrease both the magnitude and the steepness of reignition overvoltages.