Insulation Coordination for a Medium-Frequency DRU-MMC HVDC System for Offshore Wind Power

This paper investigates the overvoltage characteristics and insulation coordination for a medium-frequency Diode Rectifier Unit-Modular Multilevel Converter (DRU-MMC) HVDC system for offshore wind. Switching overvoltages under various faults are analyzed via PSCAD/EMTDC simulations at operating frequencies from 50 Hz to 200 Hz. Results show that a higher frequency increases the maximum overvoltage at several offshore station locations and alters the worst-case fault types. Subsequently, after implementing a surge arrester configuration, simulations were performed for 20 fault scenarios to ultimately determine the required insulation levels for the main equipment. Under the arrester configuration scheme selected in this paper, the equipment’s insulation level is not affected by the increase in the collection system’s frequency.