Cable Overvoltage Characteristics in Bipolar VSC-HVDC Configuration with Multiple Operation Modes

A bipolar VSC-HVDC system with multiple operation modes can improve the reliability of power grids. However, the overvoltage level is different for multiple HVDC links, which may lead to inadaptability of the existing insulation coordination. This paper proposes an improved cable transient model with the multi-layer structure and taking the effects of temperature and frequency on the wave propagation into account. Based on the proposed model, a bipolar system with dedicated metallic return cable (MRC) is established. Then, the magnitude and spatial dependency of the overvoltage on both cable core and sheath are analyzed. The results reveal that, compared with other operation modes, the bipolar configuration with MRC can attain desirable performance to limit overvoltage level. The results also indicate a high transient overvoltage exists on the core and sheath of the MRC which should be considered in operation.