Impact of recovery and sympathetic inrush phenomena on VSC HVDC systems

The converter transformer of a VSC HVDC station can be driven into saturation caused by external grid events as short-circuits or the energization of nearby transformers. These effects are classified as inrush phenomena and named recovery inrush and sympathetic inrush, respectively. In this paper, a thorough study on different influencing factors on the inrush magnitude and its impact on the operation of the HVDC system is analyzed based on electromagnetic transient analysis using an average based EMT MMC HVDC model. As important parameters for the analysis of the recovery inrush the short-circuit ratio, the time point of fault inception and the fault duration, the fault distance and the fault resistance are selected. The impact of these parameters on the inrush intensity and the transients of the transformer and converter currents as well as active and reactive powers during the inrush events are analyzed and worst-case scenarios evaluated. By evaluation of internal converter signals, it is checked whether the converter is able to maintain stability for different inrush intensities.