Research on Transformer Saturation Mechanism and Restraining Measures in VSC-HVDC Black Start Process

Voltage Source Converter based High Voltage Direct Current technology has the ability of power supplying for passive loads in black start mode. The transformer at VSC-HVDC black start side will bear the voltage boosting process at the converter valve side during the black start process. If the saturation characteristic of transformer and the control function for black start is inadaptive, the transformer will be deeply saturated during the black start process, which will threaten the safety of transformer equipment and even cause HVDC tripping. In order to identify the major factor impacting the transformer saturation during black start process, this paper analyzes the saturation mechanism of the transformer at the black start side in view of a practical VSC- HVDC tripping event. Meanwhile, the saturation phenomenon consistent with the project is simulated based on the RTDS simulation platform. Then the research on the suppression measure of increasing the rated voltage climbing time from 0.2s to 60s and changing the tap changer position into the specified position for black start process, is carried out and proposed. Finally, the method proposed in this paper is verified by simulation and applied in practical projects, which proves the effectiveness of the method proposed in this paper and provides an effective solution to the transformer saturation problem during VSC-HVDC black start process.