A Phase Selection Closing Strategy for LCC-HVDC Converter Transformers Based on the No-Inrush Current Closing Angle Interval

Inrush current generated during the commissioning of converter transformers will seriously threaten the stability of power system. Existing closing strategy cannot suppress inrush current when the AC circuit breaker operation is decentralized and the remanence measurement is inaccurate. This paper first analyzes the magnetic linkage of converter transformers during no-load commissioning, quantifies the suppression effect of pre-insertion resistance on inrush current, and proposes a calculation method of the no-inrush current closing angle interval, which expands the existing research's no-inrush current closing angle into an interval. Then a phase selection closing strategy for LCC-HVDC converter transformers based on the no-inrush current closing angle interval is proposed. Finally, a simulation model is constructed using PSCAD/EMTDC to verify the proposed method. The results show that inrush current can be effectively suppressed with proposed method under the conditions of ±2 ms deviation in circuit breaker operation and ±1.0 p.u. deviation in residual magnetism flux, demonstrating strong robustness.