Abstract: During auxiliary power switching, transient characteristics such as voltage fluctuations, phase shifts, and load impacts may cause relay protection misoperation or failure to operate, affecting power supply reliability. To address the coordination issues of high-voltage auxiliary transformer differential protection, overcurrent protection, and zero-sequence protection during the switching process, optimization schemes including differential and backup protection coordination, overcurrent protection time-delay coordination, zero-sequence protection selectivity coordination, and coordination between the automatic bus transfer device and protection logic are proposed. The proposed schemes effectively reduce the probability of protection misoperation and improve the reliability of auxiliary power switching.