Analysis of the action of converter bridge differential protection caused by magnetizing inrush current of converter transformer

In the event of a failure in the converter transformer protection system during the operation of the converter station, there is a risk to the safety of the equipment, as well as disruption to the smooth operation of the system and the uninterrupted supply of power. This issue pertains to the professional concepts of a DC transmission system and a converter station. The DC protection system is configured with three sets of converter bridge differential protection ($87 \mathrm{CBY} / 87 \mathrm{CBD}$), of which B and C sets of converter bridge differential protection (87CBY/87CBD) auctioned. According to the waveform of the fault recording system, the accident process was analyzed, and combined with Simulink simulation verification, the analysis showed that the differential current of $Y / \Delta$ converter transformer was caused by a large magnetizing inrush current, which met the differential protection criterion of B and C converter bridge, so as to make the protection action.