By drawing on the analytical method of sympathetic inrush current

the generation mechanism and variation characteristics of symmetrical inrush current caused by the energization of a set of two ultra-high voltage(UHV)converter transformers are dealt with. Based on an ultra-high voltage direct current(UHVDC)transmission project simulation model

the phenomenon of symmetrical inrush currents in the cases of UHV converter transformer energization are simulated. The reason for failure of the secondary harmonic restraint criterion to block the converter connection-transformer differential protection is explained

which provides a means for enhancing the operation reliability of the converter transformer differential protection for UHV converter stations.