The HVDC system reduce-voltage operation is a special strategy adopted by abnormal DC transmission system and has been paid more attention in the process of debugging

so

it is particularly important to make a thorough analysis on the key reason for the failure of DC step-down operation caused by the reactive power supplied by AC system. In this paper

based on a block event happened on the ±800 kV Nuozhadu UHVDC project reduce-voltage operation debugging field

according to the converter controller selecting control principle

it has been found that the fundamental reason is inverter station controller entered the current control mode by mistake because of reactive power insufficient in rectifier station. By only reducing DC load to solve the problem of insufficient reactive power

the debugging personnel redo the reduce-voltage operation test successfully

it has been verified by the test result that the foregoing blocked reason. The key points for HVDC reduce-operation are summarized

and the main notices are proposed which need to be considered before HVDC reduce-operation process.