The Research On Differential Protection Of The Converter Transformer In DC System

The HVDC system has many special merits,which makes it more and more popular. The characteristics of HVDC system make the converter transformer have something different with power transformer in structure,because the valve is non-linear and brings out a lot of harmonic.In addition,the control and adjust action to fault from the direct current control systems,which makes the protection exist differences between the converter transformer and the power transformer.In addition,if the DC magnetic bias of the converter transformer is serious,it can affect the differential protection of the converter transformer. This paper researched different typical conditions of the CIGRE standard test system based on PSCAD/EMTDC emulator,which includes No-load closing,the internal faults of the converter transformer,including the lead-out wire fault and the interturn fault.Finally,it analyzed the harmonic of the converter transformer and the DC magnetic bias for the typical faults and computed by MATLAB.It analyzed the different conditions and drawn the conclusion of the differential current harmonic traits and its influences.