Operation behavior of converter bridge differential protection in converter station of HVDC system

Aiming at the abnormal operations of converter bridge differential protection of high voltage direct current(HVDC) transmission project, the operation behavior simulation of converter bridge differential protection under various fault conditions is carried out and the reason of the abnormal operations of converter bridge differential protection are explained and analyzed on the basis of PSCAD/EMTDC model. The simulation results indicate that, the converter bridge differential protection can operate correctly when a fault current difference exists between the sampled values of current trans formers (CTs) on the A bridge and Y bridge of the valve side. If the fault current flows or does not flows simultaneously into the CTs on the A bridge and Y bridge of the valve side, the refusal-operation of converter bridge differential protection will occur.