Abstract: By taking the wye/delta converter transformer in Pu’er converter station in Nuozhadu-Guangdong ±800 kV DC Transmission Project as an example, the calculating settings and sensitivity checking of differential protection are discussed. A 12-pulse inverter DC transmission model is established by MATLAB for simulation of the AB phase-to-phase fault on the valve side of wye/delta converter transformer, and the testing data and waveforms from the XUJI GROUP’s converter transformer protective device-RTDS in CSG’s project are used for proof. A comprehensive analysis indicate that, for HVDC systems ,since tube A is used in the differential protection of the wye/delta converter transformer, the sensitivity should be calculated according to the three-phase short-circuit on the valve side of wye/delta converter transformer under the system’s minimum operating mode rather than the conventional phase-to-phase short-circuit.

Key words: HVDC, wye/delta converter transformer, tube, TA, differential protection, sensitivity, RTDS