Abstract
Problems related to DC bias of HVDC transmission affect the reliability of transformer differential protection. By expressing the newly defined “pseudo-flux characteristic” in terms of exponential function, a new method is proposed to discriminate fault under DC bias. Pseudo-flux characteristics are obtained through inrush current, the parameters of which are determined by differential evolution algorithm (DE). The test of the pseudo-flux characteristics acquisition method is completed on the single-phase transformer in the laboratory. The method of acquiring pseudo-flux characteristics is simple and has high accuracy in the saturation interval. In addition, a simulation of DC bias magnetism was built in PSCAD, and the magnetic flux characteristics of inrush current, DC bias and faults were compared. It illustrates the feasibility of using the transformer pseudo-flux characteristic model to protect in such scenarios and the superiority compared with the second harmonic restraint method.