Simulation analysis of transformer remanence on inrush current under different closing phases

Abstract

This bachelor’s thesis mainly studies the relationship between transformer magnetisation inrush current and transformer core residue and switching phase angle. The transformer inrush current is a transient phenomenon, which can reach dozens of times the rated current, which is easy to cause differential protection error, voltage drop, and mechanical stress increase in modern power systems. Although previous studies have analysed the core magnetic field or the switching phase angle respectively, the problem of mutual influence between the two has not been well solved.

This work represents the nonlinear core magnetisation characteristics by establishing a transformer simulation model, in which the residual flux is represented by the equivalent initial flux bias. Using 0.1 A to 0.9 A controllable DC bias current to process before magnetisation, different equivalent residual magnetic flux levels can be obtained. According to the equivalent initial flux bias model, the switching process is simulated at various closed phase angles between 0°and 120°. Obtained the key influx current characteristics, namely the peak size and total harmonic distortion (THD).

From the simulation results, it can be seen that the return level and the switching phase angle will affect the amplitude and asymmetry of the inflow of current. In addition, according to the specific operating conditions, its comprehensive effect can aggravate or reduce the degree of inrush current. These findings provide data for analogue reference by injecting current into the analysis transformer, and are conducive to improving the switch arrangement and protecting the connection in the power grid.