Abstract: This paper addresses the issue of excitation inrush current during zero-crossing power regulation on the high-voltage side of an electric heating transformer. A simulation model is established using the MATLAB platform to systematically investigate the influence of key factors such as firing angle, core residual flux, load rate, and load characteristics on the inrush current under loaded conditions. Quantitative and qualitative analyses are performed on the variation characteristics of the primary-side current and core flux during zero-crossing power regulation. The results show that load characteristics significantly affect the inrush current: the inductive reactive component of the load exacerbates the inrush current, whereas the capacitive reactive component can mitigate it to some extent. Moreover, when the closing angle is 90°ahead, the inrush current can be completely eliminated. Regarding inrush current suppression methods, phase-selection control achieves excellent suppression but involves high complexity, while soft-start control is simple to operate but generates a large number of odd harmonics.

Key words: electric heating transformer, excitation inrush current, zero-crossing power regulation, phase selection control, soft-start