Analysis and suppression method of transformer no-load closing excitation inrush current

The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.

一种适用于ZVS的可饱和换向电感器

文章介绍一种小型的适用于零电压开关（zvs）换向的可饱和电感器。电感器的饱和条件由以下两个冈素决定：一是使用了含有可饱和铁心的PWM控制器；二是使用的饱和变压器产生电流反馈时，在不增加传输损耗的条件下，减少开关损耗以及开关的浪涌电流和电压。采用这种电感器的直流电压变换器，可以在1MHz的开关工作频率上获得高达90％以上的效率。这是由于流经开关的无功电流非常小，开关中的浪涌电流和电压得到了抑制，故开关损耗大为降低。