*3.3. Ground Inductor*

Figure 7 shows the peak current, zero crossing time (ZCT), and rectifier current stable time (RST) depending on the ground inductor. ZCT is the time the main switch is turned off at the main current branch. The fault current is equal to the LC resonant current, so this generates a current zero. RST is the time until the current in the rectifier stage is stabilized (usually less than the steady-state current).

Increasing the ground inductor causes less LC resonant current to flow to ground and more LC resonant current to emit to the main switch. Therefore, ZCT is shortened because more resonant current is emitted. However, the larger ground inductor, the less the current returned to the DCCB by increasing its own impedance after the main switch breaks. As a result, the ground current decreases and the rectifier stage takes a long time to stabilize.

In the graph, when the value of the ground inductor is small, the characteristic change in characteristics is very small, but when it is greater than 10−<sup>3</sup> H, the effect is remarkable, so the value of the ground inductor has a trade-off relationship between ZCT and RST. Since ZCT and RST cannot be designed well at the same time, the trade-off characteristics must be considered in the DCCB design procedure.

**Figure 7.** The emitted resonant current, ground current, zero-crossing time (ZCT), and rectifier stable time (RST) depending on the ground inductor.

The ground inductor has the same characteristics when changed to a resistive element. Even in the case of the resistors, there is no significant power loss when the reverse charge capacitor is fully charged. Likewise, the larger the resistance, the more LC resonant current is emitted to the main switch, but less current is returned to the DCCB after the main switch break. However, when using an inductor on the ground, the more the current changes over time, the higher the impedance and the less current flow. Therefore, less current flows to the ground than when using a resistor, and conversely, more resonant current can be effectively emitted to the main switch. Because of these characteristics, in this paper, we use a ground inductor for the DCCB with better characteristics.
