## 4 Discussion
### Behavior of Residual Space Charges
#### 4.1.3 Pressure and Gas Spacing  
The motion characteristics of space charges during a single breakdown is illustrated in Figure 16. Under pulsed voltage, the medium adjacent to the rod electrode undergoes collision ionization and forms streamer discharges. Positive SF\({}_{6}\) ions generated by collision ionization slowly move toward the rod electrode and enter it under the influence of applied voltage, while electrons rapidly move toward the plate ground electrode. As the applied voltage increases, the number of streamer channels increases, leading to the formation of a stable corona layer that envelops the rod electrode. Due to their large volume and mass as well as poor mobility, positive SF\({}_{6}\) ions tend to accumulate in significant quantities near the rod electrode rather than entering it. However, due to their high mobility, electrons quickly move toward the plane electrode, resulting in the formation of space-charge fields \(\mathbf{E}_{\text{I}}\), \(\mathbf{E}_{\text{II}}\), and \(\mathbf{E}_{\text{III}}\), as shown in Figure 16d. The space-charge field causes significant distortion to the distribution of the electric field in the gap, thereby affecting the breakdown process. The positive space charges generate an electric field \(\mathbf{E}_{\text{I}}\) in region I, which enhances the field intensity and facilitates meeting the conditions for self-sustaining discharge. Consequently, the initial electron avalanche can easily develop into a streamer discharge, resulting in corona formation. The electric field \(\mathbf{E}_{\text{II}}\) generated by positive space charges and electrons weakens the field intensity in region II, making it difficult for streamer corona to extend toward the plate electrode and cause breakdown. Therefore, the presence of space charge makes the negative rod-plate electrode more susceptible to corona discharge while making complete breakdown of the gap more difficult [41; 42]. As a result, it exhibits a good corona-stabilization effect, repetitive breakdown stability, and excellent insulation recovery performance. In the switch filled with SF\({}_{6}\), the residual space charge is more difficult to move under high-pressure conditions. Therefore, more residual space charges remain in the discharge gap. As a result, when the subsequent voltage is applied, more initial free electrons will be generated through collision de-attachment, triggering more intense corona discharge. This effect enhances the corona stabilization during the subsequent breakdown, improving both the breakdown stability and insulation recovery performance of the switch. For a corona  
Figure 16: Schematic diagram for the motion of space charges during the breakdown process in a rod-plate gap: (**a**) stage 1; (**b**) stage2; (**c**) stage 3; (**d**) stage 4.  
stabilized switch operating at a pressure of 0.05 MPa, the density of the gas molecules decreases, causing space charges to enter the electrode more quickly. This results in a weakened distortion effect of space charges on the external electric field and leads to a deterioration in the switch's insulation recovery (see Figure 15). The relationship between gas pressure and breakdown voltage exhibited a saturation characteristic, as shown in Figure 10a. The transport and accumulation of space charges may be the primary cause of this phenomenon. When the pressure is low, space charges can easily move to a suitable position, resulting in a good corona-stabilization effect. Therefore, as the pressure increases (from 0.05 to 0.1 MPa), the electrical strength of the gap rapidly increases. However, as the pressure further increases (from 0.1 to 0.4 MPa), the mobility of the space charges deteriorates, as does the corona-stabilization effect. Consequently, the withstand voltage of the switch exhibits saturation characteristics [43; 44]. The saturation characteristics of the breakdown voltage at 2 kHz were less apparent than those at 1 Hz.