# Development of Electrode of Electric Impulse Chamber for Coal Grinding
## 3 Results and Discussion
### The Test Results of the Positive Electrode
The values of the electrical impulse discharge parameters and the geometric parameters of the device (electrode and insulation diameter, distance between insulation and electrode) represent averaged values based on multiple measurements results. The insulation resistance to electric pulse discharges was assessed after every 2000 discharges. Based on the data in Table 2, it was found that when selecting an insulation diameter with D = 3 \(\times\) d, the fluoroplastic material collapsed after 4000 discharges at U = 30 kV pulse discharge voltage. With a ratio of D = 4 \(\times\) d, damage occurs after 6000 discharges. At D = 5 \(\times\) d, the fluoroplast undergoes deformation, while at U = 30 kV, the insulator is damaged after 8000 discharges. At a ratio of D = 6 \(\times\) d, the insulation withstands electrical impulse action (results at U = 30 kV). However, when the voltage is increased to U = 40 kV, damage occurs after only 6000 more discharges. From the results obtained for sample N 1, we can see that even with an increase in the insulation diameter up to 6 times the diameter of the metal electrode, fluoroplast does not withstand the effects of the pulsed discharge. It was observed that the insulation did not deform at D = 7 \(\times\) d. Since a further increase in the electrode diameter leads to a decrease in the volume of the working chamber, experiments with this type of sample were discontinued. For sample N 2, the distance between the metal electrode and its insulation was S = 2.5 mm (Table 3). The following optimal test results were obtained for this model type, depending on the electric impulse discharge:  
* by increasing the insulation diameter 4 times relative to the metal electrode diameter (D = 4 \(\times\) d), an effective working electrode variant, resistant to electric impulse discharge impact, was achieved;
* based on the experimental results, a possible saving in insulation material was observed compared to sample N 1. The following studies focused on determining the optimal distance ratio between the electrode and its insulation (see Figure 7). During the tests, the gap between the insulator and the electrode varied from 1 mm to 8 mm. The experiment was conducted under the following conditions: number of pulsed discharges (N)--2500-10,000, capacitor capacity--C = 2 uF, and discharge voltage (U) 30-50 kV (Table 4). Figure 7: Front end of the working electrode: S is the distance between the electrode and its insulation, d is the electrode diameter (D = 4 mm), and D is the insulation diameter (mm). The results of the research showed that the ratio (S) between the insulation of the positive electrode and its metal rod, one of the main devices for forming a pulsed electric discharge in a liquid medium, should be from 3 mm to 8 mm. A further increase in the space between the electrode and its insulation led to a thinning of the insulation thickness of the electrode system. The resistance of an electrode of this shape to electrical impulse discharges is explained as follows:  
* The liquid (technical water) in the space between the electrode and the insulation serves as additional insulation and prevents damage to the fluoroplastic. * The protruding part of the electrode from the insulation diverts streamers from the fluoroplastic. This is explained by the fact that streamers usually grow intensively from the end of the electrode. * The active surface of the end of the thin electrode protruding far from the insulation, due to its small diameter, does not exceed the active surface of the usually used thick electrode, which slightly protrudes from the insulation [28]. * Thus, the electrode design promotes efficient electric field distribution and reduces the risk of electrical breakdowns in the fluoroplastic insulation. This ensures high electrode reliability under pulsed discharge conditions, protecting the insulating materials from degradation and extending the device's lifespan [29].