# Analysis of the Possibility of Using Drill-Type Electrodes for Air Ionization
## 4 Analysis and Interpretation of Results  
Figure 5 shows the dependence of the voltage values U\({}_{\rm o}\), U\({}_{\rm s}\), U\({}_{\rm b}\) on the distance between electrodes for eleven systems of drill-type electrodes of different diameters. Distances between electrodes are expressed in centimeters and values of U\({}_{\rm o}\), U\({}_{\rm s}\), U\({}_{\rm b}\) are expressed in kilovolts. In Figure 5, each of the eleven presentations (from a to k) shows three waveforms. The first shows the U\({}_{\rm o}\) voltage waveform as a function of the distance between electrodes, the second shows the U\({}_{\rm s}\) voltage waveform and the third shows the U\({}_{\rm b}\) voltage waveform. The presentations demonstrated in Figure 5 enable the evaluation of results obtained, both in terms of compliance with the data published in the literature and compliance with the physical understanding of the mechanism of the development of partial discharges occurring in fields of non-uniform intensity. In diagrams shown in Figure 5, at each measuring point the calculated standard deviation of the results is marked. After the analysis of the variability of waveforms, it can be concluded that the values of their standard deviations are small, while their maximum values do not exceed 10% of the measured voltage. The analysis of results of U\({}_{\rm o}\), U\({}_{\rm s}\) and U\({}_{\rm b}\) voltage measurements generated in drill-type electrode systems shows that differences in values of individual waveforms are subtle and a different approach is necessary to make them visible. It should be noted here that the voltage measurements are point-based (one point for each distance between electrodes) and as such should be represented on diagrams as single points (or bars). For the purpose of the analysis, the registered measuring points are described with regression curves, which represent models of U\({}_{\rm o}\), U\({}_{\rm s}\) and U\({}_{\rm b}\) voltage waveforms as a function of distance between electrodes. Models of the corona voltage U\({}_{\rm o}\), over the whole range of measured distances (up to 16 cm), regardless of the diameter of the drill-type electrodes, are difficult to distinguish, the waveforms overlap. Figure 10: Spatial diagrams showing changes in the corona voltage U\({}_{\rm o}\) (**a**), sparking voltage U\({}_{\rm s}\) (**b**) and breakdown voltage U\({}_{\rm b}\) (**c**) in partial discharges generated in systems of drill-type and needle electrodes depending on the distance between electrodes and their needle angles [21]. A comparison of the models of the waveforms of the sparking voltages occurring in the systems of drill-type electrodes of different diameters indicates an equal course of these relationships in the range from 2 cm to 12 cm. At longer distances between electrodes (12 to 16 cm), waveforms of the voltage models are clearly distinguishable. Figure 5 also shows the model waveforms of the breakdown voltage values \(\mathrm{U_{b}}\) for the eleven tested systems of drill-type electrodes. In terms of safety, knowing the dependence of the breakdown voltage \(\mathrm{U_{b}}\) on the distance between the drill-type electrodes, is the most important. The comparison shows that initially, up to a distance of 6 cm, regardless of the diameter of the drill-type electrodes, waveforms are very similar. With the distances of the drill-type electrodes above 6 cm, curves vary-differences in the breakdown voltage values \(\mathrm{U_{b}}\) reach about 10%. The highest values of the breakdown voltage between drill-type electrodes are found for drill-type electrode systems with a diameter of 0.7, 0.8 and 0.9 mm.