# Assessment of Partial Discharges in the Air by Application of Corona Camera
## 6 Results and Discussion
In the spark gap, where the distance between the blade electrodes was equal to 2 cm and its breakdown voltage was 26.5 kV, PDs were generated for two voltage values: 13 kV and 15 kV (49% V\({}_{\text{b}}\) and 56.7% V\({}_{\text{b}}\), respectively). The results given in Figure 8a,b clearly confirm the significant effect of the camera's distance from the source of PDs on the value of the recorded count of UV impulses. For example, for a distance of 2 cm the number is 10.900 impulses, and for a distance of 11 m the total impulses are 1700 (for a camera gain of 150). For signals generated in this spark gap at a distance of 3 cm, the respective numbers are 12,400 and 3300 impulses. This type of dependence between the number of registered UV emission pulses and the distance of the UV camera from the source of PDs is confirmed by all curves presented in Figures 7b and 8a, regardless of the value of the adopted camera gain. 3. The results given in Figures 9 and 10 can be applied to determine the effect of camera gain values on the count of UV impulses. The results presented in these graphs were obtained in the same metrological conditions as the previous cases (Figure 8). All curves presented in Figures 9 and 10 clearly demonstrate that the highest numbers of UV impulses are recorded for the camera gain of 150. This conclusion is confirmed by all curves obtained for different distances of the camera from the source of PDs. It is understood that the number of recorded UV impulses is the highest for the shortest distance between the camera and the source of PDs. 4. The results given in Figures 13-15 serve the purposes of verifying results gained previously (Figures 8-10). These results were obtained in a different electrode system with non-uniform field distribution (needle-plate), in which the magnitude of the electric field was lower. The analysis of the results (Figures 13a, 14a and 15a) leads to the conclusion that the assumption of the camera gain value of 150 in this system forms the most suitable option and confirms the results and conclusions relating to the needle-needle system. It can even be said that the curves obtained in this system confirm this conclusion more clearly. This is particularly confirmed by the curves derived for the smallest distance (2 m) from the source of PDs to the camera. Based on the obtained results, it is possible to apply the optimal gain to the analysis of other geometric shapes of electrodes that generate non-uniform distribution of the electric field. The results presented in Figures 13b, 14b and 15b present the effect of the distance between the camera and the source of PDs on the registered count of UV impulses. The results relate to changes in distance in the range of 2 m to 7 m. It can be estimated that the number of UV impulses recorded for a 2 m distance from the camera to PD source is about 2 to 2.5 times greater than that recorded for a distance of 7 m. Trends in curve changes are presented in Figures 13b, 14b and 15b and are fully consistent with the results reported in previous studies (Figure 8). (5) An analysis was performed with regard to the distribution of mean values of the number of counts with the purpose of determining the optimal gain values in percentage points (Figures 16 and 17). The closest distance between the camera and the PD's generation source was adopted as the reference value, which was 2.5 m for the needle-needle gaps and 2.0 m for the needle-plate gaps. This distance was determined due to the need to safely locate the UV camera in relation to the tested systems applied for the generation of PDs. (6) On the basis of the analysis of the resulting characteristics, we can conclude that the most favorable distribution was obtained for the gain values equal to 200 and 250 (Figures 16 and 17). According to the authors, the optimal gain will be 200, as it is characterized by an exponentially declining model.