# Assessment of Partial Discharges in the Air by Application of Corona Camera
## 6 Results and Discussion  
The results of measurements of UV emission spectra generated by PDs in the air, occurring in electrode systems with a non-uniform distribution of the electric field discussed in this paper, clearly demonstrate the applicability of the camera technique for detection and measurement of partial discharges. The more important results are discussed below:  
1. The results presented in Figures 4-6 demonstrate the dependence of the counts of UV emission impulses originating from PDs on the value of the voltage used to generate them. All waveforms are non-linear. Initially, they increase exponentially, at 32 kV (i.e., 52% of the breakdown voltage V\({}_{\text{b}}\)), until they assume a maximum value (1.8 \(\times\) 10\({}^{4}\) impulses), followed by a linear decrease to 45 kV (73% V\({}_{\text{b}}\)), for which the number of registered pulses is equal to 1 \(\times\) 10\({}^{4}\). This may indicate that at a voltage of 32 kV there is the highest ionization energy. With a further increase in the value of PDs' generation voltage, the emission of UV pulses increases linearly, reaching a voltage of 1.1 \(\times\) 10\({}^{4}\) at 55 kV (92% V\({}_{\text{b}}\)). This dependence between the UV emission and the voltage of PD generation applies regardless of the diameter of the electrode needles (and, consequently, also regardless of the radius of their needle), between which PDs are generated. This analysis showed that the change in the thickness of the spark gap does not significantly affect the counts recorded by the UV camera, therefore only models (b) and (c) from Figure 3 were used for detailed analysis. The registered UV emission waveforms in the function of PD generation voltage provide interesting input since they are clearly different from those that were recorded in the  
Figure 14: Characteristics of the dependence between the count of UV impulses and distance from the camera to the source of PDs for different values of camera gain parameter (**a**) and comparative characteristics of the dependence of the counts of UV impulses on the camera gain value for different distances from the camera to the PD’s source (**b**). PD generation voltage U = 31 kV, for a distance between electrodes of 3 cm. Figure 15: Characteristics of the dependence between the count of UV impulses and distance from the camera to the source of PDs for different values of camera gain parameter (**a**) and comparative characteristics of the dependence of the counts of UV impulses on the camera gain value for different distances from the camera to the PD’s source (**b**). PD generation voltage U = 38 kV, for a distance between electrodes of 3 cm. visible light spectrum. According to the present authors, the explanation of these phenomena should be sought in the analysis of physical mechanisms responsible for the formation and development of PDs occurring in electric fields with non-uniform distribution. Recorded waveforms clearly indicate that the energy transformations associated with air ionization in the UV spectrum and in the visible light spectrum are different. The decrease in the number of counts observed in Figures 4-6 is associated with the ionization process, where after reaching a certain level of saturation, part of the ionization energy begins to be transferred in another form, including kinetic energy and in the form of radiation. This phenomenon is most often already visible to the naked eye (in appropriate conditions, of course) as a bright glow. The gas dielectric (in this case, air) is locally ionized and the ionization energy share decreases despite the voltage increase. A UV camera detector that works in the wavelength range from 240 nm to 280 nm is able to register this phenomenon. A further explanation of these differences requires further research and analysis. 2. Figure 8 presents the effect of the camera's distance from the PD's source generated in the needle system on the registered UV emission.