# Assessment of Partial Discharges in the Air by Application of Corona Camera
## 2 Measurement System, Characteristics of UV Cameras, Measurement Range
The second type of measurement involved the determination of the effect of camera gain factor, distance between the camera and the source of PDs and the voltage value of the spark gap on the magnitude of the signals emitted by UV radiation originating from and generated in the needle spark gap with cone electrodes, for an angle of \(\alpha\) = 20\({}^{\circ}\) (Figure 3b). The third type of measurements was performed for PDs generated in the conical nee-dle (\(\alpha\) = 20\({}^{\circ}\))-plate spark gap (Figure 3c). The purpose of this experiment involved the determination of the effect of camera gain, distance of the camera from the PD's source and the supply voltage of such a spark gap on the value of the signals emitted as UV radiation originating from PDs. Results of Measurements of Number of UV Impulses Generated by PDs in Needle Spark Gaps in the Function of the Generation Voltage  
Figures 4-6 demonstrate the characteristics of the mean distribution represented by the number of counts of UV impulses originating from PDs as a function of voltage delivered to the needle electrodes. Needle spark gaps with three diameters of 0.23 mm, 0.40 mm and 0.50 mm were applied for the purposes of PD generation. In each of the spark gaps, the distance between the electrodes was constant during measurements and was equal to 8 cm. The values of the breakdown voltage V\({}_{\text{b}}\) in the spark gap were equal to 65.98 kV, 58.75 kV and 60.29 kV, respectively. The value of the generation voltage of PDs was varied stepwise by increments of 5 kV, in the range of values from 5 kV to 55 kV. The distance between the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline UV spectral range & 250–280 & nm \\ Visible light range & 380–780 & nm \\ Sensitivity within UV range & \(3\times 10^{-18}\) & W/cm\({}^{2}\) \\ Minimum sensitivity of illumination & 1 & Lux \\ Matrix & 640 \(\times\) 480 & Pixels \\ Lowest detectable PDs & 1.5 (for a distance of 8m) & PC \\ Presentation of UV image/visible light & Solid angle with accuracy & miliradian \\ Operating modes & Visible/UV/combined & - \\ Operating and storage temperatures & \(-\)20 \(\ldots\) +55 & \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of technical parameters of the DayCor Superb camera. Figure 3: Needle–needle spark gap with thin needle (**a**), needle–needle spark gap with conical electrodes with a needle angle of \(\alpha\) = 20\({}^{\circ}\) (**b**), needle–plate spark gap (**c**). camera and the source of PDs was constant and maintained at 160 cm, the camera gain was also constant and equal to 100. For better interpretation of the presented characteristics with the obtained results, a trend model marked as the fit curve was used. This model was determined using typical interpolation techniques available in the MATLAB environment (smoothing spline interpolation method). Effect of Camera Gain and Distance from the PD Source and Generation Voltage on the Registered Count of UV Impulses Determined for Needle Spark Gap  
With the purpose of determining the effect of the distance between the camera and the PD's source on the registered count of UV impulses resulting from PDs, the characteristics were established with regard to this relation. The recording of these dependencies was  
Figure 4: Mean value of registered count of impulses within UV radiation range in the needle spark gap with the diameter of 0.23 mm (**a**); trend line representing the variations in the number of impulse counts in the function of the PD generation voltage (**b**). Figure 5: Mean value of registered count of impulses within UV radiation range in the needle spark gap with the diameter of 0.40 mm (**a**); trend line representing the variations in the number of impulse counts in the function of the PD generation voltage (**b**).