## 4 Analysis of Experimental Results  
### The Relationship Between Spot Area and Voltage  
In this experiment, UV videos of insulators under ten voltage levels between 1 kV and 10 kV were taken. The frame rate of the UV video stream obtained by the UV imager is 30 fps. The resolution is 720 \(\times\) 480 pixels. The video format is AVI. The trend curve of  
\begin{table}
\begin{tabular}{c c} \hline
**Items** & **ZS-10/4** \\ \hline Nominal voltage (KV) & 10 \\ Creepage distance (mm) & 230 \\ Structure height (mm) & 210 \\ Weight (kg) & 6 \\ \hline \end{tabular}
\end{table}
Table 2: Insulator parameters.  
the spot area can be obtained by calculating and counting the size of the facular area of consecutive frames of UV images. This article makes statistics on the facular area in the 30-s stable discharge video at 10 different voltage levels. Each video has a total of 900 frames of UV images. The average facular area in 30 frames of UV images per second is calculated, and the average facular area per second is used to analyze the changing trend of the facular area under different voltages across insulators. As shown in Figure 12, when the voltage across the insulator rises to 6 kV for a period of time, the contaminated insulator begins to leak. A small number of light spots appear. The 6-8 kV facular area has an obvious trend of increasing with the increase in voltage. At the voltage level of 6-8 kV, the facular area has an obvious trend of increasing with an increase in voltage. When the voltage across the insulator reaches 9 kV, the facular area of the insulator increases with the increase in voltage across the insulator, and the increasing trend is not obvious. As can be seen from Figure 12b, under different voltage levels, the spot area changes within a certain range. The increase in the facular area at the voltage level across the insulator from 6 kV to 7 kV is more obvious. Figure 12c shows that when the voltage across the insulator reaches 10 kV, the facular area does not show an upward trend. When the voltage level across the insulator reaches about 11 kV, the sample polluted insulator flashover. Similar conclusions can be obtained by analyzing the relationship between the facular area and the voltage level at different shooting distances.  
The statistical characteristics of the change trend of facular area at shooting distances of 9 m and 5 m are shown in Tables 3 and 4. Tables 3 and 4 list the six statistical characteristics of facular areas. There are sum, maximum, minimum, range, standard deviation, and average of the spot area. From these six statistical characteristics, it can be seen more intuitively that the facular area increases significantly at 6-8 kV. When the shooting distance is 5 m, the increase is greater than when the shooting distance is 9 m. When the voltage reaches 9 kV and 10 kV, the facular area does not change much. This phenomenon is due to  
Figure 12: The relationship curve between voltage level and spot area at 9 m shooting distance. (**a**) Trend curve of the facular area with voltage. (**b**) Change the interval of the facular area under each voltage level of 0–10 kV. (**c**) Change in facular area under each voltage level average value.  
the saturation of the leakage current of the pollution insulation, and a flashover is about to occur. Experiments show that the changing trend of the facular area can be used to characterize the changing trend of leakage current. The facular area is affected by the detection distance. For insulators of the same pollution class, under the same humidity and shooting distance, the relationship between voltage and the facular area is nonlinear.