**4. Discussion**

In order to estimate the effect of the design on the dry band dimensions, the total dry-band extension of the selected designs for a given ESDD and fog spray rate were plotted on the same graph, as shown in Figure 10. The graph shows a selection of calculated dry band extensions for all four insulator designs with an applied pollutant on the surface equal to ESDD 0.64 mg/cm2, and a fog spray rate equal to 3 L/h. It is clear that the conventional design exhibits dry-band formation much earlier than textured insulators. As early as after 1 min, the conventional (CONV) samples start to develop dry bands which continue to extend with increasing applied voltage. This trend is significantly delayed on textured (TT) samples, where the total dry-band length starts to be significant only after 4 min. The curves before flashover shows different trends. In fact, the dry-band dimensions on the TT6 design increases sharply, whereas for TT4 and TTS4 a delayed increase and a lower maximum width is observed before the flashover event. If the analysis was limited to only flashover voltage levels, the test results would not have highlighted any other details such as the clearly visible differences in this graph [10]. This suggests that the new procedure can offer a valuable tool to analyse and compare insulator performance under pollution.

**Figure 10.** Comparison of the dry-band extension on all the trunks for the five designs, with ESDD = 0.64 mg/cm2, and a fog spray rate of 3 L/h.
