# Wet Snow Flashover Characteristics of 500-kV AC Insulator Strings with Different Arrangements
## 3 Results
### The Flashover Test of \(\Lambda\)-string
For anti-icing shed insulators, the wet snow flashover voltage increases as the connection angle increases up to 60\({}^{\circ}\), and then deceases when the connection angle increases further. The reason for an improved flashover performance of the tilted insulator string configuration is obvious. If the insulator string is placed at vertical, the air gaps formed by the ice and icicles can be easily shorted and insulator sheds can even be bridged in the worst case. When the insulator string is tilted, the formed vertical icicles have an angle with the insulator string and the insulator shed cannot be bridged as easily as under the vertical configuration. For the red line (the anti-icing shed structure), there are two points to be noticed. One is 2\({}^{\circ}\) at which the flashover voltage increases dramatically compared with that of vertical arrangement and the other is 90\({}^{\circ}\) at which the flashover voltage is even lower than that at 60\({}^{\circ}\). When the connection  
Figure 5: Model of the 90\({}^{\circ}\)\(\Lambda\)-string. Figure 6: Relationship between the voltage change ratio \(\beta\) and connection angle for the common and anti-icing sheds  
angle was changed from 0\({}^{\circ}\) to 2\({}^{\circ}\), there was an increase of 150 mm in the horizontal distance between two high voltage terminals and a voltage increase of 18.7 kV. Although the increase of distance was minor, it had a great influence on the flashover process. Due to the larger diameter of the anti-icing sheds, there were always floating arcs between the two insulators when the distance between the two high-voltage terminals was 450 mm during the flashover tests. Increasing the distance between high voltage terminals can make the arc develop relatively independently and therefore increase the flashover voltage. The discharge paths of iced insulator strings with anti-icing sheds and common sheds are shown in Figure 7a,b. It can be seen that both discharge paths are shorter than their leakage distances. For the anti-icing insulator at the left side of Figure 7a, the air gap between the icicles of the third big sheds from the high voltage end and the conductor is shorted by the arc, which is much longer than the arc in air of the common shed insulator in Figure 7b. The morphology of the 90\({}^{\circ}\) arrangement with anti-icing sheds is shown in Figure 8. Due to the large diameter of the anti-icing sheds, the deposited snow on the large sheds is more than that on the common sheds. Furthermore, the water in the snow flows to the bottom of the inclined sheds to form icicles up to 300-mm long. Thus, the top of the inclined sheds appears white while the lower end is translucent, as shown in Figure 8. With the increase of connection angle, the insulator sheds are even harder to bridge. This is a positive factor for the insulator flashover performance. However, as the icicles on the anti-icing shed are very long, combined with a smaller angle between the insulator string and conductor, the breakdown of the air gap between the icicles and the conductor is more likely to happen. According to the test results that flashover voltage is higher at the connection angle of the 60\({}^{\circ}\) than that of 90\({}^{\circ}\) arrangement, it can be concluded that, in this case, the icicle-conductor air gap shortening effect counteracts and even exceeds the effect of icicle bridging mitigation with the increase of connection angle. Figure 8: The morphology of ice accreted on the anti-icing sheds when the connection angle is 90\({}^{\circ}\). Figure 7: The flashover arcs of \(\Lambda\)-string. (**a**) The 90\({}^{\circ}\) with anti-icing sheds, (**b**) The 90\({}^{\circ}\) with common sheds.