# Wet Snow Flashover Characteristics of 500-kV AC Insulator Strings with Different Arrangements
## 3 Results
### The Flashover Test of \(\Lambda\)-string  
During the test, the insulators were covered with snow and ice, which had negative effect on their electrical performance. To investigate the electric field distribution, numerical simulations were carried out using finite element method by ANSYS Maxwell with electrostatic as the solver. The parameters used in the electric field calculation model are listed in Table 4[26; 27; 28]. The simulation was performed in 2D. In the simulation, the snowed insulators were placed in a square with side length of 50 m. The high voltage was applied to the high-voltage ends of the insulators while the earth ends of the insulators and four sides of the square were grounded. When the ambient temperature was raised to around 0 \({}^{\circ}\)C, ice and snow started to melt and a water film formed on their surface. The water film was assumed uniform in the simulation. As this simulation calculated the electric field distribution before flashover, static electric field was also assumed. The relative permittivity of the water film was set at 81 and snow layer was set at 6.0. The length of icicles on anti-icing sheds was set at 300 mm. To set the value of water volume conductivity, a water collector was placed under the insulator to collect and measure the melted water during the flashover test. The average water conductivity was about 670 \(\mu\)S/cm. The simulated results of the 90\({}^{\circ}\)\(\Lambda\)-string arrangement with anti-icing shed are shown in Figure 5. It can be seen that the electric field concentrates on the terminals of insulator strings, and is distorted at the icicle tips. Areas with high electric field strength are susceptible to partial discharge, which poses a challenge for the safe operation of insulator strings. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameters** & **Silicone Rubber** & **Ice** & **Snow** & **Water Film** & **Air** \\ \hline Relative permittivity, \(\varepsilon_{\text{r}}\) & 6.0 & 70 & 6.0 & 81 & 1.02 \\ Conductivity (\(\mu\)S/cm) & 0 & 1 & 100 & 670 & 0 \\ Thickness (mm) & - & Variable & Variable & 0.15 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters used in the simulation model. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Common Shed**} & \multicolumn{3}{c}{**Anti-Icing Shed**} \\ \cline{2-7}
**String** & \multicolumn{2}{c}{**Flashover**} & \multirow{2}{*}{\(\sigma\) (\%)} & \multirow{2}{*}{\(\beta\) (\%)} & \multicolumn{2}{c}{**Flashover**} & \multirow{2}{*}{\(\sigma\) (\%)} & \multirow{2}{*}{\(\beta\) (\%)} \\
**Arrangements** & & & & & & Voltage (kV) & \\ \cline{1-1} \cline{5-7} Single string & 391.0 & 15.5 & 0.0 & 450.0 & 5.1 & 15.1 \\ II-string(450 mm) & 373.5 & 5.1 & \(-\)4.5 & 416.3 & 3.3 & 6.5 \\ \(2^{\circ}\Lambda\)-string & 381.5 & 10.1 & \(-\)2.4 & 435.0 & 12.2 & 11.2 \\ \(30^{\circ}\Lambda\)-string & 410.6 & 1.2 & 5.0 & 458.2 & 9.4 & 17.2 \\ \(60^{\circ}\Lambda\)-string & 439.4 & 11.8 & 12.4 & 499.5 & 7.3 & 27.7 \\ \(90^{\circ}\Lambda\)-string & 450.1 & 13.7 & 15.1 & 479.8 & 13.2 & 22.7 \\ II-string(650 mm) & 385.6 & 17.3 & \(-\)1.3 & 444.3 & 2.6 & 13.6 \\ \(60^{\circ}\)V-string & 436.0 & 5.2 & 11.5 & 512.3 & 6.7 & 31.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Flashover voltage of various arrangements. To get a clear and visual comparison of the \(\Lambda\)-string configurations, the results are plotted in Figure 6, which makes it convenient to compare the wet snow flashover voltage for various arrangements and find tendencies. It can be seen from Figure 6 that, for the \(\Lambda\)-string configuration using common shed insulators, wet snow flashover voltage increases with an increase of the connection angle up to 90 \({}^{\circ}\)C. It is also observed that the slope of the black line (the common shed structure) decreases when the connection angle is higher than 60\({}^{\circ}\).