## 3 Results and Discussion
### Effect of Voltage Urparting for 132 kV Transmission Tower on the Voltage Profile under Still Air
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Types of Overvoltages** & **Applied BIL** & \
\begin{tabular}{c} **Phase-to-Earth Minimum** \\ **Clearance at Crossarm Section** \\ \end{tabular} &
\begin{tabular}{c} **Percentage Difference between** \\ **Estimated CFO and Simulations (\%)** \\ \end{tabular} \\ \hline \multirow{4}{*}{Backflashover} & BIL & L4 = L5 & 14.4 \\  & BIL & L6 & 17.9 \\  & BIL + 10\% & L4 = L5 & 6.1 \\  & BIL + 25\% & L6 & 10.0 \\  & BIL & L4 = L5 & \(-\)6.9 \\  & BIL & L6 & \(-\)4.7 \\  & BIL & L4 = L5 & 37.0 \\  & BIL & L6 & 33.2 \\  & BIL + 10\% & L4 = L5 & 30.4 \\  & BIL + 25\% & L6 & 26.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: The voltage magnitude and the percentage difference between CFO and simulation results. Figure 13: Voltage magnitude due to (**a**) backflashover, and (**b**) shielding failure activities. Effect of Voltage Urrating for 132 kV Transmission Tower on the Voltage Profile under Extreme Wind Condition  
Under extreme wind conditions, the string suspension swings by 57\({}^{\circ}\), and its electrical clearance is significantly lower than still air and normal wind conditions. The percentage of difference in electrical clearances between under still air and extreme wind conditions is between 58.3% and 68.8% at the different crossarm sections, as summarised in Table 12. It is believed that a normal operating voltage of 132 kV uprating the transmission line could lead to flashover due to insufficient electrical clearance. The withstand voltage of the power frequency is much lower than transient overvoltages withstand voltages. Hence, the withstand voltage of the power frequency was considered in this study. The simulations results clearly show that a similar trend of stresses and voltage profiles was obtained for all cases. Both cases under BIL, BIL +10%, and BIL +25% at different crossarm sections, none of the cases experienced high stress or having maximum voltage magnitude exceeds the CFO for the distances that could potentially give the 50% of having the flashover as can be seen in Figure 14. The insulation strength of the proposed voltage uprating of the 132 kV transmission under extreme wind conditions benefits withstanding capability. The electrical clearance of the phase-to-earth under extreme conditions is almost double the required minimum electrical clearance of 0.51 m for the power frequency needed for 275 kV transmission line operation. Meanwhile, the percentage of the difference between the estimated CFO and all cases ranges from 19.2 to 68.7 %. It is worth mentioning that the margin could be sufficient for load operating conditions. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Types of Overvoltages**} & \multirow{2}{*}{**Applied BIL**} & \multicolumn{2}{c}{**Phase-to-Earth Minimum**} & \multicolumn{2}{c}{**Percentage Difference between**} \\  & & **Clearance at Crossarm Section** & **Estimated CFO and Simulations (\%)** \\ \hline \multirow{4}{*}{Backflashover} & BIL & L7 = L8 & 36.4 \\  & BIL & L9 & 36.3 \\  & BIL + 10\% & L7 = L8 & 29.3 \\  & BIL + 25\% & L9 & 29.0 \\  & BIL + 25\% & L7 = L8 & 19.6 \\  & BIL & L9 & 19.2 \\  & BIL & L7 = L8 & 68.4 \\  & BIL & L9 & 68.7 \\  & BIL + 10\% & L7 = L8 & 65.5 \\  & L9 & 66.7 \\  & BIL + 25\% & L7 = L8 & 60.8 \\  & BIL + 25\% & L9 & 61.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: The voltage magnitude and the percentage difference between CFO and simulation results. Figure 14: Voltage magnitude due to **(a)** backflashover, and **(b)** shielding failure activities.