## 5 Conclusions  
Based on the experiments and simulation, this paper studied the influence of overvoltage on the internal temperature rise of the arrester and explained the relationship between the overvoltage and the arrester burst. The arrester internal temperature rise test was designed, and the internal temperature rise characteristics of the normal arrester under power frequency overvoltage and high-current impulse were obtained. An electrothermal coupling model of the arrester was established. Research on the internal temperature rise characteristics of the arrester under the action of typical overvoltage under different contaminations was carried out. The conclusions are as follows:  
1. After working at a continuous operating voltage for 3 h, the maximum temperature of the arrester valve plate increases by 5.2 \({}^{\circ}\)C. In the impulse current experiment, the maximum temperature of the arrester increases by 97.6 \({}^{\circ}\)C. The valve plates near the  
Figure 20: The temperature distribution of the arrester under different air velocities. (**a**) Passing section overvoltage. (**b**) Steep impulse overvoltage. \begin{table}
\begin{tabular}{c c c} \hline \hline
**The Air Velocity (km/h)** & \(\mathbf{R_{e}}\) & \(\mathbf{h\) (W/(m\({}^{2}\cdot\)K))** \\ \hline
50 & \(1.1\times 10^{5}\) & 50.3 \\
150 & \(3.3\times 10^{5}\) & 112.2 \\
250 & \(5.5\times 10^{5}\) & 168.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Air heat transfer coefficient at different flow rates. two sides of the arrester dissipate heat faster and have a lower temperature. Applying multiple large currents continuously may cause harm to the roof arrester. 2. The simulation results showed that, under the action of passing section overvoltage and steep impulse overvoltage, the internal temperature of the normal arrester reached 36.57 \({}^{\circ}\)C and 241 \({}^{\circ}\)C, respectively, in a short time. Under the action of high-harmonic overvoltage, the temperature rise was only 0.2 \({}^{\circ}\)C. This indicated that the high-amplitude overvoltage may be the main reason for the heat of the arrester. 3. When the valve plate had electric tree defects, the internal temperature rise of the arrester was small under the action of high-harmonic overvoltage. Under the action of passing section overvoltage and steep impulse overvoltage, the temperature increases obviously with the number of defective valve plates, and the maximum temperature reaches 536 \({}^{\circ}\)C when the number of defective valve plates is 3. 4. With the increase in air velocity, the internal temperature of the arrester decreased slightly under the passing section overvoltage and steep impulse overvoltage, so the EMU running at high speed has little influence on the internal temperature rise of the arrester under the action of overvoltage. 5. The internal simulation temperature of the normal arrester and the defective arrester under the action of the steep impulse overvoltage was 8 times and 18 times that of the internal temperature of the arrester under the action of the power frequency overvoltage, respectively, which indicated that the roof overvoltage will not only accelerate the performance deterioration of the arrester but even lead to thermal collapse. The passing section overvoltage and steep impulse overvoltage have high amplitudes and many occurrences, so the roof overvoltage of the EMU is an important reason for the arrester burst. Conceptualization, S.W. and Q.O. ; methodology, S.L. and H.L. ; software, S.M. ; validation, Q.O. ; formal analysis, S.L. ; investigation, Q.Z. ; resources, J.L. ; data curation, S.W. ; writing--original draft preparation, Q.O. and S.W. ; writing--review and editing, Q.O. and S.W. ; visualization, Q.Z. ; supervision, S.W. ; project administration, F.L. ; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.