## 1 Introduction  
The roof arrester is an important piece of overvoltage protection equipment of the Electrical Multiple Unit (EMU) [1, 2, 3]. Due to the complex operating environment, its performance will gradually deteriorate or even form burst accidents [4, 5, 6]. According to statistics, from 2017 to 2021, a total of 12 arrester burst faults occurred in China's CRH5 EMUs. For example, the pressure-release vent of the arrester was burst on 21 December 2019. The on-site accident picture is shown in Figure 1.  
The internal temperature of the arrester may rise sharply under some types of overvoltage, leading to thermal collapse. In order to analyze the influence of overvoltage on the internal temperature rise of the arrester and whether it will cause the thermal collapse of the arrester, it is necessary to measure the on-site overvoltage waveform and study the internal temperature rise of the arrester so as to help explain the cause of the roof arrester burst. In view of the causes and characteristics of roof overvoltage and the thermal characteristics of the arrester, relevant scholars have carried out some studies. According to the theoretical analysis of the literature [7; 8], the pantograph is prone to the arc phenomenon when the EMU passes through phase separation, which will cause a sudden voltage increase and form a trapezoidal pulse. In the literature [9], the waveform of high-harmonic overvoltage was obtained from the field-measured data. The oscillation duration of overvoltage can be up to 2 min, and when the overvoltage amplitude is high, the roof arrester will burst. Since the metal oxide arrester (MOA) does not have clearance, the leakage current will flow through the valve plate under normal voltage, which will result in power loss and the valve plate heating [10; 11; 12; 13; 14; 15]. The literature [16] pointed out that the leakage current under overvoltage was the direct cause of the heating. In the literature [17], through the disassembly and inspection of the arrester, it was found that the causes of its abnormal heating are internal dampness, the aging of the valve plate and the contamination of the external insulation. In the literature [18], the internal hot spot and maximum temperature can be estimated by measuring the external temperature of the arrester. The literature [19] pointed out that the energy absorption process of MOA under the action of impulse current is an adiabatic temperature rise process. When the temperature is high enough, the material properties will change or even burn out. The literature [20] analyzed the temperature of the arrester through simulation and found that when the valve plate is damaged, its operating state can be judged by temperature. The literature [21] used COMSOL to establish the temperature field calculation model of the arrester and found that the internal temperature rise of the defective arrester was significantly higher than the external surface temperature rise, and there was a partial overheating phenomenon. Based on the above research status, it can be seen that the current research mainly focuses on the analysis of a single type of overvoltage waveform and the internal temperature rise of the arrester under the action of the working voltage. At present, there is still a lack of on-site overvoltage measurements and comprehensive statistical analyses of the roof overvoltage waveforms, along with a lack of research on the internal temperature rise of the arrester under the action of on-site measured overvoltage. Therefore, in this paper, experiments and simulation based on on-site measured overvoltage were carried out to study the relationship between overvoltage and the internal temperature rise of the arrester and conduct a comprehensive statistical analysis of the on-site-measured overvoltage, which can explain the relationship between the roof overvoltage and the arrester burst.