## 2 Arrester Temperature Rise Test
### Test Results and Analysis
#### 2.4.2 Temperature Rise Analysis under High-Current Impulse  
In the impulse current experiment, the impulse current waveform generated by the impulse voltage generator and the residual voltage of the arrester is shown in Figure 6.  
It can be seen from Figure 6 that the residual voltage amplitude is about 92 kV with an impulse current of 10 kA. As the temperature of the valve plate reaches 115 \({}^{\circ}\)C, it can accelerate the aging of the arrester. We stopped applying voltage and let it cool naturally  
Figure 5: Temperature test of the arrester under continuous operation voltage.  
Figure 6: Impulse current and residual voltage waveform.  
at this time, and then we observed the temperature changes in each channel, as shown in Figure 7.  
Figure 7 shows that the temperature distribution in each channel under the impulse current is similar to the continuous operating voltage. Among the five channels, channel 3 reached the highest temperature at 8500 s, which was 121.6 \({}^{\circ}\)C, and that in channel 1 was the lowest, which was 87.8 \({}^{\circ}\)C. The temperature distribution was high in the middle and gradually decreased to both sides, which is due to the uneven voltage distribution and the heat dissipation of the metal at both sides of the valve column.  
At the beginning stage of heating up, the temperature in each channel increased slowly. Subsequently, the temperature rise rates of channels 2, 3 and 4 were significantly accelerated, which may due to channels 1 and 5 being closer to the metal part and the heat conduction being faster than that in other channels. After the impulse experiment was stopped, the temperature overshoot was small and immediately began to decline slowly. From the declining trend, although channel 1 is close to the metal part, the temperature decrease rate is lower than that of the other channels; this is because a large amount of hot air gathered in the upper part, and there is only limited heat conduction through the metal end.  
In the experiment, the maximum temperature difference of the arrester at the same position at different times is 97.6 \({}^{\circ}\)C, and that at different positions at the same time is 33.8 \({}^{\circ}\)C. Before and after the experiment, the valve plate temperature difference is large, and the highest temperature exceeded 115 \({}^{\circ}\)C. The arrester will accelerate the aging of the valve plate under this condition. The EMU often suffers from operating overvoltage and lightning overvoltage, and the arrester will absorb a large amount of energy when the overvoltage amplitude is too large or there are multiple overvoltage shocks in a short time. With the increase in active power loss, the internal temperature rises sharply and eventually leads to thermal collapse.  
Based on the above study, under the continuous operation voltage, the energy absorbed by the arrester was small, the temperature increased by 5.2 \({}^{\circ}\)C within three hours and the temperature distribution of the internal valve plate was uniform. Under the action of high-current impulse, the energy absorbed by the arrester was large, the temperature rise reached 97.6 \({}^{\circ}\)C and the temperature varied greatly at different positions inside. Therefore, the study of the temperature distribution characteristics under the action of large impulse overvoltage is conducive to analyzing the cause of its faults. Since it is difficult to measure the internal temperature rise of the arrester under the action of actual overvoltage, the simulation method is adopted to carry out the relevant research.  
Figure 7: Arrester temperature test under impulse current.