# Research on Ultra-Fast Transient Overvoltage Characteristics of Electric Locomotive
## 3 Testing Results  
Tables 2-4 list the overvoltage amplitude in different rounds. For divider A, the trigger level of the high-speed oscilloscope is set as 51.60 kV, and it turns out to be 5.10 kV for divider B. '/' indicates that the oscilloscope is not triggered, or the tested overvoltage on the high-voltage terminal is lower than the trigger level. According to the field test results, the operating overvoltage amplitude of point 1 is between 112.40 kV and 328.60 kV, while test points 2, 3, 4 are relatively low, only in the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Operation** & \multicolumn{2}{c}{**Pantograph Lifting**} & \multicolumn{2}{c}{**Main Breaker Closing**} & \multicolumn{2}{c}{**Main Breaker Opening**} & \multicolumn{2}{c}{**Pantograph Dropping**} \\ \hline
**Test Point** & **1** & **5** & **1** & **5** & **1** & **5** & **1** & **5** \\ \hline
7 & 193.47 & 11.60 & / & / & / & / & 253.70 & 15.97 \\
8 & 185.23 & 10.74 & 90.78 & 40.54 & / & / & 236.33 & 13.40 \\
9 & 184.63 & 10.17 & 103.40 & 43.90 & / & / & 305.60 & 18.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the third round of test (unit: kV). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Operation** & \multicolumn{2}{c}{**Pantograph Lifting**} & \multicolumn{2}{c}{**Main Breaker Closing**} & \multicolumn{2}{c}{**Main Breaker Opening**} & \multicolumn{2}{c}{**Pantograph Dropping**} \\ \hline
**Test Point** & **1** & **2** & **1** & **2** & **1** & **2** & **1** & **2** \\ \hline
1 & 155.72 & 7.41 & 112.43 & 7.39 & 155.09 & 50.15 & 222.46 & 8.03 \\
2 & 176.1  
range of 46.80 kV to 50.20 kV. To further study the relationship between the operational conditions and the overvoltage amplitude, Table 5 summarizes the peak overvoltage and steepness of the four operations in all test rounds. It shows that the peak overvoltage occurs during the main breaker closing process, where the amplitude is up to 328.60 kV and the corresponding steepness is 39,470.00 kV/us. During the pantograph lifting and main breaker closing operation, the overvoltage steepness range is 25,000.00-40,000.00 kV/us, which is much higher than that of the main breaker opening and pantograph dropping operation (5000.00-22,000.00 kV/us). The field test results of the overvoltage are 2-3 times higher than existing research results, and the steepness is about \(10^{6}\) times higher than current studies. Such high-amplitude and high-steepness operating overvoltage poses a serious threat to the insulation of high-voltage equipment of electric locomotives. In the standard GB/T 24837-2009 [11], the operating overvoltage is defined as a voltage with a wavefront time of 250 us and a half-peak time of 2500 us. In the standard IEC 60071-4 [12], VFTO is defined as the time to rise to the first peak in the range of 3 ns to 100 ns, the frequency of the fast oscillation part in the range of 0.3 MHz to 100 MHz, and the amplitude as high as 300.00 kV. In this paper, the characteristics of the test data are closer to the high-amplitude and high-steepness characteristics expressed by VFTO, so it can be considered that the measured overvoltage is a very fast transient overvoltage existing in the high-voltage system of the electric locomotive. Figure 5 shows the corresponding overvoltage waveforms based on data in Table 5. Since there is a main breaker among test points 2, 3, 4 and test point 1, the equivalent capacitance of the vacuum gap between the breaker contacts is small, and the equivalent impedance is large. Thereby, the overvoltage transmission is effectively blocked, resulting in a much smaller overvoltage amplitude of test points 2, 3, 4 than test point 1. In Figure 5a,d, there are multiple arc reignition phenomena in the overvoltage waveform during the pantograph lifting and dropping process. During the pantograph lifting, the peak overvoltage usually appears in the first arc stage and the overvoltage amplitude of arc reignition decreases along with time.