# Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers
## 3 Research on Impulse Aging Characteristics of MOVs
### Result and Discussion
Figure 9: The relationship between various parameters and the impulse number n under different impulse current amplitudes: (**a**) the impulse number n and various voltage change rates; (**b**) the impulse number n and leakage current \(I_{\mathrm{L}}\); (**c**) the impulse number n and residual voltage ratio \(K\); (**d**) the impulse number n and non-linear coefficient \(\alpha\). As shown in Figures 3-8 and 9, the leakage current \(I_{\rm L}\) showed a rising trend and its value increased to 10.60 \(\upmu\)A before the test samples were damaged. Regarding the 175 A-10 group of samples, it can be seen from Figures 3-8 and 9 that test samples were damaged after 590 impulses. During the 590 impulses before the samples were damaged, \(U_{\rm 1 mA}\) first slightly increased and then showed a decreasing trend, with its value increasing by a maximum of 5.77% compared to its initial value. \(U_{\rm 0.1 mA}\) firstly increased and then had a decreasing trend, with its value decreasing by 2.07% compared to its initial value. \(U_{\rm 0.01 mA}\) voltage changed with a decreased trend, with its value decreased by 13.61% compared to its initial value. As shown in Figures 3-8 and 9, the leakage current \(I_{\rm L}\) showed a rising trend and its value increased to 17.90 \(\upmu\)A before the test samples were damaged. Regarding the 200 A-10 group of samples, it can be seen from Figures 3-8 and 9 that test samples were damaged after 620 impulses. During the 620 impulses before the samples were damaged, \(U_{\rm 1 mA}\) first slightly increased and then showed a decreasing trend, with its value increasing by a maximum of 2.94% compared to its initial value. \(U_{\rm 0.1 mA}\) had a decreasing trend, with its value decreasing by 5.86% compared to its initial value. \(U_{\rm 0.01 mA}\) voltage changed with a decreasing trend, with its value decreasing by 13.50% compared to its initial value. As shown in Figures 3-8 and 9, the leakage current \(I_{\rm L}\) showed a rising trend and its value increased to 18.67 \(\upmu\)A before the test samples were damaged. The change rate of the \(U_{\rm 1 mA}\) of the three test samples in groups 150 A-10, 175 A-10, and 200 A-10 did not exceed \(\pm\)10%, and \(I_{\rm L}\) also did not exceed 20 \(\upmu\)A. After the samples were damaged, the voltage value in the low-current region rapidly decreased to nearly 0 A, and the MOV valve sheet no longer had insulation performance. The leakage current \(I_{\rm L}\) value rapidly increased to 249.8 \(\upmu\)A. From Figure 9, it can be seen that the residual voltage ratio \(K\) of the three groups of samples showed a trend of first decreasing and then increasing with the number of impulses n. Before applying the 30 th, 220 th, and 20 th impulses, the residual voltage ratio \(K\) of the three groups of samples showed a decreasing trend, and, after this, the residual voltage ratio of each group showed a slight increase. During the process of applying the 30 th, 220 th, and 20 th impulses to the three groups of samples (the initial stage of impulse aging), due to the electron trap process, \(U_{\rm 1 mA}\) increased slightly macroscopically, while \(U_{\rm res}\) remained basically unchanged, resulting in a decrease in the residual voltage ratio \(K\), which can still be explained by the dual Schottky barrier distortion. From Figure 9, it can be seen that the nonlinear coefficient \(\upalpha\) of the three groups of samples showed a trend of rapid decrease followed by a stable decrease with the increase in the number of impulses. During the impulse process, when the value of the nonlinear coefficient \(\upalpha\) is less than 30, it can be regarded as starting to age under the impulse current. In the whole impulse process, for the 150 A-10 group, the nonlinear coefficient \(\upalpha\) decreased rapidly from 40.5 to 28.8 in the first 60 impulses, and then decreased slowly from 28.8 to 22.3 from the 60 th to 430 th impulses.