# Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers
## 3 Research on Impulse Aging Characteristics of MOVs
### Result and Discussion
For the 175 A-10 group, the nonlinear coefficient \(\upalpha\) decreased rapidly from 43.4 to 29.4 in the first 30 impulses, and then decreased slowly from 29.4 to 19.2 from the 30 th to 590 th impulses. For the 200 A-10 group, the nonlinear coefficient \(\upalpha\) decreased rapidly from 42.9 to 29.8 in the first 30 impulses, and then decreased slowly from 29.8 to 18.0 from the 30 th to 620 th impulses. Therefore, the 150 A-10, 175 A-10, and 200 A-10 groups can be regarded as starting to age under the 60 th, 30 th, and 30 th impulses, respectively. By comparing the changes in the nonlinear coefficient \(\upalpha\) of the samples under the three impulse conditions, it can be found that the larger the amplitude of the impulse current, the fewer impulses are needed to make \(\upalpha\) less than 30, and the faster the aging speed. At the same time, when \(\upalpha\) is less than 30, the change rate of \(U_{\rm 1 mA}\), the change rate of \(U_{\rm 0.01 mA}\), and \(I_{\rm L}\) of the three groups of samples were 3.23%, 0.87%, \(-\)2.82%, and 5.4 \(\upmu\)A; 3.21%, 0.62%, \(-\)3.2%, and 4.8 \(\upmu\)A; and 1.96%, \(-\)0.40%, \(-\)1.75%, and 5.37 \(\upmu\)A, respectively. None of these parameters reached the commonly used aging judgment criteria, especially after the samples were damaged, and none of the parametersreached the standard values. Therefore, conventional methods for judging the aging and impulse aging degree of MOVs have obvious delays. Test 3: Impulse current amplitude of 200 A and the number of impulses per round is 10, 15, and 20. Nine MOV samples with similar initial parameters were selected and divided into three groups (200 A-10, 200 A-15, 200 A-20). Each group contained three samples. Multiple rounds of impulse aging were conducted on each test sample of the 200 A-10 group, 200 A-15 group, and 200 A-20 group using an impulse current generator that produces the impulse current with an amplitude of 200 A. The DC static parameters of the test samples were tested after each round of impulse by changing the number of impulses, and the \(U_{\mathrm{1 mA}}\), \(U_{\mathrm{0-1 mA}}\), and \(U_{\mathrm{0,01 mA}}\), and \(I_{\mathrm{L}}\) of the test samples were recorded. The change rate of static parameters in the low-current region, residual voltage ratio \(K\), and non-linearity coefficient \(\alpha\) were calculated. Since the recorded data trends for each parameter of the three groups of samples were similar, the data of one sample from each group was selected to plot the relationship curves between the change rate of DC static parameters in the small current region, leakage current \(I_{\mathrm{L}}\), residual voltage ratio \(K\), nonlinear coefficient \(\alpha\), and the number of impulses n under different impulse times per round, as shown in Figures 3-9 and 10a-d. The initial values of each parameter were as follows: \(U_{\mathrm{0,01 mA}}=5.133\) kV, \(I_{\mathrm{L}}=2.47\)\(\mu\)A, \(K=1.31\), \(\alpha=42.9\). It can be seen from Figures 3-9 and 10a that the test samples of the group of 200 A-10 were damaged after 620 impulses. During the 620 impulses before the samples were damaged, \(U_{\mathrm{1 mA}}\) first slightly increased and then showed a decreasing trend, with its value increasing by a maximum of 2.94% compared to its initial value. \(U_{\mathrm{0-1 mA}}\) had a decreasing trend, with its value decreasing by 5.86% compared to its initial value. \(U_{\mathrm{0.01 mA}}\) voltage changed with a decreasing trend, with its value decreasing by 13.50% compared to  
Figure 10: The relationship between various parameters impulse number n under different impulse per round: (**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 \(\alpha\). its initial value.