# Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers
## 3 Research on Impulse Aging Characteristics of MOVs
### Accelerated Impulse Aging Test of MOVs  
We explored the impulse aging characteristic of MOVs by increasing the impulse current amplitude and changing the number of impulses per round. The changes in the parameters of the MOV were continuously recorded throughout the whole test. Due to the fact that the DCCB only acts when a fault occurs, it is mostly in a sleep state; thus, the  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline \(C\) (\(\upmu\)F) & 52 \\ \(L\) (\(\upmu\)H) & 4225.5 \\ \(R\) (\(\Omega\)) & 73.9 \\ \(U_{0}\) (V) & 11,268 \\ \hline \end{tabular}
\end{table}
Table 4: Partial parameters in impulse current test platform.  
Figure 5: Experimental waveform of the aging test platform: (**a**) impulse current waveform and residual voltage waveform of the MOV; (**b**) absorbed energy waveform of the MOV.  
impact of temperature on the sample during the impulse aging test was ignored in this study. The process for the aging test is displayed in Figure 6.  
The MOV valve sheets produced by the same manufacturer with similar initial static parameters were selected for the test. The test samples are labeled SD18/1411B, and the size is \(\Phi\)32 mm \(\times\) 31 mm, as shown in Figure 7.  
After cleaning and drying the MOV sample with anhydrous ethanol alcohol, the following tests were performed to explore the short-circuit impulse aging characteristics of the MOV valve sheets. Four current levels were determined for the test, which were 150 A, 175 A, 200 A, and 300 A.  
* Conduct multiple rounds of impulse tests with the impulse current amplitude of 300 A and one impulse per round;
* Conduct multiple rounds of impulse tests with varying impulse current amplitudes (150 A, 175 A, 200 A) and ten impulses per round;
* Conduct multiple rounds of impulse tests with an impulse current amplitude of 200 A and varying numbers of impulses per round (10, 15, 20).  
Figure 6: Flow diagram of aging tests.  
Figure 7: ZnO valve sheet.  
After each round of impulse, the MOV sample was cooled to room temperature before the next round of impulse.  
The aging degree of the MOV is generally determined according to the \"Operating Surge Protector Testing Standards\" published by Chinese standards press, and the MOV valve sheet is considered to be aged if the fluctuations of the U1 mA is more than 10% or leakage current IL is more than 20 \(\mu\)A. After each group of tests, we need to determine if the test sample has been damaged.  
If there was no damage to the test sample, the static parameters of the MOV in the low-current region were measured, which include voltage values \(U_{\rm 1 mA}\), \(U_{\rm 0\mbox{-}\rm 1 mA}\), and \(U_{\rm 0.01 mA}\), to explore the aging degree of the MOV during the impulse test. We also explored the aging degree of the MOV using some other factors, including the residual voltage ratio \(K\), the leakage current \(I_{\rm L}\) (0.75 \(U_{\rm 1 mA}\)), and the nonlinear coefficient \(\alpha\). If the test sample did not experience aging, we continued to perform the impulse aging test on the sample.  
If the test samples were damaged, their states were observed and recorded.