# Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers
## 3 Research on Impulse Aging Characteristics of MOVs  
### Construction of MOV Impulse Aging Test Platform  
The schematic diagram of the test platform is illustrated in Figure 3. The impulse test platform mainly relies on the lightning impulse wave A-wave module that was independently developed by the Institute of Power Electronics Specialized Equipment of Xi'an Jiaotong University. Figure 3: Schematic diagram of the aging test platform. T\({}_{1}\): Regulator, T\({}_{2}\): high-voltage transformer, D: High-voltage rectifier, R\({}_{0}\): Current-limiting resistor, C: Energy storage capacitor, G: Isolation gap, Modulation resistor, Modulation inductor, R\({}_{1}\), R\({}_{2}\): Resistor divider, R\({}_{3}\): splitter. Figure 2: Voltage and current waveforms of hybrid DCCB in dynamic simulation model. The specific process for impulse aging test is as follows. At the beginning, the capacitor bank \(C\) is charged by the DC charging device. When the charging voltage of the capacitor bank \(C\) reaches the set value, the trigger impulse control signal is output, and the discharge gap G breaks down instantly to connect the discharge circuit. Then, the capacitor bank \(C\) discharges to the test sample MOV through the wave-regulating resistor \(R\) and wave-regulating inductance \(L\), forming the impulse current waveform that we need. The impulse current waveform is measured by a Rogowski Coil, while the residual pressure of the MOV valve sheet is measured by the voltage divider. The impulse current waveform and the residual voltage waveform are recorded by the Tektronix DPO 3012 oscilloscope. The static parameters and leakage current \(I_{\mathrm{L}}\) of the MOV valve sheet are measured using the MOV-III zinc oxide resistor sheet parameter tester developed independently by the Institute of Power Electronics Specialized Equipment of Xi'an Jiaotong University. The parameters of the impulse current waveform and the elements in the current generator circuit are designed according to the simulation results. The short impulse current waveform flowing through the MOV, which is magnified from Figure 2, is illustrated in Figure 4.  
It can be seen from Figure 4 that the maximum current \(I_{\mathrm{MOV-max}}\) flowing on the MOV is 136 A. The wave front time of impulse current \(T_{1}=135\)\(\upmu\)s, and the half-peak time of the impulse wave tail \(T_{2}=2970\)\(\upmu\)s, and \(T_{2}/T_{1}\) is 22. So, the impulse current generator is set to generate an impulse current with the amplitude of 150 A (\(i_{\mathrm{m}}\)) and waveform of 135 \(\upmu\)s/2970 \(\upmu\)s for the impulse aging test. According to the \"Pulse Current Technology\" published by Xi'an Jiaotong University, the normalized solution of the impulse current waveform is calculated as follows: the damping coefficient of the impulse current circuit \(\zeta=4.2\), normalized wavefront time \(T_{1}\)* = 0.288, and normalized current \(i_{\mathrm{m}}\)* = 0.12. The circuit parameters (capacitance \(C\), inductance \(L\), total circuit resistance \(R\), and charging voltage \(U_{0}\) of capacitance \(C\)) can be calculated through Formulas (2)-(4). \[i_{m}^{*}=i_{m}/\frac{U_{0}}{\sqrt{L/C}} \tag{2}\]  
Figure 4: Simulation impulse current waveform of the MOV: (**a**) impulse current waveform; (**b**) apparent wave front time T\({}_{1}\) of impulse current; (**c**) apparent time T\({}_{2}\) of half peak of impulse wave tail.