# Application of Surge Arrester in Limiting Voltage Stress at Direct Current Breaker
## 5 Experimental and Simulation Results
The current zero-crossing time is 5.5 ms and 8.5 ms for 280 V and 500 V tests, respectively, in this case. It is important to note that diodes D1 and D2 may not turn on in the absence of any voltage-restricting strategy at the breaker's input terminals. Figure 5: Conventional Breaker. Figure 6: (**a**) Conventional DCCB configuration, (**b**) fault current disruption under 260 V and 500 V tests. Case 3: Hybrid DCCB with surge arrester  
The proposed hybrid DCCB equipped with a surge arrester is used in this case (see Figure 1). As explained in Case 2, SW2 operates faster than SW1 upon the starting of the current disruption, leading to a voltage rise at C2 (\(V_{\text{C2}}\)) and the conduction of diode D1 (Stage 2). However, the surge arrester in this case provides a current path for the upstream current, leading to a reduced breaker terminal voltage at which the SW2 voltage is clamped; thus, \(V_{\text{C2}}\) overvoltage is controlled. Next, the downstream current loops around the RL circuit comprising SW1, D1, and downstream inductance, since SW1 has not opened yet (Stage 3). Subsequently, SW1 opens, leading to a risen \(V_{\text{C1}}\) and the turning of D2 (Stage 4), which in turn clamps \(V_{\text{C1}}\) at the breaker input-terminal voltage (surge-arrester voltage), which has started to fall at this point. Thus, the downstream current flows back into the surge arrester via an RL circuit comprising D2, downstream inductance, D1, and the surge arrester (Stage 5). The peak capacitor voltages (switch voltages) in this case are 420 V and 805 V for 280 V and 500 V tests, respectively, compared to 700 V and 1100 V in Case 2. The current zero-crossing times are 4.5 ms and 9.6 ms for the 280 V and 500 V tests, respectively, which are comparable to those of Case 2 and are significantly improved compared to those in Case 1 (see Figure 8). A longer arc at SW1 causes a delay in the operation of the proposed breaker, as well as a longer disruption time in this case. Note that some overvoltage is still present due to the characteristics of the selected surge arrester, but it is significantly less than that in the original hybrid DCCB [11] and there is a significant arc reduction compared to the mechanical breaker alone. In summary, the proposed hybrid DCCB has an improved downstream voltage and clearing time due to the bypassing capacitors, which provide soft switching in the mechanical switches, redirect diodes that restrict the capacitor voltages, and impose negative voltage on the downstream inductance, and the surge arrester, which prevents a voltage rise at the DCCB input terminals. Figure 8: The voltages and current during fault disruption using the proposed hybrid DCCB with the surge arrester of Figure 1b under initial (**a**) 280 V and (**b**) 500 V supplies. Figure 7: The voltages and current during fault disruption using the original hybrid DCCB [11] under (**a**) 280 V and (**b**) 500 V supplies. Case 4. Simulation results  
In the following, the hardware test results are compared with those from the simulation model using MATLAB/Simulink (R22b). A surge-arrester model is adopted that is described by  
\[\frac{V_{SA}}{V_{ref}}=K_{i}\left(\frac{I_{SA}}{I_{ref}}\right)^{\frac{1}{k_{i}}}, \ i=1,\ 2,\ \text{and}\ 3 \tag{10}\]  
where index \(i\) corresponds to any of the three operating regions in the V-I characteristics of the surge arrester, as depicted by Figure 9[24]. The surge arrester majorly operates in regions 2 and 3. The reference voltage \(V_{ref}=300\) V (the test voltage) and manufacturer value for reference current \(I_{ref}=150\) A are considered. From the experimental results of 280 V tests, parameters \(K_{1}=0.95\), \(K_{2}=1\), and \(K_{3}=0.9915\) and \(\alpha_{1}=50\), \(\alpha_{2}=4\), and \(\alpha_{3}=1.5\) are obtained. These parameters are then used to run the simulations for the 500 V test, where two surge arresters are put in a series similar to in the hardware tests. This, in turn, leads to \(V_{ref}=600\) V and \(I_{ref}=150\) A.