## 4 Verification of Self-generated Inductor Current Uniformity  
Even a minimal difference in the V-I characteristic curve can lead to a large deviation in the current between columns. According to the above simulation calculation, the self-generated inductor of the spiral core of the \(\pm\)550 kV DC GISA is calculated by simulation to be 6.4 \(\upmu\)H. The core can be regarded as three 6.4 \(\upmu\)H self-generated inductors connected in parallel by three columns, as shown in Figure 15.  
When a variable voltage is applied to the arrester, the current of each column changes, and the current of each column is different due to the difference in V-I characteristics. When the impulse current rapidly changes, a voltage drop occurs on the inductor. The greater the rate of change in the inrush current, the greater the voltage drop on the inductor. Due to the difference in the nonlinear V-I characteristics of the three columns of the arrester, the inductor voltage of the column with a more significant current change rate is larger, so the voltage of the ZnO varistor is smaller, and the current of the column decreases to achieve current uniformity, as shown in Figure 16.  
The function of the self-generated inductor of each column is to dynamically correct the current between the columns and reduce the uneven coefficient of current distribution between the columns. The arrester is simulated as three columns in parallel. The nonlinear V-I characteristics of each column are set to make the coefficient of the current distribution different. The 1 mA reference voltage of the ZnO varistor columns is set to 600 kV, 640 kV, and 680 kV, respectively. The three-column current distribution characteristic curve is plotted when a variable voltage is loaded for the three-column parallel arrester.  
Figure 14: Three-dimensional temperature distribution of \(\pm\)550 kV DC GISA.  
Figure 15: Topology diagrams of a linear structure and a spiral structure of a \(\pm\)550 kV DC GISA. (**a**) is the topology diagram of the linear structure. (**b**) is the topology diagram of the spiral structure.  
Figure 17a shows the current distribution of the three-column arrester with a linear structure; Figure 17b shows the current distribution of a three-column arrester with a spiral structure (6.4 \(\upmu\)H inductor in series).  
Three identical moments are selected to calculate the non-uniform current distribution coefficient and current deviation coefficient of the three columns in parallel. When the single-column has no inductor in series, the three-column currents corresponding to t\({}_{1}\) are 10.732 kA, 11.435 kA, and 12.119 kA; the three-column currents corresponding to t\({}_{2}\) are 10.464 kA, 11.122 kA, and 11.844 kA; and the three-column currents corresponding to t\({}_{3}\) are 10.152 kA, 10.854 kA, and 11.531 kA. The current deviation coefficients for these three moments are 10.61, 10.63, and 1.063, respectively. When the single column has a 6.4 \(\upmu\)H inductor in series, the three-column currents corresponding to t\({}_{1}\) are 10.021 kA, 10.252 kA, and 10.474 kA; the three-column currents corresponding to t\({}_{2}\) are 10.665 kA, 11.192 kA, and 11.698 kA; and the three-column currents corresponding to t\({}_{3}\) are 10.374 kA, 10.985 kA, and 11.442 kA. The current deviation coefficients for these three moments are 1.021 kA, 1.044 kA, and 1.045 kA, respectively. The current deviation coefficients of the three moments in Figure 17a are 6.1%, 6.3%, and 6.3%. The current deviation coefficients of the three moments in Figure 17b are 2.1%, 4.4%, and 4.5%. The current deviation coefficients are reduced by 28-65%. The self-generated inductor of the spiral structure has a significant current-sharing effect on the multi-column parallel arrester.