# Evaluating the High Frequency Behavior of the Modified Grounding Scheme in Wind Farms
## 4 Simulation Results and Discussion
### Single Wind Turbine
#### 4.2.1 Indirect Strike  
The occurrence of indirect lightning strikes coming from the indirect effect of lightning discharges has recently received significant attention. This is due to the sensitive nature of the vital electronic equipment, which is highly vulnerable to such indirect effects. A study of the effect of indirect lightning on component voltage rates is presented next. Impact of the PMGS on transient overvoltages: This case study assumes that lightning with a peak current value of 10 kA and a duration of 10/350 us strikes the ground near the tower. The maximum overvoltages reach nearly 1.5 kV for both the LV side and the control circuit, which shows that this strike can be tolerated by the wind turbine without failure. Additionally, this amount is negligible for the HV side (see Figure 3). Figure 4 presents a comparison of previously-designed models (see Section 2.6) and the PMGS. At first glance, it is clear that transient voltages in the constant resistance model have the highest values, so that in the worst condition, they escalate to 36 kV at the control circuit. Like constant resistance, nonlinear resistance did not considerably diminish the rate of overvoltage on the LV side; however, the peak value was reduced by 30% on the HV side and at the control circuit. Despite improving the grounding model over the typical expanded grounding system, nonlinear resistance was unable to limit the peak value to the level that can be withstood by wind turbine equipment. In the best condition, the peak value decreased to 13 kV at the control circuit, which is still higher than the upper  
Figure 3: Impact of PMGS on transient overvoltages. (**a**) LV side of the main transformer; (**b**) HV side of the main transformer from node to ground; (**c**) control circuits. Figure 2: EMTP-RV circuit of the simulated single wind turbine with PMGS. limits. Finally, the PMGS seems to be successful in suppressing transient voltages that exceed upper limits, as the overvoltages reduce to 1.5 kV and 1.2 kV, respectively, on the LV side and at the control circuit. Moreover, the overvoltage is less than one hundred volts on the HV side, which is negligible. Impact of high-frequency surge arrester on transient overvoltages: Although using the PMGS leads to a significant reduction in the maximum overvoltage, there is still a great need to install a high-frequency SA to protect a wind turbine against lightning. Therefore, in this subsection, a 1-kV high-frequency SA is added, as shown in Figure 5, to verify its effect on the overvoltage. The simulation indicates similar results for the PMGS as in the previous subsection (see Section 4.2.1), and the high-frequency SA plays an important role in suppressing overvoltages and protecting the wind turbine from abnormal conditions (see Figure 6). As a result, further study of the combination of the PMGS and high-frequency SAs can lead to powerful protection against lightning and the resulting transition states. Figure 4: Comparison of different types of grounding schemes. Figure 5: Circuit of the simulated wind turbine with a surge arrester. Impact of frequency-dependent cable on transient overvoltages: In this section, the FD cable model is added between the generator and the main transformer in order to see the effect of transient overvoltages beyond the PMGS effect (see Figure 7). Figure 8 shows that the peak voltages are confined within the allowable limit, less than 1.5 kV, so it can be concluded that the FD cable behavior regarding voltage reduction is similar to how an SA and the PMGS behave toward limiting voltage and preventing extreme breakdowns. As a result, its vital role in the wind turbine protection model cannot be ignored, and it will be attached to the wind turbine system with the PMGS, in addition to adding a high-frequency SA, in subsequent sections. Figure 6: Impact of high frequency SA on transient overvoltages. (a) LV side of the main transformer; (b) HV side of the main transformer from node to ground; (c) control circuits.