## 4 Simulation Analysis
### Analysis of Simulation Results  
#### 4.2.1 TT Configuration Ground Fault Analysis  
Within the simulation model, an earth fault is induced at the termination of phase A on line 1, with a fault resistance of 1 k\(\Omega\). To facilitate a comprehensive comparison, the inherent residual current of line 1 is standardized at 200 mA, uniformly distributed along both the line and the load. The residual current levels at the beginning, middle, and end of the line during the occurrence of the earth fault are meticulously recorded. The outcomes of this analysis are visually presented in Figure 7.  
From Figure 7, it is evident that the inherent residual current decreases as it nears the end of the line, with the residual current close to 200 mA at the head end and minimal mutation of the residual current post fault. Traditional residual current protection methods such as amplitude comparison and protection techniques relying on amplitude and phase discrimination based on the residual current amplitude prove to be largely ineffective. This observation underscores the challenges of activating intermediate and general protection upstream of the site and the issue of low sensitivity. Notably, closer to the end position,  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Equipment** & **Types** & **Parameters** \\ \hline \multirow{4}{*}{Transformer} & \multirow{4}{*}{10 kV/0.4 kV} & Configuration: A/Y \\  & & Capacity: 1250 kVA \\  & & No-load loss: 1.36 kW \\  & & No-load current percentage: 0.27\% \\  & & Short-circuit loss: 12 kW \\  & & Short-circuit voltage percentage: 4.5\% \\ \hline \multirow{2}{*}{Power line} & \multirow{2}{*}{YIV-0.6/1 kV} & Conductor cross-section: 16 mm \\  & & Direct current resistance: \textless{1.15}\)ohm/km \\ \cline{1-1}  & & Carrying capacity: 100 A \\ \hline \hline \end{tabular}
\end{table}
Table 1: The parameters of main equipment.  
Figure 6: Schematic of ground fault in low-voltage distribution network.  
where the inherent residual current is lower, the mutation in the residual current amplitude due to a fault becomes more pronounced, showcasing improved performance with the existing protection methods.  
An earth fault is introduced in the middle phase of line 1 with a grounding resistance of 1 k\(\Omega\). The closed section for residual current, as depicted in Figure 6, is established with terminals at positions A, B, and C, and the corresponding waveform data are presented in Figure 8.  
Upon comparing subfigures (a) and (b), it becomes apparent that the residual current within the closed section remains minimal in the absence of faults. Following a fault occurrence, the fault current is more accurately reflected, effectively mitigating the impact of the inherent residual current and relying solely on the upstream monitoring point. It is evident that the single-point residual current protection method lacks sensitivity compared to closed-section residual current protection, as the amplitude current experiences insignificant changes pre and post fault. Notably, the residual current amplitude after the fault in Figure 8a is measured as 255 mA, while in Figure 8b, it reaches 296 mA. By combining the inherent residual current with the fault current, a partial cancellation occurs, reducing the fault current amplitude. This aligns with the earlier observation that the phase angle of the fault current is arbitrary. Consequently, the closed-section residual current protection demonstrates higher reliability and resistance to transitional variations.  
Figure 7: Residual current distribution along the line during terminal leakage fault: (**a**) residual current waveform at the head end of line 1 in the TT configuration after the fault; (**b**) residual current waveform in the middle of line 1 in the TT configuration after the fault; (**c**) residual current waveform at the end of line 1 in the TT configuration after the fault.