# Leakage Detection Method of Coal Mine Power Supply System Based on 3 AC
## 5 Conclusions  
A set of asymmetric three-phase capacitors with appropriate parameters are added at the head of the line of the power supply system, and a constant zero-sequence current is artificially generated in the system. This current can be effectively detected even when the symmetry of the three-phase insulation performance decreases, which is the core innovation of this method. The relationship formulas between \(\dot{U}_{0}\), \(R_{\mathrm{d}}\), and \(\dot{I}_{\mathrm{C0}}\) in seven typical leakage fault forms are derived by a mathematical model. The current phasor \(\dot{I}_{\mathrm{C0}}\) and system phase voltage phasor directly measured by sampling are substituted into seven formulas, respectively, and seven groups of resistance complex numbers are calculated and then screened according to the characteristics. The calculation results with a negative real part and an imaginary part are excluded, and then the results with the positive real part and imaginary part are compared. The real part of the 'complex resistance' corresponding to the minimum imaginary part is the real insulation resistance value, and the calculation formula corresponding to the calculation result is also the type of leakage fault that occurred in the system. This method can not only detect single-phase leakage fault but can also realize the detection of a three-phase uniform leakage fault and can determine the fault type and fault phase line. It is a new leakage protection method using simple hardware circuit to realize complex protection function. Although adding asymmetric three-phase capacitors at the beginning of the line may have some impact on the system, these impacts can be controlled through reasonable parameter selection and design. Moreover, in practice, the three-phase-to-ground distributed capacitance of a line is often inherently asymmetric. Therefore, adding an appropriate asymmetric capacitor at the beginning of the line would not cause significant issues. When designing the 3 AC leakage protection device, the key lies in selecting suitable, current transformers, voltage transformers, signal conditioning circuits, microcontrollers, and other necessary hardware components, and developing the correct computational logic to ensure the system's reliability and accuracy.  
Conceptualization, S.P., Y.W. and T.M.; Methodology, T.M.; Software, J.C.; Formal analysis, J.C.; Investigation, J.C. and T.M.; Writing--original draft, S.P.; Writing--review & editing, Y.W., J.C. and T.M.; Project administration, Y.W.; Funding acquisition, S.P. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Natural Science Foundation of China under Grant 52474188.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Theoretical Results**} & \multicolumn{2}{c}{**Simulation Result**} & \multirow{2}{*}{**Real Part: Imaginary Part (\%)**} \\ \cline{2-2} \cline{4-6}  & **Real Part** & **Imaginary Part** & **Real Part** & **Imaginary Part** & \\ \hline Formula (1) & \(-\)33,000 & 31,832 & \(-\)32,749 & 37,903 & removal \\ Formula (2) & 45,568 & 13,528 & 41,925 & 15,448 & 36.84 \\ Formula (3) & \(-\)9568 & \(-\)45,361 & \(-\)6198 & \(-\)42,994 & removal \\ Formula (4) & 6284 & 22,680 & 4587 & 21,675 & 472.51 \\ Formula (5) & 18,000 & \(-\)15,916 & 17,863 & \(-\)13,772 & removal \\ Formula (6) & \(-\)21,284 & \(-\)6764 & \(-\)19,474 & \(-\)7545 & removal \\ Formula (7) & 1000 & 0 & 992 & 119 & 12 \\ \hline \hline \end{tabular}
\end{table}
Table 9: If phase ABC leakage is 1 k\(\Omega\).  
**Conflicts of Interest:** Author [PERSON] was employed by the company State Grid Beijing Electric Power Company Maintenance Branch. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.