# Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device
## 4 Test Results and Discussion
### Magnetic Field near substation 3  
Substation 3 is designed to provide power together inside the magnetic shielding device. The working state of the tested substation 2 is 9 kW. The height of the measuring support from the ground is 1.1 m. The site photos are shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test Point**} & \multicolumn{2}{c}{**B\({}_{\mathbf{X}}\) (East-West)**} & \multicolumn{2}{c}{**B\({}_{\mathbf{Y}}\) (Vertical to the Ground)**} & \multicolumn{2}{c}{**B\({}_{\mathbf{Z}}\) (North–South)**} \\ \cline{2-7}  & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} &
\begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} \\ \hline Test point 1 (10 m) & 369.1 & 49.5 & 887.0 & 49.5 & 1347.0 & 49.5 \\ Test point 8 (60 m) & 12.1 & 48.5 & 18.3 & 48.5 & 35.3 & 48.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Magnetic field spectrum analysis results of substation 2. Figure 12: Magnetic field spectrum diagram of test point 8. (**a**) B\({}_{X}\) point; (**b**) B\({}_{Y}\) point; (**c**) B\({}_{Z}\) point. Figure 13: Image of substation 3. We take seven test sample points at substation 3, which are 1 m (test point 1) to 10 m (test point 3) away from the substation working equipment, with a step length of about 5 m (more points are selected around the critical point for testing). The remanence test results after high-frequency filtering are shown in Figure 14 (DC data of magnetic field):  
According to the test results, substation 3 at test point 1 has a large impact on the DC magnetic field, which is about 1.7 times that of the Earth's magnetic field. When the distance between the test point and the substation increases, the magnetic field gradually decreases, and at about 5 m (point 4), decays to the Earth's magnetic field level, which is similar to the simulation results. Similarly, in order to obtain the magnetic field contribution of each frequency band, the Mag-03 fluxgate is used to collect and record the real magnetic field before filtering (the sampling frequency is 1000 Hz), and the spectrum diagram is drawn. Figure 15 shows the spectrum analysis diagrams of the east-west, north-south, and vertical to the ground magnetic fields of test point 2. The maximum amplitude in the magnetic field spectrum of each direction of the test point and frequency corresponding to the maximum amplitude in the test frequency band are listed in Table 3.  
Figure 14: DC magnetic field test results of substation 3. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{2}{c}{\(\mathbf{B_{X}}\) (East-West)} & \multicolumn{2}{c}{\(\mathbf{B_{Y}}\) (Vertical to the Ground)} & \multicolumn{2}{c}{\(\mathbf{B_{Z}}\) (North–South)} \\ \cline{2-7}
**Test Point** & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz\({}^{1/2}\))** \\ \end{tabular} &
\begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} \\ \hline Test point 4 & 11.9 & 49.5 & 14.9 & 49.5 & 20.2 & 49.5 \\ \hline \end{tabular}
\end{table} 
Table 3: Magnetic field spectrum analysis results of substation 3. Figure 15: Magnetic field spectrum diagram of test point 2. (**a**) \(\mathbf{B_{X}}\) point; (**b**) \(\mathbf{B_{Y}}\) point; (**c**) \(\mathbf{B_{Z}}\) point.