# Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device
## 4 Test Results and Discussion
### Magnetic Field near substation 2  
Substation 2 is designed to supply power to the degaussing coils. The working state of the tested substation 2 is 1630 kW. The height of the measuring support from the ground is 1.1 m. The site photos are shown in Figure 9:  
We take eleven test sample points at substation 2, which are from 10 m (test point 1) to 70 m (test point 7) away from the substation working equipment, with a step length of 10 m (more points are selected around the critical point for testing). The remanence test results after high-frequency filtering are shown in Figure 10 (DC data of magnetic field): \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test Point**} & \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}  & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz1/2)** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz1/2)** \\ \end{tabular} & \begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Amplitude** \\ **(nT/Hz1/2)** \\ \end{tabular} &
\begin{tabular}{c} **Frequency** \\ **(nT/Hz1/2)** \\ \end{tabular} \\ \hline Test point 1 (5 m) & 32.5 & 50 & 35.7 & 49.5 & 38.4 & 50.5 \\ Test point 5 (15 m) & 11.2 & 49.5 & 15.4 & 49.5 & 20.5 & 49.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Magnetic field spectrum analysis results of substation 1. Figure 8: Magnetic field spectrum diagram of test point 3. (**a**) \(\mathbf{B_{X}}\) point; (**b**) \(\mathbf{B_{Y}}\) point; (**c**) \(\mathbf{B_{Z}}\) point. Figure 7: Magnetic field spectrum diagram of test point 1. (**a**) \(\mathbf{B_{X}}\) point; (**b**) \(\mathbf{B_{Y}}\) point; (**c**) \(\mathbf{B_{Z}}\) point. According to the test results, substation 2 at test point 1 has a large impact on the DC magnetic field, which is about 2.4 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 60 m (point 8) decays to the Earth's magnetic field level, which is similar to the simulation results. Similarly, in order to obtain the influence of magnetic field fluctuation, 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 11 shows the spectrum analysis diagrams of the east-west, north-south, and vertical to the ground magnetic fields of test point 1. Figure 12 show the spectrum analysis of the three-axis magnetic field at test point 6. Figure 11: Magnetic field spectrum diagram of test point 1. (a) B\({}_{X}\) point; (b) B\({}_{Y}\) point; (c) B\({}_{Z}\) point. Figure 10: DC magnetic field test results of substation 2. Figure 9: Image of substation 2. According to Figure 11, it can be found that the magnetic field near the power frequency (50 Hz) of test point 1 of substation 2 is large and has an impact on multiple frequency bands. According to Figure 12, it can be found that the impact of power frequency and other frequency bands is reduced at six test points 60 m away. 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 2.  
According to the spectrum data, the magnetic field generated by substation 2 is mainly power frequency magnetic field. The magnetic field in the power distribution room fluctuates greatly, and the spectrum curve is raised as a whole. The maximum amplitude near 50 Hz can reach 1347.0 nT/Hz\({}^{1/2}\), indicating that substation 2 has a great impact on the space magnetic field. However, when the test point is 60 m away from the substation, the magnetic field fluctuation is reduced by about 90%.