# Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device
## 4 Test Results and Discussion
### Magnetic Field near Substation 1  
Substation 1 is intended to provide power for the active compensation coil. The working state of substation 1 tested is 323 kW power and 415 A current. The height of the measuring support from the ground is 1.1 m. The site photos are shown in Figure 5:  
We take nine test sample points at substation 1, which are from5 m (test point 1) to 25 m (test point 5) away from the substation working equipment, with a step length of 5 m (more points are selected around the critical point for testing). The test data are high-frequency filtered through the LabVIEW program, and the test results of the DC magnetic field are shown in Figure 6.  
Figure 4: Image of testing device: (1) fluxgate magnetometer probe, (2) PC, (3) acquisition board.  
Figure 5: Image of substation 1.  
According to the test results, substation 1 at test point 1 has a large impact on the DC magnetic field, which is about 1.6 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 15 m (point 5), decays to the Earth's magnetic field level. In the simulation calculation, the geomagnetic field value obtained from the actual test is added through the \"background field\" function of the finite element simulation software, and the test results are similar to the simulation results.  
At the same time, in order to obtain the influence of magnetic field fluctuation, the Mag-03 magnetic flux gate (noise lower than 6 ptrms/hz\({}^{1/2}\)@1 Hz; the bandwidth is up to 3 kHz (- 3 dB), and the measurement accuracy is less than 0.1 nT) is used to collect and record the real magnetic field before filtering (the sampling frequency is 1000 Hz), and a spectrum diagram is drawn (according to the sampling law, the frequency of concern is less than 500 Hz, and in order to obtain effective data and avoid clutter interference, the spectrum diagram is processed at an average of 1 Hz). Figure 7 shows the spectrum analysis diagrams of the east-west, north-south, and vertical to the ground magnetic fields of test point 1. Figure 8 shows the spectrum analysis of the three-axis magnetic field at test point 3.  
According to Figure 7, it can be found that the magnetic field near the power frequency (50 Hz) of test point 1 of substation 1 is large and has an impact on multiple frequency bands. The source of non-50 Hz harmonic peak is the multiple frequency interference of 50 Hz, which may be due to the nonlinear load (demagnetization coil and active compensation coil of magnetic shielding device) in the substation, is the main cause of harmonic generation, and the harmonic current generated by the substation causes the multiple frequency interference of magnetic field fluctuations. According to Figure 8, it can be found that the impact of power frequency and other frequency bands is reduced at three test points 15 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 1.  
Figure 6: DC magnetic field test results of substation 1.  
According to the spectrum data, the magnetic field generated by substation 1 is mainly the power frequency magnetic field. When the test point is 15 m away from the substation, the magnetic field fluctuation is reduced by about 70%. Based on the analysis of DC magnetic field and fluctuating magnetic field, when substation 1 is used, the construction site of the magnetic shielding device should be at least 15 m away from the radius of substation 1.