# Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device
## 2 FEM Results of Substation Magnetic Field Influence  
The magnetic shielding device usually consists of a passive shielding layer, an active compensation coil, and a degaussing coil. The passive shielding layer mostly uses soft magnetic materials such as permalloy to shield the magnetic field through the principle of flux diversion. The active compensation coil generates a magnetic field opposite to the Earth's magnetic field through [PERSON]'s law to offset the magnetic field. The degaussing coil is arranged on the passive magnetic shielding layer, the magnetic field generated by [PERSON]'s law makes the passive magnetic shielding reach the magnetic saturation state, gradually reduces the magnetic field, and reduces the influence of factors such as the stress of the passive magnetic shielding layer during installation on the shielding performance. The experiment was carried out in the internal extremely weak magnetic field space. Common measuring instruments include SERF atomic magnetometer, SERF atomic gyroscope, electric dipole moment test system, and so on. The structure is shown in Figure 1. Due to different applications, active compensation coils, degaussing coils, and instruments need power supplies with different power requirements, among which, the active compensation coils need long-term operation and stable power supplies, the degaussing coils need power supplies with high power and fast response, and the instruments need less power. Therefore, magnetic field analysis is conducted for 323 kW (active compensation coil), 1630 kW (degaussing coil), and 9 kW (instrument) substations according to different power demands. Through the finite element simulation software COMSOL, the finite element model of a substation is established, including primary coil, secondary coil, and iron core. The magnetic field generated by 323 kW, 1630 kW, and 9 kW substations is simulated by finite element method by changing the current and other parameters (the number of elements s is 58,000 (substation 1), 76,000 (substation 2), 27,000 (substation 3), and the current is 415 A  
Figure 1: Schematic diagram of magnetic shielding device. (substation 1), 3000 A (substation 2), and 15 A (substation 3), and the impact of different substations on the environmental magnetic field is analyzed. The three substations have the same type and use the same model for calculation. The current in the substation is modified by modifying the current value of the primary coil. The simulation results are shown in Figure 2, the unit of magnetic field is nT. According to the simulation results, the influence range of the magnetic field generated by the substation is analyzed. The magnetic field section is drawn through the 3D drawing group, and the magnetic field distribution is obtained. The magnetic field of the substation weakens at different speeds in different directions. In order to ensure that the magnetic field attenuates to a safe size under a certain radius, the radius is determined according to the maximum magnetic field value (to ensure that the maximum magnetic field value under the radius is less than the Earth's magnetic field). According to the analysis results, for substation 1 (323 kW), the magnetic field can be attenuated to a level close to the Earth's magnetic field (about 50,000 nT) beyond the radius of 15 m around the substation. For substation 2 (1630 kW), the magnetic field can be attenuated to a level close to the Earth's magnetic field beyond the radius of 60 m around the substation. For substation 3 (9 kW), the magnetic field can be attenuated to a level close to the Earth's magnetic field beyond the radius of 5 m around the substation. As shown in Figure 3, this result proves that the substation has an impact on the environmental magnetic field, and the impact attenuates with the increase in distance. Therefore, the construction of a magnetic shielding device must maintain a safe distance from its supporting substation. Figure 3: Influence range of substation environmental magnetic field.