Impedance Frequency Characteristics of Ions Electromigration in Soil Macropores

Abstract

Grounding is the key to power system operation, lightning protection and personnel safety, and soil impedance characteristics are the decisive factors for its performance. The electromigration of ions in soil pore water is a key element of its impedance characteristics, and macropores are the main channels to control the movement of water, characteristic ions and air in the soil. As the current passing through the grounding grid and the frequency components of the current show a diversified trend, it is necessary to study the migration of characteristic ions in the soil at multiple frequencies. Since chloride ion, calcium ion and magnesium ion are the main ions in soil pore water, this paper takes these three ions as the object, and prepares CaCl2 and MgCl2solutions with the same concentration to replace soil pore water; then insulating materials are used to build capillary models instead of soil pores. Different solutions are tested for frequency impedance characteristics under the same experimental conditions, and a control group experiment is performed to eliminate the influence of the experimental equipment. Because most of the soil electrical conductivity is now measured by soil resistivity, the data is processed to obtain the resistance frequency characteristic curves of the two solutions in the 0.4(mm) and 0.7(mm) pore models respectively. Combining the obtained experimental data with theoretical analysis, the following conclusions are summarized: Firstly, the ions make a cyclical reciprocating movement under an AC electric field, and its frequency is the same as the frequency of the external power supply. Secondly, the lighter ions have a longer movement distance in one cycle at low frequencies,, and the movements of the ions are close to in-situ vibration at high frequencies. This study revealed the frequency characteristics of the electromigration of ions in the pores of the soil, and explained the influence of the nature of some ions on the migration movement from some perspectives, and provided experimental basis for further research on the conductive mechanism of the soil and measures to reduce resistance.