Research On The Conductive Mechanism Of Capillary And The Influencing Factors Of Impedance

With the rapid development of UHV transmission systems,the grounding system has more and more problems in subway stray current,high resistance of frozen soil,DC grounding,etc.At the same time,the short-circuit current of substations has also increased correspondingly.The grounding grid requirements of substations are also higher.The impedance characteristic of the grounding system is mainly determined by the electrical conductivity of the soil,so it is necessary to study the electrical conductivity of the soil.Existing studies have shown that multiple factors such as porosity,ion concentration,ion type,water content,and solid particle diameter affect the impedance characteristics of soil.However,the existing research mainly focuses on the movement characteristics of the fluid in the capillary,and there are few studies on the migration characteristics of the charged particles.Most of the current researches analyze the influence of a single factor on the electrical conductivity of soil from a macroscopic perspective,and the electrical conductivity mechanism of soil pores is not yet clear.This article focuses on the following aspects:Since soil is a large and complex network of pores,the inner diameter of soil pores is at the nanometer level,and its pores have capillary effects.In this paper,capillary tubes are used to simulate soil pores and a capillary experiment platform is built to study the effects of capillary inner diameter,ion concentration,and ion type on the pore test.The influence of the frequency characteristics of the impedance.The study found that the smaller the inner diameter of the capillary,the greater the impedance of the pore sample;the lower the ion concentration,the greater the impedance;the heavier the relative atomic mass of the ion,the greater the impedance mode of the pore sample where the solution is located.Then,the reason for the experimental results is explained from the physical point of view of ion migration movement.This paper proposes a preliminary equivalent circuit model of an RLC capillary.The calculation method of the model parameters and their frequency variation are studied.It is found that regardless of the type of ionic solution and the inner diameter of the capillary,the resistance r decreases with increasing frequency.The smaller the inner diameter,the greater the resistance value.Large,the inductance value l is always negative as the frequency increases,and the absolute value of the inductance is larger at low frequencies and gradually decreases to near 0,and the smaller the inner diameter,the greater the absolute value of the inductance at low frequencies;RL branch impedance The angleφis always less than 0,and the absolute value ofφis gradually reduced to 0 and then increased as the frequency increases.In view of the negative value of inductance,this article proposes two hypotheses.One is that there is a parallel capacitor in the equivalent circuit model due to measurement error and the increase of the dielectric constant after adding the solution.This parallel capacitor causes the inductance to be negative.After analysis,the first hypothesis was eliminated.The second is that there is a series capacitance in the equivalent circuit due to the ion migration movement in the capillary.The positive and negative ion clusters in the capillary move in the opposite direction under the action of the electric field to form an internal capacitor C₂.The current flowing through the internal capacitor is the same as the current flowing through the resistance and inductance.Therefore,the internal capacitor C₂ should be connected in series with the rl branch.By analyzing the vector diagram of the new equivalent circuit with series capacitors,it is verified that there is a series capacitor in the original equivalent circuit,and the original equivalent circuit model is revised.Finally,based on the discovered series capacitive effect,this article also explored the influence of ion mass,pore diameter,and power supply frequency on the capacitive effect and the law of influence,and verified the correctness of the inference through experiments.