Study on current density and conductivity mathematical model of SF6 under DC uniform field strength

Under the DC uniform electric field, the current density and conductivity of the SF₆ gas can be divided into three regions, namely, ohm conduction region, saturation current region and current surge region. However, for ohm conductance region and saturated current region, the traditional mathematical models ignore the microscopic process of space recombination and plate composite. Due to the dynamic instability of the ionization coefficient with temperature, gas species, etc., the traditional mathematical model In current surge region is limited in application. In this paper, a new mathematical model of SF₆ gas DC current density and conductivity is studied, which considers the microscopic processes, such as ions generation, space migration, space recombination, and diffusion and so on. The influence of electric field strength and environmental factors on the model is studied emphatically. The results show that the new model improves the transition process of the ohm conductance region and the saturation current region. The model avoids the limitation of the ionization coefficient of the current surge region. For the current density and the conductivity, the new model is not only easy to explain the influence of the electric field and the environmental factors, but also provides a good theoretical reference for further study on the DC conductivity.

I. Introduction

Although GIL has been widely used in AC transmission in special environments. It has become the preferred solution for replacing overhead transmission lines. However its application in HVDC transmission has been greatly limited, mainly because the current space charge problem greatly restricts the development of DC pipeline transmission technology. Under the action of a unipolar voltage for a long period of time, the insulating medium can easily lead to the accumulation of space and surface charges, leading to hidden dangers in line insulation [1–2]. Under DC voltage, electric field distribution depends on the electrical conductivity of the insulating material. The electrical conductivity of the insulating material is also affected by many factors such as temperature, humidity, electric field strength, and pressurization time [3–4]. Therefore, under the DC field strength, it is very important to explain the microscopically reasonable current density and conductivity mathematical model.