Abstract
The environmental conditions affect the external insulation performance of power equipment. In order to study the physical characteristics of air discharge, the microscopic process of electron–molecule collision in the air based on the Boltzmann equation has been studied in this paper. The influence of humidity on the air gap insulation performance was also analyzed. The calculation results show that with the temperature 300 K and the pressure 1.0 atm, the electron energy distribution function and electron transport parameters varied with the air relative humidity. As the air relative humidity is increased by each 30%, the average electron energy decreases by about 0.2 eV, the reduced electron mobility decreases by about 0.25 × 1023 [1/(V·m·s)], the reduced electron diffusion coefficient decreases by about 0.2 × 1024 [1/(m s)], and the effective ionization coefficient decreases by about 4 × 10−24 m2. As the air relative humidity increases from 0% to 60%, the critical breakdown electric field increases by 1.22 kV/cm.
Highlights
In order to transmit a large-capacity power supply by long transmission distance, a UHV power grid has been constructed and developed rapidly in China (Zhao et al, 2015; Xun et al, 2020a; Xun et al, 2021a)
For every 30% increase in air humidity, the reduced electron diffusion coefficient decreases by about 0.2 × 1024 [1/(m.s)] showing that water molecules can weaken the diffusion of electrons
According to the collision cross-section data of different electron collision reactions, the reduced ionization coefficient, reduced attachment coefficient, and effective ionization coefficient under different humidity are studied with Boltzmann equation
Summary
In order to transmit a large-capacity power supply by long transmission distance, a UHV power grid has been constructed and developed rapidly in China (Zhao et al, 2015; Xun et al, 2020a; Xun et al, 2021a). To design the structure of EHV transmission lines in high altitude areas, Liu Youwei and other scholars (Liu et al, 1990) analyzed the characteristics of corona around the conductor with different humidity in detail. Their experimental results showed that humidity had a significant impact on the corona inception electrical field of the conductor. The variation of air humidity will affect the electronic transport parameters during air discharge that lead to different insulation performance of air gaps and may threaten the operation characteristics of external insulation of power equipment. The effect of humidity on electron energy distribution function (EEDF), reduced electron mobility (μ/N), reduced electron diffusion coefficient (D/N), and critical breakdown electric field are simulated and analyzed
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