Department : Physics
Study Level : Ph. D.
Title of (Thesis / Dissertation) :
Theoretical Calculations Including the Break-down Voltage and Related Transport Parameters in Some Industrial Gases and Its Mixture
Student Name : Mahir Sami Salih
Supervisor Name : Prof. Dr. Raad Hameed Majeed
Aime of the Study :
The main aim of the present work is to estimate the break-down voltage in electrical discharge used industrial gases which mostly using in electrical equipment as a dielectric medium and comprehend how discharge geometry and other factors affect these processes. The break-down voltage was estimated as a function of plate space using BOLSIGPLUS simulation program. Hence, after understanding the behavior of the breakdown voltage curves with respects to the gas concentrations for a specific gaseous mixture and repeating the trials for the four gas mixtures and by comparison with their exists experimental results, compatible scientific decision has been reached to deducing the optimum gaseous mixture acts as an insulating medium taking into consideration reducing the percentage of SF6 gas in the insulation equipment as much as possible
Abstract :
In the present study, the breakdown voltage and related transport parameters are theoretically studied and calculated for some industrial gases and their mixtures using Boltzmann equation. The theoretical model was investigated based on Boltzmann equation that solved analytically using simulation method by Bolsigplus program.
The Breakdown voltage has been calculated theoretically for Sulphur hexafluoride gas ( and its mixtures with different concentrations and multi plate spacing for each mixture. The gases have been adopted as a buffer gases in this study are: Sulfur tetra-fluoride, Carbon dioxide, Nitrogen, and Argon.
Breakdown voltage calculated based on variety physical parameters such as: ionization coefficient, attachment coefficient, and the reduced electric field (E⁄N).
Study and calculate of the breakdown voltage according to theoretical scenario of sulfur hexafluoride gas mixtures with different concentrations, which, as far as we know, is being studied for the first time. This may contribute to minimize the use of sulfur hexafluoride in industry and scientific applications, which could reduce the effect of global warming.
The electron energy distribution function (EEDF) was also studied for the adopted gases and their mixtures separately. On the other hand, study the electron transport coefficients that include the electron mobility, electron diffusion, total collision frequency, momentum frequency, and means energy of electrons, Townsend ionization coefficient and the Townsend attachment coefficient. The EEDF and breakdown voltage curves have been plotted using (MATLAB 2013) program. The calculated results were compared with the available experimental published results, and a good agreement with those results has been achieved
Recommendations :
The present work leads to the following conclusions that play an important role in designing or constructing specific electrical equipment. The study shows that, it is necessary to select or choose a range of low concentrations for the SF6 gas mixed with other gases in order to avoid or at least reduce the global warming caused by SF6 gas. According to that the obtained results, the following binary gas mixtures are employed in the present calculations:
– In conclusion, the SF6 + CF4 gases achieved high appropriate values of the breakdown voltage(58.128) kV for the case of (6mm) plate spacing with as possible as a minimum value of SF6 concentration to avoid the disadvantage of existing the SF6 gas with high concentration level. The case (SF6 + CF4) mixture as a strong option chooses in applicable. In addition to that, the case of (SF6 + CF4) shows good agreement with the experimental published data.
– The SF6 + CO2 gases achieved acceptable appropriate values of the breakdown voltage(45.2628) kV for the case of (6mm) plate spacing with as possible as a minimum value of SF6 concentration, this case (SF6 + CO2) mixture as secondary option chooses in application.
– The SF6 +N2 gases achieved another acceptable appropriate value of the breakdown voltage and reached (41.3358) kV for the case of (6mm) plate spacing with a low concentration of SF6, this case (SF6 + N2) as the third option in the experimental application.
– The SF6 +Ar gases achieved less appropriate of the breakdown voltage and reached (29.7972) kV for the case of (6mm) plate spacing with a low concentration of SF6, this case (SF6 + Ar) as the weak option in the application.
– The (SF6 and CF4) mixture gases show excellent dielectric strength with higher breakdown compared with other mixtures gases according to the electronegativity of these gases.
– High values of breakdown voltage enhance the insulation behavior of the gas for a long time before transforming the gas from insulator to conductor (break down). Hence, the equipment may be annihilated or damaged.
– The maximum plate spacing of 6mm achieved the highest value of breakdown voltage in four sample gas mixtures.
– Breakdown voltage is proportional directly to the plate spacing and the optimum case comes true by adjusting the plate spacing to suitable spacing.
– It’s necessary to take into account high dielectric strength gases, availability and natural gases, low cost and simple mechanism of gas mixing conditions in designing specific industrial electrical systems in the power project.
