Development Of Electrical Breakdown Research Articles

Rock breaking mechanism of electrode bit in heterogeneous granite formation and its optimization

Electro-pulse-boring (EPB) technology is one of the most potential and nearly industrialized new rock breaking methods in geothermal drilling. However, the mechanism of EPB is not clear, and the structural parameters of EPB electrode bit are not well matched with the corresponding strata parameters and voltage parameters, which seriously hindered the commercialization process of this technology. Based on the dynamic electrical breakdown model (DEBM), a single electric breakdown of rock is realized by coupling the circuit field, the current field and the breakdown field. At the same time, considering the heterogeneity of rock, the three-dimensional numerical simulation of full-bit electrical breakdown using five kinds of electrode bits with different structures is conducted. From these five kinds of electrode bits, an electrode bit suitable for EPB is selected. Finally, the adaptability between the structural parameters and voltage parameters of the selected electrode bit is studied. The results show that the initiation and development of electrical breakdown are affected by the mineral composition, mineral quantity and mineral position of the rock. The petal-structural electrode bits with the same clearance between the high voltage electrode and all ground electrodes are more suitable for EPB drilling due to their higher chip removal function. Moreover, the minimum initial output pulse peak voltage, i.e., the adaptive voltage, of petal-structural electrode bit under different structural parameters is calculated by fitting, which is the best rock breaking voltage parameter. This research can provide reliable help for the design of EPB electrode bit, the optimization of structural parameters and voltage parameters of electrode bit to increase geothermal resources.

Numerical electric breakdown model of heterogeneous granite for electro-pulse-boring

The problems of cost, environmental protection and efficiency of hard rock fragmentation in petroleum exploration, drilling and other projects need to be solved urgently. Electro-pulse-boring (EPB) technology has attracted attention due to its advantages of low rock breaking energy consumption, low wear and low time cost. However, there is still no more accurate description model for EPB and rock fragmentation, and the existing models have limited guidance on the parameter optimization of EPB tools. This paper introduces an electric breakdown model, which realizes the whole electric breakdown process under a single high-voltage pulse by coupling the five fields: circuit field, current field, breakdown field, heat transfer field and solid mechanical field. The multi physics model comprehensively considers the circuit structure parameters of the electric impulse generator (EIG), the initiation and development of electric breakdown, the dependence of electric breakdown strength and time, and the heterogeneity of rock. The model results found that the breakdown channel originates from the weak electric strength in the rock, and the development of the channel is highly dependent on the heterogeneity of the rock medium. The rock fragmentation process with a single pulse is accompanied by local electric fragmentation and hydroelectric fragmentation, When the pulse voltage rise time (PVRT) is greater than 500 ns, the hydroelectric fragmentation mode is dominant. The temperature and thermal stress values of the discharge channel are consistent with the previous studies results, and the temperature distribution at the electrode tip is the highest, which shows that the ablation problem of the electrode in EPB process can not be ignored. This model has the potential to establish the relationship between rock-breakingparameters and rock-breaking efficiency of EPB, and can provide a practical method for the development and parameter optimization of EPB and rock breaking tools.

Trapping and scattering effect of charge carriers on impulse breakdown characteristics of nano‐fluids

Propylene carbonate (PC)-based nano-fluids (NFs), containing only 2 ppm TiO2 nano-particles, exhibit more than 60% higher negative impulse breakdown voltage than that of base liquid. It is found that the resistance of the test gap containing PC remains basically invariable when subjected to high amplitude voltage before the development of electrical breakdown. However, for the NF case, the resistance increases by a factor. Moreover, compared with PC, the streamers in NFs are more complex branched. These experimental results indicate that the charge carriers in NFs can be effectively captured and scattered by nano-particles, which is verified by means of the thermally stimulated current method.

Estimation of Post-Arc Neutral Vapor Density in the Gap Volume Generated by Evaporating Macroparticles in a Diffuse Vacuum Arc

This paper presents a mathematical model of calculations of the density of atoms evaporated from macroparticles in a diffuse vacuum arc. The influence of the initial temperature, diameter, and average velocity of the droplets, as well as the kind of the cathode metal on vapor density in the volume surrounding the electrodes was investigated. Both the initial density and the decay of vapor density were calculated for Cu and Cd electrodes following the extinction of the arc. The calculated densities constitute the basis for evaluating the influence of evaporating droplets on the development of electrical breakdown in a vacuum gap after arcing.

The Search for Universal Features of Electrical Breakdown in Solids, Liquids and Gases

This paper discusses the commonality of electrical breakdown phenomena in gases, liquids, and solids. It is shown experimentally that the change in density fluctuations occurring in the three phases is the strongest common influence in the development of electrical breakdown.