DC Breakdown Characteristics Research Articles

Impact of Graded AlGaN Buffer Layer Thickness on the DC, RF, Linearity, Intermodulation and Off-State Breakdown Characteristics of AlGaN Channel HEMT

This study examines the extraction of small-signal equivalent circuit parameters, linearity and intermodulation metrics, and capacitance–voltage characteristics for both AlGaN and GaN channel HEMTs. Compared to GaN channel HEMTs, AlGaN channel HEMTs have better linearity and intermodulation distortion. In the instance of AlGaN channel HEMTs, the device parasitics are decreased. Additionally, the effect of graded AlGaN buffer layer thickness on breakdown characteristics and linearity is examined. For breakdown characteristics, the 200 nm-graded AlGaN buffer layer thickness yields superior results with VBOff 157 V for a thickness of 200 nm (147 V in the case of 500 nm). At 200 nm thickness, the linearity and intermodulation distortion FOMs are also reasonably good, and the remaining device properties are essentially unchanged. Hence, the graded AlGaN buffer thickness can be reduced for high-voltage applications. For higher-voltage applications, the graded AlGaN buffer thickness can, therefore, be decreased.

DC Breakdown Characteristics of Transformer Oil with Different Cellulose Impurity Concentrations

DC Breakdown Characteristics of Transformer Oil with Different Cellulose Impurity Concentrations

Investigations on AC and DC breakdown characteristics of epoxy- alumina nanocomposites

Investigations on AC and DC breakdown characteristics of epoxy- alumina nanocomposites

Investigation of temperature-dependent DC breakdown characteristics of nano-Al2O3/epoxy composites at low temperatures

Epoxy resin is extensively utilized as an insulating material in low-temperature superconducting devices. Nevertheless, its breakdown behavior and mechanism at low temperatures have rarely been studied. This study aims to investigate the breakdown characteristics of bisphenol F epoxy resin and its nano-alumina composites under different temperatures. Additionally, a thermally stimulated current (TSC) platform was established to examine the molecular relaxation and trap charge parameters of epoxy from 4.2 K to 300 K. The epoxy resin matrix was modified by incorporating a series of nano-alumina particles (1%, 2%, 3%, 4%, 5%). In this paper, a breakdown transition temperature (Tb) between 77 K and 150 K was observed for epoxy resin, with a significant decline in insulation performance above and below Tb. This phenomenon can be attributed to the interplay between collisional ionization and thermal breakdown mechanisms. The inclusion of nano-alumina particles in the epoxy resin matrix demonstrates an improvement in insulation performance at low temperatures, with an optimal filler ratio of approximately 2%. However, an excessive amount of alumina nanoparticles may reduce the insulating capabilities of the epoxy resin. The experiments conducted on thermally stimulated currents revealed that trap charges within the resin are more readily excited at low temperatures.

Effect of solid particle type, concentration and size on DC breakdown voltage of short needle‐plate air gap: An experiment and simulation study

AbstractUnclean air discharge refers to the discharge phenomenon of a large number of polluting gases, droplets or solid particles floating in the air, which will cause insulation breakdown and safety accidents for the power transmission equipment that have been left outdoors for a long time. In order to investigate the effects of particle concentration, particle size and dielectric constant on DC breakdown characteristics of unclean air gap, a self‐made discharge chamber was designed in this study. The air was filtered and passed into the discharge chamber to remove the influence of impurities contained in the air on the experimental results. Then, solid particles with different concentration, particle size and particle dielectric constant were added to the discharge chamber to carry out the DC positive polarity breakdown characteristic experiment. The experimental results show that compared with dry clean air, the presence of solid particle increases the breakdown voltage of the gap, and the increase proportion of breakdown voltage is related to the particle concentration, particle size and particle dielectric constant. With the same particle type and particle size, the increase proportion of breakdown voltage increases with the higher concentration, which up to 10.49%. For further investigating, the fluid mechanics model was selected to simulate the process of streamer discharge in unclean air. The results show that compared with dry clean air, the presence of particles enhances the gap discharge ionisation process, but also enhances the adsorption of particles, and the latter has stronger effect than the former, thus increases the gap breakdown voltage. At the same time, the enhancement of adsorption effect increases the electric field intensity of the gap and speeds up the development process of streamer discharge.

Changes of cross-linked network and DC electrical properties of nanocomposite silicone rubber under thermal aging

Nano dielectrics have brought hope for solving the problem of cable insulation at high voltage levels. In this paper, nano Al2O3 and MgO are doped to silicone rubber and the nanocomposites are aged at 200 °C for 0-80 days. The electrical conductivity and DC breakdown characteristics of aged materials are investigated. The microscopic and elemental properties are also analysis. It is found that with the increase of thermal aging time, electrical conductivity of all sets decreases first and then increases, while the DC breakdown voltage experiences a process of first increasing and then decreasing. During the initial aging process, secondary vulcanization of silicone rubber occurs, however, the cross-linked network degrades with further aging, which could explain the changes in electrical properties. The introduction of metal oxides could react with exfoliated radicals to form s table compounds, thus, the performance of Al2O3 and MgO doped materials have better electrical properties under thermal aging.

DC Breakdown Characteristics of Needle–Needle–Plane Electrodes With Insulation Barrier and Thermal-Induced Bubbles in Liquid Nitrogen

Insulation barriers are an effective way to improve the insulation strength of the resistive-type superconducting fault current limiters (R-SFCLs). The objective of this article is to obtain the dc discharge characteristics of composite insulation systems including two liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) gaps in series, but separated by a solid insulation barrier mixed with vapor bubbles. The needle–needle–plane stainless steel electrodes with the insulation barrier and bubbles generation systems are used to simulate the electric strength under quenching conditions of the R-SFCLs. The results show that the composite systems’ breakdown characteristic switched from insulation barrier breakdown to surface flashover with the insulation barrier approaches the needle electrodes side. The breakdown voltage of the composite systems decreased due to the thermal induced bubbles. The presence of the bubbles increases the probability of the surface flashover of the insulation barrier. The results have guiding significance for the design of the high-voltage R-SFCLs.

DC Breakdown Characteristics of C₄F₇N/CO₂ Mixtures With Particle-in-Cell Simulation

The breakdown characteristics of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures under dc condition are investigated with a particle-in-cell method. The processes of elastic, excitation, ionization, and attachment collisions are all considered. The elastic cross section of electron scattering from C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N is modeled through quantum mechanical spherical complex optical potential formalism. Based on the cross-sectional data, the dielectric strength of pure C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N is studied. The threshold of breakdown is in good agreement with the experiment. Besides, the dielectric strength of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures is also obtained. The threshold of breakdown in 80% C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N and 20% CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is larger than that of pure C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N when the gas pressure is larger than 1300 torr. The results show that the energy loss of electrons is mainly caused by excitation collision with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> when the energy of electrons <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{e}$ </tex-math></inline-formula> is smaller than 5.5 eV. When <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}/{P}$ </tex-math></inline-formula> is small, the proportion of low-energy electrons is large and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{e}$ </tex-math></inline-formula> increases with the ratio of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N. Therefore, the effective ionization rate first decreases and then increases as the ratio of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N increases.

Effects of Pre-Crosslinking on Space Charge and Breakdown Characteristics of XLPE Cable Insulation

This study focused on the effect of pre-crosslinking on the electrical properties of XLPE insulation for HVDC cables. The XLPE samples were pre-crosslinked at 140, 150 and 160 °C. The space charge and DC breakdown characteristics of the XLPE samples with and without pre-crosslinking were investigated. The results show that the pre-crosslinked XLPE samples have an obvious space charge injection and transportation, resulting in more severe electric field distortion. Under the electric field of 100 kV/mm, the electric field distortion rates of the XLPE samples pre-crosslinked at 150 and 160 °C reached 51% and 72% respectively, which were much higher than that of the XLPE sample without pre-crosslinking (14%.) Compared with the XLPE without pre-crosslinking, the breakdown strengths of XLPE pre-crosslinked at 140, 150 and 160 °C were reduced by 11%, 6% and 7% respectively, at the temperature of 50 °C. It is concluded that the pre-crosslinking leads to imperfect crystallization and micro-defects in the amorphous region of XLPE, thereby leading to more space charge accumulation and reduced DC breakdown. The pre-crosslinking of XLPE insulation therefore should be prevented during HVDC cable manufacturing.

Inhibition Effect of Solid Products and DC Breakdown Characteristics of the HFO1234Ze(E)-N2-O2 Ternary Gas Mixture.

HFO1234ze(E) is an environmentally friendly SF6 substitute gas with prominent application potential. To suppress the generation of the HFO1234ze(E) solid decomposition products, which may cause great hazards to the gas–solid insulation strength, a gas mixing scheme screening method based on the reactive force field (ReaxFF) molecular dynamics (MD) simulation was innovatively proposed. The simulation results show that the inhibitory effect of O2 on the formation of HFO1234ze(E) solid products is better than those of CO2 and CF4. Further study shows that when O2 accounts for 3.33% of the gas mixture, the solid precipitate content is reduced by 48%. The experimental study shows that an O2 content of 3.33% can inhibit the generation of solid products by more than 50%. Besides, compared with HFO1234ze(E)-N2, the DC breakdown voltage of HFO1234ze(E)-N2-O2 is slightly increased, and the breakdown voltage dispersion degree and continuous breakdown voltage drop rate are decreased. This work gives a feasible solution for the suppression of HFO1234ze(E) solid decomposition products and provides an efficient method for solving similar problems of environmentally friendly insulating gas in C/F/O/N systems.

Negative DC Breakdown Characteristics of C3F7CN / CO2 Gas Mixture for Application in High Voltage Accelerators

This study investigates the technical feasibility of retro-filling a C3F7CN/CO2 gas mixture for existing SF6-insulated accelerators. Negative DC breakdown characteristics of 20% C3F7CN / 80% CO2 gas mixture and SF6 for varying pressure, gap distance and field uniformity are analyzed experimentally using four distinctly different electrode configurations. The C3F7CN/CO2 gas mixture shows a higher breakdown strength than SF6 for configurations with high field uniformity, whereas SF6 outperforms C3F7CN/CO2 gas mixture under the non-uniform field. Importantly, 20% C3F7CN / 80% CO2 gas mixture exhibits comparable insulation capability to SF6 in a 10/30 mm coaxial geometry with similar field uniformity as found in the practical gas-insulated equipment. The results of this work contribute to the development of a potential retro-fill solution using 20% C3F7CN / 80% CO2 gas mixture for accelerators.

DC breakdown characteristics and charges accumulation behaviour of thermally upgraded paper aged in natural ester

Considering that the working temperature is much higher in high-voltage direct-current (HVDC) convert transformers than in conventional AC transformers, the combination of thermally upgraded paper and natural ester might be a better choice to withstand high temperature in long-term operation. This study compares the chemical structure, DC breakdown voltage, space charge and trap distribution of thermally upgraded paper aged in natural esters and mineral oil. The relationship between DC breakdown and accumulated charges was analyzed. Results show that the thermally upgraded paper aged in natural ester (NEI-TUP) has a higher volume resistivity and DC breakdown voltage than that aged in mineral oil (MOI-TUP). The NEI-TUP group has a larger deep trap density than the MOI-TUP group due to the chemical structure of natural ester. The larger deep trap density could contribute to the lower charge accumulation quantity and higher DC breakdown voltage. The thermally upgraded paper immersed in natural ester presents better insulation capability under thermal and DC electrical stress than that immersed in conventional mineral oil. This research indicated that the combination of thermally upgraded paper and natural ester might be a potential alternative for the mineral oil immersed paper in the future.

Research on influence factors of DC breakdown characteristics in gas discharge gap

Research on influence factors of DC breakdown characteristics in gas discharge gap

Temperature Stability of DC Conductivity and Breakdown of Crosslinked LLDPE

In this paper, a way to improve the temperature stability of DC conductivity and breakdown characteristics of polyethylene (PE) is proposed using a crosslinked linear low density polyethylene (LLDPE). The ratio of DC conductivity, as well as breakdown strength values under 90 to 30°C is used to determine the temperature stability of DC properties. The closer it is to 1, the better the performance of temperature stability. The results show that when using crosslinked-LLDPE material, the ratio of DC conductivity under 90 to 30°C is 10.5, while it is 461.6 for crosslinked-LDPE samples with the same DCP content. And the ratio of DC breakdown strength is 0.97 for crosslinked-LLDPE, while it is 0.32 for crosslinked-LDPE. The gel permeation chromatography (GPC) method, hot-set test, differential scanning calorimetry (DSC) analysis and scanning electron microscopy (SEM) images show that the fine arrangement and smaller molecular weight between crosslinks of molecular and morphology structure that LLDPE owns contribute to the improvement in comparison with LDPE. The findings may contribute a solution to the development of HVDC power cable insulation materials.

Barrier position effect on bubble triggered DC breakdown characteristics in liquid nitrogen

The objective of this study is to determine the effect of different barrier positions on the DC breakdown characteristics of liquid nitrogen (LN 2 ), with and without bubbles. The DC breakdown voltage is measured of a needle-to-plane electrode, with 9 mm gap distance, with and without PTFE barrier insulation of 40 μm thickness. The presence of bubbles lowers the breakdown voltage and the effect of have the barrier at various distances from the tip of the needle electrode is studied. The results show that with and without bubbles, the closer the barrier to the needle electrode, the higher the breakdown voltage. Observations using a high-speed camera show that the presence of the insulation barrier triggers the breakdown of the LN 2 /insulation barrier composite system.

Effect of a PTFE film on bubble triggered DC breakdown characteristics in liquid nitrogen

In the resistive type DC superconducting fault limiter (R-SFCL), the insulation strength will be decreased seriously when the R-SFCL quenched. Insulation barriers are used inside of the R-SFCL to enhance the electrical breakdown strength of the SFCLs. The objective of this paper is to study the barrier effect on the DC breakdown characteristics of the liquid nitrogen (LN2)/insulation barrier composite system with and without bubbles. In the experiment, the DC breakdown voltage of a pair of rod-plane electrodes with an insulation barrier was measured in the presence of thermal bubbles. The results show that for both the positive and negative polarities, the breakdown voltage of the LN2/insulation barrier composite system is higher than that without the barrier. In the presence of the bubbles, the breakdown voltage of the LWinsulation barrier composite system is about 1.5 times higher than without the barrier. Furthermore, the breakdown voltage of the LN2/insulation barrier composite system with 0.04 mm PTFE is higher than with 0.1 mm PTFE. The results suggested that the barrier effect could not only improve the insulation strength of the normal state but also the quench state of the R-SFCLs.

Barrier Effect on the DC Breakdown Characteristics of Cryogenic Nitrogen Gas Evaporated From Liquid Nitrogen

In superconducting power equipment, such as a resistive-type superconducting fault current limiter (R-SFCL), liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and cryogenic nitrogen gas (CGN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) act as not only the cooling media but also the insulation media. In R-SFCLs, CGN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> will coexist with the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The objective of this article is to determine a barrier effect on the dc dielectric strength of the CGN2 evaporated from LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The dc breakdown voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> of a pair of rod-to-plane electrodes with an insulation barrier was measured. The gap distance b was 13.6 mm, in which the distance from the rod electrode to the insulation barrier was a and the distance from the rod electrode to the plane electrode was b. Three cases were measured, which were a/b = 1/7, 3/7, and 5/7, respectively. The materials of the insulation barrier were polytetrafluoroethylene (PTFE) and Kapton, respectively. The experimental results showed that, for both positive and negative polarities, when a/b was 1/7, the breakdown voltage was approximately two times higher than that without the barrier. When a/b was 3/7, the average breakdown voltage was approximately 1.5 times higher than that without the barrier. When a/b was 5/7, the breakdown voltage was nearly the same as that without the insulation barrier. Therefore, it suggested that the closer the insulation barrier was to the rod electrode side, the higher the breakdown voltage was. When a/b = 5/7 and the thickness of the insulation barrier was 0.10 mm, the breakdown voltage of the CGN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /insulation composite insulation system with the Kapton film was higher than that with the PTFE film. A high-speed camera observation showed that the discharge started in the CGN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and then, a further breakdown occurred in the insulation barrier. An equivalent circuit model was built up to describe the breakdown process, which showed that the lower the electrical conductivity of the insulation barrier was, the higher the breakdown voltage was.

DC breakdown characteristics of XLPE/BNNS nanocomposites considering BN nanosheet concentration, space charge and temperature

Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable. In this work, the effect of boron nitride nanosheets (BNNSs) concentration, space charge and temperature on DC breakdown strength have been explored. Cross-linked polyethylene (XLPE)/BNNS nanocomposites were prepared by the melt blending method, and the basic characteristics of nanoparticles and composite were characterised. The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix. The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%, which is about 33% higher than that of pure XLPE. Further, the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges. For the samples with different BNNS contents, all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges. Besides, it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C, which is due to more charge accumulation at 50°C. It reaches 2.06 × 10 −8 C which increases by about 2.2 times than the room temperature.

The effect of electrode surface roughness on the breakdown characteristics of C3F7CN/CO2 gas mixtures

C3F7CN/CO2 gas mixtures have been widely studied in recent years. And they are considered a potential alternative for replacing SF6 in high voltage power equipment. In this paper, the DC breakdown characteristics of 6%C3F7CN/94%CO2 mixtures in a uniform electric field were studied at electrode surface roughness levels of 0.4 μm, 1.2 μm, 2.1 μm and 3.8 μm. At the same time, in order to provide reference for the power engineering, the gas pressure was set between 0.3 MPa and 0.7 MPa. Meanwhile, the results at 0.4 MPa gas pressure were compared with it of SF6. The growth rates of positive and negative DC breakdown field strengths of C3F7CN/CO2 mixtures decreased gradually with the increasing of gas pressure, and the decreasing trend of growth was more obvious with the increase of electrode surface roughness. At higher levels of surface roughness, the polarity effect of the C3F7CN/CO2 mixture was more significant. At 0.4 MPa gas pressure, as the surface roughness increasing from 0.4 μm to 3.8 μm, the decline degree of positive and negative DC breakdown field strengths of C3F7CN/CO2 mixtures were significantly lower than that of SF6 gas between 0.4 μm and 3.8 μm. The critical breakdown field strength, (E/N)crit, and coefficient, β, of 6%C3F7CN/94%CO2 mixture and SF6 were obtained by Steady State Townsend method(SST), and (Nh)crit values were calculated to characterize the sensitivity of these gases to surface roughness. The (Nh)crit value of the 6%C3F7CN/94%CO2 mixture was higher than SF6. It showed that the 6%C3F7CN/94%CO2 was less sensitive to roughness than that of SF6.

Numerical Prediction of DC Breakdown Characteristics in LDPE With Current Profile as Critical Index

Understanding the DC breakdown characteristics of polymeric insulators is essential for stable operation of high-capacity DC electrical equipment. To predict the breakdown characteristics of low-density polyethylene (LDPE), we propose a numerical methodology with a new critical index in which the internal current varying with temperature, thickness, and injection barrier height. To evaluate this current-based index, we applied the fully coupled bipolar charge transport (BCT) and molecular chain displacement (MCD) models to analyze the influence of each variable on breakdown phenomena. The results of this analysis revealed that the amount of space charge accumulation within the insulator has a maximum value at approximately 50 °C, which corresponds to the known morphological transition temperature of LDPE. The breakdown strength calculated using this numerical model was found to decrease with increasing temperature and thickness. Although injection barrier height at the electrode was found to be negatively correlated with breakdown strength, its effect was not as significant as that of the other variables. The breakdown strength values obtained using this numerical method were found to be in close agreement with values reported in the literature. Based on these results, we newly suggest the physical quantity to predict the breakdown strength, the current relaxation speed, which is the slope of the Boltzmann sigmoid function, as a positively correlated index. Finally, we determined that the breakdown phenomena are initiated when the amount of impact accumulated in the insulator changes discontinuously and analyzed the contribution of factors affecting the breakdown using the Pearson correlation coefficient and the Sobol sensitivity index.