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Wide bandgap (WBG) semiconductor devices are developing rapidly due to their superior performance compared to traditional silicon-based devices. However, the packaging technology of traditional devices has limited the application of WBG semiconductor devices because of the challenges in electrical insulation. The complex environment of high blocking voltage, high frequency, and high temperature is the major reason for insulation failure of encapsulation structure. Therefore, in this article, an epoxy resin composite with nonlinear conductivity is proposed to be used as a coating to improve the electric field distribution of high-voltage high-power IGBT modules. First, an electrical field simulation model was built considering the thermal stress. It was found that the electric field in high temperature was improved compared with that in room temperature due to the temperature-dependent conductivity of silicone gel. Nevertheless, the risk of insulation failure still exists. After the application of nonlinear conductivity materials (NCMs) coating, the maximum electric field at the triple junctions and the ratio of electric field distortion in high field areas were significantly decreased. Further analysis showed that the optimization ratio of electric field increased with the increase of the blocking voltages or power losses in the IGBT chip. The results have demonstrated that the NCMs can reduce the maximum electric field in the IGBT encapsulation structure by 73% under the operating conditions of 120 W 10 kV. Partial discharge (PD) tests show that the partial discharge initial voltage (PDIV) of the substrates with NCM coating is increased by 33% compared with the normal encapsulation structure and the coating significantly inhibits the growth of electric trees. The presented results indicate that the NCMs have the potential to improve the insulation performance of high-voltage high-power IGBT modules. [ABSTRACT FROM AUTHOR]

In this paper, a calculation method is proposed to predict the dielectric strength (DS) of gases and the DS of some promising SF 6 alternative gases and their mixtures is further evaluated by DC breakdown tests. The calculation method is based on the density functional theory (DFT), so that the DS of the gases can be obtained by only calculating their molecular parameters, including the average static electronic polarizability and adiabatic ionization energy. The paper also presents the DC breakdown strength of the C 4 F 7 N, C 5 F 10 O, and HFO-type gases, and it is found that the experimental DS values are in good agreement with the calculated values. In addition, DC breakdown tests for gas mixtures are also conducted and their synergistic effect is discussed in detail. The results show that the DS of C 4 F 7 N mixed gases is equivalent to that of pure SF 6 gas even under high pressures, indicating their potential applications in HV electrical equipment. The DS of C 5 F 10 O mixed gas is slightly lower than that of C 4 F 7 N mixed gas. Compared with CO 2 , mixing with air brings stronger synergistic effect in C 5 F 10 O and C 4 F 7 N in our experiment. The DS of HFO mixture is substantially less than that of SF 6 because of the weak synergistic effect when mixed with CO 2 or N 2. This paper presents an effective method to evaluate DS of SF 6 alternative gases and the results are useful for their future engineering applications. [ABSTRACT FROM AUTHOR]

This paper addresses the prediction of microparticle-initiated breakdown in mm-scaled air gaps which has a transition Pd value of about 200 Pa.m. Predictions by Townsend theory and streamer inception are compared with experimental measurements and the results indicate that the Townsend theory is in better agreement. Based on this method, the breakdown voltage of an air gap with a single microparticle is calculated and drops quasi-linearly with its radius at a decay factor about 35 V/μm. The relative reduction rates of U b caused by single r m =10 and 100 μm microparticle reaches 3.1 and 37.3%, respectively. However once r m =10 μm microparticles cluster, the reduction rate rises to 7.2 and 35.5%. This provides a prediction method to assess the effects of microparticles on gas breakdown, especially in mm-scaled gap with transition Pd value and contributes to development of insulation performance. [ABSTRACT FROM AUTHOR]

In order to study the characteristic of the electrical explosion of copper and aluminum powders, a multilayer generator was designed, an experimental system was set up, and the parameters of metal powder electrical explosion were measured and analyzed. The results show that the duration of the electrical explosion process increases significantly due to the addition of metal powder. The duration of aluminum powder electrical explosion jet flow is ~86.36 ms due to its self-sustained combustion, which releases a large amount of energy, and a small fraction of aluminum powder particles is not burned. The duration of copper powder electrical explosion jet flow is ~15.84 ms, and most of the copper powder particles are in the solid state. The current pause process is absent; instead, the first discharge process is connected to the second discharge process. The effect of copper powder on the first discharge process is greater than that of aluminum powder. Furthermore, the ignition ability of copper powder electrical explosion to solid propellant is stronger than that of aluminum powder in a closed bomb experiment. These results are indubitably meaningful for the application of metal powder electrical explosion and ignition of solid propellant in an electrothermal chemical gun. [ABSTRACT FROM AUTHOR]

The C 4 F 7 N/CO 2 gas mixture has attracted much attention due to its excellent insulation property and eco-friendly character. In order to evaluate the feasibility of its application in DC GIL, this paper focuses on the surface charging characteristics of spacers under DC stress in the C 4 F 7 N/CO 2 mixture. First, the DC insulation strength was tested under uniform field. The results show that the critical dielectric strength of pure C 4 F 7 N is more than twice that of SF 6 and the dielectric strength of 15%∼20% C 4 F 7 N/CO 2 mixture is equivalent to that of SF 6. Next, the surface charge measurement of spacers was performed in C 4 F 7 N/CO 2 mixtures, which reveals that the surface charge density decreases slightly with the increase of C 4 F 7 N content. However, the surface charging level in 25% C 4 F 7 N/CO 2 mixture is still much higher than that in SF 6. It is found that most of the surface charge stems from partial discharges (PDs) near the flange. The PD measurement shows that in SF 6 , there are more PDs with low magnitude, but much less PDs with high magnitude compared to that in the 15%∼25% C 4 F 7 N/CO 2 mixtures. It is the different PD behaviors between C 4 F 7 N/CO 2 mixtures and SF 6 that lead to their different surface charging characteristics. [ABSTRACT FROM AUTHOR]