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The use of organic insulation in the motor has insulation temperature limitations, which limit its usage and further increase its power density. In response to this issue, this paper proposes a high-temperature resistant motor with the micro-arc oxidation ceramic insulated wire, of which the long-term service temperature is able to exceed 350 °C. Firstly, the generation conditions, formation principles, structural characteristics and electrical characteristics of micro-arc oxidation ceramic insulated wires were introduced. Secondly, the high temperature motor base on micro-arc oxidation ceramic insulated wires is proposed, and the temperature analysis is presented, the influence of motor load on temperature rise was studied. Then, the manufacturing process and insulation method of the motor were introduced. Finally, the high-temperature motor prototype was made, and the high-temperature resistance performance of the high-temperature motor prototype was tested, and the temperature distribution of the motor under different load conditions was verified.

C4F7N/CO2 gas mixtures have attracted extensive attention because of their excellent insulating properties and environmental friendliness. High electrical and thermal stability is an important indicator for evaluating their performance, but there have been few molecular dynamics studies of their decomposition mechanisms. In this study, using ReaxFF molecular dynamics simulations and quantum chemistry theory, the decomposition mechanism of a C4F7N/CO2 gas mixture and the effect of the O2 content on the decomposition of the mixture were simulated on the microscopic level. It was found that there are three main decomposition pathways of C4F7N molecules, of which the generation of C3F4N⋅ and CF3⋅ free radicals is the most likely to occur. COF2 is the main oxygen-containing product of the C4F7N/CO2 gas mixture, and its generation is significantly affected by the simulation time and temperature. COF2 can be regarded as the characteristic decomposition product of the C4F7N/CO2 gas mixture. The addition of O2 slightly promotes the decomposition of C4F7N, whereas the maximum decomposition rate of CO2 decreases by 0.3% and 1% after the addition of 2% and 8% O2, respectively. Relevant results of this research can provide a theoretical basis and guidance for research into the performance of C4F7N/CO2 gas mixtures and practical engineering applications of these mixtures in the future. [ABSTRACT FROM AUTHOR]

Electron emission from micro-protrusions on the surface of metal electrodes is crucial for vacuum breakdown. The emission characteristics of cathode micro-protrusions and the impact of the space charge effect are investigated in this study, with a comparison to the Murphy–Good (MG) theory analysis. Precise calculations of the emission current density and the Nottingham effect are achieved. A thermal-field emission model for copper micro-protrusion is established to analyze emission characteristics and clarify the mismatches between the results of simulations and MG theory. The results indicate that, for copper micro-protrusions, before breakdown, the emission current is primarily field emission, with thermal emission constituting only 7% of the total. The Nottingham effect results in consistent heating during this phase. The field enhancement factor obtained through the MG theory (γ MG) is slightly smaller than that derived from the geometric model (γ geom). This is because γ geom reflects the characteristics of the apex of the protrusion, while γ MG reflects the characteristics of the entire electron emission region. The space charge effect bends the MG plot curve and decreases its slope, making it impossible to analyze the emission current using MG theory at this point, which is consistent with the theoretical derivations recorded in the current literature. [ABSTRACT FROM AUTHOR]

To optimize the performance of vacuum circuit breakers, it is critical to gain a comprehensive understanding of the intricate physical processes that occur during vacuum interruptions. One of these processes, postarc sheath expansion is of particular importance for dielectric recovery. Previous simulation studies have examined sheath expansion by assuming uniform residual plasma at current zero. However, this approach deviates from physical realism because the discreteness in the cathode spot typically causes a nonuniform plasma distribution. This distribution cannot be analyzed by previous 1D or 2D models. To address this deficiency, this paper presents a 3D hybrid simulation model that comprehensively considers the simulation of postarc sheath expansion with nonuniform residual plasma at current zero. The model differentiates between the treatment of ions and electrons to achieve an optimal balance between computational accuracy and efficiency. The model captures the inherent nonuniformity of the plasma distribution through 3D modeling. A comparative analysis was conducted on several factors that influence the sheath expansion rate, including plasma density, transient recovery voltage rate, and ion drift velocity. The study focused on the impact of nonuniformity in the residual plasma distribution. It was demonstrated that this nonuniformity can impede the overall sheath expansion and result in the local enhancement of the electric field. The simulation aims to study the postarc sheath expansion and provide insight into the underlying physical mechanisms that govern this complex process. [ABSTRACT FROM AUTHOR]

Copper–chromium alloy material, as one of the most important electrode contact materials in the field of electrical contact, has been widely used in vacuum interrupters. To replace the SF6 circuit breakers at higher voltage levels and larger breaking capacities, there is an urgent need for new electrode contact materials to meet the comprehensive electrical performance requirements of high withstand voltage, high insulation, and erosion resistance. In this study, a novel electrode contact material, CuCr55, for a 252 kV single break vacuum interrupter was prepared by the arc melting method, and the microstructures of arc-cast CuCr25, melt-infiltrated CuCr50, and arc-melted CuCr55 materials were compared. The vacuum arc ignition and erosion characteristics of arc-melted CuCr55 contact materials were analyzed in detail. A high-speed camera was used to capture the arc ignition characteristics of short-circuit currents, and the critical currents for the formation of anode spots for different materials were obtained. The micro-morphology of the contact surface after erosion was observed using electron microscopy. The research results showed that the arc-melted CuCr55 contacts had a fine and uniform distribution of chromium particles with spherical and dispersed microstructures. After vacuum arc erosion, there was no material fracture or significant protrusion on the surface of CuCr55 contacts, and they exhibited a higher critical current for anode spot formation and good uniform erosion characteristics. [ABSTRACT FROM AUTHOR]

Featured Application: The proposed surge arrester is applied to a DC GIS in an offshore wind farm converter platform, significantly reducing the space the equipments take up by up to 95%, which performs well especially in the new power system. The employment of a multi-column parallel connection is intended to enhance the energy absorption capability and reliability of surge arresters. However, the disparity in reference voltage between each varistor column and the uneven current distribution may result in a reduction in performance or even failure of the surge arrester. The objective of this study is to investigate the spiral structure of a ±550 kV DC gas-insulated switchgear (GIS) parallel arrester and its influence on the current distribution characteristics. This research develops a model of a ±550 kV DC GIS arrester and performs an in-depth theoretical analysis using multi-physics field simulations. Subsequently, a ±66 kV miniature prototype is constructed, and the accuracy of the theoretical analysis and simulation results is validated by experiments, validating the effectiveness of the proposed method. This study calculates the self-generated inductance in the spiral structure of ZnO varistors using simulations. The influence of the self-generated inductance on the current distribution of the multi-column arrester when absorbing energy is further investigated. The results indicate that the self-generated inductance of the spiral structure can reduce the current deviation factor by 28–65%. This research provides a novel approach to improving current equalization in the parallel surge arresters of DC GISs for offshore wind power converter platforms. [ABSTRACT FROM AUTHOR]

DC circuit breakers (DCCBs) are the key equipment to rapidly interrupt the fault current in high-voltage DC power grids and ensure the safe operation of the system. However, most DCCBs do not take current-limiting measures and rely solely on current-limiting reactors in the system to limit the rate of current rise during the interruption process. The extensive use of fully controlled power electronic devices in circuit breakers (CBs) results in high costs. To address the issues above, this paper proposes a DCCB topology with a current-limiting function based on thyristors and diodes, which can reduce the cost of CB while ensuring reliable interruption. The impact of various parameters on CB performance is analyzed using numerical calculations to optimize the parameters. Then, a simulation model of a 500 kV/16 kA DCCB is built in PSCAD/EMTDC, and the performance of the proposed CB topology is compared with the other CB topologies. By comparison, the proposed DCCB topology can reliably isolate fault currents and reduce the amplitude of fault currents and the cost of CBs. Significantly, the energy absorbed by the metal oxide varistor (MOV) during the interruption process decreases by 64.2%, reducing the cost and volume of the MOV. Finally, the feasibility of the CB is further verified in the ±500 kV 4-terminal high-voltage DC power grid simulation model. The results show that the proposed DCCB topology can limit the fault current rise rate, interrupt and isolate the fault reliably, and reduce the cost. [ABSTRACT FROM AUTHOR]