To develop high‐voltage‐pulsed power switches with better performances, a multi‐gap laser‐triggered vacuum switch is proposed in this study. Based on established test prototype for double‐gap laser‐triggered vacuum switch, closing processes of double‐gap laser‐triggered vacuum switch are discussed combined with laser‐produced plasma. Closing performances of double‐gap laser‐triggered vacuum switch under different gap polarity configurations, operating voltages, laser energies and laser split ratios are investigated. Closing time delay characteristics of double‐gap laser‐triggered vacuum switch and single‐gap laser‐triggered vacuum switch are compared later. The test results prove that, affected by the imbalanced developed initial plasma between gaps, double‐gap laser‐triggered vacuum switch with two positive gaps and 1:1 laser split ratio presents best closing performances than other switches. With the rise of laser energy, closing delay time and jitter time of double‐gap laser‐triggered vacuum switch both decrease, while the influences from increasing voltages are weak. Closing delay time of P–P type double‐gap laser‐triggered vacuum switch can be controlled within 103 ± 1.5 ns under 90 mJ laser energy, and it is about 10 ns longer than single‐gap laser‐triggered vacuum switch. For some direct current applications with changing voltage directions, P–N type double‐gap laser‐triggered vacuum switch with 1:1 laser split ratio shows more stable closing performances. In addition, closing performances of double‐gap laser‐triggered vacuum switch can be further improved by optimizing the developments of initial plasma in series gaps.

Grading capacitors are required to balance the voltage distribution of the double-break vacuum circuit breaker. However, large grading capacitors increase the magnitude and duration of the reignition current. To reduce grading capacitors, a synthetic circuit with double vacuum breaks was set up to study the effects of arcing time on voltage distribution. The voltage distribution of the upper break decreases from 61% to 52% with arcing times of two breaks decreasing from 6.6 to 3.4 ms synchronously. The experimental results demonstrate that reducing the arcing times can balance the voltage distribution during the transient recovery voltage (TRV) rising phase. The unbalance of TRV distribution can be further improved by adopting appropriate arcing times in the two breaks with grading capacitors having a capacitance of 3000 pF.

Surface flashover triggered vacuum switch (STVS) working performance mainly depends on the electrical characteristics of trigger pulse. This article presents an experimental investigation of the trigger process. The influence of the electrical properties of the trigger pulse on the trigger characteristics is focused. Based on the self-developed high-performance STVS product, the experimental test platform was established. The experimental results show that a shorter delay time of STVS can be obtained by heightening trigger voltage. However, the effect of trigger voltage on time jitter is not obvious. The slight increase in trigger current has evident influence on trigger delay time. It also does not affect the stability of trigger delay. With the increase in trigger voltage rise rate, the trigger delay time and time jitter can be optimized. Finally, the long-term stability of STVS is discussed. After 300 trigger times, the delay time changes from about 140 ns to more than 150 ns and the jitter changes from about 5 ns to more than 10 ns. In the design of STVS products, it is recommended to adopt a trigger system with a fast rise rate of trigger voltage and trigger current.

Working performances of laser-triggered vacuum switch (LTVS) mainly rely on the interactions of laser with target materials. Influences from target configuration, which is one of key factors in the interactions, are neglected so far. The trigger performances of LTVS with different target configurations are studied in this paper. Relevant influence factors about target configurations are discussed briefly based on theoretical analysis about the trigger process. The test prototype is established based on detachable vacuum chamber. The trigger characteristics of LTVS with different target structures, target depths, and laser focal positions are compared. The relationships between target configurations and trigger performances of LTVS are analyzed and discussed. The preferred targets in LTVS are suggested while considering its lifetime. The test results prove that the conical target shows the best trigger performances compared to other targets. Due to the enlarged laser irradiated area and shortened plasma moving distance, the delay time of LTVS reduces with the decrease in conical target angle and the increase in target depth, while the delay time is controlled within 32 ns. Benefited from laser reflection and plasma collision, the trigger performances of conical targets can be enhanced by focusing laser on the target side surface. In particular, the 90° conical target with 1.5 mm depth is suggested to be employed in LTVS products.

In order to reveal the migration and evolution of gas molecules in the actual oil–paper insulation composite system of transformer from the molecular level, the diffusion behavior of seven gas molecules (H₂, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆) generated during the operation and aging of oil-immersed transformers in the oil–paper composite insulation system is studied by molecular dynamics. Firstly, based on the molecular dynamics software, the model of the oil–paper composite insulation system and the gas molecule model is constructed. In order to compare and analyze the diffusion properties of gas molecules in a single medium, a single model of insulating oil and cellulose is also constructed. Then, the diffusion coefficients of gas molecules in the insulating oil, cellulose, and oil–paper insulating composite system are simulated and calculated. And the differences in the diffusion properties of gas molecules in the three insulating mediums are discussed. Finally, the microscopic mechanism of diffusion of different gas molecules in the three mediums is analyzed. The simulation results show that among the three mediums, the diffusion coefficient of H₂ is the largest, while the diffusion coefficients of the other gas molecules are not very different. The diffusion coefficients of the seven gas molecules are the smallest in the oil-immersed paper composite insulation system, followed by cellulose, while the diffusion coefficients are the largest in mineral oil. It indicates that the diffusion of gas molecules is inhibited in oil–paper insulation systems where the insulating paper is completely immersed in oil. This is mainly due to the fact that the insulating oil completely penetrates into the paper, filling the pores and voids between the fibers, resulting in a reduction in the transition vacancies of the intermediate gas molecules, which hinders the diffusion of the gas molecules.