In electromagnetic pulse (EMP) generators, insulation components are often subjected to megavolt-level high-voltage pulses. Once surface flashover occurs, it will cause fatal damage to the entire generator. However, the characteristics and mechanisms of long-distance surface flashover in SF6 gas remain poorly understood, hindering engineering insulation design. This study investigates long-distance surface flashover under bipolar polarity. Voltage-time (U-t) characteristics of flashover voltages were obtained for surface distances ranging from 300 to 500 mm. The results show that the flashover voltage exhibits an approximately inverse proportional relationship with the flashover delay. Meanwhile, when the flashover delay varies, the polarity effect and surface distance sensitivity of the flashover voltage also differ. Based on spatiotemporal variations in optical intensity before flashover, the influence of different time delays on flashover mechanisms was analyzed. It is considered that when the flashover delay decreases, the dominant mechanism of flashover discharge gradually transitions from the precursor leader mechanism to the stem leader mechanism. Finally, distinct discharge mechanisms for long-distance surface flashover were systematically elucidated.

Abstract Surface flashover at gas–solid interfaces is a critical factor in electromagnetic pulse simulator reliability. To accurately predict flashover events over a wide surface distance range (15–500 mm), this paper develops a machine-learning-based classification model. Three experimental platforms with output ranging from ± 80 kV to ± 2000 kV were constructed, yielding 1245 valid data samples covering various surface distances, voltage polarities, gas pressures, electrode configurations, and voltage waveforms. To address severe class imbalance (flashover proportion > 85%) under certain experimental conditions, a data augmentation method based on the three-parameter Weibull distribution is proposed: non-flashover samples are generated by sampling below a low cumulative probability threshold ( U 10% recommended) after estimating Weibull parameters of flashover voltages, effectively mitigating imbalance and overfitting. Six algorithms including Support Vector Machine (SVM), Multilayer Perceptron (MLP), Random Forest (RF), Gradient Boosting (GB), Extreme Gradient Boosting (XGBoost) and Light Gradient Boosting Machine (LightGBM) are trained with Bayesian hyperparameter optimization. The SVM model achieves the best performance on the test set: F1 score of 0.9111 and AUC of 0.9590. MLP achieves the second-best performance. The tree‑based ensemble methods show slightly lower F1-scores and exhibit a tendency towards overfitting. Feature importance and SHAP analysis are carried out to verify whether the model captures physically consistent mechanisms rather than spurious statistical correlations.

The breakdown process of a self-triggered preionized switch with the four-electrode structure under nanosecond pulses is studied based on optical diagnosis. The breakdown of both subgaps initiates from the main electrode surface in the form of uniform discharge. A uniform-like low-impedance discharge channel forms first in the cathode side subgap. Then several streamer-like high-impedance discharge channels form later in the anode side subgap. Therefore, the anode side is under overvoltage after the cathode side discharge channel forms. The intensity of discharge channels indicates that the anode side subgap first breaks down. When the injection time of preionization is postponed, the uniform discharge in the cathode side converts into streamer. It is also proved that the trigger discharge can preionize each subgap separately, indicating that both photoemission and photoionization mechanisms contribute to the preionization process.

Self-triggered preionized switches with four electrode structures are widely used in large pulsed power generators. Reducing its time delay jitter is an essential requirement. To understand the time delay, this article investigates its breakdown processes and mechanisms. The switch is divided into two symmetrical sub-gaps with a sphere-plate structure. The breakdown processes of the sub-gaps in nitrogen are photographed by an intensified charge coupled device (ICCD) camera. It is observed that two sub-gaps can be separately preionized by the spark discharge. Uniform discharge can be stimulated from the main electrodes of two sub-gaps. Increasing the gap distance or postponing the injection time of preionization makes the uniform discharge easier to transfer to streamer discharge. Combining the discharge phenomena and the spectra of trigger gap discharge, it is inferred that the initial electrons are generated through photoemission and cascade ionization. Furthermore, a large number of excited molecules generated by preionization will accelerate the breakdown process. Under the same voltage pulse, a uniform-like discharge channel with relatively low resistance (k Omega class) first forms in the cathode side sub gap. In a practical four-electrode switch whose grading resistors are in k Omega to 10 k Omega class, the anode side sub-gap will withstand overvoltage and break down first after the channel in the cathode side forms.

With the development of high voltage devices, various methods have been taken to avoid the insulation failure. Ceramic coating, as one of the methods, can be used as electrical insulation in demanding conditions, like high-temperature ambience or other harsh environment. However, the breakdown characteristics of ceramic coating switch have been little discussed, especially under pulse voltages. In this paper, to study the effect of alumina coating on breakdown characteristics, the high voltage experiments have been carried out in 0.3 MPa SF6 under nanosecond pulses. The electrode substrates were treated by a method of plasma electrolytic oxidation (PEO) to produce a layer of alumina coating. Four pairs of electrodes with varied thickness of alumina coating (20$\mu$m, 60$\mu$m, 100$\mu$m and 120$\mu$m), as well as one pair of electrodes without coating, were employed in this experiment. The applied voltage was produced by a compact Marx generator, and the rise time of it was about 40 ns. The breakdown voltage and breakdown time delay have been measured. The results showed that the thickness of coating layer have little effect on breakdown strength. And as the pulse steepness increased, the effect of coating will get strong at first and then go into a gently-changed period. Comparing the secondary electron emission coefficients of steel and alumina and the U-t curves of the four pairs of electrodes, the different process of discharge initiation and time delay might be the main causes for this phenomenon. Since the discharge initiates differently from cathode and anode, the coating electrode was utilized respectively as cathode and anode to investigate the effect of coating layer on initial process.

Surface flashover of dielectric materials often causes extensive damage to pulse power devices. Nowadays, this insulation issue is exacerbated by the demands for ever-higher operating voltages. To solve this issue, the flashover voltage and the streamer development characteristics were investigated under positive and negative nanosecond impulse, respectively, in pressured SF6 gas. First, the surface flashover strength was obtained and the Weibull distribution is introduced to describe the statistical characteristics. The results showed that the negative flashover voltage was much higher than the positive one for Al2O3-epoxy. Within the range of 0.1–0.3 MPa, the negative voltage increased with the gas pressure, while the positive one performed independent with pressure. Then, to investigate the streamer evolving process, a high-speed camera was used to get the discharge picture and the instant velocity of streamers at different conditions. Surface morphology change after the flashover was also analyzed. At last, the possible mechanisms for polarity and pressure effects were given.

为研究Marx发生器机芯在公路运输条件下的力学环境适应性,基于随机振动理论和有限元分析方法对Marx机芯进行了仿真分析和随机振动试验.首先,建立了八级模块化Marx机芯的有限元动力学仿真模型,模拟确定了机芯的应力集中点;然后,通过振动台运输振动摸底试验修正了有限元模型,对机芯结构进行了优化设计,使Marx机芯整体一阶频率由15.4 Hz提高到19.7 Hz,降低了整机垂向的动力学响应,提高了机芯的力学环境适应性.试验结果表明,Marx发生器结构设计需要重点考虑其在垂直方向的可靠性;振动过程中,机芯整体连接稳定,振动应力集中于机芯与U型支撑杆连接处、支撑杆与支撑板连接的角片处,以及开关连接件处,是结构设计的薄弱环节.

This work investigates the pulsed breakdown processes and mechanisms of self-triggered pre-ionized switches with a four-electrode structure in nitrogen through intensified charge coupled device photographs. The diameter of the trigger plane hole mainly determines the switch’s electric field distribution. Two configurations with minimum and maximum trigger plane holes are adopted for comparison. In the switch with a minimum trigger plane hole, the maximum electric field distributes at the surfaces of the main electrodes. Although charged particles in the triggering spark channel cannot drift out, homogeneous discharges can be stimulated from both the cathode and anode surfaces through ultraviolet illumination. Two sub-gaps are likely to break down simultaneously. In the switch with a maximum trigger plane hole, the maximum electric field locates near the trigger electrodes. Discharges in both sub-gaps initiate from the trigger electrodes in the form of a positive or negative streamer. Due to the lower breakdown voltage and electric field threshold for discharge initiation, the cathode side sub-gap breaks down first. The analysis of two extreme examples can be referenced in the future design and improvement of self-triggered four-electrode switches with different trigger electrode structures.

氧化铝掺杂环氧树脂复合材料在电力绝缘设备中应用广泛,然而人们对其在纳秒脉冲下的绝缘性能研究较少,这限制了它在指导脉冲功率装置中的应用.为探究其在纳秒脉冲下的沿面绝缘性能,对氧化铝掺杂环氧树脂复合材料在前沿数十ns快脉冲电压下的闪络特性进行了研究,结果显示,其闪络电场较纯环氧有较大提高,闪络电压符合韦伯分布.实验表明,闪络电压随电压上升率的增加而显著增加,从5.8 kV/ns时的108 kV上升到20.5 kV/ns时的226 kV,增幅超过1倍.闪络时延随电压上升率的上升呈现"先快速下降、后趋于平缓"的趋势.在试样闪络通道表面观测到明显的碳化现象,说明实验中的闪络放电对复合材料有破坏性影响.

Extensive research has been carried out to improve the breakdown strength (BDS) of polymer materials used in high-voltage power equipment. However, almost all the modifications, including nanocomposites, polymer blends, and multilayer films have enhanced the BDS by introducing alien material, which inevitably resulted in an increase in the dielectric losses. Therefore, we propose a multilayer structured film simplex composed of polypropylene (PP) to simultaneously achieve high BDS and low losses. By including virgin and fluorinated bi-axially oriented PP (BOPP) films, three different interface structures were constructed. All the multilayer PP films showed DC BDSs that were improved by varying degrees, compared to the single-layer film. In particular, owing to the enhanced electron trap depth and density caused by fluorination, the DC BDSs of multilayer films with fluorinated BOPP reached 458.7 kV mm−1, which was 20% higher than that of a single-layer PP film of the same thickness, while their dielectric loss was even lower than that of the single-layer film.

This paper presents a high-voltage fast risetime pulse generator. Marx generators are one of the common approaches to meet this need. However, the serious disadvantages of Marx generators include the delay time due to the series of inductances. To alleviate this effect, peaking capacitors have been used to produce fast risetime pulses. This paper describes results from the design, development, and testing of a 600 kV, 2 ns-risetime, and 25-ns-duration pulse generator using a peaking capacitor. The peaking capacitor, with a capacitance of 160 pF, was designed to be highly stressed at a maximum voltage of 1 MV when insulated with 0.5 MPa SF6. The effects of the peaking capacitor were studied by modeling the generator circuit. The influence of various parameters was investigated. There is good agreement between the theoretical and experimental results.

通过电磁仿真重点研究线栅天线金属拉线的疏密和线径对双锥-平面线栅结构的水平极化辐射波天线辐射特性的影响.采用三维电磁仿真软件建立双锥-平面线栅天线的模型,在脉冲源和激励等参数相同的情况下,设单侧线栅天线拉线根数分别为24根、48根、96根和192根,研究不同条件下辐射场的特性,分析不同疏密栅板天线的作用机理;令金属拉线的半径在1～40 mm之间变化,研究拉线线径对辐射场的影响;估计该型模拟器的实验区域.结果表明:双锥中心正下方测点基本不受线栅疏密程度和拉线线径的影响,其他位置上,线栅疏密主要影响电场水平极化分量的前沿和峰值,线栅越疏,前沿越小,峰值越低;对于给定测点,当拉线根数由24根增加到192根时,峰值变化率约5％,前沿变化率约10％,随着拉线根数增加,峰值变化率逐渐减小,根数超过96根后,峰值基本不变;拉线线径对辐射场的影响可以不计.天线样机实验证明,当单侧极板拉线根数为48根时,距地面4 m高水平面上模拟器实验区范围为12 m×16 m.

模态分析可以获得结构的动特性参数.对32级模块化Marx发生器机芯进行了力学特性仿真分析和模态试验,用以评估Marx发生器的力学环境适应性.首先,建立了模块化Marx机芯的有限元模型,获得了初步振型;其次,在自由边界条件下分别开展了Marx机芯整体模态试验、局部模态试验和传递特性试验,得到了整体和局部结构的模态参数.研究表明,模块化Marx机芯在23.58 Hz处出现整体一阶扭转;机芯局部结构固有频率较高;机芯在x,y,z三个方向的振动传递率的范围分别为5～15,6～10和10～35,为后续工程中Marx发生器机芯的针对性设计提供了参考.

A rectangular pulse generator plays an important role in the calibration of impulse measurement as well as the investigation into electromagnetic pulse effect. In addition, the characteristics of an output switch have a direct impact on the generator's output waveform. Following the basic requirements for the switch in a rectangular generator, this paper proposes a new type of laser-triggered film switch with a compact structure and high repeatability. The mechanical structure and operating mechanism of this switch have been elaborated. To verify the feasibility of this switch model, the irradiation experiments were carried out to study the interaction between the laser and the film, and the inductance of the switch has been estimated. Then, to test the characteristics of the switch, a Blumlein rectangular pulse generator based on this switch has been constructed. The experiment results show that the generator worked well in consecutive jobs and had a wild adjustable amplitude range from 2 kV to 10 kV, with a minimum rise-time of less than 1 ns. The effect of the laser loophole and the thickness of the film on the switch have also been investigated. Finally, the plasma developing process of the laser-triggered film switch has been discussed.

Surface electrical insulation performance is an important issue in pulse power devices. In order to investigate the surface flashover characteristics in an environment of high pressure SF6, a flashover experiment platform was established with nanosecond pulse voltage supply. The flashover characteristics of polymethylmethacrylate (PMMA) specimens with circular truncated cone shapes were subsequently determined under incremental SF 6 pressures from 0.2 to 1.0 MPa. As the angle of cone increased, the flashover voltage (FV) rose under low pressure condition, but fell at first and then rose at high pressure. The surface length and the field nonuniform factor were the main influences of FV with angle. In addition, the FV rose linearly at first and then reached its maximum when gas pressure increased, and it was easier to reach the maximum when the field nonuniform factor was higher. A high speed camera was also applied to get the photos at different period of flashover, and the luminous processes of flashover along different specimens were discussed in particle perspective.