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Abstract The flashover in vacuum is a rapid interfacial discharge across the insulator surface when subjected to high applied voltage. Here a theoretical model covering above‐surface processes is introduced. The model calculates the flashover threshold in vacuum, with revised secondary electron emission avalanche theory and improved desorbed neutral transport model. The model serves as the first part of an integrated flashover model, aiming for consistent treatment of both above‐surface and subsurface processes during the entire flashover development. The flashover threshold is obtained by combining the desorbed neutral pressure at given applied voltage and the gas breakdown criterion dictated by the Paschen's law. An analytical formula for threshold estimation containing physical parameters, and a simplified formula consisting of empirical coefficients are introduced, catering for both conceptual understanding and practical application. The derived formulae are validated by experimental data for a variety of insulator materials. The theory generalisation for non‐uniform electric field distribution is further discussed.

Abstract Excessively high temperatures inside a power transformer can accelerate the ageing rate and even cause unplanned outages. Accurately estimating the hot‐spot temperature (HST) of a power transformer is important for regulating the load and ensuring long‐term operation. In this study, a closed‐loop model of a 110‐kV product transformer with an oil natural/air forced (ONAF) cooling mode is built to predict HST, in which the compression ratio of windings, equivalent heat source and radiator geometry are considered. According to the flow field of the winding, the ‘dead oil zone’ and reverse oil flow are observed in the horizontal oil channels. The accuracy of the proposed model is experimentally validated by temperature‐rise tests. The results show that the absolute errors between the measured results and simulation are below 5°C, and the average error is ∼2°C. Furthermore, the arrangements of windings and radiators are studied to enhance the oil circulation. By adding 5 washers to the high‐voltage winding, the average temperature can be decreased by 6°C compared with the case without a washer. Elevating the radiator can also mitigate the characteristic temperatures, and the optimal height difference between the radiator and winding centre is suggested to be 0.66 m.

Abstract Background In the study, we aimed to evaluate the ability of micro‐histology combined with cytology to improve the quality of slides and diagnose endometrial lesions. Methods Endometrial specimens were collected from Li Brushes. Every specimen was prepared for micro‐histological and cytological slides, using cell block (CB) and liquid‐based cytology (LBC) technologies. Semi‐quantitative scoring system was used to evaluate the qualities of slides. CB slides were assessed by 5‐category scoring system. Diagnostic accuracy was calculated in LBC, CB, and LBC + CB groups based on the histological gold standard. Endometrial atypical hyperplasia, and endometrial cancer were considered positive, whereas others were considered negative. Results A total of 167 patients were enrolled. CB slides were inferior to LBC slides only in cellularity (p

Abstract Vacuum‐dielectric interface is the most vulnerable part of vacuum insulation systems where surface electrical breakdown is prone to happen, hence severely restricts the development of advanced electro‐vacuum devices with large capacity and its miniaturisation. Generally, a direct and effective way to improve vacuum surface insulation is to alleviate the initiation and development of multipactor phenomena. Inspired by this approach, the authors report a 3D‐printed insulation structure designed with a millimetre‐scale surface cavity covered by periodic through‐pore array via stereolithography, exhibiting remarkable multipactor suppression and flashover threshold improvement, well outperforming the conventional flashover mitigation strategies. Experiments and simulations demonstrate that electrons in the multipactor region pass through‐pores and are unlikely to escape from the cavity, hence no longer participate in the above‐surface multipactor process, and eventually improve flashover threshold. The proposed approach provides new inspiration for the design of advanced insulators featuring ultra‐high electrical withstanding capability and brings up new insight into pertinent industrial applications.

Abstract Ulcerative colitis is a chronic disease that increases the risk of developing colorectal cancer. Conventional medications are limited by drug delivery and a weak capacity to modulate the inflammatory microenvironment. Further, gut microbiota dysbiosis caused by mucosal damage and dysregulated redox homeostasis leads to frequent recurrence. Therefore, promoting mucosal healing and restoring redox homeostasis is considered the initial step in treating ulcerative colitis. Plasma‐activated solutions (PAS) are liquids rich in various reactive nitrogen species (RNS) and reactive oxygen species (ROS) and are used to treat multiple diseases. However, its effect on ulcerative colitis remains to be examined. Therefore, using a DSS‐induced mice colitis model, it is found that PAS has the potential to treat colitis and prevent its recurrence by promoting intestinal mucosal repair, reducing inflammation, improving redox homeostasis, and reversing gut microbiota dysbiosis. Further, an equipment is designed for preparing PAS without using nitrogen; however, after treatment with the Nitro‐free PAS, the therapeutic effect of PAS is significantly weakened or even lost, indicating that RNS may be the main mediator by which PAS exerts its therapeutic effects. Overall, this study demonstrates the treatment of ulcerative colitis as a novel application of PAS.

Abstract Dissolved gas analysis (DGA) is an efficient technique to diagnose transformer faults; however, the imbalance of the sample datasets is frequently observed in DGA, which has become one of the main challenges for accurate fault diagnosis. A generative adversarial network (GAN) model is proposed to realize the data augmentation for addressing these problems. The GAN model is nested by two backpropagation neural networks (BPNN) containing a generator and a discriminator. The generator produces real‐like data and continuously shapes the real‐like data approximate to real data. The discriminator works to distinguish between the real‐like data and the real data until the real‐like data cannot be discriminated. Under this adversarial learning, the generator output obtains the real‐like DGA samples to supplement the minority samples. To verify the diagnosis accuracy after the DGA data augmentation, three typically intelligent models, that is, BPNN, support vector machine (SVM) and deep belief network (DBN) are introduced to establish the diagnostic models. The results show that the recognition accuracy of the minority samples acquires average 30%, 25% and 50% increases for the three models respectively. It is shown that the GAN model well balances the sample datasets and strengthens the performance of the fault diagnostic models.

Abstract To improve the insulation, strength of materials is a permanent topic in the fields of high voltage and insulation, and surface insulation is one of the difficulties. Research shows that the surface fluorination by a non‐equilibrium plasma is a promising method to enhance the surface flashover characteristics of insulating materials. However, the determinants of flashover characteristics are so many that the mechanism is not well known. This paper aims to find out the reasons for the surface insulation improvement and optimise the plasma process parameters. The epoxy resin surfaces are modified by a fluorocarbon plasma, and the flashover voltages in vacuum and secondary electron emission yield are tested experimentally. Combined with the state of the art and the authors' previous work, the mechanism of improved surface flashover performances is investigated in depth from three aspects: the plasma process parameters, the surface physical and chemical properties and the surface electrical performances. A comprehensive understanding of the mechanism is concluded, of which the whole processes from the plasma surface modification of materials to the surface insulation performances are taken into account. It is hopeful to promote the practical applications of plasma fluorination in electrical engineering through the findings of this paper.

Abstract Interfaces between different materials, for instance, electrode–dielectrics and vacuum/air/SF6‐insulators and oilpaper, are universal in high‐voltage insulation systems. Targeted tailoring of the interfacial properties, e.g. chemical structures, micro‐/nanoscale morphology, the charge injection barrier, trap states, and surface conductivity, is thought to be an effective approach to improve insulation properties such as breakdown and flashover strength, corona/tracking resistance, and wettability. In this article, the authors review recent progress in interface tailoring methods and their application to improve various insulation properties. The potential application scenarios of interface tailoring in different facilities are first summarised, and the desired insulation properties of various applications are highlighted. Interface tailoring methods are classified as physical/chemical surface modification and surface coating (inorganic, organic and composite), and the features of different techniques are described in detail. The structure–property relationships between interfacial states and various microscopic parameters such as charge injection barrier, trap distribution and surface conductivity are discussed together with the tailoring mechanisms for different insulation properties. Finally, the future development prospects of interface tailoring methods and their applications, e.g. multifunctional coating and stimuli–response smart coating, are presented.

Abstract In recent years, frequency domain spectroscopy (FDS) is often used to evaluate oil paper insulation state in power transformer bushing. But it is still very difficult to evaluate the moisture content accurately and quickly. In order to solve this problem, this paper proposes an intelligent algorithm based on random forest regression (RFR) to construct an efficient evaluation method through segmented FDS curves. Furthermore, the characteristics of FDS curves were studied and the intelligent method was compared with support vector regression (SVR) and deep neural networks (DNN). The results show that the dielectric loss, the real part and imaginary part of complex capacitance all move upward with the moisture increasing, so they can be used as the input feature of the evaluation model; The moisture content evaluation accuracy of the RFR model in the whole frequency band is higher than that of SVR and DNN models; With the increase of lower cut off frequency (FDS test stop frequency), the FDS test time is greatly shortened, and the accuracy of the RFR model can still meet the evaluation requirements. Therefore, the data in a compromise frequency band can be used to evaluate the moisture content of oil paper insulation accurately and quickly.

Abstract Surface charges accumulated on solid insulating materials in electrical apparatuses and electronic devices could distort the initial electric field and severely damage the insulation performance. Accurate transient surface charge measurement is critical to determine the mechanisms of charge transport and flashover occurrence, and estimate surface insulation strength under high voltage. The measurement technique based on the Pockels electro‐optic effect is considered as the only approach for 2‐D dynamic charge distribution behaviour so far, and it has good capability to avoid original electric field distortion caused by conventional methods featured by metal probes. This paper reviews recent progress of the non‐invasive dynamic surface charge measurement systems on the Pockels technique. We focus especially on typical systems with transmitting and reflecting configurations and the frequently used fast inversion algorithms. It can be inferred that higher spatial‐temporal resolution, higher signal‐to‐noise ratio, and better compatibility for both transparent and opaque materials are the future development trends, which greatly depend on multiple technological breakthroughs at impact‐resistant electro‐optic crystals, advanced high‐speed photography and high‐performance inversion algorithms. In addition, the recent studies on transient behaviour of surface discharge, together with the present limitation and future prospects are discussed. It is expected that more ideas will be inspired in transient surface charge measurement by the Pockels technique and other relevant electro‐optic methods.

Abstract Background Shaanxi province, located in the upper Yellow River, has been evidenced as the geographic origin of Chinese civilization, Sino‐Tibetan‐speaking language, and foxtail or broomcorn millet farmers via the linguistic phylogenetic spectrum, archeological documents, and genetic evidence. Nowadays, Han Chinese is the dominant population in this area. The formation process of modern Shaanxi Han population reconstructed via the ancient DNA is on the way, however, the patterns of genetic relationships of modern Shaanxi Han, allele frequency distributions of high mutated short tandem repeats (STRs) and corresponding forensic parameters are remained to be explored. Methods Here, we successfully genotyped 23 autosomal STRs in 630 unrelated Shaanxi male Han individuals using the recently updated Huaxia Platinum PCR amplification system. Forensic allele frequency and parameters of all autosomal STRs were assessed. And comprehensive population genetic structure was explored via various typical statistical technologies. Results Population genetic analysis based on the raw‐genotype dataset among 15,803 Eurasian individuals and frequency datasets among 56 populations generally illustrated that linguistic stratification is significantly associated with the genetic substructure of the East Asian population. Principal component analysis, multidimensional scaling plots and phylogenetic tree further demonstrated that Shaanxi Han has a close genetic relationship with geographically close Shanxi Han, and showed that Han Chinese is a homogeneous population during the historic and recent admixture from the STR variations. Except for Sinitic‐speaking populations, Shaanxi Han harbored more alleles sharing with Tibeto‐Burman‐speaking populations than with other reference populations. Focused on the allele frequency correlation and forensic parameters, all loci are in accordance with the minimum requirements of HWE and LD. The observed combined probability of discrimination of 8.2201E‐28 and the cumulative power of exclusion of 0.9999999995 in Shaanxi Han demonstrated that the studied STR loci are informative and polymorphic, and this system can be used as a powerful routine forensic tool in personal identification and parentage testing. Conclusion Both the geographical and linguistic divisions have shaped the genetic structure of modern East Asian. And more forensic reference data should be obtained for ethnically, culturally, geographically and linguistically different populations for better routine forensic practice and population genetic studies.

As an indispensable part of high-voltage direct current (HVDC) cable, the semiconductive shielding layer plays the role of uniforming electric field in the cable. However, cable shielding materials >35 kV mainly rely on foreign imports in China, which belongs to the technical weak issues in the field of electrical materials. At present, there are few systematic reports on semiconductive shielding material of HVDC cable. In the work, the mechanisms of charge conduction and thermal conduction of semiconductive material have been introduced. Effect of raw material, carbon black content and the second conductive filler on the resistance characteristics of the semiconductive layer, the charge accumulation characteristics of the insulating layer and the interface characteristics have been studied. A kind of semiconductive layer as a high voltage terminal charge emission method has been proposed to study charge emission from the semiconducting layer to the insulation layer. This work can provide theoretical guidance for the research of semiconductive shielding materials.

Overvoltage caused by faults or switching is one of the decisive factors affecting the insulation level of equipment in UHVDC transmission systems. As for ±1 100 kV transmission projects, there has been no clear conclusion about the overvoltage distribution characteristics along transmission lines. This paper studies characteristics of the overvoltage distribution along ±1 100 kV transmission lines after building the simulation platform of ±1 100 kV UHVDC transmission systems with the use of PSCAD software. The typical fault conditions are simulated such as monopolar line-to-ground fault and line-broken-down fault of transmission lines. The distribution characteristics of overvoltage along the line under different faults are obtained. The simulation results show that the arresters installed along the lines can significantly reduce the switching voltage level of DC lines. The voltage-current characteristics and the installation density of the arresters along the line have an important influence on the overvoltage suppression effect. Through the comparative analysis, a configuration scheme of arresters along the lines is proposed, which has a great effect for overvoltage suppression. The results are instructive for the design of insulation coordination in practical projects.