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In this paper, an electro-thermal based surface charge accumulation model is established. Heat conduction, heat convection and heat radiation are included. The gas flow is coupled with fluid equations to describe the motion of charge carriers, and gas current density is also corrected by the gas velocity. In terms of it, the surface charge and electric field on a basin-type insulator in vertical laid DC gas insulated switchgear (GIS) and gas insulated transmission line (GIL) under different temperatures and pressures are studied. The results show that a temperature gradient is formed in the gas from top to bottom in the vertical direction, and the increase in pressure leads to a higher temperature of the lower surface. The surface charge density and tangential electric field increase with the temperature and decrease with the pressure. As a comparison, the surface charge and tangential electric field are calculated without considering temperature and without considering heat convection. The former leads to a lower tangential electric field than this model, while the latter brings about a higher electric field. This paper provides a more accurate reference for the design of DC GIS/GIL through a more comprehensive model.

Surface flashover on an insulator caused by the charge accumulation at the gas–solid interface is one of the main reasons limiting the development of gas insulated equipment in high voltage direct current (HVDC) condition. Therefore, it is helpful to clarify the mechanism of surface flashover and surface charge behavior by measuring charge distribution with high accuracy. In this article, a surface charge inversion algorithm based on constrained least square filter (CLSF) is proposed for surface charge measurement in a shift-invariant system. By taking the image restoration technology as an analogy, the algorithm transfers matrix equation into frequency domain by 2-D Fourier transform, which significantly simplifies the computational process. Then the CLSF is used to suppress the noise signal and actualize the conduction from surface potential distribution to surface charge density distribution. The calculation process and accuracy of the algorithm are discussed in detail with the simulated examples, and the inversion performance of CLSF is compared with Wiener filter. At last, the effectiveness of the algorithm is verified by performing surface charge measurement and dust figure. This methodology gives an innovative idea of potential-charge transformation process with higher accuracy and stability, which benefits the development of surface charge measurement technology.

In this study, a simulation model of surface charge accumulation on a basin-type insulator was constructed. Three accumulation mechanisms were considered, i.e. electrical conduction within the gas, electrical conduction through the insulator and along insulator surface. For the gas electrical conduction, the generation, diffusion, drift and recombination of charge carriers in SF6 were taken into consideration. The surface conductivity is treated by directly defining parameters instead of surface thin layer, which improves the calculation range of surface conductivity in ion flow model. Additionally, surface charge accumulation characteristics with different parameters were studied. The results indicated that the polarity of surface charge would change with the ion pair generation rate, volume conductivity and surface conductivity. Based on the surface charge and electric field distributions, it was found that the dominant surface charge accumulation mechanism changes from volume conduction to gas conduction as the ion pair generation rate increases. When the volume conductivity increases from 1 × 10−19 to 1 × 10−14 S/m, the dominant mechanism changes from gas conduction to volume conduction. Furthermore, as the surface conductivity increases, the dominant mechanism is surface conduction. The proposed study is helpful for understanding the mechanism of surface charge accumulation and provides insight into charge accumulation inhibition.

Due to the serious charge accumulation at gas-solid interface, the surface flashover voltage of insulator in gas insulated equipment may be significantly reduced. In order to pursue a method inhibiting surface charge accumulation, the epoxy composites modified by nano-SiC particles were coated on the insulator surface in this paper. The thickness of coating was 300 μm, and the SiC content was 5, 7 and 10 wt%. With the help of a couple of finger-shaped electrodes, the insulators with different coatings were charged at −10 kV voltage, and then the dynamic surface potential distributions were investigated. The results showed that only positive potential appeared on the surface and it mainly distributed near the high voltage electrode. With the passage of charging time, the shrinking phenomenon of high-potential region and the expansion of low-potential region can be observed. In addition, with the increase of SiC content, the average value of surface potential decreased monotonously and the shrinking speed of high-potential region seemed to be increased. Especially when the SiC content rose to 7 and 10 wt%, the magnitude and distribution area of surface potential declined sharply from 40 to 60 min. After 60 min, the surface potential distribution of the insulator with 5 wt% SiC/Epoxy coatings nearly unchanged, whereas it remained a slight fluctuation with 7 and 10 wt% fillers. Our study indicates that the coating with nano-SiC fillers has an inhibition effect on surface charge accumulation.

In order to suppress surface charge accumulation, a nano-SiC/epoxy composite with nonlinear conduction characteristic was employed to coat a pure epoxy substrate in this paper. Surface potential distributions on the insulator were measured after being charged by a pair of finger-shaped electrodes (one was powered at −10 kV, and the other was grounded). For the insulators with and without coating, there were mainly positive potentials on the whole surface, and the area with higher potential located near the high voltage electrode. As the charging time increased, the high potential area began to shrink, indicating a possible charge migration. When the charging time exceeded 60 min, the potential distribution was almost kept unchanged. Compared with the pure epoxy substrate, the amount of surface charges had a slight increment after being coated with 3 wt% nano-particles. The accumulated surface charges were progressively reduced when the content of fillers became higher. Especially for the samples with 7 wt% and 10 wt% ingredients, there was a sharp decrease of accumulated surface charges in the distributed area and magnitude from 40 to 60 min. In terms of surface trapping characteristics and nonlinear conduction of the composite, the effect of coating on the surface charge accumulation was discussed.

ObjectiveThe aim of this study was to evaluate the incidence and risk factors of gestational trophoblastic neoplasia (GTN) from hydatidiform moles (HMs) cytogenetically diagnosed in a prospective cohort setting.MethodsThe prospective observational cohort study included cases of cytogenetically defined molar pregnancies, which were diagnosed by a multiplex short tandem repeat polymorphism analysis. Cases were classified as androgenetic complete HMs (CHMs), diandric monogynic triploid partial HMs (PHMs), or biparental abortion. Gestational trophoblastic neoplasia was diagnosed according to the International Federation of Gynecology and Obstetrics 2000 criteria. Incidences for each category, that is, CHM, PHMs, and biparental abortion, were calculated. Clinical variables (age, partner age, gravidity, parity, height, weight, BMI, and gestational age) and laboratory data (serum human chorionic gonadotropin [hCG], white blood cell count, hemoglobin, and platelet count) were compared between spontaneous remission cases and GTN cases in androgenetic CHMs.ResultsAmong 401 cases, 380 were classified as follows: 232 androgenetic CHMs, 60 diandric monogynic PHMs, and 88 biparental abortions. A total of 35 cases (15.1%) of CHMs, but only 1 case of PHM (1.7%) and no biparental abortions, exhibited progression to GTN. The hCG value before evacuation was significantly higher in GTN cases than in spontaneous remission cases (P = 0.001, Kruskal-Wallis test). Patient age was also significantly higher in GTN cases than in spontaneous remission cases (P = 0.002, Student t test).ConclusionsUnder the cohort cytogenetic diagnosis setting, the traditional risk factors for GTN after molar pregnancy, hCG value before evacuation and age, were confirmed in androgenetic CHMs. The risk of GTN was lower for PHMs than for CHMs. However, 1 patient with cytogenetic PHMs developed into GTN.

Mitochondrial DNA (mtDNA) and genomic DNA are produced in separate subcellular compartments. Human mtDNA is transmitted via maternal transmission in general. Complete hydatidiform moles (CHMs) represent major trophoblastic diseases that are cytogenetically exceptional because the chromosomal genomic DNA is derived only from sperm cells, making them strikingly different from normal concepti. However, few reports have described the mtDNA-transmission pattern in hydatidiform moles. To evaluate mtDNA transmission in androgenetic CHMs, we compared the sequences of hypervariable regions in 16 trios sets of mtDNAs from maternal, paternal, and villous samples of androgenetic CHMs diagnosed by short tandem repeat-polymorphism analysis. All mtDNAs in androgenetic CHMs were maternally derived, in line with the general human inheritance pattern. Three maternal mtDNAs were heteroplasmic. The heterozygous status of maternal mtDNA was reflected in villous tissue, in which variants status was also heterozygous. CHMs are composed of paternal chromosomes and maternal mitochondria.

Investigating the propagation characters of UHF partial discharge (PD) signals in cable joint is helpful to the application of UHF method in XLPE PD monitoring. In this paper, a propagation model about UHF signal in a prefabricated joint is constructed. Based on it, it effects of some factors, i.e. longitudinal distance of detection location, lateral location of detection, detecting angle, pulse width, pulse amplitude, the size of metal shield and the thickness of semiconductive layer, on the PD signal propagation are studied. It is found that the signal amplitude decays faster in the joint than that in the body, and the signal intensity is much stronger inside the metal shield than that outside. The maximum amplitude of electromagnetic wave radiated by the PD source appears in the radial direction along the radius of the cross-section. The short duration of discharge pulse contributes to the appearance of high-order modes, while the response signal is proportional to the PD source. The metal shield and semiconductive layer increase the signal attenuation. These results provide insight into some design parameters of UHF antenna and its installation location.

Monitoring partial discharge (PD) activities in the joint of cross-linked polyethylene (XLPE) cables has attracted much attention due to its extensive application and high fault rate. In this paper, we designed a wide-band sensor with simple configuration, which was embedded in the outer semi-conductive layer of the cable. Based on the analysis of circuit and antenna models, the structural parameters of sensor were determined, and it was found that the effective bandwidth reached up to 500 MHz. In addition, the sensor had a quick response to the pulse with a rising time longer than 2 ns by testing its square response, as well as a linear input-output characteristic and a sensitivity of 3 pC. At last, the sensor was applied to insulation defect type identification in the cable joint. As for three common defects, both the single PD pulse and PD patterns showed distinct. These indicated that the sensor had a potential application prospect in the PD online detection for cable joint.