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The power outage caused by decay-like fracture of composite insulators significantly impacts the power grid. In this paper, a decay-like fractured insulator of 500 kV transmission line is taken as a research object. The detailed observation of core rod and silicone rubber housings, discharge results, temperature rises, and electric field distribution are obtained. (a) The fractured insulator has abnormal heating on the exposed core rod and sheath surface, and the ambient temperature and humidity significantly influence the temperature rise. (b) It is proposed that one of the most obvious characteristics of decay-like insulator is abnormal temperature and temperature rise (such as T > 50°C, ΔT > 30 K). (c) Under the same conditions, temperature rises, electrical discharge, and electrical field strength of decay-like insulator are higher than those of other insulators, and the discharge at the bare core rod is intense. (d) The electric field strength distribution and discharge distribution of decay-like insulator are different from other aging and new insulators. However, the measurement results are significantly affected by test conditions. Therefore, it is difficult to determine whether the composite insulators are decay-like using electric field distribution and UV measurement on site. [ABSTRACT FROM AUTHOR]

Our study evaluated the use of amniotic membrane-derived stem cells for repairing osteochondral defects in a weight-bearing area in rabbits. Twenty-four 3-month-old male or female New Zealand white rabbits were selected. The rabbits were randomly divided into 3 groups of eight, according to the treatment received for an experimentally inflicted femoral medial malleolus lesion, group I received a human acellular amniotic membrane seeded with bone marrow-derived mesenchymal stem cells (HAAM-BMSCs) implant; group II received a simple HAAM implant and the control group received no experimental lesion or treatment. The rabbits were sacrificed at 12 and 24 weeks after the procedures (4 rabbits in each time-point) and the cartilage repair status in each animal was evaluated under the microscope. The tissue of the HAAM-BMSCs group grew well covering an area in the visual field that was significantly larger than that of the HAAM group (p<0.05). The percentage of collagen II-positive area in the HAAM-BMSC group was significantly higher than that in HAAM group (p<0.05). The number of chondrocytes determined by toluidine blue staining was higher in the HAAM-BMSC group than that in the HAAM group (p<0.05). The Wakitani scores of the HAAM and HAAM-BMSC groups were significantly higher (worse) than those of the normal control group (p<0.05), but the score in the HAAMBMSC group was significantly lower than that in the HAAM group (p<0.05). The Wakitani scores in the HAAM-BMSC group were not different between the two time-points taken. Based on our findings, the amniotic membrane-derived stem cells had a good therapeutic effect in repairing the osteochondral defects in the weight-bearing area, and the number of chondrocytes in the injured area was increased significantly, which accelerated the repair of the damaged tissue in rabbits. [ABSTRACT FROM AUTHOR]

Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO3, KNO3, NH4NO3, MgSO4, Ca(NO3)2 and CaSO4), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO4. The correction agreed with the flashover test results of insulator polluted by three types of soluble mixture. Research results indicate that the flashover gradient correction method proposed in this paper performs well in reducing the calculating error. It is recommended to carry out component measurements and flashover gradient correction to better select outdoor insulation configuration. [ABSTRACT FROM AUTHOR]

Icing poses a serious threat to power transmission in many countries. Various studies on the icing mechanism and icing growth process of transmission lines have been carried out all over the world, whereas there are few reports about the icing growth mechanism and its influencing factors on insulators to date. In this paper, artificial tests of insulator icing were carried out; the influences of temperature, median volumetric diameter (MVD), and wind velocity on the icing accretion process, ice shape, and ice type on the surface of insulators were analyzed systematically; and the icing growth performance of different types of insulators were also analyzed. Test results show that under different icing environments, the icing growth of insulators is always nonlinear; the growth rates of icicles and ice layers increase with the decrease of temperature; with the increase of wind speed, all of the ice thicknesses and the length and diameter of icicles increase significantly; for wet growth, the impact of MVD on icing growth of insulators is not significant; the structure of the insulator has some influence on the icing growth process; and with the increase of length and diameter of icicles, the growth rate of the ice layer on the insulator surface decreases significantly. [ABSTRACT FROM AUTHOR]

The electrical performance of outdoor insulators decreases under low air pressure conditions. The ac pollution flashover performance of various types of insulators are investigated in the multifunction artificial climate chamber in the State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University. The field investigation of the ac pollution flashover voltage performance are carried out at three different high altitudes including Wangkun station (altitude of 4484 m), Nachitai station (altitude of 3575 m) along the Qingzang railway and Geermu urban (altitude of 2820 m). The test results indicate that the characteristic exponent n describing the influence degree of air pressure on pollution flashover voltage, which has influence on the pollution flashover voltage of insulators, is variable, and the value of n is related to the pollution, insulator type etc. Under ac voltage, n is 0.45-0.85. The composite insulators are superior in external insulation selection in high altitude and heavy polluted areas. The relative error between the field test results and laboratory test results is less than 8 %, so the research results obtained in the laboratory can be applied to engineering design. [ABSTRACT FROM AUTHOR]

The external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. However, a few investigations at the high altitude sites of 3000 m and above have been conducted. This paper reports on the laboratory tests of artificially polluted cap-and-pin porcelain insulators performed at the high altitudes of 2800 m to 4500 m. The test results and analysis show that the pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.29 and the one characterizing the influence of nonsoluble deposit density is 0.09 to 0.15. The ac pollution flashover voltage Uf will decrease with the decrease of air pressure P and increase with the decrease of ambient temperature t. Uf is a power function of the ration of air pressure P/Po and also is a power function of the ambient temperature coefficient (1 + 0.02(t - 20)). The average exponent characterizing the influence of air pressure is about 0.56 and the exponent characterizing the influence of ambient temperature is about 0.21 for the three types of insulators in the paper. [ABSTRACT FROM AUTHOR]

Fine-tuning of ethylene production plays an important role in developmental processes and m plant responses to stress, but very little is known about the regulation of ethylene response factor (ERF) proteins in ethylene biosynthesis genes and ethylene production. Identifying cis-acting elements and transcription factors that play a role in this process, therefore, is important. Previously, a tomato (Solanum lycopersicum [f. sp. Lycopersicon esculentum]) ERF protein, LeERF2, an allele of TERF2, was reported to confer ethylene triple response on plants. This paper reports the transcriptional modulation of LeERF2/TERF2 in ethylene biosynthesis in tomato and tobacco (Nicotiana tabacum). Using overexpressing and antisense LeERF2/TERF2 transgenic tomato, we found that LeERF2/TERF2 is an important regulator in the expression of ethylene biosynthesis genes and the production of ethylene. Expression analysis revealed that LeERF2/TERF2 is ethylene inducible, and ethylene production stimulated by ethylene was suppressed in antisense LeERF2/TERF2 transgenic tomato, indicating LeERF2/TERF2 to be a positive regulator in the feedback loop of ethylene induction. Further research showed that LeERF2/TERF2 conservatively modulates ethylene biosynthesis in tobacco and that such regulation in tobacco is associated with the elongation of the hypocotyl and insensitivity to abscisic acid and glucose during germination and seedling development. The effects on ethylene synthesis were similar to those of another ERF protein, TERF1, because TERF1 and LeERF2/TERF2 have overlapping roles in the transcriptional regulation of ethylene biosynthesis in tobacco. Biochemical analysis showed that LeERF2/TERF2 interacted with CCC box in the promoter of NtACS3 and with dehydration-responsive element in the promoter of LeA CO3, resulting in transcriptional activation of the genes for ethylene biosynthesis in tomato and tobacco, which is a novel regulatory function of ERF proteins in plant ethylene biosynthesis. [ABSTRACT FROM AUTHOR]

Carbon foam templates were prepared from a mixture of mesophase pitch (MP) and Si particles, followed by foaming and carbonization. Subsequent molten Si infiltrated into the carbon foam at 1500°C for 4 h in an inert atmosphere resulted in the formation of porous SiC ceramics. Micrographs were investigated by a scanning electron microscope (SEM), and phase identification of porous SiC ceramics was performed by X-ray diffraction (XRD). The flexural strength and bulk density of porous SiC ceramics were also measured and calculated. The results revealed that the flexural strength of porous SiC ceramics increases with increasing Si content and decreasing porosity. The addition of Si in MP results in an increased densification of porous SiC struts. With 50 wt% Si, porous SiC ceramics with a high flexural strength of 23.9 MPa and a porosity of 55% were obtained. [ABSTRACT FROM AUTHOR]

Abiotic stresses such as drought, cold, and salinity affect normal growth and development in plants. The production and accumulation of reactive oxygen species (ROS) cause oxidative stress under these abiotic conditions. Recent research has elucidated the significant role of ethylene response factor (ERF) proteins in plant adaptation to abiotic stresses. Our earlier functional analysis of an ERF protein, JERF3, indicated that JERF3-expressing tobacco (Nicotiana tabacum) adapts better to salinity in vitro. This article extends that study by showing that transcriptional regulation of JERF3 in the oxidative stress response modulates the increased tolerance to abiotic stresses. First, we confirm that JERF3-expressing tobacco enhances adaptation to drought, freezing, and osmotic stress during germination and seedling development. Then we demonstrate that JERF3-expressing tobacco imparts not only higher expression of osmotic stress genes compared to wild-type tobacco, but also the activation of photosynthetic carbon assimilation/metabolism and oxidative genes. More importantly, this regulation of the expression of oxidative genes subsequently enhances the activities of superoxide dismutase but reduces the content of ROS in tobacco under drought, cold, salt, and abscisic acid treatments. This indicates that JERF3 also modulates the abiotic stress response via the regulation of the oxidative stress response. Further assays indicate that JERF3 activates the expression of reporter genes driven by the osmotic-responsive GCC box, DRE, and CE1 and by oxidative-responsive as-1 in transient assays, suggesting the transcriptional activation of JERF3 in the expression of genes involved in response to oxidative and osmotic stress. Our results therefore establish that JERF3 activates the expression of such genes through transcription, resulting in decreased accumulation of ROS and, in turn, enhanced adaptation to drought, freezing, and salt in tobacco. [ABSTRACT FROM AUTHOR]

The possibility of insulator flashover would be higher with the increase in icing degree. Therefore, the method of monitoring the icing weight of the insulator is of vital importance. In this study, the estimation method of icing weight on composite insulator in rime icing was proposed. By quite a few experiments under different rime icing conditions, results showed good agreement between estimated value and measured icing weight. Therefore, the estimation method of icing weight proposed by this study was effective and may be used for predicting icing weight. Based on the estimation method, this study discusses the effect of key structural parameters of composite insulator under different rime conditions on icing weight. In order to better apply the composite insulator to electric transmission line in icing area, several suggestions on design optimisation of structural parameters are proposed. [ABSTRACT FROM AUTHOR]

The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is well understood that heavy rain can wash away contamination from the surface of high voltage (HV) insulators and thereby reduce the risk of pollution flashover. This study examines the cleaning effect of natural wetting conditions on HV insulators on four 500 kV transmission lines in Hunan Province, China. Historical meteorological data, monthly equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements taken over a period of five years were analyzed to investigate the relationship between rainfall intensity and insulator cleaning. The measured data show that the ESDD/NSDD changes with the seasonal variation, which accumulates in dry season (January–April, about 117–122 days) and is washed off in the wet season (June–October, about 118–127 days). According to the measured data, the ESDD and NSDD on the surface of insulators were affected by the rainfall intensity (in the dry season it is about 1 mm/day and in the wet season it is about 5 mm/day). Based on a comparison of the four study sites, we propose a mathematical model to show the functional relationship between rainfall intensity and insulator self-cleaning capability. The mathematical model’s coefficient of determination (R2) is greater than 0.9 and the effective rate of self-cleaning capability reaches 80%. [ABSTRACT FROM AUTHOR]

Ice melting with dc is one of the key technologies to prevent the Chinese power grid from ice storms. Especially after the severe ice storm in the southern part of China in early 2008, dc ice-melting technology has drawn more attention than ever before. However, there are few satisfactory methods to select correct parameters so the ice-melting project rarely achieves desired effects in some cases when applied in Hunan, Guizhou, and other provinces in China. Therefore, it is of great significance to develop a method to estimate parameters which is applicable in the practical situation for dc ice melting. To handle this, the factors, such as wind velocity, ambient temperature, current density and ice-layer thickness were analyzed and then a dc ice-melting model is put forward in this paper. Both the results of simulations and experiments show that the ice-melting process can be divided into three stages composed of temperature rising, ice melting, and ice shedding, among which the ice melting is the key stage consuming most of the ice-melting time. In this stage, an elliptic airgap is formed and widened gradually with an influence on the ice-melting time and the temperature of the conductor. The experiments in the artificial climate chamber demonstrate that the results of the presented model are consistent with those of the experiments generally, so it can be employed to estimate the parameters of ice melting in practical engineering as reference. [ABSTRACT FROM AUTHOR]

Differences in the amount of pollution on the top and bottom surfaces of an insulator have a great influence on the dc pollution flashover voltage. Up to now, many investigations have been carried out on non-uniform pollution flashover performance of porcelain and glass insulators, but very few on composite insulators. In this paper the influence of non-uniform pollution distribution on dc composite insulators on their flashover performance was analyzed, and a correction formula for the non-uniform pollution flashover voltage was proposed, based on artificial pollution tests carried out on short samples of a composite insulator intended for ±800kV UHVDC. The test results showed that, when the ratio (T/B) of the salt deposit density (SDD) on the top surface to that on the bottom surface is between 1/1 and 1/10, the value of the characteristic exponent a indicating the effect of SDD on the flashover voltage ranges from 0.22 to 0.255. The value of a is nearly independent of T/B. However, the flashover voltage U50 decreases with the increase in T/B. The correction formula indicating the influence of non-uniform pollution distribution on the flashover voltage could be expressed as K=1 - b×log(T/B). For the tested composite insulators, the factor b was 0.141 to 0.156, which is smaller than that of porcelain or glass insulator. That is to say, the influence of T/B on the flashover voltage of the composite insulator is weaker than those on the porcelain and glass insulators. [ABSTRACT FROM AUTHOR]

The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai-Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the ac artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the ac pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the ac flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m. [ABSTRACT FROM AUTHOR]

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 °C to 28.5 °C and the absolute humidity is between 4.11 g/m³ to 9.69 g/m³. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% 1°C for negative SI and 0.099% to 0.108% 1°C for positive SI at the ambient temperature of from 6.7 °C to 28.5 °C. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators. [ABSTRACT FROM AUTHOR]

Artificial pollution tests have been carried out to study ac flashover performances of various types of porcelain, glass, and polymeric insulators in this paper. The experimental results show that the polluted flashover voltage Uf is affected by equivalent salt deposit density ρESDD and nonsoluble deposit density ρNSDD, the influences of which are independent of each other. Based on the analyses of the flashover voltages, the correction formulas of the flashover voltages Uf of various insulators at various ρESDD and ρNSDD levels are pointed out. The experimental results also show that thereis a distinct difference among the flashover voltages of various types of polluted insulators. At the same pollution degree, the antipollution performance of the fog-type glass insulator is better than those of the outer-rib porcelain insulators. In terms of the effectiveness of creepage distance of insulators, the antipollution performance of polymeric insulators is superior to those of porcelain and glass insulators. [ABSTRACT FROM AUTHOR]

Based on the artificial pollution tests, the effects of pollution and high altitude on the flashover performance of short samples of five kinds of UHV/EHV dc composite long rod insulators are analyzed. The exponent characterizing the influence of salt deposit density on the flashover voltage is related with the profile and the material of the insulator shed. The values of the samples' exponents vary between 0.24 and 0.30, which are smaller than those of porcelain or glass cap-and-pin insulators, namely, the influence of the pollution on the composite long rod insulators is less, relatively. Thus, the composite insulators have certain advantages in severe pollution regions. The best ratio of the leakage distance to the arcing distance is about 3.35. The exponent characterizing the influence of air pressure on the flashover voltage is related with the profile and the material of the insulator shed and the pollution severity, the values of the samples' exponents vary between 0.6 and 0.8, which are larger than those of porcelain or glass cap-and-pin insulators. Therefore, the dc composite insulator used in high altitude regions should have enough arcing distance. Based on the test results, if insulator sample Type E is selected for the ±800 kV UHV dc transmission lines, the basic arcing distance should be no less than 8.16 m and the basic leakage distance no less than 30.2 m. [ABSTRACT FROM AUTHOR]

Based on the results of experimental investigations performed on the polluted and iced IEC standard suspension insulator strings of 3∼21 units, the ac flashover performance and discharge process are discussed in this paper. It is put forward that the icing stress product (ISP), defined as the product of the ice-layer conductivity and the ice layer weight per centimeter of dry arc distance can be taken as a characteristic parameter to indicate the effect of ice accretions and contaminants on the flashover voltage. The flashover stress of an ice-covered insulator string can be expressed as a power function of ISP and has a linear relationship with the length of the insulator string. The partial arc of an iced insulator string is initiated by the breakdown of the air gaps between the tips of icicles and iced insulator surface and the persistence is much longer than that of a polluted insulator string. [ABSTRACT FROM AUTHOR]

Background/Aims: A few Rho GTPase activating proteins (RhoGAPs) have been identified as tumor suppressors in a variety of human cancers. ARHGAP17, a member of RhoGAPs, has been reported to be involved in the maintenance of tight junction and epithelial barrier. The present study aimed to explore its expression in colon cancer and the possible function in colonic carcinogenesis. Methods: The mRNA and protein expression was assessed by realtime PCR and immunoblotting, respectively. Cell Counting Kit-8 (CCK-8) and Transwell assays were performed to evaluate cell proliferation and invasion, respectively. Results: We found that ARHGAP17 expression was obviously lower in colon cancer specimens than in normal colonic mucosa. ARHGAP17 expression was associated with tumor stage, size and differentiation. In vitro analysis demonstrated that ARHGAP17 overexpression inhibited cell growth and invasion of HCT-8 and HCT-116 cells. In addition, an in vivo experimental metastasis model showed that ARHGAP17 overexpression restricted cancer metastasis to the lung. Mechanically, we found that Wnt signaling contributed to the functions of ARHGAP17 in colon cancer cells. Gene set enrichment analysis (GSEA) in The Cancer Genome Atlas dataset showed that the Wnt signaling pathway was negatively associated with ARHGAP17 expression. The mRNA expression of β-catenin (an important signaling transducer of canonical Wnt signaling) gene (CTNNB1) was negatively correlated with ARHGAP17 expression. Immunoblot analysis of downstream effectors of β-catenin (c-Myc/p27 and MMP7) in ARHGAP17 overexpressing colon cancer cells and metastatic tumors within the lung also validated the GSEA result. ARHGAP17 overexpression increased the phosphorylation of glycogen synthetase kinase 3b, and decreased β-catenin nuclear localization and transcriptional activity. Furthermore, inhibition of Wnt signaling by Wnt Inhibitor Factor-1 (WIF-1) in HIEC cells with ARHGAP17 knockdown significantly attenuated the promotion effects of ARHGAP17 knockdown on cell proliferation, invasion and the activation of β-catenin. Conclusion: these results suggest that ARHGAP17 might serve as a tumor suppressor in colon cancer progression and metastasis through Wnt/β-catenin signaling pathway. [ABSTRACT FROM AUTHOR]

Transferring the current of bundled sub-conductors through smart switching modules is a promising de-icing method. This study explores the application of line impedance modulation to line de-icing. The control requirements of the de-icing method by transferred current are illustrated according to the characteristics of the method, and two key parameters, namely, critical ice-melting current and ice-melting time, are introduced. The analytical expression for the critical ice-melting current is deduced theoretically. On this basis, the effect of icing shape on the critical ice-melting current is analysed and discussed, along with the calculation of the critical ice-melting current when icing on the windward surface of conductor. A simplified method for calculating ice-melting time is presented on the basis of the heat balance equation during the ice-melting process. With the control requirements of this method as a framework, the calculation and selection of the grouping mode and current duration for the sub-conductors are discussed, and the control scheme of the de-icing method by transferred current is established. The control scheme is preliminarily validated by laboratory investigations conducted in an artificial climate chamber. The results can serve as a reference for obtaining the ice-melting scheme when de-icing via the transferred current of bundled conductors. [ABSTRACT FROM AUTHOR]

In China external discharge accidents caused by heavy rain is growing. However, the rain effect is not considered in atmospheric correction for external insulation design in IEC 60071‐1(Edition 8.1, 2011) or domestic standard. Hence, a series of experiments are implemented with positive switching impulse, a typical kind of overvoltage of power grid, to analyse the discharge performance of rod‐plane short air gap under rain conditions. The effects of rain and its intensity, rain conductivity and ambient temperature on the discharge voltage are explored, and the theory behind them, which can help in the development of discharge mechanism of air gap under rain condition, are respectively given. The results show that under the experimental rain condition, the discharge voltage can be up to −10.9, −9, −8.5, −3.2 and −2.3% lower than under dry condition for clearance distance of 0.1, 0.2, 0.3, 0.4 and 0.5 m, respectively. Besides, it decreases with increase in rain intensity, rain conductivity and ambient temperature, respectively. Among them, the rain intensity is the most significant one, next is temperature, whereas rain conductivity is the minimum and trifling. Finally, a correction formula for breakdown voltage (positive switching impulse) of rod‐plane air gap under rain condition is proposed for reference. [ABSTRACT FROM AUTHOR]

DC flashover performance of ice-covered composite insulators with a parallel air gap (CI/PAG) is an important technical consideration when such insulators are used to isolate ground wires for the purpose of DC ice-melting. Tests on tension and suspension types of CI/PAG were thus carried out in the artificial climate chamber to investigate their DC icing flashover performance. The influences of parallel air gap, ice thickness, pollution severity and air pressure on DC negative 50% flashover voltage (U50%) of CI/PAG were investigated. Test results show that the parallel air gap affected both the discharge path and U50%. With increasing ice thickness, U50% declined by up to 52%; this effect was more evident when the breakdown occurred in the air gap. The pollution severity affected U50% only when the flashover happened along insulator surface. With a decrease of atmospheric pressure, U50% decreased. U50% and the ratio of air pressure were in a power function relationship with a positive characteristic exponent which was relevant to the discharge path. [ABSTRACT FROM AUTHOR]

In the construction or reconstruction of transmission lines for cold climate region, selection of ice thickness design criterion is an important factor to improve the lines anti‐icing performance. Indeed if the designed ice thickness selection is excessively thin, it is hard for the conductors to keep safe and stable operation under icing conditions; and if the designed ice thickness selection is excessively large, the investment of the construction or the reconstruction can several times increase. Hence, how to determine the reasonable ice thickness design criterion and make it meet the economy and safe demands is an important problem to the construction and reconstruction project of the lines. The influence mechanism of diameter on conductors icing is analysed in this study. Based on the results of icing accretion on conductors at several natural ice observation stations in recent years, the diameter correction coefficient (Kφ) of icing thickness on conductors is proposed. The Kφ can meet the demand of the ice thickness design of the lines for observed regions. Moreover, the influence of height on ice thickness on conductors is analysed. The results may provide invaluable reference for engineering applications designing reliable power transmission lines for cold climate region. [ABSTRACT FROM AUTHOR]

The pollution flashover performance of insulators is generally tested by the steam fog method. However, environmental temperature in tests differs greatly, so the dispensability of test results is high. Moreover, the influence of fog‐water conductivity has not been taken into account. Compared with the steam fog method, the cold‐fog method simulating natural fog is more consistent with the actual operating conditions of transmission line insulators. This deals with the influence of salt deposit density (SDD) and fog‐water conductivity on pollution flashover performance. The influence of the two factors is determined by analysing the results of laboratory experiments where polluted insulators were tested by using the cold‐fog method. The results show that the 50% AC pollution flashover voltage (U50) decreases as SDD and fog‐water conductivity increase. The correction coefficient (K) indicating the influence of fog‐water conductivity on U50 can be expressed as an exponential function, where the factors are 0.0476, 0.0587 and 0.0567 for samples A, B and C, respectively. [ABSTRACT FROM AUTHOR]

In this study, icing flashover performance tests of typical DC porcelain, glass, and composite insulators are systematically carried out in a multifunction artificial climate chamber. The DC icing flashover voltages of seven typical insulators under various conditions of icing thickness, pollution severity before icing, string length, and atmospheric pressure are obtained. The relationships between icing thickness, salt deposit density as well as atmospheric pressure and the 50% icing flashover voltage are analyzed, and the formulas are obtained by regression method. In addition, the DC icing flashover voltage correction method of typical porcelain, glass, and composite insulator in the coexisting condition of high altitude, contamination, and icing is proposed. [ABSTRACT FROM AUTHOR]

During their long-term outdoor field service, overhead transmission lines will be exposed to strikes by lightning, corrosion by chemical contaminants, ice-shedding, wind vibration of conductors, line galloping, external destructive forces and so on, which will generally cause a series of latent faults such as aluminum strand fracture. This may lead to broken transmission lines which will have a very strong impact on the safe operation of power grids that if the latent faults cannot be recognized and fixed as soon as possible. The detection of broken strands in transmission lines using inspection robots equipped with suitable detectors is a method with good prospects. In this paper, a method for detecting broken strands in transmission lines using an eddy current transducer (ECT) carried by a robot is developed, and an approach for identifying broken strands in transmission lines based on an S-transform is proposed. The proposed approach utilizes the S-transform to extract the module and phase information at each frequency point from detection signals. Through module phase and comparison, the characteristic frequency points are ascertained, and the fault information of the detection signal is constructed. The degree of confidence of broken strand identification is defined by the Shannon fuzzy entropy (SFE-BSICD). The proposed approach combines module information while utilizing phase information, SFE-BSICD, and the energy, so the reliability is greatly improved. These characteristic qualities of broken strands in transmission lines are used as the input of a multi-classification SVM, allowing the number of broken strands to be determined. Through experimental field verification, it can be shown that the proposed approach displays high accuracy and the SFE-BSICD is defined reasonably. [ABSTRACT FROM AUTHOR]

The phytohormone ethylene is a key signaling molecule that regulates a variety of developmental processes and stress responses in plants. Transcriptional modulation is a pivotal process controlling ethylene synthesis, which further triggers the expression of stress-related genes and plant adaptation to stresses; however, it is unclear how this process is transcriptionally modulated in rice. In the present research, we report the transcriptional regulation of a novel rice ethylene response factor (ERF) in ethylene synthesis and drought tolerance. Through analysis of transcriptional data, one of the drought-responsive ERF genes, OsDERF1, was identified for its activation in response to drought, ethylene and abscisic acid. Transgenic plants overexpressing OsDERF1 (OE) led to reduced tolerance to drought stress in rice at seedling stage, while knockdown of OsDERF1 (RI) expression conferred enhanced tolerance at seedling and tillering stages. This regulation was supported by negative modulation in osmotic adjustment response. To elucidate the molecular basis of drought tolerance, we identified the target genes of OsDERF1 using the Affymetrix GeneChip, including the activation of cluster stress-related negative regulators such as ERF repressors. Biochemical and molecular approaches showed that OsDERF1 at least directly interacted with the GCC box in the promoters of ERF repressors OsERF3 and OsAP2-39. Further investigations showed that OE seedlings had reduced expression (while RI lines showed enhanced expression) of ethylene synthesis genes, thereby resulting in changes in ethylene production. Moreover, overexpression of OsERF3/OsAP2-39 suppressed ethylene synthesis. In addition, application of ACC recovered the drought-sensitive phenotype in the lines overexpressing OsERF3, showing that ethylene production contributed to drought response in rice. Thus our data reveal that a novel ERF transcriptional cascade modulates drought response through controlling the ethylene synthesis, deepening our understanding of the regulation of ERF proteins in ethylene related drought response. [ABSTRACT FROM AUTHOR]

In the current study, a multi-arc predicting model for DC critical flashover voltage of iced and pre-contaminated long insulator strings under low atmospheric pressure is developed. The model is composed of a series of different polarity surface arcs, icicle-icicle air gap arcs, and residual layer resistance. The calculation method of the residual resistance of the ice layer under DC multi-arc condition is established. To validate the model, 7-unit and 15-unit insulator strings were tested in a multi-function artificial climate chamber under the coexistent conditions of low air pressure, pollution, and icing. The test results showed that the values calculated by the model satisfactorily agreed with those experimentally measured, with the errors within the range of 10%, validating the rationality of the model. [ABSTRACT FROM AUTHOR]

Abstract-The Qinghai-Tibet Railway is the highest railway in the world. Up to now, there were no test and service data for the external insulation of the power-supply project of the railway system above 4000 m above sea level (a.s.l.). The "g" parameter method recommended by IEC Publication 60.1 (1989) has a limited applicable range. Therefore, based on the former tests carried on the artificial climate chamber (ACC), in this paper, a series of test investigations is conducted on the positive switching impulse (PSI) discharge performance of rod-plane air gaps with gap spacing of 0.25 to 3.0 m at the six high-altitude sites along the Qinghai-Tibet Railway with altitudes of 2820 to 5050 m. With analyses of the mathematical optimization method on the test results, the new correction method of discharge voltage is proposed. They are also checked and compared with the test results obtained from the simulation tests carried out in the ACC. It is indicated that the 50% PSI discharge voltage U[sub50] of the air gap at high altitude is a power function of gap spacing d, also a power function of relative pressure of dry air and absolute humidity. The influence law of atmospheric parameters on U[sub50] obtained at high-altitude sites is the same as that obtained in the ACC. U[sub50]. obtained in the ACC, is about 8.15% higher than that obtained at high-altitude sites due to the influence of nonsimulated factors, such as ultraviolet ray and cosmic radiation. The "g" parameter method is not applicable to the regions with an altitude above 2800 m. [ABSTRACT FROM AUTHOR]

Based on the artificial pollution tests, the fiashover performance of various types of dc porcelain and glass suspension insulators as well as composite long-rod insulators were analyzed and compared. The test results show that there is a nearly linear relation between the pollution fiashover voltage and the disc-type insulator string length. The flashover voltage gradients of the insulators are affected by their materials and shed shapes. The antipollution performances of glass insulators are superior to those of porcelain insulators with the same profile. The fiashover voltage gradients of composite insulators are higher than those of porcelain or glass ones. The exponent characterizing the influence of salt deposit density on the pollution flashover voltage is dependent on the profile and the material of insulators, and the values of the composite insulators' exponents are smaller than those of porcelain or glass insulators, namely, the influence of the pollution on the composite insulators is relatively less. The effectiveness of leakage distances of porcelain or glass insulators is less than 0.9 while that of composite insulators is higher than 0.9. [ABSTRACT FROM AUTHOR]

Although recent studies have established a significant regulatory role for abscisic acid (ABA) and ethylene response factor (ERF) proteins in plant pathogen resistance, it is not clear whether and how ABA performs this role. Previously, it was reported that an ERF protein, TSRF1, activates the expression of GCC box-containing genes and significantly enhances the resistance to Ralstonia solanacearum in both tobacco and tomato plants. Here, it is reported that TSRF1-regulated pathogen resistance is modified by ABA application. TSRF1 activates the expression of ABA biosynthesis-related genes, resulting in the increase of ABA biosynthesis, which further stimulates ethylene production. More interestingly, ABA application decreases, while the inhibitor of ABA biosynthesis fluridone increases, the TSRF1-enhanced resistance to R. solanacearum. This observation is further supported by the finding that ABA and fluridone reversibly modify the ability of TSRF1 to bind the ethylene-responsive GCC box, consequently altering the expression of element-controlled genes. These results therefore establish that TSRF1-regulated resistance to R. solanacearum can be modified in tobacco by ABA. [ABSTRACT FROM PUBLISHER]

A method is introduced for testing insulators under icing conditions. The method is based on and developed from those described in the standard of IEC60-1, IEC 60507 and IEEE Task Force on Insulator Icing Test Methods, which give instructions to test insulators under pollution. Then, the paper explores the effects of various factors, including ice thickness, pollution severity on the surface of insulators before ice accretion, atmospheric pressure, and shed profiles, on the flashover performance of short samples of two different types of silicone rubber (SIR) composite long rod insulators intended for ultra high voltage (UHV) ac transmission lines. The experiments were carried out in the multi-function artificial climate chamber in the High Voltage and Insulation Technological Laboratory of Chongqing University, China. The experimental results reveal the regularity of the effects of ice thickness, pollution severity and atmospheric pressure on the average flashover voltage of two types of composite insulators. Those can provide reference for the outdoor insulation design for UHV ac transmission lines. [ABSTRACT FROM AUTHOR]

Switching impulse discharge performance of air gaps at high altitudes, which is a fundamental in the extremely high voltage external insulation design, remains an unsolved key technology across the world. Due to the limited applicable range of ‘g’ parameter method recommended by IEC Publication 60-1(1989), this paper aims to explore the relationship between positive switching impulse 50% discharge voltage U50 of rod-plane air gaps and atmospheric parameters, and proposes two new voltage correction methods based on the parameter ‘g’ and the atmospheric pressure ratio, respectively. The two methods have been proved by the experimental investigations carried out on 1-m rod-plane air gap both in the artificial climate chamber and at three spots of different high altitudes in this study. The results show that, if the additional influence of absolute humidity is considered, the positive switching impulse 50% discharge voltage U50 of rod-plane air gaps is a power function of relative pressure and relative air density; the ‘g’ parameter method in IEC Publication 60-1(1989) is not applicable to the regions with an altitude above 2000 m or the condition of h/δ > 15 g/m³ compared with the correction method based on the ‘g’ parameter method, the correction method based on relative atmospheric pressure has a wider applicable range and less error; when the absolute humidity increases 1 g/m³, U50 varies within the range of 1.0%–1.15%. [ABSTRACT FROM AUTHOR]