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This paper studies the atmospheric corrosion characteristics of grid metal frame equipment in Chongqing. Through the standard field test method of atmospheric corrosion -"exposure" method, this study carried out the substation site hanging test of the Q235 steel of the power transmission and transformation engineering structural material in the atmospheric environment, and mastered the corrosion data of Q235 steel in different corrosion stages. It was found that the morphology, quantity and characteristics of corrosion products on the metal surface varied greatly with the progress of corrosion. According to the metal corrosion morphology of different corrosion time, combined with image processing technology and wavelet transform algorithm, the parameters such as gray mean M, corrosion standard deviation σm, corrosion energy E, and energy percentage of wavelet image coefficient were selected as corrosion characteristic variable. At the same time, the BP neural network algorithm was used to qualitatively evaluate the corrosion state of the electrical equipment metal. By testing the on-site samples of the two substations, the corrosion state values of the samples were 0.946 and 0.8071, respectively, which is consistent with the actual corrosion degree, and the system had a good evaluation result.

Natural esters usually show higher dielectric losses, a higher conductivity and higher viscosity. It has become clear that more research is required to ascertain the long-term safe operation of transformers where natural ester is used. This paper made comparative experimental analysis of the cellulosic particles accumulation and its effect on the electric field distribution in natural ester and mineral oil under AC electric field. When the AC voltage was applied on the oil with cellulose particles, it is worth noting that in mineral oil, the particles were concentrated at the end of the spherical positive and negative electrodes, while in the natural ester, the particles are concentrated in the sphere of the positive and negative electrodes. The adsorption of fiber particles decreases the field intensity near the spherical electrode, however, increases the field strength in the middle region of the electrode. Besides, in the case of particles adsorbed on the electrode surface, the maximum electric field strength appears at the particle edge in mineral oil is a little higher than the value in natural ester.

Optimizing the grounding grid configuration is an effective approach to improve the performance of grounding grid. On the other hand, configuration of grounding grid is necessary for some defect diagnosis method to detect the faults existing in grounding conductors. This paper employs the transient electromagnetic (TEM) method to draw the configuration of a substation grounding grid. The surface magnetic field is recorded by receiver coils above the grounding grid. Based on the regular distribution characteristics of a recorded magnetic field, the grounding conductor is accurately located from the curve of magnetic intensity. The complete process of configuration detection of the grounding grid is described in detail. After fast inversion calculation of the recorded magnetic field, the equivalent resistivity is obtained. The configuration of the grounding grid will be clearly and accurately shown in the contour map and three-dimensional (3-D) surface map of equivalent resistivity. Model study is performed, and a field test is also conducted. The results are in good agreement to demonstrate the effectiveness of TEM method for configuration detection of the substation grounding grid.

Metal structure materials of power equipment will be seriously corroded in the polluted atmosphere. Impedance spectrum and polarization current are effective means to monitor metal corrosion status, early warning and take protective measures. The corrosion characteristics and mechanism of metal materials in power equipment in high temperature, high humidity, high Cl- and industrial pollution atmospheres were investigated by scanning electron microscopy and electrochemical measurement. Results indicate that with the increase of corrosion time, the surface morphology and products of Q 235B low carbon steel are transformed from cracks in the precorrosion stage and flaky γ-FeOOH to the products of cotton-like α-FeOOH and constitute a dense rust layer gradually. The surface rust layer of galvanized steel also gradually changes to thicker and denser. The corrosion current I corr of carbon steel increases rapidly and then decreases slowly. The corrosion current I corr of galvanized steel rises slowly and then decreases rapidly. During the corrosion process, the corrosion current of carbon steel is larger than that of galvanized steel. The lowfrequency capacitive reactance arc radius of carbon steel and galvanized steel and the charge-transfer resistance R t after fitting are first reduced, then increased˗the charge transfer resistance R t of the galvanized steel after corrosion is greater than carbon steel. The rust layer of carbon steel will accelerate corrosion in the early stage, and the dense rust layer will resist corrosion in the later stage, but the effect is small. The rust layer of galvanized steel has better resistance to corrosion.

Phosphate pollution of aquatic ecosystems is of great concern and requires the development of high-performance materials for effective pollution treatment. To realize efficient phosphate removal from aqueous solution, an easily separable magnetic (Fe

As a new environmentally friendly liquid dielectric material, vegetable insulating oil has been used in oil-filled transformers more and more widely. In transformers, ageing, overheating faults, and discharge faults cause the decomposition of insulating oil and insulating paper, and then cause dissolved gases in the oil. These transformer fault diagnosis and prediction can be realized by Dissolved Gas-in-oil Analysis (DGA) method, which is closely related to the diffusion process of gas in oil. However, few research involves diffusion processes of dissolved gases and thus no effective DGA method for vegetable insulating oil-filled transformers has been proposed. In this paper, in order to have a better understanding for vegetable oil transformer fault process and improve the effective of DGA method as theoretic support for vegetable oil transformers, the research of diffusion properties and mechanism of characteristic gases in camellia insulating oil is very meaningful. The molecular dynamics simulation based on polymer consistent force field (PCFF) was adopted to analyze diffusion processes of characteristic gases. Impacts of gas species as well as temperatures for molecular diffusion coefficients were studied. The result provides theoretic support for fault condition assessment and operating maintenance of vegetable insulating oil-filled transformers, and also has great theoretical reference value for ensuring safe operation of vegetable insulating oil-filled transformers.

As a new kind of environmentally friendly liquid dielectric, the natural ester has excellent physicochemical properties, together with high fire point and low toxicity. So it is regarded as suitable insulating material for transformer. There already existed a large amount of distribution transformers using natural ester in service in the world, while the use of natural ester in power transformer is still under developing for the higher requirement caused by the high electrical field strength, large insulating structure and the complicated electrical field distribution within power transformer. Streamer discharge tests were carried out in mineral oil, soybean oil and rapeseed oil under long oil gap. The influence of electrode polarity and oil types in propagation characteristics of streamer were analyzed. When the applied voltage is close to the breakdown voltage, the maximum stopping length of the two reaches the 60% of the overall length of the oil gap. The accelerating voltage of the natural ester under positive lightning impulse is almost equal to the breakdown voltage. The positive acceleration voltage of mineral insulating oil reaches two times of the breakdown voltage.

Pure and Pt-decorated ZnO nanosheets were synthesized via a facile and environment-friendly hydrothermal process, and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS), respectively. Side-heated chemical gas sensors were fabricated with the synthesized ZnO based powders and their sensing properties to methane CH4, an important characteristic hydrocarbon contaminant extracted from power transformer oil with overheating or discharging fault, were systemically investigated. Interestingly, Pt decoration not only obviously increased the gas response of sensor fabricated with the synthesized ZnO nanosheets to CH4, but also effectively reduced its optimum operating temperature. Its highest response to 50 ppm of CH4 was about 63.45 at 240 °C, which was about two times larger when compared with the pure one. Meanwhile, the Pt-decorated ZnO nanosheets sensor exhibited shorter response-recovery characteristic, good linearity in low concentration range and excellent stability towards CH4. Those superior sensing features indicate the synthesized Pt-decorated ZnO nanosheets is a promising candidate for fabricating high-performance CH4 sensor.

The formation of space charge in oil/paper insulation system can lead to material degradation in the region of high electric field. Therefore, it is important to understand the factors that affect space charge formation in oil/paper insulation system. In this paper, the effect of oil aging on space charge dynamics in oil/paper insulation system is investigated using the pulsed electroacoustic (PEA) technique under a DC electric field at room temperature. The ultraviolet/visible (UV/vis) spectrum of the oil shifts to longer wavelengths, and the oil acidity increases as the aging time increases. It has been found that the oil property has a significant effect on the space charge distribution in the oil/paper insulation sample. The more the deterioration of the oil, the larger amount of negative and positive charges accumulated in the bulk of the oil/paper insulation sample. The total amount of slow moving charges, the surface trap energy density, and the electric field distortion of the oil/paper insulation sample increased with the degree of deterioration due to oil aging. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The power transformer is an important equipment in the power system. Its running state is directly related to the safe and stable operation of the power grid. The volume fraction of the dissolved gas in the oil of the transformer body and its variation law are closely related to the fault mode of the transformer, therefore, the dissolved gas analysis (DGA) technology in transformer oil is widely used. Actually, the relationship between the volume fraction of the dissolved gas in transformer oil and the time is a multi-dimensional time series. The sequences are arranged in the same time interval or in different time intervals, which contains the external environment of the power transformer, the operation conditions and the inherent relationship between the gas content in the transformer oil. Therefore, the operation status of the power transformer can be revealed by the prediction of the time series. Based on this, the fault type of the transformer can be determined. At present, many literatures have been applied to a single time series forecasting method, such as BP neural network and radial basis function neural network. The single prediction method can obtained certain accuracy by adjusting the weights and thresholds of the network. To further improve the prediction accuracy, a combined forecasting model should be proposed. The research result of this paper is to predict the DGA data of transformer, and has a certain guiding significance to determine the transformer fault types. The proposed method for time series prediction can also be used in other time series prediction of the electric power system.

Moisture has a detrimental effect on oil-paper insulation life by lowering electrical breakdown strength. How does the space charge behavior of the oil-paper insulation system consisted by oil gap and oil immersed insulation pressboard with different moisture content? The space charge characteristics of the mixed insulation consisted of oil gap and pressboard with three moisture content were investigated using the PEA measurement system. The space charge accumulation behaviors at the interface between oil gap and pressboard were analyzed. The distortion of the electrical field in the oil gap and pressboard was also analyzed. Results show that there are many charges injected into the oil and the pressboard. The charges accumulated at the interface between oil gap and pressboard. The charges accumulated in the mixed insulation system become less with the moisture content increased. The difference of the electric field strength in the oil gap and pressboard become smaller with the moisture content increased.

In this investigation, we have synthesized pure and copper decorated tin oxide nanostructures with a facile yet environment-friendly hydrothermal route. The sensing materials are characterized by X-ray diffraction, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. Thick-film gas sensors are fabricated from the as-prepared samples, and their gas sensing performances towards sulfur dioxide are calculated and evaluated by a Chemical Gas Sensor-8 intelligent gas sensing analysis system automatically.

It is important to assess the condition of the cellulose insulation in transformer. However, taking paper samples from a transformer is both impractical and destructive. In this paper, a new method for assessment ageing condition of oil impregnated insulation pressboard based on frequency domain spectroscopy (FDS) was proposed. The FDS measurements were taken on oil impregnated insulation pressboards with five ageing levels at moisture content of 1.22%, 2.06%, 3.02% and 3.87%. The dielectric loss of all the samples were calculated by tanδ (f) interpolation and the ageing condition assessment database which contains data of five ageing levels and 1%-4% moisture content was built. It is found that the tanδ (f) interpolation is more sencentive to ageing and moisture. It could realize the ageing condition assessment by comparing the tanδ (f) interpolation curve with the curves in the database.The assessing result of the middle-low main insulation life of a 220kV transformer valided that it is effective and time saving to use the new method for ageing condition assessment.

There are many researches about the effect of oil/paper proportion, testing temperature, AC/DC ratio and other effects on the breakdown characteristics of oil-paper insulation under the composite electric field. However, the breakdown characteristics of oil-paper insulation under the composite electric field in the process of ageing are rarely reported. In this paper, the breakdown characteristics of the oil impregnated insulation paper with different ageing condition under the composite electric field were investigated. Results show that there is no necessary link between the breakdown characteristics and the ageing degree of oil-paper insulation. The breakdown voltage value decreased with the rise of the AC component under the composite electric field. The breakdown voltage with aged paper changed by new paper is slightly higher than that of the aged oil being changed by new oil.

The diffusion behaviour of hydrogen, carbon monoxide, carbon dioxide, methane, acetylene, ethylene and ethane in oil and paper medium was examined using molecular dynamics to reveal the diffusion mechanism of gas molecules in transformer oil–paper insulation system at the microscopic level. These compounds are commonly used in the dissolved gas analysis of power transformers and produced during the ageing process of oil–paper composite insulating material. Two groups of models were constructed using molecular dynamics simulation software to simulate the diffusion behaviour of the aforementioned seven types of small gas molecules in oil and paper. The diffusion coefficients, displacement features, free volume characteristics and interaction energies of the gas molecules were investigated. In particular, the diffusion micro-mechanism of the gas molecules was observed. The differences in diffusion features among the gas molecules were discussed, and the factors influencing the diffusion of the gas molecules ...

Sulfur dioxide (SO2) is a typical sulfur hexafluoride (SF6) decomposition by product in gas insulated switchgear (GIS). Online monitoring and analyzing SO2 gas concentration can timely and effectively evaluate the insulation performance of SF6-gas-insulated apparatus. In this study, pure and 3 at % Cu-doped SnO2 microspheres were synthesized via a simple and facile hydrothermal method, and were characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, respectively. Chemical gas sensors were fabricated with the conventional indirect heating technology and their gas sensing properties versus SO2 were investigated in detail. The gas sensor fabricated with 3 at % Cu-doped SnO2 microspheres exhibits lower optimum operating temperature and higher gas response than that of pure SnO2 microspheres. Meanwhile, it demonstrates good stability and fast response-recovery. Most importantly, this sensor holds excellent discrimination with other SF6 decompositions, including SOF4, SOF2, SO2F2 and HF. All results provide a good candidate in fabricating high-performance SO2 sensor in practice.

Hydrogen is an effective fault gas dissolved in transformer oil, and online monitoring its concentration has important meaning on condition assessment and fault diagnosis of power transformer. A facile and simple synthesis method of ultra-sensitive SnO2nanofibers through a hydrothermal approach was reported. The crystalline phases and microstructures were performed by X-ray powder diffraction and field-emission scanning electron microscopy. The gas sensor based on prepared SnO2 nanofibers was fabricated by a side-heated preparation, and its gas sensing performances to H2were measured. The fabricated sensor exhibits excellent sensing properties to H2, such as low optimum operating temperature, high gas response, rapid response and recovery time, good stability and repeatability.

Gas insulated switchgear (GIS) is an important electric power equipment in a substation, and its running state has a significant relationship with stability, security, and reliability of the whole electric power system. Detecting and analyzing the decomposition byproducts of sulfur hexafluoride gas (SF6) is an effective method for GIS state assessment and fault diagnosis. This paper proposes a novel gas sensor based on flower-like ZnO nanorods to detect typical SF6decompositions. Flower-like ZnO nanoparticles were synthesized via a simple hydrothermal method and characterized by X-ray powder diffraction and field-emission scanning electron microscopy, respectively. The gas sensor was fabricated with a planar-type structure and applied to detect SF6decomposition products. It shows excellent sensing properties to SO2, SOF2, and SO2F2with rapid response and recovery time and long-term stability and repeatability. Moreover, the sensor shows a remarkable discrimination among SO2, SOF2, and SO2F2with high linearity, which makes the prepared sensor a good candidate and a wide application prospect detecting SF6decomposition products in the future.

Silicone rubber insulators are widely used in the power grid. An accurate estimation of the insulator aging status is necessary for electric power safety. In this study, a novel unilateral nuclear magnetic resonance (NMR) method to quantify insulator aging status is proposed. Firstly, a unilateral NMR sensor was designed specifically for measuring the transverse relaxation time (T2) of insulators. The main magnetic field B0 generated by the sensor possesses a constant gradient of 4.6 T/m along the vertical direction. And the B0 strength variation is less than 338 ppm in a 10×10 mm2 lateral area 1.9mm above the sensor. Secondly, in order to understand better the aging rules of silicone rubber insulators with the depth under the insulator surface, a step motor system was employed to control the penetration depth of the measurement area precisely. The transverse relaxation decay curves were obtained with the sensor by using the Carr-Purcell-Meiboom-Gill sequence at each layer. Thirdly, a data-processing method based on FFT and band-pass filter was utilized. With this method, the transverse relaxation information of the layer with the desired thickness was extracted. Finally, one-dimensional T2 distributions of each layer were obtained by applying inverse Laplace transformation on the filtered transverse relaxation decay curves. The mean values of the long NMR transverse relaxation time component (T2long-mean) were calculated to characterize the aging status of silicone rubber insulators. The one-dimensional depth profiles taken from three kinds of 220 kV silicone rubber insulators with different service times were compared. The results demonstrate that the insulator with a longer service time is characterized by a shorter relaxation time. Moreover, an increase in the penetration depth into the insulators clearly results in an increase in T2long-mean. However, all insulators tend to have nearly the same T2long-mean values at 0.75mm penetration depth into the insulators. This method could be applied to on-site detection in power system to take nondestructive examination of the insulating material aging status.

Overvoltage measurement has been an important field of high voltage engineering. In this paper, an optical intense E-field sensor which is based on the electro-optic effect of lithium niobate, has been studied comprehensively. First, the principles and key issues in sensor design are presented. Second, after fabrication, the input/output characteristics of the sensor are obtained and calibration under lightning impulse. Then, the designed electric field sensor is applied in overvoltage measurement.

In this study, a tunable distributed-feedback (DFB) diode laser based photoacoustic spectroscopy (PAS) system was proposed for the purpose of detecting carbon monoxide CO dissolved in power transformer oil. According to the HITRAN 2008 molecular spectroscopic database, a characteristic absorption line at 6380.3012 cm−1 was selected as the molecular spectral line of CO gas. CO detection characteristics, namely the photoacoustic signal versus CO gas pressure ranging from 0.03 to 0.12 MPa, operating temperature ranging from 280 to 330 K, laser power in the range of 3 to 14 mW and CO concentration ranging from 300 to 2000 mL/L were measured and discussed in detail, respectively. All results indicate that the proposed PAS method may be an effective and feasible way for CO gas detection.

Sulfur dioxide SO 2 is an important decomposition byproduct of sulfur hexafluoride SF 6 under partial discharge in GIS apparatus. Responsive characteristics of semiconductor chemical gas sensors can be extremely improved by morphology tailoring of the sensing materials. In this manuscript, hierarchical flower-shaped ZnO sensing materials were synthesized with an environmental-friendly hydrothermal method and characterized by X-ray powder diffraction, scanning electron microscope, and energy dispersive X-ray spectroscopy, respectively. Planar chemical gas sensor was prepared and obtained with the synthesized powders and its responsive characteristics towards SO 2 were systematically performed. The measured sensor optimum operating temperature was about 260 °C. Its corresponding maximum response to 30 and 60 ppm of SO 2 were 16.72 and 26.14. The saturated gas concentration of the fabricated sensor to SO 2 was 2000 ppm with a response value of 67.41. Moreover, a quick response and recovery feature of 7s and 8 s versus 80 ppm of SO 2 and good stability were also observed.

Firstly, some commonly used terms of medium-voltage distribution networks’ reliability assessment are briefly introduced. Then, some normative suggestions about key points of reliability assessment, such as assessment indexes, parameters, and methods, are systematically put forward. In addition, some key issues of models, parameters, and methods for reliability evaluation are analyzed, and corresponding reasonable disposal methods are given. As for distribution network models, the establishing idea is given, where an organic connection is established between the reliability assessment and reliability statistics. Moreover, some ideas of applying reliability assessment in the phases of network planning, renovation, operation, and maintenance are proposed, improving the power supply reliability fundamentally and bringing more benefits for the power supply enterprises. The reliability assessment of 5 cases is conducted, which can test the effects of load switches, load curves, equipment capacity constraint, and load shedding on the reliability indexes, and the results indicate that the presented normative suggestions are practical.

To mitigate the impacts of grassland degradation on the Qinghai–Tibetan Plateau (QTP), in recent decades China has been implementing large-scale conservation programs and has invested about 42 billion CNY (7 billion USD). However, these programs are faced with major challenges involving trade-offs between ecological function, livestock production and income of pastoralists. Scientific assessments, as well as technical and policy issues, have not fully captured the complex ecological, social and economic dynamics of the challenges facing grassland management on the QTP. Pastoral livestock production on the QTP is characterized by imbalance in both quality and quantity between livestock seasonal nutrient requirements and herbage production, which forces pastoralists to keep larger numbers of livestock for longer periods, leading to overgrazing. To solve these problems, an integrated crop-livestock system is promoted to improve the efficiency of livestock production and conserve natural grassland as well for a sustainable system for the QTP.

The automation and intelligence of the overhaul technology are related to the level of the whole substation automation and intelligence. Aiming at the problems of low automation level of substation high-voltage equipment overhaul, this paper mainly studies robot-based live overhaul technology. The design for robot system is completed and the function test for live overhaul is finished. Besides, the work efficiency and reliability are enhanced.

Icing on transmission line threats to the safe operation of power grid. At present widely used coatings including RTV coating have the hydrophobic property whose contact angle is about 110° and cannot have good anti-icing effect. Here super-hydrophobic surface whose contact angle is about 150° and contact angle hysteresis less than 5° is prepared and its anti-icing characteristic is detected. The leakage current test in time-domain and frequency-domain, ultraviolet imaging test and AC icing flashover voltage test are adopted. Results show that compared with RTV coating, the super-hydrophobic surface owns less leakage current, fewer ultraviolet photons and higher AC flashover voltage which shows great application potential of super-hydrophobic surface in external insulation field.

The icing flashover is increasingly becoming a serious problem with the development of the extra-high voltage engineering. Reducing the bonding strength between the substrate and the ice by super-hydrophobic coating is a choice for the anti-icing. The bare insulator, RTV coated insulator and the super-hydrophobic insulator are chosen for comparing. The experimental facility is set up. The vertical bonding strength, the vertical fracture energy, the shear bonding strength and the shear fracture energy are detected after first ice glaciations and second one. Results show that bonding strength between the super-hydrophobic substrate and the ice is less than that of the RTV coated insulator and the ice. The deiced surface still shows good super-hydrophobicity and the small ice bonding strength keeps almost the same which show good prospect for the anti-icing and de-icing.

Ice accretion on high voltage overhead transmission lines is a serious problem for power system and there's no satisfactory solution to solve icing problem at present. Ordinary glass insulators can obtain super-hydrophobic and self-cleaning properties by coating super-hydrophobic coating on surfaces. The current research shows that super-hydrophobic coating has potential to fix icing problem, because of its excellent hydrophobicity. In this paper, key point is focused on de-iced super-hydrophobic coating's hydrophobicity and surface micro-structure for verifying super-hydrophobic coating's long-term efficacy. Related experiments were completed, and room temperature vulcanized silicone rubber (RTV) coating and blank sample were used as reference samples. The experiments' results showed that de-iced super-hydrophobic coating's static contact angle still reached 158° and its surface still maintained its binary micro-nano coarse structure, and there were no signs of damage on its surface. These phenomena indicate that super-hydrophobic coating's surface micro-structure has outstanding mechanical strength, which can resist the negative impact of de-icing process and keep its outstanding hydrophobicity. Therefore, super-hydrophobic coating has long-term stability under freeze-thaw cycles.

ObjectiveThe present study aimed to evaluate the independent associations between serum leptin concentration and dietary patterns in a Chinese population.DesignA cross-sectional study.SettingData obtained from the 2006 wave of the China Health and Nutrition Survey in Jiangsu Province, China.SubjectsThe sample contained 1061 Chinese adults (488 men and 573 women). BMI was calculated as a parameter of obesity. Factor analysis was used to derive dietary patterns. ANCOVA was performed to assess the associations between serum leptin concentration and the dietary patterns.ResultsFour dietary patterns were derived: Western, High-wheat, Traditional and Hedonic. The Western pattern (rich in meat, milk and cake) was significantly associated with a higher level of serum leptin in men and women, both in an unadjusted model (both P for trend < 0·001) and after adjusting for sex, age, income, total energy intake, physical activity, smoking status and BMI (P for trend = 0·007 for men and P for trend < 0·001 for women). The other three dietary patterns were not significantly associated with serum leptin after adjustment. Sensitivity analysis showed there was an interaction between age and the Western pattern in relation to leptin level. An interaction also existed between current smoking status and the Western pattern.ConclusionsSerum leptin concentration was positively associated with the Western dietary pattern in a Chinese population independent of BMI, energy intake and other factors.

The aim of the present study was to examine the association between dietary patterns and insulin resistance in Chinese adults without known diabetes. Study subjects were 1070 Chinese adults aged 18 years and above in Jiangsu Province who participated in the 2006 wave of the China Health and Nutrition Survey. Usual dietary intake was assessed by using a validated FFQ. Dietary patterns were identified by factor analysis using a principal component analysis method. Insulin resistance was defined as the highest quartile of the homeostasis model assessment of insulin resistance (HOMA-IR) scores. We derived four dietary patterns in our population by factor analysis: the Western, High-wheat, Traditional and Hedonic pattern. After adjusted for potential confounders, the Western pattern was significantly associated with greater odds for insulin resistance (P for trend = 0·009), while a significant negative association was found between the Hedonic pattern and insulin resistance (P for trend = 0·035). Compared with the lowest quartile of the Western pattern, the highest quartile had higher odds of insulin resistance (adjusted OR 1·89, 95 % CI 1·12, 3·19). There was a 42 % decrease in the odds after adjustment for all covariates in the highest quartile of the Hedonic pattern, compared with the lowest quartile (adjusted OR 0·58, 95 % CI 0·34, 0·99). HOMA-IR levels as a continuous variable also increased across the quartiles of the Western pattern and decreased across the quartiles of the Hedonic pattern. In conclusion, dietary patterns were significantly associated with insulin resistance in Chinese adults without known diabetes.

Since the XLPE cables are widely used in power system and electrical treeing is one of the major breakdown mechanisms for solid dielectrics subjected to high electrical stresses, it's of great importance to study the electrical treeing phenomena in XLPE cable insulation for the improvement of safety and reliability of power system. The process of electrical treeing includes three stages: initiation, propagation and breaking down. In this paper, the initiation phenomena of electrical treeing in XLPE cable insulation are studied. XLPE samples are obtained from a commercial XLPE power cable, in which electrical trees have been grown from pin to plane. The process of electrical treeing in XLPE samples are uninterrupted recorded by an online microphotograph system. The growing time and structure of tree initiation subjected to various voltages, frequencies and pin-plane spacings are analyzed. The results show that trees in different structures have the similar initiation structure. With the larger voltage and shorter pin-plane spacing, the time for initiation was longer and less dispersed. The influence of frequency on initiation is relatively small.

This paper presents a feature extraction algorithm combining S transform (ST) and two-directional two-dimensional principal component analysis ((2D)2 PCA) for partial discharge (PD) pattern recognition. S transform (ST) is firstly employed to obtain a time-frequency representation of the recorded UHF signals. Then, (2D)2 PCA is applied to compress the ST amplitude(STA) matrices to extract various feature vectors with different (d 1 , d 2 ) combinations, i.e. (5, 5), (5, 10), (10, 5) and (10, 10). The extracted features are examined by both PSO-SVM classifier and BPNN. Experimental results show that the classification accuracies by PSO-SVM are all higher than that by BPNN under four circumstances of (d 1 , d 2 ) combinations. The success rates of the PSO-SVM with the four feature vectors are above 94% in all cases. It can be found that the proposed feature extraction and classification algorithm can be effectively applied to PD pattern recognition.

The signal of UHF electromagnetic wave was produced when partial discharges occurred in transformer. Using UHF antenna can capture partial discharges signal and realize on-line detection. In this paper, the basic principle of Hilbert fractal antenna was introduced. At the same time, The constructional parameters influencing the fractal antenna properties were also analyzed emphatically. Though simulation calculation, the optimum parameters of a 3rd order Hilbert fractal antenna which suit to detect partial discharges in transformer are given: length of side L=30mm, order n=3;, line width b=2mm.

The composite insulators are widely used in power system, because of its remarkable performance on pollution prevention. In this paper, some 500kv insulators with different working time and manufactory are tested on their hydrophobicity, electrical character, mechanical character and aging character of the shed's material. The experimental results show that the hydrophobicity of composite insulators used this area degrades fast. The value of hydrophobicity of composite insulators is HC2–HC5 at the working age of 3 years, the HC5–HC6 at the 6 years, HC4–HC6 at the 9 years. And the samples also showed the bad performance on transfer, loss and recovery of hydrophobicity. It was found that the high temperature and humidity of environment was the main reason causing the decline of hydrophobicity. However the electrical and mechanical character of these old composite insulators still can meet the request of some regulations. The samples can resist the voltage of power frequency and lighting pulse respectively, and the destructive mechanical values are greater than the rated mechanical intensity. With the increase of the using time, the tensile strength, tearing strength and electrical erosion resistance strength of the sheds become worse. These operation characteristics are the good reference for the operation of power grid.