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With the commencement of high voltage alternating current (HVAC) and high voltage direct current (HVDC), the demands on insulating reliability of power transformer is getting more and more imperative. The mineral oil (MO/TO) in conjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers. To strengthen the insulation level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose. Recently, a unique novel effort of suspension of nanoparticles (NPs) into mineral oil (MO) has been carried out and the results have exhibited improved insulation characteristics of transformer oil. The Al 2 O 3 nanoparticles with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The transformer oil-based nanofluids (NFs) were prepared with nanorod shape, oleic acid (OA) surface modification and 0.8 g/L concentration of NPs. The pressboards were cut into the desired sizes (85 mm.55 mm). The thickness of the pressboards was 2 mm applied in flashover tests. The prepared pressboards were put into an oven at 105 °C for almost 48 h to carry out the hot air drying operation. Then they were put in the vacuum drying at 85 °C for 48 h. The impregnated pressboards were prepared by impregnating them into dried oil and NF under vacuum beneath 1 kPa at 80 °C for almost 48 h to obtain the oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) respectively. Additionally, the prepared insulation system samples of liquid (MO and NFs) and solid (OIPs, NIPs) were thermally aged at 130 °C for 30 days. The effect of alumina NPs on thermal aging of transformer oil and pressboard were also investigated. The results showed that Al 2 O 3 NPs can slow down the aging of oil and pressboard. The average AC and positive LI BDV of aged NFs was 11% higher than aged MOs. The average LI creeping FOVs of NIPs were 6% higher than OIPs. Additionally, average AC creeping FOVs of NIPs were 8% higher than that of OIPs. The enhancement in insulating performance of aged NFs and NIPs as compared to MO and OIPs is interpreted in light of electron traps theory. • Nanoparticles have the potential to influence the breakdown performance of oil/paper insulation system. • Suspension of Al2O3 nanoparticles may slow down the aging process of the oil/paper insulation system. • The enhancement in insulting performance of oil/paper insulation system may be interpreted in light of electron traps theory. [ABSTRACT FROM AUTHOR]

This paper presents an online hydrophobicity measurement technique for silicone rubber (SIR) insulators on transmission lines and its field test results. Based on the hydrophobicity classification (HC) method, an online hydro-phobicity measurement device was developed, which consists of a controllable sprayer, a video camera and a hydrophobicity analyzing software. Online hydrophobicity inspection was conducted for the polluted SIR insulators on three ac transmission lines in the north of China for more than one year by using the device. Some SIR insulators operated for 8 years were analyzed in the laboratory by using the scanning electron microscopy and the infrared spectroscopy. The results show that the surface hydrophobicity of the SIR insulators varies remarkably with seasons. We also find that the microstructure of the pollutants significantly influences the hydrophobic transfer, and that the aging phenomena happen on the surfaces of the weather-shed materials of the SIR insulators operated for 8 year. It is proposed to strengthen the hydrophobicity inspection for the SIR insulators in service. [ABSTRACT FROM AUTHOR]

This paper shows a dynamic change of hydrophobicity on the surface of silicone rubber (SIR) insulators with seasons in a semi-wet warm-temperature zone of China based on the data from the dynamic testing in an outdoor test field and the on-line dynamic testing in a 220 kV and three 110 kV transmission lines for over a year. It is found that the surface hydrophobicity of SIR insulators served in the semi-wet warm-temperature zone of China can gradually decrease from HC1-HC3 to HC5-HC7 in winter, and recover to HC1-HC3 in summer. The combination of continuous pollution deposition, low ambient temperature and poor pollution washing by precipitation could be the reason leading to the low surface hydrophobicity of the SIR insulators in winter. It is also found that the pollution layer with the dense micro-structure could block the hydrophobicity transfer from the material to the surface of the pollution layer, resulting in the low surface hydrphobicity of the SIR insulators even in summer. Based on the results, a dynamic inspection method on the surface hydrophobicity of SIR insulators is proposed, in which the surface hydrophobicity decrease in winter and the recovery in summer are considered. [ABSTRACT FROM AUTHOR]

The corona pattern from porcelain insulator strings on high voltage (HV) transmission lines has been investigated for inspecting faulty insulators on-line. Corona patterns from HV conductive line, metal accessory, and discharge patterns from bad connection, power stations, have also been studied for background pulse noise elimination. A pattern recognition method for inspecting faulty porcelain insulators is proposed, which consists of several criteria. It is found that the harmonics and carriers from the transmission lines influence the recognition seriously, which can be eliminated by choosing a high frequency band of sensors (2 MHz-20 MHz). Based on the above investigations, an instrument was developed and used on the field measurements in Lanzhou and Zhengzhou power utilities in China. The field results show a strong support for this method. On the measurement of 76 towers, the measuring accuracy of inspecting faulty `insulators was about 87.5%. [ABSTRACT FROM AUTHOR]

This paper presents a method for partial discharge (PD) source location in power transformers based on detecting electromagnetic (EM) radiation emitted from PD. The key problem of PD location by EM waves is the difficulty in getting the accurate time arrivals of the signals from the source to multiple sensors. Several measures are taken to improve the time arrival resolution. Firstly, a measuring frequency band (1 GHz - 5 GHz) within RF band is proposed to accurately pick up the fast rise time of the signals. Secondly, an antenna array with diamond-shaped configuration is designed to improve the correlation coefficient of the waveforms from multiple sensors. Thirdly, two antenna arrays are proposed to eliminate the influences of the EM wave scattering caused by the iron core. Fourthly, an algorithm is proposed to increase the signal to noise radio and to measure the time arrivals automatically through cross-correlation and averaging operation. Lastly, a Hyperboloid-Genetic algorithm is developed to search the PD source. Experiments on a single-phase transformer model were conducted in the laboratory. The tested results proved the validity of the proposed method and showed that the location error in 16 cm, mostly is about several cm. [ABSTRACT FROM AUTHOR]

The article presents the case study of several children who developed plastic bronchitis during the outbreak of the A(H1N1) influenza virus in China in the winter of 2009. Based on diagnosis of the nasopharyngeal swab and BAL fluid, there is a positive assay for the influenza virus. The patients recovered following bronchoscopic extraction of casts and antiviral treatment. Plastic bronchitis is commonly linked with congenital heart disease or sickle cell acute chest syndrome.

The electrical strength of insulator in vacuum is much lower than either the insulator itself or the vacuum gap in the same dimension, and one of the considerable factors that could affect the electric field or even the surface flashover is the surface charge accumulation. In order to capture the surface charge characteristics and its impacting mechanism on electric field of ceramic insulator under nanosecond voltage in vacuum, this paper employed electrostatic capacitive probe to develop a surface charge measurement system. The accumulating and dissipating characteristics of surface charge on four Al2O3 ceramic insulators with different manufacturing conditions were captured, indicating that, (1) the surface charge mainly accumulates near the anode, but there presents various distribution patterns of different samples; (2) the charge density of different samples also shows different increasing trend with the voltage application counts increasing, and the maximum difference could reach 78.07%; (3) within 1 h after the voltage cutting off, the maximum density of dissipated surface charge on all samples is less than 7.0%, ensuring the reliability and effectiveness of experimental results. The surface micro-morphology and surface traps characteristic take the joint actions to make the explanations for the surface charge accumulation and migration mechanisms. Finally, based on surface charge measurement results and field simulation results, the quantitative impact of surface charge on surface electric field were proposed in this paper, aiming at providing meaningful references for the insulation design. [ABSTRACT FROM AUTHOR]

Nanoparticles currently in use are challenged in further improving the dielectric strength of insulating oil. There is a great need for a new type of nanoparticle to promote the application of insulating oil-based nanofluids in electric industries. This paper experimentally investigates the effect of nanoparticle morphology on pre-breakdown and breakdown properties of insulating oil-based nanofluids. The positive impulse breakdown voltage of insulating oil can be significantly increased by up to 55.5% by the presence of TiO2 nanorods, up to 1.23 times that of TiO2 nanospheres. Pre-breakdown streamer propagation characteristics reveal that streamer discharge channels turn into a bush-like shape with much denser and shorter branches in the nanofluid with TiO2 nanorods. Moreover, the propagation velocity of streamers is dramatically decreased to 34.7% of that in the insulating oil. The greater improvement of nanorods on the breakdown property can be attributed to the lower distortion of the electric field. Thus, when compared with nanospheres, pre-breakdown streamer propagation of nanofluid is much more suppressed with the addition of nanorods, resulting in a greater breakdown voltage. [ABSTRACT FROM AUTHOR]

TiO2 nanoparticles with an average diameter of 6 nm were synthesized and well dispersed in transformer oil to prepare nanofluids (NFs). Influence of nanoparticles on the ion migration property of NFs was investigated via reversal polarity method under different applied electric fields and temperatures. It was found that the ion mobility in TiO2 nanofluid is increased to 4 times of that in pure oil (PO) under the electric field of 5 kV/m, and then decreased abruptly and keeps around one tenth of ion mobility in PO from 50 to 150 kV/m. While the case in PO keeps almost constant throughout the applied fields. The results of the conductivity and ion characteristics of PO and NFs reveal that the presence of nanoparticles can reduce the diameter of impurity ions by shrinking hydrated solvated shell and greatly enhance their mobility at low electric fields. With the increasing of electric stress, the charged nanoparticles become the major conduction contributor and drift slowly due to the higher viscous resistance from oil molecules. [ABSTRACT FROM AUTHOR]

Dissolved hydrogen is a symbol gas decomposed by power transformer oil for electrical faults such as overheat or partial discharges. A novel D-shaped fiber Bragg grating (D-FBG) sensor is herein proposed and was fabricated with magnetron sputtering to measure the dissolved hydrogen concentration in power transformer oil in this paper. Different from the RI (refractive index)-based effect, D-FBG in this case is sensitive to curvature caused by stress from sensing coating, leading to Bragg wavelength shifts accordingly. The relationship between the D-FBG wavelength shift and dissolved hydrogen concentration in oil was measured experimentally in the laboratory. The detected sensitivity could be as high as 1.96 μL/L at every 1-pm wavelength shift. The results proved that a simple, polished FBG-based hydrogen sensor provides a linear measuring characteristic in the range of low hydrogen concentrations in transformer oil. Moreover, the stable hydrogen sensing performance was investigated by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Heavy ice coating of high-voltage overhead transmission lines may lead to conductor breakage and tower collapse causing the unexpected interrupt of power supply. The optical load cell applied in ice monitoring systems is immune to electromagnetic interference and has no need of a power supply on site. Therefore, it has become a hot research topic in China and other countries. In this paper, to solve the problem of eccentric load in measurement, we adopt the shearing structure with additional grooves to improve the strain distribution and acquire good repeatability. Then, the fiber Bragg grating (FBG) with a permanent weldable package are mounted onto the front/rear groove of the elastic element by spot welding, the direction deviation of FBGs is 90° from each other to achieve temperature compensation without an extra FBG. After that, protection parts are designed to guarantee high sensitivity for a light load condition and industrial safety under a heavy load up to 65 kN. The results of tension experiments indicate that the sensitivity and resolution of the load cell is 0.1285 pm/N and 7.782 N in the conventional measuring range (0-10 kN). Heavy load tension experiments prove that the protection structure works and the sensitivity and resolution are not changed after several high load (65 kN) cycles. In addition, the experiment shows that the resolution of the sensor is 87.79 N in the large load range, allowing the parameter to be used in heavy icing monitoring. [ABSTRACT FROM AUTHOR]

Fe3O4 nanoparticles with an average diameter of 10 nm were prepared and used to modify streamer characteristic of transformer oil. It was found that positive streamer propagation velocity in transformer oil-based Fe3O4 nanofluid is greatly reduced by 51% in comparison with that in pure oil. The evolution of streamer shape is also dramatically affected by the presence of nanoparticles, changing from a tree-like shape with sharp branches in pure oil to a bush-like structure with thicker and denser branches in nanofluid. The TSC results reveal that the modification of Fe3O4 nanoparticle can greatly increase the density of shallow trap and change space charge distribution in nanofluid by converting fast electrons into slow electrons via trapping and de-trapping process in shallow traps. These negative space charges induced by nanoparticles greatly alleviate the electric field distortion in front of the positive streamer tip and significantly hinder the propagation of positive streamer. [ABSTRACT FROM AUTHOR]

The insulation characteristics of high temperature superconducting (HTS) coil or winding are significant for their power application, which mainly includes partial discharging (PD), withstand voltage, breakdown voltage, flashover, fatigue effect through thermal cycles and lifetime. In this paper, we focused on investigation of the partial discharging of two HTS DP made of commercial multifilamentary Bi2223/Ag tapes and YBCO coated conductors. PD test was performed in order to ascertain the partial discharge inception voltage of DP in different conditions, which included static and quenching conditions. Experimental results revealed that PD density does not change obviously in different conditions. Useful results with combined conditions for PD characteristics were experimentally obtained. [ABSTRACT FROM AUTHOR]

The current distribution and stability of low temperature superconductor (LTS) and high temperature superconductor (HTS) hybrid superconductor, made of NbTi wire and YBCO coated-conductor, are described. The current distribution, quench propagation velocity (QPV) and the minimum quench energy (MQE) are numerically analysed by finite element method (FEM) based on the different power-law models since the n value in LTS is much larger than that in HTS. It is shown that the transport current in LTS is larger than in HTS if both of them have the same critical currents, and the ratio of transport current in LTS to that in HTS decreases with increase of the total transport current near their critical currents. The stability of the hybrid NbTi/YBCO composite conductor is also simulated, which indicates that MQE in the hybrid conductor is much higher than in NbTi wire but smaller than in YBCO conductor. However, the quench propagation velocity is in the range of low-temperature superconductor through the high-temperature superconductor. With advantages of high engineering current density and improvement of stability, the hybrid superconductor is expected to have potential application in large scale magnet and conducting-cooled magnet particularly. [ABSTRACT FROM AUTHOR]

Background: Multidrug resistance is an occasionally seen phenomenon in children with idiopathic nephrotic syndrome (INS), but the mechanism of multidrug resistance is not clear as yet. The purpose of the present study was to investigated whether expression of Pad1 homologue ( POH1) plays a role in the onset of multidrug resistance of INS. Methods: Comparison was done of the mRNA level of POH1 on real-time quantitative polymerase chain reaction in peripheral blood mononuclear cells among children with multidrug-resistant INS, children with steroid-sensitive INS and healthy controls. Results: The POH1 mRNA level of the onset INS group (5852.3 ± 2676.4 copies/µg) was significantly lower than that of the control group (10 877.1 ± 2386.6 copies/µg; P < 0.05). The POH1 mRNA level of the onset INS group with multidrug resistance was not significantly higher than that of the onset INS group without multidrug-resistance before treatment (6977.1 ± 6312.3 copies/µg vs 5281.3 ± 1926.7 copies/µg; P > 0.05), but significantly higher than that of the onset INS group without multidrug resistance after treatment (436 579.6 ± 99 727.4 copies/µg vs 38 438.2 ± 16 772.5 copies/µg; P < 0.001). The POH1 mRNA level of non-onset multidrug-resistant INS group (337 446.4 ± 107 423.5 copies/µg) after treatment was not significantly higher than that of the onset INS group with multidrug resistance after treatment (436 579.6 ± 99 727.4 copies/µg; P > 0.05), but was significantly higher than that of the onset INS group without multidrug resistance after treatment (38 438.2 ± 16 772.5 copies/µg; P < 0.001). Conclusions: Disorder of POH1 expression is involved in the onset of INS, and confers multidrug resistance in children with INS. [ABSTRACT FROM AUTHOR]

The flashover phenomenon of the insulator is the main cause for insulating failure of GIS/GIL, and one of the most critical impacting factors is the accumulation of surface charge. The common methods to restrain the surface charge accumulation are reviewed in this paper. Through the reasonable comparison and analysis of these methods, nano-coatings for the insulator were selected as a way to restrain the surface charge accumulation. Based on this, six nano-coated epoxy resin samples with different concentrations of P25-TiO2 nanoparticles were produced. A high precision 3D surface charge measurement system was developed in this paper with a spatial resolution of 4.0 mm2 and a charge resolution of 0.01 µC (m2 · mV)−1. The experimental results for the epoxy resin sample showed that with the concentration of nanoparticles of the coating material increasing, the surface charge density tended to first decrease and then increase. In the sample coated with 0.5% concentration of nanoparticles, the suppression effect is the optimum, leading to a 63.8% reduction of charge density under DC voltage. The application test for actual nano-coated GIS/GIL basin insulator indicated that the maximum suppression degree for the charge density under DC voltage could reach 48.3%, while it could reach 22.2% for switching impulse voltage and 12.5% for AC context. The control mechanism of nano-coatings on charge accumulation was proposed based on the analysis for surface morphology features and traps characteristics; the shallow traps dominate in the migration of charges while the deep traps operate on the charge accumulation. With the concentration of nanoparticles in nano-coating material mounting up, the density of shallow traps continuously increases, while for deep traps, it first decreases and then increases. For the sample with 0.5% concentration of nanoparticles coated, the competition between shallow traps and deep traps comes to the most balanced state, producing the most significant suppression impact on surface charge accumulation. [ABSTRACT FROM AUTHOR]

Nanotechnology provides a new way to improve the insulating properties of traditional dielectric materials. In this study, three types of mineral oil based nanofluids were prepared by suspending Fe3O4, TiO2 and Al2O3 nanoparticles all of which were surface modified by oleic acid. The inception voltage, stopping length and propagating velocity of streamers in the nanofluids under positive lightning impulse voltage were experimentally studied. It is found that nanoparticles can restrain the initiation and propagation processes of positive streamers in transformer oil depending on the types of nanoparticles. In addition, the trap characteristics in pure oil and nanofluids were comparably studied. The relationship between the trap characteristics and mobility of charge carriers in oil samples were then established. The increased trap density in nanofluids diffuses kinetic energy of ionized electrons and converts them into negative ions, resulting in the reduced electrical field strength in front of positive streamer and increased breakdown strength of nanofluids. [ABSTRACT FROM AUTHOR]

Surface charge accumulation can incur changes in electric field distribution, involved in the electron propagation process, and result in a significant decrease in the surface flashover voltage. The existing 2D surface charge measurement fails to meet the actual needs in real engineering applications that usually adopt the 45° conical frustum insulators. The present research developed a novel 3D measurement platform to capture surface charge distribution on solid insulation under nanosecond pulse in a vacuum. The results indicate that all surface charges are positive under a positive pulse and negative under a negative pulse. Surface charges tend to accumulate more near the upper electrode. Surface charge density increases significantly with the increase in pulse counts and amplitudes. Accumulation of surface charge results in a certain decrease of flashover voltage. Taking consideration of the secondary electron emission for the surface charge accumulation, four materials were obtained to demonstrate the effects on surface charge. Combining the effect incurred by secondary electron emission and the weighty action taken by surface charge accumulation on the flashover phenomena, the discharge mechanism along the insulator surface under nanosecond pulse voltage was proposed. [ABSTRACT FROM AUTHOR]