Applied Mechanics and Materials Vols. 672-674

Abstract: In this communication, Ag0.9Na0.1(NbyTa1-y)O3 (y=0.5,0.6,0.7,0.9)（ANNT） mixed oxide powder was synthesized by citrate wet chemical method. TG-DTA, XRD and TEM analyses showed that the reaction temperature was 800°C, the calcining time was three hours, and the product was pure ANNT in well-dispersed grain structure (45nm in average).

Abstract: With starch as base material, acrylamide (AM) as raw material, polyethylene glycol (PEG20000) as dispersing medium, in aqueous two-phase system synthesized starch grafting acrylamide polymer. Through the indoor experiment, determine the optimum process conditions of polymerization reaction, the initial monomer concentration was 15%, PEG20000 concentration of 10%, m (ST) : m (AM) = 3:7, dosage of initiator is 0.1%, T = 50 °C, T = 6 h. Get monomer conversion was 98.5%, the characteristic viscosity.methods according to 761.5 mg/L of graft copolymerization. Of product have been characterized through infrared spectrum and analysis.

Abstract: Chitosan (CTS) was added into poly (vinyl alcohol) (PVA) hydrogels to get their antibacterial properties. A series of CTS/PVA hybrid hydrogels were prepared by freezing/thawing method. The swelling properties of all hybrid hydrogels are better than those of the original PVA hydrogel. The CTS/PVA hybrid hydrogels show excellent antimicrobial performance towards Escherichia colis.

Abstract: Organic Rankine Cycle (ORC) is widely used in the field of low temperature waste heat recovery, including solar, biomass and geothermal energy, among others. Based on the thermodynamic model of ORC system built up in Matlab, this study employ Genetic Algorithm (GA) on ORC system for parametric optimization and select a ratio of heat transfer area to total net power output as the performance evaluation criterion to predict the economy of system. R11, R113, R123 and isopentane are choosed as the working medium. The results show that the ORC system with isopentane has the minimum objective function value of 0.429m2/kw. The corresponding condensing temperature and degree of supercooling are generally located at lower boundary over their parametric design ranges, and the corresponding pinch point temperature difference are located at upper boundary. For different working fluids, there exist an optimum evaporating temperature and degree of superheat.

Abstract: The decomposition of sulfur hexafluoride (SF6) in overheated electric equipment at different temperature in high humidity was simulated in the study. SF6 is very stable and not significantly decomposed at 200 °C, 250 °C and 300 °C. SF6 is significantly decomposed at 350 °C. SF6 is more easily to be decomposed and decomposed more rapidly at higher temperature. The concentrations of SF6 byproducts are much higher at higher temperature. SF6 will be decomposed to format HF. The concentration of HF will decrease when its concentration increases up to a certain concentration. It may be because that HF was strongly corrosive and its corrosion to inner equipment made the concentration of HF decreasing.

Abstract: High voltage three-phase three-element combined transformer, widely used in power systems of 10kV, 35kV and the like, is important in guaranteeing the safe and stable operation of power system, and ensuring the fair and equitable metering of electric power. At present, when verified by single-phase verification method, combined transformer exposed to the situation which doesn’t match its actual operation situation, as a result, verification results can’t reflect the true error characteristics of combined transformer. So, it is suggested to adopt three-phase verification method to verify combined transformer. However, when combined transformer is verified by three-phase verification method, it has not been clear yet that what influence electric field generated by voltage has on current error. In this paper, through current error test on combined transformer with three-phase verification method at different voltage, it is discovered that electric field has a larger influence on current error at lower current (especially at 1% rated current),with the increase of current, the influence of electric field on current error decrease gradually till negligible. The use of three-phase verification method and appropriate modification of current error limits are recommended when combined transformer is verified.

Abstract: Based on the trip faults data of 10kV and 20kV distribution lines which come from actually power grid in China, this paper has done a large number of statistical analyses and investigations. Trip faults are classified and analyzed by fault positions, monthly changes, fault causes and so on. Preliminary analysis suggests that main factors which lead to trip faults are outer forces, meteorological conditions, improper operation and maintenance, quality of equipment and design processes. Rains, strong winds and lightnings have the worst impact on distribution lines in a period from June to August. External forces caused the most faults on conductors, towers and stay wires. According to different failure reasons, countermeasures are put forward pointedly,so can provide references for improving power supply reliability in distribution network.

Abstract: The effect of electrical aging on the trap parameter of HVAC XLPE cable insulation was investigated in this work. Thermally Stimulated Current (TSC) was used to measure depolarization current. The variation of trap parameter was calculated by means of start-up method based on the Gaussian fitting curve of TSC data. It was found that, the activation energy and the amount of trap charge obtained from TSC peak at 243K and 348K were increased after electrical aging, which may be benefit to characterize the degree of aging. The amount of trap charge in the two peaks increases as the increase of oxide dipole after electrical aging. And charge trapped described by the TSC peak at melting temperature increased after aging. It is considered that the increase of charge in the TSC peak can be attributed to the release of trap charge in the melt crystallization process, which corresponds to the α relaxation process in XLPE insulation.

Abstract: At high altitudes, 330 kV dampers usually have corona discharges on their weights, which affects the lives of the surrounding residents. To suppress the corona, optimizing the structures of the dampers is a recommended measure to reduce the electric field intensities on their weights. In this paper, three-dimensional computational models of 330 kV FDN dampers were constructed to calculate the electric field distributions on their weights, based on finite element method (FEM). The structure of the small end was optimized to reduce the electric field strength on its surface. When the radius was increased from 25 to 35 mm, the maximum electric field intensity could be decreased from 2987 V/mm to 2390V/mm. According to the results, new dampers were manufactured to test their corona characteristics. The test results show that the new dampers can prevent corona discharge at altitudes below 3500 m.

Abstract: In different geographical conditions all kinds of failures due to lightning stroke occur in 220/110kV transmission lines. In the high resistivity region lightning back-flashover mainly occurs. This paper, according to the idea of the application manual of 220(110kv) transmission line typical design program put forward by the State Grid Corporation, analyses the width of the corridor, steel consumption of tower, lightning effects, operation and maintenance, and the State Grid recommendation on Shangzi-tower, Portal steel tower, Cup-type tower, Cat-head type tower and Ganzi-tower. And study on Cup-type tower and Cat-head type tower is furthered. Considering various factors, ATP/EMTP method is finally adopted to simulate the lightning withstand level and back-flashover trip rate of two types of tower. The results show that, taking the grounding resistance of 25Ω condition, the lightning back-flashover performance of cup-type tower is slightly better than the cat-head type tower with the same parameters.