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The charge phenomena under sine and half‐wave sine voltages within the frequency range of 500 Hz are studied here. Based on the pulsed electro‐acoustic method, the traditional circuit design under high‐frequency voltages is first analysed. It is found that the selection of a 186 pF protection capacitor and a 333 kΩ protection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input. Based on this design, experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode. Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half‐wave sine and DC conditions, and the samples under lower‐frequency conditions show more charge accumulation. The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz, and their values are 68.55 and 81.82 kV/mm, respectively. Therefore, the charge characteristics are easily affected by the voltage’s waveform and frequency parameters. The results obtained here can provide guidance for the application of insulating materials under special voltage environments.

The resolution performance of space charge measurement method determines its application environment and measured information, which has put forward higher temporal and spatial resolution requirements for the charge evaluation of electronic equipment insulation. Based on the ellipsometry detection principle and the photoelastic effect of the sensor, a novel optical method for space charge measurement is proposed. The potentials of the method in terms of single measurement with high signal-to-noise ratio, terahertz bandwidth and nanometer spatial resolution are analyzed. By deriving the mathematical relationship of the signal transmission, it is indicated that the light intensity difference measured by the system can linearly present the elastic force generated from space charge. Based on the built ellipsometry detection system, it is found that the detected signal from the sensor can quickly track the imposed elastic waves with different amplitudes and frequencies, which verifies the feasibility of the crucial detection part and the fast measurement speed of the proposed method. Further simulation results indicate that the refractivity performance of the sensor under the effect of elastic waves can present the deformation variation with a spatial resolution of 2 nm. Therefore, the given explorative research can provide the key theoretical basis and experimental verification for the proposed method.

This paper focuses on the effect of unipolar and bipolar square, sine and triangle voltages on space charge characteristics inside solid insulation based on the bipolar charge transport model. According to the model solution process and the polarization characteristics, it is found the algorithms for the model should be chosen with regard to the direction of the electric field at each subdivision inside the calculation sample. Further comparison shows that the charge amount under different conditions is mainly determined by the input power of the imposed voltage, while the migration depth of the injected charge is less than 20 μm from the sample surface. Correlation between the current injection and the charge amount indicates that the variation trends of them follow basically the same. The results under unipolar conditions are not affected by the frequency provided it is larger than 10 Hz, while the charge amount under bipolar ones is negatively correlated to the frequency. Meanwhile, the impact of the initial phase of bipolar polarization decreases rapidly with the increased simulation time. Hence, for space charge measurement inside dielectrics under such conditions, a reliable system should be established according to the polarity and waveforms of the polarization.

This paper reports the effect of DC and pulse wave voltages on space charge characteristics of polyimide material for high-frequency insulation. The pulsed electroacoustic method is used to measure the charge distribution inside the material under the pulse wave voltages with different amplitudes, polarities, frequencies and duty ratios. Comparative results show that positive charge is more likely to accumulate inside the polyimide. The amount of accumulated charge under pulse wave voltages is larger than that under DC voltages. With frequency, more space charge is accumulated under negative pulse wave voltages with a frequency above 50 Hz, while it is not larger than 100 Hz under positive voltages. The maximum distortion of electric field appears under the negative pulse wave voltage with the frequency of 500 Hz, which is 1.19 times the applied field strength. When the duty ratio of the pulse wave voltage exceeds 50%, the distribution of accumulated charge tends to be stable. The research results can provide a reference for the practical application and modification design of polyimide materials in power electronic equipment.

The 14 MeV neutron activation analysis method was used to measure talc in flour. The neutron yield of a D-T neutron generator was maintained at 1.32 × 107n∙s−1 to irradiate flour samples for one hour. A 1779 keV characteristic γ-ray produced by the 28Si(n,p)28Al reaction and 1369 and 2754 keV characteristic γ-rays produced by the 24Mg(n,p)24Na reaction were measured by a 3-inch NaI(Tl) detector and a 2-inch LaBr3(Ce) detector, respectively. The accuracy and detection limit of the talc content measured by the two detectors with different characteristic γ-rays were discussed. The results show that the best scheme for measuring talc content is measuring the 1779 keV γ-ray with the 3-inch NaI(Tl) detector. The detection limit reaches 0.07%, and the relative error of multiple measurements of the same sample is 2.07%. The relationship among the mass thickness of the sample, the talc content and the characteristic peak area was plotted.

In this paper, large amount of pure carbon microspheres and fullerenes, with good morphology in uniform diameter, have been successfully obtained via CVD method by using acetylene and toluene as the carbon source. After different graphitization treatments on the amorphous materials, the graphitization degree is enhanced greatly with undestroyed morphologies. Nitrogen adsorption isotherms are measured on different kinds of carbon spheres at 77 K. The results show that their adsorption isotherms are exactly the same, all of which are very complex. Among these five kinds of carbon spheres, Fe-encapsulated carbon onions' adsorption ability and specific surface area are the largest, about 500 cm3/g and 30.5 m2/g, respectively. The hollow carbon onions' pore volume is the largest, about 0.284631 cm3/g. After different graphitization treatments, the carbon microspheres' specific surface area increases to 4.8 m2/g, but the pore volume decreases to 0.022538 cm3/g.

The long-life, high yield deuterium-deuterium (D-D) neutron tube has become one of the research hotspots. Here, deuterated polyethylene target, heavy water target and titanium target were investigated by Stopping and Range of Ions in Matter (SRIM). The calculation showed that the deuterated polyethylene target, which was a potential target material, had the highest yield at an incident energy of 120 keV. Further, considering the unfavorable factors such as impurity ions and high temperature, the coating was used to protect the target material. Diamond, boron carbide, boron nitride, silicon carbide, and aluminum carbide were selected. The simulation results showed that the diamond composite deuterated polyethylene film had the best sputtering resistance, and the aluminum nitride composite heavy water target film had the lowest sputtering yield. The two coating materials shield the target, reduced the energy loss of incident ions, and provided a new method for the research of high yield and long life neutron tube.

Prompt gamma-ray neutron activation analysis method (PGNAA) was used to measure the talc content in flour. Neutron activation prompt gamma spectrum measured by NaI(Tl) detector has complex components, poor energy resolution, and high Compton plateau, how to obtain accurate element content from the prompt γ spectrum is one of the core problems of PGNAA. To reduce the systematic uncertainty caused by the variation of the neutron energy spectrum and γ self-absorption in different samples, the spectral decomposition method based on library least-squares was improved. As a result, the average relative deviation between the calculated values from measured spectra and the theoretical values based on the known composition was reduced from 6.1% to 0.3%. The relative uncertainty of 30 measurements on the same sample was reduced from 4.8% to 3.0%. The detection time can be reduced to 1 min, which meets the requirement of on-line measurement for talc in flour.

The electrospinnability of lignin was improved by blending in a solution of polyacrylonitrile (PAN) resulting in the reduction of the nanofiber cost. The compositions containing low concentration of the lignin shows good spinnability. The influences of main process parameters, such as flow rate, voltage and concentration on the nanofibers morphology were studied by scanning electron microscope (SEM). The results indicated that by changing parameters, nanofibers with good morphology were obtained. According to the study, when other parameters were kept unchanged, the parameters to prepare ideal nanofibers are as follows: flow rate is 0.04 mm/h; the voltage is 25 kV and the lignin amount is 2 wt.%. The results of this work showed that this novel method is a quite promising technique for preparation of biomass based carbon nanofiber precursors.

This paper investigated the influence of sintering temperature on the dielectric performance of alumina ceramic. Three different kinds of alumina ceramic samples were prepared using the same formula with three different sintering temperatures. The flashover voltage and surface charge distribution of the test samples were measured with a finger type electrode system under a positive pulse voltage application in a 1×10-4Pa vacuum circumstance. The experimental results showed that the samples with higher sintering temperature have worse dielectric performance. Based on the SEM observation, the change of dielectric performance could be attributed to the change of microstructure of alumina ceramics.

This paper has investigated the influence of corona intensity on the hydrophobicity recovery characteristics of HTV silicone rubber (SIR) deteriorated by corona discharge. The accelerating aging experiments of HTV silicone rubber were carried out with five levels of corona voltage. The hydrophobicity recovery with time was measured by static contact angle method. The experimental results show that the hydrophobicity of HTV silicone rubber can get some recovery after the corona deterioration, and the corona intensity play an important role on static contact angle of HTV SIR. In general, the procedure of hydrophibicity recovery would be varied with the different corona intensity and varied corona deterioration duration. And the hydrophibicity would not be recovered as original when the corona intensity is high enough under an certainty deterioration duration time.

The flashover of insulators in vacuum is the main factor to limit the performance of insulation in vacuum insulation system. It is believed that the pre-flashover phenomena would play a very important role in the procedure of the flashover in the interface between the insulators and vacuum. This paper is mainly concerned on the pre-flashover phenomena of alumina insulators in vacuum. There are 24 different types of alumina insulators were tested with a 0.7/4 /spl mu/s pulsed voltage under a 1x10/sup -4/ Pa vacuum. The observed pre-flashover phenomena were classified and the pre-flash-over characteristics were concluded. It is useful to study further on the flashover mechanism in vacuum.

This paper has investigated the trap distribution of alumina ceramics samples prepared under different sintering temperature. Compared with the flashover performance of these samples in vacuum, it was found that the trap distribution could influence the flashover performance. According to the experimental results, there is some relationship between the trap distribution and the surface flashover performance of insulators in vacuum. The role of the trap distribution on the surface flashover in vacuum has been analyzed.

Partial discharge (PD) can indicate defects in insulation of generator stator windings. In this paper, some generator model bars were made and some typical PD phenomena in generator stator windings were simulated. PD tests were also tried to find the features of composite PD. The data obtained from the test were analyzed and the spectrums of different types of PD were plotted using statistical parameters to reveal the feature of different patterns of PD. A BP neural network was also used to recognize the PD patterns.