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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.

Active sensing and planning in unknown, cluttered environments is an open challenge for robots intending to provide home service, search and rescue, narrow-passage inspection, and medical assistance. Although many active sensing methods exist, they often consider open spaces, assume known settings, or mostly do not generalize to real-world scenarios. We present the active neural sensing approach that generates the kinematically feasible viewpoint sequences for the robot manipulator with an in-hand camera to gather the minimum number of observations needed to reconstruct the underlying environment. Our framework actively collects the visual RGBD observations, aggregates them into scene representation, and performs object shape inference to avoid unnecessary robot interactions with the environment. We train our approach on synthetic data with domain randomization and demonstrate its successful execution via sim-to-real transfer in reconstructing narrow, covered, real-world cabinet environments cluttered with unknown objects. The natural cabinet scenarios impose significant challenges for robot motion and scene reconstruction due to surrounding obstacles and low ambient lighting conditions. However, despite unfavorable settings, our method exhibits high performance compared to its baselines in terms of various environment reconstruction metrics, including planning speed, the number of viewpoints, and overall scene coverage., https://sites.google.com/view/active-neural-sensing/home

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.

This article reports the evaluation system of the insulating properties based on the pulsed electro-acoustic (PEA) method and the current integration charge $Q(t)$ method. According to the basic principles of the methods, the relationship between the charge ratio and dielectric relaxation time in $Q(t)$ data is first derived, by which a new method is proposed to calculate the material conductivity. By further analyzing the charge results of different materials, it is pointed out that the PEA method focuses on the related characteristics of the net charge distribution captured by deep traps, while the $Q(t)$ method reflects the changing process of the total charge amount and related characteristics. No single method can completely analyze all the charge characteristics of the material, and thus the necessity of the combination of the two methods is determined. Meanwhile, based on the theoretical derivation and experimental results, it is indicated that when the charge ratio of $Q(t)$ data exceeds 2, the electrical state inside the sample basically stabilizes. At this stage, the distorted electric field can be analyzed by the PEA method, and the $Q(t)$ method can calculate the leakage current, dielectric relaxation time, and conductivity. Therefore, the combination of the two methods can provide a more reasonable assessment for the insulation property and state.

Accurate measurement of the space charge inside insulating materials facilitates reliable assessment of insulation performance. In this paper, an improved calibration scheme based on the pulsed electro-acoustic (PEA) methodology is proposed for space charge measurement. First, according to the transmission-line model of the measurement system, the simulation results indicate that the acoustic impedances of the upper electrode and the sample may affect the recorded waveforms. Then, taking into account the actual situation that the acoustic impedances of the semiconducting electrode and the sample are different, an improved calibration method is presented by analyzing the propagation process of the acoustic waves. Comparison of the results further indicates that the material of the semiconducting electrodes may affect and lower the accuracy of the traditional PEA method. In contrast, the recovered results by the proposed method are more accurate and reliable. The improved method is thereby applied to calibrate the signals from polyimide (PI) samples. Combining with the simulation results, it is concluded that different semiconducting electrodes render sensible impact on the accumulation rate and process of the space charge. Furthermore, two groups of calibrated results under the same electric field are used to verify the effectiveness of the proposed method. Since the electrode material may be an influential factor in the measurement, it should be properly chosen according to the practical applied conditions of the insulation samples to achieve a better evaluation of the charge accumulation process.

Surface coating technology is an effective way to solve the interface insulation problem of DC GIS/GIL basin insulators, but the performance of the coating will change greatly, and the insulation strength will be completely lost, after long-term use in the extreme conditions of corona erosion. In this research, the multi-needle-plate electrode platform was constructed to explore the long-term use performance of SiC-doped nanocomposite exposed to corona discharge in SF6 gas. Samples with a high SiC content have advantages in maintaining physical and chemical properties such as elemental composition, erosion depth, surface roughness and mass loss. The nanocomposite doped with 6 wt.% SiC has prominent surface insulation strength after long term exposure to corona, and the others are close to losing, or have completely lost, their insulating properties. Furthermore, the degradation mechanism of physicochemical properties of composite exposed to corona discharge was investigated with the proposed ReaxFF MD model of energetic particles from SF6 decomposition bombarding the epoxy surface. The reaction process of SF particles and F particles with the cross-linked epoxy resin, and the SiC nanoparticles providing shelter to the surrounding polymer and mitigating their suffering direct bombardment, have been established. The damage propagation depth, mass loss and surface roughness change of nanocomposite material bombarded by SF6 decomposition products is reproduced in this simulation. Finally, the deterioration mechanism of insulation properties for the SiC-doped composite was elucidated with DFT analysis. The band gap of the molecule containing S drops directly from the initial 7.785 eV to 1.875 eV, which causes the deterioration of surface electric properties.

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.

To achieve the measurement of space charge inside insulating materials under high-frequency voltage conditions, an optical method based on stress birefringence effect is proposed. The method is expected to achieve high spatial and temporal resolutions due to its high signal-to-noise ratio, picosecond-scale excitation, and continuous wave detection by using Terahertz wave and ellipsometry measurement method. An ellipsometry system is then built to verify the key part of the proposed method. It is found that the measured signal from the balanced detector can accurately show the displacement process of actuator with different amplitudes and frequencies. The explorative research in this paper will be an important basis for the further development of the proposed optical method.

© 2019 John Wiley & Sons, Ltd. Wind turbine blades are subject to lightning strikes, which may result in severe damage of the blade materials. The withstanding performance of different blade materials needs to be classified in order to maximize their operational safety. Lightning impulse voltages were applied to model blades with different core materials (polyvinyl chloride [PVC], polyethylene terephthalate [PET], and balsa wood) to characterize the breakdown points (electrically vulnerable areas) on the blades. It has been found that the areas subjected to puncturing are located in the back part (toward the trailing edge) of the sandwich structure, especially at locations close to the main beam. Model blades made of balsa wood are more susceptible to puncturing breakdown than PVC and PET. High impulse currents were imposed at the most probably stricken spots in the impulse voltage tests to compare the severity of damage for PVC, PET, and balsa wood in an attempt to understand the thermal effect of lightning discharge following the final jump. Results show that balsa wood is most resistive to while PVC suffers most damage due to the thermal impact of lightning. Molecular simulation of the chemical degradation process and thermal gas production dynamics was performed at atomic level to explain the damage mechanisms of the three core materials. The performance data of the blade core materials against lightning strike obtained in the present work provide strong guidance on the optimal design of wind turbine blade structure and selection of blade core material.

For the sake of investigating the contribution of inorganic nanoparticles in reduction of partial discharge (PD) activity, and insulation durability, PI/TiO 2 nanocomposite thin films were fabricated with weight percentage of 2 and 3 via in-situ polymerization. PD aging tests were carried out for both the pure and PI/TiO 2 nanocomposite films to collect partial discharge data until the insulation breakdown occurred in order to analyze the nanoparticles impact on partial discharge characteristics parameters and insulation durability i.e. PD number per cycle and per second and maximum PD amplitudes. FTIR analysis were conducted for both aged and unaged pure polyimide (PI) and PI/TiO 2 nanocomposite samples for investigating bonding structure and the interactions happening between nanoparticles and polyimide matrix at the interface. Based on bonding structure analysis, it was noticed that incorporation of nanoparticles into polymer matrix introduces abundant amount of hydrogen bonds between TiO 2 nanoparticles and -OH groups, which offers hitch to partial discharge occurrence resulting greater insulation lifetime and durability. Besides, less degradation had been observed in aged PI/TiO 2 nanocomposites as compare with aged unfilled PI.