Weikang Cao

Bio: Weikang Cao is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Space charge & Partial discharge. The author has an hindex of 3, co-authored 5 publications receiving 52 citations.

Insulating property of polypropylene nanocomposites filled with nano-MgO of different concentration

Abstract: Polypropylene (PP) has special advantages in replacing conventional crosslinked polyethylene (XLPE) to be insulation material of power cable. In order to reveal the effects of nano-filler addition on PP, five kinds of experiments, namely TEM, DSC, breakdown strengths (BDs), space charge and dielectric measurement were investigated to evaluate the insulating properties of PP and its nanocomposites with surface-treated nano-MgO of different concentration. It is revealed that, with the addition of nano-MgO, favorable dispersibility of nano-filler and significant increase of crystallinity of polymer are observed. BDs under dc voltage increase apparently with loading of nano MgO, but when the nano concentration reaches higher than 1 wt%, the BDs have a slight decline compared with 1 wt%. It is clarified that space charge and electric field distortion are well restricted with the addition of nano-MgO, while this effect is not obvious with the nano concentration reaches 6 wt%. Permittivity has trends of increase with the rise of temperature at first and then decrease when the temperature reaches about 333 K, and the addition of nano-filler MgO could also decrease permittivity. When the nano-filler concentration reaches high, dielectric loss increases to a high level. Low nano-filler concentration in MgO/PP shows better electrical insulation properties compared with PP and high nano-filler concentration composites.

Experimental study on space charge and electrical strength of MgO nano-particles/polypropylene composite

Abstract: The electrical and thermal characteristics of isotactic polypropylene (i-PP) are revealed to be superior to polyethylene (PE), and i-PP is suitable for recycle use as the recent environmental requirement. The electrical characteristics of nano-filler/PP composite are investigated and studied in this paper. Nano-particles of MgO were added to i-PP to prepare nanocomposites for testing of AC/DC breakdown strength (BDs), permittivity, differential scanning calorimetry (DSC) and distribution of space charge. It is found that MgO nano-particals improve AC BDs (breakdown strength) of PP, while DC BDs decreases with loading of nano-MgO. The value of DC BDs is higher than that of AC BDs. The distribution of space charge was investigated by PEA devices, and few volume of space charge appeared in PP under low electrical field (10 kV/mm and 30 kV/mm). A lot of Heter-opolar space charges appeared in PP under electrical field of 50 kV/mm. The volume of space charge decreases with increase of particles' concentration. It is revealed that nano-MgO is considered to have an effect of suppression of charge injection in PP composite. The differential scanning calorimetry (DSC) measurement was carried out to investigate the melting and crystallizing temperature of PP composites. The crystallization temperatures of the PP show a large increase of 4 K as loaded by MgO nano fillers, which indicates that the nanoparticles act as nucleating agents during the crystallization of PP. The electrical capacitance bridge was used to detect the permittivity of composites. The permittivity of sample was measured under frequency of 50 Hz and temperatures of 293, 303, 313, 333, 363 and 383 K. The results show that the permittivity of PP increases slightly with loading of nano-MgO, and it increases first and then decreases with temperature.

Studies on electric field distribution and partial discharges of XLPE cable at DC voltage

Abstract: Partial discharge (PD) detection is considered as a reliable method to analyze the operating status of the electrical equipment. But there are only a few literatures about PDs of cross-linked polyethylene (XLPE) cable at DC voltage. So this paper mainly concentrates on electric field distribution and PD phenomena of DC XLPE cable. Numerical simulation method is applied to analyze electric field distribution in normal and four typical insulation defect (corona defect, cavity defect, scratch defect and creepage defect) models. Electro-thermal coupling model is established to solve this problem. The simulation result shows that four defects can cause different electric field distortion. Among them, corona defect has the most serious distortion and creepage defect has the most slightly distortion. The high voltage test is applied to verify the simulation result. The H(q, Δt) spectrums of PD signals confirm that serious electric field distortion can cause severe PD phenomena.

Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A

Abstract: The diffuse Galactic $\gamma$-ray emission, mainly produced via interactions between cosmic rays and the diffuse interstellar medium, is a very important probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. In this work we report the measurements of diffuse $\gamma$-rays from the Galactic plane between 10 TeV and 1 PeV energies, with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO). Diffuse emissions from the inner ($15^{\circ}10$~TeV). The energy spectrum in the inner Galaxy regions can be described by a power-law function with an index of $-2.99\pm0.04$, which is different from the curved spectrum as expected from hadronic interactions between locally measured cosmic rays and the line-of-sight integrated gas content. Furthermore, the measured flux is higher by a factor of $\sim3$ than the prediction. A similar spectrum with an index of $-2.99\pm0.07$ is found in the outer Galaxy region, and the absolute flux for $10\lesssim E\lesssim60$ TeV is again higher than the prediction for hadronic cosmic ray interactions. The latitude distributions of the diffuse emission are consistent with the gas distribution, while the longitude distributions show slight deviation from the gas distribution. The LHAASO measurements imply that either additional emission sources exist or cosmic ray intensities have spatial variations.

Study on space charge and electrical conductivity of polypropylene insulation material

Abstract: The electrical and thermal characteristic of isotactic polypropylene (i-PP) is revealed to be superior to polyethylene (PE), and i-PP is suitable for recycle use as the recent environmental requirement. The electrical characteristic of PP are investigated and studied in this paper. A kind of specimen of Isotactic polypropylene was prepared for space charge and electrical conductivity experiments, which was expected to be insulation of DC cable. It is found that electrical conductivity increase with temperature of specimen. The value of high field conductivity under 90°C is three times of that under room temperature. Space charge experiments were investigated by PEA devices, and few volume of space charge appeared in PP under low electrical field (10kV/mm and 20kV/mm). A lot of Heteropolar space charges appeared in PP under electrical field of 50kV/mm. During the process of short circuit or discharging, it is found that space charge in specimen can be released completely, rapidly after half hour's charging time under electrical field of 10kV/mm and 20kV/mm. However, a lot of space charge remains inside specimen of pp after half hour's charging time under electrical field of 50kV/mm.

Recyclable Dielectric Polymer Nanocomposites with Voltage Stabilizer Interface: Toward New Generation of High Voltage Direct Current Cable Insulation

Abstract: Long-distance and large-capacity transmission systems have been strongly demanded in modern society, which requires the development of high voltage direct current (HVDC) cables. However, the currently used cross-linked polyethylene (XLPE) insulated cables not only cannot fulfill the environmental sustainability but also cannot withstand HVDC electrical stress. In this study, recyclable cable insulation which can withstand HVDC electrical stress was successfully prepared by incorporating newly synthesized voltage stabilizer functionalized silica nanoparticles into a thermoplastic isotactic polypropylene. The introduction of voltage stabilizer functionalized nanoparticles resulted in significantly enhanced breakdown strength, suppressed space charge injection, and greatly improved thermal stability. For example, the breakdown strength was increased by about 46% by adding 4 wt % voltage stabilizer functionalized silica. Surface potential decay, crystallinity, and supramolecular structure of the polypropylene...

Submarine Power Cables Design Installation Repair Environmental Aspects

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Polypropylene nanocomposite for power equipment: a review

Abstract: Polypropylene (PP), with high breakdown strength, low dissipation and good processibility, is one of the most widely used dielectric material for power equipment, especially in power capacitors and power cables. The improvement of PP-based dielectric material can benefit the properties enhancement of power capacitors and cables, and thus to meet with the rapid development of the power system. Nanocomposite provided a promising orientation to reach the target and recent research approaches of PP nanocomposite for power equipment were reviewed in this paper. In this paper, we linked the nanofillers to the improved properties of PP nanocomposite, and categorised the research works into nanoclay/PP composites, metal oxide/PP nanocomposite, conductive particles/PP nanocomposite, and PP core-shell nanocomposites chronologically, corresponding to the enhanced thermal and mechanical property, breakdown strength property and energy storage property, respectively. Based on the achieved approaches, prospective for future research was proposed, providing a worth-considering direction for the future work.