Chang Ming Li

Research on DC dielectric properties of polyaniline nanofibers/LDPE composites

In this article, polyaniline (PANI) nanofibers were prepared and added to low-density polyethylene (LDPE) to produce PANI nanofibers/LDPE composites. LDPE and the composites were tested for direct current (DC) conductivity, breakdown strength, and space charge characteristics. The results suggested that DC breakdown strength of PANI nanofibers/LDPE composites significantly declined once PANI was added, and the decline was more evident with the increase of PANI nanofibers. Meanwhile, the addition of PANI nanofibers contributed to a decrease in the conductivity of LDPE. As the content of PANI nanofibers increased, the conductivity of the composites declined first and then raised. DC conductivity properties of LDPE could be improved by adding an appropriate amount of PANI nanofibers. Compared with LDPE, the space charge distribution was changed in LDPE due to the addition of PANI nanofibers. With the increase of content of PANI nanofibers, the amount of space charges close to the electrodes decreased gradually.

Effect of Magnetic Field Treatment on Temperature-Sensing Property of Polyethylene-Based PTC Composites

A static magnetic field is applied during the hot press molding of high-density polyethylene (HDPE)/carbon black (CB)/ferrous powder composites and HDPE/CB/carbon nanotube (CNT) composites. The effect of magnetic field treatment on the temperature-sensing property of polyethylene-based positive temperature coefficient (PTC) composites is investigated. Experimental results indicate that the magnetic field treatment can lead to the alignment of ferrous powders and CNT in HDPE along the direction of the applied external magnetic field, thus guaranteeing the composites have low room-temperature resistivity and high PTC intensity as the concentration of CB is cut down. This also can significantly improve mechanical property and processability of the composites. When the mass concentrations of ferrous powders and CNT are equal, HDPE/CB/ferrous powder composites present better PTC property than HDPE/CB/CNT composites after the magnetic field treatment.

Inhibition of Electrical Tree Initiation inside High-Voltage Cross-Linked Polyethylene Cable with Nonlinear Shielding Layer

Electrical tree aging is one of the leading factors causing degradation and breakdown of insulation performance of high-voltage cross-linked polyethylene (XLPE) cable. A lot of attention has been paid to inhibiting electric tree initiation and propagation inside high-voltage cable. In this study, insulation composites with nonlinear electrical conductivity are prepared. Experimental results show that these composites are helpful for enhancing the apparent breakdown electric field strength of XLPE in the pole electrode system. A kind of high-voltage XLPE insulated cable with new structure is designed by using these composites as nonlinear shielding layer. Numerical simulation results indicate that nonlinear shielding layer can obviously improve the distribution of electrical field at the defect of insulation surface of high-voltage XLPE cable, and decrease the maximum electrical field strength at the defect. This new structure is potential for effectively inhibiting electrical tree initiation inside high-voltage XLPE insulation cable, thus increasing life span and operational reliability of the cable.

Improvement on Temperature-Sensing Property of Low-Density Polyethylene Based PTC Composites with Static Magnetic Field Treatment

A stable magnetic field was applied during hot press molding of low-density polyethylene (LDPE)/carbon black (CB)/ carbon nanotube (CNT) composites and HDPE/CB/nickel powder composites. The effect of magnetic field treatment on the temperature-sensing property of LDPE-based positive temperature coefficient (PTC) composites was investigated. Experimental results indicate that the magnetic field treatment can lead to an alignment of CNT and nickel powder in LDPE along the direction of the applied external magnetic field. The alignment of these filler particles can endow the composites with low room-temperature resistivity and high PTC intensity when the concentration of CB is decreased. The alignment also can significantly improve mechanical property and processability of the composites. Compared with CNT, nickel powder with strong magnetism has more sensitive response to external magnetic field and is much easier to align in LDPE. Addition of nickel powder is beneficial for developing PTC composites with excellent comprehensive properties.