Search

To study the effect of a cross-linking agent on the cross-linking degree and electrical properties of cross-linked polyethylene, different mass fractions of cross-linked polyethylene and their electrical properties were investigated. The cross-linking degree of cross-linked polyethylene with different mass fractions was tested by the extraction method. The breakdown field strength was tested by DC voltage breakdown tester, and the space charge injection of two kinds of cross-linked polyethylene was tested by Pulsed Electro-Acoustic. In addition, the resistivity was measured with conductivity test. The obtained results show that the crossing degree and breakdown field are the highest when the mass fraction of DCP is 2.5 wt% and BIPB is 1.5 wt%, which is 89.39% and approximately 310 kv mm ^−1 , respectively, while the cross-linking degree and breakdown field are 88.28% and approximately 340 kv mm ^−1 , respectively. At the same time, when DCP is used as the cross-linking agent, the amount of the same cross-linking agent is greater, which leads to more impurities contained in the material and increased space charge accumulation in the material; thus, the breakdown strength is lower than that of BIPB, and the conductivity is higher with the cross linking agent of DCP.

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation. [ABSTRACT FROM AUTHOR]

Dielectric capacitors have a high power density, and are widely used in military and civilian life. The main problem lies in the serious deterioration of dielectric insulation performance at high temperatures. In this study, a polycarbonate (PC)‐based energy storage dielectric was designed with BN/SiO2 heterojunctions on its surface. Based on this structural design, a synergistic suppression of the carrier injection and transport was achieved, significantly improving the insulating properties of the polymer film. In particular, the composite film achieves optimal high‐temperature energy‐storage properties. The composite film can withstand an electric field intensity of 760 MV m−1 at 100°C and obtain an energy storage density of 8.32 J cm−3, while achieving a breakthrough energy storage performance even at 150°C (610 MV m−1, 5.22 J cm−3). Through adjustment of the heterojunction structure, free adjustment of the insulation performance of the material can be realized; this is of great significance for the optimization of the material properties. [ABSTRACT FROM AUTHOR]

Space charge accumulation in the cable insulation will cause local electric field distortion, and accelerate the aging of the material. The inner semi‐conductive layer as an important structure of cable will affect the charge injection characteristics in the insulation layer. This work intended to explore the method of modifying the semi‐conductive layer with the Nitrogen‐doped graphene (NG) to suppress the charge accumulation utilizing the super‐smoothness of graphene and electron adsorption of N element. First, the NG is prepared using N‐modified graphene, and the semi‐conductive layer with different NG content is fabricated. Second, the physical and chemical properties of the semi‐conductive composite are carried out, then the charge accumulation characteristics in the insulation layer under the effect of the semi‐conductive layer are characterized. The results showed that an appropriate amount of NG doping can significantly inhibit the charge accumulation in the insulation layer. The surface roughness decreased by about 32.13% when the doped NG content is 0.5 phr. With the increase of NG content from 0 to 1 phr, the accumulation charges inside the insulation layer decreased by about 36.84%. This research provided a new approach for suppressing space charge accumulation in the insulation material of high voltage cable. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) is the core of electric energy conversion and circuit control, which is widely used in the field of electric vehicles. Higher service temperature, higher power density, and higher operating voltage are the tendency for IGBT in which packing materials have to possess more stable temperature resistance and better insulating properties. In this work, cyanate ester (CE) and polyhedral oligomeric silsesquioxanes (POSS) are introduced into epoxy with various filling ratio to improve the dielectric and thermal properties. The curing process of every system is determined by non‐isothermal differential scanning calorimetry (DSC). N and Si element distribution mappings indicate that there are good compatibility between POSS, CE, and epoxy. The dielectric test shows that the dielectric constant decreases from 4.34 to 2.84 at 1 MHz and from 4.76 to 2.93 at 1 kHz when the filling ratio is 60 wt%. Meanwhile, the DC breakdown strength increases from 172.7 to 286.4 kV/mm. Furthermore, the glass transition temperature (Tg) increases from 180 to 263°C and the yield of residual carbon increases from 6.2% to 23.7%. A new packing material, which can endure 250°C of operating temperature and has excellent dielectric properties has been synthesized. [ABSTRACT FROM AUTHOR]

Polyimide film has the weakness of high processing temperature and low corona resistance, which restrain its further development. Kapton 100 HN polyimide films with a thickness of 50 pm were aged by needle-plane electrode under 4 kV bipolar pulse voltages for 4 h at different frequencies (300-900 Hz). The surface morphologies of the pristine and aged polyimide films were analyzed using an atomic force microscope, and the changes in chemical bonds during corona aging were analyzed by Raman spectra. Different surface morphologies are observed using AFM, and the parameters all have sharp increases, which reveal that the surface morphology is obviously influenced by the corona aging under the bipolar pulse voltage. Raman results show that there are peak shifts and changes of the relative band intensities, which demonstrate that the chemical bonds in the polymer chains are reoriented by the electric field. Moreover, the corona aging of the polyimide film became severe at high frequency. POLYM. ENG. SCI., 53:1536-1541, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION The pulse-width modulated (PWM) variable speed drive (inverter) is one of the newest and fastest evolving technologies in nonlinear devices used in motor drive systems. With increasing emphasis of [...]