Chuanjie Lin

The control mechanism of surface traps on surface charge behavior in alumina-filled epoxy composites

To investigate the role surface traps play in the charge injection and transfer behavior of alumina-filled epoxy composites, surface traps with different trap levels are introduced by different surface modification methods which include dielectric barrier discharges plasma, direct fluorination, and Cr2O3 coating. The resulting surface physicochemical characteristics of experimental samples were observed using atomic force microscopy, scanning electron microscopy and fourier transform infrared spectroscopy. The surface potential under dc voltage was detected and the trap level distribution was measured. The results suggest that the surface morphology of the experimental samples differs dramatically after treatment with different surface modification methods. Different surface trap distributions directly determine the charge injection and transfer property along the surface. Shallow traps with trap level of 1.03–1.11 eV and 1.06–1.13 eV introduced by plasma and fluorination modifications are conducive for charge transport along the insulating surface, and the surface potential can be modified, producing a smoother potential curve. The Cr2O3 coating can introduce a large number of deep traps with energy levels ranging from 1.09 to 1.15 eV. These can prevent charge injection through the reversed electric field formed by intensive trapped charges in the Cr2O3 coatings.

Fe-N gradient thin films prepared by facing targets sputtering

The functionally gradient materials (FGMS) are important in both theory and practical applications. UP to now, almost all previous work has been concentrated on bulk materials. This paper describes the preparation of Fe-N gradient thin films by a facing targets sputtering system. Rutherford backscattering spectrometry (RBS) shows that the concentration of Fe atoms or N atoms varies gradually from the substrate to the surface throughout the whole thickness of the film. The Fe-N gradient films contain crystal phases of zeta -Fe2N, epsilon -FexN(2

Fluorine gas treatment improves surface degradation inhibiting property of alumina-filled epoxy composite

Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.

The potentially neglected culprit of DC surface flashover: electron migration under temperature gradients

This report intends to reveal the role of electron migration and its effects in triggering direct current (DC) surface flashover under temperature gradient conditions when using epoxy-based insulating composites. The surface potential and the surface flashover voltage are both measured using insulators that are bridged between two thermo-regulated electrodes. The space charge injection and migration properties under different temperature are detected. The results show that the surface potential rises significantly because of electron migration near the high voltage (HV) electrode under high temperature conditions, thus creating an “analogous ineffective region”. The expansion of this “analogous ineffective region” results in most of the voltage drop occurring near the ground electrode, which serves as an important factor triggering positive streamers across the insulation surface. This work is helpful in understanding of DC surface flashover mechanism from a new perspective and also has important significance in design of a suitable DC insulator to avoid surface flashover problem.

Formation of metastable crystalline phases by solid state reaction in Ni-Nb multilayered films

Two new metastable crystalline (MX) phases were formed in the Ni-Nb system by solid state reaction (SSR) of multilayered films at medium temperatures. The first one was the Ni-rich hcp phase and the second one was the Nb-rich fcc-I MX phase. A Gibbs free energy diagram of the system was constructed by calculation of the free energy curves of the alloy phases, and the MX phase formation is correlated with the constructed diagram. The growth kinetics of the MX phases is also discussed.

Surface charge inversion algorithm based on bilateral surface potential measurements of cone-type spacer

To study the surface charge distribution of high-voltage direct-current (HVDC) spacers for gas insulated lines (GIL), a surface charge inversion algorithm based on surface potential measurements is necessary. However, previous studies on inversion calculation of surface charge density only considered the surface potential of one side, neglecting the effect of residual surface charge on the other side of the spacer; this leads to an inaccurate inverted surface charge distribution. In this paper, the inversion algorithm methods used to determine surface charges over the past few decades were summarized, and their advantages and disadvantages were discussed. Based on the previous charge inversion algorithms, an improved surface charge inversion algorithm considering the surface potential of both sides of a cone-type model spacer was developed. The improved method was verified experimentally using a cone-type model spacer. Compared with that obtained by previous charge inversion algorithms, the charge distribution derived from the improved algorithm was closer to the situation determined from theoretical analysis. This work has practical relevance for the surface charge measurement of cone-type spacers and offers a new orientation in the surface charge analytical algorithm.

Hot electron injection regulation in Al 2 O 3 -filled epoxy resin composite using Cr 2 O 3 coatings

Al2O3-filled epoxy resin has been widely used as basic materials for insulators in ac/dc power transmission applications. Under normal working condition, charges injection from electrodes accelerates the dielectric aging rate and distorts the surface electric field, which is followed by dielectric degradation and breakdown. Therefore, to restrain the charge injection is of very important significance, especially when the dielectric was operating under temperature gradients. In this paper, to regulate the charge injection of dielectrics under temperature gradient, Cr2O3 coatings composed of dense well organized Cr2O3 molecules were created on the insulation surface. The surface potential appears low increments for modified samples, which indicates less charge injection phenomenon. Only slight surface potential increment was found using samples modified by Cr2O3 coating with thickness of 1000 nm, even when the temperature of HV electrode reaching 100 °C. Therefore, we believe that the Cr2O3 coating can effectively suppress the charge injection from the electrode, which has excellent application significance.