The influence of thermal aging on absorption phenomena in cross-linked polyethylene cable insulation

Absorption-controlled charge and discharge currents in cross-linked polyethylene (XPE) cable insulation before and after thermal aging have been measured. The experimental dependences were analyzed in terms of the equivalent Voigt scheme. Known parameters of the Voigt scheme were used to calculate the frequency dependences of relative dielectric permittivity, loss factor, and loss tangent of XPE films in the region of low frequencies (ω = 10^–3–1 s^–1) at high temperatures. Results of analysis of the absorption characteristics of XPE were applied to modeling of the process of thermal aging of cable insulation.

     

Anisotropic diffusion of point defects in a two-dimensional crystal of streptavidin observed by high-speed atomic force microscopy

The diffusion of individual point defects in a two-dimensional streptavidin crystal formed on biotin-containing supported lipid bilayers was observed by high-speed atomic force microscopy. The two-dimensional diffusion of monovacancy defects exhibited anisotropy correlated with the two crystallographic axes in the orthorhombic C 222 crystal; in the 2D plane, one axis (the a-axis) is comprised of contiguous biotin-bound subunit pairs whereas the other axis (the b-axis) is comprised of contiguous biotin-unbound subunit pairs. The diffusivity along the b-axis is approximately 2.4?times larger than that along the a-axis. This anisotropy is ascribed to the difference in the association free energy between the biotin-bound subunit-subunit interaction and the biotin-unbound subunit-subunit interaction. The preferred intermolecular contact occurs between the biotin-unbound subunits. The difference in the intermolecular binding energy between the two types of subunit pair is estimated to be approximately 0.52?kcal?mol(-1). Another observed dynamic behavior of point defects was fusion of two point defects into a larger defect, which occurred much more frequently than the fission of a point defect into smaller defects. The diffusivity of point defects increased with increasing defect size. The fusion and the higher diffusivity of larger defects are suggested to be involved in the mechanism for the formation of defect-free crystals.     

An investigation of the potential of ethylene vinyl acetate/polyethylene blends for use in recyclable high voltage cable insulation systems

Ethylene vinyl acetate (EVA) co-polymers can potentially provide novel materials for inclusion into extruded high voltage cable systems, providing a degree of electrical conductivity whilst avoiding the dispersion problems associated with conventional particulate fillers or conducting polymers. Although a degree of conductivity can decrease the electrical breakdown performance, it can help to suppress the development of space charge and increase the tree initiation voltage leading to enhanced dielectric properties. In addition, novel two phase morphologies can be formulated leading to the ability to control key thermal and mechanical properties and the ability to tailor these to suit the application. In addition, one of the problems with conventional cross-linked polyethylene (XLPE) is that it cannot easily be recycled; therefore, in this time of increasing environmental awareness, it is prudent to begin investigations into alternative recyclable materials to replace XLPE in extruded cables for the medium to long term. The current article focuses on the crystallisation behaviour, morphology, mechanical and dielectric properties of a range of polymeric insulation systems based on an EVA co-polymer together with a high density polyethylene (HDPE) component. The morphology was controlled by choosing co-polymers containing different vinyl acetate contents together with appropriate crystallisation routes. The relationships between the morphology and the mechanical and dielectric properties were explored. Blends containing a low vinyl acetate content co-polymer combined with HDPE have significant potential to replace XLPE in cable systems and have the advantage of being easily recycled at the end of their service life.     

Determination of insulation defects by measuring currents in underground pipelines

The determination of the size of insulation defects in underground pipelines by measuring the attenuation factor of currents flowing in them is discussed. Analytical expressions for the size of defects are derived and results of calculations are presented. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 47–49, June, 1999.     

Fractal analysis of side channels for breakdown structures in XLPE cable insulation

The role of frequency in the range 20 through 300 Hz on the breakdown voltage and the breakdown path is studied in cross-linked polyethylene (XLPE) cable insulation using embedded needle. A maximum breakdown voltage of 25 kV is found at 240 Hz, and side channels are observed on the flank of the main channel of the electrical breakdown path. Fractal analysis of the side channel is carried out and it is induced that the frequency dependence of the fractal dimension D of the side channel are similar to that of the electrical trees before breakdown. It is suggested that the space charge can be injected from the needle tip. This leads to partial discharge causing progress of the electrical tree and the breakdown path. Space charge will also result in field-moderating cloud around the needle tip and turn to sidewall charges in the side channels. The frequency dependence of the breakdown voltage of the XLPE with the embedded needle can be clarified based on the fractal analysis of the side channel and the electrical tree of the XLPE insulation.     

Review of tape materials for cable insulation at liquid nitrogen temperatures

This Paper reviews the electrical breakdown, partial discharge and loss angle characteristics of taped cable insulation impregnated with liquid nitrogen. Also life expectancy and the effects of semiconducting screens are surveyed. With the recent announcement of a superconductor at liquid nitrogen temperatures a review of cable insulation impregnated with liquid nitrogen is felt to be appropriate.     

Review of super-resolution fluorescence microscopy for biology

Several methodologies have been developed over the past several years for super-resolution fluorescence microscopy including saturated structured-illumination microscopy (SSIM), stimulated emission depletion microscopy (STED), photoactivated localization microscopy (PALM), fluorescence photoactivation localization microscopy (FPALM), and stochastic optical reconstruction microscopy (STORM). While they have shown great promise for biological research, these techniques all have individual strengths and weaknesses. This review will describe the basic principles for achieving super resolution, demonstrate some applications in biology, and provide an overview of technical considerations for implementing these methods.     

Color indicator of cuprate superconductivity observed by polarized light microscopy

A common mineralogical technique for identifying individual crystals in a heterogeneous, polycrystalline sample involves the observation at room temperature of their colors in reflected polarized light (colors of polarization). Here we present the observation that a brownish yellow (golden) color of polarization is not only characteristic of the YBa₂Cu₃O₇ superconductor, but of the cuprate superconductors in general and is correlated with the occurrence of superconductivity.     

High voltage insulation of bushing for HTS power equipment

For the operation of high temperature superconducting (HTS) power equipments, it is necessary to develop insulating materials and high voltage (HV) insulation technology at cryogenic temperature of bushing. Liquid nitrogen (LN₂) is an attractive dielectric liquid. Also, the polymer insulating materials are expected to be used as solid materials such as glass fiber reinforced plastic (GFRP), polytetra-fluoroethylene (PTFE, Teflon), Silicon (Si) rubber, aromatic polyamide (Nomex), EPDM/Silicon alloy compound (EPDM/Si).In this paper, the surface flashover characteristics of various insulating materials in LN₂ are studied. These results are studied at both AC and impulse voltage under a non-uniform field. The use of GFRP and Teflon as insulation body for HTS bushing should be much desirable. Especially, GFRP is excellent material not only surface flashover characteristics but also mechanical characteristics at cryogenic temperature. The surface flashover is most serious problem for the shed design in LN₂ and operation of superconducting equipments.     

Polarizability of G4-DNA observed by electrostatic force microscopy measurements

G4-DNA, a quadruple helical motif of stacked guanine tetrads, is stiffer and more resistant to surface forces than double-stranded DNA (dsDNA), yet it enables self-assembly. Therefore, it is more likely to enable charge transport upon deposition on hard supports. We report clear evidence of polarizability of long G4-DNA molecules measured by electrostatic force microscopy, while coadsorbed dsDNA molecules on mica are electrically silent. This is another sign that G4-DNA is potentially better than dsDNA as a conducting molecular wire.     

Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy

The use of magnetic nanoparticles in the development of ultra-high-density recording media is the subject of intense research. Much of the attention of this research is devoted to the stability of magnetic moments, often neglecting the influence of dipolar interactions. Here, we explore the magnetic microstructure of different assemblies of monodisperse cobalt single-domain nanoparticles by magnetic force microscopy and magnetometric measurements. We observe that when the density of particles per unit area is higher than a determined threshold, the two-dimensional self-assemblies behave as a continuous ferromagnetic thin film. Correlated areas (similar to domains) of parallel magnetization roughly ten particles in diameter appear. As this magnetic percolation is mediated by dipolar interactions, the magnetic microstructure, its distribution and stability, is strongly dependent on the topological distribution of the dipoles. Thus, the magnetic structures of three-dimensional assemblies are magnetically soft, and an evolution of the magnetic microstructure is observed with consecutive scans of the microscope tip.     

Three-dimensional optical microscopy of water trees in polyethylene

Polyethylene is used as high-voltage electrical insulation in cable, and fails when subjected to the combination of water environment and electrical field. The three-dimensional microstructure of water trees, which are precursors to dielectric breakdown, has been revealed with laser scanning confocal optical microscopy. Two-dimensional images which represented optical serial sections were recorded in digital form, and reconstructed in a computer to produce three-dimensional views of the microstructure. Both stereo pairs and computed tomographic reconstructions were made. The material was stained with a fluorescent dye and the fluorescent image was compared to the standard unstained image. The dye was found to increase the signal-to-noise ratio and improve the quality of the image significantly.     

The Raman spectra of high modulus polyethylene fibres by Raman microscopy

Raman-microscopy has been used to analyse a series of high modulus polyethylene fibres. The high degree of orientation within the material means that upon 90° rotation of the samples and/or polarisation analyser, marked variations in band intensities occur throughout the spectra. Measurements of the 1131 : 1064 cm–1 band intensity ratio of the fibres are made and related to their Young's modulus. This relationship is useful in morphological studies of polyethylene fibres.     

Morphology of polyethylene nanolayers: a study by evanescent light microscopy

Thin films morphology investigation of polyethylene by the differential evanescent light intensity (DELI) imaging method has been performed. The films of nanometer thickness were obtained by the matrix-assisted pulsed laser evaporation (MAPLE) technique. MAPLE was demonstrated to be suitable for the synthesis of organic materials in form of nanostructures. To prepare targets, 3% polyethylene powder was dissolved in toluene and frozen at liquid nitrogen temperature. In MAPLE, the organic material is protected by the frozen solvent against the direct laser and plasma action. Polyethylene thin films of various thicknesses, below 200 nm, were thus fabricated by varying the deposition conditions. We applied the DELI microscopy technique for fast and low cost morphology investigation of large polyethylene nanolayer zones. A phenomenological model for the interaction between the evanescent waves and the deposited material is presented.     

Four-dimensional microscopy of defects in integrated circuits

We demonstrate four-dimensional microscopy of defects in integrated circuits by a technique that combines laser-scanning confocal reflectance microscopy with one-photon optical-beam-induced current (1P-OBIC) imaging. Accurate information is obtained about the three-dimensional structure of the defect and the kind of material (metal, semiconductor, or dielectric) that is damaged by the defect. The same focused probe beam simultaneously produces the 1P-OBIC and reflectance signals from the illuminated sample spot. The hardware development cost is minimal for a laser-scanning confocal microscope, and the image reconstruction procedure is computationally efficient. Imaging is demonstrated on defects that are caused by electrical overstress and unwanted generation centers. Exclusive three-dimensional distributions of the semiconductor and metal sites in the integrated circuit reveal defect features that are difficult to recognize with confocal or 1P-OBIC imaging alone.