Dependence of XLPE insulated power cable wave propagation characteristics on design parameters

Propagation losses occur in medium voltage power cables as pulses propagate through them. Since cables have many components, these can make different contributions to the propagation losses. The relative contributions of the conductors, insulation and semi-conducting screens to the propagation characteristics of the cable are analyzed. The propagation characteristics of the cables are studied by a developed "approximate" model providing analytical expressions that can quantify the contributions to the losses by the different parts of the conductor and dielectric system. The model is compared with an "exact" model and is tested on four cables     

Critical Currents of High-Temperature Superconductors in Homogeneous Magnetic Fields

In this paper we report on the measurements of the critical current of a tape-formed high-temperature superconductor in a magnetic field corresponding to the field at different positions in a (transformer, reactor or magnet) winding. An applied magnetic field reduced the perpendicular component of the self-field of the sample. The measurements were performed in liquid nitrogen on a silver-sheathed Bi-2223 conductor. The results show a significant increase of the critical current with reduction of the perpendicular component of the self-field.     

Measurement technique for high frequency characterization of semiconducting materials in extruded cables

Knowledge on the dependence of wave propagation characteristics on material properties and cable design is important in establishing diagnostic methods for cable insulation. In this study, a high frequency measurement technique to characterize the semi-conducting screens in medium voltage cross-linked polyethylene (XLPE) cables has been developed. The frequency ranges from 30 kHz to 500 MHz. The influence of the experimental set-up, sample preparation methods, pressure and temperature are investigated. A dielectric function is developed for the semiconducting screens and this is incorporated into a high frequency model for the cable. The propagation characteristics obtained from the high frequency cable model are compared with those obtained from measurements made on the same cables.     

A Procedure for the Development of a Low-Cost Treatment Technology of Raw Biogas for Application in a Gas Engine. A Case of Sizing a Carbon Dioxide Removal Unit

A test laboratory (lab) for carbon dioxide (CO₂) adsorption from raw biogas onto a novel adsorbent was used to size a CO₂ removal unit in the development of a low-cost biogas treatment technology. The novel adsorbent was made out of clay and burnt maize cob particles, impregnated with hot natural alkaline solution of pH 10 ± 0.5, degassed, and then activated at a temperature of 250°C, thereby making it low cost. The activated absorbents were spherical balls of average diameter 17 mm, density 410 kg/m³, and surface area 128 m²/g, and contained exchangeable ions due to the presence of clay and increased pore sizes due to impregnation, degassing, and activation. The effect of pressure drops on CO₂ removal, the breakthrough curve, and the absorption isotherm were studied. As a result, reduced pressure drops enhanced CO₂ removal and 102 Pa/m was the suitable pressure drop; pressure drops less than 102 Pa/m were impractical because the biogas did not exit. The breakthrough curve was in typical s-shape and thus satisfied its use for determining the adsorption rate constant (k₁) to be 0.001952 l/mg s and the maximum percent of CO₂ removal to be 87.8% at 102 Pa/m pressure drop and temperatures ranging from 20 to 28°C. The isotherm was found to closely conform to the definition of the Freundlich equation with the Freundlich coefficient of 0.01809 (l/g)ⁿ, where n = 1.37 at the same temperature range. Therefore, the determined k₁ and fitted Freundlich isotherm can be used to size the CO₂ adsorption unit under these conditions.