Temperature effect on space charge dynamics in XLPE insulation

This paper reports on space charge evolution in crosslinked polyethylene (XLPE) planar samples approximately 1.20 mm thick subjected to electric stress level of 30 kVdc/mm under four temperature 25 oC, 50 oC, 70 oC and 90 oC for 24 hours. Space charge profiles in both as-received and degassed samples were measured using the laser induced pressure pulse (LIPP) technique. The dc threshold stresses at which space charge initiates are greatly affected by testing temperatures. The results suggest that testing temperature has numerous effects on space charge dynamics such as enhancement of ionic dissociation of polar crosslinked by-products, charge injection, charge mobility and electrical conductivity. Space charge distributions of very different nature were seen at lower temperatures when comparing the results of as-received samples with degassed samples. However at higher temperature, the space charge distribution took the same form, although of lower concentration in degassed samples. Space charge distributions are dominated by positive charge when tested at high temperatures regardless of sample treatment and positive charge propagation enhances as testing temperature increases. This can be a major cause of concern as positive charge propagation has been reported to be related to insulation breakdown

The effect of degassing on morphology and space charge

It is believed that space charge buildup in cross-linked polyethylene (XLPE) insulation is the main cause for premature failure of underground power cables. The space charge activities in XLPE depend on many factors such as additives, material treatment, ambient temperature, insulator/electrode interface, etc. Degassing is one of the material treatment process commonly employ in cable manufacturing to improve insulation performance. In this paper, investigation on the effect of degassing period has on the morphology and space charge was carried out. Planar XLPE samples of the same composite were subjected to different degassing time. It is discovered that apart from removing volatile by-products, degassing also anneal XLPE material; changing the morphology as a result

Fire resistance of steel beam to square CFST column composite joints using RC slabs: Experiments and numerical studies

In this paper, experimental investigation and numerical simulation of steel beam to square concrete-filled steel tube (CFST) column composite joints that use reinforced concrete (RC) slabs subjected to localized and global fire conditions are presented. Eight joints were tested under the ISO 834 fire standard, and the effect of different parameters including the load ratio of beams, the beam-to-column ratio of linear stiffness, and different fire scenarios was studied during testing. The failure patterns and the thermal responses of the structural members including the temperature distribution, axial displacement of columns, vertical deflection of the beam ends, and fire resistance of the joints were recorded and discussed. The results show that tube buckling of the square CFST columns, flange buckling of the steel beams, and separation between the top flange of the steel beams and the RC slabs were the primary failure patterns of this type of joint. Moreover, the temperatures of structural members within the connection zone were lower than those in the other regions. Compared with other factors, the load ratio of the beams demonstrated a significant influence on the displacement of the structural members and the fire resistance of the joints. A three-dimensional finite element analysis (FEA) model was built to simulate the fire performance of this type of composite joint. The simulation results were compared to the test results in terms of failure patterns, temperature distributions, displacements, and fire resistances, and good agreement in general was achieved. Finally, the FEA model was adopted to examine the effect of parameters on the fire resistance of the composite joints with axial and flexural constraints applied at the ends of the beam

N K Pi molecular state with I=1 and J(Pi)=3/2-

The structure of the molecule-like state of $NK\pi$ with spin-parity $J^{\pi}={3/2}^-$ and isospin I=1 is studied within the chiral SU(3) quark model. First we calculate the $NK$, $N\pi$, and $K\pi$ phase shifts in the framework of the resonating group method (RGM), and a qualitative agreement with the experimental data is obtained. Then we perform a rough estimation for the energy of $(NK\pi)_{J^{\pi}={3/2}^-,I=1}$, and the effect of the mixing to the configuration $(\Delta K)_{J^{\pi}={3/2}^-,I=1}$ is also considered. The calculated energy is very close to the threshold of the $NK\pi$ system. A detailed investigation is worth doing in the further study.Comment: 11 pages, 3 figures; accepted for publication in Phys. Rev.

Arithmetic purity of strong approximation for homogeneous spaces

We prove that any open subset $U$ of a semi-simple simply connected quasi-split linear algebraic group $G$ with ${codim} (G\setminus U, G)\geq 2$ over a number field satisfies strong approximation by establishing a fibration of $G$ over a toric variety. We also prove a similar result of strong approximation with Brauer-Manin obstruction for a partial equivariant smooth compactification of a homogeneous space where all invertible functions are constant and the semi-simple part of the linear algebraic group is quasi-split. Some semi-abelian varieties of any given dimension where the complements of a rational point do not satisfy strong approximation with Brauer-Manin obstruction are given