Optimization of cable terminations

This paper describes a study of various termination constructions for medium voltage cross-linked polyethylene (XLPE) power cables. A special device was used for electrical field measurements around the cable termination which made it possible to monitor how stress relief materials with different permittivity and placement of isolated or grounded embedded electrodes (EE) affected electrical stress grading. The results of measurements for each configuration were examined by mathematical modeling based on the finite element method (FEM). Finally, the selected constructions of cable termination have passed severe test conditions with load cycling     

A new concept in construction of cable terminations for mediumvoltages

This paper describes a new concept in construction of cable terminations for medium voltages. Layers with a high permittivity and embedded electrodes (EEs) were used. Three groups of configurations were examined. In the first group, the layer of high permittivity was placed partly over the cable insulation and partly over the cable screen. In the second group, the high permittivity layer (HPL) was placed partly over the cable insulation and partly under the semiconducting material, connecting with the cable insulation screen. In the third group the cable screen was partly inserted into the HPL whose other part was placed over the cable insulation. The EEs were made in a shape of rings around the HPL. The rings were made either of copper tape or copper wire. Different positions of the EEs were examined. Numerical models of the cable terminations were used to monitor how the electric field changes as a function of the EE distance from the cable screen end. Finally, the new terminations were tested in a high voltage laboratory, according to the standards VDE 0278 and IEEE-404     

The behavior of water in XLPE and EPR cables and its influence onthe electric characteristics of insulation

This paper presents the latest results of continuous investigations of cable insulations degradation of crosslinked polyethylene (XPLE) and ethylene-propylene with rubber based formulation (EPR) when subjected to electric stress and heating in the presence of water or water vapour. The paper deals with water absorption and diffusion in two kinds of crosslinked polyethylene insulation-dry-cured and steam-cured, and steam-cured EPR insulation. The aim of this investigation is to present the results of the influence of changing of water or water vapour pressure in the conductors of XLPE and EPR cables in different service conditions on the electric characteristics of XLPE and EPR insulations-breakdown voltage (AC BDV), dissipation factor (tan δ) and rata of partial discharge (RPD). In this paper, RPD is defined as, the maximum electrical field when the beginning partial discharge in the cable insulation and partial discharge were measured in accordance with the IEC standard. This paper also shows the relation between AC BDV and water content, and AC BDV and tan δ in XLPE and EPR insulations. In this testing the tap water was put in the cable conductors and the ends were properly closed by terminal boxes. The results indicate that the combined effects of water or water vapour, pressure, moisture, electric field and temperature will greatly accelerate deterioration of XLPE and EPR insulations     

Investigation of water effects on degradation of crosslinkedpolyethylene (XLPE) insulation

This paper presents the results of the study of the influence of moisture on the electrical characteristics of XLPE power cable insulation under various service conditions. Tap water was put into the cable conductors and the ends were properly closed by terminal boxes in the first case, and opened in the second case. The samples of cables were subjected to electric stress and heating. Results from the accelerated aging tests of XLPE cables in these conditions are reported with reference to the changing of the XLPE's electrical characteristics. On the basis of the compared performances of XLPE cables given by this investigation, the lifetime of XLPE cables was estimated in the case of service under these conditions. Results of testing indicate that the combined effects of pressure of water or water vapour, electric field and temperature will greatly accelerate the deterioration of XLPE insulation     

New Recursive Algorithms for the Unified Forward and Inverse MDCT/MDST

Forward and inverse MDCT are two of the most computationally intensive operations in the MPEG audio coding standard. In this paper we derive sinusoidal recursive formulas for transforming kernels of the MDCT/MDST and IMDCT/IMDST. Then we efficiently implement MDCT/MDST and IMDCT/IMDST of the general length using the regressive structure derived from the sinusoidal recursive formulas. The proposed regular structure is particularly suitable for parallel VLSI realization. Our solution requires significantly less operations as well as less hardware compared with a recently proposed one.     

The influence of the water on water absorption and density of XLPEcable insulation

This paper presents the results of a continuing investigation into effect of water on water absorption and density of crosslinked polyethylene (XLPE). The experimental set up was made for the following XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and without water tree retardant crosslinked polyethylene (natural XLPE). During tests, the tap water was injected (1) into the cable conductor with cable ends closed, (2) into the cable conductor with cable ends opened, and (3) into the metallic screen with cable ends opened. The XLPE cable insulation together with the water present in the cable was subjected to electrical stress and heating. The results were analyzed theoretically and experimentally. The aim of this paper is to present the results of the influence of the water on water absorption and density of various kinds of XLPE cable insulation in different service conditions