Arc ignition through pre-arc from extra fine copper wire
Metal ignition wires are widely used in power arc tests on insulator sets and similar. Finer metal ignition wires are preferred from the point of view of influence on the apparatus tested. However, if the metal ignition wires are too fine, the arc cannot be sustained. To perform power arc tests successfully, therefore, they need to have some degree of thickness. With these requirements in mind, we proposed a new arc ignition method that allows the use of extra fine wires by leading to the pre-arc in a current of several dozens amperes, and examined it for practical use. In this paper, the sustainment characteristics of arcs ignited from extra fine copper wires using this new method were investigated with a gap between the rod electrodes. The results showed that kA-class arcs with a gap length of 1.5 m could be ignited through pre-arc from 0.03 mm diameter copper wire at a voltage of 12 kV. The influence of the ignition wire thickness on arc characteristics was also studied by comparing the arcs ignited by this new method with those ignited by the general method in which copper wires exceeding 0.3 mm in diameter was used.
Calculation of net emission coefficient of thermal plasmas in mixtures of gas with metallic vapour
The net emission coefficient of Ar-Cu, N2-Cu, SF6-Cu and Ar-Fe mixtures was calculated for homogeneous and isothermal plasmas at atmospheric pressure in the temperature range between 3000 and 25000 K. The increase in power radiated due to the presence of metal vapours depends on the vapour itself (the net emission is higher with iron than with copper) and on the type of gas. The influence of pressure was calculated for the SF6-Cu mixture. In the last part of the paper the values of the net emission coefficient were used to calculate the temperature profile in stationary arc in Ar-Cu and N2-Cu mixtures. The influence of copper on radiation is preponderant on the temperature field at higher currents whereas the effect on electrical conductivity is important at lower currents.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.