Experiments are reported on two techniques for melt-texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper-rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser-heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: ‘‘faceted plane front,’’ ‘‘cellular dendritic’’ or ‘‘equiaxed blocky.’’ The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the ‘‘root’’ of the solidification front dropped, but temperature of the solidification front ‘‘tip’’ did not. A solidification model is developed and employed to interpret experimental observations. The model assumes limited diffusion of solute in the liquid during the growth of the superconducting phase. The model shows, in agreement with experiment, that growth rate of the low temperature solid phase has a strong effect on ability to obtain the desirable faceted plane front, and that thermal gradient has only a small effect. Interparticle spacing of the high temperature phase, BaY2CuO5, is also predicted to have a strong effect.
Water tree is one of the degradation aspects of XLPE cables used for under-ground distribution or transmission lines. We have developed the loss current method using 3rd harmonic in AC loss current for cable diagnosis. Harmonic components in loss current arise as a result of the non-linear voltage-current characteristics of water trees. We confirmed that the 3rd harmonic in AC loss current had good correlation with water tree growth and break down strength. After that, we have applied this method to the actual 66 kV XLPE cable lines. Up to now, the number of the application results is more than 120 lines.In this method, it is sometimes said that the degradation signal (3rd harmonic in loss current) is affected by the 3rd harmonic in the test voltage. To indicate and solve this problem, we investigated the extent of influence by 3rd harmonic in the test voltage, and found the rule of the influence. As a result, we developed a new technique of harmonic-noise reduction in loss current method that enabled a more highly accurate diagnosis and confirmed the effectiveness of this new technique by simulations and experiments with actual cables. CV
Residual charge method", which has been developed for detection of non-bridged water tree, is well known as a high reliability water tree deterioration diagnosis technique for XLPE cable, and it has been applied for on-site cable system diagnosis.Traditional residual charge method measures the amount of electrical charge, and the information of cable length is required to evaluate the result. In this paper, we would like to introduce our development of the new technique of residual charge method which does not need the information of cable length to evaluate the deterioration degree.
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