在绝缘诊断试验技术的发展中了解水树机理

近来 ,有几种测量介电常数和介质损失的诊断方法已被发展为用来对水树枝劣化 XL PE电缆进行非破坏性试验。当所施加的试验电压超过一定值时 ,发现临界劣化不仅仅与介电性能成比例。本文采用一种力学模型来描述水树枝现象的这种非线性。绝缘中的水树枝被认为是由被微裂纹区隔离的一系列充水微孔构成 ,在相对较低的含水量和较低试验电压下 ,有的裂纹区即可能产生自愈合作用并且恢复绝缘状态。当试验电压上升时 ,Maxwell电机械应力将导致水分侵入裂纹区 ,并导致拉长的水滴间出现电接触。对电场和损耗的有限元法数值计算结果表明 ,这种影响将使导电通道端部的电场增强 ,同时导致含水树枝绝缘的介质损耗增加。

Understanding water treeing mechanisms in the development of diagnostic test method

Critical degradation is found to be associated with a more than proportional in crease of the dialectical properties when increasing the applied test voltage above a certain level. In this article, an explanation to this nonlinealy is presented, using a mechanical approach to the water treeing phenomenon. The water treed insulation is considered to consist of small water filled voids separated by crazing zones. At relatively low water content and low applied test voltage, some crazing zones are likely to be closed and insulating. But when increasing the test voltage, Maxwell mechanical stresses will cause water to penetrate into the crazing zones, thus making electric contact between the elongated water droplets. Results from FEM calculation of electric and losses show that the effect of this will enhance the electric field at the top of these conductive channels and to increase the deilectric losses of the water treed insulation.