Early prediction of surge arrester failures by dielectric characterization

Metal oxide varistors based on ceramic technology are extensively used nowadays as limiting voltage devices, covering an amazing range of systems from microelectronics equipment up to very large power system networks. These varistors are formed through the sintering of a mixture of ZnO or SnO<;sub>2<;/sub> metal oxides with several other metal oxide dopants containing the elements of O<;sub<;2<;/sub>, Bi, Sb, and Cr [1], [2]. The electrical behavior is governed by the microstructure in which the conductive zinc oxide grains are surrounded by a resistive intergranular boundary of other oxides, forming “microcomponents” and acting like diodes with relatively low voltage turn-on [3]. This results in a highly nonlinear voltage-dependent conduction mechanism, or the I-V characteristic. This article presents an extension of earlier works [9], [10] utilizing lightning impulses to cause catastrophic failures of the surge arresters and applying diagnostic tests covering the transition from the new state to failure.