INVESTIGATION OF DIAGNOSTIC TECHNIQUES FOR METAL OXIDE SURGE ARRESTERS FOCUSED IN THE POLARIZATION/DEPOLARIZATION CURRENTS

Abstract- This work deals with the assessment of working conditions and reliability of metal oxide arresters using dielectric response techniques. Varistors are polycrystalline ceramics in which the conduction is controlled by the Schottky barriers existing in the grain-boundary region. The resulting insulation resistance values are in the range of several Megaohms in the non-conducting region of the VxI characteristic curve. Nevertheless, the degradation process of the components changes the microstructure in the ZnO varistors and/or the insulation properties, affecting the conduction mechanism. Measurements of polarization/depolarization currents and DC conductivity using very sensitive equipment can reveal the evolution of this process. The aim of this work is to analyze different test techniques to assess the insulation condition of surge arresters subjected to lightning discharges. Thus, test samples were submitted to a degradation process up to fail. Throughout of this stressing procedure electric tests were carried out using techniques frequently applied for diagnosis (reference and residual voltage, resistive current) in addition with the new ones, based in direct current measurements. Results are compared and commented