Avaliação do efeito da temperatura no processo de degradação dos para-raios à base de óxido de zinco (ZnO).

Abstract

The effect of temperature on the degradation of ZnO-based nonlinear resistors has been reported in this thesis. The nonlinear resistors have been subjected to thermal and electrical stresses. The electrical stresses consisted of a continuously applied alternating voltage and 10 KA, positive polarity, standard (8 x 20 us) current impulses. An electric oven with temperature control was used for simulating the thermal stresses. A total de 19 samples provided by two different manufacturers were used in this study. The samples were subjected to five different types of stresses: - alternating voltage applied at ambient temperature; - alternating voltage applied at temperatures of 60°C and 80°C; - alternating voltage applied at ambient temperature with the periodic application of current impulses; - alternating voltage applied at temperature of 60° and 80°C with the periodic application of current impulses; - same as above but with the ambient temperature maintained at 60° and 80°C, respectively. Thermal instabihty was observed whenever the energy absorbed by the nonlinear resistors exceed a limiting value. Degradation and loss of the nonlinear properties of the resistors followed thermal instabihty. It was also observed that there is a lmuting value of the resistive leakage current at which thermal instability is initiated.