The paper presents results of investigation of microstructure and micro-hardness for material of ZnO varistors applied to 110 kV surge arrester and surge arrester counter. The research combined two pairs of varistors, each consisted of one varistor subjected before to operation, while the other one was brand new unit and constituted a reference. All varistors were made of the same material by the reputable manufacture. The tests revealed a different degree of the material degradation for varistors subjected before to operation. This also refers to different degradation mechanism observed for the material of these varistors, if typical effects of degradation of aged ZnO varistors were considered as a reference. Physical state of spinel in the microstructure had a significant impact on the material degradation, however a considerable loosening of the microstructure associated with bismuth oxide was observed too. It was surprising, since the precipitates of the bismuth oxide phase most often showed very good binding to the ZnO matrix and high resistance to associated electrical, thermal and mechanical effects. The degradation effects in the ZnO matrix proved to be limited only.

Abstract The paper treats the thermooptical sound generation in the magnetoactive two-layered medium on the condition of tunnel interference of electromagnetic waves. It were studied the conditions of complete suppression of the photoacoustic signal amplitude in response to the polarization type of oppositely interacting waves, the difference in their initial phases as well as the intensities of one of the oppositely interacted beams. The given paper provides an effective method of managing the thermooptical sound generation in the magnetoactive structural element during the tunnel electromagnetic interference of electromagnetic waves.