Testing of varistors using thermography was carried out in order to assess their protective properties against possible overvoltage phenomena in the form of high-level voltage surges. An advantage of the thermography technique is non-contact temperature measurement. It was proposed to assess the properties of varistors working in electronic devices as protective elements, on the basis of estimating temperature increments on varistor surfaces, registered by an infrared camera during surge resistance tests with standard voltage levels. To determine acceptable temperature increments on a tested varistor, preliminary testing was performed of P22Z1 (Littelfuse) and S07K14 (EPCOS) type varistors, working first at a constant load and presently during surge tests,. The thermographic test results were compared with measured varistor capacity values before and after tests. It was found that recording with thermography temperature increments greater than 6°C for both P22Z1 and S07K14 varistor types detects total or partial loss of varistor protective properties. The test results were confirmed by assessment of protective properties of varistors working in output circuits of low nominal voltage devices.

Varistors are commonly used elements which protect power supply networks against high-voltage surges or lightning. Therefore, quality and endurance of these elements is important to avoid losses when an expensive laboratory equipment would not be protected from random overvoltages. Additionally, excessive leakage currents generate serious costs due to high energy consumption. The paper presents shortly properties of varistors that comprized different ZnO grain types and can have various quality which changes continuously during exploitation (due to exposition to overheating and overvoltage pulses). Therefore, it is important to monitor varistors during their ageing (causing changes within their microstructures). A few methods of varistor property diagnosis were considered and compared with the methods currently applied in laboratory or industry applications. A new measurement (diagnostic) system that can monitor varistors during ageing and can be widely applied in power networks is presented. The proposed system fulfills requirements of the industrial customers which demand various methods for power line protection. The proposed system can be simply developed into a more advanced wireless diagnostic system of long power supply lines.

In this paper, a study of the lightning phenomenon and its harmful effect on Aqaba Thermal Power Station (ATPS), located in the south-western border of Jordan, is presented using the Electromagnetic Transients Program – Alternative Transients Program (EMTP- ATP). This study has been arisen due to an installation need of appropriate lightning arresters (LAs) for the 15/410 kV step-up transformers of the ATPS to eliminate the destructive effect of lightning. The simulation is carried out for two cases, once without using LAs and once more with using them. Two scenarios are applied for each of these cases, once when lightning strikes the primary side of the transformer and once more when it strikes the secondary side. The results obtained by the simulation indicate the necessity of LAs installation. This study, with using the EMTP-ATP program, is done for the first time with additional details that help researchers, designers, and engineers to get a broad overview of the ATPS in order to protect it against lightning.

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.

The paper presents investigations of microstructure of varistors of damaged surge arrester counters. A similar ZnO varistor, not subjected before to operation, was a point of reference in this research. The results of investigations of the ZnO varistors show an untypical phase composition of their material, which was characterized by unsatisfying homogeneity and cohesion. The degradation processes of varistor material in the subsequent stages were recognized and described. A harmful impact of humidity inside the untight surge arrester counter on its operation and its ZnO varistors was proved. Some conclusions being the result of the operation checking of surge arrester counters were presented too.