This thesis addresses one of the possible ways of calculating lifetime of a varistor at normal operating conditions. For some of the devices or components life test at normal operating conditions would take too much time (e.g. more than one year). This problem also arises with life test for a varistor.
To solve this problem, we can use accelerated testing. There are several different reasons for a failure of a varistor, therefore accelerated tests are also done in different ways. The available equipment allowed us to make accelerated testing in climatic chamber under operating voltage load. Varistor failure times were recorded at different temperature exposures. Later survival analysis models were used to determine lifetime of a varistor under increased temperature.
From results provided by survival analysis, activation energy was calculated, and then using extrapolation it was possible to estimate lifetime of a varistor at 85 °C. It was assumed that activation energy coefficient is constant for the given ceramic.
After mean time to failure was estimated it was tested whether starting varistor characteristics are related to varistor failure times or not.
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