Reliability estimation for populations with limited and heavily censored failure information

Statistical analysis of the life data, is a useful tool helping to assess the life-time of populations of high-voltage components. More specific, the results of such analysis give overview over the failure behavior of the population under investigation, i.e. number and trend of expected failures. For the analysis, the detailed information about ages and numbers and ages of installed units and failed units has to be collected. Subsequently, the distribution representing the behavior of the population is fitted to the data. The latter allows deriving the time-dependent failure rate function, which in turn, directly indicates the trends of the future failures. However, this method requires homogeneous and independent data of sufficient amount. The latter becomes a problem, particularly that for past periods the failure data is often unavailable. It is important to estimate the population reliability and number of expected failures, for the whole population of components being operated. This is also important in the case when the available failure data comes only from one part of the area where the components are installed. In this paper we will show how to deal with populations where the available failure data is heavily censored, and what will the influence of the data division according to the regions in which the transformers are operated, on the failure expectancy.