Many of the electric power apparatuses that were installed at the period of high economic growth in Japan are reaching their supposed lifetime. Therefore, an important issue is how to effectively maintain, manage, and replace the many aged electric power apparatuses. Hence, it is necessary to develop a condition diagnosis technique and a method of confirming the healthy condition of an aged power apparatus. Consequently, the establishment of a maintenance standard for such aged power apparatuses, which is helpful for judging the possibility of prolonged operation with satisfactory reliability and the replacement time, is required.
From the above-stated viewpoint, we have aimed to establish a method of judging the condition of aged power apparatuses by executing on-site insulation tests. If an insulation test of the aged power apparatus is executed, it is important to estimate the risk (increase in the cumulative insulation fault probability) considering the background (life-stress) of the voltage application, including the on-site insulation test. In this paper, we discuss the influence of the insulation test of aged power apparatus on the cumulative insulation fault probability using a Weibull distribution.