Railway vehicles carry electric equipment including traction inverters. It is very important to establish the dependability of these devices. To obtain the data required for the maintenance and renewal work of traction inverters mounted on recent EMUs, we discussed a method to estimate the average failure rate of plastic ICs, which are one of the parts of the inverters. Three types of accelerated durability tests proved that the failure rate of ICs averaged over 40 years was 21 Fit when the operating conditions were: ambient temperature +50ºC, relative humidity 50%, difference between the maximum and minimum temperatures of the day 50ºC, power turned on for 15 hours, which is converted into the average life time of 4.7 × 10⁷ hours. This is longer than that of aluminum capacitors or resistors. However, analysis of failed ICs proves that it is difficult to clarify the failure mechanism.

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