Stefan Tenbohlen and Dan Martin gave the "Analysis of AC Transformer Reliability" tutorial at the CIGRE Session in Paris at the end of August 2024. This tutorial presents the analysis of transformer failures collected by WG A2.62 of CIGRE Study Committee A2 “Power Transformers and Reactors”. Based on a transformer population with more than 425,000 unit-years and 1,159 major failures, a failure rate of app. 0.3 % p.a. was determined. Failure location and mode analysis is presented for different voltage classes, along with external effects. The presentation of the age distribution of transformers from different continents and the associated hazard curves provided a deep insight into transformer life assessment. The tutorial was very well attended with over 250 participants.
