Foreword 
In 1974, the Transformer Reliability Working Group was formed to develop a guide for reporting failure data for power transformers and shunt reactors. In the early years, considerable time and effort was spent on developing definitions necessary to establish the ground rules for doing power transformer reliability work. The reliability guide attempted to establish rules so that all parties would be working with the same definitions and parameters. Prior to this work, each organization established its own criteria for definitions, reporting failure data, establishing the requirements by which meaningful data could be collected, and generating failure statistics. Two important issues emerged: (i) establishing the requirements by which meaningful data could be collected, and (2) bringing together the efforts of user and manufacturer within the confines of confidentiality. The joint effort between user and manufacturer has not been approached previously and holds a promise for future development. Work has also been completed by the statisticians on system reliability; however, detailed work in component reliability (such as power transformers) has not been addressed in sufficient detail to generate statistics. Another area explored by the Transformer Reliability Working Group was the joint effort required by all parties to use common language and establish cooperation.
As work progressed, it became obvious that much work and effort was required to ensure that adequate failure investigations are conducted when transformers fail. Questions regarding this subject led to many more unanswered questions. As a result, a proposal was issued to establish a Transformer Failure Analysis Working Group, which would be responsible for the preparation of a document that would assist the failure investigation work.
Many papers have been written and many conferences have been held regarding reliability, availability, and maintainability of transformers. Between the Transformer Reliability Working Group and the Transformer Failure Analysis Working Group, issues will be explored, and the efforts will perhaps answer some of the unanswered questions. It is only a start regarding transformer reliability and transformer failure investigation. Many areas in the life history of a transformer need further definition, exploration, documentation, and clarification.
Scope
This guide recommends a procedure to be used to perform a failure analysis. Although the procedure may be used for an investigation into any ac transformer failure, it is primarily focused on power transformers used on electric utility systems.