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IEEE C57.117

86th Edition, 1998

Complete Document

Guide for Reporting Failure Data for Power Transformers and Shunt Reactors on Electric Utility Power Systems

Includes all amendments and changes through Reaffirmation Notice , May 10, 2005

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(This Foreword is not a part of ANSI/IEEE C57.117-1986, IEEE Guide for Reporting Failure Data for Power Transformers and Shunt Reactors on Electric Utility Power Systems.)

The IEEE Transformer Reliability Working Group was formed in 1974 under the Performance Characteristics Subcommittee of the IEEE Transformers Committee. The purpose of this working group was to investigate the feasibility of pursuing transformer reliability on electric utility power systems. To best address the subject of transformer reliability, the IEEE Working Group concentrated on this guide.

Early in the development of this guide, it was recognized that the Edison Electric Institute (EEI), and in particular, the Electrical System and Equipment Committee (ES&E Committee), had an existing data collection system for summarizing equipment outages, and in particular, one category devoted to power transformers. An effort was made to develop this guide in such a manner that common goals between IEEE and EEI could be established. It was the intent that by working together, both groups could develop a single, flexible dynamic system that would benefit the whole transformer industry, both user and manufacturer alike.

The EEI data base summarizes installations and failures for power transformers 2.5 MVA and above. Although the principles proposed in this guide can be used for any homogeneous population, it is anticipated that initial efforts using the principles of this guide will be directed toward large MVA transformers installed on electric utility power systems.

The thrust of this guide is to define reliability terms and to establish guidelines for a data base and reporting mechanism for power transformer failures. In developing this guide it was discovered that the subject of failure analysis could support a document of its own. Accordingly, a separate working group has been formed and assigned a project to perform this task.


This guide addresses the reporting and statistical analysis of reliability of power transformers and shunt reactors used on electric utility power systems. Included are the following types and applications of transformers:

power transformers


regulating transformers

phase-shifting transformers

shunt reactors

HVDC converter transformers

substation transformers

transmission tie transformers

unit transformers

unit auxiliary transformers

grounding transformers

For the purpose of abbreviation in this document, the term “transformers(s)” refers to“power transformer(s) and shunt reactor(s).” For further clarification of the meaning of “transformer” as used in this guide, refer to the definitions and 6.5.5 and 6.5.6.