IEEE C57.139:2015

Revision Standard - Active.
General types of load tap changer (LTC) mechanisms, breathing configurations, and electrical designs, described for reference for determining methods of testing and evaluating dissolved gases in mineral-based transformer oils in LTCs, are discussed and recommended in this guide. Measurements of dissolved gas concentrations in the LTC oil are required to implement this guide. This guide is not manufacturer specific, rather category specific. ** Downloads file posted at http://standards.ieee.org/downloads/C57/C57.139-2015/

This guide discusses and recommends methods of testing and evaluating dissolved gases in mineral based transformer oils found in load tap changers (LTCs). General types of LTC mechanisms, breathing configurations, and electrical design will be included for evaluation criteria in determining when mechanical damage or failure has occurred. Dissolved gas analysis (DGA) of the oil in the LTC is required. This guide is not manufacturer specific, rather category specific.
The purpose of this guide is to assist the responsible parties who are in charge of the operation and maintenance decisions in evaluating the condition of an LTC without the need to de-energize the transformer to inspect the LTC in question. Additionally, repairs to the LTC can be made in a timely fashion based on accurate interpretation of the gas analysis, minimizing premature repairs or post failure rebuilds.