IEEE PC57.139

Revision Standard - Active - Draft.
General types of on-load tap-changer (OLTC) mechanisms, breathing configurations, and electrical designs, described for reference for determining methods of testing and evaluating dissolved gases in mineral-based transformer oils in OLTCs, are discussed and recommended in this guide. Measurements of dissolved gas concentrations in the OLTC oil are required to implement this guide. This guide is not manufacturer specific, rather category specific.

This guide describes methods of evaluating dissolved gases in insulating liquids used with load tap changers (LTCs). General types of LTC mechanisms, breathing configurations, and electrical design are included for evaluation criteria in determining when mechanical damage, deterioration or failure might have occurred.
The purpose of this guide is to provide non-invasive methods for evaluating the condition of an LTC.