DGA has been demonstrated to be the most accurate and reliable method of assessing the overall condition of power transformers. This analysis can indicate specific defects within the transformer, including insulation breakdown, loss of dielectric efficiency, or short circuits in the windings.  There are a number of ways to interpret this data; one of the most popular methods is known as the Duval Triangle, developed by Michel Duval of IREQ, Canada.  This method plots the ratios of methane, ethylene, and acetylene and then provides a diagnosis based on their relative concentrations.  A number of analyzer manufacturers have modeled their software on this method.  For more information, please refer to this IEEE article.

 

While DGA has been a standard PM item for large distribution transformers, this practice has not been widely adopted for ESP transformer/rectifier sets.  Weidman Diagnostic Solutions, the leading transformer oil analysis lab in North America, estimates that less than one-third of all T/Rs are analyzed on an annual basis.  Karl Jakob of Weidman has recently produced a whitepaper that addresses the unique aspects of T/R gas analysis.