Although developed in the 1970s, DGA is still the most accurate and reliable way to assess 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.  The Duval Triangle plots the ratios of methane, ethylene, and acetylene, and then provides a diagnosis based on their relative concentrations.  A number of DGA analyzer manufacturers incorporate this model into their software.  For more information, please refer to this IEEE article written by M. Duval.

 

While DGA has been a standard Preventive Maintenance procedure 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 Electrostatic Precipitator 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.