A power transformer acts as a center piece in the electricity supply chain. Furthermore, it is the insulation system of these power transformers that strikes an optimum balance between life expectancy and operational cost. A typical oil-immersed transformer insulation system contains of cellulosic kraft paper and pressboard, and mineral oil for maximum protection.

Dissolved gas analysis (DGA) of insulation oil is a popular technique to monitor the overall health status of power transformers. This technique analyzes oil samples to evaluate potential or incipient faults within the transformers using some well-defined rules. It helps in providing an early warning of an impending fault and allows the transformer engineer to take suitable corrective actions. Simply put, DGA is one of the most cost-effective tools for finding thermo-chemical problems inside a transformer.

A DGA test evaluates seven prime gases in oil i.e. hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, and carbon dioxide besides nitrogen and oxygen. An individual gas or a combination of various gases can identify if there is any impending fault, the rate of fault development, reliability checks, and/or any assistance is necessary for fault correction.

Some of the well-known methods for interpretation of DGA results are Duval’s triangle, key-gas, Dorenberg, and Roger’s ratio method. More information on such methods is given in IEC60599.