Transformers are vital components in both the transmission and distribution of electrical power. The early detection of incipient faults in transformers reduces costly unplanned outages.

The most sensitive and reliable technique for evaluating the health of oil filled electrical equipment is dissolved gas analysis (DGA). Insulating oils under abnormal electrical or thermal stresses break down to liberate small quantities of gases. The qualitative composition of the breakdown gases is dependent upon the type of fault. By means of dissolved gas analysis (DGA), it is possible to distinguish faults such as partial discharge (corona), overheating (pyrolysis) and arcing in a great variety of oil-filled equipment. Information from the analysis of gasses dissolved in insulating oils is valuable in a preventative maintenance program. Several samples must be taken over time to develop trends.

Data from DGA can:

  • Provide advance warning of developing faults
  • Provide a means for conveniently scheduling repairs
  • Monitor the rate of fault development

Fault Identification


Large amounts of hydrogen and acetylene are produced, with minor quantities of methane and ethylene. Key Gas: Acetylene.


Low-energy electrical discharges produce hydrogen and methane, with small quantities of ethane and ethylene. Key Gas: Hydrogen.

Overheated Oil

Decomposition products include ethylene and methane, together with smaller quantities of hydrogen and ethane. Key Gas: Ethylene.

Overheated Cellulose

Large quantities of carbon dioxide and carbon monoxide are evolved. Key Gas: Carbon monoxide.

Interpretation and Historical Data

Powertech has a comprehensive insulating oil data management system and interpretation guide. This system performs graphical trend analysis for gas-in-oil data. The reports contain recommended actions based on the latest accepted guidelines and Powertech’s extensive experience. Powertech will maintain historical records for each customer. This data is used to update and improve the diagnostic process.


A computer-generated dissolved gas analysis report will be emailed to the customer.


Insulating oil samples for dissolved gas analysis must be collected in hermetically sealed glass syringes with matched pistons to avoid exposure to air. Exposure to sunlight should also be avoided and the samples should be sent to the laboratory as soon as possible. For detailed sampling information, please refer to ASTM D923. Syringes are available from Powertech upon request.