Gas in Oil Analysis

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.

Dissolved Gas Analysis

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. A number of samples must be taken over a period of time for developing trends.

Data from DGA can:

Fault Identification

Arcing

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

Corona

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 one of the most comprehensive insulating oil data management systems and interpretation guides. This system does 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. These data are used to update and improve the diagnostic process.

Results

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

Sampling

Insulating oil samples for dissolved gas analysis must be taken 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. Glass syringes for dissolved gas analysis are loaned to customers at no charge.

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