Dissolved Gas Analysis (DGA)
Dissolved gas analysis (DGA) is the industry standard for detecting faults in a transformer. Often, detection of these gases alone does not point to any specific fault. Rather, you need the specific combination, concentration, change over time, and movement from the baseline test results for a true understanding of what is happening inside a transformer.
In interpreting DGA results with our own proprietary method, SDMyers uses internal guidelines. In addition to the gas levels, our DGA interpretations are based on a large number of variables, such as equipment type, liquid type, past history/trending, manufacturer, equipment age, kVA, voltage, gallons, breather type, temperature, and service history, among others.
We also utilize statistical analysis and other industry standard diagnostic tools such as Rogers Ratios, Duval Triangles, and Duval Pentagons, when appropriate. The results either indicate healthy electrical power equipment that maximizes reliable life or diagnoses of fault conditions that closely match what is found in maintenance activities and post-failure forensic investigations.
Find out more about testing and analysis by downloading the SDMyers guide, Understanding Transformer Testing: A Guide to Diagnostic Tests for Oil-Filled Transformers.
Understanding Dissolved Gases
New transformer oil contains small amounts of dissolved combustible gases. Additional dissolved combustible gases form when an abnormal condition exists, which is often attributed to a fault. By measuring the concentration of a gas in transformer oil, it is possible to narrow down what event caused it to form, how severe or recurrent that event was, and whether the transformer is still reliable. Here are a few examples:
HYDROGEN
Hydrogen accompanies most known transformer faults. An excellent indicator that further analysis is needed.
ACETYLENE
Presence of acetylene is an indicator of arcing/sparking and severe overheating. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, and methane.
METHANE
The presence of methane indicates low energy electrical or thermal faults. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane.
ETHANE
The presence of ethane indicates electrical or thermal faults, with production of ethane starting at around 250 degrees Celsius. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane.
ETHYLENE
Like acetylene, ethane, and methane, Ethylene indicates a thermal fault. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane. The higher the temperature of the fault, the greater the concentration of Ethylene.
OXYGEN
The presence of oxygen suggests ingress of outside air into the transformer tank and greatly increases the conditions that lead to accelerated degradation of the cellulose insulation.
CARBON MONOXIDE
Elevated levels of carbon monoxide and carbon dioxide are indicators of possible cellulose insulation degradation.
CARBON DIOXIDE
Elevated levels of carbon monoxide and carbon dioxide are indicators of possible cellulose insulation degradation.
NITROGEN
Nitrogen, as well as oxygen, can be an indicator of air ingress to the tank.
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