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Dissolved Gas Analysis in Transformer Oil
International standards and technical diagnosis
Dissolved Gas Analysis (DGA) is one of the most important tools used to detect internal faults in power transformers. Understanding the differences between international frameworks is essential when comparing laboratories and making reliable maintenance decisions.
Two types of standards used in transformer diagnostics
DGA involves two different types of technical standards.
1. Measurement standards (how gases are analyzed)
These standards define how oil samples are taken and how gases are measured in the laboratory.
2. Interpretation standards (how faults are diagnosed)
These standards explain what the gas patterns indicate about the internal condition of the transformer.

Two main international frameworks are used worldwide to interpret these gases: IEEE standards (United States) and IEC standards (Europe). Both systems analyze the same gases measured in laboratory tests, but the interpretation methodology can differ.
Latest update of the IEEE standard
The most recent version is:
Current Standard
IEEE C57.104 – 2019
This version represents a major revision compared to the previous version (2008).
Key updates include:
New gas concentration limits
Larger statistical datasets
Interpretation based on larger statistical datasets
Improved condition thresholds
Gas generation trends
Greater emphasis on gas generation trends
Modern diagnostic methods
Integration of modern diagnostic methods
This revision significantly modernized the standard.
Current status of the European standard
The European equivalent is:
European Standard
IEC 60599 – 2015
This standard focuses on the interpretation of dissolved gases in mineral-oil-filled transformers.
Current Status
Although it introduced important improvements, it has not undergone a revision as extensive as IEEE 2019.
Looking Ahead
Many experts expect an updated edition of IEC 60599 in the coming years.
Fundamental difference between the approaches
IEEE and IEC standards are based on different technical philosophies.
IEEE approach
Focused on asset management and operational monitoring.
It relies on:
Statistical gas limits
Alarm level classification
Trend monitoring
Fleet-wide predictive maintenance
This approach is widely used by electric utilities in the United States.
IEC approach
Focused on physical fault diagnosis.
It relies on:
Gas ratios
Comparing ratios between specific dissolved gases to identify fault signatures.
Chemical patterns
Identifying characteristic chemical patterns associated with different fault types.
Estimated fault temperature
Estimating the temperature range of the fault based on gas composition.
Graphical diagnostic methods
Using graphical tools such as the Duval Triangle for visual fault identification.
This approach is widely used in Europe and Asia.
The Duval Method (European diagnostic tool)
In Europe, one of the most widely used diagnostic methods is the Duval Triangle.
This method uses three key gases:
Key Gases
How it works
By plotting these gases on a triangular diagram, engineers can identify the likely internal fault. This method allows engineers to directly diagnose the physical phenomenon occurring inside the transformer.
Types of faults identified
The Duval Triangle maps gas ratios to specific fault codes, enabling precise diagnosis:
This method allows engineers to directly diagnose the physical phenomenon occurring inside the transformer.
The IEEE key gas method
The IEEE approach focuses on identifying dominant gases.
Dominant Gas → Probable Fault
Operating Conditions
This method is particularly useful for large transformer fleets.
Why the same analysis may produce different diagnoses
The same laboratory results can sometimes lead to different interpretations depending on the methodology used.
Example Gas Values (ppm)
Possible interpretations
IEEE interpretation
Moderate warning condition
IEC + Duval interpretation
Possible partial discharge
This is why combining multiple interpretation methods improves reliability.
What advanced laboratories do
Leading laboratories typically combine several diagnostic approaches:
01
IEEE C57.104 interpretation
02
IEC 60599 gas ratios
03
Duval Triangle analysis
04
Gas generation trend analysis
05
Transformer operating context
This integrated approach significantly reduces the risk of incorrect diagnoses.
Best practices in transformer diagnostics
Reliable DGA diagnostics require:
Proper oil sampling procedures
Accredited laboratory analysis
Correct interpretation methodology
Long-term trend analysis
When done properly, DGA allows operators to:
Detect incipient faults early
Prevent catastrophic failures
Extend transformer service life
Optimize asset management strategies
About Us
Confiamex
Technical architecture for international power projects
Our approach is based on three principles:
Technical rigor
Application of international standards.
Operational viability
Solutions that work in real field conditions.
Technical trust
Clear interpretation for confident engineering decisions.
If you are exploring an international project in the electrical or industrial sector, let’s talk:
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