Dissolved Gas Analysis (DGA) of Transformer Oil: Types, Benefits and Fault Detection

Transformers are essential components of electrical power systems. Unexpected transformer failures can lead to costly repairs, operational disruptions and power supply interruptions.

Regular condition monitoring helps maintenance teams identify potential issues before they develop into serious failures.

One of the most valuable diagnostic techniques is Dissolved Gas Analysis (DGA) of transformer oil. This method examines gases dissolved in insulating oil to help identify potential thermal and electrical faults inside oil-filled transformers.

By analysing gas concentrations and changes over time, maintenance professionals can obtain valuable information about the condition of transformer insulation and internal components.

What Is Dissolved Gas Analysis of Transformer Oil?

Dissolved Gas Analysis is a diagnostic test used to measure gases dissolved in transformer insulating oil.

When electrical or thermal faults occur inside a transformer, they can decompose the oil or solid insulation and generate gases. Some of these gases dissolve in the oil and can be measured through laboratory analysis.

The results help engineers investigate possible problems, monitor changes in transformer condition and determine whether further diagnostic work is needed.

DGA is particularly valuable as part of a structured transformer oil testing and condition-monitoring programme.

Why Is DGA Testing Important?

DGA testing can help identify developing problems that may not be immediately visible during routine inspections.

Its key benefits include early identification of potential internal faults, monitoring changes in transformer condition, supporting predictive maintenance, helping prioritise inspections and corrective actions, reducing the likelihood of unexpected failures through timely investigation, and providing information for long-term maintenance planning.

DGA does not predict every transformer failure, and its results should not be interpreted in isolation. Oil test results, loading history, equipment design and previous measurements all matter.

Important Gases Analysed During DGA

DGA analysis of transformer oil commonly includes the measurement of several gases.

Hydrogen (H₂): Hydrogen can be associated with certain electrical discharge processes and other fault conditions. Its significance depends on the overall gas pattern and operating history.

Methane (CH₄): Methane may be generated under certain thermal and electrical fault conditions.

Ethane (C₂H₆): Ethane can provide additional information about thermal decomposition processes occurring in the insulating system.

Ethylene (C₂H₄): Ethylene is often considered when evaluating thermal faults involving oil. Its concentration and relationship with other gases can assist fault interpretation.

Acetylene (C₂H₂): Acetylene may be associated with high-energy electrical discharges, including arcing. Its presence and concentration require careful interpretation.

Carbon Monoxide (CO): Carbon monoxide can be associated with the degradation of cellulose-based insulation and other processes.

Carbon Dioxide (CO₂): Carbon dioxide may also provide information about the ageing and degradation of paper insulation, particularly when considered alongside other measurements.

The presence of an individual gas does not automatically confirm a specific fault. Reliable diagnosis depends on gas concentrations, trends, ratios where appropriate and the transformer's operating context.

How Is the DGA Test of Transformer Oil Performed?

Step 1: Oil Sample Collection — A representative sample is collected using appropriate equipment and procedures to minimise contamination and gas loss.

Step 2: Sample Preparation — The sample is handled and prepared according to the laboratory's validated testing method.

Step 3: Gas Extraction and Measurement — Dissolved gases are extracted and measured using an appropriate analytical technique, commonly gas chromatography.

Step 4: Gas Concentration Analysis — The concentrations of individual gases are measured and documented.

Step 5: Technical Interpretation — The results are assessed using an appropriate diagnostic framework, relevant standards and the transformer's operating history.

Step 6: Reporting and Follow-Up — The laboratory report provides the measured results. Where technical interpretation is included, it may help determine whether additional investigation or repeat testing is appropriate.

Common Transformer Faults Investigated Through DGA

Thermal Faults — Excessive heating can cause decomposition of insulating oil and may affect paper insulation. Gas concentrations and patterns help engineers assess possible thermal issues.

Partial Discharge — Partial discharge involves localised electrical discharges that do not necessarily bridge the insulation completely. Certain gas patterns may indicate this type of activity.

Electrical Arcing — Arcing can generate gases associated with high-energy electrical discharge. Detection of relevant gas patterns may indicate the need for prompt technical investigation.

Paper Insulation Degradation — The ageing of cellulose-based insulation may contribute to the generation of carbon oxides and other degradation products. Additional tests, such as furan analysis, can provide complementary information.

DGA findings should be assessed by qualified personnel. Diagnostic conclusions and maintenance actions should reflect the severity of the findings and the equipment manufacturer's guidance.

DGA Standards and Interpretation

IEC 60599 provides guidance on interpreting dissolved and free gases in mineral oil-filled electrical equipment.

Other recognised methods and industry guidance may be relevant depending on the testing objective, transformer type and laboratory procedure.

A proper DGA report should identify the gases measured, the relevant units and the analytical method used.

When monitoring a transformer over time, changes in gas concentrations and gas generation rates can be particularly informative.

DGA vs BDV Testing: What Is the Difference?

DGA Testing — Investigates potential internal thermal and electrical faults; measures concentrations of dissolved gases; supports transformer condition monitoring.

BDV Testing — Evaluates dielectric breakdown strength; measures voltage at electrical breakdown under specified conditions; supports insulating oil quality assessment.

Both tests can contribute to a transformer maintenance programme, but neither replaces the other.

The Role of Transformer Oil Testing Laboratories

A professional transformer oil testing laboratory supports equipment maintenance by providing reliable measurements and test reports. Organisations may also compare a transformer oil testing lab in India based on the required test scope.

When choosing a transformer oil analysis laboratory, organisations should assess relevant analytical capabilities, sample handling and testing procedures, appropriate equipment and quality controls, compliance with applicable standards, accreditation scope where required, and clarity and completeness of test reports. Where applicable, confirm whether NABL certified transformer oil testing is within the laboratory's accredited scope.

For organisations seeking electrical testing and calibration support, Oorja Technical Services Pvt. Ltd. can be contacted to discuss relevant service requirements and testing capabilities.

Specific DGA services, accreditation and testing arrangements should be confirmed directly with the company before booking.

How Often Should Transformer Oil Be Tested?

The frequency of transformer oil testing depends on transformer capacity and importance, operating conditions and loading, equipment age and maintenance history, previous test results, manufacturer recommendations, and applicable regulations, standards and organisational policies.

Some transformers may require more frequent monitoring because of their critical role or unusual operating conditions.

A suitable maintenance schedule should be established by qualified personnel based on the specific equipment and risk profile.

transformer oil testing as per IS 335 / IEC 60296 can be considered as part of a suitable transformer oil condition-assessment programme.

Conclusion

Dissolved Gas Analysis of transformer oil is a valuable tool for monitoring transformer condition and investigating possible internal faults. By analysing gases such as hydrogen, methane, ethylene, acetylene and carbon oxides, maintenance teams can obtain useful diagnostic information.

When combined with BDV testing, acidity testing, moisture measurement and other appropriate diagnostic techniques, DGA contributes to a more comprehensive transformer maintenance strategy.

Oorja Technical Services Pvt. Ltd. supports organisations seeking technical testing and calibration solutions. Contact the team to discuss your electrical testing requirements and identify suitable services for your application.

Contact Oorja Technical Services Pvt. Ltd.

Website: oorjatechnical.in

Email: [email protected]

Phone: +91-9907759797