Dissolved Gas Analysis (DGA): A Crucial Diagnostic Tool for Transformer Maintenance

Dissolved Gas Analysis (DGA)  

Dissolved Gas Analysis (DGA) is an essential diagnostic test used in the maintenance of oil-immersed transformers. By analyzing the concentration and composition of gases dissolved in transformer insulating oil, DGA provides early detection of internal faults, enabling corrective action before severe damage occurs.

Here, we explain the analytical method and what you can expect to diagnose.

What Is Dissolved Gas Analysis (DGA)?

DGA is a diagnostic process that examines the gases dissolved in the insulating oil of a transformer. During normal operation, electrical and thermal stresses within a transformer can cause the oil and cellulose insulation to decompose, releasing specific gases. The composition and levels of these gases correlate with certain fault types, such as overheating, partial discharge, or electrical arcing.

How Does DGA Work?

  1. Oil Sampling: Insulating oil is sampled from the transformer under specific conditions to ensure the integrity of the sample and prevent contamination.
  2. Gas Extraction: Specialized techniques, such as vacuum extraction or headspace gas extraction, are used to isolate dissolved gases from the oil.
  3. Gas Chromatography: The extracted gases are analyzed using gas chromatography, which identifies and quantifies each gas. Common gases include:
    • Hydrogen (H₂): Indicates arcing or partial discharges.
    • Methane (CH₄), Ethane (C₂H₆), Ethylene (C₂H₄): Linked to thermal degradation of oil.
    • Acetylene (C₂H₂): Strongly associated with high-energy arcing.
    • Carbon Monoxide (CO) and Carbon Dioxide (CO₂): Signify insulation degradation.
  4. Interpretation: Gas concentration levels and ratios are analyzed to identify potential faults using established diagnostic methods, such as Duval Triangles or Key Gas Analysis.

Why Is DGA Important in Transformer Maintenance?

Transformers are vital to electrical systems, and their failure can lead to costly outages or equipment damage. DGA offers the following benefits:

  • Early Fault Detection: DGA can detect issues such as overheating, insulation breakdown, or electrical arcing at their early stages, allowing for proactive maintenance.
  • Minimizing Downtime: By identifying faults before they escalate, DGA reduces unexpected outages and extends transformer service life.
  • Non-Invasive Testing: Since DGA only requires oil sampling, it is a non-destructive testing method that can be conducted without de-energizing the transformer.
  • Comprehensive Fault Analysis: Fault types can be pinpointed and classified, aiding in root cause analysis and effective remediation.

Common Fault Types Detected by DGA

  1. Partial Discharge:
    • Characterized by low concentrations of hydrogen and methane.
    • Indicates early-stage degradation of insulation.
  2. Thermal Faults (Overheating):
    • Detected by elevated levels of methane, ethane, and ethylene.
    • Categorized by temperature thresholds: low (<300°C), medium (300–700°C), and high (>700°C).
  3. Arcing:
    • Signaled by the presence of acetylene in combination with hydrogen.
    • Indicates severe electrical faults requiring immediate attention.
  4. Insulation Decomposition:
    • High levels of carbon monoxide and carbon dioxide.
    • Indicates aging or mechanical stress in cellulose insulation.

Best Practices for Implementing DGA

  1. Routine Testing: Establish a regular DGA testing schedule to monitor transformer health over time.
  2. Trend Analysis: Track gas levels and ratios to identify gradual changes that may indicate evolving faults.
  3. Threshold Monitoring: Use manufacturer-recommended thresholds and diagnostic standards, such as IEEE C57.104, to assess gas levels and determine fault severity.
  4. Integration with Other Diagnostics: Combine DGA with other maintenance tools, such as infrared thermography or insulation resistance testing, for a comprehensive transformer health assessment.

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