DGA Oil Sample Test Method for a Transformer

DGA Oil Sample Test Method for a Transformer

DGA oil sampling is done to collect a representative oil sample that contains dissolved gases formed due to internal transformer faults.
Equipment Required: 
  • Gas-tight glass syringe (50–100 ml)
  • Sampling tube and valve adapter
  • Clean container (for flushing oil)
  • Lint-free cloth
  • Labels and marker
    • Procedure Steps to follow:
  • Ensure transformer is operating under normal load and record temperature
  • Wear PPE and inspect sampling valve for safety
  • Clean the sampling valve thoroughly with a lint-free cloth
  • Open valve and flush 1–2 liters of oil to remove stagnant oil
  • Connect gas-tight syringe securely to the sampling valve
  • Draw oil slowly into the syringe without creating air bubbles
  • Check and remove any air bubbles (discard sample if bubbles persist)
  • Fill syringe completely and avoid any headspace
  • Close and seal the syringe immediately to maintain airtight condition
  • Close the transformer sampling valve properly
  • Label the sample with transformer details, date, time, temperature, and load
  • Store the sample upright and protect it from heat and sunlight
  • Transport the sample carefully to the laboratory
  • Ensure testing is carried out within 24–48 hours
  • Upon the visual inspection "Transformer oil is healthy if clear, bright, light golden, and free of foaming or gas bubbles." 
  • "Transformer oil is unhealthy if dark brown to black with foaming or gas bubbles."
  • Incase of DGA, Measures gases dissolved in oil: H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂, 
  • DGA Results : Low gas levels → healthy transformer
  • High combustible gases → thermal or electrical faults