What does the presence of gas in transformer oil indicate?

• A. External contamination or leakage causes gas in oil.
• B. Gas in oil is a normal condition.
• C. Internal faults such as insulation breakdown or overheating.
• D. Low oil level in the transformer.

Answer: (D)

Gas appearing in transformer oil comes from internal activity inside the transformer, typically caused by insulation degradation or overheating. When the insulating paper and windings are stressed, the materials break down and release gases. These gases—hydrogen, methane, ethane, ethylene, and acetylene—are indicators used in analysis (DGA) to identify fault type and severity. This is not a normal condition, and it doesn’t primarily point to external contamination, a simple oil leak, or a low oil level. A low oil level signals coolant loss or leakage, which is a separate issue from gas generation. So the presence of gas in the oil most strongly indicates internal faults such as insulation breakdown or overheating.