What does the presence of gas in transformer oil typically 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: (C)

Gas in transformer oil is a sign of internal activity under electrical or thermal stress. In a healthy transformer, only trace amounts of gas are present because the oil mainly serves as an insulator and coolant. When insulation breaks down or components overheat, the oil and paper insulation decompose and release gases such as hydrogen, methane, ethane, ethylene, and acetylene. Those gases can accumulate in the oil and indicate internal faults like insulation breakdown or overheating. External contamination or leakage doesn’t typically produce the characteristic fault-related gases, and a low oil level points to cooling or sealing issues but doesn’t directly explain gas generation. Gas analysis is used to interpret the types and amounts of gases to diagnose the fault.