Which statement correctly describes the insulation media and typical applications of oil-filled and dry-type transformers?

• A. Oil-filled use mineral oil; dry-type uses air or gas; oil-filled handles higher MVA and better cooling, while dry-type is cleaner and lower fire risk.
• B. Oil-filled use water-based coolant; dry-type uses refrigerant gas.
• C. Oil-filled uses mineral oil; dry-type uses mineral oil as well.
• D. Dry-type can handle higher MVA than oil-filled.

Answer: (A)

The main idea is how insulation media affect cooling, fire risk, and typical use. Oil-filled transformers use mineral oil both as insulation and coolant, which lets them handle very large power ratings because heat is removed efficiently. Dry-type transformers rely on solid insulation with air or a gas (such as SF6) for cooling, which makes them cleaner, easier to install indoors, and much lower in fire risk. Because of the superior cooling and higher voltage ratings possible, oil-filled units are chosen for large, outdoor or substation applications, while dry-type units are favored for indoor, occupied spaces or environments where oil leaks and fire hazards must be minimized. The statement matches these realities: mineral oil for oil-filled, air or gas for dry-type, and the tradeoff of higher MVA and better cooling for oil-filled versus cleaner, safer operation for dry-type. The other options use incorrect media or misstate typical capabilities, such as water-based coolant or refrigerant gas for dry-type, or claiming the dry-type handles higher MVA than oil-filled.