Where is the pressure valve for a transformer located?

• A. At the bottom of the oil tank
• B. Above the oil level
• C. Inside the winding
• D. On the exterior housing

Answer: (B)

The concept here is how a transformer vents overpressure from the oil-fill space. The pressure-relief valve must be located above the oil level so it can respond to gas buildup and vent to atmosphere when the oil expands or gas forms. If the valve were at the bottom, hydrostatic pressure from the oil would prevent it from opening properly, and the overpressure wouldn’t be relieved. Placing it inside the winding is impractical and unsafe, and putting it on the exterior housing wouldn’t expose it to the oil space to sense and relieve internal pressure correctly. So, situating the valve above the oil level ensures it can effectively vent and protect the transformer.