What is the primary reason for keeping the oil in a transformer tank moisture-free?

Keeping the oil in a transformer tank moisture-free is primarily important to prevent voltage breakdown. The presence of moisture can significantly reduce the dielectric strength of the oil, which is critical for maintaining high voltage insulation within the transformer. When moisture is present, it leads to a decrease in the oil's ability to insulate, increasing the risk of electrical failure or breakdown due to inadequate insulation.

In addition to preventing voltage breakdown, moisture can also contribute to other issues such as corrosion of internal components, but the most critical concern in terms of transformer functionality and safety is related to the dielectric properties of the insulating oil. Ensuring the oil remains moisture-free helps maintain the reliability and operational stability of the transformer under high voltage conditions.