Moisture in Oil Transformer Tanks: Avoiding Mechanical Breakdowns Remember the ol’ transformer oil purification experiment from applied chemistry class? Thinking of it as you learn about moisture and oil contamination can be very useful. Internal moisture in transformer oil tanks is not distributed uniformly, and can be concentrated in the most dangerous parts of the system. Water in the presence of oxygen, even at microscopic levels, is a contaminant that reduces the insulation properties of Oil. Water enters into the transformer oil over time, which reduces the oil’s dielectric (insulation) properties. As the transformer becomes wetter, it decays even faster, which increases the