What is the substance used to absorb moisture in a transformer unit?

The substance commonly used to absorb moisture in a transformer unit is silica gel. Silica gel is a hygroscopic material that effectively captures and retains moisture from the air, helping to maintain the insulation properties of the transformer's oil and prevent degradation. In some cases, other desiccants like molecular sieves may also be used for moisture control. Proper moisture management is crucial for the longevity and efficiency of transformer operations.