For the definition of action priorities and choice of countermeasures, it is necessary to diagnose whether the criticality originates internally (paper degradation) or externally (atmospheric influences).
If the origin of the moisture is internal (degradation of paper and oil) the countermeasures are:
Physical treatment,
Physical treatment, in the first instance to be performed off-load and subsequently on-load (transformer under load). This activity can be aided by applying dehumidifying cartridges
Direct dehydration (cycle B).
Direct dehydration of the transformer (papers) consists of heating the windings through circulating the oil.
Then there are other techniques, some of which require handling of the transformer. These techniques require that the transformer be opened and treated, in some cases through drying of the nucleus in autoclave, in other cases using appropriate solvents (derivatives of aviation kerosene). These modes, which are far more expensive, are taken into consideration when, in addition to the water problem, there are other electromechanical criticalities which require replacement of parts or in any case extraordinary maintenance of the transformer.
If the origin is external, it is necessary to identify air inlet points and restore the seals. If necessary, it is advisable to change the drying salts, and consider increasing the amount or geometry of the container to increase the drying power.
