Moisture in transformers

Moisture management in operating transformers is quite complex. It may exist internally or externally in transformers. Despite drying, most of the moisture may be present in the paper/pressboard insulation of transformers. Excess moisture in paper can deteriorate its integrity and cause faults in transformers. Nevertheless, it is largely undesirable for safe operation of transformers.

The moisture in paper insulation is not static.  As winding temperature increases, bulk moisture diffuses  from paper to oil. On the other hand, as temperature drops due to abrupt shut-down, moisture migrates back from oil to paper. This behavior is termed as temperature-driven moisture dynamics of insulation components. Therefore, traditional methods require regular sampling of transformer oil. 

Moisture monitoring methods

Various methods are available to determine moisture in transformers with respect to the dynamics between oil and cellulose. Most of these solutions rely on measurement of oil-moisture directly due to easy accessibility. These approaches can be laboratory or sensor based. With the expansion of internet, many on-line sensors are available to detect relative humidity in operational transformers. Interested readers can click here,  to know more on such solutions.

On the other hand, no real-time tools are available to determine absolute moisture in cellulose during operation. Infact, the solutions that are available use sorption isotherms for indirect prediction of cellulosic moisture. Such an approach has multiple limitations because temperature  in transformer insulation moves faster than moisture.

Besides, oil temperature neat the bottom and top of winding varies exponentially. Almost everyone can agree that despite the ideological appeal and obvious challenges, there is a need to improve moisture determinations techniques in the transformer industry.

Hence, some mathematical observations were discussed to assimiliate on-field experiences into the existing moisture models for their improvement. Read more about us and our interest in transformer condition monitoring by clicking here!

These views were presented at the 10th International Conference on Electrical and Electronic Insulation Materials and Systems (INSULEC-2019), Mumbai (India). The attendees of this event were vendors, suppliers, manufacturers and owners of various electrical and electronic utilities. To know more drop an email at