Transformer Dielectric Frequency Response Analysis
Transformer Dielectric response analysis also known as dielectric frequency response analysis is utilized to assess the moisture content of the cellulose insulation and thus determine its condition.
Moisture in oil paper insulated power transformers is generated by paper aging (or) enters the transformer via leaky seals (or) breathing.
It leads to a reduced breakdown strength and an increased aging of the insulation.
Knowing the moisture content is important for the condition assessment of the power transformer and its bushings.
This measurement is also utilized for new transformers to prove the low moisture content after the drying process.
There are no other noninvasive ways to assess moisture in a transformer which provide comparable accuracy.
The moisture content is directly determined in the cellulose and not deduced from the moisture in the oil.
Thus the method is applicable at all temperatures and there is no need to wait until moisture equilibrium between paper and oil has been reached.
The assessment is performed according to IEC 60422 which provides categories for moisture levels.