A field study of two online dry-out methods for power transformers

Dry-out methods for transformers, using cellulose cartridges and molecular sieves, were compared. The latter are preferable for keeping a dry transformer dry, whereas the former are more efficient in drying a wet transformer. In this article, we compare the effectiveness of the cellulose cartridge filter and molecular sieve methods. Two identical transformers with similar insulation wetness were used. We estimated the water content of the paper (WCP) insulation from (1) the water activity of the oil, (2) the dielectric response of the transformer, and (3) the water content of individual paper samples determined by Karl Fischer titration. We also measured the acid number of the oil, its interfacial tension, dielectric strength, furan content, dissolved gas content, and particle count.