The paper outlines the problems of transformer insulation operation as well as assesses the influence of moisture on dielectric characteristics of insulation, the rate of oxidation processes in oil and thermal aging of insulation. The influence of moisture content on the service life and load capacity of transformers is shown. A comparative analysis of traditional methods of solid insulation and liquid dielectric drying is carried out. We confirmed the need to develop online methods for insulation drying of operating transformers and formulated basic requirements for automatically controlled moisture management systems of transformer equipment. The British technology “TRANSEC” was modified on the basis of these requirements. The paper presents results of trial installations of improved automatically controlled moisture monitoring and management system on several operating transformers. We determined the scope of application for moisture management system. Introduction of such systems will improve reliability and operation efficiency of power transformers.