The expert system (ES) intended for assessment of condition of the insulating system of oil-filled transformers has been presented. ES is based on the analysis of the processes of polarization and depolarization proceeding in volume of insulating intervals of the power equipment; it allows to create effectively the conclusion about a condition of controlled object as parameters of control act not so much as characteristics of materials but as characteristics of processes of dielectric designs' aging. A distinctive feature of expert system is the possibility to obtain necessary information about operation parameters defining reliability and duration of work and providing high efficiency of power equipment service
