The task of reliability increasing and economical sustainability and mass-dimensional indicators of oil transformer, by analyzing of transformer-rectifier unit functional diagram and calculation of transfer functions, dynamic characteristics of the unit installation. To achieve this goal, parameters calculating of electrical machines and electric drives, as well as methods for calculating the transfer functions of elements of automated control systems and their dynamic characteristics. The analysis, development and calculation of the structural diagram are carried out, the transfer functions of the elements are calculated, analysis of the obtained dynamic characteristics of the elements is provided. The developed block diagram of the transformer-rectifier unit makes it possible to determine the transfer function of the automated control system, draw up the characteristic equation of the transient process, determine its roots and calculate the transient process for any conditions. The introduction of proposed units will increase their reliability, economic and mass-dimensional indicators