The article lists the types of reactors: current limiting reactors, smoothing reactor and arc suppression reactor. The principles of electrical energy conversion and methods of compensation of the electric current are described. In addition, the frequency of inspections is established including unplanned, current and capital repairs of equipment. The list is formed of the examined units, as well as the features of thermal imaging diagnostics of reactors with voltages up to and above 1000 V, including the design of a smoothed reactor with a voltage of 780 V and concrete reactor of voltage 10 kV. The thermograms of defects of contact connections are presented. The calculation of the angle dielectric loss tangent tg δ and the steady-state voltage is performed. As a result of the analysis of thermograms, the cause of defects in current limiting reactors with a voltage of 10 kV is formed. On the basis of the calculated value of tg δ, the method of reactor inspection is made; the calculation of the permissible voltage deviation based on the calculated nonlinearity coefficient is carried out. The calculation of the economic damage from the reactor failure depending on the value of the total power, current load and duration of shutdown, as well as the conclusion about the effectiveness of this type of diagnostics are made