The article describes the directions and features in the field of control of power lines. A method is created for determining the prebreakdown state. The dependence of the development of partial discharges in polymeric materials is studied. The process of exposure to high-frequency currents before the onset of a breakdown state under constant operating modes of electrothermal high-voltage equipment is described. The results of the dynamics of the emergence of discharges under high-frequency exposure are given in the form of graphic images. The graph of the dynamics of partial discharges is described. In this work, a methodology for monitoring and protecting against electrical breakdown, when the frequency of occurrence of partial discharges changes. The results of practical tests for diagnosing the residual life of insulation are presented.