The relevance of the work is caused by the fact that electric machines are one of the most common types of electrical industry products, and they are used in varied industries. The failure of the electrical machine leads to a crash, shutdown and, consequently, to high economic cost of eliminating the results of machine failure. The results of the electric machines failure are especially tangible in exploration, production and transportation of geo-resources in the oil, mining, coal, chemical and other industries, as these industries are currently the basis for the formation of the budget of the country. The reliability and uptime of these machines are largely determined by impregnation and drying of windings, as these operations form the important qualitative characteristics of the windings: insulating, thermal, moisture and mechanical. All these properties depend on the degree of filling winding cavities with impregnating composition and the degree of its polymerization (curing). In the case of lack of dryness (compound curing completion; polymerization, etc.) of the windings after impregnation the defects can occur in the inter-turn insulation during storage and transportation of equipment to the operation site, which inevitably leads to the decrease of windings resistance insulation. Improvement of the operations is impossible without adequate methods of non-destructive quality control of carrying out these operations. Therefore, the development of methods to control the quality of impregnation and the degree of rejection of the impregnating composition in the windings is very topical. The aim of the work is to demonstrate the possibility of controlling the impregnating composition distribution in the winding and the degree of its curing by the results of measuring the capacitance of the windings relative to the magnetic core at two frequencies of the electromagnetic field. Research methods: electromagnetic, to study the dependence of the dielectric permittivity of the impregnating composition on the electromagnetic field frequency and curing degree. Results. The paper considers the capacitive method of monitoring the curing degree of the impregnating composition in the windings of electrical products and introduces the experimentally obtained graphs of the dependence of the compound KP-34 dielectric permeability on the electromagnetic field frequency taken at different dryness degrees of the compound. The authors have justified the physical bases of controlling the quality of impregnation and drying. The paper introduces the main criteria for assessing the quality of these technological operations and the diagram of the monitoring device and considers the principle of its operation.