Rohynskyi O. The influence of design and technological factors on electrical characteristics of high-voltage composite electrical insulation system of electric machines

The dissertation is devoted to the solution of the actual scientific and applied problem on introduction of modern high - voltage electroinsulating composite systems with the adapted technology and modern monitoring systems at a technological stage for maintenance of a complex of power characteristics of electric machines. The first section provides an analytical review of the current state and requirements for the electrical insulation characteristics of high-voltage electric machines. Modern electrical insulating systems of hull thermosetting insulation based on pre-impregnated glass mica tapes or not impregnated with vacuum injection impregnation in epoxy compound are considered. It is shown that ensuring the reliability and durability of high-voltage electric machines is associated with the need to reduce the degree of inhomogeneity of the electric field in which the housing insulation of the stator winding (rod or coil). The constructive decisions which provide reduction of inhomogeneity of an electric field in groove and frontal parts of windings are resulted. The main directions are formulated and the main tasks of dissertation researches are defined. The second section shows for the first time the influence of electrophysical characteristics and thickness of the mica-dielectric barrier on the distribution of the electric field in high-voltage composite insulation based on pre-impregnated glass mica tapes, based on the model of surface charge accumulation at the interface of the dielectric barrier and impregnating composition. For the first time, the effect of the dielectric barrier thickness on the short-term electrical strength of thermosetting models based on glass-mica tapes was experimentally proved. It is proved that the models with tapes with a high content of mica barrier and fiberglass of smaller thickness have (8-16)% higher values of short-term electrical strength. The developed method of calculating the electric field distribution on the insulation surface along the front part of the rods of a high-voltage electric machine allows determining the upper limit of the resistivity of the semiconductor coating for smooth distribution of electric potential on the insulation surface, which ensures no surface discharges. The credibility of numerical calculations is proved by experimental studies of the potential distribution on the surface of the semiconductor nonlinear coating along the frontal part of the samples of the hydrogenerator rods at a linear voltage of 10,5 kV. The third section considers the most typical types of technological defects in the manufacture of composite electrical insulation system and analyzes the sensitivity of the time trend of insulation resistance to determine technological defects in high-voltage insulation of additional poles of the magnetic system of DC traction motor. The efficiency of registration of partial discharges in the composite body insulation of the stator winding of turbo- and hydrogenerators for detection of technological defects at the stage of manufacturing electrical insulation structures and adjustment of the technological process is confirmed. For the first time, the efficiency of detecting technological defects by the tangent of the dielectric loss angle at the resonant frequency for the assessment of the state of a composite thermosetting electrical insulation system is substantiated. The expediency of application of complex diagnostic tests for detection of defects at the technological stage of manufacturing and operation of electric machines on the basis of the analysis of characteristics of case electrical insulating system in the mode of measurements of aggregate dielectric parameters and inductance and Q-factor on resonant frequency of electric motor samples is shown. The fourth section substantiates for the first time the use of insulation resistance as an integral parameter of the stability of the technological process of manufacturing high-voltage electrical insulation systems to prevent the appearance of defects in electrical machines. The efficiency of statistical regulation is shown and the technique of control of technological process of manufacturing of electroinsulating system based on construction and the analysis of special schedules of individual values and cumulative sums of resistance of isolation is developed. The analysis of stability of technological process for three variants of case isolation of magnetic system of the traction electric motor of a direct current is resulted. For the first time the use of control maps of cumulative sums of insulation resistance for the analysis of stability of technological process of manufacturing of electroinsulating systems that allows defining early frustration in technological process of manufacturing of electrical machines is substantiated.