The results of comparative tests of the main electrophysical properties of a new type of high effi ciency heat conducting insulation for turbo generators with air and hydrogen cooling as compared to the tra ditional insulation are presented. It is shown that the addition of modified varnish with a high thermal con ductivity coefficient to the insulation material does not yield any deterioration of its electrical properties.
Issues related to the reliability of the electrical insulation system of high-load powerful turbogenerators with indirect gas cooling are considered and analyzed. The mechanisms of aging of the main components (main insulation, slot filling elements) of the insulation system under operating conditions exposed to electrical and thermal fields, and mechanical forces are studied. Modern ideas about the mechanisms of aging of main insulation and slot filling elements under the action of internal and external impacts (slot and spark discharges) are analyzed. The degradation of insulating materials during operation begins, first of all, in a weak local area of the main insulation, characterized by a large number of technological defects (cavities filled with gas), in which internal partial discharges occur. However, thermosetting insulation of high-voltage electrical machines can function normally throughout its lifetime in the presence of rather intense internal discharges. At the same time, no service life deterioration is observed due to the specific properties of modern main insulation, which contains a mica barrier. The greatest danger is posed by slot partial discharges (SPD) and vibration spark discharges (VS) that occur in the slot area of the stator winding. To reduce the intensity of these discharge processes, it is necessary to optimize the design of the anti-corona coating. On the basis of the performed analysis, a scheme was developed of the aging of the electrical insulation system of the stator winding of air-cooled turbogenerators. Based on the results of prototype tests, an estimated assessment of the "lifetime" of the electrical insulation system of the stator winding, developed using promising electrical insulating materials, was carried out.
The purpose of the article is to provide potential tools that can make a significant contribution to the identification of partial discharges (PD). Different types of partial discharges occur in stator winding insulation and a few partial discharges may occur simultaneously. Internal partial discharges are electrical discharges that occur in voids in the insulation of the stator winding. In typical stator insulation systems that use epoxy bonded mica tapes, insulation degradation due to internal partial discharges is usually slow (many years or decades). External partial discharges (slot PD and surface PD in the end-winding) are more dangerous and lead to the destruction of the insulation in a short time (several months or years). Therefore, the identification of insulation defects is essential. The analysis of existing methods for identification of defects in the insulation of high-voltage electrical machines using the results of measuring the partial discharges characteristics is carried out. The advantages and disadvantages of each of the groups of identification methods are characterized. It is shown that among the models of knowledge representation in solving problems of diagnostics of insulation systems for high-voltage electrical machines, identification methods, including field tests using training samples, are among the most suitable ones. It is noted that detection of insulation defects and their identification cannot be carried out only by direct measurements of PD characteristics and other dielectric parameters (electrical resistance, dielectric loss, polarization index). For this, special computing programs based on pattern recognition methods should be used. Results are presented of identification of technological defects in the insulation of the stator winding at the stage of factory testing, obtained using the PD identification method developed by the authors
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