| With the development of industry in recent years,the voltage class of the motor is getting higher,and the higher voltage class means thicker insulation size.However,in the current technology,because of various limitations on materials,processes,manufacturing costs,etc.,insulation size cannot be infinitely thickened,and it is urgent to develop an excellent and reliable insulation structure in combination with the characteristics of materials such as varnish and mica.In this paper,7 insulation structures were designed,through comparison of dielectric loss and breakdown voltage at normal temperature and high temperature(155°C),two kinds of insulation structures with low dielectric loss were selected for the aging life test at 2.5U_N(U_N is rated voltage).Finally,by means of the electric aging life test of2.5 U_N,the best insulation structure was structure 7,i.e.,the main insulation structure with optimal rated voltage 13.8k V class is a semi-clad13 layer D mica tape with a single-sided thickness of 3.12 mm.In order to further verify the performance of main insulation structure7,the electrothermal combined aging test was carried out for each cycle of100h and for a maximum of 7 cycles.The electrothermal combined aging parameter was 2 U_N,155°C.IRC,physical and chemical of samples with different aging cycles were analyzed.By fitting the correlation between the dielectric loss and breakdown voltage of the winding bars under different aging cycles,it is found that as the degree of aging deepens,the tanδat 0.6U_Nand higher voltages will suddenly increase,and when the dielectric loss is measured at low voltage,the correlation between dielectric loss and residual breakdown voltage is poor.Therefore,when the dielectric loss is used for evaluation of the aging performance of the electrode winding bar,the test voltage of the dielectric loss should be appropriately increased.The test data of isothermal relaxation current shows that the insulation structure presents an enhanced interfacial polarization effect at the initial stage of aging,as the aging progresses,the original interface polarization is partially transformed into microscopic defects and causes space charge polarization.Base on isothermal relaxation current method,the calculation method of calculating the residual breakdown of main insulation aging index is proposed.Infrared spectroscopy analysis of the insulation under different aging cycles found that the epoxy resin was mainly cracked in the insulation,and the mica and glass fibers were not aged basically.The TGA testing of the insulation under different aging cycles found that as the weight loss rate increases,the fastest weight loss rate will shift to the high temperature direction,indicating that the small group or the epoxy with low degree of crosslinking will preferentially decompose and escape during the aging process,and the rest will be further polymerized and cured under the action of heat.For the TMA testing under different aging cycles,it is found that as the aging degree is deepened,the expansion coefficient of the insulation structure is lower.Therefore,the rate of change of the expansion coefficient of the main insulation can be used as a reference index for measurement of the aging degree of the main insulation structure.Based on the physical and chemical parameters changes after aging of the main insulation structure,the calculation method of calculating the main insulation aging index is proposed.The aging index has three individual parts:whole condition aging factor,status factor,and defect factor,they are used to reflect the trend of whole condition,physicochemical property and partial defect of main insulation structure during aging process,which make an overall evaluation for aging.The aging index curve of 13.8k V main insulation structure is obtained.It is found that physicochemical property will obvious decline when aging index larger than 3.5. |
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