Study On Frequency Domain Dielectric Response Of Epoxy-Mica Insulation For Large Electric Machine

Epoxy-mica insulation is a material often used for the main insulation of large electric machine stator bars,and its performance is related to the operating reliability of the unit.At this stage,many large-scale motors in our country have been operating for more than 20 years,and the insulation problem is worrying,and the insulation state needs to be estimated urgently.During the operation of large motors,they are subject to the effects of various aging factors such as thermal stress,electrical stress,mechanical stress and environmental stress,which will gradually age,which in turn leads to motor failure.Electricity is the core of modern economy,and the insulation problem of large motors cannot be ignored.At this stage,the development of dielectric response theory provides new ideas for evaluating epoxy-mica insulation state system,which has engineering application value and guiding significance.Based on the dielectric response theory,this dissertation uses frequency domain dielectric spectroscopy(FDS)to study the dielectric properties of epoxy-mica insulation.The aging mechanism of the dielectric is described,and the insulation degradation process under the combined action of multiple aging factors is analyzed in combination with epoxy-mica insulation.The macroscopic characteristics and microscopic mechanism of the polarization of the dielectric are introduced in detail,and the dielectric relaxation model of the dielectric is analyzed based on the frequency domain dielectric response theory.The results show that there are many polarization forms in epoxy-mica insulation,but under the power frequency voltage,the leading role is the polarization.Therefore,the Davidson-Cole model is used to study the dielectric properties of epoxy-mica insulation.Build a thermal aging platform,an insulation moisture test platform,an absorption ratio test platform,and a frequency domain dielectric spectroscopy(FDS)test platform to carry out experimental research.In the test,the epoxy-mica insulation samples were subjected to multi-period thermal aging test,damp test and combined with the absorption ratio parameter to study the insulation performance changes;the frequency domain dielectric spectrum and polarization mechanism of epoxy-mica insulation samples with different degrees of aging were studied,And used the Davidson-Cole model to extract characteristic parameters to study the influence of temperature on the frequency domain dielectric test of epoxy-mica insulation.The results show that the absorption ratio reflects the deepening of the aging degree of the epoxy-mica insulation sample and the gradual deterioration of the performance after being damp;the Davidson-Cole model extracts the characteristic parameters at different test temperatures and the activation energy based on the transition state theory can be used to characterize the epoxy-mica insulation The characteristic that changes with temperature;the frequency temperature shift factor can eliminate the influence of the test temperature on the frequency domain dielectric spectrum,and the experimental verification results are consistent.At the same time,an electric-thermal-mechanical aging platform was built to conduct aging tests on generator stator bars,and a Davidson-Cole model was established to extract the relationship between characteristic parameters and aging time to calculate the degree of insulation aging.Finally,an FDS field test was conducted on a motor in a factory in Shandong.The results showed that the field test and the experimental research conclusions are basically the same.The frequency domain dielectric spectroscopy method can be extended to the field assessment of the insulation aging state of the stator bar of large electric machine.