Research On Characteristics Of Water Absorption In Generator Epoxy/Mica Insulation Based On Dielectric Response

As the main electrical equipment of energy conversion in the power system,the stator insulation system is one of the key part of generators,which will directly affect the life of generators.It provides a new though of condition assessment of generator insulation to assess the condition of generators based on dielectric response method.The presence of moisture will affect the test results of generator stator insulation seriously,at the same time,moisture is one of the important factors of accelerating the generator stator insulation ageing.Hence,it is significant for the safe operation of generators and the accurate diagnosis of stator insulation to study the water absorption of generator stator insulation.In this paper,the dielectric theory was interpreted with microscopic polarization mechanism,and the mathematical formula of tangent of dielectric lose angle and the real and imaginary parts of complex permittivity of frequency domain dielectric spectroscopy(FDS)were derived.The Debye model of single relaxation and Cole-Cole model of multiple relaxation were introduced.The Cole-Cole model of multiple relaxation with dc conductivity was established to analysis the relaxation process of the frequency domain dielectric spectrum of dielectric.The results show that the Cole-Cole model of multiple relaxation with dc conductivity is more conform to the relaxation process of composite dielectric with multiple dielectric than the Debye model of single relaxation.The stator bar was accelerated ageing through the constructed multifactor ageing platform for generation bar in the laboratory.Then the ageing stator bar was put in different humidity container and was tested with traditional parameters by the testing platform of resistor and capacitor and with FDS.The traditional time constant ?0 was calculated by traditional test results and the Cole-Cole model with dc conductivity and two relaxation process was established to study the effect of environmental humidity(M)on FDS test of stator bar insulation with the microscopic relaxation.The results show that it can judge whether the stator bar insulation be damped with the dried boundary of ?0 in different temperature and moisture condition.The Cole-Cole model with dc conductivity and two relaxation process shows a good fitting result with the FDS of stator bar insulation in different M.With M increasing,the polarization intensity of interfacial polarization ??1 increases and the polarization intensity of dipole polarization ??2 decreases in 10-3?103Hz,besides,the band ?f interfacial polarization plays a leading role gradually widens.The interfacial polarization relaxation time constant ?1 shows a linear exponential relationship with M,and it can eliminate the influence of M on FDS test of the stator bar insulation with relationship between ?1 with M in the process of data analysis.At the same time,the stator bar was conducted with water immersion experiments and FDS tests.The generator epoxy/mica insulation sample of different thickness were made and the water absorption experiments of different thickness in different temperature were carried out.The water absorption process of the epoxy/mica insulation sample were fitting by the Fickian law.The results show that the water absorption process of epoxy/mica insulation is made by the water absorption process of epoxy and the water absorption process of interface regions,and the initial water absorption process of epoxy/mica insulation is mainly caused by epoxy resin.The saturated water absorption rate of interface regions is higher than the saturated water absorption rate of epoxy resin.When the epoxy/mica insulation absorb enough water,the water is mainly stored in the interface regions,which makes the interface polarization strength of the stator bar insulation of high moisture content increase and the dielectric spectrum of ?" appears relaxation peak.It should be done in generator maintenance process for avoiding water immersing in the interior insulation and reducing the life of the stator insulation to check water cooling channel liquidity and dry the surface of stator insulation regularly,which provides important practical application value for the generator maintenance.