Research On Characteristics Of Multi-Factor Aging In Generator Stator Insulation Based On Dielectric Response

As an integral part of the stator winding insulation system of turbine-generator, the performance of stator insulation will directly relevant to the operation reliability, lifetime and technical-economic index of generating unit. During the generator service, stator insulation will deteriorate gradually by the cooperation of muliple factors, such as electrical, thermal, mechanical and environmental, which will lead to generator failure and threat to grid security seriously. At present, to carry out the state evaluation of stator insulation is relies mainly on the online monitoring and traditional off-line test, but it is difficult to realize comprehensive and accurate evaluation due to the problems which are existed in practice. In recent years, the development of dielectric response theory provides a new clue for new model system of insulation condition assessment study, which is of great significance for the accurate evaluation of stator insulation state by using the dielectric response method.In this paper, some research work has been carried out on the aging characteristics of the stator insulation of generator which is based on frequency domain dielectric spectroscopy (FDS). The article gave a detailed introduction on microscopic polarization mechanism of dielectric, explained the frequency domain dielectric response theory and frequency domain dielectric spectrum method according to the basic principle of the dielectric polarization theory, and analyzed the relaxation Debye model of a single and dual further. The results show that the dielectric response phenomena of the epoxy-mica composite insulation material is caused by the sum of the multiple relaxation contribution, so fitting analysis for the dielectric spectrum of measured by the extended Debye model is proposed, the dielectric relaxation characteristics of material can be research according to the model parameters and dielectric parameters.In the laboratory, a combined aging test platform and FDS test platform was built for the stator bar, and the traditional electrical tests of IR、dielectric loss、partial discharge and FDS test were carried out on the samples which are in different aging situation; In addition, the dielectric properties under different temperature and moisture content were analyzed, and its FDS phenomenon was analyzed with dielectric polarization theory, Debye model is established and a new method to calculate activation energy AG* and activation entropy ΔS? of bar insulation is proposed based on transition state theory. The experiment results show that the change rule of absorption ratio K and dielectric loss tanδ can reflect stator insulation was deteriorate gradually with aging; The extended Debye relaxation model established of 3 branches can well reflect experimental datas; Characteristic parameters of activation energy and activation entropy were selected to show dielectric property changes with temperature, so temperature-dependency of dielectric properties of bar insulation could be interpreted with transition state theory; The low frequency of frequency domain dielectric spectrum was obviously influenced by aging, the characteristic dielectric parameters of frequency domain (complex dielectric constant ε and dielectric loss tanδ) and the maximum discharge increasing rate Nq meet certain function relation.At the same time, the stator bar of 02# generating unit was carried out FDS field test on Zhuhai Power Plant, the results show that the change rule of field test results and the conclusions of laboratory research are basically the same, the dielectric response method can be a preliminary application in field condition evaluation of generator stator insulation.