Analysis Of Moisture Content In Oil Paper Insulation Using Time Domain Dielectric Response Method

Moisture has a serious impact on the electric endurance and mechanical span of oil-immersed transformer insulation system, and accelerates the aging rate of oil paper insulation materials, the operation life will be seriously influenced. Therefore, the assessment of moisture content of transformer oil paper insulation makes great sense for the safe and reliable operation of transformer. Time domain dielectric response method, as a new way to assess oil paper insulation state of transformer, have caught much attention in recent years and been developed from the laboratory studies to the field measurements. Because there is still no universally accepted parameter to characterize the polarization characteristics of oil paper insulation, polarization conductivity, as a new parameter, based on time domain dielectric response method was proposed to model the oil paper insulation system. An experimental system was designed to measure the polarization conductivity of oil paper insulation at different temperatures and moisture contents, and the polarization conductivity of oil immersed paper was calculated. The results show that oil gap as an influence factor on polarization characteristic of oil paper insulation should be considered. Polarization conductivity increases with the increasing of temperature and moisture content, so it can well characterize the polarization characteristics of the oil paper insulation, and has a definite relationship with the complex permittivity, providing a new way for the state assessment of oil paper insulation.Moisture diffusions in oil paper insulation stay in a long-term unbalanced state, large errors would be made by the way to calculate moisture content in papers by steady distributions of moisture diffusion in oil paper insulation. Moisture distribution of in papers could be obtained by Fick’s second law, concentration polarization is generated by unbalanced moisture diffusion distribution, time-domain polarization model is built in this paper, polarization and depolarization current of transient moisture diffusions is established by means of when it is steady, and the model was verified its validity by experiments.The higher request on the transformer insulation system is put forward due to the continuous improvement of the transmission line voltage level, so the work of oil paper insulation modified by nanoparticles is developed. Different concentrations of transformer oil modified by nanoparticles was prepared and AC breakdown voltage experiment was conducted to choose a certain concentration of nanoparticles in transformer oil, and the polarization and depolarization current was tested for ordinary oil paper insulation and oil paper insulation modified by nanoparticles at different temperatures and moisture contents in this paper. The results show that the general model well reflects the polarization and depolarization current of oil paper insulation at different temperatures and moisture contents. a new polarization mechanism is introduced by adding nanoparticles, making the increase of polarization and depolarization current. Besides, DC conductivity of oil paper insulation also increases, making the decrease of insulating properties of oil paper insulation.The close relationship between moisture content and DC conductivity is affected by temperature, therefore, the fitting function between moisture content and DC conductivity, modified by temperature, as a method of assessing the status of oil paper insulation and moisture contents is verified, and it can provide references for the diagnosis the status and the moisture content of transformer oil paper insulation.