Study On Time Domain Dielectric Characteristics Parameters For The Aging Of Oil-paper Insulation In Transformer Based On Transfer Function Analysis

Transformer oil-paper insulation system will degrade under the cooperative action of many factors such as the electromagnetic field,high temperature,mechanical stress and water,gradually leading to the degradation of electrical and mechanical insulation performance of transformer,so the performance of oil-paper insulation system decides the service life of the transformer.Water as a product and catalyst of oil paper insulation aging,becomes an critical factor to accelerate the aging of oil-paper insulation system,so how to effectively evaluate the paper moisture of the insulation system has important practical significance.Existing research is a qualitative analysis of the relationship between time domain dielectric spectroscopy and the aging state of oil-paper insulation,how to extract the characteristic parameters effectively,and to assess the aging condition of and moisture content oil-paper insulation quantitatively,especially feature extraction which is not affected by the geometry of the transformer has always been the difficulty problem in this field,therefore to solve these problems has important practical significance in further research.In this paper,the PDC measurement was performed with different water content and degree of aging under laboratory conditions,analyzing the influence of those conditions to curve of polarization and depolarization current.The time domain dielectric characteristics of moisture content and aging degree was extracted effectively based on extended Debye model and the transfer function.The results show that large time constant of the pole of oil-immersed insulation paper is very sensitive to degree of polymerization under low moisture content,which can evaluate the aging degree of insulation paper quantitatively.The optimized characteristics which are extracted through effective information fusion can avoid the influence of the choice method of poles to the accuracy evaluation,it is more accuracy to evaluation the aging degree of transformer pressboard quantitatively,and this characteristic has nothing to do with the size and geometric structure of transformer pressboard;The transfer function zeros is sensitive to moisture the content of insulating paper,among those zeros,the critical zero contains more information of moisture content of insulating paper,besides it is the most comprehensive and has the least interference information which can reflect the moisture content of insulating paper more effectively.The optimized characteristic which has the higher accuracy to evaluate the moisture content of insulation paper is extracted through fusion of effective information among all zeros,and this characteristic parameter also has nothing to do with the geometrical dimensions of insulation board.This paper analyzes the influence of actual non-uniform aging conditions to time domain dielectric which reflects the aging degree and the moisture content to the effect of assessment through non-uniform accelerated thermal aging experiments.The results show that,there is little different between the parameters of modified Debye model and the extended Debye model of specimen,the non-uniform aging of transformer pressboard can be descripted by extended the Debye model.The polymerization degree of any layer of insulating paper cannot be an index of the aging degree of uneven aging insulation paper,but it has good correlation between the polymerization degree of middle layer of insulation paper and the proposed feature.It can look forward to have a relationship which can measure the relationship between pole characteristics and the comprehensive degree of polymerization of uneven aging insulation system quantitatively.In the course of aging,there is still a good function relationship between the extracted characteristic of time domain dielectric and moisture content insulating paper,and there is little influence of uneven aging to the evaluation accuracy,that is,proposed characteristic of time domain dielectric is still sensitive to the moisture content,therefore,this characteristic is more suitable for aging state evaluation of insulation system of on-site service transformer.