Characteristic Parameters and Assessment Methods of Frequency-Domain Dielectric Spectroscopy of Oil-Paper Insulation for Transformers
Yang Lijun1, Qi Chaoliang1, Lü Yandong2, Liao Ruijin1, Gao Jun1, Shi Jiangling3
1. State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University Chongqing 400044 China; 2. Alstom Grid Technology Center Co., Ltd. Shanghai 201114 China; 3. State Grid Beijing Tongzhou Electric Power Supply Company Beijing 101100 China
Abstract:In order to apply the technology of frequency-domain dielectric spectroscopy(FDS) to assess the aging condition of the main insulation of transformer more accurately, the method of distinguishing the influence of moisture content and aging product on the dielectric property of oil-paper insulation in frequency domain is investigated in this paper. FDS properties of oil-paper insulation with different moisture contents and aging degrees are measured in laboratory under controllable condition. The loss factors tanδ corresponding to different measurement frequency points are proposed as characteristics to distinguish the influences of moisture contents and aging degrees. The quantitative relationships between the characteristics and the moisture content or aging degree are initially proposed. The results show that in the range of 10-3 to 102 Hz, tanδ increases with the increase of moisture content, while the aging degree only affects the value of tanδ in the range of 10-3 to 10-1Hz; An exponential rule is observed in the relation between the tanδ at different frequency points and moisture content as well as the degree of polymerization(KDP) of the insulation paper. A preliminary validity of the proposed method is verified by applying it to a power transformer in service to evaluate the moisture content and KDP of its main insulation paper.
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