Preparation of Oil-Paper Insulation Samples with Moisture Equilibrium and Frequency Domain Characteristic Parameters Extraction for Moisture Assessment
Gao Jun1, Liao Ruijin1, Wang Youyuan1, Lü Yandong2, Yang Lijun1, Liu Jiefeng1, Wang Ke3
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. China Electric Power Research Institute Beijing 100192 China
Abstract In order to promote the applicaton of the frequency-domain dielectric spectroscopy (FDS) to the nondestructive diagnosis of oil-paper insulation states of transformer, it is necessary to establish a reliable dielectric response database of oil-paper insulation with different equilibrium moisture contents in the laboratory. In this paper, a new preparation method for oil-paper insulation samples with different equilibrium moisture contents is proposed and the transient and stable frequency domain dielectric responses of oil-paper insulation during the migration process of moisture between oil and pressboard are deeply investigated. In the meanwhile, the quantitative relationships between moisture and characteristic parameters extracted from frequency domain dielectric properties are established. Finally, the actual moisture content of pressboards is measured by the Karl Fischer moisture meter to verify the validity of the proposed preparation method. Results show that in the migration process of moisture between oil and pressboard, the real part C′ of the complex capacitance increase obviously within 10-3~100 Hz, while the imaginary part C″ of the complex capacitance and the dielectric loss parameter tanδ present a clear tendency towards the high frequency region. The clear functional relationships between tanδ, C′, C″ and the moisture content in the pressboard are respectively observed in their characteristic frequency points(f=10-3Hz, 10-2Hz, 10-1Hz, 100Hz). The sample preparation method proposed in this paper can be used to accurately manufacture the pressboards with expected equilibrium moisture contents.
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2015, Vol. 30 
