Investigation on frequency domain dielectric characteristics parameters for condition assessment of transformer oil-paper insulation

The electrical properties and service life of power transformers are directly affected by the moisture and aging of oil-paper insulation. To investigate the influences of moisture and aging on frequency domain spectroscopy (FDS) for accurately evaluating the moisture content and aging state, some experimental pressboards with different moisture contents and aging states were firstly prepared, and then the complex capacitance spectroscopy (C*) was measured. After that, a new method which can assess the moisture content and aging state by using the imaginary part of complex capacitance (C″) was proposed. The frequency domain dielectric characteristics (FDDC) utilized as the evaluation of moisture content and aging state of pressboards were also extracted, and the quantitative relations between FDDC and moisture content & degree of polymerization (DP) were proposed. Finally, the temperature influence on C* was eliminated by introducing frequency shift of FDS. Results show that the FDDC proposed in this paper are very sensitive to moisture content and aging state. The master curve of C* obtained by frequency shift of FDS could eliminate the temperature influences on C*. ©, 2015, Diangong Jishu Xuebao/Transactions of China Electrotechnical Society. All right reserved.