Description
I. Background
Transformer’s insulation structure profoundly determines device’s lifetime. As novel method, Frequency Domain Spectroscopy, which based on the principle of dielectric response, attracts researchers all over the world for its advantages of richer information details, excellent interference immunity and non-destructive. However, Frequency Domain Spectroscopy's characteristic parameters related to insulating condition are not easy to extract, which makes it limited to utilize on site. Based on that, The concept of dielectric modulus is introduced to assess the transformer's insulation condition in this thesis.
II. Method
Based on theoretical analysis and deduction, the physical meaning of dielectric modulus spectrum is explained. Then, the differences and connections between frequency domain spectroscopy and dielectric modulus spectrum are investigated. After that, we prepared oil immersed paper samples with water content of 1%, 2%, 3%, 4% and 6% and obtained their dielectric modulus spectrums by IDAX206. Meanwhile, the influence of temperature is studied by testing dry samples under different temperatures.
III. Results
An obvious relaxation peak related to dielectric material's polarization process reveals in the low band of dielectric modulus spectrum rather than frequency domain spectroscopy. By extracted the frequency of relaxation peak, which is easy to be gained , as the characteristic parameter, the water content of oil-paper insulating structure could be quantitatively evaluated by fitting equation. The relationship between temperature and the characteristic parameter obeys Arrhenius formula， by which the influence of temperature on the dielectric modulus spectrum could be eliminated.
