Study On Evaluation Of Bushing Insulation Based On Frequency Dielectric Spectroscopy

Bushing is one of the most important components of transformer in the power system. The deterioration of the bushing insulation, influenced by the high-voltage, electromagnetic and high-temperature operating environment, will cause damage of the transformer, and interrupting the power supply, causing huge economic losses. Therefore, the insulation detection and evaluation of high voltage transformer bushing is very important for the safe operation of the power system.As an electrical diagnostic technique, frequency domain dielectric response method based on dielectric response has been widely used in research and application, but the research about applying it to the insulation detection and evaluation of high voltage transformer bushing is rarely reported. Therefore, the paper researches the frequency domain dielectric response method applying to the insulation detection and evaluation of high voltage transformer bushing. Firstly, the simulation model of the HV oil-paper bushing is built and simulated. Then, the oil-paper bushing simples are designed, and some thermal aging research on those simples are conducted. The frequency domain dielectric spectroscopy (FDS) is tested in the different aging simples, and the paper finds the correspondence between the capacitance(C) or dielectric loss factor (tanδ) FDS and the aging time or the aging state. And the research of the correspondence provides a theoretical basis for the frequency domain dielectric response method applied n on the insulation detection and evaluation of high voltage transformer bushing. The main results of the research obtained are listed belows:(1) The paper builds the Debye simulation models of the oil-paper insulation of HV bushing by deep research of the structure of the oil-paper condenser bushing and the theory of the dielectric frequency response.(2) Through simulation and thermal aging experiment analysis, the correspondence between the capacitance of bushing and the aging state is found. The dielectric loss factor reflects the aging status of bushing only in the 1Hz.(3) The simulation and experimental study finds that the capacitance C in the frequency domain spectral curve can be well fitted with the function of f(x)=a*exp(b*x)+c*exp(d*x).(4) Experimental research and analysis shows that there is a secondary polynomial function not only between aging time and integral value of capacitance frequency domain curve, but also between insulation state and integral value of capacitance frequency domain curve. The relationship provides a new theory for the frequency response method applied to the insulation detection and evaluation of HV transformer bushing.