Search

The 1000 kV transformer is one of the most important equipment in ultra high voltage (UHV) power grid, and its service life largely depends on the state of its oil paper insulation system. Especially when micro-bubbles appear in oil paper insulation, the insulation performance of oil paper insulation will be greatly reduced. In this paper, the oil paper insulation micro-bubbles generation platform has been built in the laboratory for 1000 kV transformers. Based on the platform, the influence of temperature rate on oil paper insulation micro-bubbles was studied firstly. By setting the heating power, the micro-bubbles generation experiment of oil paper insulation samples with 3.0% water content was carried out. It is found that with the increase of heating rate, the initial temperature of micro-bubbles generation will increase and the time interval of micro-bubbles escape will be shorten. Then, the oil paper insulation samples aged for 0 day, 20 days and 40 days were tested. It is found that the longer the thermal aging time, the higher the micro-bubbles begin temperature, which directly shows that thermal aging could inhibit the generation of micro-bubbles. In addition, it is found that different layers of insulation paper also have an effect on the generation of micro-bubbles. These results can provide theoretical data support for the operation load setting and fault diagnosis of 1000 kV transformers.

As a new nondestructive diagnosis method of insulation state, frequency domain spectroscopy (FDS) has been widely used in the field detection of power equipment. However, the quantitative correlation between FDS measurement results and insulation state is not clear for transformer bushing, which seriously affects its detection effect. In order to solve this problem, the FDS modeling and parameter identification of transformer bushing has been studied in this paper. Firstly, the transformer bushing model was built in the laboratory, and the FDS measurement data of transformer bushings with different water content were collected. Then, a fusion algorithm of improved artificial bee colony algorithm and sequential quadratic programming algorithm was used to identify the parameters of transformer bushing model. After modeling and analyzing the FDS measured data, it is found that there is a good consistency between the measured spectrum of complex capacitance and the reconstructed spectrum of the model, and the goodness of fit of the model to the measured FDS exceeds 0.95. In addition, the identified values of resistance and capacitance in the equivalent model are within the reasonable range of 109Ω and 10−9F respectively. These results show that the extended Debye model and parameter identification algorithm can accurately model the frequency domain dielectric response of transformer bushing in a wide frequency range, and can provide an effective tool for more accurate analysis of transformer bushings insulation state.

Frequency domain spectroscopy (FDS) technology has been widely used to evaluate the insulation state of electrical equipment. However, there are still many in-adaptability when using FDS technology to evaluate the insulation state of transformer bushings. Especially, the result will be affected by temperature in the quantitative diagnosis of moisture degree. The influence of different temperatures on FDS detection data of transformer bushings has been studied to solve this problem in this paper. To obtain the FDS test data curves of transformer bushings at different temperatures, the transformer bushings experiment platform was built in the laboratory. And the bushing samples at different temperatures was measured by FDS detection method, which started at 30 °C and rising at 10 °C intervals until the temperature reached 80 °C. The result shows that the temperature will have a serious impact on the FDS detection data, especially the R0 and C5 in the extended Debye model. To solve the influence of temperature, FDS data correction curves with different temperature has been built in this paper. And its feasibility has been verified by FDS data of transformer bushings with 0% and 1.89% water content. The obtained results can promote the application of FDS method in the evaluation of transformer bushings insulation state.