Xianping Zhao

Influence of temperature on polarization and depolarization current of oil-paper insulation

Temperature is one of the most crucial factors that influence the field measurement results of dielectric response methods. The distribution of moisture between oil and paper in a transformer insulation system is also highly temperature dependent. This research tests were carried out in a home-made oil/paper insulation system, which made it possible to regulate and control the temperature and humidity. Polarization and depolarization current of oil/paper samples with different moisture content are measured at different temperature. Research results show that both polarization and depolarization current increase with temperature. An inflection point appears in the depolarization current when moisture content is lower, and the time of inflection point shifts to lower with temperature increased. A master curve can be formed by shifting the polarization and depolarization current at different temperature when water content is lower, and the influence of temperature can be eliminated in this way. However, this is not feasible when moisture content is higher. Both time-shift factor and amplitude-shift factor meets the Arrhenius equation, and the activation energy of oil paper samples solved by these factors are almost the same.

The perspective detection of the X-ray digital radiography for the electrical equipment

The manufacture and installation factor is quite large occupied in the induced factor of electrical equipment insulation defects. However, the nowadays technology methods of the power system, such as ultrasonic, partial discharge, which the abnormities can be found, but the detection data are not visual, uncertainty is existed in the results decision and blindness has in the maintenance strategy. Aiming at the above shortcoming, in this paper, it is proposed the utilization X-ray digital radiography (DR) technology to detect the power facilities. In order to know the influence of electrical facilities insulation medium, the research is done by the highest energy of the X-ray, and is determined the application range of X-ray DR system. Determining the X-ray DR system application scope in the power equipment, the GIS typical defects are simulated and visualized detection. After the X-ray DR system is utilized to detect the facilities in the power production field. The experimental results demonstrate that the X-ray DR detecting system does not any influence for the solid and SF6 gas of the insulation medium, and the insulation oil has influence by the X-ray long time irradiation. The power equipment is visual detected by the X-ray digital radiography system without power cut and disintegration. Thus, the X-ray digital radiography system is used to detect the power facilities, which is feasible, safe and effect.

Cloud model-based risk assessment of power transformer

It is necessary that risk assessment is made for power transformer to identify the risk of potential failure, effect of risk and make corresponding measure to reduce risk of potential failure. Failure mode and effects analysis (FMEA) is a methodology for the analysis of potential failure modes within a system and has been extensively utilized for examining potential failures to power transformer in risk assessment. The critical issue of FMEA is determination of risk priorities of potential failure modes. In order to provide the basis for risk assessment and preventive maintenance decision-making, this work proposes the FMEA based on cloud model for prioritizing failures modes. The actual example is utilized to illustrate the potential applications of the proposed FMEA.