Study on Electromagnetic Environment around Electric Power Facitities

点击翻译按钮获取中文摘要

Magnetic field around power transmission line exhibits complicated characteristics. It is 3-dimensional distribution and affected by three-phase current and various condition of current, such as unbalanced current and superimposed harmonics. Magnetic field distribution may be distorted by transmission towers. However the influence of these parameters on the generated magnetic field has not been clarified.In this study, we investigated the low frequency (60Hz) magnetic fielddistribution using 1/40 reduced-scale power transmission line and tower model. We made clear the effect conductor sag and towers on the magnetic field distribution by comparing calculated and measured field.In order to make clear the magnetic field behavior around power transmission line and the tower, we measured the magnetic field distribution using 1/40 reduced-scale transmission line and tower model.This model enables us to analyze the precise 3-dimentional profile of magnetic field as well as the effect of the c … More onductor sag and the tower. As a result, we found that the magnetic field component parallel to the line emerges around the tower and a main factor influencing the characteristics was the conductor sag. We could also obtain the perpendicular distribution of magnetic field around the transmission tower.Partial discharge (PD) may take place due to residual defects like metallic particles or microprotrusions inside SF_6 gas insulated power apparatus such as GIS,leading to the failure breakdown. Thus, PD measurements are very effective and promising technique to diagnose GIS under operating conditions. However, the signal of PD occuring in SF_6 gas is very weak and susceptible to external noises which mainly consist of PD in air. Thus, it is important to distinguish the PD in SF_6 gas more sensitively from the external noises.From the above points of view, we have been investigating characteristics of electromagnetic wave spectrum radiated from PD in SF_6 gas and in air using wide-band antennas. In this study, we propose "phase gate control method" in order to reveal the dependence of the polarity of ac voltage on the electromagnetic wave spectrum. Using the phase gate control method, an attempt is made to separate electromagnetic spectrum caused by PD occurring in SF_6 gas from that in air. We also investigate the frequency range where PD spectrum in SF_6 gas alone can be detected under noisy conditions. On the basis of these results, we discuss the minimum detectable PD charge in SF_6 gas as a function of measuting frequency. Less