Estimation of radiated high frequency magnetic and electric fields in a 245kV GIS

Abstract

The transient high frequency electric and magnetic fields are generated in Gas insulated substations (GIS) systems during switching operations by both radiation and conduction mechanisms. In this paper the radiated transient electric and magnetic fields are measured by using high frequency field sensors at important locations in the 245kV GIS were presented. The measurements are carried out at three important locations including at bus link, cable termination and C.T position respectively. The frequencies of transient field's ranges from 25MHz to 40 MHz and are observed at various locations considered for measurement. The magnitudes of transient fields are compared at each location. These results are very useful in order to prepare some precautionary protection measure to avoid malfunctioning of secondary equipment and metering equipment in GIS systems. I INTRODUCTIONGas insulated substations (GIS) have been used in power systems for more than 30 years, even up to the system voltages of 745kV. However, the measurement of transient electric and magnetic fields are important for the GIS systems more than 132kV. In the present study a 245kV GIS system is considered for the measurement of Transient electric and magnetic field measurements are important for the insulation diagnosis of gas insulated switchgear [1]. For the insulation diagnosis of such apparatus, the detection of electromagnetic wave caused by Disconnector switch(DS) is a practical technique, and a lot of research have been performed [1]- [3]. There are two types in these research, one is UHF technique [4]- [8] in which the electromagnetic wave propagated in GIS is directly detected by UHF disc sensor in GIS. The other is antenna detection method [5]- [7] in which the electromagnetic wave radiated out of GIS is detected by outside antennas. In both cases for the high-sensitive measurement, it is necessary to discriminate electromagnetic signal in SF 6 gas from external noises. Moreover, we should notice that the frequency characteristics of electromagnetic wave can be strongly influenced by position of the disconnector switches. The frequency characteristics of EM signal may also be affected by the construction of GIS aperture such as spacer configuration, bushing, and besides the polarization and the radiation pattern of electromagnetic wave. As a result, the received electromagnetic wave due to DS operation detecting by sensors finally has the complicated spectrum consisted of total frequency characteristics mentioned above. However, such frequency characteristics have not been elucidated in spite of the necessity from the viewpoint of insulation diagnosis of GIS. Therefore, it is important to clarify how individual frequency characteristic is determined and how these frequency characteristics will be superimposed. In this paper, we measured the radiated electromagnetic waves which was affected by the construction of model GIS, such as aperture like insulation spacer and bushing. We compared the magnitudes of EM fields at various locations in a 245kV...