Investigation and Simulation of Grounding Safety and Electromagnetic Shielding for High-Power Radio Broadcasting Stations

• Main Authors: Chi-ming Wang, 王啟珉
• Other Authors: C. H. Lee
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/76496878962553414825

碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 92 === A high-power radio broadcasting station is an environment with high-field strength of electromagnetic waves. The station has sources that may produce high-power radio frequencies and may interfer audio signal processors and electronic monitors. As a result, the method of grounding systems and shielding in the station becomes important. Since there are currently no criteria for designing a high-power radio broadcasting station in Taiwan, one will use the criterion of grounding safety and shielding as presented in IEEE Std.80, 2000 in this study. Based on numerical simulations, one will evaluate whether the grounding system in the station is within safety limits or not. Hopefully, the results obtained in this study may be useful as a reference for constructing a grounding system and shielding in a new broadcasting station. According to numerical simulations, the actual touch and step voltages in the station are smaller than the tolerable touch and step voltages. Moreover, the shock durations derived from the mesh and step voltages are greater than the shock duration required by the station. This means the design of grounding systems in the station is safe. On the other hand, the simulation of shielding shows the effectiveness of the whole-object shielding is functioned of waved frequencies, wave impedances, shielding materials as well as shielding thickness. For a higher frequency and a thicker shielding, a better efficiency of shielding can be obtained. In other words, the shielding of electromagnetic waves for short-wave bands is better than middle-wave bands. As a results, the conductivity and permeability of shielding materials for short-wave bands should choose higher values for better shielding efficiency; the conductivity of shielding materials for middle-wave bands should use higher values but their permeability should select smaller. For non-whole metal shielding mat, the effectiveness of shielding not only is functioned of wave frequencies, shielding materials as well as shielding thickness, but it is also directly relative to number of holes of metal mat, diameter or width of rectangular aperture as well as depth of aperture. For example, the efficiency of shielding for the circular aperture of metal mat in the opening format is slightly better than the rectangular aperture of metal mat. In conclusions, the shielding effectiveness of short-wave bands is better than middle-wave bands in the whole-object shielding; while the shielding effectiveness of middle-wave bands is better than short-wave bands in the non-whole- object shielding.