|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|703069||891126||2016||9 صفحه PDF||سفارش دهید||دانلود کنید|
• Wave propagation in a high frequency region, fe < f < fs, shows transition between TEM and TE or TM modes in calculated results by the TL approach and by the numerical electromagnetic code NEC in a frequency domain. FDTD method confirms the transition is from TEM to TM mode. In a frequency lower than the critical frequency fc, the wave propagation is dominated by the earth-return path, and it is called “earth-return wave propagation”. In a frequency higher than the frequency fc, so-called “surface wave” (TM mode) propagation or Sommerfeld-Goubau propagation, which is determined by the conductor internal impedance, is completed. The phenomenon was pointed out by Kikuchi in 1950s.
• In a high frequency region, f > fs, where the surface wave is completed, the earth-return impedance has minor contribution to the wave propagation. Thus, the earth-return impedance can be approximately neglected in the TL approach in this frequency region.
• A numerical electromagnetic analysis method such as NEC can give, in general, a more accurate result than a conventional TL theory approach. However, the accuracy of NEC depends on the mesh size and terminating conditions which may result in numerical instability. On the contrary, the TL approach is more stable but it is applicable only to a limited frequency range.
• A TL approach with Wise's earth-return admittance and the accurate earth-return impedance together with the conductor internal impedance can deal with wave propagation from a low frequency in the power engineering field to a high frequency in the communication engineering field including mode transition and Sommerfeld-Goubau propagation as predicted by Kikuchi. The TL approach is expected to be effective to study electromagnetic noises in a very high frequency region produced by transmission/distribution lines and gas-insulated substations.
High frequency wave propagation on overhead conductors has been evaluated by TL (transmission line) approach. The results are compared with those calculated by the numerical electromagnetic code (NEC) in the frequency domain. Both results show transition of wave propagation between TEM (transverse electromagnetic) and TM (transverse magnetic) modes in the frequency region fc < f < fs where fc is the critical frequency at which the transition starts and fs is the frequency above which a surface wave is completed. In the frequency region higher than the frequency fs, the earth-return impedance has minor contribution to the wave propagation, because it is no more an earth-return wave but a surface wave. This has been also investigated in the time domain based on simulation results by FDTD (finite-difference time-domain) method to confirm the results by the TL approach.
Journal: Electric Power Systems Research - Volume 136, July 2016, Pages 12–20