Corrective Measures for Minimizing the Interaction of Power Lines with MF Broadcast Antennas

Abstract

New high-voltage power lines are often built in close proximity to MF/AM broadcast antennas. The "skywire" which joins the tops of the power-line towers creates closed loops for RF current on the power line and its image in ground, and these loops can be resonant in the MF band. If the broadcast antenna operates on such a resonant frequency, it induces large currents on the skywires and power-line towers, and "reradiation" from these induced currents can considerably alter the broadcast antenna's radiation patterns. This paper uses computer modeling to systematically examine several techniques for "detuning" the power line, namely: isolating towers from the skywire, series insulators in the skywires, stub detuners on the skywires, and short capacitively terminated stub detuners on the towers. The mechanism which makes each detuner effective is seen from the RF current distribution computed for the power line and detuner. The bandwidth of each detuner is assessed. Consideration is given to the difficulties that can arise in the implementation of each detuner design on a real power line. All of these detuner designs have been tested by scale-model or full-scale measurements. Only when detuning has been made a systematic economical procedure can this special EMC problem be regarded as solved.

Analysis of Induced Current on Power Transmission Lines for the Reradiation Interference in Medium Wave Based on Characteristic Modes

“…Considering that the smallest unit that constitutes a PTL is two adjacent power towers within a span and the ground wire connecting the power towers. Terefore, the study in [6] only calculated the induced current on the PTL within the representative span and found that the calculated result of the induced current was in good agreement with the measured result. For this reason, this paper also simplifes the simulation model in Figure 4 and only considers the PTL within a representative span in the subsequent calculation of the induced current.…”

“…In this method, the power towers and the ground wires are equivalent to wire antenna models with diferent radii in diferent frequency bands, and the conductors could be ignored in the modeling because it is perpendicular to the direction of the excitation electric feld. Although these methods of simulation calculation can obtain the numerical value of the induced current on PTL, they cannot reasonably explain the variation of the induced current [6].…”

Resonant Frequency Estimation of Reradiation Interference at MF from Power Transmission Lines Based on Generalized Resonance Theory

“…Based on loop antenna theory and the results reported in [15][16][17][18][19][20], Trueman C.W. et al explained the mechanism of RRI resonance in AM radio frequency band (535 kHz~1705 kHz) when towers are connected to grounding wires.…”

“…According to [15][16][17][18][19][20], conventionally in 535~1,705 kHz, a tower is equivalent to a line antenna of 2.13~4.88 m. Trueman et al established the numerical model of a 500 kV double-circuit transmission line with V1S towers [20], as shown in Fig. 2.…”

“…Firstly, we establish a Padé rational function, which is similar to (15), based on MBPE. As mentioned in Chapter 4.2, we set both the orders of the rational function's numerator and denominator to be 4.…”