Resonant Frequency Evaluation on Reradiation Interference from Power Transmission Line Based on the Generalized Resonance

IEEE was not able to give the resonance mechanism of reradiation interference (RRI) above 1.7 MHz from power lines based on research works of electric field. In order to solve this problem, the generalized resonance theory is introduced, and a method based on the electromagnetic (EM) energy balance theory is proposed to predict the RRI resonant frequency. Taking a large-scale space including UHV power lines and antenna arrays as a generalized closed system, the expression of EM open systems’ generalized resonance factor is derived based on the complex Poynting theorem. Then the RRI resonant frequency corresponds to the zero point of the generalized resonance factor's imaginary part. Taking the case researched by IEEE as an example, the maximum deviation of the resonant frequency between the values predicted by the generalized resonance theory and the measurement values obtained from scaled model experiments are less than ±0.169 MHz in the frequency band below 1.7 MHz.

I. Introduction

Based on the antenna theory, IEEE revealed the variation law of reradiation interference (RRI) of power lines by the induced current and the electric field intensity under the excitation of wire antenna [1]. Studies were conducted to describe the resonance mechanism within 535–1705 kHz, obtain the calculation method of RRI, and derive the prediction formula of resonant frequency at MF [2]–[6]. The RRI of power lines can be divided into two kinds of situations according to the IEEE standard: 1) Towers and grounding wires are not insulated and a grounding wire links two adjacent towers. The three objects, along with their mirror images in the ground, form a loop antenna. When this loop antenna's length equals 1.08 times of integral multiples of the wavelength, there will be RRI resonance, where 1.08 is an empirical coefficient obtained from calculation and experiments. 2) When towers and grounding wires are insulated, there would be RRI resonance when the height of the tower equals a quarter of the wavelength according to the half-wave antenna theory. Moreover, the tower's electrical height is larger than its practical height by 15% if taking its cross arms into consideration. However, these works based on electric field intensity cannot explain the RRI resonance that exists in frequency band over 1.7 MHz. According to reference [7], the traditional study method based on field strength failed to clarify the generation mechanism of RRI at SF or predict the resonant frequency. This calls for new theories and analysis methods in the related researches.