Measurements of Medium-Frequency Propagation Characteristics of a Transmission Line in an Underground Coal Mine

An Introduction to a Medium Frequency Propagation Characteristic Measurement Method of a Transmission Line in Underground Coal Mines

“…A long conductor carrying RF signals running in a tunnel has been modeled as an RF TL in previous studies [1][2][3][4][5][6][7]. Consideration of a long conductor parallel to the ground surface to carry RF signals using a ground return was also modeled as an RF TL [8][9][10][11].…”

“…Consideration of a long conductor parallel to the ground surface to carry RF signals using a ground return was also modeled as an RF TL [8][9][10][11]. These studies indicated that propagation characteristics of an aboveground transmission line could be evaluated by taking the electrical properties (permittivity, permeability and conductivity) of the ground into account, suggesting that the propagation characteristics of a TL in a coal mine could also be estimated by taking the electrical properties of the surrounding coal and rock of the tunnel into account [6,7].…”

“…We recently presented an easy-to-use method to obtain the characteristic impedance and power loss rate of a TL in a tunnel in [6,7]. The method was developed based on a coaxial cable TL model for a longitudinal conductor in a tunnel.…”

“…The tunnel's TL equivalent circuit is shown in Figure 3. We use the transverse electromagnetic (TEM) approximation to estimate the propagation parameters [6,7]. In Figure 3, R(f ) and L(f ) represent the equivalent series per-unit-length resistance and inductance of the conductor, coal, and rock, while G(f ) and C(f ) represent the per-unit-length shunt admittance and capacitance between the conducting materials.…”

“…However, it is difficult to make the measurements of R(f ), L(f ), G(f ), and C(f ) in a coal mine environment. Previous research [13] showed that a pair of open and shorted line impedance measurements at a given frequency at the input end of the TL could be used to derive the characteristic impedance, Z 0 (f ), the power loss rate, Loss(f ), and the propagation attenuation constant, α(f ), as given in (4), (5), and (6). Figure 4 illustrates the configuration for the measurements of an open line impedance, Z inoc (f ), and a shorted line impedance, Z insc (f ), at the input end of a TL of length x = l. Also as shown in previous research [13], multiple pairs of Z inoc (f )s and Z insc (f )s at different frequencies can be used to obtain β(f ) from (7), the propagation velocity, v p (f ), from (8), and velocity factor, VF (f ), from (9).…”