Narrowband PLC Channel Attenuation Due to a Multi-Grounded Neutral

This paper presents a theoretical study on the influence of a multi-grounded neutral on the transmission of narrowband power-line communication (PLC) signals through a two-wire medium-voltage distribution line. Three different methods are proposed to calculate the transfer function of the line in the 3-500 kHz range: (i) nodal admittance method; (ii) travelling wave method; (iii) electrically-short line approach. The validity, advantages and shortcomings of each method are presented and discussed. It is shown that improving the grounding impedance at the transmitter and receiver locations will contribute to reducing the channel attenuation. It is also shown that the number of intermediate grounding points along the neutral is more relevant for the attenuation of PLC signals than their impedance. In general, increasing such number will always reduce the attenuation in frequencies where the line is electrically short. A similar behavior is observed at the higher end of the 3-500 kHz range provided the grounding interval is less than 300 m, which is half wavelength of the 500 kHz frequency. If the separation between grounding points is greater than that, reducing the number of grounding points is likely to reduce the average channel attenuation, but at the cost of introducing multiple resonant frequencies.