Filtering device for high-voltage power lines used as high-frequency transmission media

Claim 1

A filtering device for use at an end of an isolation section in a high-voltage electricity distribution network; the network comprising energy-transporting line sections which extend between sub-stations and which additionally perform the function of transmission media for high-frequency carrier-wave telecommunications between communications sets of adjacent ones of the sub-stations; the carrier-waves lying in a frequency range ΔF which extends between a lower frequency f and an upper frequency F; the isolation section being one of said line sections over which telecommunications take place in n frequency bands lying within said frequency range ΔF and none of which n bands are used in any of the other line sections connected to the sub-stations of the said isolation section; the filtering device comprising: a blocking filter comprising an inductance for connection in series between the end of the isolation section and the sub-station, and a tuning circuit connected in parallel with the inductance and adjusted to block frequencies in the lower part of said frequency range ΔF; a capacitor with one terminal connected to the isolation section side of said blocking filter; a drain coil connected in series between the other terminal of the capacitor and earth; and a selective filter assembly connected in parallel with said drain coil and adjusted to stop the said n frequency bands of the isolation section.