Electrical transmission or interconnection systems – Conductor arrangements or structure
Patent
1980-09-03
1982-12-28
Askin, Laramie E.
Electrical transmission or interconnection systems
Conductor arrangements or structure
174 2, 174 40R, H02G 722, H02G 1300
Patent
active
043663923
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to means for transmitting electric energy from one location to another and, in particular, to aerial power transmission lines.
Prior Art
Known in the art are aerial power transmission lines comprising phase wires suspended from supports and lightning protection cables secured to said supports and designed also to convey information in the form of r-f signals (cf., for example, USSR Inventors Certificate No. 399,030, published in Discoveries, Inventions, Industrial Designs, Trade Marks, No. 38, Sept. 27, 1973, Bykhovski Ya. L.).
Such aerial power transmission lines, particularly those designed to transmit voltages of the order or 1000 kV and higher, have been generally unsatisfactory due to substantial power losses associated with the corona condition and a high radio-interference level, another disadvantage being the effect of noise level in r-f channels over the lightning protection cables thereof.
Also known in the art are aerial power transmission lines comprising phase wires suspended from supports and a lightning protection system secured to said supports and designed also to convey information in the form of r-f signals. The lightning protection system includes two wires spaced a certain distance apart and forming an r-f channel to convey relevant information. The wires are secured on the supports in a substantially horizontal plane. (cf., for example, USSR Inventor's Certificate No. 456,371 published in Discoveries, Inventions, Industrial Designs, Trade Marks, No. 1, Jan. 5, 1975, Ishkin V. H.).
In the event of single wires forming a cable and suspended from the supports of the power transmission line the total capacitance between said wires and the respective support is about 70 to 80 pF. With two wires suspended from the same support the capacitance between said support and the near wire exceeds by 1.5 to 2 pF the capacitance between said support and the far wire with the wires being spaced some 40 to 60 cm apart and the distance from the support being about 1 m.
Over a length of 1 km the capacitance difference between wires comprised in the lightning protection system varies from 4.5 to 6 pF/km, while the capacitance difference between said wires and phase wires is only from 2 to 2.5 pF/km.
The presence of this capacitance difference between the support and the horizontally disposed wires of the lightning protection system introduces noticeable assymetry into the r-f data transmission channel, a disadvantage causing a high noise level in the r-f channels over the respective cables and substantially increasing the effect of said channels upon the nearby navigational systems, radio reception and so forth.
SUMMARY OF THE INVENTION
The present invention resides in providing an aerial power transmission line having a lower noise level as compared with the prior art by reducing the assymetry introduced by the support into the r-f data transmission channel.
The foregoing object is attained by that in an aerial power transmission line wherein phase wires are suspended from supports and a lightning protection system secured thereto is designed also to convey information in the form of r-f signals and comprises at least one pair of wires suspended from said supports, spaced a certain distance apart and forming an r-f data transmission channel, according to the invention, the wires of the lightning protection system are suspended from the supports one under the other in a substantially vertical plane.
BRIEF DESCRIPTION OF DRAWINGS
The other objects and advantages of the present invention will become apparent from the discussion of a specific embodiment thereof, taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a length of an aerial power transmission line, according to the invention;
FIG. 2 illustrates frequency versus cross attenuation of a signal in the power transmission line, according to the invention.
PREFERRED EMBODIMENT OF THE INVENTION
Turning initially to FIG. 1, the aerial power transmission line forming the subje
REFERENCES:
Bourgsdorf, V. V., et al., "Design of the EHV 1150 kV AC Transmission Line", report at the session of CIGRE No. 31-03, published 1976, publishing house CIGRE (Paris, France), 7 pages.
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