| CLAIMS
1. An overhead conductor with spectrally selective surface consists of a conductive body which can be bare or insulated and of accompanying parts which make an integral part of the conductor and participate in the conduction of the electric current and the heat, to which is applied or, as previously described, on which is being formed a layer of material with selective properties, characterized that the coefficient of emission in the area of conductors operating temperatures is initially higher than 0,7, with the coefficient of solar absorption which is at the same time initially smaller than 0,3.
2. An overhead conductor with spectrally selective surface according the claim 1, characterized that the appertaining equipment which has the ability to conduct the electric current or heat, and which is directly exposed to the solar radiation, has the same surface characteristics as the conductor itself, i.e. initially E>0,7 and A<0,3. |
OVERHEAD CONDUCTOR WITH SPECTRALLY SELECTIVE SURFACE
DESCRIPTION OF INVENTION Technical Field
This invention is related to overhead conductors and cables whose surface conditions are improved for the purpose of achieving as low operating temperature as possible, and according to the international patent classification (IPC) it can be classified as: H 01 B 7/42 - cables, conductors and insulators intended for dissipation and conveyance of heat. It has been known that temperature is the main limiting factor of the transmission capacity of overhead conductors and cables, besides, the temperature rise shortens the lifespan of insulation, it can cause degradation of conductive material, and also increase the losses in the conductive material due to increased resistance. An additional problem with overhead conductors is sag, which also stands in a positive correlation with the temperature. Background Art The most common approach to the improvement of cooling of overhead conductors is the so called surface blackening, which improves heat dissipation by radiation. This approach can significantly increase the transmission capacity of certain types of high-temperature overhead conductors, the so called black conductors. Black coatings are exceptionally unselective, that is, they have a large emissivity i.e. absorptivity in a broad spectrum of electromagnetic radiation from the far infrared to ultra-violet, and although they increase the transmission capacitiy at higher operating temperatures, their deficiency is that they intensely absorb the solar radiation and thus increase the losses at lower loads. Their application to the conductors of operating temperature up to 12O 0 C is thus questionable. Another approach to the improvement of cooling is to enlarge somehow the external surface of the conductor and to blacken it additionally, what would improve the heat conveyance through convection and radiation. We have such an approach for instance in the Japanese patent PCT/JP99/01257, which, beside winding of additional wire around the existing conductor, repeatedly mentions in the claims 2, 6, 7, 8, 9, 10, 11, 18 etc. the surface blackening with a coefficient of emission of 0,7 or higher. It is known that blackened conductors often have the coefficient of absorption which is higher than 0,9, i.e. they intensely absorb the solar radiation, what has an adverse effect upon the properties of overhead conductors.
Disclosure of the Invention
Pursuant to generally recognized calculation methods for overhead conductors current rating, such as for instance IEEE 738 standard, there are two parameters of the conductor surface which have a direct effect upon the current rating i.e. the conductors temperature. These are the previously mentioned coefficient of heat emission E and coefficient of solar absorption A.
Since, in the case of an overhead conductor, the absorption and the emission take place at different wave lengths, the absorption mainly in the visible and near infrared electromagnetic spectrum, and the emission in the far infrared spectrum, it is possible to made material having in that sense selective properties, i.e. a weak absorption of solar radiation A<0,3, along with a high coefficient of emission in the far infrared spectrum E>0,7. Therewith it is possible to bring the conductor surface into a state which would have these characteristics, in a way that a layer of the stated characteristics is being formed on its surface. It is very important to point out that due to a low coefficient of solar absorption, in this approach one can not speak of black conductors. The stated difference represents an obvious shift from the state of the art, as due to its selectivity i.e. the low coefficient of solar absorption in the visible part of the spectrum, the surface will be white, reflecting or will generally have a brighter colour along with the coefficient of heat emission in the far infrared spectrum E>0,7. Under the far infrared spectrum is implied radiation at operating temperatures of overhead conductors in the approximate range of 50 to 25O 0 C. Detailed description of at least one way of invention realization
It is possible to bring the surface of overhead conductor into a state of selectivity by applying a coating of prescribed thickness with selective characteristics at the conductor surface, or by a chemical treatment of the surface, i.e. the preparation of the surface-layer of the insulation at insulated overhead conductors or cables. In the case of a reflecting surface with a low coefficient of solar absorption, such as for instance a polished aluminium, the selectivity can be achieved by applying a coating which is transparent to the solar radiation and whose coefficient of emission in the far infrared area exceeds 0,7. In general, when applying the coating, one has to respect the instructions of the manufacturer for the specific coating, in order to achieve as good as possible contact between the conductor and the coating. This includes cleaning, degreasing, proper drying etc., as defined by the manufacturer. It is also possible to apply a patented procedure for
applying of black polyurethane coating to overhead conductors which adhere exceptionally well to aluminium, except that it is a selective layer which will be applied in that case, and specifically in white colour or generally brighter. The market offers quite a number of selective coatings intended for space industry and construction. Here are listed only some of the best known types with appropriate trade names and coefficients of absorption and emission.
A E A/E
Barium Sulphate with Polyvinyl Alcohol 0.06 0.88 0.07
Biphenyl- White Solid 0.23 0.86 0.27 Catalac White Paint 0.24 0.90 0.27
Dupont Lucite Acrylic Lacquer 0.35 0.90 0.39
Dow Corning White Paint DC-007 0.19 0.88 0.22
GSFC White Paint NS43-C 0.20 0.92 0.22
GSFC White Paint NS44-B 0.34 0.91 0.37 GSFC White Paint NS-74 0.17 0.92 0.18
Hughson White Paint A-276 0.26 0.88 0.30
Hughson White Paint V-200 0.26 0.89 0.29
Hughson White Paint Z-202 0.25 0.87 0.29
Hughson White Paint Z-255 0.25 0.89 0.28 Mautz White House Paint 0.30 0.90 0.33
3M-401 White Paint 0.25 0.91 0.27
Magnesium Oxide White Paint 0.09 0.90 0.10
Magnesium Oxide Aluminium Oxide Paint 0.09 0.92 0.10
Opal Glass 0.28 0.87 0.32 OSO-H White Paint 63W 0.27 0.83 0.33
P764-IA White Paint 0.23 0.92 0.25
Potassiuml Fluorotitanate White Paint 0.15 0.88 0.17
Sherwin Williams White Paint (A8W11) 0.28 0.87 0.32
Titanium Oxide White Paint with Methyl Silicone 0.20 0.90 0.22
Titanium Oxide White Paint with
Potassium Silicate 0.17 0.92 0.18
Zerlauts S-13G White Paint 0.20 0.90 0.22
Zerlauts Z-93 White Paint 0.17 0.92 0.18 Zinc Orthotitanate with Potassium Silicate 0.13 0.92 0.14 Zinc Oxide with Sodium Silicate 0.15 0.92 0.16 Zirconium Oxide with 650 Glass Resin 0.23 0.88 0.2 The other way is a chemical treatment of the conductors surface or application of insulation with selective properties at insulated overhead conductors and cables. The characteristic feature of overhead aluminium conductors is that selectivity of the surface can be achieved by a simple procedure of the so called clear anodisation by which a thicker layer of transparent aluminium oxide with selective properties of the surface is obtained with A=0.27, E=0.76, i.e. A=0.35, E=0.84. Although in this case the selectivity is not as marked as in some other commercial coatings, the advantage of this procedure is an exceptionally good adherence of that layer, which is practically monolithic with the aluminium base and does not get lost in the course of time. If we have an insulated overhead conductor or cable, instead of coating we can prepare the external layer of insulation in such a way that the layer as such will have selective properties.
All equipment, such as for instance joints and similar elements, able to conduct the electric current or the heat and directly exposed to solar radiation, is also treated in order to obtain the surface conditions similar to those of the conductors themselves, i.e. the cables, and to make them compatible in view of thermal and electrical load. Industrial Applicability
The invention can be applied in the manufacturing process of overhead conductors and of the appertaining equipment, thus improving the characteristics of the conductors and of the appertaining equipment, as already stated. Besides, as it is possible to apply the selective coatings to the already installed distribution and transmission lines, i.e. the power- transmission lines, the invention can be applied at the places of congestions within the transmission or distribution grid when it is necessary to increase the transmission capacity of the existing transmission or distribution lines.