Electric heating – Inductive heating
Reexamination Certificate
2000-04-06
2001-03-27
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
C219S636000, C219S679000, C174S0400CC, C191S0330PM
Reexamination Certificate
active
06207939
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices for removing the snow or the ice that can build-up for example on electrical lines or cables, and relates more particularly to a device and a method for de-icing an elongated structural element like a high-voltage electrical line or a guyed tower.
BACKGROUND OF THE INVENTION
In cold regions, the structural tubular elements, no matter the shape that they exhibit, i.e. rectangular, square or circular, are often subjected to atmospheric ice precipitations, like hard frost, black ice and wet snow. The ice accumulation on these elements may cause mechanical overloads that will deform them, even going so far as to sometimes produce disastrous mechanical breakages. So far, there are no methods truly efficient from the energetic and automatized point of view, that are capable of reducing the ice accumulation on these structural elements.
The U.S. Pat. No. 4,690,353 (HASLIM) and the U.S. Pat. No. 5,411,121 (LAFORTE et al.) describe devices or systems using high intensity electromagnetic impulses to break the ice.
In the case of HASLIM, the system is applicable to planar surfaces, and has been developed to remove the ice on the wing of an airplane. Electromagnetic pulses are injected in a thin double ribbon of copper positioned (embedded) in a rubber film.
In the case of LAFORTE et al., the device is applicable to stranded conductors, like a stranded cable. To break the ice, electromagnetic impulses are injected in some of the insulated, integrated conductive wires in the last stranded layer of the cable. These conductive wires are insulated for this purpose during the manufacturing process of the cable.
The publication entitled “An Investigation of Power Line De-icing by Electro-Impulse Methods”, published in the paper IEEE Transaction on Power Delivery, Vol. 4, No. 3, July 1989 in the name of EGBERT et al., describes a test with an ACSR conductor coated with rubber bands containing flexible copper strips in which electromagnetic impulses have been injected. In this test, the rubber bands surrounding the conductor had not an appropriate shape and the copper strips, too thin, were not providing a sufficient mechanical resistance to break the ice, so that under the effect of impulses, the coating was deforming instead of breaking the ice, the mechanical resistance of the copper strips being lower than that of the ice. As underlined by the authors as a conclusion of their experimentation, the use of this type of overlapping does not allow to efficiently de-ice the closed surface of a conductor.
SUMMARY OF THE INVENTION
The invention provides a device for de-icing an elongated structural element having a closed contour, comprising: at least one pair of electrically conductive wires preformed for winding, one next to the other, along and around the structural element following a substantially helicoidal trajectory while embracing substantially the contour of the structural element with a predetermined gap between the conductive wires and the structural element, the conductive wires having first ends for receiving electromagnetic impulses, and second ends opposite to the first ends, the conductive wires being sized to withstand a current causing, between the conductive wires of the pair, a repulsion having an intensity capable of breaking the ice or the frost on the structural element by a separation of the conductive wires from each other in response to the repulsion, the conductive wires having rigidity and elasticity properties such that the conductive wires recover their shape around the structural element after the separation caused by the repulsion; means for electrically connecting the second ends of the conductive wires of the pair together; and means for electrically insulating the conductive wires of the pair from each other and from the structural element.
The invention also provides a method for de-icing an elongated structural element having a closed contour, comprising the steps of: positioning at least one pair of conductive wires along the structural element, the conductive wires being preformed for winding, one next to the other, along and around the structural element following a substantially helicoidal trajectory while substantially embracing the contour of the structural element with a predetermined gap between the conductive wires and the structural element, the conductive wires having first and second opposite ends, the conductive wires being provided with means for electrically insulating the conductive wires from each other and from the structural element, the conductive wires being sized to withstand a current causing, between the conductive wires of the pair, a repulsion having an intensity capable of breaking the ice or the frost on the structural element by a separation of the conductive wires from each other in response to the repulsion, the conductive wires having rigidity and elasticity properties such that the conductive wires recover their shape around the structural element after the separation caused by the repulsion; electrically connecting the second ends of the conductive wires together; and applying electromagnetic impulses between the first ends of the conductive wires to generate said current in the conductive wires.
The de-icing device according to the invention is adaptable to any already existing aerial structural element, electric insulator or conductor, whose surface exhibits a closed contour like, for example, the aerial rods and cables of various sections: circular, square, rectangular, etc. The de-icing device is applicable to a conductor of an electrical line under voltage, around which it forms a kind of jacket or sheath. The de-icing method only requires a low level of energy; being of mechanical type, that uses electromagnetic impulses, it requires 100 to 1000 times less energy than thermic type techniques. The de-icing device forms an independent unit as such from the structural element that it covers. Thus, it does not need to be fasten to the structural element. It can be installed on the cables during their industrial manufacturing or on the cables already in place.
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Robert I. Egbert et al, “IEEE Transactions on Power Delivery” vol. 4, No. 3,An Investigation of Power Line De-Icing by Electro-Impulse Methods,pp. 1855-1861, (Jul. 1989).
Allaire Marc-Andre
LaForte Jean-Louis
Foley & Lardner
Hydro-Quebec
Leung Philip H.
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