Electricity: conductors and insulators – Insulators – With conductor holding means
Reexamination Certificate
1999-02-03
2001-10-16
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Insulators
With conductor holding means
C174S0050SG, C174S155000, C174S15800R, C174S176000, C174S189000, C174S209000
Reexamination Certificate
active
06303870
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to protective barrier structures for electrical insulators, and more particularly to particular cover structures for shed-type insulators and their use with power transmission lines.
(2) Description of the Related Art
In the field of electrical power transmission, high voltage power lines (typically operating in excess of 1 kV) are supported by structures such as utility poles. To prevent leakage of power from the lines into the supporting structure, the lines are advantageously held at one end of an insulator, which in turn is held at its other end by the supporting structure. Common insulators are formed of ceramic, porcelain, epoxy, or other electrically nonconductive materials. As such insulators are used in the open, they are exposed to rain (including acid rain), humidity, salt fog, acid fog, particulate pollutants, and other environmental contaminants.
If a continuous surface of electroconductive moisture existed between the ends of the insulator (e.g., deposited as rain), it would provide a conductive path between the line and the supporting structure. To avoid this, insulators are configured so that water does not accumulate over a continuous surface between the two ends. In “shed”-type insulators this may involve providing the insulator as the combination of: a body (also known as a core or stem) which is formed in a generally circular cylindrical or frustoconical shape; and a number of “sheds” formed as annular flanges projecting radially outward and longitudinally/vertically downward from the body. Both the upper surface of each shed and the lower surface (underside) of each shed along substantial portions thereof are inclined downward, leaving the underside of each shed largely protected from falling rain and preventing a continuous flow of water from end-to-end.
The surfaces of such insulators may be contaminated in other ways so as to compromise their insulative properties. For example, in coastal areas, wind-blown, salt-laden, mist may deposit salt over substantially the entire exposed surface of the insulator. Such salt can become embedded in the porous surface of the insulator and, eventually, provide a conductive pathway from the wire to the supporting structure. Wind-blown sand may abrade the surface of the insulator, increasing porosity and rendering the insulator more susceptible to later water or salt contamination. In industrial areas, chemical and particulate pollution may similarly compromise the insulator. To partially address these problems, it is known to periodically wash the insulators with a high pressure stream of water. Such a stream may be delivered from the ground or from the air such as from a helicopter. To avoid the risk of conducting electricity from the lines through the stream of water, power to the lines is advantageously shut off during cleaning. Although shutting off the power for cleaning may be optional, it is substantially required during replacement of the insulator. Furthermore, cleaning may not be complete and the service life of the insulator may be diminished.
It is thus desirable to reduce the required cleaning of insulators and extend their service lives.
BRIEF SUMMARY OF THE INVENTION
Accordingly, in a first aspect, the invention is directed to an insulative cover having a first end secured to the insulator adjacent the insulator's first end and a second end secured to the insulator adjacent the insulator's second end. The cover enshrouds a central portion of the insulator. The cover may define a substantially sealed volume surrounding the central portion. The insulative cover may have first and second pieces, each being the unitarily-formed combination of a body, first and second vertical flanges extending along first and second sides of the body, and first and second collar sections at first and second ends of the body. The bodies may form a series of reduced diameter regions alternating with a series of enhanced diameter regions, each reduced diameter region having a minimum diameter smaller than a maximum diameter of an adjacent enhanced diameter region. Each enhanced diameter region may accommodate an associated shed of the insulator.
The reduced and enhanced diameter regions may form a series of sheds on the cover. Each of the cover's sheds has an upper surface which substantially slopes downward in the outward radial direction and a lower surface which substantially slopes downward in the outward radial direction. An end surface joins the upper and lower surfaces.
The first and second pieces may be formed essentially from a fluorocarbon-vinylidene fluoride/hexifluoropropylene. The first and second insulator ends may be formed by first and second metallic end caps and first and second tie wraps may secure the respective first and second cover ends proximate the first and second insulator ends.
In a second aspect, the invention is directed to a combination for supporting a power line relative to a support structure in an electrical power transmission system. An insulator has a first end secured to the support structure and a second end carrying the power line. An insulative cover has a first end secured to the insulator adjacent the insulator's first end and a second end secured to the insulator adjacent the insulator's second end. The cover defines a volume substantially enclosing a central portion of the insulator. The insulator's first end may be an upper end and the insulator's second end may be a lower end. The volume may be a sealed volume or it may include at least one vent hole preferably no greater than 1 sq. mm in cross-section. The support structure may be a utility pole and the insulator's first end may comprise a metal fitting bolted to the pole. The insulator's second end may comprise a metal fitting into which at least one eyebolt is threaded for supporting the power line.
In a third aspect, the invention is directed to a method for protecting an insulator in an electrical transmission system from environmental contaminants. An insulative cover is provided. The insulator is surrounded with the cover. A first end of the cover is secured to the insulator adjacent to the insulator's first end. A second end of the cover is secured to the insulator adjacent to the insulator's second end. This defines a substantially sealed volume surrounding a central portion of the insulator which is effective to protect such central portion from environmental contaminants. The surrounding step may include placing a first cover half on a first side of a separation plane extending longitudinally through the insulator and placing a second cover half on a second side of the separation plane. The first half is then secured to the second half. The method may be performed in situ while the power line is supported by the insulator and carries an alternating current voltage (e.g., in excess of 1 kV).
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
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Greenberg Glen
Nazaryan Nikolay
Orkin Stanley S.
Nino Adolfo
Reichard Dean A.
Slate William B.
Turbine Controls, Inc.
Wiggin & Dana
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