Electricity: conductors and insulators – Insulators – Insulator and conductor embracing holder
Reexamination Certificate
1999-06-16
2001-06-19
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Insulators
Insulator and conductor embracing holder
C174S156000, C174S154000, C174S167000, C174S168000
Reexamination Certificate
active
06248956
ABSTRACT:
This invention relates to an insulating article for protecting electrical equipment and to such equipment having the article mounted thereon.
Electrical equipment, such as power transmission lines, insulators, surge arrestors, switchgear and transformers, operating at voltages in excess of 1 kV and particularly in excess of 10 kV (such voltages hereinafter being referred to as ‘high voltage’), often have parts thereof or parts associated therewith that are not insulated from the surrounding air. Thus, an exposed portion of such equipment can be at high voltage and be longitudinally separated from another portion at low voltage, for example at earth potential. The exposed high voltage portion may be physically supported by an insulator, for example when an overhead power line is mounted on an insulator that spaces it from a supporting tower that is itself at earth potential, or for example when a high voltage cable is terminated at a bushing or switchgear whose metal housing is at earth potential. In such instances outdoors, the larger wildlife such as squirrels and birds with large wingspans may be big enough to form a direct bridge, ie. an electrical short circuit, between the high voltage equipment and earth potential, with serious, usually fatal, consequences for themselves and often with serious consequences for the electrical equipment and the supply of electrical power—usually at least a fuse is actuated or a circuit breaker triggered such that the power supply is interrupted.
One solution to this problem is to insulate the exposed parts of the high voltage equipment, at least in regions where a short circuit to earth is more likely to occur, for example unintentionally by wildlife, and products such as RAYSULATE insulation tapes and pre-shaped components are available from Raychem for this purpose. Such components include heat-recoverable polymeric sheds, which may be mounted on porcelain sheds of existing insulators so as to increase the creepage length thereof, or otherwise so as to improve electrical performance. Although such products may incidentally make it more difficult for wildlife to bridge the electrical terminals of an insulator, their design is not optimised for this purpose and their method of installation in some circumstances may not be particularly convenient.
Another solution is to mount an insulating guard on the apparatus so as physically to increase the distance between the two portions at such significantly different, ie. harmful, electrical potentials such that it is impossible, or at least more unlikely, that the wildlife will be able to form a direct bridge therebetween. A typical insulator for outdoor use may be made of porcelain or polymeric material and is usually provided with a plurality of rain sheds or skirts, that extend circumferentially around a central cylindrical core of the insulator and that are spaced apart along its length. A protective guard, referred to as a squirrel shield device, for preventing short-circuiting of such an insulator by wildlife is disclosed in WO 95/10844, the guard comprising two semi-circular discs that are brought together from each side of the insulator between two adjacent sheds. The semi-circular discs partially overlap and are interlocked, for example by means of projections on a face of one disc that engage apertures in the other disc. The diameter of the guard is typically about three times that of the sheds, and when in place provides an effective obstacle to wildlife prostrating themselves along the length of the shedded insulator from earth to high voltage. However, a guard of this configuration is not very convenient to position on the insulator, which may be difficult to access, as being mounted on top of a pole of about 4 m height for example. It is necessary to support the two halves separately, bring them together in overlapping relationship, and then to operate the interlocking mechanism. This usually cannot be done from a distance, from ground level for example, and the power supply to the electrical equipment, to the power line supported on the insulator for example, may have to be interrupted in order properly to fit the guard.
A generally disc-shaped polymeric insulating article for protecting electrical equipment such as a high voltage insulator is disclosed in WO 96/16416. This article is also in two parts, with a first part being substantially C-shaped to fit around the insulator core, and a second part comprising an insert that slidably engages the first part so as to secure the article in place.
It has been known for many years to mount additional barriers, sometimes referred to as booster sheds or creepage extenders, on to porcelain or polymeric insulators in order to improve their electrical performance. Such barriers are of generally circular or conical configuration and are to be mounted on the core of the insulator or on existing laterally-extending sheds thereof. It is advantageous for retrofitting such barriers on to insulators that are already connected into an electrical supply or distribution system, for them to be of wraparound configuration so as to avoid the need for any dismounting of the insulator. Thus, these barriers are annular and have a radial slit that is generally closed after positioning around the insulator. GB-A-1542845, WO 92/08237, and EP-A-0328365 exemplify articles of this kind. GB-A-1542845 discloses an annular discharge barrier of integral construction that is wrapped around the insulator and closed by having a series of pegs press fitted tightly into holes at overlapping edges. WO 92/08237 discloses an annular barrier that may be integral or that may be formed of a plurality of components connected together with discontinuities therebetween. Closure of this barrier may be by a rod extending through loops or by the peg and hole system of GB-A-1542845. The barrier of WO 92/08237, which although initially may be formed as a flat sheet, has to adopt a frusto-conical configuration when it is closed around an insulator by overlapping its free edges. EP-A-0328365 discloses a wraparound creepage extender whose free ends need not be connected together, but which may be secured by fasteners. Difficulties may be experienced with products having these features in securing them on to the underlying insulator, especially if that is still connected to a power source.
It is one object of the present invention to provide an article that can more conveniently be mounted on electrical equipment so as electrically to protect the equipment, and thus associated electrical components, from being short-circuited, for example due to the presence of wildlife.
Thus, in accordance with one aspect of the present invention, there is provided a substantially planar electrically insulating article for protecting electrical equipment that is of generally elongate configuration and that has two longitudinally spaced-apart portions that, in operation, are at significantly different electrical potentials, the article comprising:
(a) two substantially planar parts that are linked to each other at a pivot point such that relative rotation of the two parts about the pivot point causes the parts to move between an open condition and a closed condition of the article, wherein, in the open condition, the article can be applied to the elongate electrical equipment, and wherein, in the closed condition, the article encircles the equipment so as to extend generally transversely thereof; and
(b) closure means arranged to secure the two parts of the article together when in the closed condition so as to retain the article securely mounted on the equipment.
The direct distance between the two portions at significantly different electrical potentials is the shortest distance between those portions that could be bridged by wildlife such as squirrels or large birds, and is typically about twelve to fourteen inches minimum.
The insulating article of the present invention is thus provided as a relatively rigid component that can be applied in an open condition to the electrical equipment effectively as
Barrett Donald Christopher Cowley
Cook Michael Robert
Harben Michael
Spalding Matthew
Myers Bigel & Sibley & Sajovec
Nguyen Charlie
Reichard Dean A.
Tyco Electronics U.K. Limited
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