MXPA97001664A - Improved polymetal hood for weather and lightning, and method of production of mi - Google Patents

Abstract

An elastomeric arrester housing includes a sleeve having a tubular central portion and radiant bells. The sleeve is molded in a first configuration and, when the central portion is stretched radially, it adopts a second configuration in which the bells adopt a configuration arranged downwards. The bells in the second configuration, includes an upper surface that has a frustoconical shape in general. The housing can be made using conventional molding techniques, which requires substantially less material than if the housing were directly in the second configuration desired

Description

IMPROVED POLYMERIC HOOD FOR WEATHER AND LIGHTNING SYSTEMS AND THEIR PRODUCTION METHOD The present invention relates in general to electric power distribution equipment. In particular, the invention relates to lightning rods. More particularly, the invention relates to lightning rods employing polymeric weather hoods.

Under normal operating conditions, electrical transmission and distribution equipment is exposed to stresses within a fairly small range. Due to lightning discharges, transient surge surges or other system disturbances, portions of the power grid may experience momentary or transient voltage levels that greatly exceed the levels experienced by the equipment during normal operating conditions. If left unprotected, essential and high-cost equipment such as transformers, switching devices, computer equipment and electrical machinery can be damaged or destroyed by such surges and resulting instantaneous currents. Therefore, it is routine practice to protect such devices from dangerous voltages by the use of lightning rods.

A lightning arrester is a protective device that is commonly connected in parallel with a comparatively high cost electrical equipment to bypass or divert from the equipment the instantaneous currents induced by overvoltages, thus protecting the equipment and its internal circuitry from deterioration. When a lightning conductor is operated, it forms a current path to earth that has a very low impedance in relation to the impedance of the equipment that is protected. In this way, the instantaneous currents that would otherwise be conducted through the equipment are diverted or diverted through the lightning conductor to ground.

Conventional lightning rods typically include an elongated outer housing made of an electrical insulating material, a pair of electrical terminals at opposite ends of the housing to connect the lightning conductor between a conductor to line and ground potential and a set of other electrical components forming a path in series between the terminals. These components typically include a stack of voltage-dependent non-linear resistive elements. These non-linear resistors or "varistors" are characterized by having a relatively high resistance to normal stationary voltages and a much lower resistance when the lightning rod is subjected to transient overvoltages. Depending on the type of lightning rod, the lightning rod may also include one or more electrodes, heat sinks or sets of burners housed inside the insulating housing and electrically connected in series with the varistors.

To ensure proper operation of the lightning rod, varistors and other internal components must be isolated from moisture and environmental contaminants. The lightning rod housing serves to seal the components of the environmental environment. In addition, most lightning rod housings include "skirts" or "bells" spaced apart along the length of the housing. A lightning rod, once installed in the open, will be exposed to polluting products or environmental contaminants that are deposited on the surface of the housing by rain, wind and other conditions. These pollutants, over time, can accumulate so much that they form a current path. Such an accumulation effectively reduces the distance between energized components or potential line and ground. In this way, the surface resistivity of the arrester housing will decrease until a contour surface discharge can occur and result in a short circuit. Accordingly, weather hoods have traditionally been included in a lightning conductor housing in order to increase or lengthen the surface of the housing and increase the effective distance between the energized terminal of the lightning arrestor and ground. Additionally, the weather hoods have been designed to increase the capacity of the lightning rod to resist or minimize the extent to which dust and environmental contaminants may accumulate on the external surface of the housing. Such designs have included varying the radius of adjacent bells, the use of specially designed materials that resist the effects of contamination, and the variation of the quantity and size of bells in the housing.

Lightning rods made with porcelain were at one time in the industry. Unfortunately, such lightning rod housings were fragile and frequently exposed to vandalism. In addition, the porcelain housing was heavy and required substantial support elements for mounting the lightning rod. Also, when a lightning rod with porcelain housing failed, it was not unusual for the housing to explode, sending porcelain fragments at high speeds in all directions. Such failures presented the obvious danger potential for personnel and equipment deterioration.

Currently, at least in distribution class lightning rods, a polymeric housing has become a standard feature. A polymeric housing is of lower manufacturing cost, is not fragmentary and is less susceptible to deterioration during transport, installation and use compared to previously known porcelain housing. In addition, a polymeric housing is substantially lighter, allowing a simpler and less expensive installation.

The polymeric housing for lightning rods is typically molded with silicone rubber or other elastomeric material. The housing includes a central portion and radiant bells or skirts that are molded integrally with the central portion. The central portion includes an internal orifice or chamber that is substantially of the same diameter as the varistors and other components of the lightning rod to be housed therein. Where a particular shape or orientation of the bells is desired, the mold for the housings is fabricated to provide that desired configuration. Current molding techniques effectively limit the configuration and arrangement of bells in a polymeric lightning arrester housing.

In addition, due to limitations in the molding process, the manufacture of housing with certain orientations of weather hoods is expensive and difficult. Also, the current methods for obtaining a good bond between the interior surface of the housing and the internal components is high cost and generates a substantial amount of waste material.

Accordingly, there is a need in the art to have a polymeric arrester housing that has an improved weather hood design that resists the buildup of environmental contaminants and, at the same time, is relatively simple to manufacture using conventional molding technique. It would also be advantageous if the housing provides a better connection between the inner surface of the housing and the internal electrical components. Taking into account the current cost of silicone rubber and other elastomeric materials known to be used in lightning rod housings, it would be further advantageous if the weather hoods could be manufactured using less material than what is currently used for similar housings.

SUMMARY OF THE INVENTION The present invention includes an elastomeric housing for a lightning rod that includes a deformable flared sleeve with a central tubular portion having a central hole and a plurality of axially spaced bells radially disposed from the central portion. The sleeve has a first configuration when the central portion is not stretched, and a second configuration when the central portion is stretched.

When the central portion is radially stretched, the bells adopt a new configuration in which the upper surface is generally frustoconical and in which the ends of the bells move axially from their initial configuration; however, the ends of the bells remain in the same predetermined radial position in both the first configuration and the second configuration. It is preferred that the bells are disposed downward from the central portion at an angle between about 10 ° and 60 °, and more preferably between 10 ° and 45 °, when the sleeve is in the stretched configuration.

The elastomeric housing is preferably made with a silicone rubber and is molded in the first unstretched configuration. In that configuration, the upper surface of the bell joins the central portion in a shoulder having a radius of curvature Rl, and the lower surface of the bell joins with the central portion in a lower shoulder having a radius of curvature R2, I feel Rl greater than R2. Additionally, in the first configuration, the bell surface includes a first transition point where two frustoconical surface segments meet. Also, in the first configuration, the lower surface of the bell includes a second transition point at the intersection of a pair of frustoconical surface segments. The frustoconical surface segments on the surface are tapered downwards while the frustoconical surface segments on the underside surface are tapered upwards. The bells are configured so that the second transition point is closer to the geometry axis of the housing than the first transition point, in addition, the downward angle on the upper side is preferably greater than, or equal to, the upward angle in the lower side.

The present invention allows an elastomeric housing for lightning rods to be created with bells arranged downwardly, appropriately configured, but allows the housing to be molded with the bells substantially perpendicular to the axis of the housing. This provides significant manufacturing advantages, since it is a much simpler procedure to mold an elastomeric housing having bells disposed substantially perpendicular to the housing axis. Additionally, the invention allows an elastomeric housing to be stretched or deformed so that it has a particularly advantageous configuration of bells disposed downwardly, wherein the housing is fabricated using a volume of elastomeric material significantly less than if the housing were molded in the configuration finally desired using conventional techniques.

These and other features and advantages of the present invention will be readily apparent to those skilled in the art in the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For an introduction to the detailed description to the preferred embodiment of the invention, reference will now be made to the accompanying drawings, in which: Figure 1 is an elevation view, partially sectioned and with parts removed and partially in cross section, showing the lightning rod and lightning arrestor housing of the present invention.

Figure 2 is a cross-sectional view of the lightning arrestor housing shown in Figure 1.

Figure 3 is a cross-sectional view of the housing shown in Figure 3 in its molded and unstretched configuration.

Figure 4 is a magnified view of a portion of the molded, non-stretched housing shown in Figure 3.

Fig. 5 is a view similar to that shown in Fig. 4, illustrating a cross-sectional view of a portion of the weather hood before and after it has been stretched to accommodate and accommodate the components of the lightning rod shown in Figs. Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS It should be understood that the following components are representative of the contexts in which the present invention may be used and are not intended to be an exhaustive identification thereof. Referring first to Figure 1, the lightning rod 10 and the lightning arrester housing 20 of the present invention are shown. The lightning rod 10 generally comprises a support 12, an upper terminal bolt 14, a lower terminal bolt 16, a ground disconnect 18 and an elastomeric housing 20. The lightning rod is supported by the support 12 which, in turn, is mounted on a pole or other support element (not shown). The housing 20 contains a set 22 of lightning arrestor components that is maintained in an end-to-end stacked arrangement by an insulating element retaining member 28. The retaining element 28 may comprise, for example, an insulating coating such as that disclosed in United States of America 4,930,039 or filament winding as disclosed in the patents of the United States of America.

United States Numbers 5,138,517, 4,656,555 or 5,043,838. It is preferred, however, that the component insulating retainer 28 be made in the form of a hardened resinous coating, reinforced with glass fibers, and having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the electrical components. in the assembly 22, in order to provide an axial load on the components once cured and cooled. Such an embodiment is described in the co-pending United States of America application entitled "Autocompressive Lightning Rod Module and Self-Production Method", serial No. 60 / 012,667, filed March 1, 1996, the full disclosure of which is incorporated in the present descriptive memory by way of reference.

The assembly 22 includes electrodes 25, metal oxide varistors (MOV) 26 and end terminals 24 at each end. An upper conductive pin 14 and a lower conductive pin 16 are screwed into threaded center holes (not shown) at the ends of the terminals 24 so as to provide an element for connecting conductors to line potential and grounding conductors ( not shown) to the lightning arrester 10. The conventional grounding disconnect or spacer 18 is disposed about the terminal pin 16 to provide an element to explosively disconnect the grounding conductor in the event of a lightning rod failure. MOV 26 varistors are stacked within the assembly in end-to-end relationship with electrodes arranged between opposing surfaces of MOV varistors 26 adjacent. The MOV 26 varistors may be in the form of any conventional disposable metal oxide varistor. While not shown in Figure 1, the assembly 22 may also include a variety of other electrical components, including heat sinks or spacer elements, or sets of burners that may include ceramic materials, such as silicon carbide rings having resistors dependent on tension.

The housing 20 is best shown in Figure 2. The housing 20, as shown, has particular utility when employed in a distribution class lightning arrester. While the principles of the present invention can be employed in lightning rods having other physical dimensions and performance characteristics, the invention will be understood and described herein with reference to the 10KA-10KV heavy duty distribution class lightning arrester that is shows in figure 1.

With reference to Figure 2, the housing 20 generally comprises a sleeve having a central tubular portion 30 and bells 36 directed downwards linked to the central portion 30 in axially spaced relationship. Therefore, the housing 20 can be described as a flared sleeve. The central portion 30 includes a central hole 31, an internal cylindrical surface 32 and an external cylindrical surface 34. The bells 36, which are integrally molded with the central portion 30, extend from the outer surface 34 and include an upper surface 38, a lower surface 40 and an outer edge 42. The upper surface 38 and the lower surface 40 are shaped frustoconical in general although, as described in more detail below with reference to Figure 5, each of the surfaces 38 and 40 includes certain segments 61, 63 that are concave and other segments 62 that are convex. The bells 36 are arranged radially outwards from 1 central portion 30 and are preferably inclined between about 10 ° and 60 °, and more preferably between 20 ° and 45 °, with respect to a plane perpendicular to the central axis of housing 20. This angle of inclination indicates the angle of the largest surface Top 55 of the bell.

The inclined bell shape has several advantages. The inclined surface ensures that a portion of the hood is protected from contamination and wetted so that it maintains a high surface resistivity. The remaining surface can be contaminated with salts and dust and will have a much lower surface resistivity when wet, but the s will tend to wash and dislodge a large amount of the contamination.

Referring again to Figure 1, the central portion 30 in its configuration as used includes an inner diameter DI measured between opposite sides of the inner cylindrical surface 32 and an outer diameter D2 measured between opposite ends 42 of the bells, as shown in Figure 2. In this embodiment, DI is substantially equal to 43 mm and D2 is substantially equal to 91.5 mm. The housing 20 is molded with an elastomeric material to allow the housing to be stretched as described below. Preferably, the housing is made of polymeric material, such as silicone rubber. To allow the required stretch and deformation, the housing must be made with silicone rubber. While other elastomeric compounds can be used, silicone rubber is preferred because of its natural resistance to ultraviolet radiation. Although these compounds can be formulated to resist degradation by ultraviolet radiation, some surface deterioration will occur, increasing the risk of propagation of tears coming from defect sites. The advantage of using silicones to form the housing consists of the ability of the silicones to repel water. When water filled with pollutants forms droplets on the surface, the surface resistivity is much greater than if the water were present as a surface wetting film.

Other materials have provided a hydrophobic quality when they are new, but they lose this quality as they get older. Suitable materials for housing 20 are those supplied by Dow Corning STI, General Electric Silicones, Wacker Silicones, DuPont, and Uniroyal that have elongation at break according to ASTM D412 greater than stretched elongation levels and that They also have good physical and electrical performance characteristics for their operating environment in accordance with standards known in the industry. The preferred polymeric arrangement is a very full silicone arrangement containing aluminum trihydrate ("ATH") containing fumigated silica surface-treated with aluminum trihydrate ("ATH") and optionally extensive fillers such as silica powders. This arrangement preferably has an elongation at break greater than 300%, a hardness in Shore A durometer of less than 50, and a performance characteristic of wet arc surface discharge of 180 minutes at 6 KV when the sample is tested stretched to a level of approximately 125% of the level in the application. A convenient additional criterion is the failure mode after the wet arc surface discharge test so that it is of a nature that does not produce surface discharges, that is, due to the erosion of the material, and so that there is no evidence of propagation of the material. torn at the site of failure. If these conditions are met, the housing will continue to withstand stresses and will have an extended service life, even after a localized material fault has occurred.

Referring now to Figure 3, the housing 20 is shown in its molded configuration, before being stretched and deformed to the use configuration so as to accommodate MOV 26 varistors and other components of the arrester assembly 22. In this unstretched configuration, the bells 36 are spaced axially from each other by approximately 35 mm and the central portion 30 has a diameter DI and an outer diameter D2. In its unstretched configuration, DI is approximately 30.5 mm, or 60 to 90% DI. It is important, however, that the outer diameter D2 of the unstretched housing 20 is substantially the same as the outer diameter D2 of the housing 20 when stretched. To achieve this desired configuration of the housing 20 as shown in Fig. 2 when the inner diameter DI is increased DI, it is important that the housing and, particularly, the bells 36 be molded to have inclinations and radii of curvature and degrees of taper particular.

More specifically, and with reference now to Figure 4, the upper surface 38 of the bell 36 joins the outer surface 34 of the central portion 30 on the upper arched surface 46. The terms "upper" and "lower" are used below to refer to relative positions and orientations as shown in the figure. The upper arc surface 46 has a radius of curvature designated Rl which, in the embodiment shown, is substantially equal to 9.5 mm. Similarly, the lower surface 10 of the hood 36 intersects the outer surface 34 of the central portion on the lower arch surface 48, which has a radius of curvature equal to R2. In this embodiment, R2 is substantially equal to 2.36 mm. Irrespective of the precise radii, to achieve the desired change in inclination and shape of the weather hoods 36 from what is shown in Fig. 1 to that shown in Fig. 2, Rl must be greater than R2 and is preferably at least double R2. In addition, the downward angle on the upper side is preferably greater than or equal to the upward angle on the upper side is preferably greater than or equal to the upward angle on the lower side.

Still referring to Figure 4, the upper surface 38 and the lower surface 40 each include a pair of frusto-conical segments having varying degrees of inclination or declination measured from a plane substantially perpendicular to the longitudinal axis of the housing 20. These frustoconical segments are best described with reference to transition points 51-54. As molded, the hood 26 includes an upper surface comprising a first upper frustoconical segment 55 and a second lower frustoconical segment 56 and a lower surface 39 comprising a first upper frustoconical segment 57 and a second lower frustoconical segment 58. The first surface segment The upper frustoconical 55 is disposed between the transition point 51 and the transition point 52 and is inclined downward according to an inclination with respect to the horizontal equal to Al. The second upper frustoconical surface segment 56 is arranged from the transition point 52 to the shoulder 59 adjacent the outer edge 52, and is tapered downwardly at an angle with respect to the horizontal equal to A2. The first lower frustoconical surface segment 57 is disposed between the transition points 53 and 54 and is inclined upwards from the horizontal at an angle equal to A3. The second lower truncated surface segment 58 is disposed between the transition point 54 and the outer edge 42 and is inclined upwards relative to the horizontal at an angle equal to A4. The angles A1-A4 will vary depending on the size of the housing 20 and the desired precise functional orientation of the bells 36, however, for the embodiment shown in Figure 1, for example, the angles A1-A4 will have the following values Angle Degrees at 10 ° a2 Io a3 0.5 ° a4 0.5 ° Without taking into account the precise values of al-a4, according to the invention, the transition point 51 must be at a greater radius from the geometrical axis 21 of the housing 20 than the transition point 53, and the transition point must be at a greater radius than the transition point 54. In the specific embodiment described, the transition point 52 is located at a radial distance substantially equal to 36 mm while the transition point 54 is located at a radial distance approximately equal to 33. , 5 mm. Also, in this embodiment, the transition point is located at a radial distance substantially equal to 9.3 mm and the transition point 53 is located at a radial distance substantially equal to 2.3 mm.

In some cases, although not shown, it may be preferred to use only a single frustoconical section for the lower surface 40. This surface is disposed from a single transition point, said single transition point being between the two transition points 51,52 of the upper surface 38.

In its unstretched configuration shown in Figures 3 and 4, the central portion 30 of the housing has a wall thickness of substantially 2.8 mm and an outer edge 42 that is approximately 27.7 mm from the external surface 34 of the central portion 30, so that D2 is equal to approximately 91.8 mm ID is substantially equal to 30.9 mm When the lightning rod 10 is assembled, the varistors MOV 25 and the terminals 24 are fixed in a sub-assembly by means of retaining elements 28. To install the subassembly inside the housing 20, a blunt conical part is placed on a terminal 24. The conical piece includes a base portion that is substantially the same diameter as the terminal 24 and a conical or tapered end spaced from the base end and disposed away from the assembly 22. The tapered end of the conical piece has a termination that is diameter smaller than DI. One end of the accommodation not stretched (shown in Figure 3) is arranged around the tapered end of the conical piece and the housing 20 and then carried over the assembly 22. As the housing 20 is carried over the assembly 22, it is stretched so that it fits the assembly 22 and adopts the configuration shown in Figure 2. When stretched to fit the assembly 22, the length of the housing 20 contracts by approximately 8% as compared to its length before being radially stretched. to accommodate the assembly 22. Once the housing 20 is stretched from the components of the lightning rod, the remaining steps in the mounting procedure of the lightning rod 20 are carried out in the following order.

The arrester module is primed with a low temperature low viscosity neutral cure silicone.

The curing of the primer is accelerated at a temperature between 100 and 200 ° C. Before the housing is applied, a neutral silicone lubricating film of curing at lower ambient temperature is applied, which joins the housing to the lightning rod module. The silicone can be cured at an accelerating temperature, although this is not necessary. The remaining stages of the assembly are comparable with those known in the art for lightning rods.

Referring now to Figure 5, bell 36 is shown in profile in the molded, unstretched configuration, generally referred to by reference numeral 66, and in its configuration after drawing 68. As has been indicated above, the ends 42 of the bell 36 remain in substantially the same radial position with reference to the axis 21 of the housing, although the inner surface 22 and the outer surface 24 of the central portion 30 are displaced radially outward over substantial distances. In the stretched configuration 68, the upper surface 38 generally comprises three interconnected curved surfaces 61-63, the curved surfaces 61 and 63 being concave in general, while the curved surface 62, which is intermediate between the surfaces 61 and 63, is convex in general. The stretched configuration is a function of the relative volumes of the upper portion and the lower undrawn upper portion of each bell.

The flared elastomeric housing of the present invention provides superior performance characteristics and has a less manufacturing cost than many previously known housings. The savings in costs is due to the fact that the perpendicular bells of the present invention are much easier to demold during the manufacturing process. The ease of demolding allows the bells of the housing of the present invention to be significantly thinner, requiring the use of less material. The quality of the housing is improved because the simpler molded shape results in fewer defects in the molded parts.

The performance characteristics are improved because the elastomeric housing can conform to irregularities in the assembly, particularly if it is used in conjunction with a surface treatment with silane and / or a curing material at room temperature inside. The surface treatment with silane and / or the silicone material of curing at higher ambient temperature act to polish the housing of the present invention to the assembly so as to prevent the ingress of moisture therebetween and also functions as a lubricant and filler compound of holes during the insertion of the lightning rod module. The method of the present invention is advantageous with respect to conventional methods of molding a housing on an assembly, since this molding process requires silicone compounds of lower viscosity to prevent the joint from slipping due to the high force that are placed during molding. . Other suitable bonding agents include silane primers, silicone greases, silicone sprays and similar substances, but do not prefer substance that provides a bonded interface.

The ability to act under operating conditions is affected by the interface quality between the housing and the assembly. A good measure of the operating characteristics can be made using multiple voltage techniques commonly applied to insulators and polymeric lightning rods, such as the DY1009 procedure in the CEI (National Electric Company of Italy) or the IEC1109 (1992) procedure, of the Commission and IEC. Proper performance characteristics have been achieved according to the ENEL procedure due only to the pressure exerted on the interface by the level of stretching, provided that the interface is substantially free of air or that the air pockets are sufficiently large and positioned in controllable form so as to avoid the creation of highly localized stresses in the dielectric that are unacceptable. The degree of flexibility of the accommodation depends on the material selected and the level of anticipated tension. Suitable performance characteristics have been demonstrated in a lightning rod having a fiberglass cage with open tissue filled with air similar to that described in U.S. Patent No. 5,043,838. Good performance characteristics have also been demonstrated in lightning arrester products that utilize a silicone grease that substantially displaces the air at the interface in lightning rods constructed as described in the United States of America patent no. 4,656,555 and the copending application mentioned above. The best combined characteristics and the construction of the lightning rod module described in said co-pending application. An adequate bond has been achieved by using a neutral silicone curing compound at room temperature at the interface between the housing and the assembly. As noted above, this material also lubricates the housing during the placement of the housing on the assembly. Further improvements have been observed when the resin coated modules have been primed with a base primer or a cured coating at room temperature, sprayed and cured, similar to those commonly used to coat high voltage ceramic insulators.

While preferred embodiments of the invention have been illustrated and described, modifications thereto can be made without departing from the spirit and scope of the invention. The embodiments described in the present specification are only by way of example, and not limitative. Many variants and modifications of the invention and apparatus disclosed in the present specification are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description cited above, but is only limited by the claims that follow, this scope including all the subject equivalents of the claims.

Claims (33)

1. CLAIMS Having thus specially described and determined the nature of the present invention and the way it has to be put into practice, it is declared to claim as property and exclusive right: 1.- An elastomeric housing for electrical appliances, comprising: a sleeve flared bell having a central axis and comprising a central tubular portion with a central hole and a plurality of axially spaced bells disposed from said central portion; wherein said sleeve has a first configuration when said central portion is not stretched and a second configuration when said central portion is stretched; and wherein said bells are arranged from said central portion according to a first angle in relation to said geometric axis when said sleeve is in said first configuration and are arranged from said central portion according to a second angle in relation to said geometric axis when said sleeve it is in said second configuration.
2. 2. An elastomeric housing according to claim 1, wherein when said sleeve is in said configuration, said bells are disposed downwardly from said central portion at an angle comprised between approximately 10 ° and 45 ° measured from a plane perpendicular to said axis. geometric. A housing according to claim 2, wherein said bells are arranged substantially perpendicularly from said central portion when said sleeve is in said first configuration and wherein said sleeve assumes said second configuration when said central portion is stretched radially outward. A housing according to claim 2, wherein when said sleeve is in said first configuration, said bells include an upper surface that joins said central portion in a first shoulder having a radius of curvature Rl, and a lower surface that joins said central portion in a second shoulder having a radius of curvature R2, and in which R1 is greater than R2. 5. A housing according to claim 4, wherein R1 is at least twice R2, when said sleeve is in said first configuration. A housing according to claim 2, wherein said sleeve has substantially the same outer diameter in said first configuration and in said second configuration. A housing according to claim 6, wherein in said first configuration, said central hole has a diameter equal to DI, and in said second configuration said hole has a diameter equal to D2, where D2, is greater what DI A housing according to claim 2, wherein said bells include a first end arranged in a predetermined radial position relative to said geometric axis and a second end connected to said central portion, and in which when said sleeve is in Said second configuration, said bells include a frustoconical upper surface in general and a convex portion in said upper surface between said first end and said second end. 9. A housing according to claim 1 wherein said bells include ends arranged at predetermined radial and axial positions when said sleeve is in said first configuration and wherein when said bells are deformed to said second configuration, said ends of the bells are arranged in the axial direction away from said first predetermined position but remain in said first predetermined radial position. 10. A housing for electrical appliances comprising: an elastomeric sleeve having a central tubular portion with a central axis and central hole having a plurality of bells radiating from said central portion; wherein said bells have ends disposed to a predetermined radial distance from said geometric axis; and wherein said bells include a surface comprising a first frustoconical surface segment joined to said central portion in an upper ledge having a radius of curvature Rl, and a second frustoconical surface segment joined to said first frustoconical surface segment in a first IT transition point; and wherein said bells include a bottom surface comprising a third segment of frustoconical surface joined to said central portion in a lower shoulder having a radius of curvature R2, which is less than Rl, and a fourth segment of frustoconical surface attached to said third frustoconical surface segment at a second transition point T2, which is radially closer to said geometric axis than TI. A housing according to claim 10, wherein said first frustoconical surface segment is tapering downwardly from said first superior shoulder to said first transition point according to an angle at and wherein said second frustoconical surface segment is tapering down from said first transition point towards said end of said bell at an angle a2 is less than at. A housing according to claim 11, wherein said third frustoconical surface segment is tapered upwardly from said lower projection to said second transition point at an angle a3, and wherein said fourth frustoconical surface segment is tapering upwards from said second transition point to said end of said bell at an angle a4 that is less than a3. 13. A housing according to claim 12, wherein al is at least twice a2. 14. A housing according to claim 12, wherein al is at least equal to four times a2. 15. A housing according to claim 12, wherein a3 is substantially equal to a4. 16. A housing according to claim 12, wherein a2 is at least twice a4. A housing according to claim 12, wherein said first frustoconical surface segment intersects said upper boss at a third transition point and said third frustoconical surface segment intersects said lower boss at a fourth transition point, and wherein said transitional room is radially closer to said geometric axis than said third transition point. 18. A housing according to claim 12, wherein R1 is at least twice R2. 19. A housing according to claim 10, wherein said sleeve is deformable of a first configuration when said central portion is not stretched to a second configuration when said central portion is stretched radially outwardly, said ends of said bells being lower when said sleeve is in said second configuration in comparison to the first configuration. A housing according to claim 19, wherein when said sleeve in said second configuration, said ends of said bells are at said predetermined radial distance from said geometric axis. 21. An elastomeric housing for electrical appliances comprising: a deformable flared sleeve having a central axis and comprising a central tubular portion with a central hole having an inner diameter and a plurality of axially spaced bells having an upper surface and a lower surface and radiating from said central portion in a first configuration; said sleeves being configured so that the stretching of said central portion to increase said inner diameter causes said bells to deform to a second configuration in which said bells adopt a downward position and said surface of said bells is generally frustoconical. 22. An elastomeric housing according to claim 21, wherein in said first configuration each bell is substantially perpendicular to said geometric axis. An elastomeric housing according to claim 21, wherein when said sleeve is in said configuration, each of said surfaces, top and bottom, includes at least one frusto-conical portion. 24. An elastomeric housing according to claim 23, wherein when said sleeve is in said first configuration, said frustoconical portion intersects a plane perpendicular to said geometric axis at an angle of approximately 2.5 °. 25. An elastomeric housing according to claim 23, wherein each of said surfaces, top and bottom, includes two concentric frusto-conical portions. 26. An elastomeric housing according to claim 25, wherein when said sleeve is in its first configuration, said frustoconical portion intersects a plane perpendicular to said axis at an angle of less than about 2.5 °. 27. An elastomeric housing according to claim 21, wherein when said sleeve is in said first configuration, said upper surface intersects said central portion in a first shoulder having a radius of curvature R1, and said bottom surface intersecting said surface. said central portion in a lower shoulder having a radius equal to R2, and in which R1 is greater than R2. 28. An elastomeric housing according to claim 27, wherein R1 is at least 2 x R2. 29. An elastomeric housing according to claim 28, wherein each of said surfaces, top and bottom, includes a first frustoconical portion, said first frustoconical portion intersecting said first ledge at a first upper transition point and intersecting said first frustoconical portion to said second projection e a first lower transition point, said first transition point being greater than a radial distance greater than said geometric axis than said first lower transition point. An elastomeric housing according to claim 29, wherein each of said surfaces, upper and lower, further includes a second frustoconical portion, said second frustoconical upper intersecting said first frustoconical upper portion at a second upper transition point and said second frustoconical portion intersecting said first frustoconical lower portion at a second lower transition pointsaid second transition point being greater than a radial distance greater than said geometric axis than said second lower transition point. An elastomeric housing according to claim 21, wherein each hood has an upper surface and a lower surface, and wherein when said sleeve is in said second configuration, said upper surface includes a first circumferentially concave portion and a second circumferentially concave portion and a first circumferentially convex portion therebetween. 32. An elastomeric housing according to claim 21, wherein said bells comprise radially arranged elements having external edges, said radially-thickening elements decreasing toward their outer edges. An elastomeric housing according to claim 32, wherein in said first configuration and in said second configuration said external edges of said bells are substantially the same radial position in relation to said geometric axis.-