Abstract:
A breather assembly for permitting atmospheric venting to the interior of electrical apparatus such as a high voltage fuse while preventing moisture from entering the fuse comprises three separate chambers communicating in such a way that the atmosphere can be vented to the interior of the fuse but moisture is precluded from entering the interior of the fuse regardless of the orientation of the fuse body.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to breather assemblies for electrical apparatus, and more particularly, to a breather assembly which permits venting to the atmosphere of the interior of a high voltage fuse to maintain equal pressure while precluding the admittance of moisture to the interior of the fuse. 
     2. Description of the Prior Art 
     High voltage fuses for interrupting current in high voltage circuits are well known in the art. For example, U.S. Pat. Nos. 3,267,235 - Barta, 3,575,683 - Fahnoe, 3,176,100 - Barta, and 3,855,563 - Cameron et al., illustrate typical fuses for high voltage electric power circuits. Such high voltage fuses are often mounted outside on utility poles, and thus are directly exposed to adverse weather conditions including rain, sleet, hail, and snow. Since such high voltage fuses usually comprise an arc quenching material such as boric acid or other such materials which if exposed to moisture will deteriorate thereby jeopardizing proper operation of the fuse, such high voltage fuses typically have been hermetically sealed to prevent the entrance of moisture to the interior thereof. Any sealing material used to seal such fuses must provide a moisture tight seal without degradation despite years of outdoor exposure. 
     Despite attempts to provide a reliable hermetically sealed fuse which will maintain its sealed relationship even after years of use, it has been discovered that rough handling, thermal expansion of various parts of the fuse formed from dissimilar materials, corrosion, and exposure to adverse weather conditions all contribute to cause small leaks to develop after a period of time despite the best attempts to totally and completely hermetically seal a fuse. Once even the smallest of leaks develops, a phenomenon called &#34;pumping&#34; results which causes the ingress of moisture into the interior of the fuse. Pumping results because of the well known physical relationship of pressure, volume, and temperature. Since the fuse has a constant interior volume, any change in the temperature of that volume correspondingly results in a change in the pressure in the interior of the fuse. Thus, when the temperature of the fuse drops rapidly, such as during a rainstorm, the interior pressure of the fuse tends to drop rapidly so that the interior pressure is less than the atmospheric pressure causing any moisture on the surface of the fuse to be sucked through any existing leaks around the various hermetic seals of the fuse. Once moisture is sucked into the fuse, it is retained in the fuse because there is no atmospheric venting to dry the interior of the fuse so that after a period of time there is a deterioration of the interior components of the fuse. 
     Accordingly, it has been discovered that it would be an advantageous advance in the art to provide a versatile, economical breather assembly for high voltage fuses which permits atmospheric venting to the interior of the fuse while precluding the admittance of moisture to the interior of the fuse regardless of the positional orientation of the fuse but which does not degrade the efficiency of the current interruption function of the fuse. The present invention is directed to such a breather assembly for a high voltage fuse and other electrical apparatus. 
     Breathers for switch operating mechanisms are known in the art as illustrated in U.S. Pat. No. 3,696,729 - Chabala, et al., but the fuse breather described and claimed herein is believed to be unique. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates to a breather assembly for atmospheric venting of the interior of electrical apparatus comprising a first chamber means communicating with the interior of the apparatus; a second chamber means communicating with the first chamber means; and a third chamber means communicating with the second chamber means and with the atmosphere in such a manner that moisture cannot flow directly in a straight line from the atmosphere to the first chamber irrespective of the positional orientation of the apparatus. 
     The first chamber means is formed by a first circular wall extending essentially perpendicularly from a base member which is mounted over an open end of the apparatus. The first chamber means communicates with the interior of the fuse through at least one opening through the base member. The second chamber means is formed between the first circular wall and a second circular wall extending essentially perpendicularly from the base member and surrounding the first circular wall. The second chamber means communicates with the first chamber means along the extending edge of the first circular wall. The third chamber means is formed between the second circular wall and a side wall of a cap member. The cap member comprises an end wall joined to the side wall which overlies and engages the extending edge of the second circular wall. The third chamber means communicates with the second chamber means through at least one opening through the second circular wall and communicates with the atmosphere through at least one opening through the side wall. The openings through the side wall are positioned away from the openings in the second circular wall so that moisture cannot flow directly in a straight line from the atmosphere to the first chamber means. Thus, moisture entering the opening in the side wall tends to collect in the third chamber, and if any moisture passes to the second chamber it tends to be collected in the second chamber so that it cannot enter the first chamber and the interior of the apparatus. 
     Thus, it is a principal object of the present invention to provide a breather assembly for a high voltage fuse that prevents water ingress to the interior of the high voltage fuse regardless of the positional orientation of the fuse while freely allowing the atmosphere to vent to the interior of the fuse. 
     Yet another object of the present invention is to provide a breather assembly for a high voltage fuse which allows the internal pressure of the fuse to rise and fall simultaneously with atmospheric pressure thus making seals less critical. 
     Yet another object of the present invention is to provide a breather assembly for a high voltage fuse which performs its desired function with equal efficiency with any positional orientation of the fuse. 
     Yet another object of the present invention is to provide a breather assembly for a high voltage fuse which enhances the operation of the fuse in interrupting current flow. 
     Yet another object of the present invention is to provide a breather assembly for a high voltage fuse which is economical but yet relatively rugged so that proper performance will not be affected by normal handling. 
     These and other objects, advantages and features will hereinafter appear, and for the purposes of illustration, but not for limitation, an exemplary embodiment of the present invention is illustrated in the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side partially fragmentary view of a high voltage fuse having a preferred embodiment of the present invention mounted thereon. 
     FIG. 2 is a side cross-sectional, partially fragmentary view of the preferred embodiment of the present invention. 
     FIG. 3 is a cross-sectional view of the preferred embodiment taken substantially along line 3--3 in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, high voltage fuse 10 can take the form of any of a variety of well known high voltage interrupter fuses such as the fuse disclosed and described in U.S. Pat. No. 3,267,235 - Barta or the fuse disclosed in co-pending applications Ser. Nos. 740,930; 741,015; 741,026; 741,027; 741,028; all filed Nov. 11, 1976, assigned to the same assignee as the present invention. Fuse 10 comprises an exhaust ferrule 12 to which is mounted a breather assembly 14 in accordance with the present invention. 
     With reference to FIGS. 2 and 3, ferrule 12 has a hollow interior 16 that communicates with the interior of fuse 10. Formed along the interior edge of ferrule 12 are threads 18 to which breather assembly 14 is threaded. 
     Breather assembly 14 comprises a base member 20 having an annular extending flange 22 upon which are formed threads 24 that mate with and engage threads 18 on ferrule 12. Annular flange 22 is joined to a base wall 26 of base member 20 which extends entirely across the open end of ferrule 12 along a narrowed or reduced section 23, the purpose of which will be more fully described below. Base wall 26 has a first circular wall 28 extending essentially perpendicularly therefrom so that a first chamber 30 is formed within first circular wall 28. Openings 32 are formed through base wall 26 and communicate between the interior of the fuse 10 and first chamber 30. 
     Also extending from base wall 26 is second circular wall 34 that surrounds the first circular wall 28. Formed through second circular wall 34 are openings 36 having chamfered edges 38 slanted in such a manner so as to increase the surface tension of any moisture forming along the edge of openings 36 to reduce the possibility that moisture will flow through the openings 36. A second chamber 40 is formed between the first and second circular walls 28 and 34. Second chamber 40 communicates with first chamber 30 along the circular extended edge 42 of first circular wall 28. 
     Positioned over base member 20 and mounted thereon is a cap member 44. Cap member 44 comprises an essentially flat circular end wall 46 and an annular side wall 48 joined along the peripheral edge of end wall 46 and extending essentially perpendicularly therefrom. Formed through side wall 48 are openings 50 having chamfered edges 52 slanted in such a manner that the surface tension of any moisture forming along the edge is increased to reduce the possibility that moisture will flow through the openings 50. 
     A third chamber 54 is formed between side wall 48 and second circular wall 34. Openings 50 allow communication of the atmosphere with the third chamber. The openings 50 are positioned in such a way that they are not directly aligned with openings 36 through the second circular wall 34. Thus, any moisture flowing through openings 50 cannot flow directly in a straight line through an opening 36 but must flow around and through third chamber 54 before approaching an opening 36. 
     It should be noted that the particular orientation of the walls and openings of breather assembly 14 substantially precludes the possibility that moisture will gain access to the interior of fuse 10 irrespective of the orientation of the fuse. With the fuse in a vertical position so that breather assembly 14 is positioned at the bottom of the fuse, it can be seen that while some moisture may flow through openings 50 and 36, since openings 32 in base wall 26 would be positioned well above such moisture, the moisture will not flow into the fuse. However, air will freely flow into the fuse through openings 32 thereby providing atmospheric venting to the interior portion of the fuse. If the fuse is oriented in a vertical position so that breather assembly 14 is at the top of the fuse, it can be seen that while moisture may flow through openings 50 and 36, it is very unlikely that sufficient moisture would collect in the second chamber 40 to the point where the moisture would flow over the extending edge 42 of first circular wall 28 and thereby gain access to the interior of the fuse 10 through openings 32. Correspondingly, if the fuse is positioned in a horizontal position (as illustrated in FIG. 1) moisture tending to flow through an opening 50 would tend to flow along the surfaces of third chamber 54. While some of the moisture might flow through an opening 36, that moisture would tend to flow along the interior surface of second circular wall 34 to the lowermost opening 36 and then flow back out of the second chamber 40. It would be highly unlikely that sufficient moisture would collect in second chamber 40 to enter first chamber 30 or openings 32. Thus, as can be seen, regardless of the positional orientation of the fuse 10, it is virtually impossible for moisture to form around or over any of the openings 32 so that it can be drawn into fuse 10. Accordingly, while the air can freely be drawn into the fuse as the pressure within the fuse changes due to temperature changes, moisture will not be drawn into the fuse since the moisture will not gain access to the openings 32. 
     To assure relatively low cost of breather assembly 14, it preferably is fabricated from plastic material and may be formed by injection molding. However, breather assembly 14 can also be formed of metallic material if desired. 
     It can be seen that breather assembly 14 allows the internal pressure of fuse 10 to rise and fall simultaneously with the atmospheric pressure thereby making the hermetic seals less critical while precluding the admittance of moisture into the interior of the fuse regardless of the physical orientation of the fuse. Further, since breather assembly 14 is typically formed of a relatively frangible material such as plastic, it does not hinder operation of the fuse since it will be blown off the end of the fuse along reduced section 23 when a high current is interrupted, and at low current interruption the breather 14 even tends to enhance fuse operations by allowing arc gas pressure to accelerate contact separation within the fuse. It has been found that restriction of venting during low current interruption and during the initial portion of high current interruption assists in the interruption process. However, free or unrestricted venting is essential to the interruption of high currents. Thus, reduced section 23 can be dimensioned to retain the breather assembly 14 over the end of the fuse until a predetermined pressure is developed whereupon reduced section 23 fractures so that the breather is expelled permitting free venting. In this manner, breather assembly 14 can enhance fuse operation. 
     It should be apparent to anyone reasonably skilled in the art that various changes, alterations, or modifications of the preferred embodiment illustrated herein can be made without departing from the spirit and scope of the present invention as defined in the appended claims.