Abstract:
A transformer is provided that utilizes a substantially fully integral, generally outwardly convex casing or tank for enclosing an electrical transformer in a dielectric environment. The casing has fully integral side and top and bottom end walls, and has an open portion in its top end wall of sufficient size to serve both as a positive low to high pressure release and a maintenance hand hole. An easily inserted and removed cover assembly employs an operating stem, a domed cover member, a clamping member, a nut carrying bracket member and a spring that may be adjusted to a desired pressure relief setting by rotating the stem in one direction. Rotation of the stem in an opposite direction releases its clamping setting and loosens the parts of the cover assembly in such a manner as to permit it to be easily and quickly removed from the open portion by tilting it with respect to and out of the open portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to a pole mounting type of electrical distribution transformer such as used for converting a 13,200 volt A.C. input to a 240/120 volt, single phase A.C. output for domestic and other usage that will permit hand hole entrance for maintenance and repair work and also provide total safety protection when used with a suitable current limiting fuse from the standpoint of avoiding blow-out of the top end wall under a build-up of high, fault-produced, internal fluid pressure.  A phase of the invention deals with an improved transformer casing that has a pre-shaped wall construction based on its being subjected to relatively high positive internal fluid pressure, and that will have a combined hand hole cover and a simple and highly effective pressure relief means capable of efficient operation between lower cut-off to materially higher internal fluid pressures. 
     2. Description of the Prior Art 
     In recent years there has been a growing problem in the construction of overhead pole type distribution transformers from the standpoint of the blowing-off of upper cover end walls under internal fluid pressures developed by over-pressure phenomena, such as caused by electric arcing and other electrical faulting. Such transformers are mounted near the top of utility poles in residential areas, thus they tend to menace both persons and properties, since oil or other content may be ejected to fall as a hot and possibly fiery rain on anything or anyone in the immediate vicinity. Although so-called bleeder or light duty valve means have been mounted on the side of transformer tanks or housings for normal relatively low pressure venting, such means has been found totally unsatisfactory from the standpoint of a sudden and particularly high fluid pressure generation within the transformer such as may occur due to a fault of electrical equipment therein. 
     A conventional end wall cover which is retained in position over the upper edges of the side wall of a tank or housing by a take-up clamping chime ring similar to those used on dry bulk storage drums, represents a type that is most likely to be dislodged with considerable force under such conditions. Such covers for pole type transformers are made removable, since there are no other openings to permit access to the inside of the housing for modifying internal connections, operating internal tap changing switches and, in general, for easy maintenance. 
     Another type of end wall cover is removably mounted over the upper edge of the side wall of a transformer housing by means of a centrally projecting lug bolt whose inner end is threaded into an integrally secured cross piece within the housing and which serves to draw up the cover to a tightened relation on the circumferential edge of the housing. Both of these constructions entail risk from the standpoint of cover blow-off under high or sudden internal fluid pressure applications, such as occur from a failure to relieve quickly arising pressure that develops rapidly within the casing due to a fault which may result from the formation of an electrical arc under the oil dielectric. Such an arc may be caused by insulation failure or the fusing-apart of wires within or near the transformer windings, such as may occur under adverse operating conditions or as a result of some defect. Cover end wall blowing may be due to a very rapid internal pressure rise that can lift the oil column and slam it against the cover, simultaneously producing a force in the opposite direction against the bottom of the tank or housing and as well as forces against its sides. A second type has a fairly slow rise which gradually builds up in the transformer top and results in a blown cover and/or a deformed tank. The fault may or may not cause vaporization of the oil within the air space above the normal dielectric level therein. 
     As above indicated, side mounted relief devices have been provided to act as safety valves against normal pressure build-ups, such as due to loading and overloading of transformers. These valves are relatively small and inadequate to effectively relieve rapid build-up of pressure such as may occur as when internal arcing is present. There has been a need for an improved type of transformer tank or housing construction which can be relatively inexpensively produced and which will meet the problem involved in previous constructions, particularly from the standpoint of preventing high pressure dislodgement of the upper end wall and, in general, pressure deformation of a transformer tank or housing and, at the same time, which will permit entry to the inside of the casing for maintenance and repair of the electrical equipment therewithin. 
     SUMMARY OF THE INVENTION 
     It has thus been an object of the invention to provide an improved and more efficient enclosure construction for an overhead or pole type of transformer, particularly from the standpoint of providing a safe and sure type of venting or relief of fault-produced internal pressure build-up. 
     Another object of the invention has been to develop a new and and improved form of casing or housing construction for an overhead type of dielectric containing electrical transformer which will be effective to relieve normal minor operating fluid pressure and which, at the same time, under emergency conditions of high pressure build-up, will provide immediate and effective pressure relief without damaging its casing, blowing its end wall cover, and spewing hot fluid such as oil therefrom. 
     A further object of the invention has been to provide a transformer casing which may be substantially integral throughout its construction and will thus not require separate grounding connections as between its top end wall and its main cylindrical body, and which will enable a combined maintenance entry to its interior and a safety venting under high pressure build-up. 
     A further object has been to provide a transformer installation that in combination with a current limiting input fuse will assure a fully effective blow-off protection against fault-generated internal pressure. 
     A still further object of the invention has been to provide a practical, removable hand hole cover and safety relief construction for utilization with an enclosing upper end wall of an electrical transformer. 
     These and other objects of the invention will appear to those skilled in the art from the illustrated embodiment and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view in elevation of a transformer devised and constructed in accordance with the invention; 
     FIG. 1A is a circuit diagram showing the use of at least one current limiting fuse in the transformer input circuit; 
     FIG. 2 is a top plan view of the transformer of FIG. 1 and on the same scale as FIG. 1; 
     FIG. 3 is an enlarged fragmental side section in elevation taken along line III--III of FIG. 2; 
     FIGS. 4, 5 and 6 are side sectional details in elevation on a greatly enlarged scale, particularly illustrating the construction and utilization of a combined pressure relief and hand-hole cover of the invention; 
     Specifically, FIG. 4 shows a tilted and slightly separated relation of the parts of the cover assembly that may be employed when the assembly is being inserted or removed from within an open entry end portion of the integral end wall; 
     FIG. 5 is illustrative of an adjusted, fully mounted position of the cover assembly at which its spring means is set to provide a tension closing action that is based on the force at which it is desired to have the cover assembly open to relieve internal fluid pressure; 
     FIG. 6 is illustrative of a uniform full opening of the cover member assembly, as effected by compressing the spring under force exerted internally of the transformer housing, such as may be occasioned by arcing within its chamber; 
     And, FIG. 7 is a fragmental section on the scale of and taken along line VII--VII of FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring particularly to FIGS. 1 and 2 of the drawings, an electrical power transformer unit A of an overhead or pole-mounting type is shown having a pair of high voltage input terminals B, and a group of side-mounted secondary or output terminals C. The unit A is shown provided schematically with a primary transformer winding D and a secondary winding E in a submerged relation within a dielectric liquid such as oil whose level is indicated as F. The hollow casing, housing or tank of the unit A has a cylindrical, upwardly extending, elongated side wall 10, and outwardly convex, integral, top and bottom end walls 11 and 12. It will be noted that end walls 11 and 12 are shown integral with and hermetically sealed with respect to the side wall 10 by continuous weld beads w (see FIG. 1). The side wall 10 has an angle-shaped, upper rim flange 10a whose inclined, inturned, uppermost portion serves as a receiving face for a complementary-shaped, outwardly sloped, over-fitting, mounting flange or rim 11a of the upper end wall 11 (see FIG. 3). Also, the side wall 10 has a circular, downwardly extending flange portion 10b of at least the full depth of the convex curvature of the bottom end wall 12. The outward convex shape of the angle-shaped mounting flange 11a, as well as the outward convexity of the side wall 10 and the end walls 11 and 12 provide a container construction of generally outwardly convex curvature that is able to withstand internal pressure forces that may otherwise tend to deform and thus weaken the casing or tank. The strength characteristics of the casing can thus be accurately predicted on the basis that fault-produced fluid pressure exerted internally against the wall, will have no deforming effect on its walls. 
     With particular reference to FIGS. 3 to 7, inclusive, the upper end wall 11 of the generally outwardly convexly shaped casing or tank of the unit A has a slightly sidewise-offset, open hole portion therethrough that provides a combined pressure relief and maintenance hand hole as defined by a seating flange 11b thereabout. As shown particularly in FIG. 3, the flange 11b is of angle-shape and has a horizontally planar underside portion a which is adapted to receive and position a cross-extending clamping member 30 (shown on channel-shape) to retain a cover assembly 15 in position with respect thereto. An innermost ring-like rim portion b of the flange 11b surmounts a horizontally planar upper seating face of ledge portion c that is in a direct parallel and opposed relation with respect to the underface a. When the cover assembly 15 is in a closed position such as shown in FIG. 3, the ledge portion c, in combination with the rim portion b, serves to receive and position a ring-like resilient seating gasket 17 of rectangular section thereon. 
     The assembly 15 has an outwardly convex or dome-shaped cover part or cap 16 that has a central opening therethrough to position and receive an operating stem 20. The cover 16 has a sealing flange portion 16a which on its underside is horizontally planar in a complementary manner with respect to the opposed upper face c of the flange 11b, and which is downwardly surmounted by a rim edge portion to receive and cooperate with the gasket 17. The gasket 17 may be cemented to either the under surface of flange 16a or to the upper face c of the flange 11b in such a manner that the opposed flanges will serve to provide a full closure of the open portion defined by the inwardly extending flange 11b of the end wall 11. 
     The operating stem 20 is carried for rotative movement with respect to the cover 16 by a bearing gasket 21 of a suitable relatively stiff resin material such as Teflon that is secured on the upper side of the cover. A handle portion, such as a cross bar or lever 22, is carried in a secured relation on the upper end of the stem 20 for manually rotating or turning it within and with respect to a nut 28 that is mounted on its lower threaded end portion 20a. The lower extent of the threaded portion 20a is sufficient to permit the cover assembly 15 to, as shown in FIG. 4, have its parts loosely retained in position with respect to each other for insertion and removal with respect to the open portion defined by the flange 11b. An end collar or flange 20b serves as a stop for limiting the maximum upward movement of the stem 20 within the nut 28 to thus prevent a separation of the cover assembly, such as may entail a fishing operation within the interior of the transformer tank. 
     Spring and clamping means is carried on the stem 20 and has a U-shaped bracket 27; the nut 28 is secured to an underside of its horizontal connecting portion, as by weld metal w. The bracket 27 has a pair of leg portions which extend upwardly from its central connecting portion to at least the height of the clamping member 30, in order to cooperate with opposite sides of the member 30 and prevent turning of the nut 28 when the stem 20 is being rotatably adjusted. The clamping member 30 which may also be a solid bar rather than a channel-shaped member, as shown particularly in FIGS. 6 and 7, is adapted at one end to abut against a downwardly projecting latching or stop lug or pin 13 that is shown welded to the underside portion a of the flange 11b, see FIGS. 3 and 7. The pin 13 limits rotation of the member 30 during turning movement of the stem 20 and thus, indirectly prevents rotation of the nut 28 through the agency of the bracket 27 whose legs project upwardly on opposite sides of the member 30. 
     Spring means 25, shown as a so-called Belleville washer type, may also for example, comprise one or more concentric helical springs. The spring means 25 at its upper end engages the underside of the clamping member 30 and its lower end may either directly engage the underside of the bracket 27 or engage abutment washer 26 that may be provided on the innerside of the connecting portion of the bracket 27. The spring means 25 is thus operatively positioned along the stem 20. When the stem 20 is, for example, rotated clockwise to effect upward rise of the nut 28 and the bracket 27 (see FIG. 6) by turning threaded portion 20a within the nut 28, a maximum compression force is exerted on the spring 25 that corresponds to the maximum normal operating pressure force to be permitted in the container or tank before it is released. It may, for example, be approximately 9 or 10 lbs./sq. in. The use of a lower force action eliminates any need for a conventional side-mounted relief valve; and rotating the stem 20 in the opposite direction to remove the cover 16 operates to bleed-off gas under moderate pressures below the operating pressure of the assembly. 
     The amount of potential tension force to be exerted by the spring means 25 is thus controlled by the upper extent of the threaded portion 20a. The operation of the assembly 15 is such that it will not only open at a set lower operating pressure force such as 9 to 10 lbs./sq. in., but will also immediately and effectively have a uniform opening cation under fault-generated high pressures of several hundred lbs./sq. in., to thus immediately relieve such pressure as it starts to build up and during its full period of exertion. This instant relief action prevents a large build-up of the pressure force which would tend to blow-off a cover or distort or damage the walls of the container. 
     The casing or tank of the unit A may be of any suitable material such as metal coated on the outside with a protective resin, the gasket 17 may be of a resilient resin or rubber-like construction, and the cover assembly 15 may also be of metal. It will be noted that the construction and operation of the cover assembly 15 is such that it will open substantially uniformly to define a fully circular opening to relieve pressure. Due to the operation of the spring means 25 the assembly 15 may be only slightly opened for normal operating low pressure release, but will be fully opened when the pressure is of a type such as generated by a transformer fault. 
     In the representative circuit diagram of FIG. 1A, a pair of high voltage input leads 31, 32 are shown connected to the primary D of the transformer unit A through at least one current limiting fuse 33. However, for maximized protection from the standpoint of a possible grounding, a second current limiting fuse 34 is shown. These fuses may be mounted outside the unit A. The output from the secondary E of the transformer is shown as consisting of leads 35, 36 and 37, with the lead 37 providing a neutral terminal that is grounded to the transformer casing consisting of side wall 10 and integral end walls 11 and 12. 
     By way of example, a pole type of transformer of the invention may be provided with a casing or tank designed to withstand about 200 lbs./square inch pressure. A typical transfer rate of efflux of about 60 cu. ft. per second atmospheric will result from an internal (tank) pressure of about 25 lbs./sq. inch gauge. The current limiting fuses 33 and 34 positioned outside the transformer may each have a current cut-off rating of or be set at about two times the current rating of the transformer. At least one such fuuse is important in limiting the period of fault-generated pressure build-up in the transformer to thus assure total blow-out protection. This protection not only applies to the blow-out of oil or dielectric fluid, but also of melted copper windings, paper and other material that may be activated by the transformer fault to seek release from the securely sealed or integral, closing-off side and top and bottom end walls of the transformer enclosure. 
     The exemplary so-called Belleville washer spring type is generically a tension-exerting stack of conical disc spring elements. A bell-mouthed shaped stacked spring assembly or any other suitable type of axially aligned tension-exerting spring may be employed for the spring means 25.