US3652812A

US3652812A - Tap changer switch with radial pressurized movable contact structure

Info

Publication number: US3652812A
Application number: US75916A
Authority: US
Inventors: Donald J Ristuccia
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-09-28
Filing date: 1970-09-28
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28
Also published as: CA926901A

Abstract

A tap changer switch for mounting within the casing of an electrical transformer, and operable from outside the casing. An insulating base member carries a plurality of stationary contacts, adapted for connection to the transformer winding, and a shaft member is disposed through an opening in the insulating base member such that it extends outwardly from both sides thereof. One outwardly extending portion of the shaft member carries a movable contact assembly which selectively shorts two adjacent stationary contacts, and the other outwardly extending portion of the shaft member is adapted to extend through the wall of the casing of the associated transformer, and it includes a handle for rotating the shaft and selecting the two stationary contacts to be shorted.

Description

United States Patent Ristuccia [451 Mar. 28, 1972 [72] Inventor: Donald J. Rlstuccia, Athens, Ga.

[73] Assignee: Westinghouse Electric Company, Pittsburgh, Pa.

[22] Filed: Sept. 28, 1970 [21] Appl. No.: 75,916

[52] US. Cl. ..200/8 R, 200/11 TC, 200/166 BB [51] ..H0lh 19/56 [58] Field of Search ..200/8 R, 11 TC, 166 BB [56] References Cited UNITED STATES PATENTS 2,903,530 9/1959 Wilson, Jr. ..200/8 R X 1,285,786 11/1918 Nies ..200/8 R 1,412,002 4/1922 Hendricks, Jr ..200/8 R 1,458,484 6/1923 Habicht ..200/8 R X 1,725,078 8/1929 Hill ..200/8 R 1,785,575 12/1930 Blume ..200/8 R 3,170,048 2/1965 Glatz et al... ...200/11 TC 3,467,794 9/1969 Ristuccia ..200/11 TC Primary Examiner-J. R, Scott AttorneyA. T. Stratton, F. E. Brouder and D. R. Lackey [5 7] ABSTRACT A tap changer switch for mounting within the casing of an electrical transformer, and operable from outside the casing. An insulating base member carries a plurality of stationary contacts, adapted for connection to the transformer winding, and a shaft member is disposed through an opening in the insulating base member such that it extends outwardly from both sides thereof. One outwardly extending portion of the shaft member carries a movable contact assembly which selectively shorts two adjacent stationary contacts, and the other outwardly extending portion of the shaft member is adapted to extend through the wall of the casing of the associated transformer, and it includes a handle for rotating the shaft and selecting the two stationary contacts to be shorted.

10 Claims, 7 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to tap changers for electrical transformers, and more specifically to tap changers adapted. for mounting within the casing of a transformer and operable from outside the casing.

Description of the Prior Art US. Pat. No. 3,467,794, which is assigned to the same assignee as the present application, discloses a tap changer switch of the type which is mounted wholly within the casing of an electrical distribution type transformer, and connected to a plurality of taps on the high voltage winding thereof. The desired tap position is selected by the electrical utility at the time of installing the transformer, as required by the specific operating location within the electrical distribution system. If the conditions change at some time in the future, requiring a higher or lower tap setting to provide the desired output voltage, the tap changer switch may be set to the desired new operating position. However, since the tap changer switch is mounted wholly within the casing, the transformer cover, or the cover of a sealed hand-hole opening in the cover, must be removed to permit access to the operating handle of the tap changer switch. While the frequency of required tap changes during the normal service life of a distribution transformer is very low, it would be desirable to be able to operate the tap changer without breaking the transformer seal. In addition to being time consuming and, therefore, costly, each time the transformer seal is broken opportunities are present for contaminating the mineral oil, which may shorten the useful operating life of the transformer.

The tap changer switch disclosed in the hereinbefore mentioned US. Pat. substantially reduced the manufacturing cost of the tap changer, compared with certain tap changers of the prior art, and it would therefore be desirable to utilize the basic switching mechanism of this tap changer for an externally operable tap changer switch. However, extending the 'length of the operating handle of this switch through a sealed opening in the casing of the distribution transformer presents both space and functional problems. The movable contact of the switch mechanism is at an elevated potential, i.e., such as about 50 percent of the line potential, and therefore the handle must be extended to provide the required clearance between the movable contact and the wall of the casing. The length of the required shaft extension is such that the switch requires a substantially larger space within the transformer, interfering with the space and electrical clearances required by the secondary circuit breaker, as well as other apparatus mounted in the oil above the transformer, such as protective fuse links. Thus, changing the orientation of the switch operating shaft from vertical to horizontal and bringing the shaft through the side wall of the casing to make it externally operable, presents problems in obtaining the desired insulating clearances, and may require a larger tank size than would .be required by a similar switch wholly mounted within the casing. Maintaining the switch in its prior art vertical position and ,extending the shaft through a sealed opening in the cover of the transformer isalso undesirable, as not only would a long.

operating shaft be required in order to keep the switch operat-. ing mechanism below the oil level, it would present assembly problems. Longtap leads would have to be connected to the.

switch if the switch were to be mounted on the cover, which would create mechanical and electrical problems whenthe cover is mounted on the tank. The switch would also be more difficult for the lineman to actuate.

An unduly long operating shaft on the tap changer switch may present functional problems, as at least theportion of the shaft'to which the movable contact member is fixed must be formed of an insulating material, such as wood or a synthetic resin material, which may warp, bend or twist if supported only at its extreme inner end and at the tank wall, and actu- SUMMARY OF THE INVENTION "Briefly, the present invention is a new and improved tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, which enables the relatively low cost but reliable contact mechanism disclosed in U.S. Pat. No. 3,467,794 to be utilized without requiring the useof an unduly longoperating shaft which would present the space and support problems hereinbeforedescribed. Specifically, the new and improved tap changer switch includes an insulating base member having first and second ends or sides, an opening which extends between its sides, and a plurality of stationary contact members which extend outwardly from its first side in spaced, circumferential relation about the opening. A shaft member having first and second ends is disposed through the opening, rotatably supported by bearing means associated with the insulating base member, such that the shaft issupported near its midpoint, with the first end of the shaft extending outwardly past the first side of the insulating'base member, and past the ends of the outwardly extending stationary contacts, and the second end of the shaft extending outwardly past the second side of the insulating base member, and through an opening in a mounting hub, which is sealingly mounted through an opening in the transformer casing. The shaft extends through the mounting hub for a sufficient distance to enable an operating handle to be fixed to this end of the shaft, which is outside the casing. The insulating base member is thus disposed between the movable contact and outwardly extending stationary co'ntacts, and the casing, enabling the insulating base and contact structure to be mounted close to the. wall of the tank or casing. The operating shaft, being supported near its midpoint, and also at the wall of the casing by its mounting hub, ensures that it will not warp, bend or twist to the point where it would hinder or prevent operation of the tap changer at some future date.

BRIEF DESCRIPTION OF THE DRAWING FIG. 3 is an end-view of the tap changer switch FIG. 2,as viewed from outside the casing of the'dis'tribu'tion transformer;

FIG. 4 is a side elevational view, partially in section ora ap changer switch constructed according to 'aIiotlferernbodiment of the invention; I

FIGJS is an exploded perspective view Iof the movable contact structure of the tap'changer switchshdwn inFIG. 4;? FIG. 6 is a fragmentary sectional'elevationof a tap cha n ger switch constructed accordingto another 'embodIment of the invention; and

FIG. 7 is an exploded perspective view of the "mdvable'bon tact structure of the tap changer switch s'hown in'FlG. 6.

DESCRIPTION or PREFERRED: EMBODIMENTS Referring now to the drawings, F IG'. 1 is a partialiy exploded perspective view of a tap changer switch 10 constructedac cording'to the teachings of the'inventiomand' FIGS. 2 and 3 are side and end elevational views, respectively, of tap changer switch 10 shown mounted through the side wall por tion 12 of an electrical distribution transformer. The operating mechanism 11 of tap changer switch is disposed below the oil level 14 of the transformer, and it includes contacts, such as

contacts

32 and 40, which are connected to the high voltage winding of the transformer, such as via

electrical leads

16 and 18, respectively.

Tap changer switch 10 includes an insulating base member 20 formed of an insulating material compatible with the mineral oil insulating and cooling dielectric normally used in distribution transformers, such as a molded glass filled polyester material, with the insulating base member 20 having first and second sides or

ends

21 and 23, and a substantially centrally disposed hub portion 22. Hub portion 22 has first and

second ends

24 and 26 located on

sides

21 and 23, respectively, of the insulating base member 20, and a main opening 28 which extends between its ends. Main opening 28 in hub 22 has a first inside diameter which steps outwardly to larger second and third inside diameters adjacent its first and

second ends

24 and 26, respectively, providing a shoulder or step between the first and second inside diameters, and a shoulder or step between the first and third inside diameters, for purposes which will be hereinafter explained.

Insulating base member 20 also includes a plurality of additional openings which extend between its first and

second sides

21 and 23, for receiving a plurality of stationary electrical contact members. The plurality of additional openings are disposed about the main opening 28, and spaced circumferentially about an imaginary circle whose center coincides with the axis of the main opening 28. The number of these additional openings depends upon the number of operating positions the tap changer 10 is to include. As illustrated in the Figures, tap changer 10 has five operating positions, which requires a total of six stationary contacts referenced 30, 32, 34, 36, 38 and 40, and thus six openings are required through the base member 20 for receiving the stationary contact members.

The

stationary contact members

30, 32, 34, 36, 38 and 40 each have first and second ends, such as first and second ends 42 and 44, respectively, on stationary contact member 32, with their second ends being disposed in one of the openings which encircle the main opening 28. The stationary contact members are fixed in the openings such that their first ends extend perpendicularly outward from at least the first side 21 of the base member 20 for a predetermined dimension. As will be hereinafterexplained, the loading on the stationary contacts will be radial, and not axial. Therefore, the stationary contacts may be constructed of cylindrical, tubular electrically conductive material, such as copper tubing, having predetermined inside and outside diameters. The predetermined outside diameter is selected to provide a clearance fit with the diameter of the plurality of openings in the base member 20. The contact members are cut to length from the tubing, and they are each flared outwardly with a suitable tool to provide a circumferential bulge or protrusion therein apredetermined dimension from their second ends, such as the circumferential bulge 46 shown on contact member 32. The stationary contact members may have their second ends inserted into the plurality of openings, starting at the first side 21 of the insulating base member 20, until their circumferential protrusions reach the start of its associated opening in the base member 20. The dimension of the circumferential protrusion near the second end of each contact member is selected such that its second end extends outwardly from its associated opening for a distance sufficient to allow it to be flared radially outward and provide a lip, such as lip 48 on the second end 44 of stationary contact member 32, adjacent to the opening, to firmly secure the stationary contact members within their associated openings.

The opening in each of the tubular stationary

electrical contact members

30, 32, 34, 36, 38 and 40, facilitates the connection of the electrical leads from the transformer winding thereto. For example, as shown in FIG. 2, the electrical insulation may be stripped from the ends of the tap leads, and each may be inserted into the opening in one of the stationary contacts, starting at its second end, such as lead 16 shown entering the second end 44 of contact member 32. The wall of the tubular contact adjacent the bared end of the lead may then be crimped or otherwise pressed inwardly, as shown at 50 on contact member 32, to firmly grip the lead and provide an excellent electrical contact between the stationary contact member and its associated electrical lead.

A metallic mounting hub 60 is provided, which may be economically die cast, such as from aluminum or brass, having first and second ends 62 and 64, respectively, a mounting flange 66 disposed between its

ends

62 and 64, and an opening 68 which extends between its ends. A first substantially cylindrical portion 70 is provided adjacent end 62, which has a plurality of threads 72 disposed on its outer surface, and parallel

flat portions

74 and 76 are cut on opposite sides thereof, which flats aid in orienting the mounting hub with respect to the insulating base member, as will be hereinafter explained. A second cylindrical portion 78 is provided adjacent end 64, which has a plurality of threads 80 disposed on its outer surface. Cylindrical portion 78 steps outwardly to provide the hereinbefore mentioned mounting flange 66, forming a flat surface 82 facing end 64 of the mounting hub 60, in which an annular groove is disposed for receiving a gasket member 84.

Opening 68 in mounting hub 60, and opening 28 in the insulating base member 20 are coaxially aligned, and this alignment maintained, as well as the required circumferential orientation of the insulating base member 20 relative to the mounting hub 60, by a bracket member which has first and second spaced

parallel portions

92 and 94, respectively, and a portion 96 which interconnects the spaced

parallel portions

92 and 94. Portion 92 of mounting bracket 90 has spaced openings therein, into which nut and

bolt assemblies

98 and 100 may be inserted, and also through similarly spaced openings in the insulating base member 20, to fix the insulating base member to the bracket member 90. Portion 94 of bracket member 90 has a single opening disposed therein, shaped to snugly receive the configuration of portion 70 of mounting hub 60, with the

flat portions

74 and 76 properly orienting the mounting hub 60 relative to the insulating base member 20. A nut 102 is threadably engaged with portion 70 of mounting hub 60, after end 62 has been inserted through the opening in portion 94 of the bracket 90, to secure the mounting hub 60 to the bracket member 90. Operating shaft means 110, having first and second ends 112 and 114, is disposed through the opening 28 in the insulating base member 20 such that the first end 112 extends outwardly past the first side 21 of the insulating base member 20, and past the ends of the outwardly extending stationary contact members, such as past the end 42 of stationary contact member 32, for a sufficient distance to carry a movable contact assembly 120, which will be hereinafter described.

Operating shaft means also extends outwardly from the second side 23 of insulating base member 20, for a distance sufficient to extend completely through the opening 68 in the mounting hub 60, and pass the second end 64 of the mounting hub for a sufficient dimension to permit an operating handle 130 to be fixed thereto, as will be hereinafter described. Shaft means 110 has first and second portions 122 and 124, of different diameters, with portion 122 being associated with the insulating base member 20, and with portion 124 extending through the mounting hub 60. Portion 122 of shaft means 110 has two spaced circumferential grooves 116 and 118 disposed therein, such that the grooves are within opening 68 of mounting hub 60, with resilient gasket or O-ring members 117 and 119 being disposed in the circumferential grooves 116 and 1 18, to seal the opening 68 while allowing rotary motion of the shaft means 1 10.

At least the portion 122 of shaft means 110, to which the movable contact assembly 120 is fixed, is formed of an electrical insulating material, such as wood or a synthetic resin, such as glass filled polyester, or a glass filled polyamide. Thus, the shaft means 110 may be of one-piece construction, being wholly formed of insulating material; or, as illustrated in FIG. 2, shaft means 110 may have portion 122 formed of an insulating material, to which the movable contact assembly is attached, and portion 124 may be formed of a metal, such as brass, with portions 122 and 124 being fixed to one another by any suitable means, such as by an extension 126 on portion 124 which enters an opening in the adjacent end of portion 122, and a pin 128 which enters aligned openings in both portrons.

Shaft means 110 is fixed within opening 28, in rotary relation with base member 20, by

washer members

132 and 134, respectively, and a pin member 136. Washer member 134 is not essential, as handle 130 will prevent axial movement of shaft 110 in the direction into the casing, but may be used if desired. Washer member 134 is a metallic retainer type washer formed of a material such as steel, which has an inside diameter sized to allow it to be pressed over the second end 114 of shaft means 110 to the desired location, and to bite into the shaft and to resist any further relative movement between the shaft and washer. Washer member 134 has an outside diameter sized to cooperate with the surface which defines the third inside diameter of opening 28, adjacent end 26 of hub portion 22, to provide a radial bearing which allows the shaft means 1 l0 and washer member 134 to rotate when the shaft is turned. In other words, the outside diameter of washer member 134 is just slightly less than the third inside diameter of opening 28 adjacent end 26. Washer member 134 is disposed adjacent the step formed by the first and third inside diameters of opening 28, with the step in washer member 134 cooperating to provide a thrust bearing when an attempt is made to move shaft 70 axially in the direction from end 23 to end 21 of the insulating base member 20.

Washer member 132 may be a conventional metallic washer formed of steel, which has an inside diameter slightly larger than the outside diameter of portion 122 of the shaft means 110, to allow it to be easily slipped over the shaft, and an outside diameter sized to cooperate with the surface which defines the second inside diameter of opening 28, adjacent end 24 of the hub portion 22, to provide a radial hearing which allows shaft means 110 to rotate when the shaft is turned. The radial bearing at end 24 of hub portion 22 may initially be between the shaft means 110 and the inside diameter of washer member 138, since the shaft outside diameter is slightly smaller than the inside diameter of washer member 132. However, if the outside diameter of the insulating portion 122 of shaft means 110 swells to the point where it causes the washer member 132 to be fixed to the shaft, the shaft and washer member 132 will turn together and the radial bearing will then be between the outside diameter of washer member 132 and the surface which defines the second inside diameter of opening 28.

The pin member 136 is disposed through a transverse opening formed in the shaft portion 122, immediately adjacent to washer member 132, such that the pin member 136 will retain washer member 132 within the second inside diameter of opening 28. When an attempt is made to move shaft 70 axially in the direction from the first end 21 to the second end 23 of base member 20, the pin 136 functions as a thrust bearing by contacting the surface of base member 20 surrounding the opening 28, and the surface of washer member 132. Any axial force placed on washer member 132 will be resisted by the step formed between the second and first inside diameters of opening 28. Therefore, the washer member 132 and adjacent step also cooperate to provide a thrust bearing.

The pin 136 extends outwardly from one side of the shaft means 110 for a predetermined dimension, which also allows it to cooperate with a projection 140, best shown in FIG. 1, which projects outwardly from end 24 of the hub portion 22, to provide a positive stop at both the lowest and highest numbered tap positions. The arcuate dimensions of projection 140, and the orientation of pin member 136, are selected according to the number of tap positions the tap changer is to have. Projection 140, in this example, is sized to allow five tap positions, with the first tap position starting between

stationary contacts

30 and 32, and the fifth tap positions being between

contacts

38 and 40. The projection and pin 136 will not allow a tap changer position between

stationary contacts

30 and 40.

The movable contact assembly 120 is fastened to portion 122 of shaft means 110. Movable contact assembly 120, in this embodiment, includes a leaf spring 142 and a contact shoe 144. Leaf spring 142, which may be formed of a good spring material such as 18-8 stainless steel, has an obtuse bend 146 therein, forming a first straight portion 148 and a second straight portion 150. The first straight portion 148 of the leaf spring 142 is fastened to shaft portion 122, such as by screws 152, such that the second straight portion 150 extends outwardly from shaft portion 122 towards end 114 of the shaft means 110. Leaf spring 142 is fixed to shaft portion 122 at a location which will cause the end of the second straight portion 150 to be adjacent to the plurality of stationary contacts.

Contact shoe 144 may be formed of any suitable electrical conductor. For example, sintered powdered copper or brass, or combinations thereof, may be used since the contact shoe may be molded to the required shape. Contact shoe 144 is fixed to the outwardly extending end of the second straight portion 150 of leaf spring .142, and it is sized such that it will extend between and contact two adjacent stationary contact members, such as

contact members

30 and 32 as illustrated in FIG. 1, under a positive radial force provided by leaf spring 142. To provide the positive detent or snap action necessary when the tap changer reaches an operating position, as well as to wipe the contacts clean as the tap changer is actuated to change tap positions, the contact shoe 144 should have a substantially trapezoidal shape or configuration in a plane which is substantially perpendicular to the axis of the shaft means 110. The small end of the trapezoidal configuration extends between two adjacent spaced stationary contact members, and the large end of the trapezoidal configuration should be longer than the distance between two stationary contacts, in order to cause the contact shoe 144 to contact the stationary contacts with its two surfaces which slope inwardly from the large end to the smaller end.

Since the force applied to the stationary contacts is radial, the movable contact assembly 120 should be positioned axially with respect to shaft means 110, such that the contact shoe 144 will contact the stationary contact members as close as practical to the points where they are secured to the base member 20, in order to insure that the stationary contacts will remain parallel with one another.

Tap changer 10, as described to this point, is now ready for mounting through an opening in the side wall 12 of the transformer casing. The desired orientation of the tap changer switch 10 may be obtained by disposing a longitudinal groove across portion 78 of the mounting hub 60, which is aligned with an oriented projection which extends into the opening in the wall 12 of the transformer casing into which the tap changer switch is to be mounted. If the bracket member 90 is formed of an insulating material, as illustrated in FIG. 2, tap changer switch 10 may be oriented as shown in FIG. 2, relative to the oil surface 14. If the bracket member 90 is formed of a metal, adequate clearance between the tap leads and the bracket member 90 may be obtained by mounting the tap changer 10 such that it is rotated from the orientation shown in FIG. 2, such as shown in the embodiment of FIG. 4.

Prior to inserting end 64 of mounting hub 60 into the opening in casing 12, gasket member 84 is placed in the annular groove in the face of the flange portion 66. Then, after end 64 has been inserted into the opening in the casing 12, gasket member 162 is inserted over end 64, against the outside wall of the casing 12, and then one or more nuts, such as nut 164, is threaded over portion 78 of the mounting hub 60, to firmly secure the tap changer 10 to the casing 12.

Operating handle 130, having a blind opening 164 sized to snugly receive end 114 of shaft means 110, and a transverse opening 166 for receiving a pin 168, is then slipped on end 114 of the operating shaft means 110, with opening 166 being aligned with a similar sized opening through portion 124 of the shaft means 110. Pin 168 is then forced into the aligned openings to secure the operating handle 130 to shaft portion 124, with the handle automatically being oriented according to the operating position of the tap changer 10. End 64 may have'numbers cast therein to identify the operating position of the switch, as shown in FIG. 3, and the tap changer operating handle 130 may be locked in the desired operating position, preventing accidental movement of the operating handle, by providing a blind opening in the end 64 of mounting hub 60, adjacent each operating position, such as

openings

180, 182, 184, 186 and 188, and a threaded opening 170 through the operating handle 130 for receiving a bolt 172. When it is desired to operate the tap changer, bolt 172 is backed out of the opening disposed in end 64, into which it is extending, the tap changer 10 is actuated to its new tap position, and then the bolt is advanced into the opening in end 64 associated with the new tap position, preventing any further rotary movement of the handle 130.

The hereinbefore described construction of tap changer l facilitates assembly of its component parts. The mounting hub 60 is preparedby attaching the bracket 90 thereto, with the nut 102. The stationary contacts may be inserted into the openings in the insulating base member 20, and then the second ends may be flared outwardly with a suitable tool, to secure them in their operating positions. The shaft means 1 may have the O-ring type gaskets 117 and 119 disposed in the annular grooves 116 and 118, respectively, pin 136 may be disposed through the transverse opening in the shaft means 110, and the movable contact assembly 120 may be fastened to portion 122 of the shaft means 110. Washer member 132 may be dropped into place in the base member or it may be disposed over the second end 1 14 of the shaft means 110. The second end 114 of shaft means 110 may then be inserted through opening 28, starting at the first end 24 of the hub portion 22. Retainer washer 134 may then be forced over end 114 of shaft means 110, as the end 1 l4 emerges from end 26 of the hub portion 22, and the shaft means 110 advanced into and through the opening 68 in the mounting hub, until the shoulder between portions 122 and 124 of the shaft means 110 contacts the first end 62 of the mounting hub 60. The bracket 90 may then be secured to the insulating base member 20 with the nut and

bolt assemblies

98 and 100, the tap changer 10 is ready for mounting in the transformer, as hereinbefore described. Before the transformer is filled with mineral oil, the tap leads are inserted into the openings of the respective stationary contacts, and secured thereto as hereinbefore described.

The operation of tap changer 10 requires only that the handle 130 and shaft means 110 be turned until the pointed end 190 of the handle 130 is in the desired tap position. Turning the handle 130 counterclockwise, viewing the tap changer 10 as shown in the position of FIG. 3, until pin 136 hits the positive stop provided by one side of projection 140, will cause the tap changer 10 to be in operating tap position No. 1. Turning the handle and shaft clockwise until pin 136 hits the positive stop provided by the other side of the projection 140 will cause the tap changer to be in operating position No. 5. As the handle and shaft are turned, one side of the contact shoe will wipe on one of the stationary contacts until reaching the small end of its trapezoidal configuration. The small end will continue to wipe across the contact, with the outwardly extending end of the leaf spring being forced inwardly toward the shaft means 110. As soon as the last portion of the small end of the contact shoe has moved over the stationary contact, the contact shoe will snap into the next operating position between two adjacent stationary contacts, under the influence of the bent leaf spring. Once in the new operating position, the leaf spring will continue to maintain a radial urging of the contact shoe against the stationary contacts, to assure good electrical contact.

FIG. 4 is an elevational view, partially in section, of a tap changer 10' constructed according to another embodiment of the invention. Like reference numerals in FIGS. 2 and 4 indicate like components, and like reference numerals, except for a prime mark in FIG. 4, indicate similar but modified components. The basic difference between the

tap changers

10 and 10 shown in FIGS. 2 and 4, respectively, is the construction of the movable contact assembly, with the construction of the movable contact assembly shown in FIG. 4 enabling the overall length of the tap changer 10' to be reduced, compared with the overall length of the tap changer 10 shown in FIG. 2. Tap changer 10' has also been modified in certain other ways, to be hereinafter described, which modifications may be used in the construction of the tap changer 10 shown in FIGS. 1 and 2, if desired.

More specifically, tap changer 10' shown in FIG. 4, is mounted through the side wall portion 12 of an electrical distribution transformer, with its operating mechanism 11' being disposed below the oil level 14 of the transformer. The insulating base member 20' of tap changer 10', including its stationary contacts, such as

stationary contacts

32 and 40, is similar to that hereinbefore described, with the base 20 being turned 180 about its longitudinal axis, compared with its FIGS. 1 and 2 orientation, to illustrate its use with a metallic mounting bracket The mounting hub 60', which may be machined or die cast of a suitable metal, such as aluminum or brass, has been changed in this embodiment to reverse the mounting flange, and thus enable the mounting hub 60' to be inserted into an opening in the casing 12 from the outside thereof, prior to its assembly with the operating mechanism 11'. Mounting hub 60 has a threaded portion 240 sized to enable it to be inserted through an opening in the casing 12, until a flanged portion 241 contacts the casing 12. The flanged portion'241 is formed by an outward step from portion 240 to a portion 242 of larger diameter. The flanged portion 241 has an annular groove formed therein which contains a gasket member 244, which hermetically seals the opening in the casing 12 when the mounting nuts 246 are threadably engaged with portion 240 and tightened. Prior to threading the nuts 246 on the threaded portion 240 of the mounting hub 60, portion 94 of the mounting bracket 90' may be inserted over the threaded portion 240, to secure the mounting bracket to the mounting hub 60.

The operating shaft includes a molded insulating portion 200, formed of a material such as a glass filled polyamide, or a glass filled polyester, and

metallic inserts

202 and 206, formed of a material such as brass, extend coaxially outward from opposite ends of the molded insulating portion of the shaft. Insert 202 includes two spaced circumferential grooves in which O-rings 117 and 119 are disposed, which seal the opening through the mounting hub 60' when the insert 202 is inserted therethrough. An opening is provided near the outwardly extending end 114 of insert 202, for receiving a pin 168 which orients and secures the operating handle 130 to the operating shaft 110'.

Insert 206 is threaded on its outwardly extending end, to receive a nut 224, the purpose of which will be hereinafter explained.

Operating shaft 1 10 also has a radial and thrust bearing 204 molded therein, instead of utilizing separate washer and pin members. Retainer washer 134 may be used, if desired, but it is not essential, as the operating handle 130 will prevent movement of the shaft 110 in the direction from its end 114' to its end 112'.

The movable contact assembly has been changed in this embodiment, to enable the axial length of the tap changer switch 10 to be reduced, compared with the tap changer switch 10 of FIGS. 1 and 2. FIG. 5 is an exploded, perspective view of the movable contact assembly 120', which will be referred to, along with FIG. 4, in the following description of the new contact assembly 120'.

The molded portion 200 of the operating shaft 110' has a circular projection 208 disposed transverse to the longitudinal metallic housing 212 having a substantially U-shaped portion 217, and a flat top portion 219 which joins the upwardly extending ends of the U-shaped portion 217. The housing 212 has first and second ends 213 and 215, a major opening 218 which extends between its ends, and aligned slots or

openings

214 and 221 which are disposed through the leg portions of the U-shaped member 217. The top portion 219 has an integral'tap portion 216 which extends outwardly therefrom, in

substantially the same shoe 144 is fixed.

The metallic housing 212, with the contact shoe 144 fixed thereto, is telescoped over end 112 of the operating shaft and aligned with the projection 208, such that spring member 236 presses against the inside surface of the top portion 219. Thus,

plane, to which the contact or shorting the housing 212 and contact shoe 144 are urged radially outward, away from the axis of the operating shaft 110', by the spring member 236.

A pin 230 is disposed through an opening 210 in the molded portion 200 of the operating shaft, such that its ends ride in the slots 214 and 22] disposed in the U-shaped housing 212. A fiat plate member 220 having first and second major opposed sides or surfaces, and an opening 222 which extends between its major opposed surfaces, is telescoped over end 112 of the operating shaft 110, against the shoulder 23] formed by the end of the molded portion 200, with one of its major surfaces being against the end 213 of the housing 212. Nut 224 is threadably engaged with the outwardly extending threaded portion of insert 206, and it is advanced inwardly until it secures the plate member 220 firmly against shoulder 231. The housing 212 and its contact shoe 144 are now free to slide back and forth without cocking or tipping, as it is guided by one of the major surfaces of the plate member 220, and by the pin member 230 riding in the

slots

214 and 221 of the housing 217. When the operating handle 130 is turned to actuate the tap changer switch 10' to a new operating position, the contact shoe 144 and housing 217 will be pushed inwardly, by one of the stationary contacts, towards the axis of the operating shaft 110' compressing the spring 236 between the housing 212 and the operating shaft. As the interfering stationary contact is cleared by the contact shoe, the contact shoe and its associated housing 212 will snap outwardly, away from the operating shaft 110, due to the influence of the spring member 236, to force the contact shoe 144 firmly between and in contact with two stationary contacts, as hereinbefore described relative to FIGS. 1 and 2.

in the assembly of the tap changer switch 10', the operating shaft 110' and its movable contact assembly 120 may be inserted through the opening in the base member The mounting hub 60 and the bracket member 90 may then be fixed to the casing 12 with the nut members 246. End 114 of the operating shaft 110' may then be inserted through the opening in the mounting hub 60', and secured in position by connecting the base member 20' to the mounting bracket 90', and by fixing the operative handle 130 to the operating'shaft 110'. Since the movable. contact assembly 120" no -longer requires a relatively. long leaf spring membenthe operating shaft 110' may be. reduced in length accordingly, which reduces the overall length of the tap changer switch 10', presentingless interference within the transformer casing to theother parts mounted above the transformer.

FIG. 6 is a fragmentary, elevationalview, partially in section, of a tap changer switch 10'' constructed according to still another embodiment of the invention. Tapchanger 10'" is similar in construction to tap changer 10 shown in FIG. 4, except for the movable contact assembly. Instead of a separate the core and coil assembly of contact housing which moves relative to the shaft, as disclosed in FIG. 4, FIG. 6 discloses an embodiment of the invention wherein the contact housing ,is fixed to theshaft, and thus it may economically be formed as an integral part of the insulating portion of the operating shaft. v

More specifically, tap changer 10' includes an insulating base portion 20", constructed as hereinbefore described, and a movable contact assembly 250. Movable contact assembly 250 includes a contact housing 256, a helical spring 260, and a roller type contact assembly 262. The contact housing 256 may be'formed as an integral portion ofthe operating shaft 252, with the remaining portion of the operating shaft being similar in construction to the operating shaft shown in FIG. 4. Contact housing 256, which may be formed of any suitable insulating material, such as a glass filled polyamide, includes first and second spaced, parallel finger"

portions

257 and 259, respectively, which definea slot'26l having an open end and a closed end. A circular projection 258,

disposed with its axis'transverse to the an er operating shaft 252, extends into the slot 261 from its closed end, and the spring 260 is disposed in the slot 261 such that it encircles the projection 258. a

The movableroller contact assembly 262, which is formed of a good electrical conductor, such as brass, has a substantially spool-like configuration, including first and second wafer or disc-shaped

contact members

264 and 266, which are held in fixed, spaced parallel relation by a coaxially disposed shaft member 268 of smaller diameter than the contact members.

The movable contact assembly 262 is disposed in the slot 261 such that the shaft 268 extends through the slot 261 and the spring 260 exerts an outward force on the shaft 268. Shaft member 268 has a diameter selected to allow a smooth, free, sliding fit between the shaft and the inner walls of the slot 261 with minimal play, and the length of the shaft 268 isselected to provide a smooth, free, sliding fit between the inner surfaces of the

contact members

264 and 266 and the surfaces of

fingers

257 and 259 which are perpendicular to the longitudinal axis of operating shaft 252, such as surface 269.

In the assembly of tap changer switch l0" the spring 260 is placed over the projection 258, the shaft portion 268 of the roller contact assembly 262'is placed in the slot 261, and pressed inwardly against the spring 260; The handle end of the base member 20, and a washer 254 is slipped over the operating shaft, which functions as a first bearing, and also to prevent axial movement of the operating shaft, if desired. Axial movement of the operating shaft in the opposite direction is prevented by projection 271 on the operating shaft, which functions as a second bearing. vThe assembly of tap changer switch 10 may then be completed ,asjhereinbefore described relative to tap changer 10' shown in F 16.4.

In the operation of tap changer 10", when the operating shaft 252 is rotated to select a new tap position, the roller contact assembly 262 will be forced inwardly byone ofthe stationary contacts, toward the axis of the operating shaft, and against the outward urging of the spring 260} As the centerline of the interfering stationary contact is passed ,'roller contact 262 snaps outwardly, under the urging influence of the

spring

260,16 force the contact members 264 and'266 of the contact assembly 262 into firm engagement with two adjacent stationary'contacts. H v

lrisur'nrnary, there has been disclosed a new and improved tap changer adapted for mounting within the casing of an electrical distributiontypetransformenwhich is operable from outside the casing. The operating shaft the gtap jchangcr extends outwardly from both sides of an insulating base assembly which carries the stationary contact, members, .toiotatably support the shaft intermediate its ends as well as-at amounting hub fixed to the casing of the transformer. The stationary contacts extend outwardly from one side of the insulating base member, away from the casing wall, and the movable contact member is mounted on the shaft on this same side of the insuother apparatus mounted above the core-winding assembly.

I claim as my invention: 1. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

a plurality of stationary electrical contact members, said stationary electrical contact members being carried by said insulating base member such that they extend outwardly from its first side, in spaced parallel relation with one another about the opening in said insulating base member,

a mounting hub having first and second ends, a mounting flange intermediate its ends, and an opening extending between its ends,

means holding said insulating base member and said mounting hub in spaced relation, with their openings in coaxial alignment,

shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension, said shaft means being a single member formed of electrical insulating material,

means rotatably supporting said shaft means in said insulating base member,

a movable contact assembly including a contact, and means urging the contact outwardly against two adjacent stationary contact members,

and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members.

2. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension,

means rotatably supporting said shaft means in said insulating base member,

said means including a leaf spring having first and second ends, with the contact being fixed to its first end, and with its second end being fixed to the shaft means, adjacent to the first end thereof,

3. The tap changer switch of claim 2 wherein said shaft means includes connected portions formed of electrical insulating material and metal, with the leaf spring being fixed to an insulating portion.

4. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

means rotatably supporting said shaft means in said insulating base member,

said movable contact assembly including a housing disposed about the shaft means to which the contact is fixed, and the means which urges the contact against the stationary contact members includes spring means disposed between a portion of the housing and the shaft means,

means guiding said housing through a predetermined movement transverse to the axis of the shaft means, against the urging of said spring means, when the shaft means is actuated to change the operating position of the tap changer switch, and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members.

5. The tap changer switch of claim 4 wherein the housing -has an outwardly extending tab member, to which the contact 6. The tap changer switch of claim 4 wherein the shaft means has a substantially circular projection transverse to the axis of the shaft means, about which the spring means is disposed.

7. The tap changer switch of claim 4 wherein the means which guides the housing through the predetermined movement transverse to the axis of the shaft means includes first and second slots disposed in opposite sides of the housing, a pin member disposed through the shaft, means such that its ends ride in the first and second slots, and a flat plate member fixed to the shaft with its major surfaces perpendicular to the axis thereof, with one of its major surfaces being aligned with and in sliding contact with an end of the metallic housing.

8. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

means rotatably supporting said shaft means in said insulating base member,

and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members, the first end of said shaft means including a contact housing fixed thereto, with said contact housing having first and second spaced finger portions which define a slot having an open end and a closed end, and a projection disposed transverse to the axis of the shaft means which extends into the slot from its closed end, said means which urges the contact against the stationary contact members including spring means disposed about the projection, with the contact riding in the slot,

9. The tap changer switch of claim 8 wherein the contact is a substantially spool-shaped roller contact having first and second spaced circular members joined by a shaft, said shaft being sized to ride in the slot defined by the spaced finger portions of the contact housing.

10. The tap changer switch of claim 8 wherein the contact housing is an integral part of the shaft means.

Claims

1. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising: an insulating base member having first and second sides, and an opening which extends therebetween, a plurality of stationary electrical contact members, said stationary electrical contact members being carried by said insulating base member such that they extend outwardly from its first side, in spaced parallel relation with one another about the opening in said insulating base member, a mounting hub having first and second ends, a mounting flange intermediate its ends, and an opening extending between its ends, means holding said insulating base member and said mounting hub in spaced relation, with their openings in coaxial alignment, shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension, said shaft means being a single member formed of electrical insulating material, means rotatably supporting said shaft means in said insulating base member, a movable contact assembly including a contact, and means urging the contact outwardly against two adjacent stationary contact members, and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members.

2. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising: an insulating base member having first and second sides, and an opening which extends therebetween, a plurality of stationary electrical contact members, said stationary electrical contact members being carried by said insulating base member such that they extend outwardly from its first side, in spaced parallel relation with one another about the opening in said insulating base member, a mounting hub having first and second ends, a mounting flange intermediate its ends, and an opening extending between its ends, means holding said insulating base member and said mounting hub in spaced relation, with their openings in coaxial alignment, shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension, means rotatably supporting said shaft means in said insulating base member, a movable contact assembly including a contact, and means urging the contact outwardly against two adjacent stationary contact members, said means including a leaf spring having first and second ends, with the contact being fixed to its first end, and with its second end being fixed to the shaft means, adjacent to the first end thereof, and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members.

4. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising: an insulating base member having first and second sides, and an opening which extends therebetween, a plurality of stationary electrical contact members, said stationary electrical contact members being carried by said insulating base member such that they extend outwardly from its first side, in spaced parallel relation with one another about the opening in said insulating base member, a mounting hub having first and second ends, a mounting flange intermediate its ends, and an opening extending between its ends, means holding said insulating base member and said mounting hub in spaced relation, with their openings in coaxial alignment, shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension, means rotatably supporting said shaft means in said insulating base member, a movable contact assembly including a contact, and means urging the contact outwardly against two adjacent stationary contact members, said movable contact assembly including a housing disposed about the shaft means to which the contact is fixed, and the means which urges the contact against the stationary contact members includes spring means disposed between a portion of the housing and the shaft means, means guiding said housing through a predetermined movement transverse to the axis of the shaft means, against the urging of said spring means, when the shaft means is actuated to change the operating position of the tap changer switch, and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members.

5. The tap changer switch of claim 4 wherein the housing has an outwardly extending tab member, to which the contact is fixed.

6. The tap changer switch of claim 4 wherein the shaft means has a substantially circular projection transverse to the axis of the shaft means, about which the spring means is disposed.

7. The tap changer switch of claim 4 wherein the means which guides the housing through the predetermined movement transverse to the axis of the shaft means includes first and second slots disposed in opposite sides of the housing, a pin member disposed through the shaft means such that its ends ride in the first and second slots, and a flat plate member fixed to the shaft with its major surfaces perpendicular to the axis thereof, with one of its major surfaces being aligned with and in sliding contact with an end of the metallic housing.

8. A tap changer switch adapted for mounting within the casing of an electrical distribution transformer, and operable from outside the casing, comprising: an insulating base member having first and second sides, and an opening which extends therebetween, a plurality of stationary electrical contact members, said stationary electrical contact members being carried by said insulating base member such that they extend outwardly from its first side, in spaced parallel relation with one another about the opening in said insulating base member, a mounting hub having first and second ends, a mounting flange intermediate its ends, and an opening extending between its ends, means holding said insulating base member and said mounting hub in spaced relation, with their openings in coaxial alignment, shaft means having first and second ends, disposed through the opening in said insulating base member, with its first and Second ends extending outwardly from the first and second sides, respectively, of said insulating base member, and with its second end also extending through the opening in said mounting hub, and beyond the second end of the mounting hub by a predetermined dimension, means rotatably supporting said shaft means in said insulating base member, a movable contact assembly including a contact, and means urging the contact outwardly against two adjacent stationary contact members, and handle means fixed to the second end of said shaft means for rotating said shaft means and selectively engaging the contact with the desired stationary electrical contact members, the first end of said shaft means including a contact housing fixed thereto, with said contact housing having first and second spaced finger portions which define a slot having an open end and a closed end, and a projection disposed transverse to the axis of the shaft means which extends into the slot from its closed end, said means which urges the contact against the stationary contact members including spring means disposed about the projection, with the contact riding in the slot.