US2779844A - Equalized multiple high pressure contact - Google Patents

Description

Jan. 29, 1957 w. KOWALSKI 2,779,844

EQUALIZED MULTIPLE HIGH PRESSURE CONTACT Filed June 2, 1955 INVENTOR.

ZMz'Zter- HowaZskz' fittorngy United States Patent EQUALIZED MULTIPLE HIGH PRESSURE CONTACT Walter Kowalsln', South Milwaukee, Wis., assignor to McGraw Electric Company, Milwaukee, Wis, a corporation of Delaware Application June 2, 1955, Serial No. 512,671

7 Claims. (Cl. 200-170) This invention relates to an electric contact and more particularly to an electric contact having a multiplicity of contact points adapted to engage in high pressure relation therebetween a switch blade which rotates on its longitudinal axis and swings on an axis normal thereto.

The present invention is an improvement over the high pressure contact described in the copending application of W. Kowalski and J. Seaquist, filed October 28, 1953, Serial No. 388,734, and assigned to the same assignee as this invention.

In air disconnect switches the design is frequently such that the current passing from the switch blade to the stationary contact with which it cooperates is compelled to make a very abrupt change in its path of flow. Ordinarily this would present no problem, but in switches where fault currents occasionally flow having magnitudes of 25,000 amperes and upwardly, very strong magnetic fields are established about both the switch blade and contacts. Those versed in the art appreciate that the magnetic fields produced where a sharp turn is made may be resolved into two components, one having a direction parallel to the direction of principal current flow and the other being normal thereto. The magnitude of the normal components of the magnetic flux varies according to the abruptness of the turn which the current is forced to make. Since the normal components of the flux established by both the blade and its cooperating contact fingers cause magnetic forces which react against each other in such manner as to separate the fingers from the blade, it is highly desirable that these components be minimized in order that contact pressure be undiminished during periods when fault current is flowing and high contact pressure is most needed.

It is also desirable that the number of points through which current is transferred from the main blade to the stationary contact fingers be large so that the magnetic forces per contact point are proportionately reduced and more evenly distributed about the blade. Moreover, it is desirable that the number of contact points he increased because there is a definite maximum current which can be carried through a single contact point above which allowable thermal rise may be exceeded.

Increasing the number of contact points as suggested above creates a problem of assuring that each one of the contacts is bearing on the switch blade with equal pressure and carrying an equal amount of current.

The present invention contemplates solving the above indicated problems by a contact which engages the switch blade in substantial endwise alignment with the axis of the blade and in which the multiple contact fingers receive their pressure creating force from a leaf spring group acting through an intermediate equalizer.

An object of this invention is to provide a high pressure contact which will electrically engage a switch blade in such manner as to transfer current therefrom without abruptly altering its direction of flow, thereby preeluding establishment of contact pressure relieving magnetic forces during inordinate current flow.

Another object is to provide a high pressure contact having a plurality of contact making points all of which exert substantially similar pressure on an engaged switch blade regardless of alignment, this effect being attained by incorporation of a novel equalizer.

A further object is to provide a multiple point high pressure contact which is rugged, compact, easy to adjust, and which will maintain consistent contact pressure after many switching operations.

A still further object is to provide a contact pressure equalizer which is simple in form, easily manufactured and easily installed.

Attainment of the foregoing and other objects will be evident throughout the specification.

The invention is illustrated in the following drawing in which:

Fig. 1 is a plan view of the switch operating mechanism of a rotatable and swingable blade air disconnect switch, with parts removed, embodying the novel multiple contact assembly;

Fig. 2 is a front viewof the contact assembly shown in Fig. 1 including the switch blade but omitting the operating mechanism therefor;

Fig. 3 is a sectional view taken on the line 3--3 of Fig. 1 showing the switch blade in full closed position;

Fig. 4 is a sectional view of the multiple contact taken on the same line as Fig. 3 but showing the switch blade axially rotated and swung downwardly in partial switch open position;

Fig. 5 represents a plan view of the pressure equalizer removed from the novel multiple contact assembly; and

Fig. 6 is a sectional view taken on the line 6--6 of Fig. 5.

p In conjunction with Fig. l, a brief description will be made of the mechanism of an air disconnect switch in which the novel contact assembly 1 is embodied. Although certain parts are omitted, the switch structure shown in Fig. 1 is of the type which would be mounted on an insulator stack (not shown) adapted for rotation to effect opening and closing of the switch.

Details of a suitable switch for incorporating the novel contact assembly are more explicitly set forth in the copending application of T. A. Fjellstedt entitled Disconnecting Switch, Serial No. 449,129, filed August 11, 1954, and assigned to the same assignee as the instant invention.

For the sake of brevity, only the essential components of the switch will be referred to here. As stated above, the switch comprises an insulator adapted to rotate on its longitudinal axis and provided with a radially swinging crank arm and connecting link (none of which are shown). The connecting link is pivotally pinned to the bottom of a blade carriage 3, as viewed in Fig. 1, so that rotation of the insulator will cause blade carriage 3 to be rotated axially and swung upwardly on pin bearings 4 carried by a blade mechanism support casting 5. Additional support is given to switch blade 2 through a blade guide 6 in which the blade is journalled on ball bearings. The blade guide casting 6 has extending from opposed sides integral yoke arms 7 which terminate in cylindrical socket portions 8 which are bored to receive pin bearing stud 4 in bearing relation. In general terms, rotation of the insulator (not shown) swings the blade guide 6 on a horizontal axis in the form of pin bearings 4 and axially rotates blade 2 by means of the blade carriage 3.

Blade 2 is made of extruded copper and on its free end 2 is provided with diametrically opposite parallel depressions substantially coextensive in length with the axial limits of the stationary contact assembly 1. Immediately adjacent depressed portions 12 on blade end 2 are diametrically opposed raised contact areas 13 having a larger radius of curvature and outside diameter than the depressed portions 12. Silver contact inserts 14 are bonded to the larger diametercross section of blade 13 for the purpose of improving conductivity with contact assenr bly 1 and the raised contact portions 13 of the blade 2' are formed of particularly heavy metal in order to assure proper thermal dissipation and mechanical strength (see Figs. 3 and 4).

In Fig. 1 it will be observed that the contact assembly 1 comprises opposed pairs of inside fingers 20 nested in longer outside fingers 21 which are anchored by bolts 17 to a plate like casting extension 16 protruding from and integral with blade mechanism supporting casting 5. These fingers are preferably made of tough, highly conductive beryllium copper or hard drawn pure copper. Laterally opposite finger ends and fingers form substantially U-shaped nestingly offset contact units. The contact ends 30 and 31 of fingers 20 and 21 respectively are arcuate in cross section so as to obtain substantially point or short line contact with the raised portions 13 of blade end 2'. Silver inserts 15 are set in'the finger tips for improved conductivity.

Fingers 20 and 21 have some inherent flexibility but the pressure which they develop against blade end 2 is predetermined by loading them through the medium of leaf spring assemblies 33 which are juxtaposed to each pair of contact fingers. A flat tie bar 22 is used to load the spring. Tie bar 22 passes through each of the leaf spring assemblies 33 and through both pairs of contact fingers 20 and 21 and is retained in bearing relation to the leaf springs 33 by means of a retainer pin 23 which is removable from the tie bar. For greater detail regarding the tie bar and leaf spring assemblies, reference may be had to the above mentioned application of Kowalski et al.

A reaction bar 18 is provided for maintaining the proper spacing of the leaf spring groups 33 and is fastened to the casting extension 16 by means of the same bolts 17 which secure fingers 20 and 21. In Fig. 2 it will be noted that reaction bar 18 consists in a piece of flat non-magnetic metal having its end milled down to form a square portion 35 having dimensions equal to the thickness of bar 18 and adapted to pass through a hole 34 perforated in the end of the longest of the leaf spring members comprising the spring assemblies 33. The loading of leaf spring groups 33 can be regulated with precislon by interposing very thin shims between the longest leaf spring and reaction bar'lS. These shims consist of nothing more than thin washers having a hole sufficiently llasrge to pass over squared end portion 35 of reaction bar The end of the longest leaf spring which is more remote from reaction bar 18 is also provided with an elongated hole for loosely receiving an anchoring pad 41 protruding from an equalizer designated generally by the reference numeral 39. Thus, it is seen that spring assemblies 33 react against the ends of bar 18 and equalizer 39.

Referring particularly to Figs. and 6, the equalizer 39 comprises a central body 46 having extending from either side thereof oppositely directed arms 42 and 43 respectively. Arm 42 is of solid construction and terminates in a rounded end portion 42 which bears in rocking relation to back-up pad 29 soldered or brazed to finger end 31 (see Fig. 1). There are really two spaced arms 43 extending from body portion 46 in a direction opposite from arm 42. Arms 43 are parallel with each other and interconnected by means of a round cylindrical cross bar 44, the arms 43 and cross bar 44 thus forming an enclosure defining an aperture 45. Outer v periphery 43' of cross bar 44 is likewise rounded and bears in rocking relation against back-up pad 29 in line with contact area of the end 30 of finger 20.

It will be observed that the arms 42 and 43 forming part of equalizer 39 are of unequal length, when measured from either side of the geometric center of pad 41, 42 being the shorter arm and 43 being the longer arm. In applying the equalizer 39 to contact assembly 1 shorter arm 42 is caused to bear on the longer of the fingers 21 and longer arm 43 bears on the shorter of the two fingers 20, the center of pad 41 constituting a pivot point about which the equalizer 39 rocks on the longest leaf of spring assembly 33. The reason for this, as stated before, is that the fingers have a certain amount of inherent flexibility, the shorter of them 20 having the least flexibility. Accordingly, a greater external force must be applied to finger 20 if it is to have the same bearing pressure between contacting end 30 and blade contact area 13 as has finger end 31 which has the shorter arm 42 bearing against it. The aforegoing indicates one means by which equalizer 39 acts to cause each of the independent fingers 20 and 21 respectively to exert equal contact pressure on blade 2'. a

When in switch open position blade 2 is completely removed in a vertical path from between fingers 20 and 21 so that equalizer 39 under the action of springs 33 tends to, cause fingers 20 and 21 to collapse inwardly, but the amount of collapse is limited by a spacer pin 26 interposed between opposite fingers 20 so that they abut shoulder portions 27 on pin 26 and so that fingers 21 strike ends 28 of pin 26 in a manner that is self evident when Fig. l is referred to. Note, however, that in Fig. l where the blade 2 is in switch closed position residing between fingers 20 and 21 that a small space exists between shoulder 27 and end 28 of the pin and their respective fingers. Thus, none of the spring pressure is absorbed by pin 26 when the switch blade is in closed position, but all of the contact pressure is exerted directly on the blades by finger tips 30 and 31.

Referring to Fig. 3, it will be observed that when the switch blade is in closed position, diametrically opposite contact areas 13 of the blade bear on a line coincident with the longitudinal axis of the fingers 20 and 21. A different situation exists in Fig. 4 where the switch has been operated to partially open position by means of the rotating insulator (not shown) causing rotation and lifting of blade carriage 3 so that the broken away end of blade 2 rises and the opposed end 2 descends. Thus, in the latter figure, blade 2 has been axially rotated sufficiently to cause the raised contact areas 13 to depart from align ment with fingers 20 and 21 and for depressed portion 12 to rotate into alignment with the fingers. Upon this event, spacer rod 26 takes up the load from springs 33 by the reaction of shoulder 27 and end 28 against fingers 20 and 21 as described above. Further swinging and rotation of blade 2 can be conducted without impediment because depressed portions 12 of the blade no longer bear on the fingers, the load being taken by spacer rod 26..

During the switch opening operation just described, any free play existing, for example, in pinbearing sockets 8 or between blade 2 and guide 6 will cause a certain amount of axial misalignment between blade 2 and the contact assembly 1. Were not this misalignment compensated for by equalizer 3i unequal contact pressure would be developed between finger ends 30 and 31 against blade raised contact areas 13, thereby causing one current interchange point to carry excessive current and the other to carry less current than that for which it is designed. In switches of the type here under discussion, where contact bearing pressures lie in the range of approximately pounds and the distance through which the contact fingers flex is very small, the effect of a small amount of blade misalignment is greatly accentuated. Moreover, since current magnitudes ordinarily found in switches of this type very often have constant load values in excess of 1,000 amperes and fault current values in excess of 25,000 amperes, it is of paramount importance that the load current be divided equally between the various contact transfer points lest destructive heating of the contact fingers result.

It should be evident from reference to Figs. 1 and 2 that aperture 45 inequalizer 39 isof such size'as to pass freely over finger 21 so that its associated arms 43 together with cross bar 44 may react against finger end 30 without interference by finger 21. This is facilitated by offsetting the fingers 20 and 21 as is apparent in Fig. 1. Also, in Fig. 1 it will be noted that arm 42 ofequalizer 39 acts independently on finger end 31 through the agency of its 'arcuate termination 42'. Arm 42 is shorter than arm 43' when measured from the geometric center of pad 41. In effect a pivot point for both arms is developed where pad 41 passes through hole 40 in the longest of the springs comprising the group 33. Each of the arms 42 and 43 develop different moment arms about this pivot point and since their corresponding moments, of course, must be equal or rotation of the equalizer will occur, the equalizer will attain a position of balance where it causes an equal force to be exerted by the contact finger ends 30 and 31 regardless of the degree of axial misalignment of blade 2.

Another important feature of the invention resides in disposing the lengths of fingers 20 and 21 in the direction of the axis of blade 2 and in the closest possible endwise alignment therewith. By this arrangement, current may be transferred from blade 2 through fingers 20 and 21 to casting extension 16 without materially having its direction altered. Thus, when heavy fault currents are flowing, fingers on opposite sides of blade 2 tend to attract each other because current is flowing in them in the same direction and in parallel, this being true even if the fingers were disposed normal to a plane passing horizontally through the blade, but in addition here, the magnetic forces caused by the current passing from one side of the blade to the fingers on the same side will have substantially no effect in repelling the fingers from their contact surfaces because, as explained early in this specification, the direction of flow is substantially in line so that very little repelling force component normal to the switch blade axis will be developed. Those versed in the art will be able to readily check this phenomena by application of the left hand mot-or rule.

From the foregoing specification it will be apparent that a novel multiple contact assembly has been described which is characterized by a plurality of contact points all of which are caused to bear with equal pressure on the switch blade regardless of the degree of misalignment between the contacts and the switch blade received therebetween. It is also evident that the contact is of such design as to minimize the eflect of magnetic repulsion developed in prior art contacts when heavy fault currents are flowing.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made the-rein without departing from the invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

It is claimed:

1. In combination with a switch blade swingable on a transverse axis and rotatable on a longitudinal axis, an electric contact comprising at least two resilient fingers each having a contact surface longitudinally spaced from that of the other and lying in substantially the same plane for simultaneously engaging one side of the blade at longitudinally spaced points, said fingers extending substantially parallel with and axially of the blade when said blade is engaged, an equalizer constantly bearing on each finger on a side thereof opposed to said contact surface, and a spring in compressive relation to said equalizer on a portion thereof remote from said contact surfaces, the force of said spring being proportionately applied to said fingers through the medium of said equalizer.

2. An electric contact comprising at least two resilient fingers anchored at one end and having parts juxtaposed to each other and each having a contact surface longitudinally spaced from that of the other in substantially the same plane, an equalizer, said equalizer including at least two arms of dissimilar lengths joined with each other at a pivot line for simultaneous rocking movement, each of said arms bearing on a finger, respectively, on a side thereof opposed to its contact surface, a spring in compressive relation to said equalizer on a portion thereof including said pivot line, whereby said equalizer may rock with respect to said spring until the force moments developed on respective arms become equal.

3. An electric contact comprising at least two resilient fingers of unequal lengths anchored at one end and having parts nestingly adjacent each other and each including a contact surface spaced longitudinally from that of the other in substantially the same plane, an equalizer including a first arm and a second longer arm joined with each other at a pivot line for simultaneous rocking movement, the first arm bearing on the longer of said fingers and the second arm bearing on the shorter of said fingers, connecting means on said equalizer including the pivot line of said arms extending away from said fingers, and spring means in compressive relation to said connecting means of said equalizer, whereby said equalizer may rock with respect to said spring until force moments developed on respective arms by said fingers become equal.

4. An electric contact comprising at least two resilient fingers of unequal lengths anchored at one end and offset so that the shorter finger lies within the offset of the other, a contact surface on each finger spaced longitudinally from that of the other and in substantially the same plane, an equalizer including a first arm and a second longer arm joined with each other at a pivot line for simultaneous rocking movement, the first arm bearing on the longer of said fingers and the second arm bearing on the shorter finger, said second arm including an aperture freely admitting said longer finger therethrough, and spring means bearing against said equalizer coincident with the pivot line of said arms, whereby said equalizer may rock with respect to said spring.

5. An electric contact comprising substantially U- shaped resilient contact fingers nested within each other, means for anchoring said fingers at their closed ends, each of said fingers having offset portions and a contact surface adjacent its free end, the contact surfaces on fingers forming one side of said U-shaped fingers being longitudinally spaced from each other and substantially coplanar and in proximate alignment with corresponding contact surfaces on the laterally opposite side, an equalizer for distributing contact force between fingers on one side, said equalizer including a first and a second longer arm joined with each other at a pivot line for simultaneous rocking movement, a leaf spring assembly adjacent each side of said fingers, said spring assemblies each including a long leaf perforated at each end, a spreader bar interposed between said long leaves and having a protrusion at each end for reception by corresponding leaf spring perforations, said equalizers each including a pad coincident with said pivot line and extending freely into the other perforation of an adjacent leaf spring, said leaf spring bearing on said equalizer and means for transversely loading said leaf spring assemblies whereupon their force may be transmitted to said equalizers.

6. In combination, a switch blade adapted to rotate on its longitudinal axis and simultaneously swing on an axis normal thereto, said blade having a free end including diametrically opposite raised contact areas and peripherally interspaced depressed areas, an electric contact for receiving said free end therebetween when said blade is in closed position, said contact comprising U- shapcd members nested within each other and including offset fingers of dissimilar lengths and contact surfaces at their open ends, the contact surfaces on one side of said blade being spaced axially along the blade and in substantial parallelism with the axis thereof, and substantially endwise contiguous with associated fingers, a median plane bisecting the lateral space between opposed fingers containing said axis, a leaf spring assembly adjacent fingers on opposite sides of said blade, means for loading said spring assembly, an equalizer-interposed between each finger on one side of the blade and a corresponding spring assembly, said equalizer having arms of unequal length in bearing relation with respective fingers and adapted to rock about the point of engagement by said spring assembly.

7. In combination, an electric contact and a switch blade adapted to swing on a transverse axis and rotate about a longitudinal axis for engagement by portions of said contact on spaced points along the longitudinal axis of said blade, said contact comprising at least two unequally long longitudinally extending fingers each having 7 a contact surface longitudinally spaced from a corresponding surface on the other and lying in a substantially simi- References Cited in the file of this patent UNITED STATES PATENTS Raettig Dec. 11, 1923 Ballou et a1. Mar. 27, 1951

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