US2948794A - Electric switch - Google Patents

Description

Aug. 9, 1960 T. A. FJELLSTEDT ETAL 2,948,794

ELECTRIC SWITCH Filed March l, 1957 3 Sheets-Sheet 1 INVENTORS, Thorsten f?. E/ZZstedt q /Qaert Enes (/ter' Kanaals/fn dames Sedia/ast Aug 9, 1960 T. A. FJELLSTEDT r-:T AL 2,948,794

ELECTRIC SWITCH 3 Sheets-Sheet 2 Filed March 1, 1957 INVENTORS. Thorsten a? F'cZZstedt Robert E'Jne.: falter Kaa/aZs/fg, Jmes JT Seagmst ttar'mgy Aug. 9, 1960 Filed March l, 1957 T. A. FJELLSTEDT ET AL 2,948,794

ELECTRIC SWITCH y s sheets-sheet :s

' Patented Aug. `9,1960

ELECTRIC SWITCH Filed Mar'. l, 1957, Ser. No. 643,429

7 Claims. (Cl. 200--166) 'This invention pertains generally to electric switches and more particularly to improved means for transferring current through the joints between relatively movable parts thereof.

The invention is illustrated as an improvement over two general types of prior art air disconnect switches. The rst of these has an elongated blade that is adapted to turn on its longitudinal axis and swing on a transverse axis into and out of direct engagementV with a pair of exposed stationary contact jaws located at opposite sides of the transverse axis. In such a switch, the blade ordinarily has a cross section whose dimensions are unequal so that the blade enters between both sets of jaws on its lesser dimension and is then rotated into high pressure engagement on its greater dimension, thus tending to spread the jaws. Obviously, maximum operating eort must be exerted when the high pressure engagement is being made or broken simultaneously at both ends of the blade. The arrangement suiers the disadvantages of having high spots which must be overcome at the most critical period during switch operation and it further lends itself to impairment by ice and corrosion since the blade and cooperating Contact jaw in the region of the blade hinge must necessarily be exposed to the atmosphere.

A second type of prior art switch improved by the present invention is one wherein an attempt is made to carry current through or past the joints interconnecting the switch parts. Examples of this type are flexible shunts, cam type wiping contact ngers that bridge the joints and rotatable screw connections.

Most of the aforementioned switch designs are inherently limited insofar as the possible number of current interchange points attainable in a joint is concerned for although they may seek to establish line or area contact between parts they in fact develop only one or two points of contact between high spots on adjacent conductive parts. Generally the problem of attaining more points of interchange is impossible to overcome in those designs because of space limitations and there results a switch that requires excessive operating'eifort and that undergoes a near maximum permissible thermal rise during use.

An important object of the instant invention is to eliminate the need for an exposed contact jaw at the hinge end of a disconnect switch blade by substituting therefor a novel multiple path concealed cuurent interchange contact in the joints between movable switch parts. By this means the mechanical losses that occur at the most critical time, that is, when the blade is entering or leaving its cooperating jaw, are reduced. This concentrates all available operating effort on the blade for breaking ice and corrosion if any are present. Likewise, it permits simplication of the `switch construction at the hinge end of the blade Iand obviates the obstacle of trying to tit larger contact jaws and more high pressure current interchange points into this region of limited space when designing for greater current carrying capacity.

A more specic object is to provide a current transfer means that produces the electrical ettect of high contact pressure through a multiplicity of lower pressure contact points which subdivide the ow of current into paths that are distributed over a great area in order to augment thermal dissipation, to obviate electromagnetic effects, and to reduce friction incident -to prior art high pressure contacts.

Another'object to provide a current interchange contact that is simple in form, economical to manufacture in all its aspects and that is compact, so that it may be easily installed without exceeding dimensional requirements of good switch design. j

A further object is the provision of a multiple point current interchange contact which in a single element combines the functions of current carrying and developing contact pressure and which is not inherently limitedin the number of interchange points but whose current carrying capacity may be multiplied by the simple expedient of stacking the novel contacts in parallel or by merely increasing the diameter of one of them.

Another object is to provide an interchange contact that is easy to incorporate in a bearing assembly and lends itself to being permanently lubricated, sealed and protected against corrosion to the end that contact pressure may be established during assembly which will be un-V aiected by wear, ice accumulation or deleterious atmospheric conditions.

Another object is' to provide a current interchange contact that maintains circuit continuity at the same eiiiciency while the switch part-s are undergoing movement as under static conditions when the switch' is closed. Fulfillment of this object is particularly important Where the switch is adapted to open under vload in conjunction with a load interrupter.l

Other more specific objects will 'be perceptible wheny proceeding through the ensuing description of the in vention. Y

In accordance with a preferred embodiment of the invention exempliiied in an air disconnect switch,'the novel current interchange contact comprises a multiple convolution helical spring member attached at its endsA` to form a toroidal shape. The toroidal shaped contact may be conined in the joint between concentric members, such as tubular blade and cylindrical housing, or between adjacent, relatively rotatable nominally planar members, the latter hereinafter being called a parallel plate application. In the preferred embodiments, one of the members is provided with a V-groove that contains and positions the spring-like contact by bearing in tangency against each convolution at two points and the other member may be smooth and bearing in tangency to a point substantially opposite, so that two parallelv current paths are created in each convolution. Where'A the members are concentric, the spring contact has all of its convolutions tilted in their natural circumferential ldirection around its toroidal shape. Where the members are nominally parallel `and carried on a common hinge axis, the convolutions are tilted away from the plane" surfaces and also circumferentially, the condition resulting from compressing the contact along its toroidal axis. Thus, the multiple convolutions are each independent of the others and each convolution in turn vdefines'v parallel independent paths for current to flow between points of contact. There is an adequate mass of metal surrounding the interchange points for accepting current and any Fig. 1 is a side elevational view of an air disconnect switch embodying the invention;

Fig. 2 is an enlarged fragmentary top view of the blade actuating mechanism at the hinge end of the switch in Fig. l;

Fig. 3 is a fragmentary sectional View of the bearing assembly and the novel means for transferring current between concentric members such as from the switch blade to its guide housing;

Fig. 4 is a fragmentary sectional view taken on a line corresponding with 4-4 of Fig. 3, looking in the direction of the arrows;

Fig. 5 is a fragmentary enlarged sectional view of the novel means for transferring current between parallel, relatively rotatable members such as in the transverse hinge joint of the switch depicted in Fig. 2;

Fig. 6 shows a portion of a current interchange contact confined between concentric cylinders and another portion confined between parallel plates, one purpose of the diagram being to illustrate the meaning of the terms inside and outside diameter as used in the design calculations;

Fig. 7 shows one enlarged convolution of the interchange contact removed from a concentric cylinder application, Fig. 4 for example, one of the purposes of the view is to identify symbols used in the design calculations;

Fig. 8 shows one convolution of the interchange contactremoved from a plane or parallel plate application, Fig. 5 for example, whose purpose is to identify symbols used in the design calculations;

Fig. 9 is an end view of one convolution comparable to that exposed where a section is taken axially of the interchange contact as in Fig. 5 and it is also comparable to a side elevation taken of Fig. 8 but with the V-groove added; and,

Fig. l is a View of one convolution as depicted in either Figs. 7 and 8 looking along a line normal to the plane of the respective convolutions.

The novel current interchange contact may be embodied in a Variety of devices such as circuit breakers and grounding switches but it is here described in conjunction with a vertical break air disconnect switch illustrated in Fig. l. Without regard for improvements that constitute the instant invention, the switch is generally comparable to one shown and claimed in the copending application of T. A. Fjellstedt, f iled August 1l, 1954, Serial No. 449,129, and assigned to the assignee of this application, so details are available from that source. For present purposes. however, it is suflicient to say that the switch is characterized by a channel iron mounting base 1 upon which stands front and rear stationary insulators Z and 3, respectively. Operation of the switch is accomplished bv axially rotating an intermediate insulator 4 through swinging an operating lever that is bolted to a suitable flange ring attached to a post 6 that carries the insulator 4. The lower end of the insulator 4 assembly is journalled in a bearing structure 7 and the upper end is journalled at 8 in the bottom of a stationary support frame 9. When lever 5 is swung it causes, by means of mechanism to be described. the main switch blade 10 to rotate longitudinally and rise angularly to a full open position.

The switch actuating mechanism includes a crank 14 fixedly held to the top of rotating insulator 4 by cap screws, for example. When crank 14 swings, a torque is transmitted to blade 10 by means of a link 15 which is connected to one end of crank 14 by a ball joint 16. The other end of link 15 engages blade 10 through the agency of a blade carriage 17 that is secured tightly on the blade by means of a cap screw 18. Carriage 17 is tubular for permitting blade 10 to extend through it and it also has a cylindrical extension portion 19, see Fig. 3, that enables it to be journalled in a concentric blade guide member 20 in ball bearings 21 held by a retainer ring 22 in a manner clearly evident in the last named figure. Thus, it is seen 4 that blade 10 is journalled for low friction rotation on its longitudinal axis within blade guide 20.

Cylindrical blade guide 20 has a pair of blade pivot arms 23 integrally cast with the former. Pivot arms 23 are adapted to swing on an axis transverse to the axis of blade 10 so that the blade will rise and descend angularly as well as rotate longitudinally when insulator 4 is turned. The axis for swinging the blade is coincident with that of opposite hexagon head bolts 24 which serve as shafts and means for physically holding opposite guide arms 23 between sides of fixed support casting 9, see Figs. 2 and 5 in particular.

Blade 10 is generally an extruded tubular shape but it has a flattened, beaver tail end 28 where it is engaged between sides of a stationary high pressure contact assernbly 29 or any other suitable contact. Stationary contact 29 is conductively supported on a terminal casting 30 to which an incoming line wire, not shown, may be attached.

At the rear end of the switch, support frame 9 is secured to the top of stationary insulator 3 in the vicinity of where reference numeral 31 is applied. The remote rear end of casting 9 is so configured, see Fig. l, that it cooperates with a bolted pressure pad 32 for compressively engaging an outgoing line wire 33 as shown.

From the structure described thus far it will be evident that when the switch of Fig. 1 is closed and conducting, current is exchanged from jaw 29, to blade 10, through an axial joint to blade guide 20, through a hinge joint to casting 9 and to the outgoing line 33. The present invention is primarily concerned with improving the efficiency of the current interchanges from blade 10 to guide 20 and from blade guide arms 23 to casting 9 and the description now proceeds with a more detailed discussion of the novel aspects for achieving improvement in this area.

Transfer of current between concentric elements such as blade 10 and guide 20 will first be described primarily in reference to Figs. 3 and 4 which are portions of the Fig. l switch isolated for enlargement and facilitating description.

A portion 36 of blade 10 is diametrically enlarged so that a copper or the like interchange contact retainer collar 37 may be easily slid over the blade and pressfit or brazed on the enlarged portion 36. The electrical resistance between collar 37 and blade 10 is immeasurably small so that this particular joint is not treated as an interchange at all. The external periphery of collar 37 defines an annular channel that is V-shaped in cross section for the purpose of retaining and providing a seal for the multiple point current interchange spring-like contact 38. The surfaces 39 and 40 that define the bottom of the V-groove diverge from each other at an included angle of about ninety-degrees in this example, although a different angle is also acceptable practice. However, it will be noted that the side 40 projects at an angle axially of the blade 10 and extends beyond the ends of guide cylinder 20 for defining a triangular seat in which is disposed an elastic sealing ring 41, preferably of silicone nlbber. This sealing arrangement excludes contaminants from the interior of guide cylinder 20 and permits packing the region about contact 38 and the ball bearings 2?.. with corrosion inhibiting, constant viscosity lubricant such as a silicone base grease.

Attention is now focused on the general character of the novel element 38 which interchanges current from collar 37 to the guide cylinder 20 when blade 1i) is static or during rotation on its longitudinal axis. Details for designing such a spring-like current interchange contact will be discussed more fully later in a manner applicable to the embodiment of Fig. 5 as well as Fig. 3 and then further as specifically applicable to those respective tigures. For the present it may be noted that interchange contact 38 is comparable to a helical spring that is disposed about the V-groove of collar 37 with the convolutions tilted in a circumferential direction of the toroid thus defined. The contact 33 is originally wound on a mandrel, like a continuous run of ordinary helical spring, but a portion including a definite number of individual turns or convolutions is then cut olf and the free ends joined by any suitable means that causes the Various turns to lie close to each other 'at the junction so that no gap appears which might reduce the number of effective contact points. The number of individual convolutions in each interchange contact 38 is determined in a manner mentioned later, but it may be noted in Fig. 4 that they lie quite closely against each other.

Note particularly in Fig. 3 that the contact 38 has a multiplicity of bearing points resulting from each convolution touching the sides 39 and 40 in tangency Where the lead lines of those numerals are affixed and that there is an opposite contact point 43 diametrically opposite the apex of the V-groove. Thus, each turn constitutes a pair of parallel current paths between points 43 and 40, and points 43 and 39. The V-groove has great signiicance in that it creates the paths and furthermore shortens them, thereby reducing the resistance drop of interchange contact 38.

Other important advantages are afforded by this construction. For example, static seizure or peak frictional drag between the contact jaw and blade is virtually eliminated by reason of a multiplicity of relatively low pressure current interchange points being always in contact and uniformly distributed about the axis of rotation of the parts. This contrasts with prior art so-called high pressure contacts usually involving two to six points of interchange that bear in very intense frictional engagement which must be overcome during the initial stage of switch opening and the nal stage of switch closing.

Moreover, the distributed, relatively low pressure contacts of the instant invention reduced wear on any particular point. Therefore the likelihood of switch failure is not as great as where yonly va small number of interchange points are used and all reliance is placed on the latter. Because the novel interchange contact lends itself readily to sealing and permanent lubrication, contact deterioration and periodic maintenance are both reduced to insignicance.

The novel interchange contact mitigates other disadvantages inherent in switches employing pairs of high pressure interchange contacts such as of the butt or wiping types that effectively interchange between only two, or at best, a very limited number `of points. prior art contacts, when current is forced to converge from a broad conductive mass to a high density interchange point and then broaden out again, several eifects are produced that contribute to thermal failure. Among them is the phenomena of eonstrictive resistance and change of material resistivity with temperature which is characterized by a marked increase in effective resistance at points of high current concentration. An incident to this phenomena is that by converging the current to a point, the eiective heat absorbing mass and heat dissipating area lare reduced, while the heat generated by current flow is increased. The thermal condition in prior art high pressure contacts is further aggravated by the fact the heat energy produced is a function of the current squared. With the heavy fault currents that these contacts are called upon 4to withstand, the generated heat energy can easily reach an unsafe level. These thermal effects are overcome in the instant invention by replacing the two, or at best, a limited number of interchange points with many separate paths `dispersed over a nomirrally broad area. The generation of heat energy is now a function of the sum tof the squares of small values of current in each individual multiple path. A non-linear reduction introduced by the square of the current accounts for an enormous reduction in heating effect and at the same time the current and heat yare distributed over a greater mass and dissipating area.

InV these YDisposing thespring-like currentv interchange contact in the V-groove, described earlier in connection with one embodiment, has the advantage of shortening the current paths through the individual convolutions and aids in rapid conduction of heat therefrom.

Magnetic considerations are also important. In a point contact interchange where the current constricts for passing through a small area, electromagnetic repulsive forces are produced which tend to separate contact members and reduce their mutual contact pressure when it is most urgently needed. This force is also a function of the current squared, so dividing the current ow into a multiplicity of separate paths deployed in a radial pattern Y reduces these forces to insignilcance.

Attention is nowV turned to the embodiment where a current interchange contact, designated 48 to distinguish it from the contact 38 in Figs. 3 and 4, is disposed between relatively rotatable parallel members such as in the blade guide hinge joint of Fig. 2 and its enlargement in Fig. 5. In this case the contact 48 has its convolu-l tions tilted in a plane normal to the toroid axis resulting from compressing the contact endwise along the axis of hinge pivot bolt 24. Switch hinge arms 23 terminate in an integrally cast pad 49 that is provided on its complementary planar face S0 with an annular interchange spring contact retaining V-groove deiined by diverging bottom surfaces 51 and 52 and an interior axial wall 53. 'Ihe convolutions of contact 48 are tangent to surfaces 51 and 52 where touched by the lead lines of those' numerals and the face 46 of casting 9 is contacted by the convolutions at 54, thus creating a circular point contact pattern and parallel paths in each convolution with advantages enunciated earlier.

It will appear later where the design data is set forth, that the term parallel surfaces means a pair of planes taken transverse to the axis of rotation of two parts. ln Fig. 5 this would be a plane such as 46 taken in con junction with an imaginary parallel plane Vthat includes a point diametrically opposite on a convolution from the point of tangency 54. This is further exemplified in Figs. 8 and 9. In other words, design of the contact at rst disregards the presence of the V-groove. Y p

The surfaces 51 and 52, constituting the V-groove bottom, diverge from each other at an angle of approximately one hundred and twenty degrees in this Vinstance and it will be noted in Fig. 5 that 52 is longer than 51. Moreover, groove wall 53 is of such length that it creates a central hub which allows placement and retention of the toroidal spring so that assembly is made easier. This is possible since the toroid in its natural condition tends to contract to form the smallest circle when not compressed axially into the bottom of the groove. When, during assembly, hinge arms 23 are placed between sides of casting '9,Y the toroid diameter increases and the contact 48 spreads until it bears on points 51, 52 and 54. This also imparts the proper inclination to the individual convolutions.

Note that hinge bolt 24 has a truncated conicular portion 5S at its head end that enables placement of an elastic circular sealing ring 56 in self tightening condition. Hinge bolt 24 is screwed into casting 9 but has a smooth bearing surface where it passes through pad 49 of hinge arm 23 and a jam nut on the bolt sets it when compression of the spring has been adjusted nally. The V-groove of the hinge bearing assembly is also packed, for life time lubrication of the current interchange =48 and the bolt shaft, with corrosion inhibiting constant viscosity lubricant such as silicone grease. Con-` taminants are excluded and the grease is retained by a flexible seal ring 59 residing on an annular bevel as is'A clearlyevident in Fig. 5. p.

The current interchange spring-like contacts 38'anld 48 are preferably made fromahigh conductivity, high temperature resistant spi'rm'g material.` It has been found that among currently available material, Beryllium copper alloy No. 10 has the best conductivity, physical properties, and the ability to withstand any expected thermal effect without change of properties.

In the ensuing paragraphs procedure for designing a current interchange spring contact will be set forth. As stated earlier and according to the implication of the disclosure there are two general cases which must be considered. One is where the contact is used between concentric, generally cylindrical elements as represented most clearly in Figs. 3, 4, 6 and 7, and two, where the contact is used between nominally parallel planes that are hinged together as most clearly shown in Figs. 5, 8 and 9.

The design procedure is based on calculating a springlike contact having maximum current carrying capacity for a given space. Error on the side of a greater safety factor is inherent in the procedure where physical configuration, such as a minimum shaft size, becomes controlling. In addition, recommendations are made for the practical range of many of the constants employed that have been verified by experience.

I. Spring interchange Contact cross sectional area The total effective cross sectional conducting area of spring material required in a particular design will depend upon the current carrying requirements of the switch and the allowable Vcurrent densities. This applies in a concentric `cylinder or a parallel plate application. The current density is governed by experience and should be verified by the generally acceptable switch testing practices since it is difficult to predict the steady state heat dissipation characteristics of a design based on purely theoretical considerations. With a spring contact material having a conductivity of above 50% (International Annealed Copper Standard) it is feasible to use densities in the range of 1000 to 2000 amperes per square inch.

In a design having large current carrying requirements it is usually preferable to use more than one spring contact in parallel, that is, arranged axially or concentrically of each other to reduce the current load on each spring contact.

Let:

Ai=total cross sectional conducting area required, in

square inches.

1=steady state load current in amperes.

Fzsteady state current density in amperes per square inch.

Then:

A- I h --F square mc es II. Approximation of wire diameter This also applies to the concentric cylinder and parallel plate cases. To simplify the design procedure an approximation can be made for the wire diameter based upon area, angle of layover (tp in Figs. 7 and 8) and a pre-selected final inside diameter (DI in either case shown in Fig. 6). The approximate final inside diameter of the spring contact when confined must be selected in view of space considerations of the proposed interchange assembly. In other words, the inside diameter may be governed to some extent by strength and size requirements of other parts such as blade 10 or hinge bolt 24 and their associated elements.

Experience has shown that the angle of layover in either case should be approximately 50 degrees for optimum design. The practical range of wire diameters has been found to run from B & S gauge No. 19 (.036 inch) to B & S gauge No. l (.102 inch). For the cases of Fig. 7 or 8, wire size considerations are the same.

Let: d^=approximate wire diameter in inches. DI'==approXimate final inside diameter of spring toroids 38 and 48 in inches.

8 =angle of layover in Figs. 7 and 8 (50 degrees recommended). Then:

d illCllGS If wire size falls outside of range suggested above, go back and reduce current density F or area per spring contact A, adopt two springs if necessary to meet this requirement. After the approximate wire size has been found, in the usual case, select the nearest standard wire size. From this the number of turns or convolutions in each springcontact can be calculated from:

2A N an Where N=number of turns per spring contact. dzwire diameter in inches.

III. Short circuit temperature rise ICt-i- To degrees F.

Where T=rnaximum short circuit temperature in F.

T0=initial temperature prior to short circuit (ambient plus steady state rise).

Ic=short circuit current per spring path.

I =total short circuit I r=time duration of short circuit in seconds.

amparos per current path *i Cls p=resistivity of the spring contact material in ohms per square inch per inch =density of spring contact material in pounds per cubic inch s=specific heat of spring contact material in B.t.u. per

pound per degree F.

'v t e4 ohmj inches o E btu.

After calculating the theoretical maximum temperature rise T, a comparison must be made with the permitted rise for the equipment being designed. Knowing the temperature withstand properties of the spring contact material particularly, a determination must be made as to whether the contact will successfully pass a heat run after short circuit conditions have subsided. Bear in mind that the calculated theoretical rise is based on the worse conditions. If this `temperature rise is less than that allowable for the material, it may be assumed that the large masses of metal confining the spring contact will carry away and radiate heat so that the theoretical rise will never be reached. This introduces a large safety factor into the design at this point.

C1 is expressed in IV. Calculations for parallel surface application The preceding computations apply to both cases. Special consideration will now be given to application of the spring Contact between two adjacent parallel surfaces amarsi" for' interchanging current between them as in the hingeV wp=turn space factor for parallel surface applications,

see Fig. 8.

DI=nal inside diameter of spring contact in inches,

see Fig. 6.

D=mean diameter of single turn in inches, see Fig. 10. (Fig. l is a view looking at a right angle to the long side of either of the turns in Figs. 7 or 8, recognizing that one portion a turn lies over the other and causes an appearance of foreshortening.)

C2=spring contact ratio factor, explained below.

f=spring contact turn deilection in inches, during layover.

G=gap between parallel planes against which actual contact by the spring is made, see Fig. 8.

(1) wp= COS qs inches (2) D1=V% d inches When a definite inside diameter DI has been set by other design limitations, the number of turns N can be varied slightly.

(3) D=C2d inches If the maximum temperature under short circuit conditions T is high compared to the allowable maximum for the spring contact material, it is benecial to hold C2 as low as possible so that heat may be conducted away from the critical mid-turn zone of the spring contact. For lower values of C2, that is, for stiller spring contacts, it has been found that some permanent set will result but Without detrimental effect on performance.

Larger values of the ratio factor C2 will yield Va softer spring contact having less contact pressure and therefore less frictional drag. In some applications it is desirable to avoid permanet set and this requires a more detailed examination of the spring wire fiber stresses. This computation will be set forth under item 6 below.

This is an approximate value of spring deection f that is accurate enough for normal applications.

)0:3022 sin 4S inches In the range of 8.5 to 13 for the spring ratio factor C2, the maximum tensile liber stress occurs in the expanded half-turn.

feEK., -lpounds per square inch V. Calculation for concentric cylinder application In this application a current interchange contact spring 38 is disposed between concentric cylinders particularly illustrated in Figs. 3, 4, at 38 in Fig. 6, and in Figs. 7 and l0. Here it is necessary to determine the cylinder diameters and the spring contact dimensions. The V- groove does not enter into the computations until later and a timely showing will be made concerning'how to calculate the groove angle. DI and D0 are not affected by the presence of the V-groove.

Let:

(l) Y 106:2@ inches c s qS N (2) Dr: Arwcd inches When a deiinite DI has been set by design limitations, .th number of turns may be varied slightly.

(3) D=C2ol inches Select C2 as set forth under part IV, item 3.

(4) f sin inches See comment in part IV, item 4. The same considerations are here involved.

(6) Follow same procedure as in part IV, item 6 where the stress calculations are set forth.

VI. Calculation of V-groove dimensions for either concentric cylinder or parallel plane applications Approximate formulas, suflicient-ly accurate for practical purposes are given below for calculating the V- groove dimensions to be used with current transfer spring contacts. The symbols used are identical to those defined earlier except Athat certain symbols appearing only in Fig. 9 are now to be introduced. In order to appreciate the ensuing calculations as they apply to a parallel plate application, those versed in the art will be interested in knowing that by theory and inspection it has been discovered that the outside diameter of a spring convolution does not change when the individual convolutions are tilted during connement. This allows treating a convolution as it appears in Fig. 9, for example, as a true ellipse and facilitates computing the points where the V-groove is tangent to the periphery lof each convolution.

The V-groove angle 0 is preselected in view of theV ll geometry of the whole interchange design and machining convenience. In Fig. 3 for instance, the angle is such that the seal ring 41 can be located within reasonable dimensional limits of collar 37. Experience dictates that 30 to 45 degrees is a satisfactory angle 0.

All preceding calculations for designing an interchange spring contact are based upon use of smooth concentric cylinders or smooth plane surfaces that are tangent to each turn only at diametrically opposite points. Addition of the V-groove does not invalidate any of those calculations. The groove serves as a means for restraining the spring contact in predictable alignment and it further creates two current paths in each turn accompanied by advantages set forth earlier.

Attention is now invited to Fig. 9.

The calculation of (z) yields a dimension that may be added to the gap dimension (G) for parallel plate applications, see Fig. 8, or subtracted from DI for a concentric cylinder application, see Fig. 7, for establishing the apex of the V-g-roove. Machining is easier if the apex is given a slight radius or illet and skilled designers can readily understand how to do this.

Although this invention has been described in considerable detail in reference to an air disconnect switch, it is to be understood that such description is intended as illustrative rather than limiting, for the invention may be variously embodied in other electrical apparatus such as circuit breakers and oil switches. Therefore the invention is to be interpreted in View of the claims which follow.

It is claimed:

l. An air disconnect switch comprising a stationary terminal, blade means adapted to rotate on its longitudinal axis for cooperating electrically with said terminal, blade guide means including a cylindrical portion surrounding a portion of said blade means in concentric spaced relation to define an annular gap, at least one of said portions being provided with an annular groove dened by diverging sides that are presented toward said other portion, contact means disposed in said gap for eiecting sliding electrical connection between said blade and guide means, said contact means comprising a toroidally shaped helical Spring-like member including a multiplicity of turns which have spaced points on their peripheries tangent to the diverging sides of said groove and at least another point tangent to the lother of said portions whereby short parallel current paths are created in each turn bridging said gap, the individual turns having their planes inclined at an angle with respect to a plane passing axially through said blade means, whereby the inherent resiliency of said turns maintains them in firm frictional relation between said portions.

2. An air disconnect switch comprising a stationary terminal, blade means adapted to swing on a transverse axis for cooperating electrically with said terminal, pivot shaft means on which said blade means swings, a stationary support for said shaft means, said blade means and said stationary support each having nominally planar portions in complementary adjacence and adapted for relative rotation about said pivot shaft means, at least one of said planar portions being provided with an annular groove surrounding the pivot axis and having diverging sides presented in the direction of the pivot axis, contact means disposed circumferentially around said groove for interchanging current between said planar portions, said contact means comprising a toroidally shaped helical spring-like member including a multiplicity of turns which have spaced pointson their peripheries tangent to the diverging sides of said groove and at least another point tangent to the other of said portions whereby short parallel current paths are created in each turn bridging said planar portions, the individual turns having their planes inclined at an angle with respect to a plane normal to said pivot axis, whereby the inherent resiliency of said turns maintains them in iirm frictional relation with said parallel portions.

3. An air disconnect switch comprising a stationary terminal, blade means adapted to rotate on its longitudinal axis for cooperating electrically with said terminal, said blade means being provided near one end with an annular groove defined by diverging sides that are presented radially outward, blade guide means including a cylindrical portion surrounding said groove in concentric spaced relation to dene an annular gap, contact means disposed in said gap for effecting sliding electrical connection between said blade and guide means, said contact means comprising a toroidally shaped helical spring-like member including a multiplicity of turns which have spaced points on their peripheries tangent to the interior of said cylindrical portion and other points tangent to the diverging sides of said groove whereby parallel current paths are created in each turn between said blade means and cylindrical portion, the individual turns having their planes inclined at an angle with reference to a plane passing axially through said blade means, whereby the inherent resiliency of said turns maintains them in lrm frictional relation between said diverging sides and said cylindrical portion.

4. An air disconnect switch comprising a stationary terminal, blade means adapted to rotate on its longitudinal axis for cooperating electrically with said terminal, said blade means being provided near one end with an annular groove having diverging sides projecting radially outwardly from the blade, a housing including a cylindrical portion surrounding a part of said groove in concentric spaced relation to deline an annular gap, at least one of said `diverging sides projecting axially beyond said housing and in proximity therewith to define an angular seal seat, a circular elastic sealing ring bearing into the angle of said seat and thereby sealing the region of the groove, and contact means disposed in said groove` for eiecting sliding electrical connection between said blade means and housing, said contact means comprising a toroidally shaped helical spring-like member including a multiplicity of turns whose planes are inclined at an angle with respect to a plane passing axially through said blade means.

5. =In electric apparatus including conductive elements that are hinged for relative rotation about a common axis, the combination of a rst element and a second nominally parallel element adjacent thereto along the axis of rotation to dene a gap therebetween, at least one of said elements being provided with a groove encompassing the axis of rotation and which groove in cross section is characterized by radially diverging sides presented toward the other of said elements, contact means disposed in said gap for interchanging current between said elements, said contact means comprising a toroidally shaped helical spring-like member including a multiplicity of turns which have spaced points on their peripheries tangent to the diverging sides of said groove and at least another point tangent to the opposite element whereby short parallel current paths are created in each turn, the individual turns having their planes inclined at an angle with respect to a plane normal to the rotational axis, whereby the inherent resiliency of said turns maintains them in tirm frictional relation with said elements.

6. In elec-tric apparatus including conductive elements that are rotatable relative to each other, the combination of a cylindrical internal element and a cylindrical eX- ternal element surrounding a part of the rst named element in concentric spaced relation to deiine an annular gap therebetween, at least one of said elements being provided with an annular groove in the region of said gap whose cross section is characterized by radially diverging sides presented toward the other of said elements, contact means in said gap comprising a toroidally shaped helical spring-like member including a multiplicity of turns which have spaced points on their peripheries tangent to said diverging sides and at least another point tangent to the other of said concentric elements whereby parallel current paths are created in each turn bridging said gap, individual turns having their planes inclined at an angle with respect to a plane passing axially through the cylindrical elements, whereby the inherent resiliency of said turns maintains them in irm frictional relation between the elements.

7. In electric apparatus including conductive elements that are movable relative to each other, the combination of a substantially cylindrical internal element and a substantially cylindrical external element surrounding a part of the first named element in concentric 4spaced relation to dene an annular gap therebetween, at least one of said elements being provided with an annular groove in the region of said gap whose cross section is characterized by diverging sides presented toward the other of said elements, contact means in said gap comprising a toroidally shaped helical spring-like member including a multiplicity of turns which have spaced points on' their peripheries tangent to said diverging sides and at least another point tangent to the other of said concentric elements whereby parallel current paths are created in each turn bridging said gap, individual turns having their planes inclined at an angle with respect to a plane passing axially through the cylindrical elements, 'whereby the inherent resiliency of said turns maintains them in firm frictional relation between the elements.

References Cited in the tile of this patent UNITED STATES PATENTS 2,436,296 Graybill et al. Febr. 17, 1948 2,449,479 Hopper et al. Sept. 14, 1948 2,734,955 Owens Feb. 14, 1956 FOREIGN PATENTS 186,526 Great Britain Oct. 5, 1922

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