US2767264A - Contact arrangement for asymmetrical resistance - Google Patents

Description

Oct. 16, 1956 w. M. sco'r'r, JR

CONTACT ARRANGEMENT FOR ASYMMETRICAL RESISTANCE Filed May 25, 1955 2 Shets-Sheet l IN VEN TOR. All/(M #2 Scar-r; \/l?.

Oct. 16, 1956 w. M. SCOTT, JR 2,767,264

CONTACT ARRANGEMENT FOR ASYMMETRICAL RESI STANCE Filed May 25, l955 2 Sheets-Sheet 2 Z7 cappze 7474 g pnrl/ 2 YEP/7TH United States Patent CONTACT ARRANGEMENT FOR ASYMMETRICAL RESISTANCE William l Scott, J12, Bryn Mawr, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., 21 corpo= ration of Pennsylvania Application May 25, 1955, Serial No. 511,027

8 Claims. (Cl. 200-48) My invention relates to a novel arrangement of conducting surfaces whereby undesirable asymmetrical resistance resulting from oxide and silver sulphide films on the cooperating surfaces of different materials .is eliminated and is more particularly directed to a dissimilar conducting surface arrangement whereby the effective resistance during the negative and positive half portion of the current cycle is equal.

In a circuit interrupting equipment, the cooperating conducting components, such as switch blade, jaw and hinge members are made of copper or copper alloys for reasons of economy. However, the exposure of the cooperating copper surfaces to atmosphere results in the formation of a cupric oxide film which has a high mechanical strength and clings to the copper with great tenacity. Hence it is extremely dificult to remove this film by wiping or rubbing action between the surfaces.

The oxidation of the current carrying surfaces results in a progressive increase in heating of the switch by the normal current. It has been customary to inspect such surfaces periodically to remove the copper oxide film. Since this maintenance routine is expensive and does not provide assurance against failure, a copper or copper alloy to a plated or brazed film of silver or silver alloy sequence of cooperating surfaces is frequently used as set forth in U. S. Patent 2,371,755 issued March 20, 1945 to Walter J. Gilson. As noted in this patent silver-tosilver cooperating surfaces tend to roughen or freeze,

so that the brazed-cn-silver layers may be stripped from the copper backing. Hence a copper-to-silver sequence is used as fully described and claimed in the above noted patent.

However, this arrangement in which different metalsare used has introduced new problems. As is well known in the art, each metal belongs to difierent voltage series, thus two different metals in contact engagement presents a lower resistance to current flowing in one direction than current flowing in the opposite direction. Accordingly, there is a degree of rectifying action when two metals 'of different compositions are employed for the cooperating surfaces. This is illustrated in the copper oxide rectifier and is fully described on pages 100108 of Electronics by Millman and Seely 1951, McGraw-&

Hill and pages 7374 Applied Electronics M. -I. T., 1948, John Wiley and Sons, Inc.

This asymmetrical resistance and resulting asymmetrical current wave are overcome by my invention even though metals of different voltage series are usedv for cooperating surfaces.

In accordance with my invention, I propose to so arrange my contact circuits so that during one half of the cycle current will flow through a first low resistance path and during the other half cycle will flow through a second low resistance path.

The above noted disadvantage of having the potential energy barrier of the cooperating surfaces eflfective 'during only one half of the operating cycle exists on switching devices. That is, a copper blade engages the cooperice ating silver brazed surfaces of the jaw member. Hence, dufing one half of the operating cycle, for example the positive half cycle when the current is flowing from the two cooperating jaws to the movable contact arm, parallel silver-to-copper paths are encountered by the current. With this sequence of the dissimilar metals, the energy potential barrier or backward resistance results in a decrease of the R. M. S. value of the load current and/ or excess of heating at the cooperating contacts. That is, since the copper has a 1.8 voltage drop with respect to aluminum and silver has a 2.25 voltage drop with respect to aluminum, the silver will have a higher potential than the copper when put into surface to surface contact therewith. Hence, the silver-to-copper sequence will be in the back direction oifering a potential energy barrier.

However, during the negative half cycle when the current flows from the copper blade to the parallel paths of the silver brazed jaws, the sequence of the dissimilar contact metals is from copper-to-silver. Since this represents the forward resistance, no potential energy barrier exists during the negative half cycle. Hence, there is no substantial increase in the resistance of the circuit during this half cycle thereby resulting in a largerl value of R. M. S. load current than occurs during the positive half cycle.

In the novel contact arrangement of my invention, which is particularly adaptable for interrupting means having parallel path flow at the cooperating contacts or at -the hinge connect-ion, i provide a silver-to-copper se- -quence in the first path and a copper-.to-silver sequence in the second path. This I achieve by brazing or plating a afilm of silver or silver alloy to the cooperating surface of the jaw and binge which is in the first path and also to the cooperating surface of the blade and hinge which is in the second path. Thus, during the positive half cycle, .a large portion of the current will flow from the blade through the first path containing the sequence of copper-to-silver and a smaller portion of the current will .ilow through the parallel second path, which has a high contact potential barrier, containing the sequence of silver-tocopper. However, during the negative half cycle, a major portion of the current will now flow through the second path containing the copper-to-silver sequence in the direction of current flow to the blade and ,a smaller portion-of the current will [flow through the first path, containing the dissimilar metal sequence of silver-to-copper in the direction of current flow, to the contact arm. Thus, it will be apparent that during both the negative and positive half cycle, the energy potential barrier encountered by the current will be equal.

Accordingly, a prime disadvantage of the prior art dissimilar metal contact arrangement, wherein a larger resistance or energy potential barrier may be encountered in alternate half cycle than in adjacent half cycles, is completely overcome in my novel contact arrangement and hence, the R. M. S. value of the load current for all half cycles is equal.

' Accordingly, one object of my invention is to provide {an arrangement for cooperating contacts under pressure which will equalize the effective resistance for both positive and negative half cycle of current flow and still mantain the advantages achieved by use of dissimilar metals at the cooperating contacts.

' [Another object of my invention is to provide a dissimilar metal contact arrangement for circuit interrupting equipment where n the contact potential barrier is equal for both the positive and negative half cycles of current flow,

' A further object of my invention is to utilize the inherent parallel path arrangement occurring at the jaw "end and hinge end of knife type circuit interrupting paths;

equipment to introduce opposite dissimilar metal sequence in the parallel paths to eliminate asymmetrical resistance.

Still another object of my invention is to provide a novel sequence of dissimilar metals to. obtain equal forward and reverse resistance throughout the full conducting cycle. i

f tb j h my cuit interrupting equipment in which a parallel path current flow is inherent in the construction, it will be; ap

parent to those skilled in the art that-the principles of the invention render it applicable to many other electrical contact applications. For example, the main'cooperating contacts of any one pole of a multipole circuit breaker canbe split into two partsso that both the stationary and moving contacthave two halves, one of silver and one of coppen The'construction permits the silver half and the copper half of; the stationary contacts, respectively, to cooperate with the copper halfand silver half of the ,movable'contact Thus, by this means, the principles These and other objects of my invention will be appari y itis is rr i f r dar ta t Thus, when the disconnect switch It) is in the closed position of Figure 1, current will enter through the terminal 80, passes through the frame casting 73 to the hinge bearing 72, then through current carrying hinge bearing 72 to the hinge casting 70, then through the current carrying connection 62 to the contact blade 63 and then divides between the parallel paths comprising 65R, 90R9 1R,

My present invention is directed to a novel arrangement for the conducting cooperating surfaces 65R, 90R, 91R and 65L, 99L,- 91L. v r

As heretofore noted in the introductory remarks, disconnect switches of the type illustrated in Figure 1 are provided with cooperating contact surfaces of silver and copper in order to'overcome the electrical and mechanical disadvantages encountered by copper-to-copper contact engagement and the economical disadvantages encountered by silver-to-silver contact engagement. Thus,

since all of theab ove described conducting components are made of copper, the copper-silver arrangement at the V cooperating s'urfaceshas heretofore been accomplished willbe from silver-to-copper.

the current diverted to thefirst parallel path comprising by placing silver, contacts on the cooperating surfaces of the members 90R, 91R and- 90L, 91L by means of a brazing or any other well-known procedure, as shown in Figure 3. a

Thus in this arrangement at the positive half cycle when the current is flowing from the terminal 101 to the switch blade 63, the sequence at the cooperating contacts the path 93 and jaws 90R, 91R will passthrough the high a pressure contact from the silver contact secured thereon ent from the following description when taken in 'connectionwith the drawings in which:

. Figure'l is aside view of a typical disconnect switch to whichmy invention is applicable.

Figure 2 is a perspective view of the jaw end of the switch of Figure 1 illustrating the manner in which the contact arrangement of my invention may be applied to the cooperating surfaces.

Figure 3 is a schematic top view illustration of the contact arrangement used in the prior art contacts in which an inherent parallel path is provide'd'.

' Figure 4 is a schematic topview similar to Figure 3 illtistrati'ng the manner in which my invention may be applied to cooperating electrical surfaces which have an inherent parallel path arrangement.

Figure 5 is an'end view taken in the direction of the arrows" 5 5 ofFigure l of the jaw end of 'a disconnect switch and illustrates the adaption of my invention thereto. Figure 6 is a schematic perspective view showing the manner in which my invention may be applied to circuit interrupting equipment which does not have an inherent conducting parallel path.

Referring now to Figure 1, the disconnect switch 10 is'inounted on base 11 by means of insulator16, 17 and 18. The base 11 is also provided with hearing 20-which carries the rotatable vertical shaft 22, the upper end of which is keyed to the insulator 23 for rotation with ver-' tical shaft or post 22a. V

The manner of moving by means of thehandle 30 is fully set forth in patent Serial No. l45,3 89 filed February The stationary contact 66 at the jaw end of the switch 7 10 comprises a pluralityof contact jaws 90R, 91R and 90L, 91L biased towards each other by ,the spring support members 92, 93 and so arranged that when the blade 63 enters at an angle to the horizontal position during the closing operation, it will clear the jaws 90 and 91 on each side. 'The spring jaws 92 and 9 3 are: current conducting and are keyed'in any suitable manner to the base plate 99 which in turn is mounted in any suitable manner to the top of the insulator'17. The base 99 of terminal Q0119 tact structure66 has an extension 101 which serves as a terminal block or connecting member.

to its cooperating copper surface 65R on the switch blade 63.1 Thus, the current will encounter the larger back resistance created as a result of the oxide and sulphide films formed by the exposure of the cooperating surface 65R and R, 91R to the atmosphere.

In like manner, the remaining portion of the current flowing. through. the second parallel path 92 and 90L, 91L through the silver contact to the cooperating copper surface 65L' on the'swit'ch blade 63 will also encounter a' large back resistance.

It will be noted that in Figures 3- and 4,; the cooperating surfaces 65L and 65R of the switch blade 63 respectively are shown spaced from the jaw members: 90L, 91L and 90R, 91R for the sake of clarity. -nowev r, these surfaces are in. effect in high pressure engagement due'to the resiliency of the jaw members 92 and 93 andthe inherent operation of the switch whereby the switch blade 63 has rotation both about its" pivot and'about its own axis. 7

On the negative-half cycle-of current conduction when the currentis fiow'ingifrom the switch blade 63 to the terminal 101, the current diverted through the first piair-azllerpath will flow from the surface 65R to the silver contact brazed to: the jaw portions 90R and 91R'and hence, a relatively small or forward resistance will be encountered by the current flow.

i like manner, the summit flowing through {the alternate parallel path 65L and 90L; 911;. will encounter the same low or forward resistance. Therefore, it will be apparent that :during the positive half eycle of current conduction; a high contact potential barrier will be encountered by the current whereas the opposite or negative half cycle will result in a very magnitude of forward resistance. 7

' witnihearran ement 'of'my inven tion, I am able w overcomethis inherent disadv ntage by providing an 'anrangement wherein .a copper-'to silver path is available to the current on both the positive and negative half cycle of current conduct-i on.

' The ar angement or twenties is illustrated in h perspective of the schematic view ofFi-gui'e 4 and the 'end viewofFigu-re'S.

That is, the portion of a the schematic top views of in any saver magenta, the sliver contact my be r applied to the cooperating surface of the jaw existing in one path and to the cooperating surface of the switch blade existing in the other parallel path. Thus, for example, the silver contact which was previously secured to the jaw 90R, 91R is now secured to the cooperating surface 65R and the switch blade 63, as seen by a comparison of Figures 3 and 4.

The sequence in arrangement for the second path comprising the jaws 90L, 91L and 65L remain the same as heretofore described in connection with the prior art arrangement illustrated in Figure 3. Thus, during the positive half cycle, the portion of the current diverted through the first conducting path 93 will flow through a sequence of copper-to-silver and thereby encounter the small forward resistance thereof.

A very small portion of the current during the positive half cycle of the current conduction will flow through the second conducting path 92 since this current will have to flow through the cooperating contact sequence of silverto-copper and will therefore encounter a large back resistance or high contact potential barrier. Hence, a major portion of the current during the positive half cycle of conduction will flow through the small resistance path 93.

' On the negative half cycle of current conduction, a major portion of the current flow through the second parallel path 92. That is, since the sequence in this path is from copper cooperating contact surface 651. to the brazed silver contact on the jaw 90L, 91L, a relatively small forward resistance will be encountered by the current. During this negative half cycle of current conduction, a relatively small magnitude of current will flow through the alternate first parallel path since this current will encounter the relatively high back resistance due to the silver brazed contact on surface 65R of the blade 63 cooperating with the copper surface of the jaw 90R, 91R.

Thus, it will be seen that both during the negative and positive half cycle of current conduction, a path is provided for the current which has a relatively small forward resistance and the current therefore will be diverted from the parallel path having the relatively back resistance.

In contradis-tinction, the contact arrangement set forth in the prior art structure of Figure 3 results in a high back resistance for both parallel paths when the current flows in the positive half cycle, and both of the paths have a relatively small forward resistance when current is flowing in a negative half cycle. Hence, the effective resistance for alternate half cycles of conduction varies considerably resulting in extreme fluctuations in current magnitude.

However, with my novel contact arrangement, a low forward resistance path is provided for the current irrespective of whether the current is in the positive or negative half portion of the conducting cycle.

A modification of my invention is illustrated in Figure 6 wherein the contact arrangement heretofore described can be applied to circuit interrupting equipment which do not have inherent parallel path current flow.

In the schematic illustration of Figure 6, the main stationary contact 200 is divided into two halves having a silver contact on the left and a copper contact :on the right.

The movable contact arm 201 pivoted at 202 on a stud 203 contains the main movable contact 204. The main movable contact 294 is divided in two halves wherein the left half is a silver contact 204L and the right half is a copper contact 204R. When the contacts are in engaged position, the silver half 200L and copper l'ralf 200R of the stationary contact, respectively, will cooperate with the copper ZML and silver half 204R of the main movable contacts. Thus, during one half cycle of current conduction when the current is flowing from the upper stud 205 to the lower stud 203, a major portion of the current flow from the upper stud 205 the low forward resistance path provided by the copper-tosilver cooperating contacts 230R, 204R through the movable contact earm 201 to the lower stud 203. A relatively small portion magnitude of current will flow through the alternate silver-to-copp'er path 200L, 204L since this sequence of metals for the direction of flow indicated will result in a high back potential barrier.

On the opposite half cycle of current conduction when the current is flowing from the lower stud 203 to the upper stud 205', a major portion of the current will now flow through the second parallel path comprising the sequence of copper to-silver 204L, 200L and :a relatively small magnitude of the current will flow through the alternate first parallel path of silver-tocopper formed 'by 204R, 200R.

Thus, it will be seen that 'by providing each of the contacts of the circuit interrupting means with two sec: tions having dissimilar metals and arranging same so that :a dissimilar sequence will exist for each portion on the engagement of the main contacts, '1 have provided a novel arrangement whereby a low forward resistance path is provided during the entire 360 current conducting cycle.

I have described my invention in connection with metals such as silver and copper. It will be noted that the term silver and copper are not intended to designate merely the pure metals but include metallic compositions consisting essentially of silver and copper respectively. It will also be apparent to those skilled in the art that the novel arrangement of dissimilar rn-etals set forth can be applied to any materials belonging to different voltage series.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claims.

I claim:

1. In a circuit interrupter comprising a switch blade, a jaw end and a hinge end all made of copper metal; said blade rotatably mounted at said hinge end; said blade having an engaged and disengagedposition with respect to said jaw end; said hinge end, said blade and said jaw end providing a current path for said circuit interrupter; engagement of said blade with said jaw providing a first and second current path for current flow through said circuit interrupter; said jaw in said first parallel path having a non-copper contact material secured to its cooperating surface; said blade in said second path having a non-copper conducting material secured to its cooperating surface.

2. In a circuit interrupter comprising a switch blade, a jaw end and a hinge end all made of copper metal; said blade rotatably mounted at said hinge end; said blade having an engaged and disengaged position with respect to said jaw end; said hinge end, said blade and said jaw end providing a current path for said circuit interrupter; engagement of said blade with said jaw providing a first and second current path for current flow through said circuit interrupter; said jaw in said first parallel path having a non-copper contact material secured to its cooperating surface; said blade in said second path having a non-copper conducting material secured to its cooperating surface; said first path being a low resistance path and said second path being a hi h resistance path for a first direction of current flow through said circuit interrupter.

3. In a circuit interrupting device for alternating current having a first and second pair of cooperating contacts under pressure; said first pair of cooperating contacts having a copper to non-copper sequence and said second pair of cooperating contacts having a non-copper to copper sequence when current flows through said circuit interrupter in a first direction.

4. In a circuit interrupting device comprising a first and second pair of cooperating contacts; said first and second pair of cooperating contacts each having movable andstationary contacting surfaces; said contacting surfaces for said movable stationary contact respectively of said first and second pair of cooperating contact surfaces being a coppermaterial; said cooperating surfaces for said movable and stationary contacting surfaces respectively of'said second and first cooperating surfaces being a non-copper material; said first and second pair of cooperating surfaces being connected in electrical parallel circuits; said first pair of cooperating surfaces being a low resistance path and said. second pair of cooperating surfaces being a high resistance path when current flows through said current interrupting device in a first direction; said first pair'of cooperating surfaces forming a high resistance path and said second pair of cooperating surfaces forming a low resistance pathwhen current flows through said circuit interrupting device in a second' direction. 7 V V p 5. In a circuit interrupting device comprising a first and second pair of cooperating contacts; said first and second pair ofcooperating contacts each having movable and stationary contactingsurfaces; said contacting surfaces for said movable stationary contact respectively of said first and second pair of cooperating contact sur- V faces being a silver materiaksaid cooperating surfaces 'forsaid movable and stationary contacting surfaces respectively of said second and first cooperating surfaces being a non-silver material; said first and second pair of cooperating surfaces being connected in electrical parallel circuits; said first pair of cooperating surfaces being a low resistance path and said second pair of cooperating surfaces being a high resistance path when current flows through said current interrupting device in a first direction; said first pair of cooperating surfaces form' ing a high resistance path and said second pair of 00- operating surfaces forming a low resistance path when current flows through said circuit interrupting device in a second direction.

6. In a circuit interrupting device comprising a pair of cooperating contacts; said cooperating contacts being stationary and moving contact surfaces; each of said contact surfaces of 'said cooperating contacts being dir 8 id d i a fi st n s n pa sa d .i Jp bein a copper material and said second part being a silver ma terial; said first and second part; respectively, of sadi stationary contact cooperating with said second and first part of said movable contact; said first part of said'stationary contact and said second part of said movable contact forming a low resistance path and said second part of saidistationary contact and said first part of said movable contact forming a high resistance path' when current flows through'said current interrupting device in a first direction; said part of said stationary contact and said second part of said movablecontact forming a high' resistance path and said second part. of said stationary contact and said first part of said movable contact forming a low resistance path when current flows through said having a silver-to-cop'per sequence and said second pair.

of cooperating contacts having a copper-to-silver sequence during the negative half cycle of current flow through said circuit interrupting means.

8. In a contact arrangement for a circuit interrupter having a first and second'parallel conducting path; said first and second conducting path having a pair of cooperating contacts; said cooperating contacts in said first path having a high contact potential barrier and said.

pair of cooperating contacts in said second path having a low forward resistance when current flows through said circuit interrupter in a first direction; said cooperating contacts in said first path having a low forwardresistance and said cooperating contacts insaid second parallel path having a high contact potential barrier when said current flows in a second direction in said circuit interrupter.

No references cited.

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