US3472984A

US3472984A - Switch for high energy circuits utilizing contact bounce reduction

Info

Publication number: US3472984A
Application number: US657712A
Authority: US
Inventors: Richard T Cusick
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1967-08-01
Filing date: 1967-08-01
Publication date: 1969-10-14
Anticipated expiration: 1986-10-14

Description

Oct. 14, 1969 cus c 3,472,984

SWITCH FOR HIGH ENERGY CIRCUITS UTILIZING 7 CONTACT BOUNCE REDUCTION Filed Aug. 1, 1967 2 Sheets-Sheet l 1 I6 I: I. Q I I I I I I4 illltlllllllm III .111

IN\ ENTOR. RICHARD I CUSICK ATTORN Oct. 14,1969

' R. T. CUSICK SWITCH FOR HIGH ENERGY CIRCUITS UTILIZING I CONTACT BOUNCE REDUCTION Filed Aug. 1, 1967 2 Sheets-Sheet 2 F'IGQZ A w P 0 Us I'll-IL Q v] p n. I @c w% I.

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United States Patent 3,472,984 SWITCH FOR HIGH ENERGY CIRCUITS UTILIZING CONTA'CT BOUNCE REDUCTION Richard T. Cusick, Laurel, Md., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Continuation-impart of application Ser. No. 467,798, June 28, 1965. This application Aug. 1, 1967, Ser.

Int. Cl. H01h 3/60 US. Cl. 200166 4 Claims ABSTRACT OF THE DISCLOSURE A switch for high energy circuits designed so as to avoid contact burning. The switch comprises a series of movable contact shoes mounted on a shaft which is caused to move by the action of hydraulic means. The contact shoes are attached to the shaft by a resilient spring-like member which continually forces the contact shoes toward bus-bar contacts after initial contact therebetween is made, thereby reducing contact bounce. To further reduce contact bounce, auxiliary contacts are fixedly mounted on the bus-bar contacts and serve to wedge the contact shoes toward said bus-bar contacts; the contact shoes and the bus-bar contacts are each provided with a curved surface so that only point contact exists therebetween; and the time between the initial activating thrust of the contact shoes and the initial contact between the shoes and the bus-bar contacts is regulated so that initial contact is made at time when contact bounce is minimal.

CROSS-REFERENCE TO RELATED APPLICATION The present application is a continuation-in-part of a copending US. patent application by the same inventor, Ser. No. 467,798, filed June 28, 1965, now Patent No. 3,344,248.

BACKGROUND OF THE INVENTION Field of the invention The subject invention relates to a pneumatically operated switch for high energy circuits, and more particularly to a high energy switch which has an extremely long contact life since harmful contact bounce, which causes arcing and burning, is greatly reduced, and since high contact resistance, which also causes arcing and buring, is avoided.

Description of the prior art Switches of the type used in high energy circuits have a characteristically short life due to arcing. Complete destruction or fusion welding of the contacts is common where the making of the circuit has not been effectively performed; and the most common deficiency of existing switches resides in poor surface contact. Hitherto, an increase in the speed of circuit closing ha produced undesirable contact bounce, with resulting arcing.

In the above-noted copending patent application, there is disclosed a high energy switch which shows a great reduction of arcing when compared with the swtiches of the prior art. In that application, a switch is disclosed wherein a line contact is initially formed between the contact shoes and the bus-bar contacts; and, as the contact shoes slide along the bus-bar contacts, the line contact is transformed into a planar contact. Though this switch shows a marked improvement over the switches known to the prior art, still a certain amount of contact burning remains.

3,472,984 Patented Oct. 14, 1969 ICC It has been discovered that where the initial contact between the contact shoes and the bus-bar contacts is in the form of a line contact, alignment is extremely criticalmisalignment being one cause of severe contact burning. It has also been found that Where the final contact between the contact shoes and the bus-bar contacts is in the form of a planar contact, contact floating, resulting from the pressure generated by ionized metal vapor, is existent. Furthermore, it has been found that high contact resistance, another cause of contact burning, exists in both the line and planar contact modes. And, finally, it has been found that contact bounce is not minimized unless the initial contact between the contact shoes and the bus-bar contacts is properly timed.

SUMMARY OF THE INVENTION The subject invention relates to a switch for high energy circuits wherein contact life is greatly increased due to a reduction in contact bounce and a reduction in contact resistance. Particularly, contact bounce is reduced by providing the contact shoes and the bus-bar contacts with curved surfaces, thereby limiting the contact therebetween to a point contact; by timing the travel of the contact shoes so that initial impact with the busbar contacts is made at a time most advantageous to bounce reduction; by attaching the contact shoes to a mounting shaft with resilient members which force said contact shoes toward said bus-bar contacts; and by providing said bus-bar contacts with auxiliary contacts for wedging the contact shoes against the bus-bar contacts. The reduction of contact resistance is accomplished by the utilization of a point contact between the contact shoes and the bus-bar contacts.

Since the subject switch utilizes only point contact between its contact shoes and its bus-bar contacts, it is obvious that the alignment diificulties and the contact floating problems, existent in the switch of the above-noted copending application, have, to a large degree, been overcome. Furthermore, the use of a point contact reduces contact resistance sufficiently so as to noticeably reduce contact burning.

It is therefore an object of this invention to provide a switch constructed so as to provide a suitable circuit closing device for high-energy circuits.

Another object of this invention is to provide a switch having a short reaction time.

A still further object of this invention is to provide an efficient yet safe switch wherein contact is made in such a manner that contact life is substantially increased.

A further object of this invention is to provide an economical switch for high-energy circuits.

An additional object of this invention is to provide a pneumatically operated switch.

Yet another object of this invention is to provide a switch in which contact bounce upon closing is substantially reduced.

A still further object of this invention is to provide a switch wherein contact resistance is greatly reduced.

Further objects and many of the attendant advantages of this invention will be readily appreciated as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of the subject switch;

FIG. 2 is a side view of the contact shoes and the busbar contacts of the switch shown in FIG. 1;

FIG. 3 is a front elevation view of the contact shoes and the bus-bar contacts shown in FIG. 2;

FIG. 4 is a top plan view of the contact shoes and its associated leaf-spring assembly;

FIG. 5 is shows a time sequence of the switch shown in FIG. 1 while said switch is closing; and

FIG. 6 shows a second embodiment of the contact shoes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit closing switch of the instant invention is adapted to be used in high-energy circuits of the type utilized in supplying D.C. power to plasma arc generators. It is contemplated that the instant switch will be used in circuits wherein 32,000 amperes (steady-state) is not uncommon (peak inrush currents being as high as 50,000 amperes) and wherein the voltage ranges up to 2,400 volts.

The switch of the present invention includes a first and a second series of bus-bar contacts having a lateral gap therebetween and having auxiliary contacts mounted thereon; a mounting shaft disposed between said first and second series of bus-bar contacts for vertical movement into neutral and activated positions; spring means encompassing said shaft and adapted to urge said shaft into said neutral position; drive means for urging said shaft into said activated position; a laterally extending resilient conducting member attached to said mounting shaft; contact means connected to said conducting means and adapted to initially engage said bus-bar contacts and subsequently move into engagement with said auxiliary contacts; and laterally extending slotted resilient spring-like members attached to said mounting shaft and adapted to insure continuous contact between said contact means and said busbar contacts.

Referring then to FIG. 1, bus-bar contacts 2 are supported by plastic or Glastex insulators 8 on supports 4 which are connected to a wall protection plate 6. Auxiliary contacts 9 are mounted on the bus-bar contacts 2. Disposed between the ends of the bus-bar contacts 2 is a mounting shaft 10 of high-strength plastic impregnated glass. Attached to the upper portion of this shaft is an insulating member 12 of high strength glass fibre which slides in a bushing -14 to guide the vertical motion of the shaft 10. The bushing 14 is attached to a bracket 16 mounted on the wall protection plate 6. The lower portion of the shaft is guided by a plate 18 which is attached to the wall plate 6 by an insulating spacer 20. Connected to the lower end of the shaft is a second insulating member 23 which effectively insulates the shaft 10 from a shaft extension 10' which is connected to the lower portion of the insulating member 23. The shaft 10' enters a pneumatic cylinder 24 containing a piston (not shown) which is adapted to drive the shaft 10 downwardly.

Mounted on the shaft 10 near its upper end is a laterally extending resilient conducting member 26. The mounting shaft extends through the conducting member 26 medially of its length and width and is secured thereto by locking nuts 28. The member 26 is formed of thin plies of copper, is of generally bow-like configuration, and is connected at its extremities to contact shoes 30 by bolts 32.

The contact shoes 30 are formed with curved portions 34 so that when said shoes are initially brought into engagement with bus-bar contacts 2, point contact is made between points represented by the arrow on the contact shoes and the arrow on the bus-bar contacts. (It should be noted that the point of initial contact and the point of final contact are not coincidental. This feature allows final contact to be made at a point not eroded by the small amount of unavoidable burning caused by initial contact.) The curved or bus bar engaging areas 34 of the contact shoes 30 are formed of high heat resistant material. In the above-noted copending application, the high heat resistant material is a sintered silver-tungsten alloy of 50% silver and 50% tungsten; but it has been found that an alloy of 25% silver and 75% tungsten is more suitable.

When the shaft 10 is moved into its lower position, as shown in full lines in FIG. 1, the curved portions 34 of the contact shoes 30 will slide on the bus-bar until the portions 35 of said shoes engage the auxiliary contacts 9. The contact portions 35 are formed of a material which is not required to be as resistant to heat as that used at the contact areas 34, since no initial contact is made between the contact portions 35 and the auxiliary contacts 9, and consequently, there is no excessive heat concentration or arcing in this area. In the above-noted copending application, it is disclosed that the contact areas 34 are of an alloy of silver and 20% tungsten; but it has been discovered that an alloy containing silver and 10% tungsten is more suitable.

Also mounted centrally on the shaft 10 below the conducting member 26 are multiple leaf springs 36 which are held in position by lock-nuts 38. The springs 36 are connected to the contact shoes 30 by bolts 40, and function to greatly reduce contact bounce. That is, when initial contact is made, the springs 36 provide the required closing force and also operate to prevent the contact shoes 30 from bouncing or braking contact with the bus-bar contacts 2, by urging said shoes toward said bus-bar contacts.

Encompassing the shaft 10 and engaging the plate 18 is a spring 42. A washer 44 is positioned on the shaft 10 below the lower lock nut 38 to provide an adequate upper spring stop. The spring 42 is adapted to urge the shaft and contacts toward the neutral, or open, position when the shaft 10 is in its activated position. Upon failure of the pneumatic drive means, the spring 42 will cause the switch to open, thereby providing inherent safety to attendant personnel.

As noted above, it has been discovered that a point contact reduces contact burning to a much greater extent than does a line contact or a planar contact, since alignment and contact floating problems, as well as high contact resistance problems, are eliminated. With reference, then, to FIGS. 2 and 3, the particular configuration of the contact shoes 30 and the bus-bar contacts 2 which give rise to point contacts will be described. As shown in FIG. 2, the bus-bar engaging areas 34 of contact shoes 30 are arcuate throughout their lengths. Therefore, if the contact surfaces of bus-bar contacts 2 were flat, line contact between contact shoes 30 and bus-bar contacts 2 would occur. (This is disclosed in the above-noted copending application.) But, as can best be seen in FIG. 3, the contact surfaces of the bus-bar contacts are also arcuate, as shown at 46. In practice, the bus-bar contacts 2 are composed of a flat plate 48 upon which curved or arcuate sections 46 are attached. It is therefore evident, since the bus-bar engaging areas 34 are curved, and since the contact surfaces 46 of busbar contacts 2 are curved, wherein the axes of rotation are normal to one another, only a point contact exists between contact shoes 30 and bus-bar contacts 2; and, as noted .above, such point contact eliminates the need for contact alignment, eliminates contact floating, and reduces contact resistance.

It should here be noted that there is a certain amount of unavoidable contact burning which occurs upon initial contact between the contact shoes and the bus-bar contacts, and therefore, there is always a certain amount of ionized metal vapor generated. It has been found that when initial contact is in the form of a line contact, the vapor is squeezed toward the area of final contact; but when initial contact is in the form of a point contact, this problem does not exist since the metal vapor is forced outwardly, away from the area of final contact. That less metal vapor appear in the area of final contact further reduces contact burning.

It should also be noted that the provision of a point contact has not reduced the oxide-scraping feature found in the above-noted copending application. When the contact shoes wipe across the bus-bar contacts, any layer of oxide which is present is still scraped away, thereby enhancing contact between the contact shoes and the bus-bar contacts.

With reference now to FIG. 4, a top plan view of the contact shoes and the leaf springs, the geometry of the springs will be discussed. Though four contact shoes are shown, it should be understood that any number of shoes can be used.

As discussed above, the contact shoes 30 are attached to the mounting shaft by leaf springs 36. As seen in FIG. 4, the leaf springs 36 span the entire array of contact shoes 30 and are slotted intermediate each pair of contact shoes. Since four shoes are shown, three slots, 50, 51 and 52 appear. It should be noted that

slots

50, 51 and 52 are of different widths, said width difference being greatly exaggerated for clarity.

The function of the slots is twofold. First, the slots allow the contact shoes to work somewhat independently, thereby avoiding alignment difiiculties; and, second, that the slots are of unequal widths causes the contact shoes to have unequal resonant frequenciesthe frequency difference increasing the probability that at least one shoe in the array is making good contact with its associated bus-bar contact at all times.

With reference now to FIG. 5, there is shown a time sequence of the position of the contact shoes between initial activation of the hydraulic drive means and final contact between the contact shoes and the bus-bar contacts. It is evident that when the hydraulic means is activated and mounting shaft is urged in the direction of the arrow 54, leaf springs 36 :and contact shoes 30 Will begin to oscillate; and, as noted above, there are times during the travel of the contact shoes 30 and the leaf springs 36 when initial contact will best reduce contact bounce. That this is true is evident when reference is made to the time sequence of FIG. 5.

FIG. 5a shows the contact shoes 30, the leaf springs 36 and the mounting shaft 10 at a time shortly after initial activation of the hydraulic drive means (arrows 56 being representative of the instantaneous direction of shoe movement); FIG. 5b shows the assembly at a time when oscillation-caused contact shoe separation is at a maximum; FIG. 50 shows the assembly at a time shortly after the contact shoes pass through their maximum separation position; FIG. 5d represents the assembly at a time when the contact shoe separation is at a minimum; FIG. 5a shows the assembly at a time shortly after the contact shoes are 'at their minimum separation position (ideal conditions for initial contact); and FIG. 5f shows the contact shoes, the leaf spring and the busbar contacts 2 at a time when contact has been completed.

As noted above, when the hydraulic drive means is first activated, the contact shoes begin to oscillate due to the resiliency of leaf spring 36 and the weight of the assembly. It is evident that if initial contact between the contact shoes 30 and the bus-bar contacts 2 occurs at a time when the contact shoes are spreading apart, contact bounce is reduced when compared with the situation wherein initial contact is made when the contact shoes are moving toward one another. Therefore, in the present switch, the time between the initial thrust of the hydraulic drive means and the initial contact between the contact shoes and the bus-bar contacts is regulated so that contact between the shoes and the bus-bar contacts is made while the contact shoes are spreading apart. FIG. 5e represents the ideal situation for initial impact, for the maximum reduction of contact bounce.

Reiterating, it has been found. that due to oscillatory motion in the contact shoe-leaf spring assembly, there is an initial impact time, during the downward motion of the contact shoes, which minimizes contact bounce. That time is when the contact shoes, due to oscillatory motion, are spreading apart. The regulation of initial impact, obviously, can be performed in numerous ways. Among the least cumbersome methods are varying the distance between the contact shoes and the bus-bar contacts while the assembly is in its neutral position, and varying the 75 oscillatory resistance of the shoe assembly by acting upon the dimensions and the materials of the assembly.

It has been noted that contact bounce can be reduced by utilizing point contacts between the contact shoes and the bus-bar contacts. It has further been noted that to still further reduce contact bounce, initial contact between the contact shoes and the bus-bar contacts should be made at a time when the contact shoes, due to their oscillatory motion, are moving apart. But even with the great reduction of contact bounce realized in the present invention, all contact bounce has not yet been eliminated. Therefore, there is still a certain amount of contact shoe burning that occurs.

When the bus-bar engaging areas 34 of contact shoes 30 have been partially eroded, the contact shoes must either be replaced or repaired. One repair method involves the replacement of bus-bar engaging areas 34. It has been found that the size of the bus-bar engaging areas 34 is not critical; and, therefore, the bottom portion of the contact shoes 30 can be milled down and rebuilt with a thick pre-shaped portion of bus-bar engaging material. This embodiment is shown in FIG. 6.

After the bus-bar engaging area 34 of FIG. 2 has been eroded, the bottom portion of the contact shoe 30 can be milled along line 58 (shown in FIG. 6) and bus-bar engaging area 60, in the form of a pre-shaped slab of silver-tungsten alloy, can be secured to the remainder of contact shoe 30.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that in the scope of the appended claims, the invention may be practised otherwise than as specifically described.

I claim:

1. A switch for high energy circuits comprising a plurality of bus-bar contacts, each having an arcuate surface formed with a first axis of rotation;

a plurality of contact shoes, each having an arcuate surface formed with a second axis of rotation normal to said first axis of rotation;

a mounting shaft capable of movement into neutral and activated positions;

drive means associated with said shaft and capable of urging said shaft into movement;

laterally extending resilient conducting means connected to said contact shoes and to said mounting shaft;

laterally extending resilient bounce reducing means connected to said contact shoes wherein said bounce reducing means is slotted intermediate each pair of contact shoes and wherein said slots are of unequal widths; and

means for regulating the time between initial activation of said drive means and initial contact between said contact shoes and said bus-bar contacts so that said initial contact between said contact shoes and said bus-bar contacts occurs when said contact shoes, due to oscillatory motion, are spreading apart, thereby reducing contact bounce.

2. The switch of claim 1 further comprising an auxiliary contact means mounted on each of said bus-bar contacts for wedging said contact shoes against said busbar contacts.

3. A switch for high energy circuits comprising,

a plurality of bus-bar contacts,

a plurality of contact shoes,

a mounting shaft capable of movement into neutral and activated positions,

drive means associated with said shaft and capable of urging said shaft into movement,

said bus-bar contacts and said contact shoes being disposed laterally on each side of said mounting shaft in confronting relationship,

laterally extending conducting means connected to said plurality of contact shoes, and

laterally extending resilient means connecting said plurality of contact shoes to said drive shaft so that movement of said shaft towards its activated position causes said contact shoes to oscillate laterally towards and away from one another and whereby initial impact between said bus-bar contacts and said contact shoes is made shortly after said contact shoes are in a condition of minimum separation.

4. A switch for high energy circuits comprising,

a plurality of bus-bar contacts,

a plurality of contact shoes,

a mounting shaft capable of movement into neutral and activated positions,

said bus-bar contacts and said contact shoes being disposed laterally on each side of said mounting shaf in confronting relationship,

laterally extending leaf spring means supporting a plu- UNITED STATES PATENTS 1,764,415 6/1930 Riley 20082.1 2,324,891 7/1943 Thumin 200146 2,716,682 8/1955 Franklin 200164 XR 2,850,602 9/1958 Breese et a1 200164 XR 3,002,063 9/ 1961 Giladett 20082 XR 3,031,548 4/1962 Robinson ZOO-82 XR RO BERT K. SCHAEFER, Primary Examiner H. BURKS, Assistant Examiner U.S. Cl. X.R. 20082, 146, 164