US3441699A - Arc control apparatus for load-break switches - Google Patents

Description

April 29, 1969 J. w. ERICKSON 3,441,699

ARC CONTROL APPARATUS FOR LOAD-BREAK SWITCHES Filed May 27, 1968 Sheet of 2 //vv/vr0/?. JOHN W ERIC/(SON April 29, 1969 J. w. ERICKSON 3,441,699

ARC CONTROL APPARATUS FOR LOAD-BREAK SWITCHES Sheet of2 Filed May 27, 1968 ar y nited States Patent US. Cl. 200-144 8 Claims ABSTRACT OF THE DISCLOSURE Arc control apparatus for a load-break switch having a movable contact that is movable along a given path into and out of engagement with a stationary contact; the arc control apparatus comprises an arc-quenching chute including a plurality of metal grid plates slotted to receive the movable contacts, the backs of the grid plates being closed by a back member formed of a material that releases a deionizing gas in the present of an arc, with apertures in the back member permit-ting escape of'gases but precluding recombination of the are behind the chute. An end grid plate of degassing material is also used. A separate arcing contact of spring construction backed up by a support member prevents arching between the main switch contacts.

Cr0ss-references to related applications This application .is a continuation-in-part of application Ser. No. 542,937, filed Apr. 15, 1966, now abandoned.

Background of the invention Load-break pressure contact switches for service entrance and like applications in which the switch may be opened or closed under fault conditions must withstand extremely high currents. Typical low voltage switches of this kind (usually 240 or 480 volts), although nominally rated for currents between 100 and 4000 amperes, may be required to withstand fault currents substantially in excess of 100,000 amperes. When a switch of this kind is actuated under fault conditions, an arc of extremely high current is established between the switch contacts. This frequently results in severe pitting of the switch contacts or even destruction of the switch. There is also a substantial possibility of fire or explosion if the arc is not extinguished almost immediately.

Conventional practice is to provide a multiple-chamber arc chute, along the path of movement of the movable switch contact, that separates the arc into segments and thus accelerate extinction of the arc. Some are chutes of this kind include side wall members that generate a deionizing gas, in the presence of an arc, to assistant in extinction of the arc. Nevertheless, substantial difficulty is still encountered even where conventional arc chutes are employed, particularly in switches of higher amperage ratings.

It has also been known to provide arcing contacts, 1n switches of this kind, that are physically separate from, though electrically connected to the stationary contacts of the switch. A separate arcing contact aids materially in reducing pitting of the main switch contacts. Further more, in conventional bolted pressure contact switches, the use of a separate arcing contact eliminates the necessity for maintaining a dragging engagement between the movable and stationary contacts of the switch during intervals in which the switch is being opened or closed, so that the switch can be thrown more rapidly then would otherwise be possible. But a separate arcing contact can 3,441,699 Patented Apr. 29, 1969 also interfere with operation of the switch if firmly engaged with the movable switch contact during opening and closing movements. On the other hand, if loose engagement or even some separation is permitted, there may be excessive pitting or other damage to the arcing contact.

Summary of the invention It is an object of the present invention, therefore, to provide a new and improved arc control apparatus for a load-break switch that comprises an arc-quenching chute of the multiple-chamber type affording improved efiiciency in operation yet constructed of inexpensive materials and affording an economic assembly.

A more specific object of the invention is to provide a multichamber arc chute construction that allows dissipation of gases from the arc chute chambers while at the same time preventing recombination of the are externally of the chute.

A further object of the invention is to provide an arc control apparatus that includes an arc chute that makes effective use of materials that produce deionizing gases during the arcing attendent upon opening and closing of a load-break switch under fault conditions, yet which maintains the strength and rigidity of met-a1 construct-ion.

An additional object of the invention is to provide a new and improved arc control apparatus for a load-break switch that comprises an arcing contact that is independent of the stationary cont-act of the switch and that is capable of diverting the are produced on opening or closing of the switch from the stationary contact without engendering excessive pitting or potential damage to the arcing contact itself.

Accordingly, the invention relates to an arc control apparatus for a load-break switch employed in service entrance and like applications in which the switch may be opened or closed under fault conditions, the switch including a stationary contact and a movable contact that is movable along a given path into and out of engagement with the stationary contact. The arc control apparatus of the invention comprises a pair of opposed side frame members mounted in spaced relation to each other on opposite sides of the aforesaid path with a plurality of metal grid plates spanning the space between the frame members and forming a plurality of chambers subdividing the are developed upon opening or closing of the switch. Each of these grid plates has a generally V-shaped opening in its forward edge through which the movable contact passes during its opening and closing movements. A back member, formed of a material that releases a deionizing gas in the presence of an arc, extends between the frame members behind the grid plates to close the back of each arc-dividing chamber. Preferably, this back member has a plurality of individual openings individual- 1y aligned with the arc dividing chambers but staggered from side-to-side of the assembly to allow release of gases from the chambers without permitting recombination of the arc. The apparatus further includes an end grid plate of substantially the same configuration as the metal grid plates and spanning the end of the frame members remote from the stationary contact of the switch, this plate also being formed of a material which releases a deionizing gas in the presence of an arc. An arcing contact, separate from the stationary contact, is located at the base end of the apparatus and constitutes a spring contact member backed up by a rigid support member with the contact member positioned to engage the end of the movable switch contact.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, shows preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention.

Brief description 07 the drawings FIG. 1 is a front elevation view of an arc-quenching chute incorporated in an arc control apparatus constructed in accordance with one embodiment of the invention;

FIG. 2 is a sectional view, taken approximately along line 22 in FIG. 1, of one pole of a load-break switch equipped with are control apparatus constructed in accordance with the invention;

FIG. 3 is a plan view of the arc-quenching chute of FIG. 1;

FIG. 4 is a rear elevation view of the arc-quenching chute of FIG. 1;

FIG. 5 is an elevation view of one pole of a 1oadbreak switch equipped with are control apparatus constructed in accordance with another embodiment of the invention; and

FIG. 6 is a detail sectional view taken approximately along line 66 in FIG. 5.

Description of the preferred embodiments FIGS. 1-4 illustrate an arc control apparatus for a load-break switch, including an arc-quenching chute 10, constructed in accordance with one embodiment of the present invention. As shown in FIG. 2. the load-break switch includes a movable contact 11 formed by two blades, only one of the blades being illustrated in the drawing. In FIG. 2, the switch is shown in closed position, with the movable contact 11 engaging a fixed or stationary contact 12. The movable contact 11 and stationary contact 12 may comprise elements of a load-break boltedpressure switch of the kind described in U.S. Patent No. 3,213,247, with the two blades of the movable contact 11 being firmly bolted in pressure engagement with the stationary contact 12 by means of a clamping bolt 19 when the switch is closed. A more detailed explanation of a typical bolted pressure contact switch construction is provided hereinafter in connection with FIG. 5. It should be understood that the present invention is capable of use with many dilferent electrical switch sizes and with a variety of different contact constructions and that the particular construction adopted for the switch or circuit breaker contacts is subject to substantial variation.

The movable switch contact 11 is pivotally mounted upon a pivot pin 13 for counterclockwise rotation from the closed position of FIG. 2 to an open position in which the movable contact is displaced from stationary contact 12. Spanning the tip end of the movable contact 11, between the two contact blades, is a contact block 14 which is a part of the movable contact structure. Contact block 14 is positioned for intermediate sliding engagement with a separate arcing contact 15 that is electrically connected to stationary contact 12. When the switch is in fully closed or fully open positions, block 14 is free of arcing contact 15; engagement therebetween occurs only during opening and closing movements of the switch. Arcing contact 15 is mounted upon a resilient conductive support member 16 secured by appropriate fasteners 17 to two conductive bars 18 which are in turn mounted on the stationary contact 12 of the switch.

From the foregoing, it will be seen that to open the illustrated pole of the switch, the blades of movable contact 1-1 are pivoted in a counterclockwise direction about pin 13. During the early part of this pivotal movement, as the movable contact blades move forwardly along stationary contact 12, contact block 14 engages arching contact 15. Block 14 remains engaged with arcing contact 15 as the contact blades move free of the stationary contact of the switch. Thus, continuous electrical contact is maintained until the free end of the movable contact, block 14, is well into the arc-quenching chute 10. If the switch is operating properly and there is no fault in the electrical circuit connected to stationary contact 12, only a relatively weak arc is drawn between contact block 14 and arcing contact 15 at the time block 14 moves free of the arcing contact and the switch is actually opened.

On the other hand, if there is a fault in the circuit controlled by the switch, it is possible that extremely highcurrent are may be formed. The fault current may reach values well in excess of 100,000 amperes. Under these conditions, the separation of movable contact 11 from stationary contact 12, and more particulary the subsequent separation of contact block 14 from arcing contact 15 results in an extremely high-current high-temperature are between contact members 14 and 15, within the arcquenching chute 10. The arc-quenching chute 10 must function to divide and extinguish this arc, preferably in less than one-half cycle, in order to avoid extreme damage to the switch and to prevent a possible fire or explosion.

The arc-quenching chute 10 includes a pair of opposed side frame members 20 and 21 of dielectric material disposed in spaced relation to each other on opposite sides of the arcuate path followed by the movable contact 11 during opening and closing operations of the switch. A plurality of metal grid plates 22 are mounted between frame members 20 and 21. Grid plates 22 are usually made of steel, although other metals may be used if desired. Grid plates 22 are aligned in spaced relation to each other and form a series of slots or chambers 23 between adjacent grid plates. Thus, as the are between contact block 14 and arcing contact 15 is drawn out with continuing movement of the movable contact of the switch, the arc is subdivided into a plurality of isolated portions.

The subdivided arc tends to expand through the chambers 23 and to recombine at the rear of the grid plates 22, particlarly under high fault conditions. Recombination of the arc externally of the arc-quenching chute 10 is eifectively prevented by a back plate 25 (see FIGS. 2 and 4) that is mounted between the side frame members 21 and 22 and that closes off the rear portion of each of the individual arc chambers 23.

A completely solid and continuous back plate 25 creates a possibility and likelihood that, under fault conditions, the arc will be forced forwardly out of the chambers 23 and will be established between the movable switch contact comprising the blades 11 and the stationary contact 12. This is prevented by .providing back plate 25 with a plurality of individual openings 26. Openings 26 permit part of the heat and gas created by the arc in the individual chambers 23 to pass through the back plate 25 and prevent the are from being blown out frontwardly of the chambers 23.

As shown in FIGS. 2 and 4, each of the apertures 26 in back plate 25 is aligned with a respective one of the chambers 23 and relieves pressure from that one chamber only. Furthermore, the individual apertures 26 are not as wide as the back portions of the related chambers 23 and do not permit the arc to blow completely out of the back portion of the arc-quenching chute. Instead, the apertures 26 are staggered from side-to-side of the chute 10 and each extends for less than one-half of the width of the back plate 25. Thus, back plate 25 blocks the individual arc-quenching chambers on a staggered basis that prevents recombination of the arc segments in series behind the arc chute. With the illustrated construction adequate pressure relief is obtained without recombination of the are behind the arc chute.

Back plate 25 and side plates 20 and 21 are each formed of a plastic, ceramic, hardboard, or even paperboard material which, when subject to high temperature, generate a deionizing gas that aids materially in extinction of the arc. A number of suitable and well-known refractories, plastics, and hardboard materials are commercially available that may be employed in the fabrication of the side frame members 20 and 21 and back member 25. Preferably, side frame members 20 and 21 are made of a molded plastic material for economy and efficiency in production. The deionizing gases developed by the side plates 20 and 21 and the back plate 25, particularly under the high temperatures developed in interruption of fault currents, aid materially in extinguishing the arc. 1

Another element in the arc-quenching chute that aids materially in preventing continuation of the are upon opening of the movable switch contact is the endmost grid plate 30, FIGS. 1, 2 and 3. Grid plate 30 is not formed of metal. Instead, it is fabricated from a suitable plastic, ceramic, or hardboard material that generates deionizing gas when subject to the high temperatures of an electrical arc. Two or more of the end grid plates can be constructed of such material, but one is usually adequate.

As best seen in FIG. 1, the preferred configuration for the end plate 30 is one which is identical to the metal grid plates 22. In the preferred construction, the metal grid plates 22 are stamped or punched from sheet steel. In a like manner, the end plates 30 maybe punched to the same configuration from a sheet of plastic or hardboard material, using the same dies. Moreover, the thickness of the end grid plate 30 is preferably the same as the steel grid plates 22.

As shown in FIGS. 1 and 3, grid plates 22 and 30 are relatively flat plates each formed with a V-sha-ped opening of decreasing size from their forward edges 34 toward a rear central surface 35. More particularly, the openings in the grid plates 22 and 30 each comprise a pair of converging oblique edges 36 and. 37 leading to rounded surfaces 38 and 39 terminating in the rounded surface 35. The shape of the openings in each of the grid plates 22 and 30 is dimensioned to surround the tip portion of the movable switch contact, comprising block 14, on three sides without contacting the block, thereby providing a wraparound arc chute for the switch. As seen in FIG. 2, grid plates 22 and 30 are arranged in an arcuate configuration along radial lines from the pivotal axis of the movable switch contact (pivot pin 13) to surround the outer ends of the movable switch contact 11 as the latter moves along its arcuate path in opening or closing of the switch. This construction assures isolation of the arc, upon actuation of the switch, within the chambers 23 where it is divided and extinguished.

For convenience of assembly, side frame members 20 and 21 are each provided with a series of slots or openings for receiving the end portions of the side walls of the grid plates 22 and 30 to hold the grid plates in their mounted position between the side frame members of the arc-quenching chute. Back plate 20is held in position against the rearward portions of the grid plates by two generally U-shaped shoulder or mounting members 40 and 41 that are a part of the side frame members 20 and 21, respectively. Thus, each mounting member has an upper generally right-angle leg 45 extending over the top grid plate 30 and a lower leg 46 extending beneath the lower grid plate 22. Mounting members 40 and 41 are shown as separate elements in the drawing but may be formed integrally with the respective side frame members 20 and 21.

Grid plates 22 and 30 and back plate 25 are all locked into the assembly comprising arc-quenching chute 10 by means of a pair of tie members 46 and 47 that extend between the side frame members 20 and 21 of the chute. Nuts 48 and 49 threaded onto the tie members hold the complete assembly together in rigid relationship. Manifestly, other kinds of mounting or securing means can be employed in lieu of bolts 46 and 47. For example,

grid plates 22 may themselves include fasteners extending through the opposed side frame members 20 and 21 and crimped to provide a rigid assembly. The illustrated construction is preferred, however, since it avoids any necessity for individual fastening of the grid plates to the side frame members.

Arc chute 10 can be mounted independently of the electrical portion of the switch. However, in the preferred construction illustrated in FIGS. 1-4, the arc chute is directly mounted upon a part of the stationary contact for the switch. More specifically, the side frame members 20 and 21 include dependent fingers 50 and 51 formed with opposed pairs of integral bosses extending toward one another. An upper pair of bosses 52 and 53 and a lower pair of bosses 54 and 55 on the side frame members receive bolts 60 and 61, respectively, to mount the arc-quenching device on the spaced bars 18 that support the arcing contact 15 and that constitute a part of the stationary contact of the switch.

With electrical switches of different ratings, the size and shape of grid plates 22 and 30 may be changed. However, the side frame members 20 and 21 may be utilized for a relatively large range of switch ratings without modification. More specifically, side frame members 20 and 21 of a given specific size may be readily employed with switches encompassing a wide range of voltage and current ratings (e.g., 120 to 480 volts and to 1200 amperes) merely by changing the size of the grid plates.

FIGS. 5 and 6 illustrate a single pole of a load-break switch that incorporates a modification of the arc control apparatus of the present invention. The movable contact 11 of the switch comprises two pairs of movable contact blades; only one blade appears in FIG. 5 but segments of each are illustrated in FIG. 6, being designated as blades 11A, 11B, 11C and 11D. As before, the movable blade contact is pivotally mounted upon the pivot pin 13. FIG. 5 illustrates a part of the operating mechanism for the switch, typical of construction used in bolted pressure contact switches.

The operating mechanism of the switch as shown in FIG. 5 comprises a crank 101 that is pivotally mounted upon pin 13, rotation of crank 101 being independent of pivotal movement of the blades 11A-11D forming the movable contact 11 of the switch. Crank 101 is pivotally connected by a pin 102 to a link 103 with the opposite end of link 103 being pivotally connected by a pin 104 to a lever 105. The lever 105 is afiixed to the bolt 19 that extends across the movable contact 11 of the switch between the two pairs of contact blades. Bolt 19 is threaded into two nuts (not shown) that are aflixed to the outside blades of the movable contact assembly. A spring 106 is connected between link 103 and the inner contact blades.

In the construction illustrated in FIGS. 5 and 6 the arcquenching chute 10 is utilized without substantial change from the embodiment described above. It includes the side frame members 20 and 21 mounted upon an extension portion 112A of the stationary contact 112, which in this instance is of hollow squared-cylinder construction. Inasmuch as the arc-quenching chute is the same as described above in connection with FIGS. 1-4, it is not shown in detail in FIGS. 5 and 6.

The embodiment of FIGS. 5 and 6 further includes an arcing contact 115 mounted upon a resilient conductive arm 116 that is aflixed to the stationary contact extension 112A. As before, the arcing contact is positioned to engage a contact block 14 mounted between the tip ends of the movable blades of contact 11. In this instance, however, the arcing contact is provided with a rigid support member 121 mounted behind the arcing contact in position to limit movement of the arcing contact away from the movable contact of the switch.

In opening of the switch, crank 101 is rotated in a clockwise direction about pin 13. The initial movement of the crank pulls link 103 to the left and pivots lever 105 in a counterclockwise direction. This rotates bolt 19 and releases the clamping pressure that presses the two pairs of movable contact blades against the legs of the stationary contact 112 when the switch is closed. Continuing movement of crank 101, after unbolting of the switch, pivots movable contact 11 in a counterclockwise direction about pivot pin 13 to open the switch in the manner described above in relation to the embodiment of FIGS. 1-4.

During opening and closing movements of the switch it is quite important that little or no mechanical drag be applied to the contacts. As the switch opens, contact block 14 on the movable cointact engages arcing contact 115. The relatively light pressure exerted by the spring arm 116 upon which the arcing contact is mounted does not interfere to any appreciable extent with the opening and closing movements of the switch. This makes it possible to open and close the switch rapidly, minimizing arcing within the switch and reducing pitting of all contacts including the arcing contact.

If the switch is opened or closed under fault conditions, the high current are produced between contact block 14 and arcing contact 115 forcibly drives the arcing contact away from block 14. With a spring 116 that is light enough to permit rapid actuation of the switch, as described above, the force applied to the arcing contact may be great enough to deform the arcing contact mount or even break it off completely. The result may be permanent damage to the stationary contact 112 through excessive arcing between the main Contacts of the switch, since the arcing contact 115 is no longer availavle for protection. Thus, it may become necessary to replace the arcing contact and the switch operator may not immediately recognize this requirement.

This difficulty is obviated by the use of the support 121 mounted close behind arcing contact 115. The relatively heavy and rigid support 121 interrupts the backward movement of arcing contact 115, under fault conditions, before the arcing contact can move far enough to elfect a permanent deformation of its spring 116. Consequently, a relatively lightweight spring 116 can be used safely without substantial likelihood of damage to the arcing contact or any other portion of the switch as the result of opening or closing of the switch under fault conditions, while at the same time avoiding excessive drag on the switch for normal opening and closing movements. The illustrated construction provides much freer movement of the switch than is possible with more conventional arrangements in which arcing contacts are engaged by pressure between the switch blades in a manner similar to that utilized in conjunction with the prinicpal stationary contact of the switch.

Hence, while preferred embodiments of the invention have been described and illustrated, it is to be understood that they are capable of variation and modification.

I claim:

1. In a load-break switch for service entrance and like applications in which the switch may be opened or closed under fault conditions, said switch including a stationary contact and a movable contact, said movable contact being movable along a given path into and out of engagement with said stationary contact to open and close the switch, arc control apparatus comprising:

a pair of opposed side frame members disposed in spaced relation to each other on opposite sidesof said path;

a plurality of metal grid plates spanning the space between said frame members to form a plurality of chambers subdividing the arc developed upon openin g or closing of the switch,

each of said grid plates having a generally V-shaped opening in its forward edge through which said movable contact passes during its opening and closing movements;

a back member extending between said frame members and disposed rearwardly of said grid plates to close the back of each of said chambers, said back member being formed of a material which releases a deionizing gas in the presence of an arc;

and an end grid plate of substantially the same configuration as said metal grid plates, spinning the end of said frame members remote from said stationary contact, formed of a material which releases a deionizing gas in the presence of an arc.

2. Arc control apparatus for a load-break switch according to claim 1 in which said back member has a plurality of individual openings extending therethrough, each opening being aligned with a respective one of said chambers, said openings each extending for less than onehalf the width of its associated chamber and said openings being staggered alternately from side-to-side of said apparatus to allow dissipation of heat and gas from the chambers without recombination of the arc externally of the chambers.

3. Are control apparatus for a load-break switch according to claim 1 in :which said side frame members each includes a plurality of slots for receiving and aligning said grid plates in an arcuate array, said apparatus further including at least two tie members extending across said device between said side frame members for securing said side frame members, said back member, and said grid plates together in a rigid assembly.

4. Arc control apparatus for a load-break switch according to claim 3 and further including a pair of mounting members, one of said mounting members extending along each of said side frame members in engagement with the edge portion of said back member to clamp said back member between said mounting members and said grid plates.

5. Arc control apparatus for a load-break switch according to claim 1 in which said grid plates are aligned in an arcuate array and are disposed along radial lines from the pivot point of an arcuately movable switch contact with the forward edges of the grid plates spaced more closely adjacent to one another than the rearward ends of the grid plates and in which said openings in said forward edges of said grid plates define a convergent arcuate passageway for said movable contact.

6. Arc control apparatus for a load-break switch according to claim 1 and further including a resilient arcing contact electrically connected to but spaced from the stationary contact of said switch, located along the path of said movable switch contact in position to engage the end portion of said movable contact with only a light pressure over a portion of said path that overlaps the separation of the movable contact from said stationary contact on opening of the switch.

7. Arc control apparatus for a load-break switch according to claim 6 in which said arcing contact is a cantilever spring supported contact positioned adjacent one end of said movable contact and further comprising an auxiliary support member mounted adjacent said arcing contact on the opposite side thereof from said movable contact in position to limit movement of said arcing contact away from said movable switch contact in the presence of high fault currents.

8. In a load-break switch for service entrance and like applications in which the switch may be opened or closed under fault conditions, said switch including a stationary contact and a movable contact, said movable contact being movable along a given path into and out of engagement with said stationary contact to open and close the switch, arc control apparatus comprising:

an arc-quencing chute, mounted in substantially encompassing relation to said path adjacent said stationary contact, for subdividing and extinguishing the are developed upon opening or closing of the switch;

a resilient cantilever-mounted arcing contact, electrical- UNITED STATES PATENTS 2,160,681 5/1939 Sandin 200147 6/1941 Graves 200144 1/1943 Rawlins 20062 4/1955 Cellerini 200144 6/ 1958 Gieffers 20062 X 3/1965 Jencks et a1. 200144 FOREIGN PATENTS 4/1964 Belgium. 10/1965 Germany.

ROBERT s. MACON, Primary Examiner.

US. Cl. X.R.

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