US2749410A

US2749410A - Arc chute with perforated barrier plates having staggered slots

Info

Publication number: US2749410A
Application number: US303988A
Authority: US
Inventors: Donald E Weston
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1952-08-12
Filing date: 1952-08-12
Publication date: 1956-06-05
Anticipated expiration: 1973-06-05
Also published as: GB735955A; DE1027281B; FR1075766A

Description

June 5, 1956 D. E. WESTON 2,749,410

ARC CHUTE WITH PERFORATED BARRIER PLATES HAVING STAGGERED SLOTS Filed Aug. l2, 1952 3 Sheets-Sheet 1 @o 9 0 o L 1 V' 3kg/l June 5, 1956 D. E. WESTON 2,749,410

ARC CHUTE WITH PERFORATED BARRIER PLTES HAVING STAGGERED SLOTS Filed Aug. l2, 1952 3 Sheets-Sheet 2 ,J 1 `O O j i-- ll 27 4 2 5 O IY G/ O LOC OOOO

CODO

3 O O (D O June 5, 1956 D. E. WESTON 2,749,410

ARC CHUTE WITH PERFORATED BARRIER PLATES HAVING STAGGERED SLOTS Filed Aug. l2, 1952 3 Sheets-Sheet 3 O f o q 35 :z Id. o @f 1Q i;

ARC CHUTE WETH PERFQRATED BARRER PLATES HAVEN@ STAGGERED SLOTS Donald E. Weston, Brookline, Mass., assigner to Aliis Chalmers Manufacturing Company, Milwaukee, Wis.

Application August 12, 1952, Serial No. 303,988

7 Claims. (Cl. 20G-144) This invention relates to circuit interrupting devices and more particularly to arc extinguishing means for use in connection therewith.

In the construction and operation of circuit interrupters, it is frequently necessary to provide means for extinguishing quickly the arc which is drawn between separable arcing contacts. This arc is usually blown by blowout means, such as a magnetic blowout coil or an air blast, into an arc chute which is arranged to quench the arc by lengthening it, cooling it, or a combination of both.

Arc chutes having spaced insulating plates to lengthen the arc or squeeze the arc into narrow slots have been used to rapidly increase the arc voltage, decrease the arc current and greatly improve the power factor, thereby facilitating interruption of the arc at a natural or forced current zero. However, it has been found in many cases that the arc voltage developed by the arc chute was not the most favorable for interrupting the power circuit.

The geometry of the arc chute determines the are voltage which will be developed for circuit interrupting purposes. This arc voltage can be expressed as a percentage of the line voltage and therefore is not limited to any particular voltage class of breaker.

The are chute for an electromagnetic type of circuit breaker is designed to perform two functions, namely, to interrupt a power circuit and to enclose the are products.

As a circuit interrupting device the arc chute of the magnetic breaker must be capable of controlling the are voltage, the arc current, the arc energy, the rate of rise of recovery voltage and the phase relationship between arc current and line voltage at the instant of interruption. As an enclosing structure for cooling and deionizing the arcing products, the arc chute of the magnetic breaker must protect all the surrounding operating parts from the effects of the are or its arcing produc-ts. All of the gases exhausted from the arc chute must be rendered harmless before being exposed to any of the surrounding circuit breaker structure or allied equipment.

It has been shown many times that the arc voltage lends itself best as the unit of measurement of all the circuit functions and therefore as an accurate indicator of the effectiveness of the invention. The average value of the arc voltage in the last loop of current prior to interruption that is considered desirable is at least sixty-tive percent of peak line voltage. The magnitude of the arc voltage is determined by two factors, the length of the arc and the voltage drop per unit length. It has been recognized for some time that olsetting the slots of barrier plates effectively increases the arc length within the relatively short distance between the arc runners. It has been learned more recently that causing the arc to pass through a series of small diameter holes or perforations is an effective way of substantially increasing the voltage gradient of the arc. It, therefore, follows that a combination of barrier plates which have perforations located in offset relationship in adjacent States arent ice 2 plates provides the greatest arc voltage drop for a particular type of arc chute structure.

A barrier plate stack which consists only of plates with small diameter holes, however, presents a higher impedance to rthe arc and an arc moving force of correspondingly greater strength than heretofore used is required to move the arc into the stack structure at the desirable speed.

A barrier plate stack consisting of an arrangement of plates, some of which have offset slots and some of which have perforations, needs only the use of the present day driving force to move the arc into the stack structure at the desired speed and at the same time greatly increases the voltage gradient of the arc for the prior art structure of the same rating.

The magnitude and time characteristic of the arc voltage drop in an arc chute has been used as a criterion of arc chute barrier stack design. In order to evaluate the effectiveness of perforations and offset slots alone or in combination in an arc chute structure, tests have been made which provided the following results. As an illustration assume that a barrier plate stack comprising only slots along the longitudinal axis of each plate and providing a straight line arc path from arc runner to arc runner produces one hundred percent arc voltage drop. Then a barrier plate stack having sixty percent of its barrier plates provided with small `diameter perforations in place of the slots and forty percent of its barrier plates provided with slots along the longitudinal axis as described above the arc chute will produce a three hundred percent arc voltage drop. If the stack consists of barrier plates having only slots but offset by one-eighth inch in each adjacent plate a voltage drop of the order of approximately two hundred sixty-five percent is produced. If adjacent slots in adjacent barrier plates are offset by one-quarter inch approximately three hundred percent arc voltage drop is produced. If the slots in adjacent barrier plates are offset by one-half inch, a voltage drop of the order of approximately three hundred thirty percent drop is produced. An arrangement having eighty percent of the barrier plates provided with one-half inch offset slots and twenty percent of the barrier plates provided with perforations along the longitudinal axis of the are chute, an arc voltage drop of approximately four hundred tty percent is produced.

Since small diameter holes limit the maximum diameter of the arc through a large portion of its length, thereby causing the increased voltage gradient, they naturally impose an impedance to the movement of the arc.

Therefore, in accordance with the invention claimed, an arc chute having a predetermined geometrical contiguration is provided adjacent a pair of arcing contacts for receiving the arc at one end thereof and exhausting the deionized arc products at the other end thereof. The arc chute employs an arc extinguishing device comprising a plurality of slotted spaced insulating plates arranged to extend longitudinally of the axis of the are chute with the slots adjacent the arcing contacts to form an arc passage. A number of the plates have their slots arranged in staggered relationship for causing the arc to elongate as it moves therethrough. At least some of the plates are provided with a plurality of apertures arranged to extend from the apexes of the slots toward the exhaust end of the arc chute for increasing the voltage gradient of the arc and for limiting flame emission from the arc chute. .y

It is, therefore, one object of the present invention to provide a new and improved arc interrupting device in which the arc may travel through a plurality of predetermined arc paths before reaching the exhaust end of the arc chute.

Another object of this invention is to provide a new and improved arc extinguishing device in which the arc is compelled to assume a tortuous or zigzag path in planes substantially at right angles to the planes of the barrier plates of the arc extinguishing device and in which means are provided for greatly increasing the voltage gradient of the arc.

A further object of this invention is to provide a new and improved means for controlling the arc Voltage, the arc current, the arc energy, the rate of rise of recovery voltage, and the phase relationship between arc current and line voltage in an arc extinguishing device.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, in which:

Fig. l is a View in cross section, of a magnetic blowout type circuit breaker employing the present invention;

Fig. 2 is an exploded view of one group of the stack of barrier plates illustrated in Fig. l;

Fig. 3 is a left end view of the group of barrier plates illustrated in Fig. 2;

Fig. 4 is a sectional view of a group of the barrier plates illustrated in Fig. 2 taken along line IV--IV of Fig. 3 dow'nstream of the zone of arc initiation;

Fig. 5 is an exploded view of a modification of the barrier plate assembly illustrated in Fig. 2;

Fig. 6 is a left end view of the group of barrier plates illustrated in Fig. 5; Y

Fig. 7 is an exploded view of a modification of the barrier plate assembly illustrated in Fig. 5;

Fig. 8 is a left end view of the group of barrier plates illustrated in Fig. '7;

Fig. 9 is a sectional View of a group of the barrier plates illustrated in Fig. 7 taken along line IX-IX of Fig. 8 downstream of the zone of arc initiation;

Fig. 10 is an exploded view of another modification of the barrier plate assembly illustrated in Fig. 2;

Fig. ll is a left end view of the group of barrier plates illustrated in Fig. l0;

Fig. 12 is an exploded view of another modification of the barrier plate assembly illustrated in Fig. 5; and

Fig. 13 is a left end view of the group of barrier plates illustrated in Fig. 12.

Referring more particularly to the drawings by characters of reference, Fig. l illustrates a magnetic blowout type of circuit breaker including as elements thereof a pair of terminal studs 6 and 7 for connecting the circuit breaker to line conductors (not shown). Although in general, circuit breakers of the type considered in Fig. 1 are provided with a plurality of similar pole structures, one for each phase of a polyphase electric circuit, only one such pole structure is shown in the drawings and the circuit breaker' will be described in detail as if it was of the single pole type.

The circuit interrupter or breaker in Fig. l comprises essentially means for opening the circuit to form the interrupting arc and an arc extinguishing structure. Specifically, the circuit opening means comprises a ixed current carrying Contact 8, a tertiary contact 9, a fixed arcing contact 10, and a movable arcing contact 11. Arcing contact 11 is mounted on `a lever 28 which is pivotally mounted at 12 on an extension 13 of the circuit breaker stud 6 and is operated by means of a reciprocally movable rod 14. The operating rod 14 is suitably connected to an actuating mechanism (not shown) for operating the movable contact between closed and open circuit positions. Fig. l illustrates the movable contact 11 in closed position. The arcing contacts are electrically connected to the lower ends of terminal studs 6 and 7. Accordingly, when the breaker is connected in series in a power circuit and the arcing contacts are separated, an arc may be initiated across the gap formed between the contacts.

For interrupting this power arc, an arc extinguishing structure, such as an arc chute 15, may be mounted so as to receive the power arc which is under the influence of the magnetic blowout means. The arc chute preferably is disposed directly about and above the arcing contacts, as shown, when the blowout means act upward, but may be mounted in any other siutable location when the blowout means act in other directions. The switch or arcing contacts and the magnetic blowout structure can assume any preferred form so that a brief description thereof will be suflicient. The magnetic blowout means may comprise a core 17, poles 18, and a coil 16 which is electrically connected to the terminal stud 7 and to a metallic arc runner 19 so that the arc current (as the arc travels along the runner) iiows through the blowout coil in a manner well known in the art.

Normally the current is carried in the closed circuit position of the breaker by the spring biased contact 8. As the movable arcing contact 11 is actuated to open circuit position, current is shunted from fixed contact S first to lixed Contact 9 and afterwards to fixed arcing contact 10. As the arc is drawn by the movable arcing contact 11, the arc terminal of arcing contact 10 is transferred to arc runner 19, which is usually an extension arm of the xed arcing contact 10. As the movable arcing contact 11 approaches or reaches its full opening stroke the arc terminal transfers from the movable arcing contact 11 to an arc runner Ztl which directs the arc in the are chute 15. The arcing contact 16 and the arc runner 19 are electrically connected in series with the blowout coil 16 and stud 7. Accordingly, the blowout coil is already energized at the inception of the are to influence the arc in a well known manner, i. e. to drive it in the arc chute 15 in an expanding loop. It will be apparent to one skilled in the art that the blowout iield can be utilized in the most eflicient manner by disposing the iron poles 18 so as to cooperate with the blowout coil in the conventional manner outside of the arc chute.

in accordance with the invention claimed arc chute 15 is provided with a plurality of slotted spaced insulating barrier plates arranged to extend longitudinally of the axis of the arc chute. As shown more clearly in Figs. 2 and 3 the barrier plates may be arranged in groups with each group comprising a plurality of types of barrier plates having different geometrical configurations. Each group may comprise a first barrier plate 23, a second barrier plate 24, and a third barrier plate 25. Barrier plate 23 has a relatively short inverted V-shaped slot 26 and a plurality of holes or perforations 27 adjacent to the apex of slot 26 and extending in a straight line from the apex of the slot toward the exhaust end of the barrier plate. The perforations 27 in plate 23 may be arranged in various Ways but the straight line arrangement shown providing a plurality of small apertures about one-eighth inch in diameter, arranged about one-half inch apart in the plane of symmetry of the arc chute structure is the preferred mode of plate perforations.

Barrier plates

24 and 25 have relatively

long slots

30 and 31, respectively, with narrow parallel ends 32 and 33 situated at opposite sides of the plane of symmetry of the are chute structure. Slot 31 and its end 33 in barrier plate 25 is a mirror image of the slot 30 and its end 32 in barrier plate 24. This out of registry or staggered relationship of

slots

30 and 31 and their

ends

32 and 33 cause the formation of a zigzag shaped arc path.

Barrier plates

24 and 25 may be provided in some applications of this invention with a plurality of apertures or perforations 29 which are arranged to extend from the downstream ends of

slots

30 and 31 toward the exhaust end of the arc chute. In other applications of this invention, the perforations 29 may be omitted from

plates

24 and 25.

As shown in Figs. 2 and 3 the

slots

26, 30 and 31 of

barrier plates

23, 24 and 25 are aligned at their upstream ends adjacent the zone of arc initiation to form an are passage and are arranged in staggered relation at their downstream ends. The staggered relation of the

slots

26, 30, and 31 cause the arc to elongate as it moves therethrough. The slot 26 in barrier plate 23 has its apex arranged near the longitudinal axis of barrier plate 23. The slot 30 of barrier plate 24 is aligned with slot 26 of barrier plate 23 at the zone of are initiation and disposed in offset relation at its apex at the other end. The slot 3l of barrier plate 25 is aligned with

slots

26 and 30 of

barrier plates

23 and 24 at the zone of arc initiation and forms a mirror image of the slot 30 of barrier plate 24. The level at which the slots in barrier plates 2d and Z5 narrow down is about the level at which the perforations start in barrier plate 23. The average width of the narrow slot portions in the

barrier plates

24 and 25 and the width or diameter of the perforation 27 of barrier plate 23 should preferably be of the same order.

Fig. 4 shows the arc path through a barrier plate stack at about the distance downstream of the zone of arc initiation represented by the line IV-IV of Fig. 3. Fig. 4 also illustrates a modification of the assembly in stack form of the barrier plates illustrated in Fig. 2. The particular barrier plate assembly illustrated in Figs. 2 and 3 is merely an example of stack structure and the barrier plates may be mounted in any other sequence and still achieve the results and benefits of this invention.

Figs. 5 and 6 illustrate a modification of the barrier plate assembly shown in Figs. 2 and 3 wherein

barrier plates

35 and 36 are similar to

barrier plates

24 and 25 with the exception that the narrow ends 32 and 33 of

barrier plates

24 and 25 are replaced by a plurality of perforations 3'7 which are arranged to extend from the ends of the apexes of

slots

30 and 31 in straight lines substantially parallel to the longitudinal axis of the arc chute toward the exhaust end of the chute. A stack or group assembly of the barrier plates shown in Fig. 5 may comprise all or a part of the particular barrier plates illustrated in any number of different sequences.

Figs. 7 and 8 illustrate a modification of the barrier plate assembly shown in Figs. 5 and 6 wherein barrier plate 23 of Fig. 5 is replaced with a barrier plate 3S. Barrier plate 38 comprises a slot 39 having the apex of its slot arranged near the longitudinal axis of the arc chute and adjacent the plates exhaust end.

Fig. 9 illustrates the arc path through a barrier plate stack at about the distance downstream of the zone of arc initiation represented by the lines IX-IX of Fig. 8. Fig. 9 also illustrates another assembly in stack form of the barrier plates illustrated in Figs. 7 and 8.

Figs. 10 and ll illustrate a modification of the barrier plate assembly shown in Figs. 2 and 3 wherein the perforations 27 of barrier plate 23 are arranged in a staggered relation near the apex of slot 26 and extending toward the exhaust end of the barrier plate.

Figs. l2 and 13 illustrate a modification of the barrier plate assembly shown in Fig. 5 wherein the perforations 37 of

barrier plates

35 and 36 are arranged in staggered relation near the apex of

slots

30 and 31 and extend from the slots toward the exhaust end of the barrier plates.

Under normal interrupting conditions, an arc is initiated immediately upon separation of the arcing contacts 10 and 31. The terminal of the arc on fixed arcing contact li? is driven over arc runner 19 by the magnetic blowout means and the thermal effect of the arc. As movable arcing contact 11 separates from lixed arcing contact 10,

the other terminal of the arc is moved from contact 11 to arc runner Ztl and is also driven by the blowout means and the thermal eiiect of the arc toward the exhaust end of arc chute 15.

As the arc terminals move along the arc runners 19 and 20 toward the exhaust end of arc chute 15, the arc is driven into the arc passage formed by the slots of the barrier plates arranged adjacent the zone of arc initiation.

The arc arises in the arc passage under the influence of the blowout means and the thermal effect of the arc and is constricted by the sides of the slots. As the arc moves through the arc chute barrier plate stack the arc is elon gated by being displaced a uniform and predetermined amount in a horizontal plane by the use of barrier plates with arc guiding slots parallel to and offset from the center line or longitudinal axis of arc chute 15. The staggered relation of the slots in some of the barrier plates causes the arc to follow a zigzag path through the arc chute. The perforations used in many of the plates limits the maximum diameter of the arc through a large portion of its length, thereby increasing the voltage gradient of the arc and retarding the arcs movement through the arc chute. The perforations of these plates also cool and deionize the arcing products so that the flame emission from the exhaust end of the arc chute is eliminated or greatly reduced. The arc length is controlled by the oiset slotted barrier plate arrangement shown, and the impedance offered tothe arc movement through the arc chute is controlled by the perforations provided in some of the barrier plates.

Although only a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

l. An electric circuit interrupter comprising relatively movable contacts, means for drawing an arc between said contacts, and an arc chute for receiving and extinguishing the arc, said lchute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a first plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute, and second and third plates having said notches arranged in staggered relation to each other and with respect to the longitudinal axes of said second and third plates for causing the arc to elongate as it moves through said chute.

2. An electric circuit interrupter comprising relatively movable contacts, means for drawing an arc between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a rst plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute, and second and third plates having notches arranged in staggered relation to each other and with respect to the longitudinal axes of said second and third plates for causing the arc to elongate as it moves through said chute, said second and third plates being provided with a plurality of apertures extending from the apexes of their notches in straight lines on opposite sides of and substantially parallel with the longitudinal axes of said second and third plates toward the exhaust end of said chute for controlling the maximum arc diameter as it passes through said chute and for decreasing liame emission from the exhaust end of said chute.

3. An electric circuit interrupter comprising relatively movable contacts, means for drawing an arc between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a first plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute, a second plate having its notch aligned at the Zone of arc initiation with said notch in said first plate and disposed in offset relation with respect to the longitudinal axis of said second plate at its other end, and a third plate having its notch aligned at the zone of arc initiation with the notches of said first and second plates and forming a mirror image of the notch of said second plate for causing the arc to elongate as it moves through said chute and to retard flame emission from the exhaust end of said chute.

4. An electric circuit interrupter comprising relatively movable contacts, means for drawing an arc between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the Zone of arc initiation to form an arc passage, at least one of said groups comprising a rst plate having the apex of said notch arranged at the exhaust end of said chute and near its longitudinal axis, a second plate having its notch aligned at the zone of arc initiation with the notch in said first plate and extending toward the exhaust end of said chute in offset relation with respect to the longitudinal axis of said second plate at its apex end, and a third plate having its notch aligned at the zone of arc initiation with the notches of said first and second plates and forming a mirror image of the notch of said second plate, said second plate, said second and third plates being provided with a plurality of apertures extending from the apex of their notches the same distance downstream from the zone of arc initiation as said notch in said first plate.

5. An electric circuit interrupter comprising relatively movable contacts, means for drawing an are between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a rst plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute, and second and third plates having said notches arranged in staggered relation with respect to the longitudinal axes of said sec- 0nd and third plates and to each other for causing the arc to elongate as it moves through said chute.

6. An electric circuit interrupter comprising relatively movable contacts, means for drawing an are between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a first plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute in a-zigzag line, second and third plates having said notches arranged in staggered relation to each other for causing the arc to elongate as it moves through said chute.

7. An electric circuit interrupter comprising relatively movable contacts, means for drawing an arc between said contacts, and an arc chute for receiving and extinguishing the arc, said chute comprising a plurality of groups of notched spaced insulating plates arranged to extend longitudinally of the axis of said chute with the notches in the edges of said plates arranged adjacent the zone of arc initiation to form an arc passage, at least one of said groups comprising a first plate having the apex of said notch arranged near the longitudinal axis of said plate and providing a plurality of spaced apertures arranged adjacent the apex of said notch and extending toward the exhaust end of said chute, and second and third plates having notches arranged in staggered relation to each other for causing the are to elongate as it moves through said chute, said second and third plates being provided with a plurality of apertures extending from the apexes of their notches toward the exhaust end of said chute in a zigzag line for controlling the maximum arc diameter as it passes through said chute and for decreasing fiame emission from the exhaust end of said chute.

References Cited in the file of this patent UNiTED STATES PATENTS 2,276,859 Nau Mar. 17, 1942 2,616,006 Frink Oct. 28, 1952 FOREIGN PATENTS 615,025 Great Britain Dec. 31, 1948 797,227 France Feb. 8, 1936