GB1574886A - Arc chute for circuit interrupter - Google Patents

Description

(54) ARC CHUTE FOR CIRCUIT INTERRUPTER (71) We, WESTINGHOUSE ELEC TRIC CORPORATION of Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania, United States of America, a company organised and existing under the laws of the Commonwealth of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates generally to circuit interrupting devices and, more particularly, to a magnetic contactor having an arc chute.

The outlying dimensions of magnetic contactors are primary considerations in their acceptance by industry and their commercial success. This is particularly true of contactors for use in industry, such as marine, railroad, mining, off-shore drilling, off-road construction, where space is at a premium. In some of these applications, machinery has already been designed around a particular size of contactor. Consequently, new contactors must be directly interchangeable with the prior contactor. Associated with the foregoing is a requirement that continuous current carrying capacity and interrupting ratings be greater than the original contactor.

It is well known in the art that forcing an arc into intimate contact with arc chute walls and/or grid plates is a definite aid to arc interruption. In conventional grid plate design, the arc loops are symmetrical so that the legs thereof are directly opposite each other on opposite sides of the grid plates, which construction has the disadvantage of creating a resulting force of zero acting on the legs so that the arc tends to center itself in the air space between the grid plates.

Another disadvantage with the grid plates of conventional arc chute construction has been ionized gas back flow which results in arc restriking with a resulting delay in arc interruption or failure to innterrupt the arc at all.

Disclosed herein is a circuit interrupter comprising cooperable contacts, an arc chute, and means effective upon separation of the contacts to cause an arc drawn therebetween to be driven into the arc chute, said arc chute comprising a housing having an arc receiving end and a venting end spaced therefrom, and which housing comprises a pair of electrically insulating side walls defining therebetween an arc compartment having an arc entrance region extending from the contacts, a constricted region extending from the arc entrance region, and an end region wider than the constricted region and extending therefrom to the venting end of the housing; a pair of arc conductors extending within the arc compartment from adjacent said contacts to said end region in spaced and diverging relationship with respect to one another, said arc conductors having respective first portions which extend from adjacent the contacts at a first angle with respect to each other, and respective second portions which extend from the first portions at a second angle with respect to each other which second angle is larger than said first angle; and a stack of grid plates disposed in said end region in spaced relationship with respect to one another, and which grid plates are inclined, at an angle other than 900, with respect to a plane substantially perpendicular to the direction in which the arc conductors are spaced apart at said end region, each grid plate having an arc-confronting bevelled edge portion which extends obliquely from adjacent one side of the constricted region towards the opposite side wall of the housing, and the arc-confronting bevelled edge portions of adjacent grid plates extending from adjacent opposite sides of the constructed region obliquely in opposite directions with respect to one another.

With an arc chute such as disclosed herein, an arc is lengthened and forced against the grid plate surfaces which cool and extinguish the arc, the unique angular positioning of the grid plates directing ionized air toward the top of the arc chute where it is deflected to cause air tubulence which helps to deionize the hot gases.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical sectional view through a contactor with an arc chute attached, and showing the contacts in the open position; Figure 2 is a front view of the contactor: Figures 3-7 are sectional views taken on lines of corresponding numbers in Figure 1; Figure 8 is a sectional view taken on the line VIlI-VIlI of Figure 7; Figure 9 is a sectional view taken on the line IX-IX of Figure 1; Figure 10 is a sectional view taken on the line X-X of Figure 9; and Figure 11 is an enlarged fragmentary view showing the manner in which an arc advances along the frontal edge surfaces of grid plates.

In Figure 1, the contactor generally indicated at 1 comprises a base plate 3, electromagnet 5, an electrically insulating housing 7, arc blowout unit 9, and an arc chute 11.

The contactor 1 also comprises a stationary contact 13, movable contact 15, which are mounted on conductor structures 17 and 19, respectively. The contacts 13, 15 are movable between closed and open positions.

The contactor to which the invention is shown applied, by way of example, is of the type generally described in U.S. Patent Specification No. 3,511,950, an electric circuit through the contactor 1 including a line terminal 21, a blowout coil 41, the contact support structure 17, contacts 13, 15, the conductor structure 19, a shunt 25, a shunt connector 27, and a load terminal 29.

The electromagnet 5 includes a coil 31, a core 33, a U-shaped magnetic frame 35, and an armature 37. The armature is pivotally mounted at 38 on the base 3 and, when the electromagnet 5 is energized, the armature 37 closes against the upper end of the frame 35, thereby pulling the movable contact 15 to a closed position with the stationary contact 13 as indicated by the broken line position 15a. Conversely, when the operating coil 31 is deenergized, the armature 37 moves to the open position as shown and thereby moves the movable contact 15 to the open position.

When the contacts 13, 15 separate under load, an arc 39 develops between them.

The arc blowout unit 9 and the arc chute 11 are provided to extinguish the arc 39 and minimize its effect upon the contacts. The arc blowout unit 9 comprises a magnetic blowout coil 41 and a ferromagnetic core 43. The coil 41, being mounted on the insulating housing 7, consists of a single turn around the core 43 and is a continuation of the line terminal 21. Inasmuch as the electric circuit moves from the line terminal 21 and through the blowout coil 41, the coil is on continuous duty. Since space is not available for a mul tiple turn continuous duty coil, an auxiliary coil 45 is provided which operates intermittently, that is, when the arc 39 strikes a line arc horn 59 after the contacts 13, 15 are separated. The auxiliary coil 45 comprises end portions 45a and 45b, the former of which is secured by suitable means, such as a screw 47, to the end of the blowout coil 41. The end portion 45b is connected to a line arc horn connector 81 through a conductor 51 extending through an insulator mounting 53.

The auxiliary coil 45 has a plurality of, such as four, coil turns around the core 43. A pair of pole pieces 55, 57 (Figure 2) extends from the ends of the core 43. The pole pieces 55, 57 are ferromagnetic flux-carrying members, one pole piece extending from one end of the core 43 and the other pole piece extending from the other end of the core and radially of the coils 41, 45 to opposite sides of the arc chute 11, wherein a magnetic field is generated between the pole pieces. The arc 39 is more readily transferred from the contacts 13, 15 to a line arc horn or conductor 59 and a load arc horn or conductor 61, as shown by the position of the arc at 39a.

Under heavy load conditions, the single turn blowout coil 41 provides sufficient magnetizing forces to saturate the ferromagnetic core 43 so that a maximized blowout field strength is available when the contacts 13, 15 separate. When the arc 39 transfers to the line arc conductor 59 and the load arc conductor 61, the auxiliary coil 45, which is connected in series with the coil 41, increases the blowout magnetizing force within the arc chute 11. Under heavy load conditions the core 43 is saturated and the additional magnetizing force developed by the auxiliary coil 45 is unnecessary. However, where lighter loads exist, the single turn coil 41 is unable to develop sufficient magnetizing force to provide an adequate blowout field strength to interrupt the arc 39. Under this condition the extra magnetizing force provided by the multiple turn auxiliary coil 45 is necessary.

When the operating coil 31 of the contactor is deenergized, the contacts 13, 15 separate and an arc 39 is drawn between the contacts if load current, voltage, and inductance are sufficient to maintain an arc.

If not, the arc 39 will be extinguished without moving off of the contacts 13, 15. In the event load conditions are such as to maintain an arc, the current flow through the single turn continuous duty blowout coil 41 will magnetize the core 43 and pole pieces 55, 57 to establish a magnetic field between the pole pieces which react with the arc 39. The relative porality of the blowout field and the arc 39 are such that the arc is propelled in an upward direction to position 39a, 39b, 39c, 39d, 39e. When the arc 39 transfers, the left end of the arc moves from the stationary contact 13 to the line arc horn 59, causing current to flow through the auxiliary blowout coil 45 to strengthen the magnetic field acting upon the arc. This increase in the are driving force is desirable to aid in driving the are through the constricted are compartment region within the are chute 11.

The arc chute 11 comprises a housing made of an electrically insulating material, such as melamine-asbestos, cement-asbestos, zircon or glas polyester, and comprising a pair of side walls 65, 67 which define therebetween an arc compartment extending from the are receiving end of the housing, at the end wall 73, to the venting end at end wall 75 thereof, the are conductors 59 and 61 being disposed in the are compartment and bounding it at its top and bottom. The are chute 11 consists of two halves secured together by suitable means, such as screws 63, the two halves being formed by the side walls 65 and 67 with portions thereof forming the opposite end walls 73, 75 and upper and lower walls 69, 71. Each side wall 65 or 67 has formed therein a pair of elongate grooves 77, 79 in which the arc conductors 59 and 61, respect ively, are seated. As seen from Figure 1, the arc conductors 59, 61 have respective first portions which extend in spaced and diverging relationship with each other from adjacent the contacts 13, 15, and respective second portions which extend from the first portions and diverge at an angle which is considerably larger than the angle of divergence between the first are conductor portions. A conductor 81 extending from the are horn 59 is con nected with a screw 83 to the conductor 51, whilst a conductor 85 connects the load are horn 61 electrically to the conductive base 3.

Thus, when an arc exists, as at 39a, between the arc horns or conductors 59, 61, a circuit extends from the coil 45 through the conductors 51, 81, the arc conductor 59, the arc, the are conductor 61, the conductor 85 and the base 3 to the load terminal 29. The side walls 65, 67 include inwardly slanting portions 87, 89, respectively (see also Figure 3), which define an arc entrance region of the arc compartment extending immediately from above the contacts 13, 15 toward and to the constricted arc compartment region 91 which, in turn, extends towards and connects with the wider end region of the arc compartment at its venting end.

In Figure 4, the are is shown located at the are position 39b within the constricted region 91, and the arc voltage required per inch of arc length to maintain the arc is higher than at arc position 39a. If the load current is too high to permit extinction of the are at this point, the are will travel on to position 39e (Figures 1 and 5) where it requires still a higher voltage for maintaining it, and whence it will enter a stack of grid plates 93-111 interdigitated in spaced relationship with each other in the above-mentioned end region of the arc compartment. It will be understood that the arc is propelled through the arc chamber and into the stack of grid plates by a force provided in part of the blowout unit 9, by the electro-dynamic reaction between the arc and the current flowing through the arc conductors 59, 61, and by the stray field from the pole pieces 55, 57.

Arc interruption is improved in the arc chute according to the invention by forcing the arc to follow a unique path of increased length which also provides increased contact of the arc with the grid plates 93-111. For this purpose, the grid plates are inclined at an angle other than 900 with respect to the length of the advancing arc 3 9c between the arc conductors 59, 61 or, in other words, with respect to a plane which extends substantially perpendicular to the direction of spacing between the arc conductors 59, 61 at the end region of the arc compartment. The angle of inclination of the grid plates preferably is about 450 but other angles, except 900, may also be found suitable.

The stack of grid plates 93-111 comprises an arc lengthening section beginning at the arc-confronting edges 115 (Figure 1) of the grid plates, and a de-ionizing section which adjoins the arc lengthening section and ends at the venting-end edges 117 of the grid plates. In the arc lengthening section, each alternate grid plate, such as plate 107 in Figures 7 and 8, has an arc-confronting edge portion 119 which is bevelled and extends obliquely from one side of the constricted region 91 toward the opposite side wall 67 and the venting-end edge of the plate or, more specifically, to a position nearer said opposite side wall 67 and said venting-end edge where the bevelled edge portion 119 ter- minates at a shoulder or lateral portion 121 of the arc-confronting edge. Each of the other grid plates, such as plate 105 in Figure 9 and 10, has a similarly bevelled arc-confronting edge portion 125, extending however obliquely from the other side of the constricted region 91 towards the opposite side wall which, in this instance, is the side wall 65, and terminating at a shoulder or lateral portion 127 of the arc-confronting edge of the plate. In other words, the arc-confronting edges 119 and 125 of adjacent grip plates 105 and 107 in the stack start from adjacent opposite sides of the constricted region 91 and are bevelled in opposite directions.

As seen from Figures 7-10, the arcconfronting edges of the grid plates cooperate with respective opposite side wall portions or fins 114, 116 to define narrow slots 113a which interconnect the adjacent spaces 113 between the grid plates and communicate with the constricted arc compartment region 91, the slots 113a in the successive planes of the grid plates and fins alternately angling toward the one and the other of the side walls 65, 67. Although the grid plates 93-111 could be individual insulating plates either assembled in a separate stack or supported from the side walls 65, 67, in the preferred embodiment they are shown as integral parts of the molded insulating side walls, the plates 93, 97, 101, 105 and 109 forming integral parts of the wall 67, and the plates 95, 99, 103, 107 and 111 forming integral parts of the wall 65.

Thus, when the two arc chute halves are assembled, the grid plates 93-111 assume their intersticial positions and form the spaces.

113 therebetween.

Again as seen from Figures 7 to 10, the arc-confronting bevelled edge portion of each grid plate also has a bevelled surface 123 (Figure 7) or 129 (Figure 9) which helps to guide the arc into the respective narrow slot 113a, the bevel of the surfaces 123, 129 being approximately 450.

As the arc passes the location 39c, it encounters the arc-confronting or front edges of the several grid plates 93-111 (Figure 11) and is guided by the bevelled front edge portions 119, 125 as well as the bevelled surfaces 123, 129 to the arc position 39e (Figure 11) where the arc impinges upon the shoulders 121, 127. Thus, the arc is stretched along an irregular zigzag path within the slots and between the grid plates. More particularly, the arc at the position 39e is forced to take an irregular path designed to minimize equal and opposite magnetic forces acting within the arc loops so as to eliminate the undesirable centering of the arc in the air spaces between the grid plates as found in the prior art grid stacks. Elimination of the arc centering forces thus allows the arc to come into intimate contact with the grid plates to provide maximum arc cooling and to increase arc interrupting ability. When the arc starts to take the zigzag or looping path, the loops themselves set up additional forces which act to enlarge the arc loops to lengthen the arc and at the same time force the arc into intimate contact with the grid plates as shown in Figures 6 and 11.

As shown in Figure 11, alternate arc loops are large and small loops. Magnetic forces developed within the small loops attempt to force the tip of the arc loop back out of the grid stack towards the arc conductor 59. Since the slots 113a between the fins 114, 116 and the bevelled edge portions 119, 125 of the grid plates are angled, the tips of the small loops are forced against the edges of the grid slots (Figure 6), rather than out of the grid stack. At the same time, the arc driving force of the arc conductors 59, 61 and the pole field are driving the tip of the small loop into the grid stack. The sum of the forces acting on the tip of the small arc loop is approximately zero when the tip of the small arc loop just enters the grid stack space so that the position of the tip of the small loop will be established at this point. Centering of the arc between the grid plates is eliminated since external magnetic forces acting on the large arc loop and magnetic forces developed within the large loop all act to force the large arc loop into the stack and against the shoulders 121, 127 and the large flat surfaces on the undersides of the grid plates 93-111. The legs of the small arc loops are on opposite sides of the grid plates, but angle downward into the paper in Figure 11 to afford an improvement in arc interrupting ability since the legs are not directly opposite each other even though they are on opposite sides od the grid plates. Moreover, as shown in Figure 6, the legs of the small loops have an angular displacement so that the magnetic forces, developed within the small loops act to increase the angular displacement still more to create additional mild arc loops to strengthen and force the arc into intimate contact with the grid plate surfaces rather than centering the arc in the air space 113 between the grid plates.

The deionizing section of the grid stack is formed by the solid portions of the grid plates 93-111. The deionizing section deionizes the ionized gases generated in the arc lengthening section of the grid stack and discharges them into their surrounding atmov phere. The deionizing section is located in the rear portion of the grid stack and has a wider dimension, as indicated by the arrow 131 (Figure 6), than the constricted compartment 91. Decreasing the space between the grid plates and/or increasing the length of the deionizing portion of the grid plates increases the deionizing ability of the grid stack, but at the same time increases the back pressure which in turn limits the volume of the gas which can be discharged from the arc chute. To reduce the back pressure, spacing between the arc chute walls is increased in the exhaust section of the grid stack, as indicated by the arrow 131. At load currents which exceed the interrupting rating of the contactor, the arc will generate more ionized gas than the grid stack can deionize and discharge. Thus, ionized gas backs up into the constricted compartment 91 ahead of the grid stack. When this accurs under heavy load conditions, the arc will restrike across the arc conductors 59, 61 at some critical point such as 39b (Figure 1) and hang on indefinitely until the arc chute is destroyed.

At lighter loads a certain amount od ionized gas .may blow back into the arc compartment 91 to cause the arc to restrike between the arc conductors, such as at arc position 39b.

In this case, the arc may then travel back into the grid stack and be interrupted, or hand on and destroy the arc chute.

In accordance with this invention, the ionized back flow in the arc chute is avoided by providing the grid plates 93-111 at an angle which will direct the ionized gas gen erated between the upper grid plates toward the top of the arc chute (Figure 1) as indicated by the broken lines 133 from where the gas is deflected downwardly to collide with streams of gas coming from the adjacent grid plates as indicated by broken lines 133.

This results in gas flow turbulence which in turn acts to deionize the gas as well as restricting gas flow into the critical area at arc position 39b. This provides an improvement in arc interrupting ability over that of arc chutes having grid plates at a horizontal position.

Finally, the inclined grid plates 93-111 eject the ionized gases from the arc chute downwardly at the same angles, such as 450. This advantage plus the increased length of the grid plates due to their inclined position rather than horizontal, increases the interrupting rating without increasing the horizontal arcing clearance or horizontal projection of the arc chute.

Accordingly, the arc chute structure of this invention solves problems of prior art construction by forcing an arc into more intimate contact with grid plates than in prior art.

Finally, ionized air is redirected towards the top of the arc chute where it is deflected to cause air turbulence which in turn helps to deionize the hot gases.

WHAT WE CLAIM IS: 1. A circuit interrupter comprising cooperable contacts, an arc chute, and means effective upon separation of the contacts to cause an arc drawn therebetween to be driven into the arc chute, said arc chute comprising a housing having an arc receiving end and a venting end spaced therefrom, and which housing comprises a pair of electrically insulating side walls defining therebetween an arc compartment having an arc entrance region extending from the contacts, a constricted region extending from the arc entrance region, and an end region wider than the constricted region and extending therefrom to the venting end of the housing; a pair of arc conductors extending within the arc compartment from adjacent said contacts to said end region in spaced and diverging relationship with respect to one another, said arc conductors having respective first portions which extend from adjacent the contacts at a first angle with respect to each other, and respective second portions which extend from the first portions at a second angle with respect to each other which second angle is larger than said first angle; and a stack of grid plates disposed in said end region in spaced relationship with respect to one another, and which grid plates are inclined, at an angle other than 900, with respect to a plane substantially perpendicular to the direction in which the arc conductors are spaced apart at said end region, each grid plate having an arc-confronting bevelled edge portion which extends obliquely from adjacent one side od the constricted region towards the opposite side wall of the housing, and the arc-confronting bevelled edge portions of adjacent grid plates extending from adjacent opposite sides of the constricted region obliquely in opposite directions with respect to one another.

2. A circuit interrupter according to claim 1, wherein said grid plates are inclined at an angle of substantially 450.

3. A circuit interrupter according to claim 1 or 2, wherein the spaces between some of the grid plates are directed, in extension, obliquely toward one of said arc conductors, and the spaces between the remaining grid plates are directed, in extension, obliquely toward the other arc conductor.

4. A circuit interrupter according to claim 1, 2 or 3, wherein the arc-confronting bevelled edge portion of each grid plate cooperates with a fin extending from said opposite side wall, so as to define therebetween a narrow slot which communicates with said constricted region and interconnects the spaces between the respective grid plate and those adjacent thereto, the narrow slots thus defined in the successive planes of grid plates and fins angling alternately toward the one and the other of said side walls.

5. A circuit interrupter according to claim 4, wherein the arc-confronted bevelled edge portion of each grid plate has a bevelled surface to assist in guiding arc into the associated narrow slot.

6. A circuit interrupter according to claim 4 or 5, wherein said fins are integral parts of the respective side walls from which they extend.

7. A circuit interrupter according to any of the preceding claims, wherein said grid plates in the stack are formed integral alternately with the one and the other of said side walls.

8. A circuit interrupter according to any of the preceding claims, wherein the arcconfronting bevelled edge portion of each grid plate terminates, in the direction toward the venting end of the housing, at a lateral edge portion of the same grid plate extending to said opposite side wall.

9. A circuit interrupter according to any

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. erated between the upper grid plates toward the top of the arc chute (Figure 1) as indicated by the broken lines 133 from where the gas is deflected downwardly to collide with streams of gas coming from the adjacent grid plates as indicated by broken lines 133. This results in gas flow turbulence which in turn acts to deionize the gas as well as restricting gas flow into the critical area at arc position 39b. This provides an improvement in arc interrupting ability over that of arc chutes having grid plates at a horizontal position. Finally, the inclined grid plates 93-111 eject the ionized gases from the arc chute downwardly at the same angles, such as 450. This advantage plus the increased length of the grid plates due to their inclined position rather than horizontal, increases the interrupting rating without increasing the horizontal arcing clearance or horizontal projection of the arc chute. Accordingly, the arc chute structure of this invention solves problems of prior art construction by forcing an arc into more intimate contact with grid plates than in prior art. Finally, ionized air is redirected towards the top of the arc chute where it is deflected to cause air turbulence which in turn helps to deionize the hot gases. WHAT WE CLAIM IS:

1. A circuit interrupter comprising cooperable contacts, an arc chute, and means effective upon separation of the contacts to cause an arc drawn therebetween to be driven into the arc chute, said arc chute comprising a housing having an arc receiving end and a venting end spaced therefrom, and which housing comprises a pair of electrically insulating side walls defining therebetween an arc compartment having an arc entrance region extending from the contacts, a constricted region extending from the arc entrance region, and an end region wider than the constricted region and extending therefrom to the venting end of the housing; a pair of arc conductors extending within the arc compartment from adjacent said contacts to said end region in spaced and diverging relationship with respect to one another, said arc conductors having respective first portions which extend from adjacent the contacts at a first angle with respect to each other, and respective second portions which extend from the first portions at a second angle with respect to each other which second angle is larger than said first angle; and a stack of grid plates disposed in said end region in spaced relationship with respect to one another, and which grid plates are inclined, at an angle other than 900, with respect to a plane substantially perpendicular to the direction in which the arc conductors are spaced apart at said end region, each grid plate having an arc-confronting bevelled edge portion which extends obliquely from adjacent one side od the constricted region towards the opposite side wall of the housing, and the arc-confronting bevelled edge portions of adjacent grid plates extending from adjacent opposite sides of the constricted region obliquely in opposite directions with respect to one another.

2. A circuit interrupter according to claim 1, wherein said grid plates are inclined at an angle of substantially 450.

3. A circuit interrupter according to claim 1 or 2, wherein the spaces between some of the grid plates are directed, in extension, obliquely toward one of said arc conductors, and the spaces between the remaining grid plates are directed, in extension, obliquely toward the other arc conductor.

4. A circuit interrupter according to claim 1, 2 or 3, wherein the arc-confronting bevelled edge portion of each grid plate cooperates with a fin extending from said opposite side wall, so as to define therebetween a narrow slot which communicates with said constricted region and interconnects the spaces between the respective grid plate and those adjacent thereto, the narrow slots thus defined in the successive planes of grid plates and fins angling alternately toward the one and the other of said side walls.

5. A circuit interrupter according to claim 4, wherein the arc-confronted bevelled edge portion of each grid plate has a bevelled surface to assist in guiding arc into the associated narrow slot.

6. A circuit interrupter according to claim 4 or 5, wherein said fins are integral parts of the respective side walls from which they extend.

7. A circuit interrupter according to any of the preceding claims, wherein said grid plates in the stack are formed integral alternately with the one and the other of said side walls.

8. A circuit interrupter according to any of the preceding claims, wherein the arcconfronting bevelled edge portion of each grid plate terminates, in the direction toward the venting end of the housing, at a lateral edge portion of the same grid plate extending to said opposite side wall.

9. A circuit interrupter according to any

of the preceding claims, wherein said side walls extend from adjacent opposite sides of said contacts.

10. A circuit interrupter according to any of the preceding claims, wherein said housing consists of two halves each comprising one of said side walls.

11. A circuit interrupter substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.