Patent Application
20060096954
1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to arc chutes for circuit breakers.
2. Background Information
Circuit breakers typically include a set of stationary electrical contacts and a set of moveable electrical contacts. The stationary and moveable contacts are in physical contact with one another when it is desired that the circuit breaker provide electricity therethrough to a load. When it is desired to interrupt the circuit, however, the moveable contacts are moved away from the stationary contacts, thus removing the moveable contacts from physical contact with the stationary contacts and creating a space therebetween.
The movement of the moveable contacts away from the stationary contacts results in the formation of an electrical arc in the space between the contacts beginning at the time the contacts are initially separated. Such an arc is undesirable for a number of reasons. For example, current flows through the circuit breaker to the load when it is desired that no such current should flow thereto. Additionally, the electrical arc extending between the contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in destruction or pitting of the moveable and stationary contacts. It is thus desired to eliminate any such arcs as soon as possible upon their propagation.
The moveable contacts typically are mounted on arms that are contained in a pivoting assembly which pivots the moveable contacts away from the stationary contacts. An arc chute is provided along the path of each arm to break up and dissipate such arcs. Such arc chutes typically include a plurality of spaced apart arc plates mounted in a wrapper. As the moveable contact is moved away from the stationary contact, the moveable contact moves past the ends of the arc plates, with the arc being magnetically urged toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken up and extinguished by the arc plates. Examples of arc chutes are disclosed in U.S. Pat. Nos. 6,703,576; 6,297,465; 5,818,003; and 4,546,336.
U.S. Pat. No. 4,229,630 discloses deionization plates which may be utilized to direct the arc into the comers of each deionization plate so that the maximum length of the plate may be utilized for cooling and deionization of the resulting plasma. The plate has an opening therein which is generally in the shape of a V. However, the apex of the V-shaped opening is directed towards one of the frame sides of the arc chute. When inserted into the frame, these plates are positioned such that adjacent plates would have their apex directed to opposite side walls or, put another way, alternate plates would have their apex directed toward the same side.
U.S. Pat. No. 4,229,630 also discloses a pair of vertical arc gassing insulation plates secured to the deionization plate. The arc gassing insulation plates are disposed on opposite sides of the generally V-shaped opening and the arcing contact. The arc gassing insulation plates are made of a suitable arc gassing material, such as glass polyester or a ceramic-type material, and are inserted on either side of the arcing contact to increase the pressure at the arcing contact to drive the resulting arc more rapidly into the arcing chamber while concurrently allowing any arcs present at the main movable contacts to enter the arcing chamber.
Low voltage air circuit breakers interrupting relatively high currents (e.g., 100,000 A and higher) with molded housings and enclosed arc chambers may often sustain damage to their housings during short circuit interruption. Arcing energy at the corresponding power levels produces a pressure wave that may crack molded composite parts and collapse sheet-metal plates. Corresponding damage to the arc chute reduces its effectiveness, which increases arcing duration, energy release and chance of failure. In addition, residual ionized gas, with vaporized conductor material, may result in dielectric breakdown between the separable contacts even after the initial arc is gone.
Arc chutes are designed to encourage the arc to enter the metal arc plates. An arc can move quickly to the top edge of the arc plates and pass between top edges of some plates, thereby completely bypassing intermediate plates. This reduces the number of arc voltage drops and the effectiveness of the arc chute. This bypassing effect further creates current and gas flow patterns that tend to collapse groups of plates together, further reducing voltage divisions in the arc chute and its cooling effectiveness.
Another shortcoming of typical arc chute designs is that the gas flow from individual arc plate gaps recombines before exiting through the vent. This allows a few gaps that are directly above the center of the arc to dominate the gas flow. Relatively little gas flow (or arc mobility) occurs in the far forward or rearward plate gaps because they are competing with the central high-pressure gaps for exit flow area. The forward and rearward plates, and therefore the full volume of the arc chamber, are underutilized.
Retention of the arc chute top, even if it has a relatively large exit vent, is very difficult at interrupting currents above 100,000 A. The pressure wave may readily shatter a molded composite arc chute top and may pull fasteners through the molded material. Metal tops may emit unacceptable stray arc currents to the circuit breaker or enclosure ground. Metal arc chute tops may also attract arc from metal arc plates below, thereby conducting current in a manner that bypasses intermediate plates.
Accordingly, there is room for improvement in arc chutes and in circuit interrupters employing arc chutes.
These needs and others are met by the present invention, which provides a circuit interrupter arc chute including a plurality of electrically conductive arc plates supported by first and second support portions, and a plurality of insulating dividing members disposed between the arc plates. The arc plates have a first edge offset from an exit portion of the arc chute and an opposite second edge distal from the exit portion. The insulating dividing members have a first edge proximate the exit portion and an opposite second edge distal from the exit portion. The second edge of the insulating dividing members extends beyond the first edge of the arc plates and toward the second edge of the arc plates. The first edge of the insulating dividing members extends beyond the first edge of the arc plates and away from the second edge of the arc plates.
In accordance with one aspect of the invention, a circuit interrupter arc chute comprises: a first support portion; a second support portion; an exit portion supported by the first and second support portions, the exit portion having at least one opening; a plurality of electrically conductive arc plates supported by the first and second support portions, the arc plates having a first edge offset from the exit portion and an opposite second edge distal from the exit portion; and a plurality of insulating dividing members disposed between the arc plates, the insulating dividing members having a first edge proximate the exit portion and an opposite second edge distal from the exit portion, wherein the second edge of the insulating dividing members extends beyond the first edge of the arc plates and toward the second edge of the arc plates, and wherein the first edge of the insulating dividing members extends beyond the first edge of the arc plates and away from the second edge of the arc plates.
The first and second support portions may be first and second side portions; the exit portion may be a top portion; the first and second edges of the arc plates may be top and bottom edges, respectively; the first and second edges of the insulating dividing members may be top and bottom edges, respectively; the arc plates and the insulating dividing members may be generally normal to the top portion and to the first and second side portions; the at least one opening may be one opening; the top edge of the arc plates may be offset below the one opening of the top portion; and the top edge of the insulating dividing members may be within the one opening of the top portion.
The at least one opening may be a plurality of openings; the top edge of the arc plates may be offset below the openings of the top portion by a first distance; and the top edge of the insulating dividing members may be offset below the openings by a second distance that is smaller than the first distance.
Each one of the insulating dividing members may be disposed between and separated from an adjacent pair of the arc plates.
The at least one opening of the exit portion may be a first opening; the exit portion may comprise a molded top and a top frame, the molded top having a second opening corresponding to the first opening of the exit portion, a molded rim around the second opening of the molded top, and a recessed area. The top frame may have a third opening corresponding to the first opening of the exit portion and be larger than the second opening. The top frame may rest in the recessed area of the molded top. The molded rim of the molded top may be adjacent to the third opening.
The molded top may be made of an insulating material; and the top frame may be electrically conductive and plated with a non-conductive material.
Each of the first and second support portions may include a wedge portion proximate the exit portion, the wedge portion being adapted to direct or divert gas toward the at least one opening of the exit portion.
The wedge portion may be made of an insulating material and may include a plurality of first grooves adapted to engage the insulating dividing members and a plurality of opposite second grooves adapted to engage the arc plates.
As another aspect of the invention, an arc chute for a circuit interrupter comprises: a first support portion; a second support portion; an exit portion supported by the first and second support portions, the exit portion having at least one opening; a plurality of electrically conductive arc plates supported by the first and second support portions, the arc plates having a first edge offset from the exit portion and an opposite second edge distal from the exit portion; a plurality of insulating dividing members disposed between the arc plates, the insulating dividing members having a first edge proximate the exit portion and an opposite second edge distal from the exit portion; and at least one gassing member, wherein the second edge of the insulating dividing members extends beyond the first edge of the arc plates and toward the second edge of the arc plates, wherein the first edge of the insulating dividing members extends beyond the first edge of the arc plates and away from the second edge of the arc plates, wherein the first and second support portions have an edge distal from the exit portion, and wherein the at least one gassing member is disposed at least substantially about the edge of the first and second support portions.
The at least one gassing member may be a single gassing member having a general U-shape with a first leg disposed substantially along the edge of the first support portion, with a second leg disposed substantially along the edge of the second support portion, and with a base disposed between the first and second legs and between the first and second support portions.
One of the arc plates may include an arc horn; and the base may be proximate the arc horn.
The at least one gassing member may include a first gassing member disposed parallel to the edge of the first support portion and a second gassing member disposed parallel to the edge of the second support portion.
The first and second gassing members may be parallel to the first and second support portions, respectively, and may include a plurality of slots receiving the arc plates.
As another aspect of the invention, a circuit breaker comprises: a first power terminal; a second power terminal; a stationary contact electrically connected to the second power terminal; a movable contact electrically connected to the first power terminal; an operating mechanism adapted to open and closed the stationary contact and the movable contact; and an arc chute comprising: a first support portion, a second support portion, an exit portion supported by the first and second support portions, the exit portion having at least one opening, a plurality of electrically conductive arc plates supported by the first and second support portions, the arc plates having a first edge offset from the exit portion and an opposite second edge distal from the exit portion, and a plurality of insulating dividing members disposed between the arc plates, the insulating dividing members having a first edge proximate the exit portion and an opposite second edge distal from the exit portion, wherein the second edge of the insulating dividing members extends beyond the first edge of the arc plates and toward the second edge of the arc plates, and wherein the first edge of the insulating dividing members extends beyond the first edge of the arc plates and away from the second edge of the arc plates.
The exit portion may be a top portion. The first and second edges of the arc plates may be top and bottom edges, respectively. The first and second edges of the insulating dividing members may be top and bottom edges, respectively. The insulating dividing members may extend above the top edge of the arc plates and overlap the arc plates, in order to prevent an arc from the stationary contact and the movable contact, when opened by the operating mechanism, from reaching the top edge of the arc plates, without lengthening, and to cause the arc to pass below the insulating dividing members.
Each one of the insulating dividing members may be disposed between and separated from an adjacent pair of the arc plates, in order to protect the top edge of the arc plates and prevent breakdown of an arc from the stationary contact and the movable contact, when opened by the operating mechanism, down the arc plates during interruption of the arc.
The top portion may comprise a molded top having a bottom surface with a plurality of grooves. Each of the insulating dividing members may include a top surface which interlocks with a corresponding one of the grooves of the bottom surface of the molded top.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
The present invention is described in association with a circuit breaker, although the invention is applicable to a wide range of circuit interrupters.
Although reference is made herein to terms such as “top,” “bottom,” “above,” “below” and “side,” it will be appreciated that those relative terms apply to one frame of reference and that equivalent frames of reference may be employed. For example, an object having a “top,” a “bottom,” and four sides may be rotated 180 degrees such that the “bottom” is now above the “top”. As another example, the object having the “top,” the “bottom,” and the four sides may be rotated 90 degrees such that one of the four sides is now on top and is now “above” another one of the sides that is now on bottom.
Referring to
As best shown in
Continuing to refer to
The top frame 26 and the molded top 24 also include openings 35 to retain the arc chute 2 to a circuit breaker housing (e.g., 80 of
The molded top 24 includes a pair of tabs 36. The top frame 26 includes a pair of openings 38 adapted to receive the tabs 36 and a pair of fasteners 40 (e.g., threaded fasteners; press-fit or snap-fit fasteners interlocked directly with the molded top 24; push on retaining nuts) adapted to engage and retain the tabs 36. Alternatively, the top frame 26 may be interlocked directly (not shown) with the arc chute side portions 4,6.
The first and second side portions 4,6 include a plurality of openings 42,44. The arc plates 12 include a plurality of tabs 46,48 that engage the first and second side portions 4,6 at the openings 42,44, respectively, thereof. The baffles 18 similarly include tabs 50,52 that engage the first and second side portions 4,6 at openings 54,56, respectively, thereof. The molded top 24 includes tabs 58,60 that engage the first and second side portions 4,6 at openings 62,64, respectively, thereof.
Although not shown in
In order to relieve the pressure in the arc chamber 78 without damaging the housing 80 of the circuit breaker 66 or the arc chute 2, the top portion 8 of the arc chute 2 has the relatively large unrestricted vent opening 10 (as best shown in
In order to prevent the arc from reaching the arc plate top edges 14, the insulating dividing baffles 18 are positioned between each metal arc plate 12. The metal arc plates 12 stop a substantial distance below the molded top 24 (
By partitioning the exit vent opening 10 (
Although relatively thicker metal arc plates 12 may be employed to reduce bending, in the event that two or more arc plates 12 bend toward each other, the insulating dividing baffle 18 between them prevents contact, and thereby maintains the effective cooling surface area and number of voltage divisions in the arc chute 2.
As best shown in
The gassing combs 102,104 also include a plurality of slots or grooves 114 (as best shown in
The insulating dividing baffles 100 of
The difference in the widths 150,152 may be, for example, 0.1 inch. This difference provides a gap that doubles the leading edge plate spacing, thereby making it easier for an arc, if formed on the outer contact arms, to enter the arc plates 12. A larger arc plate spacing provides less resistance to arc motion than tightly spaced arc plates. Otherwise, the arc might “stall” at the leading edge and track on the surface.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
