EP0359467A2

EP0359467A2 - Circuit breaker with arc gun

Info

Publication number: EP0359467A2
Application number: EP89309023A
Authority: EP
Inventors: Stephen Albert Mrenna; Jere Lee Mckee; William Ellsworth Beatty, Jr.; Yun-Ko Nickey Chien
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1988-09-12
Filing date: 1989-09-06
Publication date: 1990-03-21
Also published as: EP0359467A3; KR900005515A; AU4012289A; CN1041476A; JPH02119018A; ZA896375B; BR8904551A

Abstract

A circuit breaker having an arc impeller characterized by a circuit breaker mechanism having stationary and movable contacts operable between open and closed positions. A U-shaped member has a U-leg on opposite sides of the stationary contact and the U-shaped member is comprised of a ferromagnetic material for providing a magnetic field in a zone perpendicular to the path of current through the closed contacts so as to drive any arc away from the contacts into an adjacent arc extinguisher. A fiber barrier is located adjacent the stationary contacts, which emits are cooling gas during contact separation.

Description

BACKGROUND OF THE INVENTION

This invention relates to an electric circuit breaker having an arc gun for impelling an arc from between the contacts into an arc extinguisher.
As is known in the prior art, molded case circuit breakers are provided with operating mechanisms that include movable contacts that provide protection for an electrical circuit or system against electrical faults, such as low level short circuit, fault circuit conditions, and, in some cases, high level short circuit or fault current conditions. Circuit breakers usually employ a trip mechanism for controlling the movement of an overcenter toggle mechanism to separate a pair of electrical contacts when an overload condition occurs.
When the contacts separate, an electrical arc usually forms and it is desirable to extinguish the arc as rapidly as possible to minimize detrimental effects to the circuit breaker contacts as well as associated electrical equipment. Prior art circuit breakers, such as shown in the specification of U.S. Patent No. 4,654,491, employ current limiting conductors supporting contacts for generating repulsion magnetic forces between the contacts. Where high fault currents occur, most prior art means for moving an arc from the contacts to an associated arc extinguisher, are satisfactory. Where low current faults occur, it is necessary to provide additional needs for moving the arc from the contacts.
According to the present invention, a circuit breaker comprises an insulating housing having line and lead terminals, a circuit breaker structure within the housing and having stationary and movable contacts operable between open and closed positions, a contact arm carrying the movable contact, means coupled with the contact arm for opening and closing the contacts, an arc extinguisher disposed adjacent to the contact arm, U-shaped means comprising a U-leg extending on opposite sides of the stationary contact, the U-shaped means being susceptible to a magnetic field extending between the U-legs in a zone on the side of the stationary contact facing the movable contact and perpendicular to the path of current through a conductor when a current passes through the conductor so as to drive any arc occurring between the opening of the contacts toward the arc extinguisher, and a fiber barrier disposed between the stationary contact and at least one of the U-legs, so as to emit an arc cooling gas directed to any arc formed during contact separation.
Consequently, a fixed conductor extends to support the stationary contact, a U-shaped member comprising a U-leg extending on opposite sides of at least one of the contacts and being susceptible to a magnetic field extending between the U-legs in a zone on the side of each contact facing the other contact, which zone is perpendicular to the path of current through the conductor when the current passes through the conductor so as to drive any arc occurring between the opening contacts open toward the arc extinguisher, an insulating barrier disposed between at least one of the contacts and at least one of the corresponding U-legs for avoiding thermal damage to the U-legs.
An object of this invention is that it increases the magnetic field between the contacts to drive the arc into the arc extinguisher, and a gas evolving means evolves cooling gas on contact separation.
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 multipole circuit breaker;
Figure 2 is a sectional view taken along the line II-II of Fig. 1;
Figure 3 is a sectional view taken along the line III-III of Fig. 1;
Figure 4 is a diagrammatic view showing lines of magnetic force extending between the legs of a ferromagnetic core and showing an arc extending upwardly from a stationary contact;
Figure 5 is a plan view taken on the line V-V of Figure 4, showing the field lines around an arc together with a direction in which the arc is moved in response to the magnetic lines of course and the field lines;
Figure 6 is a perspective view of the embodiment of the invention shown in Figure 2;
Figure 7 is an in view of a second embodiment of the invention; and
Figure 8 is an elevational view of a third embodiment of the invention.

Figure 1 shows a circuit breaker 11 comprising an insulating housing 13 and a circuit breaker mechanism 15 supported within the housing. The portion of the housing shown comprises an insulating base; a corresponding insulating cover is not shown.
The circuit breaker mechanism 15 comprises an operating mechanism including a latch and trip device 17. The circuit breaker 11 is of the type that is described in the specification of U.S. Patent 3,797,009. The circuit breaker 11 is a three-pole structure comprising three compartments disposed in side-by-side relationship. The center pole compartment (Fig. 1) is separated from the two outer pole compartments by insulating barrier walls formed with the housing base 13 and the cover. The circuit breaker mechanism 15 is disposed in the center pole compartment and is a single operating mechanism for operating the contacts of all three pole units.
Each pole unit comprises a stationary contact 19 that is fixedly secured on a rigid main conductor 21, that in turn is secured to the base 13 by bolt 23. In each pole unit, a movable contact 25 is secured, such as by welding or brazing to a contact arm 27 that is mounted on the pivot pin 29. The contact arm 27 for all three pole units is supported at one end thereof and is rigidly connected on a common insulating tie bar 31 by which the arms of all three pole units move in unison. Each of the contact arms 27 is biased about the associated pivot pin 29.
The operating mechanism 15 actuates the contact arm 27 between open and closed positions. The closed position of the arm is indicated at 27a. The mechanism comprises an overcenter toggle structure similar to that shown in the specification of U.S. Patent No. 3,797,009. The mechanism includes an integral handle 33 to enable manual operation of the breaker. The circuit breaker is manually operated to the open position by movement of the handle 33 in a clockwise direction, whereby the overcenter toggle mechanism functions with the contact arm 27 for all pole units in the position shown in Fig. 1 in a manner well known in the art. Conversely, the circuit breaker is manually closed by counterclockwise movement of the handle 33 from the "off" position to the "on" position by movement of the handle to the broken-line position 33a, whereby the contact arm moves to the broken-line position 27a.
Movement of the contact arm from the closed position 27a to the open position 27 may also be accomplished automatically by the trip device 17 in response to predetermined overload conditions in the circuit breaker through any or all of the pole units in the circuit breaker as described in the specification of U.S. Patent No. 3,797,009. Thus, a circuit through each pole unit extends from a left-hand terminal 35 through the conductor 21, the contacts 19, 25, the contact arm 27, a flexible conductor 28, a conductor 39, and to a right hand terminal connector 41.
In accordance with this invention, the conductor 21 comprises means for impelling an arc out of the contacts and into an arc extinguisher. As shown more particularly in Figs. 2 and 3, an arc gun or impeller 43 and a insulating support block 45 are disposed between the upper and lower portions of the conductor 21. The gun or impeller 43 is a U-shaped member of ferromagnetic material and serves as a core for assembling and directing a magnetic field between the space U-legs 49, 51 of the impeller 43, the lower ends of which U-legs are integral portions of a bight portion 43. The bight portion is clamped (Fig. 6) between the conductor 21 and the insulating support block 45. A sheet of insulation 55 is disposed between the conductor 21 and the bight portion 43. The conductor 21 is comprised of a metal having a high coefficient of electrical conductivity, such as copper, which serves as a winding for the U-shaped core. Accordingly, when carrying a current, the magnetic field 47 (Fig. 4) extends in a zone across and above the stationary contact 19.
Associated with the means for impelling an arc away from the contacts 19, 25 is an arc extinguisher 57 (Fig. 1) comprised of a plurality of spaced stacked metal plates 59 which are secured in place between a pair of insulating plates or fiber board 61, 63. When an arc 65 (Fig. 4) occurs between the spaced contacts 19, 25, an electromagnetic field 67 (Fig. 5) occurs, encircling the current conducting arc whose field rotates counterclockwise about the arc 65 with the lower portion of the field 67 (as viewed in Fig. 5) complimenting the field lines 47a on the lower side of the arc 65. Simultaneously, the upper portion of the field 67 moves against the field lines 47b and therefore reduces the force of the field lines 47b, whereby the arc 65 moves in the direction of the arrow 69 away from the contact 19 and into the plates 59 of the arc extinguisher 57.
A second embodiment of the invention is shown in Fig. 7 in which similar numerals refer to similar parts. In this embodiment, a conductor 71 corresponding to the conductor 21 includes an arc gun or impeller 73 as an integral part thereof. In order to provide a magnetic field in the zone above the contact 19, the conductor 71 and the arc gun 73 are preferably comprised of laminated material including layers 75 and 77. The layer 75 is comprised of a ferromagnetic material to provide the magnetic field and the layer 77 is comprised of a metal of a high coefficient of electrical conductivity, such as copper, on which the contact 19 is secured. To facilitate the description, only two laminated layers 75, 77 are shown instead of a plurality thereof.
A third embodiment of the invention is shown in Fig. 8 in which similar numerals refer to similar parts. In this embodiment, an arc gun or impeller 79 is mounted on the contact arm 27 in an inverted U-shaped position. Like the arc gun 43, the arc gun 79 is comprised of a ferromagnetic material in order to provide a magnetic field 81 across the contact 25. Accordingly, when the contacts 19, 25 separate with the movable contact in the broken line position 25a, the arc gun 79a provides the magnetic field to act upon an arc (not shown) extending between the contacts 19, 25a and thereby impel the arc away from the contacts and into the arc plates 59, in a manner similar to that shown in Fig. 5. Thus, in Fig. 8 a pair of arc guns or impellers 43, 79 cooperate to rapidly move an arc into the arc extinguisher 57. It is noted that although the second arc gun 79 is provided with the embodiment of the invention shown in Fig. 5, it is also applicable to the embodiment shown in Fig. 7 in which the arc gun is integral with the conductor 71 as well as the contact arm 27.
In order to minimize damage to the arc gun, such as the U-legs 49, 51 (Figs. 2, 3), a pair of insulating plates 83, 85 are disposed between the contact 19 and the U-legs. The upper portions of the plates 83, 85 are secured such as by rivets 87 to the corresponding fiber board 61, 63 with spacers 89 between the plates 83, 85 and the corresponding fiber boards 61, 63 to provide clearance of the U-legs 49, 51. Although the insulators 83, 85 provide thermal protection for adjacent parts of the circuit breaker including the U-legs 49, 51, the insulators may also have another purpose. Where the insulators are comprised of fiber board, they emit gas, such as hydrogen, for cooling an arc. This is particularly advantageous where the circuit breaker is rated at greater than 480 volts.
In conclusion, heretofore without an arc gun, an arc dwelled on the contacts and took a longer time to move off of the contacts and into an arc extinguisher. With smaller circuit breakers, 250 ampere maximum frame size the arc chamber volume is less and therefore has less capacity in the arc extinguisher to absorb the interruption. For this reason, something extra such as the arc gun is desirable to extinguish the arc by moving it very rapidly into the arc extinguisher.

Claims

1. A circuit breaker comprising an insulating housing having line and lead terminals, a circuit breaker structure within the housing and having stationary and movable contacts operable between open and closed positions, a contact arm carrying the movable contact, means coupled with the contact arm for opening and closing the contacts, an arc extinguisher disposed adjacent to the contact arm, U-shaped means comprising a U-leg extending on opposite sides of the stationary contact, the U-shaped means being susceptible to a magnetic field extending between the U-legs in a zone on the side of the stationary contact facing the movable contact and perpendicular to the path of current through a conductor when a current passes through the conductor so as to drive any arc occurring between the opening of the contacts toward the arc extinguisher, and a fiber barrier disposed between the stationary contact and at least one of the U-legs, so as to emit an arc cooling gas directed to any arc formed during contact separation.

2. A circuit breaker as claimed in claim 1 in which the conductor is a U-shaped member having first and second conductor legs, the first conductor leg carrying the stationary contact.

3. A circuit breaker as claimed in claim 2 in which the first conductor leg is substantially parallel to the contact arm.

4. A circuit breaker as claimed in claim 3 in which the U-shaped means comprises second U-shaped member having U-legs and a bight portion extending on the side of the conductor opposite the contact and insulated therefrom.

5. A circuit breaker as claimed in any one of claims 2 to 4 in which the U-shaped means comprises U-legs extending from opposite sides of and integral with the conductor.

6. A circuit breaker as claimed in claim 5 in which the conductor is comprised of ferromagnetic material.

7. A circuit breaker as claimed in claim 6 in which the conductor comprises a laminated structure including layers of ferromagnetic and copper material.

8. A circuit breaker as claimed in any one of claims 1 to 7 in which the fiber barrier is disposed between the stationary contact and each of the U-legs.

9. A circuit breaker, constructed and adapted for use, substantially as hereinbefore described, and illustrated with reference to the accompanying drawings.