Arc extinguisher assembly for molded case circuit breaker

An arc extinguisher assembly is provided for a mould cased circuit breaker capable of reducing time for arc extinguishing and preventing contacts from being damaged due to a back flow of an arc. To this end, the arc extinguisher assembly for a mould cased circuit breaker provided with a fixed contactor and a movable contactor in the case, includes a plurality of grids made of a ferro magnetic material, each having a recess portion for allowing a movement of the movable contactor, laminated to surround contacts of the movable contactor and the fixed contactor and installed in the case, for dividing an arc when the arc is generated between the fixed contactor and the movable contactor, and a grid support plate including outer wall portions supporting the grids and inner wall portions provided adjacent to contacts of the movable contactor and the fixed contactor and compressing an arc to be narrow, the grid support plate being installed to have a U-shaped horizontal section with an aperture facing the opposite side of the contacts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a molded case circuit breaker, and particularly, to an arc extinguisher assembly for a molded case circuit breaker capable of improving current limiting performance by speedily cooling an arc generated in a procedure where the breaker interrupts an electric shortage current when a short circuit occurs.

2. Description of the Conventional Art

A molded case circuit breaker is an electrical device that protects a circuit and a load by automatically opening the circuit against an excess current such as an electric shortage current. A molded case circuit breaker that has an excellent arc extinguishing capability and can interrupt a current within a short period of time is considered to be the one with good current limiting performance.

Referring toFIGS. 1 to 4, an arc extinguisher assembly in accordance with the conventional art will now be described.

First, the construction of the molded case circuit breaker provided with the conventional arc extinguisher assembly will now be described with reference toFIG. 1that illustrates a longitudinal sectional view thereof. The conventional molded case circuit breaker100includes a first fixed contactor141formed of a conductor and having a terminal portion connected to power source or an electrical load, and a movable contactor142being rotatively movable to a position where it comes in contact with the first fixed contactor141(hereinafter, referred to as a contacted position) or a position where it is separated from the first fixed contactor141(hereinafter, referred to as a separated position). The arc extinguisher assembly140for extinguishing an arc in accordance with the conventional art is installed to surround a contact portion between the first fixed contactor141and the movable contactor142. InFIG. 1, reference numeral150designates a holder that rotatably supports the movable contactor142, and reference numeral120designates a switching mechanism that rotatively drives the movable contactor142to the contacted position or the separated position. A second fixed contactor160is connected to the movable contactor142by an electrical conductor (not shown) and has at its one end portion, a terminal portion connected to power source or an electrical load. Reference numeral170represents a trip mechanism for triggering the switching mechanism120to operate to a trip position when a current flowing through the second fixed contactor160is an excessive current such as an electric shortage current. Reference numeral180represents a handle connected to the switching mechanism120, for manually moving the movable contactor142to the contacted position or the separated position.

The detailed construction of the arc extinguisher assembly, the case, and the fixed and movable contactors in accordance with the conventional art, which are built in the molded case circuit breaker, will now be described with reference toFIG. 2.

FIG. 2is an exploded perspective view that illustrates the arc extinguisher assembly, a portion of the case receiving the assembly, the fixed contactor and the movable contactor ofFIG. 1in detail.

The arc extinguisher assembly143is installed to surround contacts141aand142aof the fixed contactor141and the movable contactor142. The arc extinguisher assembly143includes a plurality of plates143amade of metal of a ferro magnetic material, an uppermost plate144, and a support plate143bmade of an electrically insulated material and for supporting the plates143a.

The fixed contactor141is a current-limiting type one which is bent in a U-shape, and a fixed contact141ais attached onto one end portion of the fixed contactor141by way of welding or the like. An arc runner141bfor inducing an arc is attached behind the fixed contact141aon an upper portion of the fixed contactor141.

In the drawing, the case145illustrated with deviant lines represents a portion of a case and a cover, which receives the arc extinguisher assembly, and is made by molding a synthetic resin having an electrical insulation property.

The arc extinguishing operation of the arc extinguisher assembly for a molded case circuit breaker in accordance with the conventional art will now be described with reference toFIGS. 3 and 4.FIG. 3is a perspective view for describing the arc extinguishing operation by the arc extinguisher assembly ofFIG. 1, andFIG. 4is a view for describing moving directions of an arc in order to show a moving path of an arc in the arc extinguisher assembly ofFIG. 3.

If an abnormal current such as an excessive current and an electric shortage current is generated in an electrical circuit in a state that the fixed contact141aand the movable contact142aare electrically connected, the movable contactor142is rotated to be separated from the fixed contactor141by an electro magnetic repulsive force created between the fixed contact141aand the movable contact142a,thereby opening the circuit.

When the movable contactor142is separated from the fixed contactor141, an arc occurs between the fixed contact141aand the movable contact142a,and the arc generated thereby is induced to the arc runner141b(refer toFIG. 2). Then, as shown inFIG. 4, some arc (a, b and c) moves toward the arc extinguisher assembly143and the rest flows back toward the contacts141aand142a.

Then, the arc is divided and cooled by the plates143aof the arc extinguisher assembly143, thereby being extinguished. An arc gas formed as the air around the arc is heated is discharged to the outside of the molded case circuit breaker through an discharge hole146ofFIG. 3.

However, in the conventional arc extinguisher assembly for a molded case circuit breaker, a column of the arc cannot be compressed and extended, and the arc is extinguished only by the effects of dividing and cooling by the plurality of laminated plates143a. Thusly, it takes a long time to complete such extinguishing. Also, an arc may reoccur or the contacts141aand142aare damaged by a back flow of an arc and a gas around the arc toward the contacts141aand142a.

BRIEF DESCRIPTION OF THE INVENTION

Therefore, an object of the present invention is to provide an arc extinguisher assembly for a molded case circuit breaker capable of reducing time for arc extinguishing and preventing contacts from being damaged by repressing a back flow of an arc.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an arc extinguisher assembly for a molded case circuit breaker provided with an electrically insulated case, a fixed contactor and a movable contactor in the case, the assembly comprising a plurality of plates made of a ferro magnetic material, each having a recess portion for allowing a movement of the movable contactor, laminated to surround contacts of the movable contactor and the fixed contactor and installed in the case, for dividing an arc when the arc is generated between the fixed contactor and the movable contactor, and a plate support plate including outer wall portions supporting the plates and inner wall portions provided adjacent to contacts of the movable contactor and the fixed contactor and compressing an arc to be narrow, the plate support plate being installed to have a U-shaped horizontal section with an aperture facing the opposite side of the contacts.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIGS. 5A,5B and6, the arc extinguisher assembly240in accordance with one embodiment of the present invention is suitable to use in a molded case circuit breaker provided with a fixed contactor251and a movable contactor252. The fixed contactor251includes a fixed contact251aon its contact surface coming in contact with a contact252aof the movable contactor252. Reference numeral241brepresents an arc runner for inducing an arc at a position adjacent to the fixed contact251a, which is generated by separation between the movable contactor252and a fixed contactor251, toward a plate241with an electro magnetic repulsive force when an excess current such as an electric shortage current flows through the contacts251aand252a.

The molded case circuit breaker includes a case245made of an electrically insulated material, for receiving the arc extinguisher assembly240in accordance with one embodiment of the present invention.

The arc extinguisher assembly240in accordance with one embodiment of the present invention includes a plurality of plates241. Each of the plates241is made of a ferro magnetic material and includes a recess portion241cfor allowing a rotative movement of the movable contactor252. A plurality of plates241having U-shaped horizontal section are laminated in a vertical direction to surround the contacts251aand251bof the movable contactor252and the fixed contactor251for the purpose of dividing an arc when the arc is generated between the fixed contactor251and the movable contactor252.

The arc extinguisher assembly240in accordance with one embodiment of the present invention includes a pair of plate support plate242.

Each of the plate support plate242includes outer wall portions242asupporting plate241and inner wall portions242beach bent and extending from the outer wall portion242ain a U-shape and provided adjacent to the contacts251aand251bof the movable contactor252and the fixed contactor251. Here, the plate support plate242has a rough U-shaped horizontal section, and the U-shaped horizontal section of the plate support plate242is opened towards the opposite side of the contacts251aand251bso as to support the plates241and simultaneously prevent the back flow of the arc toward the contacts251aand251bof the contactors251and252.

Two cases245may be coupled together as one set by a coupling unit such as a screw or the like. The case245receives not only the arc extinguisher assembly240but also a switching mechanism (refer to reference numeral120ofFIG. 1) driving the movable contactor252, a trip mechanism (refer to reference numeral170ofFIG. 1) and another fixed contactor (refer to reference numeral160offigure 1). InFIGS. 5 to 7, only a portion of the case245that receives the arc extinguisher assembly in accordance with the present invention is illustrated, and other portions of the case (a portion extending to the right side from the case245ofFIG. 5a) that receive the switching mechanism, the trip mechanism and another fixed contactor are omitted. The case245may be constructed as a single pole unit type case that can be electrically insulated from another case of a different phase (pole) such that each arc extinguisher assembly and each pair of fixed and movable contactors are received in each case according to phases (according to poles). For example, in the case of a breaker for a molded case wire for three-phase AC, three cases of the single pole unit type may be provided, and a container receiving all of those three cases of the signal pole unit type and a cover covering an upper portion of the container may be provided. An exhausting hole246for exhausting an arc gas is provided at a predetermined position above the arc extinguisher assembly240of the case245.

The plate support plate242is for supporting the plates241and includes one pair of outer wall portions242awhich are long and face each other. In order to form a chamber242efor preventing a back flow of an arc together with the outer wall portions242a, the plate support plate242also includes one pair of inner wall portions242bbent and extending from the outer wall portions242ain a U-shape such that each end portion of its horizontal sectional surface faces the opposite side of the movable contactor. The pair of inner wall portions242bhave shorter lengths than those of the outer wall portions242aand face each other. A plurality of connection holes242cfor a connection with the plates241are provided at a surface of each outer wall portion242afacing the plates241in a vertical direction at a predetermined interval, wherein the number of the connection holes242ccorresponds to the number of the plates. In the embodiment illustrated in the drawing, seven connection holes242care provided. A guiding protrusion portion242dfor guiding a portion of the plate241inserted in the connection hole242cat the time of the connection and installation of the plate241is provided right under each connection hole242c.

In order to induce the exhaustion of the arc gas through the exhausting hole246of the case245, an upper end portion of the plate support plate242is opened, and a lower end portion thereof is closed with a bottom plate portion252f.

According to the preferred embodiment of the present invention, the plate support plate242may be made of Nylon 6, 6 manufactured by DuPont Corporation or Nylon 6 manufactured mainly by Asian textile manufacturers. Even though a temperature of an arc reach up to about 10,000° C., the plate support plate242made of Nylon 6, 6 or Nylon 6 is not melt or weakened by the arc because the arc is extremely momentarily extinguished (the arc is extinguished within about 3 milli seconds in consideration of performance that the molded case circuit breaker is required to have). The present inventor considered POM(Poly Oxy Methylene), which forms a hydrogen gas when being momentarily heated by an arc, to be a material of the support plate242. The melting point of POM(Poly Oxy Methylene) is 180° C., the melting point of Nylon 6 is 210° C., and the melting point of Nylon 6, 6 is 250° C. The temperature around the contacts reached up to 120˜130° C. at the time of current limiting operation using the electro magnetic repulsive force, and therefore, the POM having melting point of 180° C. is at least weakened and might collapse, failing to support the plate. For this reason, the inventor decided that the POM was not appropriate as the material of the plate support plate242. In that point of view, the most preferred material would be Nylon 6, 6.

When being heated instantly by an arc, the Nylon 6, 6 or Nylon 6 discharges a hydrogen gas, including other gases like carbon. Because the hydrogen gas is the lightest gas on the planet, the hydrogen gas ascends in an instant along a space between two arm portions241bof the plate and is exhausted through the exhausting hole246placed at an upper portion of the arc extinguisher assembly240of the present invention. For this reason, the hydrogen gas is used to induce the extinguishing of the arc.

When an excessive current such as an electric shortage current is accidentally generated on a circuit where a molded case circuit breaker is installed, as shown inFIG. 6, the movable contactor252is rotated to be separated from the fixed contactor251by an electro magnetic repulsive force between the contact252aof the movable contactor252and the contact251a of the fixed contactor251. Also, an arc occurs between the contact252aof the movable contactor252and the contact251aof the fixed contactor251. As shown inFIG. 5B, a distance (I) between the inner wall portions242bformed as a pair and facing each other is shorter than a distance (L) between the facing outer wall portions242aformed as a pair. Accordingly, when generated between the inner wall portions242b, the arc is compressed at a narrow gap between the pair of inner wall portions242band becomes long and narrow. The arc is generated from the contact251aof the fixed contactor251in a vertical direction by the movable contactor252rotated by the electro magnetic repulsive force, and, at that moment, the inner wall portions242bof Nylon 6 or Nylon 6, 6 emits a hydrogen gas by the momentary heating of the arc.

Accordingly, the arc is compressed further to be narrower and longer at the narrow gap between the pair of inner wall portions242bby the pressure of the hydrogen gas emitted from the inner wall portions242b. An arc gas including the hydrogen gas, the arc and the ambient air heated by the arc is introduced to a space between the two arm portions241bwhere the pressure is lower than that within the gap between the pair of inner wall portions242b. Here, an electro magnetic absorption force that is created from the plate241made of a ferro magnetic material also helps such introduction of the arc. The arc among those (the arc, the hydrogen gas and the arc gas) introduced in such a manner is divided and cooled by the plurality of plates241that are laminated, and the hydrogen gas and the arc gas ascend along the space between the two arm portions241band are exhausted through the exhausting hole246placed at an upper portion of the arc extinguisher assembly240.

As shown inFIG. 5A, each plate241is a metal plate made of a ferro magnetic material. As for such a plate241, connection protrusion portions241ainserted in the connection hole242cof the plate support plate242are provided at both sides, a recess portion241cfor allowing a movement of the movable contactor252is provided, and two arm portions241bare provided to surround the contacts251aand251bof the movable contactor252and the fixed contactor251.

As shown inFIG. 7, the generated arc is introduced in directions of arrows a, b, c by the pressure difference between the space between both inner wall portions242bof the plate support plate242and the space of recess portion241cand by the electro magnetic absorption force from the plate241. Here, an arc indicated as the arrow a is introduced toward the recess portion241cof the plate241, an arc indicated as the arrow b is introduced toward the guiding protrusion242bof the plate support plate242, and an arc indicated as the arrow c is introduced toward the two arm portions241bof the plate241and flows back toward the contacts251aand252a. However, as shown inFIG. 7, because the arc extinguisher assembly in accordance with the present invention has the plate support plate with a u-shaped horizontal section opened towards the opposite side of the contacts251aand252a, the arc which is flowing back is introduced toward the guiding protrusion portion242dof the plate241again. Accordingly, phenomena can be prevented that an arc is regenerated at the contacts251aand252aof the contactors251and252by the arc flowing back toward the contacts251aand252aor that the contacts251aand252aare damaged by the arc. As shown inFIG. 7, reference numeral242erepresents a reverse exhaustion preventing chamber242efor converting the direction of an arc that is flowing reversely toward the plate241.

As described so far, by the arc extinguisher assembly for the molded case circuit breaker in accordance with one embodiment of the present invention, a generated arc is compressed to be long and narrow at a narrow gap between the two inner wall portions of the plate support plate, and is introduced to a plurality of plates laminated in a vertical direction, thereby being divided and cooled. Consequently, the arc can be speedily exhausted.

Also, the back flow of the arc toward the contacts is interrupted to prevent reoccurrence of the arc and the durability of the molded case circuit breaker can be improved as damage to the contacts is prevented.