Abstract:
Embodiments include a circuit breaker having first and second electrical contacts, the contacts adapted to generate an electrical arc during separation, at least one of the first and second electrical contacts being a movable electrical contact. The circuit breaker also includes an expansion chamber disposed adjacent to at least one of the first and second electrical contacts such that an arcing space is defined by the first electrical contact and the second electrical contact when the first and second electrical contacts are separated. The expansion chamber includes an opening configured to permit air flow between the arcing space and a chamber of the expansion chamber.

Description:
BACKGROUND 
     The present invention relates generally to circuit breakers, and more specifically to, circuit breakers that include expansion chambers for extinguishing arcs. 
     In general, a circuit breaker operates to engage and disengage a selected electrical circuit from an electrical power supply. The circuit breaker ensures current interruption thereby providing protection to the electrical circuit from continuous over current conditions and high current transients due, for example, to electrical short circuits. Such circuit breakers operate by separating a pair of internal electrical contacts contained within a housing of the circuit breaker. Typically, one electrical contact is stationary while the other is movable (e.g., mounted on a pivotable contact arm). The contact separation may occur manually, such as by a person throwing a handle of the circuit breaker. This may engage a trip mechanism, which may be coupled to the contact arm and moveable contact. Otherwise, the electrical contacts may be separated automatically when an over current or short circuit condition is encountered. This automatic tripping may be accomplished by a tripping mechanism actuated via a thermal overload element (e.g., a bimetal element) or by a magnetic element (e.g., an actuator). 
     Upon separation of the electrical contacts by tripping of the circuit breaker, an electrical arc may be formed. This separation may occur due to heat and/or high current through the circuit breaker. It is desirable to extinguish such arc as quickly as possible to avoid damaging internal components of the circuit breaker. In low voltage alternating current (AC) circuit breakers, such as molded case circuit breakers (MCCBs), two methods are commonly used to extinguish arcs. The first method is often referred to as current limiting and it includes actively raising the arc voltage to a level higher than the system voltage, which effectively forces the current to reduce to zero. Commonly used current limiting methods include arc plates, gassing material, long arcs and so on. The second method includes using the natural current zero crossing from AC circuit to prevent re-ignition after current goes to zero. In currently available circuit breakers, due the inductance present in a circuit, a recovery voltage can be induced across the arcing space. If the recovery voltage is high enough, it can re-ignite the extinguished arc and cause failed interruptions. 
     Accordingly, there is a need for apparatus, systems and methods to extinguish an electrical arc in a circuit breaker resulting from contact separation. 
     SUMMARY 
     In one embodiment, a circuit breaker includes first and second electrical contacts, the contacts adapted to generate an electrical arc during separation, at least one of the first and second electrical contacts being a movable electrical contact. The circuit breaker also includes an expansion chamber disposed adjacent to at least one of the first and second electrical contacts such that an arcing space is defined by the first electrical contact and the second electrical contact when the first and second electrical contacts are separated. The expansion chamber includes an opening configured to permit air flow between the arcing space and a chamber of the expansion chamber. 
     In another embodiment, a method of operating a circuit breaker includes separating a first electrical contact from a second electrical contact upon tripping of the circuit breaker and responsively forming an electrical arc. The method also includes increasing an air pressure in an expansion chamber disposed adjacent to at least one of the first and second electrical contacts in response to a rising current in the electrical arc. An arcing space is defined by the first electrical contact and the second electrical contact when the first and second electrical contacts are in a separated position. The method further includes creating airflow from the expansion chamber into the arcing space through an opening in the expansion chamber in response to a decrease in the air pressure in the arcing space, wherein the airflow acts to cool the electrical arc. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIGS. 1A and 1B  respectively illustrate a cross sectional side view and a cross sectional top view of a traditional circuit breaker; 
         FIG. 2A  is a cross sectional top view of a circuit breaker with an expansion chamber in accordance with an exemplary embodiment; 
         FIG. 2B  is a cross sectional side view of a circuit breaker with an expansion chamber in accordance with an exemplary embodiment; 
         FIG. 3  is a perspective view of an expansion chamber for a circuit breaker in accordance with an exemplary embodiment; 
         FIG. 4  is a graph illustrating the relationship between a current and time during a fault in a circuit breaker with an expansion chamber in accordance with an exemplary embodiment; 
         FIGS. 5A and 5B  illustrate cross sectional side views of a circuit breaker with an expansion chamber in accordance with an exemplary embodiment; 
         FIGS. 6A, 6B, 6C and 6D  illustrate cross sectional side views of expansion chambers in accordance with exemplary embodiments; 
         FIGS. 7A, 7B and 7C  illustrate cross sectional side views of expansion chambers in accordance with an exemplary embodiment; 
         FIGS. 8A and 8B  illustrate cross sectional side views of a circuit breaker with an expansion chamber in accordance with an exemplary embodiment; and 
         FIG. 9  illustrates a cross sectional side view of a circuit breaker with an expansion chamber in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments include circuit breakers with an expansion chamber configured to prevent a re-ignition failure of the circuit breakers. In exemplary embodiments, as the arc is formed the air inside the circuit breaker and around the contacts heats up and pressurizes, which causes an airflow into the expansion chamber. After the air pressure in the area around the contacts reaches its peak and begins to drop, air will begin to flow from the expansion chamber back into the area around the contacts. This air flow will cool down the arcing space and will increase dielectric strength of the arcing space. In exemplary embodiments, the air flow on the arc also cools down the arc and increases the arc voltage, thereby providing better current limiting performance. 
     Referring now to  FIGS. 1A and 1B  a cross sectional side view and a cross sectional top view of a traditional circuit breaker  100  are respectively shown. The circuit breaker  100  includes a housing  102  that may be made up of a number of interconnecting housing sections and may include an arrangement of internal and external walls, which are adapted to contain or retain various components of the circuit breaker  100 . While the circuit breaker  100  illustrated is a molded case circuit breaker (MCCB) it will be appreciated by those of ordinary skill in the art that the present invention is applicable to other designs with similar constructions. 
     In exemplary embodiments, the circuit breaker  100  includes a handle  106  that is operably connected to an operating mechanism  108 . The operating mechanism  108  is coupled to an arm  110  that has a moveable contact  112  and an upper arc runner  114  disposed thereon. The circuit breaker  100  also includes a stationary contact  116  and a lower arc runner  118 . As best illustrated by  FIG. 1A , the circuit breaker  100  includes a plurality of arc plates  120 . As best illustrated by  FIG. 1B , the arc plates  120  have a u-shape and are disposed around the area containing the stationary contact  116  and the moveable contact  112 , such that at least a portion of the moveable contact  112  passes through the u-shaped opening in the arc plates  120  when the circuit breaker trips. As used herein the term arcing space refers to the area between the stationary contact  116  and the moveable contact  112  when the circuit breaker  100  is in the tripped state. When the circuit breaker  100  trips, an arc is between the movable contact  112  and the stationary contact  116  in the arcing space. 
     Referring now to  FIGS. 2A and 2B , a cross sectional top view and a sectional side view of a portion of a circuit breaker  200  with an expansion chamber in accordance with an exemplary embodiment are respectively shown. As illustrated, the circuit breaker  200  includes a stationary contact  202 , a moveable contact  204 , an arc plate  206  and one or more expansion chamber  208 . In exemplary embodiments, the circuit breaker  200  includes two expansion chambers  208  that are disposed on opposite sides of an arcing space  214  defined by the walls of the expansion chambers  208  and the stationary contact  202  and moveable contact  204  in a separated position. 
     In exemplary embodiments, each of the expansion chambers  208  includes an opening  210  and a chamber  212 . In exemplary embodiments, the openings  210  of the expansion chambers  208  are disposed in staggered locations relative to one another such that the air flows into and out of the arcing space  214  into the chamber  212  at different locations between the stationary contact  202  and the moveable contact  204 . In exemplary embodiments, the number, size and locations of the openings  210  and the size of the chamber  212  may be varied depending on the specifications of the circuit breaker  200 . In exemplary embodiments, the expansion chambers  208  may be molded from a suitable plastic material, a thermoset material such as glass-filled polyester, or a thermoplastic material such as a Nylon material. 
     Referring now to  FIG. 3 , a perspective view of an expansion chamber  300  for a circuit breaker in accordance with an exemplary embodiment is shown. As illustrated, the expansion chamber  300  includes an opening  302  and a chamber  304 . In exemplary embodiments, the opening  302  has a length  306  that extends the entire width of the expansion chamber  300  and a height  308 . The height  308  is selected based on the desired operating characteristics of both the circuit breaker and the expansion chamber  300 . In exemplary embodiments, the length of opening  302  covers the length of the stationary contact with a slot shape. However, as will be appreciated by those of ordinary skill in the art, other shapes and size of the opening  302 , such as circle may also be used. In addition, those of ordinary skill in the art will appreciate that the size, number and location of the opening  302  shown is merely exemplary and the number, size and location of the openings  302  may be varied without departing from the present invention. 
     Referring now to  FIG. 4 , a graph illustrating the relationship between a current and time during a fault in a circuit breaker with an expansion chamber in accordance with an exemplary embodiment is shown. During the rising portion of the current, the pressure in the arcing space is higher than the pressure in the expansion chamber, and hence flow is generated to push hot gas into the expansion chamber, as shown in  FIG. 5A . During the rising current phase the pressure in the expansion chamber is built up to match the pressure in the arcing space. In exemplary embodiments, the gas inside the expansion chamber is cooled and de-ionized due to lack of heating in the chamber. In exemplary embodiments, the chamber may contain one or more cooling elements to aide in the cooling of the gas in the chamber. 
     After current in the arc reaches peak value, the pressure in the arcing space starts to reduce. At a certain point of time, the pressure in the expansion chamber exceeds the pressure in the arcing space and an air flow is generated that blows cooled gas from the expansion chamber into the arcing space, as shown in  FIG. 5B . In exemplary embodiments, the volume of the expansion chamber and the size of the opening are selected such that the reverse flow can last until the current flow in the arc reaches the natural zero crossing, and hence significantly increase the dielectric strength of the arcing space to prevent re-ignition. In exemplary embodiment, the flowing of cooled air on the arc also cools down the arc and increases the arc voltage, thereby providing better current limiting performance. 
       FIGS. 6A, 6B and 6C  illustrate cross sectional side views expansion chambers  600  in accordance with various exemplary embodiments. As illustrated each of the expansion chambers  600  includes a chamber  604  configured to receive pressurized air from an arcing space through an opening. The expansion chambers  600  may include openings that have different cross sectional shapes to achieve different flow profiles. For example, the openings may be configured in the shape of a converging nozzle. The converging nozzle is used to accelerate the airflow through the opening. While the mass flow rate is defined by the smallest cross section, the velocity of the flow can be a lot higher than just straight channel. As shown in  FIGS. 6A and 6B , openings  602 ,  606  may be used to enable fast pressurizing of the expansion chamber  600  and slow releasing of reverse flow from the expansion chamber  600 . For example, the openings  602 ,  606  may include a tapered shape that reduces in size from the arcing space into the chamber  604 . As shown in  FIG. 6C , opening  608  may be used to achieve fast releasing and for a strong reverse flow into the arcing space from the chamber  604 . For example, the openings  608  may include a tapered shape that increases in size from the arcing space into the chamber  604 . 
     Referring now to  FIG. 6D  a cross sectional side view of an expansion chamber  600  in accordance with an exemplary embodiment is shown. In exemplary embodiments, the chamber  604  may include on or more cooling elements  610 , such as fins, disposed within the chamber  604 . The cooling elements  610  may be formed from the same or different material than the expansion chamber  600 . It will be appreciated by those of ordinary skill in the art that the arrangement of cooling elements depicted is merely exemplary and that the number, size and location of the cooling elements  610  may be varied based on the desired operational characteristics of the expansion chamber  600  and the circuit breaker. 
     Referring now to  FIGS. 7A, 7B and 7C  cross sectional side views of expansion chambers  700  in accordance with an exemplary embodiment are shown. As illustrated, the expansion chambers  700  include an opening  702 , a chamber  706  and a one-way valve  704 . In some embodiments a fast pressurizing air flow from an arcing space into the chamber  706  and a slow air flow releasing air from the chamber  706  into the arcing space are desired. In exemplary embodiments, the one-way valve  704  can be added to the expansion chamber  700  to accomplish these air flow characteristics. 
     As shown in  FIG. 7B , when the pressure in the arcing space is rising the one-way valve  704  is opened and air flows into the chamber  706  through both the one-way valve  704  and the opening  702 . As a result, the pressure in the chamber  706  is able to rapidly increase as the pressure in the arcing space is increasing. Next, as shown in  FIG. 7C , when the pressure in the arcing space in less than the pressure in the chamber  706  the one-way valve is closed. As a result, the air from the chamber is only released through the opening  702 . In exemplary embodiments, the one-way valve  704  may include a flexible member attached to the inside the chamber  706 . In exemplary embodiments, a slow pressurizing air flow from an arcing space into the chamber and a fast air flow releasing air from the chamber can be achieved using a one-way valve with an opposite configuration from that shown in  FIGS. 7A, 7B and 7C  can be used. 
     Referring now to  FIGS. 8A and 8B , cross sectional side views of a portion of circuit breaker  800  with expansion chambers  802  in accordance with an exemplary embodiment are shown. As illustrated, the circuit breaker  800  includes an arcing space  804  which is disposed between a stationary contact  808 , a moveable contact  806  and the expansion chambers  802 . Each of the expansion chambers  802  includes an opening  812  configured to allow airflow in between the chamber  814  of the expansion chambers  802  and the arcing space  804 . 
     In exemplary embodiments, each of the expansion chambers  802  also includes a moveable wall  816  that is configured to move under pressure to allow the expansion and contraction of the chamber  814 . In exemplary embodiments, the moveable wall  816  may be affixed to a spring  818  which is configured to assure a minimum air flow rate from the chamber  814  into the arcing space  804 , which is related to the characteristics of the spring  818 . In exemplary embodiments, the moveable wall  816  may be actuated with external springs  818 , as shown, or by using flexible members as chamber walls. 
       FIGS. 8A and 8B  illustrate circuit breakers  800  including two expansion chambers  802  with staggered opening  812 . In exemplary embodiments, the staggered openings  812  increase the working area of the reverse flows on the arc in the arcing space. In exemplary embodiments, multiple openings in each expansion chamber  802  can be used to cover more arc length. In alternative embodiments, the circuit breaker may include only one expansion chamber that can have one or more openings. 
     Referring now to  FIG. 9 , a cross sectional side view of a circuit breaker  900  with an expansion chamber  922  in accordance with an exemplary embodiment is shown. The circuit breaker  900  includes a housing  902  that may be made up of a number of interconnecting housing sections and may include an arrangement of internal and external walls, which are adapted to contain or retain various components of the circuit breaker  900 . In exemplary embodiments, the circuit breaker  900  includes a handle  906  that is operably connected to an operating mechanism  908 . The operating mechanism  908  is coupled to an arm  910  that has a moveable contact  912  and an upper arc runner  914  disposed thereon. The circuit breaker  900  also includes a stationary contact  916  and a lower arc runner  918 . In exemplary embodiments, the circuit breaker  900  includes a plurality of arc plates  920 . In exemplary embodiments, the circuit breaker  900  also includes an expansion chamber  922  disposed beneath the stationary contact  916 . The expansion chamber  922  includes an opening  924  that is disposed adjacent to the stationary contact. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present invention. While embodiments of the present invention have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.