Patent Application
20090002106
The present disclosure relates generally to circuit breakers and particularly to cassette type molded case circuit breakers.
While conventional molded case circuit breakers may utilize a base that is a solid structural part of the breaker and acts to bear the loads of pressure and magnetic repulsion forces during a short circuit event, cassette-type circuit breakers can utilize a breaker base that is a protective shell rather than an actual structural part of the circuit breaker. Cassette breakers disposed within the base are designed to be the load-bearing members during a short circuit event, rather than the breaker base. In an example of a 3-phase circuit breaker, the cassettes are 3 individual poles and the pressure and magnetic forces on the breaker during a short circuit event create repulsive forces between the cassettes. If left unsupported, the cassettes would then spread apart and exert a significant undesirable stress on side walls of the base of the circuit breaker.
Methods to prevent such undesirable stress include increasing a thickness of side walls of the base, increasing venting, and reducing stress concentrations in the base. Additional solutions include use of hardware such as a rivet or screw, for example to secure the cassettes to each other, and thereby prevent them from spreading apart and applying force to the side walls of the base. Although these methods may be effective, increasing side wall thickness, within defined external envelope dimensions, results in a reduction of internal volume available for active circuit protection components, to which a rated current capacity is typically directly related. Further, use of hardware to secure cassettes together has the disadvantage of typically including a metal rod to span a width of all the cassettes within the breaker, thereby potentially creating a reduction in phase-to-phase dielectric isolation.
Accordingly, there is a need in the art for a circuit breaker arrangement that overcomes these drawbacks.
An embodiment of the invention includes a circuit breaker assembly. The assembly includes a base having an interior bottom surface that includes a first engagement feature and a circuit breaker cassette having an exterior bottom surface that includes a second engagement feature. The cassette is oriented in the base to provide for a current path through the base in a first direction. The first engagement feature engages with the second engagement feature and restrains movement of the cassette relative to the base in a second direction that is perpendicular to the first direction and parallel to the interior bottom surface.
Another embodiment of the invention includes a circuit breaker assembly. The assembly includes a base having an interior bottom surface that includes a protrusion and a circuit breaker cassette having and exterior bottom surface that includes an engagement feature. The cassette is oriented in the base to provide for a current path through the base in a first direction. The protrusion engages with the engagement feature and restrains movement of the cassette relative to the base in a second direction that is perpendicular to the first direction and parallel to the interior bottom surface.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.
Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures:
An embodiment of the invention provides an engagement feature molded into a base of a cassette-type molded case circuit breaker. In an embodiment, the engagement feature interfaces inside an exhaust vent of the cassette breaker and keeps the cassette breaker in place during a short circuit event, thereby reducing stresses imparted to the side walls of the base. Use of the engagement feature to restrain the cassette breaker eliminates use of additional parts, increases an overall available internal width between side walls of the base into which the cassettes are be disposed, and assists in maintaining a desirable dielectric isolation between poles of a multi pole circuit breaker.
The cassette breaker 65 includes a moveable contact arm 110 upon which moveable contacts 115, 116 are disposed. The contact arm 110 is depicted in
As will be appreciated by one of skill in the art, the contact arm 110 may be moved between OPEN and CLOSED positions by the operating mechanism 60. Further, the contact arm will be moved from the CLOSED position to the OPEN position in response to a trip event, such as a short circuit, or a current that exceeds a defined level for a defined time, for example. In response to a trip event, such as the short circuit, an arc may be generated between the fixed contacts 120, 121 and the moveable contacts 115, 116 as the moveable contacts 115, 116 are separated from the fixed contacts 120, 121. Arc extinguishing devices (also referred to as arc chutes) 145 extinguish arcs that may be created during the trip event. Furthermore, associated with generation of the arc is a production of heat that causes an expansion of gases surrounding the arc proximate the contacts 115, 116, 120, 121. A flow path 150 of the hot, expanding gases is depicted and begins proximate the contacts 116, 121, continues through the arc chute 145, and exits the cassette breaker 65 via an opening 155 in the cassette 103 disposed at a bottom surface 153 and front end 100 of the cassette 103 known as an exhaust vent 155.
In response to a short circuit trip event of a multi-pole circuit breaker 50, such as a three-phase circuit breaker for example, magnetic repulsion forces are created by high currents running parallel in each current path 130 of each cassette breaker 65 or pole of the circuit breaker 50. These magnetic repulsion forces are directed as shown by direction arrows X, perpendicular to the direction Y of the current path 130, and act upon the two outer cassettes 65, so as to tend to cause the two outer cassettes 65 to be displaced toward the sides 75, 80 of the base 55.
Referring now to
In an embodiment, the engagement feature 95 is a protrusion that extends upward (out of the plane of the page of
The flow path 150 of hot exhaust gases depicted by wavy lines includes the obstructions described above, which divert the flow path 150 and cause the gases to exit via the exhaust ports 160 molded into the base 55. The engagement feature 95 represents an additional obstruction in the flow path 150, and can be recognized as depicted in
It will be appreciated that, as described herein, use of the mating engagements 95, 170 reduces a likelihood of damage to sides 75, 80 of the base 55 following a short circuit trip event. Furthermore, the mating engagements 95, 170 reduce the likelihood of damage while maintaining a given thickness of the sides 75, 80 within defined external dimensions of the circuit breaker 50, thereby maintaining internal dimensions of the base 55 for circuit protection components. Accordingly, a current rating for the circuit breaker 50, within the defined external dimensions may be increased. For example, use of the mating engagements 95, 170 are contemplated, within a breaker having standardized external dimensions known as an “E-Frame”, to provide sufficient internal volume for cassette breakers 65 capable of achieving a 200 kiloAmp High Interruption Current rating at 480 volts of alternating current, a rating which has heretofore been unavailable in the “E-Frame” size circuit breaker. Additionally, use of the engagements 95, 170 can result in a reduced number of openings between the cassette breakers 65 for mechanical hardware to secure the cassettes 103 together, and therefore provides an increase in dielectric isolation between the cassette breakers 65.
While an embodiment of the invention has been described employing a 3 pole circuit breaker, it will be appreciated that the scope of the invention is not so limited, and that the invention also applies to a circuit breakers having other numbers of poles, such as 1, 2, 4, or more poles, for example. Further, while an embodiment of the invention has been described having a protrusion on the base 55 projecting into the exhaust vent 155 of the cassette 103, it will be appreciated that the scope of the invention is not so limited, and that the invention also applies to circuit breakers 55 having other cassette 103 restraint arrangements, such as a protrusion extending from the cassette 103 into a recess within the bottom 70 of the base 55, for example. While an embodiment of the invention has been depicted having a engagement feature 95 with trapezoidal geometry, it will be appreciated that the scope of the invention is not so limited, and that the invention also applies to embodiments having other geometry to divert the flow path 150, such as triangular, round, and elliptical, for example.
As disclosed, some embodiments of the invention may include some of the following advantages: reduced base damage following short circuit trip events; enhanced dielectric separation between cassettes via elimination of hardware spanning a width of the cassette breaker; and an increased current rating within a given external dimensional envelope.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
