Patent Application
20110073568
1. Field of the Invention
The present invention relates to a circuit breaker and, more specifically, to a shield apparatus for protecting elements that are internal to a circuit breaker.
2. Background Information
Circuit breakers, including molded case circuit breakers, have at least one pair of separable contacts. A first contact, known as a “stationary contact”, is fixed within the housing. The other contact, the “movable contact,” is disposed on a movable contact arm that is a part of a contact arm carrier assembly which is coupled to an operating mechanism. Both contacts are disposed on conductive elements that are in electrical communication with either the line or load coupled to the circuit breaker. The operating mechanism is structured to move the movable contact between a first, closed position wherein the fixed and movable contacts are in contact and are electrically connected, and a second, open position wherein the movable contact is spaced from the fixed contact whereby the contacts are electrically disconnected. The operating mechanism may be operated manually or by the circuit breaker's trip mechanism. When a circuit breaker has multiple poles, each pole has its own set of separable contacts.
Each set of contacts is typically disposed within a separate contact chamber. The housing typically has a base portion, in which the majority of components are disposed, and a primary cover. The arc chamber is structured to dissipate an arc following separation of the contacts. That is, when the contacts are separated an arc may form, especially during an over-current event. The arc is dissipated in the arc chamber but the arc still creates gases and possibly a spray of molten debris. A problem typically exists due to the possibility of the blowback of arc gases and molten debris into the contact arm carrier assembly or the operating mechanism or both. The arc gases are typically vented through an exhaust. However, the molten debris and the arc gases, which may be corrosive, can impact on the contact arm carrier assembly components or the operating mechanism components or both, causing damage thereto. There is, therefore, a need to protect certain components that are internal to a circuit breaker during an arc event.
An improved circuit breaker having an improved shield apparatus provides protection to components that are internal to the circuit breaker during an arc event. A contact arm carrier assembly of the circuit breaker comprises a number of springs that bias a number of movable contacts that are disposed on contact arms into engagement and electrical connection with a stationary contact. As employed herein, the expression “a number of” and variations thereof shall refer broadly to any non-zero quantity, including a quantity of one. The shield apparatus is disposed on a carrier housing of the contact arm carrier assembly and is situated adjacent the springs. A shield of the shield apparatus is biased into engagement with the contact arms. When the circuit breaker is moved between the ON position and the OFF or TRIPPED positions, the shield of the shield apparatus moves between a retracted position and a deployed position, with the shield remaining in engagement with the contact arms and protecting the springs from damage in an arc event. In one embodiment, the shield member is formed of a material that generates gases when struck by an arc, and such gases can help to drive the arc into an arc chute of the circuit breaker.
Accordingly, an aspect of the invention is to provide an improved circuit breaker that protects certain internal components thereof in an arc event.
Another aspect of the invention is to provide an improved circuit breaker having an improved shield apparatus that is disposed on a contact arm carrier assembly of the circuit breaker and that moves therewith between an ON condition and an OFF or TRIPPED position, or both.
Another aspect of the invention is to provide an improved circuit breaker having a receptacle formed in a contact arm carrier assembly and having a shield member that is movably disposed in the receptacle and that is biased into engagement with a number of contact arms of the contact arm carrier assembly.
Another aspect of the invention is to provide an improved shield apparatus for use in a circuit breaker wherein the shield apparatus includes a shield member that is disposed adjacent certain components internal to the circuit breaker and that generates gases during an arc event to protect the components from damage during the arc event.
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:
Similar numerals refer to similar parts throughout the specification.
An improved circuit breaker 10 is depicted in a schematic fashion in
The circuit breaker 10 comprises a stationary contact assembly 14, a movable contact assembly 18, an operating mechanism 22, and a trip unit 26, all of which are disposed on a housing 34 of the circuit breaker 10. The housing 34 comprises a base portion 38 and a cover (not expressly shown herein). The movable contact assembly 18 is in the form of a contact arm carrier assembly and is movable with respect to the stationary contact assembly 14 between an ON operational condition, an OFF operational condition, and a TRIPPED operation condition. In the exemplary embodiment of the circuit breaker 10 depicted herein, the OFF operational condition and the TRIPPED operation condition are substantially the same.
The movable contact assembly 18 and the operating mechanism 22 are operationally connected together. The operating mechanism 22 is structured to operate the movable contact assembly 18 between the ON, OFF, and TRIPPED operational conditions. The trip unit 26 is operationally connected with the operating mechanism 22 and serves to trigger it to cause the circuit breaker 10 to move from the ON operational condition to the OFF or TRIPPED operational conditions in over-current conditions and other conditions. The trip unit 26 may include current transformers or other structures that operate in a manner well known in the relevant art to detect current flowing through a number of stationary contacts 42 of the stationary contact assembly 14 and a number of movable contacts 46 movable contact assembly 18 when electrically connected together such as in the ON operational condition of the circuit breaker 10. The circuit breaker 10 is depicted in
The movable contact assembly 18 comprises a carrier housing 58. The movable contact assembly 18 further comprises a plurality of contact arms 50, a plurality of contact arm springs 54, and a shield apparatus 30, all of which are disposed on the carrier housing 58. The contact arms 50 are connected at one end with the carrier housing 58. One of the movable contacts 46 is disposed on each contact arm near a free end thereof opposite its connection with the carrier housing 58. Although not explicitly depicted herein, each movable contact 46 is electrically connected with a shunt that is, in turn, connected with a load terminal of the circuit breaker 10.
The contact arm springs 54 are disposed on the carrier housing 58, and in the ON operational condition of the circuit breaker 10 these contact arm springs 54 bias the contact arms 50 toward the stationary contact 42, thus effectively biasing the movable contacts 46 into engagement and electrical connection with the stationary contact 42. While in the exemplary embodiment depicted herein the plurality of movable contacts 46 each engage a single, i.e., common, stationary contact 42, it is understood that other configurations are possible without departing from the present concept.
As can be understood from
The shield member 62 in the depicted embodiment is a plate-like parallelepiped solid structure that is configured to serve as a barrier to resist the impingement of arc gases and molten material on the contact arm springs 54 and other structures of the circuit breaker 10 during an arc event. The shield member 62 may be formed of a material that generates gases when struck by an electrical arc. Such materials are well known to those skilled in the relevant art. Also, the shield member 62 can be formed of a material that does not generate a gas in the presence of an arc without departing from the present concept.
As can be understood from
As can further be understood from
As can further be understood from
In certain circumstances, such as in an over-current condition, trip unit 26 triggers the operating mechanism 22 to move the circuit breaker 10 from the ON operational condition of
It is noted that the continued engagement of the shield member 62 with the contact arms 50 during movement between the ON operational condition and the OFF or TRIPPED operational conditions protects the contact arm springs 54 from arc gases and molten material at all times during movement of the movable contact assembly 18 between such operational conditions, which protects the contact arm springs 54 from damage in an arc event. Such continued engagement of the shield member 62 with the contact arms 50 is provided by the shield springs 66 which are biasing members that bias the shield member 62 in a direction from the carrier housing 58 toward the contact arms 50. It also can be seen that the shield springs 62 bias the shield member 62 toward the deployed position.
It therefore can be seen that the advantageous shield apparatus 30 and the advantageous circuit breaker 10 protect the contact arm springs 54 from damage due to arc gases and molten debris in an arc event. If the shield member 62 generates gases in the presence of an arc, the gases will tend to push the arc gases and thus the molten material toward the arc chamber 78 for extinguishment, thus further protecting the contact arm springs 54.
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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
