Electrical arcing that occurs when a circuit breaker opens causes the metal in the contacts to superheat and become molten metal. The molten metal is propelled by ionized air and gasses throughout the interior of the circuit breaker as the contacts open. Deposits of molten metal, or “splatter”, cool and solidify where they land and may interfere with the functionality of the circuit breaker. For example, the metal deposits may interfere with the motion of mechanical components and prevent proper operation. The metal deposits may also electrically connect circuit breaker components, causing a short circuit.
Often, circuit breakers have design features aimed to mitigate the effects of metal splatter by preventing contact between the metal splatter and circuit breaker components. Some circuit breakers include physical barriers or shields that protect certain components from being contacted by the metal splatter. Other circuit breakers include venting features that attempt to direct the ionized air and gasses and the metal splatter they carry out of the circuit breaker so that the gasses will not propel the metal splatter onto internal circuit breaker components.
A circuit breaker is provided that includes a pair of co-operable contacts mechanically moveable between an electrically closed position and an electrically open position and a mechanical linkage coupled to the pair of contacts to move the pair of contacts between the electrically closed and electrically open position. The circuit also includes a trip mechanism responsive to electrical current passing through the pair of contacts to actuate the mechanical linkage when predetermined current conditions are present in current flowing through the pair of contacts. The trip mechanism includes at least one splatter-resistant component that includes a splatter-resistant surface.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various example systems, methods, and other example embodiments of various aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In some examples, an element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale.
The circuit breakers described herein include at least trip mechanism component that has been provided with a splatter resistant surface. The splatter resistant surface significantly reduces the amount of metal splatter that adheres to the component, increasing the reliability of the circuit breaker. Thus, rather than attempting to prevent metal splatter from contacting circuit breaker trip mechanism components as has been done with prior art circuit breakers, the circuit breakers described herein prevent the metal splatter from adhering to the component after it has contacted the component.
The following includes definitions of selected terms employed herein. The definitions include various examples and/or forms of components that fall within the scope of a term and that may be used for implementation. The examples are not intended to be limiting. Both singular and plural forms of terms may be within the definitions.
References to “one embodiment”, “an embodiment”, “one example”, “an example”, and so on, indicate that the embodiment(s) or example(s) so described may include a particular feature, structure, characteristic, property, element, or limitation, but that not every embodiment or example necessarily includes that particular feature, structure, characteristic, property, element or limitation. Furthermore, repeated use of the phrase “in one embodiment” does not necessarily refer to the same embodiment, though it may.
The circuit breaker 10 includes a pair of co-operable contacts 15a, 15b that are moveable between a closed position shown in
The trip mechanism 20 includes one or more trip mechanism components having characteristics that are altered by the amount and/or character of current flowing through the circuit breaker. In some embodiments, the trip mechanism component is a current carrying member that carries current flowing through the circuit breaker. In the embodiment shown in
In
When an overcurrent condition exists the bimetal further deflects, moving the armature 41 and its latch surface 41a out of engagement with the latch member 51. The mechanical linkage is then urged by the spring into the open position shown in
Various solid lubricants were tested for suitability as a splatter resistant surface. A twin-wire arc gun was used to generate a metal splatter and appropriate spray parameters were established to generate splatter from Copper, 316 Stainless Steel, and Tungsten wires. The twin-wire arc thermal spray device sprayed on bimetal strips mounted on a steel plate and placed 10 feet away from the gun nozzle. Some of the bimetal strips were electroplated with tin, as is common with such devices. Other bimetal devices were not electroplated. Due to the low melting point of tin, it may be advantageous to select splatter resistant coating that has a lower cure temperature than the melting point of tin, which is 232 C.
Testing was performed on bimetal devices coated with various types of solid lubricants. The solid lubricant coatings were suspended in a liquid solution and deposited by an aerosol spray onto the bimetal device. Along with plated and unplated control samples, the testing included bimetal devices coated with Boron Nitride supplied by ZYP Coatings, Super Enhanced Graphite supplied by ZYP Coatings, low-temperature cure fluoropolymer manufactured by Sun Coating, and low-temperature cure fluoropolymer manufactured by Secoa. The fluoropolymer coatings that were tested are blends of resins and fluoropolymer lubricants.
Metal splatter of Copper and Stainless Steel was collected for 12 seconds on the bimetal device samples. Metal splatter of Tungsten was collected for 3 seconds on the bimetal device samples. After being sprayed with metal splatter, the bimetal strips were optically analyzed and a splatter count and splatter coverage was determined with respect to each metal component of the splatter. To determine the splatter count, each sample was scanned at 30× with oblique lighting to count metal splatter particles. To determine the splatter coverage, a 50× microphotograph of the greatest splatter particle area was taken. The image was analyzed to measure the total area of splatter coverage from each photo. Splatter coverage was determined to provide a better indicator of splatter resistance.
The Super Enhanced Graphite and fluoropolymer coatings all provided significant improvement in splatter resistance as compared to the uncoated control samples. Thus, any of these materials, as well as other splatter resistant coatings, may be selected, depending on cost and manufacturing considerations.
In other embodiments, other circuit breaker components may include a splatter resistant surface instead of or in addition to trip mechanism components. For example, the spring 43 or other mechanical linkage components may be adapted to include a splatter resistant surface.
While example systems, methods, and so on have been illustrated by describing examples, and while the examples have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the systems, methods, and so on described herein. Therefore, the invention is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Thus, this application is intended to embrace alterations, modifications, and variations that fall within the scope of the appended claims.
To the extent that the term “includes” or “including” is employed in the detailed description or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim.