1. Field of the Invention
This invention pertains generally to electrical switching apparatus and, more particularly, to circuit interrupters including a trip unit. The invention also pertains to trip units for circuit interrupters. The invention further pertains to trip actuators for trip units.
2. Background Information
Electrical switching apparatus include, for example, circuit switching devices; circuit interrupters, such as circuit breakers; network protectors; contactors; motor starters; motor controllers; and other load controllers. Electrical switching apparatus such as circuit interrupters and, in particular, circuit breakers of the molded case variety, are well known in the art. See, for example, U.S. Pat. No. 5,341,191.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip unit, which senses overcurrent conditions in an automatic mode of operation. Upon sensing an overcurrent condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271.
U.S. Pat. No. 6,853,279 discloses a trip actuator including a bobbin assembly, a disk spacer, a disc magnet, which is preferably magnetized after certain assembly steps, a housing, a cover, a wave washer, an upper bushing, an armature or plunger, a lower bushing, an internal retaining ring, a spring and a set screw.
A known trip actuator consists of twelve parts, including an impregnated or coated set screw for spring adjustment, a brass bushing and a brass sleeve. The impregnated set screw is used to adjust spring compression and, therefore, trip force. The threads of the set screw are impregnated with a material that locks the set screw after it has been adjusted. However, it is believed that adjusting the screw might cause particles of the impregnated material in the threads to break free and potentially interfere with the operation of, and interface between, the bottom surface of the armature and the disc spacer. Hence, such debris might prevent proper magnetic seal force for the armature or plunger and, therefore, might cause magnetic shock out. As a result, the actuator force might be released prematurely due to mechanical vibration.
Hence, there is room for improvement in trip actuators for trip units.
There is also room for improvement in trip units including a trip actuator.
There is further room for improvement in electrical switching apparatus, such as circuit interrupters, including a trip unit having a trip actuator.
These needs and others are met by embodiments of the invention, which provide a trip actuator in which a thermoplastic bushing includes a conduit therethrough. The thermoplastic bushing is coupled to a housing of the trip actuator. An armature of the trip actuator is disposable within an opening of a coil and is slidably disposed within the conduit of the thermoplastic bushing. Preferably, the armature includes a shoulder and the thermoplastic bushing is structured to act as a stop for the armature. The armature also preferably includes an elongated internal recess that receives a spring.
In accordance with one aspect of the invention, an electrical switching apparatus comprises: separable contacts; an operating mechanism structured to open and close the separable contacts; and a trip unit cooperating with the operating mechanism to trip open the separable contacts, the trip unit comprising: a sensor structured to sense current flowing through the separable contacts, a processor structured to output a trip signal responsive to the sensed current, and a trip actuator comprising: a housing including a recess, a coil within the recess of the housing, the coil having an opening therethrough, a magnet within the recess of the housing, a thermoplastic bushing including a conduit therethrough, the thermoplastic bushing being coupled to the housing, and an armature disposable within the opening of the coil and slidably disposed within the conduit of the thermoplastic bushing, the magnet attracting the armature toward the housing; and a spring biasing the armature away from the housing, in order to cause the operating mechanism to trip open the separable contacts.
The housing may further include a cover having an opening therein; and the armature may include a first end structured to pass through the opening of the cover and a second end opposite the first end, the second end including an opening therein, the spring engaging the armature within the opening of the second end thereof.
The second end of the armature may be disposable within the opening of the coil; and the first end of the armature may be slidably disposed within the conduit of the thermoplastic bushing and may be structured to pass through the opening of the cover.
The first end of the armature may be a plunger having a first diameter; the second end of the armature may have a second diameter, which is larger than the first diameter; the opening of the second end may be an elongated recess passing through the second end of the armature and into the plunger of the armature; and the spring may be an elongated compression coil spring extending within the elongated recess of the second end of the armature.
As another aspect of the invention, a trip unit is for a circuit interrupter comprising separable contacts and an operating mechanism structured to open and close the separable contacts. The trip unit comprises: a sensor structured to sense current flowing through the separable contacts; a processor structured to output a trip signal responsive to the sensed current; and a trip actuator comprising: a first sub-assembly comprising: a housing including a recess, a coil within the recess of the housing, the coil having an opening therethrough, and a magnet within the recess of the housing; a second sub-assembly within the recess of the housing of the first sub-assembly, the second sub-assembly comprising: a thermoplastic bushing including a conduit therethrough, the thermoplastic bushing being coupled to the housing of the first sub-assembly, and an armature disposable within the opening of the coil and slidably disposed within the conduit of the thermoplastic bushing, and a spring structured to bias the armature away from the first sub-assembly, in order to cause the operating mechanism to trip open the separable contacts, wherein the magnet is structured to overcome the spring and attract the armature toward the first sub-assembly.
The conduit of the thermoplastic bushing may be a first conduit; the second sub-assembly may further comprise a cover including a generally flat portion having an opening therein and a second conduit extending from the generally flat portion, the second conduit forming a continuous opening from the opening of the generally flat portion through the second conduit; and the thermoplastic bushing may be coupled to the cover at the second conduit and form a continuous opening through the first conduit of the thermoplastic bushing and through the second conduit of the cover.
As another aspect of the invention, a trip actuator is for a trip unit. The trip actuator comprises: a first sub-assembly comprising: a housing including a recess, a coil within the recess of the housing, the coil having an opening therethrough, and a magnet within the recess of the housing; a second sub-assembly within the recess of the housing of the first sub-assembly, the second sub-assembly comprising: a thermoplastic bushing including a conduit therethrough, the thermoplastic bushing being coupled to the housing of the first sub-assembly, and an armature disposable within the opening of the coil and slidably disposed within the conduit of the thermoplastic bushing, the magnet attracting the armature toward the first sub-assembly; and a spring biasing the armature away from the first sub-assembly.
The second sub-assembly may further comprise a cover including an opening therein; the thermoplastic bushing may be coupled to the cover at the opening thereof; and the armature may include a first end structured to pass through the opening of the cover and a second end opposite the first end, the second end including an opening therein, the spring engaging the armature within the opening of the second end thereof.
The first end of the armature may be a plunger having a first diameter; the second end of the armature may have a second diameter, which is larger than the first diameter; and the opening of the second end may be an elongated recess passing through the second end of the armature and into the plunger of the armature.
The first end and the second end of the armature may form a shoulder therebetween; and the shoulder may be structured to engage the thermoplastic bushing when the coil is energized and the spring forces the armature away from the first sub-assembly.
The second sub-assembly may further comprise a cover including an opening therein, a portion of the armature being structured to pass through the opening of the cover; the conduit of the thermoplastic bushing may be a first conduit; the cover may further include a generally flat portion having the opening therein and a second conduit extending from the generally flat portion, the second conduit forming a continuous opening from the opening of the generally flat portion through the second conduit; and the thermoplastic bushing may be coupled to the cover at the second conduit and form a continuous opening through the first conduit of the thermoplastic bushing and through the second conduit of the cover.
The first conduit of the thermoplastic bushing may be press fit to the cover within the second conduit of the cover.
As another aspect of the invention, a trip actuator for a trip unit comprises: a first sub-assembly comprising: a housing including a recess, a coil within the recess of the housing, the coil having an opening therethrough, and a magnet within the recess of the housing; a second sub-assembly within the recess of the housing of the first sub-assembly, the second sub-assembly comprising: a bushing including a conduit therethrough, an armature disposable within the opening of the coil and slidably disposed within the conduit of the bushing, the magnet attracting the armature toward the first sub-assembly, and a cover including an opening therein, the bushing being coupled to the cover at the opening thereof, the cover being coupled to the housing of the first sub-assembly; and a spring biasing the armature away from the first sub-assembly, wherein the armature includes a first end structured to pass through the opening of the cover and a second end opposite the first end, the second end including an opening therein, the spring engaging the armature within the opening of the second end thereof.
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:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “coupled” together means that the parts are joined together either directly or joined through one or more intermediate parts.
The invention is described in association with a trip actuator for a trip unit of a three-pole circuit breaker, although the invention is applicable to a wide range of electrical switching apparatus having any number of poles.
Referring to
A non-limiting example of a suitable thermoplastic material for the example thermoplastic bushing 14 is polyoxymethylene (POM), which is marketed by E. I. du Pont de Nemours and Company of Wilmington, Del. under the brand name DELRIN®.
Alternatively, any suitable low-friction and wear-resistant thermoplastic with good physical and processing properties and being capable of operating in temperatures of up to about 85° C. may be employed.
The bushing 14 is coupled to the housing 4 through the cover 17 as will be explained. The trip actuator 2 also includes an armature 18 disposable within the coil opening 10 (as can be seen from
The bushing 14 is, for example, a thermoplastic guide-bushing or thermoplastic press fit insert, which acts as a superior armature bushing surface and guide for the armature 18.
As shown in
Preferably, the magnet 12 is magnetized after the sub-assembly 30 of
Referring to
The magnet 12 provides a first magnetic force (e.g., without limitation, downward with respect to
Referring to
The first and second ends 54,56 of the armature 18 form a shoulder 64 therebetween. The shoulder 64 is structured to engage the thermoplastic bushing 14 at end 65 (
As shown in
Referring to
When the bobbin assembly 8 of
An example of a trip unit, excluding the disclosed trip actuator 2, is disclosed in U.S. Pat. No. 6,853,279, which is incorporated by reference herein.
Examples of circuit breakers and circuit breaker frames, excluding the disclosed trip actuator 2, are disclosed in U.S. Pat. Nos. 5,910,760; 6,137,386; 6,144,271; and 6,853,279, which are incorporated by reference herein.
The disclosed trip actuator 2 does not employ any set screw. Furthermore, the disclosed trip actuator 2 includes fewer parts than known prior trip actuators with no loss in robustness. The trip actuator 2 is also easily scalable if more force or stroke is desired.
The example thermoplastic bushing 14 precludes the possibility of brass particles (not shown) from a brass bushing (not shown) from entering the interface between the spacer 32 and the armature end 56 (see
Furthermore, the example single thermoplastic bushing 14 prevents the armature 18 from binding on the cover 17 (
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 the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.