BACKGROUND

This invention relates generally to circuit breakers, and more particularly to circuit breaker thermal magnetic trip units and methods.

Circuit breakers typically include one or more electrical contacts, and provide protection against

persistent over-current conditions and short circuit conditions. In many circuit breakers, a thermal-magnetic trip unit includes a thermal trip portion which trips the circuit breaker on persistent over-current conditions, and a magnetic trip portion which trips the circuit breaker on short circuit conditions. Existing thermal-magnetic trip units typically include a single trip bar that releases a trip mechanism to trip the circuit breaker and open the electrical contacts to stop the flow of current in the protected circuit.

However, existing thermal-magnetic trip units typically do not isolate thermal trip events from magnetic trip events.

SUMMARY

In a first aspect, a trip unit is provided for a circuit breaker that includes electrical contacts, a trip mechanism, a bimetallic strip, and an armature. The trip unit includes a first trip bar coupled to the trip

mechanism and disposed about a pivot point, and a second trip bar coupled to the first trip bar and disposed about the pivot point. In a first operating condition, the first trip bar rotates about the pivot point substantially independently of the second trip bar, and activates the trip mechanism to open the electrical contacts. In a second operating condition, the second trip bar rotates about the pivot point, causing the first trip bar to rotate about the pivot point and activate the trip mechanism to open the electrical contacts.

In a second aspect, a circuit breaker is provided that includes electrical contacts, a trip mechanism, a bimetallic strip, an armature, and a trip unit. The trip unit includes a first trip bar coupled to the trip

mechanism and disposed about a pivot point, and a second trip bar coupled to the first trip bar and disposed about the pivot point. In a first operating condition, the first trip bar rotates about the pivot point substantially independently of the second trip bar, and activates the trip mechanism to open the electrical contacts. In a second operating condition, the second trip bar rotates about the pivot point, causing the first trip bar to rotate about the pivot point and activate the trip mechanism to open the electrical contacts.

In a third aspect, a trip method is provided for use with a circuit breaker that includes electrical contacts, a trip mechanism, a bimetallic strip, and an armature. The trip method includes providing a first trip bar coupled to the trip mechanism and disposed about a pivot point, and providing a second trip bar coupled to the first trip bar and disposed about the pivot point. The trip method further includes in a first operating

condition, rotating the first trip bar about the pivot point substantially independently of the second trip bar, and activating the trip mechanism to open the electrical contacts, and in a second operating condition, rotating the second trip bar about the pivot point, causing the first trip bar to rotate about the pivot point and activate the trip mechanism to open the electrical contacts. Numerous other aspects are provided. BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which the same reference numerals denote the same elements throughout, and in which:

FIG. 1A is a side view of an example thermal- magnetic trip unit in accordance with this invention;

FIG. IB is a front view of the example thermal- magnetic trip unit of FIG. 1A;

FIG. 1C is a side view of the example thermal trip bar of FIG. 1A;

FIG. ID is a front view of the example thermal trip bar of FIG. 1C;

FIG. IE is a side view of the example magnetic trip bar of FIG. 1A;

FIG. IF is a front view of the example magnetic trip bar of FIG. IE;

FIG. 2A is another side view of an example thermal- magnetic trip unit in accordance with this invention;

FIG. 2B is a front view of an example spring-loaded actuator illustrated in FIG. 2A;

FIG. 2C is a side view of the example thermal- magnetic trip unit of FIG. 2A in an over-current operating condition; and

FIG. 2D is a side view of the example thermal- magnetic trip unit of FIG. 2A in a short-circuit operating condition .

DETAILED DESCRIPTION

The present invention provides thermal-magnetic trip units and methods that include separate thermal and magnetic trip bars that may be used to isolate thermal trip events from magnetic trip events.

Referring to FIGS. 1A-1F, an example thermal- magnetic trip unit in accordance with this invention is described. Thermal-magnetic trip unit 100 includes a first trip bar 110 disposed about a pivot point 112, and a second trip bar 210 also disposed about pivot point 112. As described in more detail below, in a first operating condition (e.g., an over-current or thermal trip

condition) , first trip bar 110 rotates about pivot

point 112, and activates a trip mechanism (not shown) to open electrical contacts (not shown) of a circuit breaker. In this regard, first trip bar 110 is also referred to herein as "thermal trip bar 110."

In addition, as described in more detail below, in a second operating condition (e.g., a short-circuit or magnetic trip condition) , second trip bar 210 rotates about pivot point 112, causing first trip bar 110 to rotate about pivot point 112 and activate the trip mechanism to open the electrical contacts of the circuit breaker. In this regard, second trip bar 210 is also referred to herein as "magnetic trip bar 210."

As described in more detail below, in the over- current operating condition, thermal trip bar 110 rotates about pivot point 112 substantially independently of magnetic trip bar 210. In a short circuit condition, in contrast, thermal trip bar 110 and magnetic trip bar 210 both rotate together about pivot point 112. As described in more detail below, the isolation of thermal trip bar 110 and magnetic trip bar 210 may be used to identify a short circuit trip event in a thermal-magnetic circuit breaker.

As shown in FIGS. 1C-1D, thermal trip bar 110 includes cylindrical support members 114a-114d, latch mechanism 116, and bi-metal interfaces 118a-118c. Cylindrical support members 114a-114d support thermal trip bar 110 about pivot point 112. For example, each

cylindrical support member 114a-114d may include a

cylindrical bore 120 concentrically aligned along a common axis 113. Although thermal trip bar 110 includes four cylindrical support members 114a-114d, persons of ordinary skill in the art will understand that thermal trip bars in accordance with this invention may include more than or less than four cylindrical support members 114a-114d. In addition, persons of ordinary skill in the art will

understand that support members 114a-114d may have shapes other than cylindrical shapes.

Latch mechanism 116 projects from a first

surface 124 of thermal trip bar 110, and includes a latch tab 126. In the illustrated example, latch mechanism 116 projects at a downward angle from first surface 124.

Persons of ordinary skill in the art will understand that latch mechanism may project at angles other than that illustrated in FIG. 1C. As described in more detail below, latch mechanism 116 is adapted to secure a spring-loaded actuator (not shown in FIGS. 1A-1F) during normal circuit breaker operation, and is adapted to release the spring- loaded actuator to trip the circuit breaker in response to a thermal trip condition or a magnetic trip condition.

In the example illustrated in FIGS. 1C-1D, thermal trip bar 110 includes three bi-metal interfaces 118a-118c, with one bi-metal interface for each electrical pole of a three-pole circuit breaker. Persons of ordinary skill in the art will understand that thermal trip bars in

accordance with this invention may include more than or less than three bi-metal interfaces 118a-118c, for use with circuit breakers that include more or less than three electrical poles. For example, a single bi-metal interface may be used with a single-pole circuit breaker. Likewise, four bi-metal interfaces may be used with a four-pole circuit breaker.

Referring now to FIGS. 1E-1F, magnetic trip bar 210 includes cylindrical support members 214a-214c,

opening 216, and armature interfaces 218a-218c.

Cylindrical support members 214a-214c support magnetic trip bar 210 about pivot point 112. For example, each

cylindrical support member 214a-214c may include a

cylindrical bore 220 concentrically aligned along a common axis 115. Although magnetic trip bar 210 includes three cylindrical support members 214a-214c, persons of ordinary skill in the art will understand that magnetic trip bars in accordance with this invention may include more than or less than three cylindrical support members 214a-214c. In addition, persons of ordinary skill in the art will understand that support members 214a-214c may have shapes other than cylindrical shapes.

In the example illustrated in FIGS. 1E-1F, magnetic trip bar 210 includes three armature interfaces 218a-218c, with one armature interface for each electrical pole of a three-pole circuit breaker. Persons of ordinary skill in the art will understand that magnetic trip bars in

accordance with this invention may include more than or less than three armature interfaces 218a-218c, for use with circuit breakers that include more or less than three electrical poles. For example, a single armature interface may be used with a single-pole circuit breaker. Likewise, four armature interfaces may be used with a four-pole circuit breaker.

Magnetic trip bar 210 optionally may include a first extension 221 and a second extension 222, each of which may be coupled to accessories (not shown) in the circuit breaker. In the illustrated example, second extension 222 projects horizontally from a second surface 224 of magnetic trip bar 210, and first

extension 221 projects vertically from a third surface 223 of magnetic trip bar 210. As illustrated in FIG. IF, first extension 221 and second extension 222 are aligned (e.g., along an imaginary x-axis) on magnetic trip bar 210.

Persons of ordinary skill in the art will understand that magnetic trip bars in accordance with this invention may include more or less than two extensions, and that

extensions may be located at other positions on magnetic trip bar 210.

Thermal trip bar 110 may be made from one or more of a plastic, a metal, a polymer, a resin, or other

suitable material. Thermal trip bar 110 may have a length of between about 150 mm and about 200 mm, a height of between about 20 mm and about 30 mm, and a thickness between about 10 mm and about 20 mm. Other dimensions may be used.

Magnetic trip bar 210 may be made from one or more of a plastic, a metal, a polymer, a resin, or other

suitable material. Magnetic trip bar 210 may have a length of between about 150 mm and about 200 mm, a height of between about 20 mm and about 30 mm, and a thickness between about 10 mm and about 20 mm. Other dimensions may be used.

As illustrated in FIGS. 1A-1B, thermal trip bar 110 and magnetic trip bar 210 may both be mounted on a

cylindrical rod 122 having a center axis 112 ' aligned with pivot point 112. In particular, cylindrical bores 120 of thermal trip bar 110 and cylindrical bores 220 of magnetic trip bar 210 each may be adapted to receive cylindrical rod 122. Further, thermal trip bar 110 and magnetic trip bar 210 each may freely rotate about cylindrical rod 122. In this regard, thermal trip bar 110 and magnetic trip bar 210 are both disposed about pivot point 112. FIGS. 1A-1B depict thermal trip bar 110 disposed on cylindrical rod 122 in an initial position, and magnetic trip bar 210 disposed on cylindrical rod 122 in an initial position, with first surface 124 of thermal trip bar 110 adjacent second surface 224 of magnetic trip bar 210. In addition, in the initial position, latch mechanism 116 of thermal trip bar 110 extends through opening 216 of magnetic trip bar 210.

Referring now to FIGS. 2A-2D, an example operation of thermal-magnetic trip unit 100 in accordance with this invention is described. Thermal-magnetic trip unit 100 may be coupled to a spring-loaded actuator 300, a bi-metal element 400 and a magnetic assembly 500 of a circuit breaker magnetic structure, such as a translational magnetic system. Spring-loaded actuator 300 includes cylindrical support members 310, a latch surface 320, a spring 330, and an extension 340. Bi-metal element 400 includes bi-metal strip 410 and a contact surface 420.

Magnetic assembly 500 includes armature assembly 510 and slide 520. Persons of ordinary skill in the art will understand that thermal-magnetic trip units in accordance with this invention may be used with other actuator, thermal detection and magnetic detection devices.

FIG. 2A depicts the configuration of thermal- magnetic trip unit 100, spring-loaded actuator 300, bi ^¬ metal element 400 and magnetic assembly 500 in an initial, non-trip condition. Spring-loaded actuator 300 pivots on cylindrical support members 310, and spring 330 tends to bias spring-loaded actuator 300 so that latch surface 320 and extension 340 pivot up and away from thermal-magnetic trip unit 100. In the configuration of FIG. 2A, latch mechanism 116 of thermal trip bar 110 and spring-loaded actuator 300 are cooperatively coupled to prevent such pivoting . In particular, latch tab 126 of latch mechanism 116 engages latch surface 320 of spring-loaded actuator 300. In this initial configuration, thermal trip bar 110 and magnetic trip bar 210 are in their initial positions, the trip mechanism of the circuit breaker is not activated, and the electrical contacts of the circuit breaker remain closed. Bi-metal strip 410 and armature assembly 510 are each in their initial positions.

Referring now to FIG. 2C, the operation of thermal- magnetic trip unit 100 in a first operating condition

(e.g., an over-current or thermal trip condition) is described. When an over-current condition occurs, the temperature of bi-metal element 400 increases, and bi-metal strip 410 begins to deflect from its initial position. If the temperature of bi-metal element 400 increases

sufficiently, due to the current draw exceeding a

predefined level, contact surface 420 engages bi-metal interface 118c of thermal trip bar 110. As a result, thermal trip bar 110 rotates clockwise about pivot

point 112 from its initial position to a second, tripped position .

In the tripped position, latch tab 126 disengages latch surface 320 of spring-loaded actuator 300, and extension 340 pivots up and away from thermal-magnetic trip unit 100 to activate a trip mechanism (not shown) and open electrical contacts (not shown) of the circuit breaker. As shown in FIG. 2C, in the over-current condition, although thermal trip bar 110 rotates about pivot point 112 from its initial position to the tripped position, magnetic trip bar 210 remains in its initial position. In this regard, in an over-current operating condition, thermal trip bar 110 rotates about pivot point 112 substantially

independently of magnetic trip bar 210. Referring now to FIG. 2D, the operation of thermal- magnetic trip unit 100 in a second operating condition (e.g., a short-circuit or magnetic trip condition) is described. The circuit breaker includes an electromagnet (not shown) that generates a magnetic field in proportion to the current level. When a short circuit condition occurs, the magnetic field is sufficiently strong to cause armature assembly 510 to move downward from its initial position on slide 520. As a result, armature assembly 510 engages armature interface 218c of magnetic trip bar 210, which causes magnetic trip bar 210 to rotate clockwise about pivot point 112. In addition, second surface 224 of magnetic trip bar 210 engages first surface 124 of thermal trip bar 110, which causes thermal trip bar 110 to rotate clockwise about pivot point 112 from its initial position to the second, tripped position.

In the tripped position, latch tab 126 disengages latch surface 320 of spring-loaded actuator 300, and extension 340 pivots up and away from thermal-magnetic trip unit 100 to activate the trip mechanism and open electrical contacts of the circuit breaker. As shown in FIG. 2D, in the short circuit condition, thermal trip bar 110 and magnetic trip bar 210 both rotate about pivot point 112 from their initial positions to the tripped position.

As described above, magnetic trip bar 210

optionally may include first extension 220 and second extension 222, each of which may be coupled to accessories (not shown) in the circuit breaker. In an over-current condition, because magnetic trip bar 210 remains in its initial position, first extension 220 and second

extension 222 each remain in their initial positions.

Thus, if the circuit breaker trips, but the first

extension 220 and second extension 222 remain in their initial positions, the cause of the trip was an over- current condition.

In a short circuit condition, in contrast, magnetic trip bar 210 rotates from its initial position to a tripped position, and first extension 220 and second extension 222 likewise move from their initial positions to tripped positions. In this regard, if the circuit breaker trips, first extension 220 and second extension 222 may be used to identify that the cause of the trip was a short circuit trip condition.

In the example thermal-magnetic trip

unit 100 described above, because bi-metal interfaces 118a- 118c are disposed on a common thermal trip bar 110, and armature interfaces 218a-218c are disposed on a common magnetic trip bar 110, an over-current condition or a short circuit on any pole of the circuit breaker will activate the trip mechanism and open electrical contacts of the circuit breaker for all poles of the circuit breaker.

The foregoing merely illustrates the principles of this invention, and various modifications can be made by persons of ordinary skill in the art without departing from the scope and spirit of this invention.