Latch mechanism for a circuit breaker

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrical circuit breakers, and more particularly to a latch mechanism for a circuit breaker.

In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.

There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.

To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.

A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross- section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range. The tripping mechanism may be housed in the same housing as the operating mechanism and contacts or it may be housed in a separate housing coupled to the housing containing the operating mechanism and contacts.

In prior art circuit breakers, in order to test the operating mechanism of the circuit breaker, it was necessary to place the circuit breaker in an electrical circuit and test it in its overload conditions, since the trip mechanism activated the operating system. Such procedures were time consuming, and placed an unnecessary duty cycle burden on the components of the circuit breaker.

Prior art circuit breakers also can be associated with auxiliary devices such as an undervoltage relay, indicator switches, shunt trip device, an auto trip interlock capability and a test button capability and the like. Prior art circuit breakers typically were designed to have a specific auxiliary device associated with that circuit breaker and either mechanically or electrically coupled to the operating mechanism. Such arrangements required specially designed auxiliary devices for each rating of a given circuit breaker frame and did not facilitate interchange of auxiliary devices with other circuit breaker ratings.

Thus, there is a need for an apparatus for operating a circuit breaker during conditions other than an overload condition. There is also a need for an apparatus for operating a circuit breaker that will disengage the latching mechanism and cause the movable contact to move. There is also a need for a molded case circuit breaker that provides the ability to test and inspect the operation of the operating mechanism independent of a trip unit. Thus there is a need for a latch mechanism that has several features that allow the introduction of accessory devices to interact directly with the operating mechanism of different rated circuit breakers.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for operating a circuit breaker. The circuit breaker includes a housing, a cradle mounted in the housing and coupled to a handle and to a movable contact. The apparatus comprises a latch frame mounted in the circuit breaker housing. A latch roller is mounted on the cradle. A latch member is configured to selectively engage the latch roller and the latch member is rotatably coupled to the latch frame. A latch shaft assembly is rotatably mounted in the latch frame and selectively engaged by the latch member. Upon rotation of the latch shaft assembly, the latch shaft assembly will disengage from the latch member and cause the movable contact to move. In one embodiment, a single latch spring is coupled to the latch shaft and the latch member. Another embodiment includes a kicker member mounted in a trip unit. The kicker member is configured to act upon a trip arm and to be moved to a reset position by the handle of the circuit breaker.

There is also provided an apparatus for operating a circuit breaker. The circuit breaker includes a housing, a cradle mounted in the housing and coupled to a handle and to a movable contact. The apparatus comprises a means for supporting mounted in the circuit breaker housing. A means for rolling is mounted in the cradle. A means for latching is configured to selectively engage the means for rolling and is rotatably coupled to the means for supporting. A means for rotating is rotatably mounted in the means for supporting. The rotation of the means for rotating will disengage the means from rotating from the means for latching and cause the movable contact to move.

There is further provided a molded case circuit breaker comprising a housing, an operating mechanism mounted in the housing. The operating mechanism has a cradle coupled to a handle and to a movable contact. An apparatus for operating the circuit breaker during a condition other than an overload condition is also included. The apparatus comprises a latch frame mounted in the circuit breaker housing. A latch roller mounted in the cradle. A latch member is configured to selectively engage the latch roller and is rotatably coupled to the latch frame. A latch shaft assembly is rotatably mounted in the latch frame and selectively engaged with the latch member. The rotation of the latch shaft assembly will disengage the latch shaft assembly from the latch member and cause the movable contact to move.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective illustration of a molded case circuit breaker which includes an exemplary embodiment of a latch mechanism that will operate the circuit breaker during a condition other than an overload condition.

FIG. 2

is a sectional view of the circuit breaker shown in

FIG. 1

along the line

2

—

2

and is used to describe a typical operation of the circuit breaker.

FIG. 3

is an exploded view of the operating mechanism, contact structure and an exemplary trip unit of the circuit breaker illustrated in FIG.

2

.

FIG. 4

is an illustration of an exemplary embodiment of a circuit breaker cover having an accessory pocket on each side of the handle opening in the cover.

FIG. 5

is a partial illustration of a circuit breaker including an exemplary embodiment of a latch mechanism for operating the circuit breaker, with the circuit breaker in the “ON” position.

FIG. 6

is a partial illustration of a circuit breaker including an exemplary embodiment of a latch mechanism for operating the circuit breaker, with the circuit breaker in the “OFF” position.

FIG. 7

is a partial illustration of a circuit breaker including an exemplary embodiment of a latch mechanism for operating the circuit breaker, with the circuit breaker in the “TRIPPED” position.

FIG. 8

is a perspective view of an exemplary embodiment of a latch shaft assembly used in the circuit breaker illustrated in

FIGS. 5-7

.

FIG. 8

a

is a partial perspective sectional view of the latch shaft assembly shown in

FIG. 8

illustrating the configuration of the center portion of the latch shaft assembly.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1

generally illustrates a three phase molded case circuit breaker

10

of the type which includes an operating mechanism

40

having a pivoting member

13

with a handle

14

. The pivoting member

13

and handle

14

are moveable between an “ON” position, an “OFF” position, and a “TRIPPED” position. The exemplary circuit breaker

10

is a three pole breaker having three sets of contacts for interrupting current in each of the three respective electrical transmission phases. In the exemplary embodiment of the invention, each phase includes separate breaker contacts and a separate trip mechanism. The center pole circuit breaker includes an operating mechanism which controls the switching of all three poles of the breaker. Although an embodiment of the present invention is described in the context of the three phase circuit breaker, it is contemplated that it may be practiced in a single phase circuit breaker or in other multi-phase circuit breakers.

Referring to

FIG. 2

, there is illustrated an exemplary embodiment of a molded case circuit breaker having a handle

14

that is operable between the “ON” and “OFF” positions to enable a contact operating mechanism

40

to engage and disengage a moveable contact

42

and a stationary contact

44

for each of the three phases, such that the line terminal

18

and load terminal

16

of each phase can be electrically connected. The circuit breaker housing

12

includes three portions which are molded from an insulating material. These portions include a circuit breaker base

12

a

, a circuit breaker cover

20

and an accessory cover

28

with breaker cover

20

and the accessory cover

28

having an opening

29

for the handle

14

of the pivoting member

13

. The pivoting member

13

and handle

14

move within the opening

29

during the several operations of the circuit breaker

10

.

FIG. 2

is a cut away view of the circuit breaker

10

along the lines

2

—

2

shown in FIG.

1

. As shown in

FIG. 2

, the main components of the circuit breaker are a fixed line contact arm

46

and a moveable load contact arm

45

. It should be noted that another embodiment of the circuit breaker

10

has a movable line contact arm to facilitate a faster current interruption action. The load contact arms for each of the three phases of the exemplary breaker are mechanically connected together by an insulating cross bar member

55

. This cross bar member

55

, in turn, is mechanically coupled to the operating mechanism

40

so that, by moving the handle

14

from left to right, the cross bar

55

rotates in a clockwise direction and all three load contact arms

45

are concurrently moved to engage their corresponding line contact arms

46

, thereby making electrical contact between moveable contact pad

42

and stationary contact pad

44

.

The operating mechanism

40

includes a cradle

41

which engages a latch mechanism

90

to hold the contacts of the circuit breaker in a closed position unless and until an over current condition occurs, which causes the circuit breaker to trip, or the latch is acted upon by a latch shaft assembly

100

as a result of a condition to be described below.

A portion of the moveable contact arm

45

and the stationary contact bus

46

are contained in an arc chamber

56

. Each pole of the circuit breaker

10

is typically provided with an arc chamber

56

which is molded from an insulating material and is part of the circuit breaker

10

housing

12

. A plurality of arc plates

58

is maintained in the arc chamber

56

. The arc plates facilitate the extension and cooling of the arc formed when the circuit breaker

10

is opened while under a load and drawing current. The arc chamber

56

and arc plates

58

direct the arc away from the operating mechanism

40

.

During normal operation of the circuit breaker

10

, current flows from the line terminal

18

through the line contact arm

46

and its stationary contact pad

44

to the load contact arm

45

through its contact pad

42

. From the load contact arm

45

, the current flows through a connector, for example a flexible braid,

48

to the bimetallic element

62

and from the bimetallic element

62

to the load terminal

16

. (See

FIG. 3

) When the current flowing through the circuit breaker exceeds the rated current for the breaker, it heats the bimetallic element

62

, causing the element

62

to bend towards a trip bar. If the over current condition persists, the bimetallic element

62

bends sufficiently to engage the trip bar surface. As the bimetallic element engages the trip bar surface and continues to bend, it causes the trip bar to rotate and thus unlatching the operating mechanism

40

of the circuit breaker. The trip can all be produced by an electronic trip mechanism that will trip the breaker when an overload condition is sensed.

FIG. 3

is an exploded isometric drawing which illustrates the construction of a portion of the circuit breaker shown in FIG.

2

. In

FIG. 3

only the load contact arm

45

of the center pole of the circuit breaker is shown. This load contact arm

45

as well as the contact arms for the other two poles, are fixed in position in the cross bar element

55

. As mentioned above, additional poles, such as a four pole molded case circuit breaker can utilize the same construction as described herein, with the fourth pole allocated to a neutral. The load contact arm

45

is coupled to the bimetallic element

62

by a flexible conductor

48

(e.g. braided copper strand). As shown in

FIG. 3

, current flows from the flexible conductor

48

through the bimetallic element

62

to a connection at the top of the bimetallic element

62

which couples the current to the load terminal

16

through the load bus

61

. The load bus

61

is supported by a load bus support

63

. It should be noted that more than one flexible conductor

48

may be utilized or that a solid bus bar can be used.

In an exemplary embodiment of a circuit breaker

10

, the cross bar

55

is coupled to the operating mechanism

40

, which is held in place in the base or housing

12

of the molded case circuit breaker

10

by a mechanical frame

51

. A principal element of the operating mechanism

40

is the cradle

41

. As shown in

FIG. 3

, the cradle

41

includes a latch surface

41

a which engages the operating surface

118

of the center portion

110

of the latch mechanism

90

. The latch mechanism

90

is held in place by latch pivot pins

98

which are on either side of the latch frame

92

. In an exemplary embodiment of the circuit breaker, the two side members of the mechanism frame

51

support the operating mechanism

40

of the circuit breaker

10

and retain the operating mechanism

40

in the base

12

a

of the circuit breaker

10

. The latch frame

92

is mounted on the mechanical frame

51

.

FIG. 4

illustrates the breaker cover

20

. The breaker cover

20

, can have two accessory pockets

22

formed in the cover

20

, with one accessory pocket

22

on either side of the opening

29

for the pivoting member

13

and handle

14

. The breaker cover

20

with the accessory pockets

22

or compartments can be formed, usually by well known molding techniques, as an integral unit. The accessory pocket

22

can also be fabricated separately and attached to the breaker cover

20

by any suitable method such as with fasteners or adhesives. The breaker cover

20

is sized to cover the operating mechanism

40

, the moveable contact

42

and the stationary contact

44

, as well as the trip mechanism

60

of the circuit breaker

10

. The breaker cover has an opening

29

to accommodate the handle

14

.

Each accessory pocket or compartment

22

is provided with a plurality of openings

24

. The accessory pocket openings

24

are positioned in the pocket

22

to facilitate coupling of an accessory

80

with the operating mechanism

40

mounted in the housing

12

. The accessory pocket openings

24

also facilitate simultaneous coupling of an accessory

80

with different parts of the operating mechanism

40

and the latch shaft assembly

100

. Various devices or accessories

80

associated with the circuit breaker

10

can be mounted in the accessory compartment

22

to perform various functions. Some accessories, such as a shunt trip, will trip the circuit breaker

10

, upon receiving a remote signal, by pushing the latch shaft assembly, causing release of the latch mechanism

90

of the operating mechanism .

40

. The shunt trip has a member protruding through one of the openings in the accessory pocket

22

and engages the operating mechanism

40

, via the latch shaft assembly

100

. Another accessory, such as an auxiliary switch, provides a signal indicating the status of the circuit breaker

10

, e.g. “on” or “off”. When the auxiliary switch is nested in the accessory pocket

22

, a member on the switch assembly protrudes through one of the openings

24

in the pocket

22

and is in engagement with the operating mechanism

40

, typically the cross bar

55

. Multiple switches can be nested in one accessory pocket

22

and each switch can engage the operating mechanism through a different opening

24

in the pocket

22

.

Referring now to

FIGS. 5

,

6

and

7

, there is illustrated a partial sectional view of circuit breaker

10

in the “ON” position (FIG.

5

), the “OFF” position (

FIG. 6

) and the “TRIPPED” position (FIG.

7

).

In the figures, there is illustrated an exemplary embodiment of a latch mechanism, also referred to as an apparatus for operating a circuit breaker

90

with the apparatus comprising a latch frame

92

mounted in the circuit breaker housing

12

. The latch frame

92

can be mounted on the mechanical frame

51

by any conventional and convenient method such as welding, riveting or bolting. The latch frame

92

is typically composed of metal but could be a suitable composite material. A latch roller

94

is mounted on the cradle

41

of the operating mechanism

40

of the circuit breaker

10

. The latch roller

94

is a single piece that spans the width of the cradle

41

and seats underneath a surface of the latch member

96

. The latch roller

94

can be composed of metal, a composite material or a combination of metal and composite material. The latch roller

94

can also be formed as an integral portion of the cradle

41

. Note that the figures illustrate only one side of the cradle, an operating mechanism

40

of the circuit breaker

10

. A latch member

96

is configured to selectively engage the latch roller

94

and is rotatably coupled to the latch frame

92

with a latch pivot pin

98

.

During an ON/OFF operation of the handle

14

of the circuit breaker

10

, the cradle

41

and the latch member

96

are maintained in substantially the same position as shown in

FIGS. 5 and 6

. In the “TRIPPED” position, the latch roller

94

moves along a surface of the latch member

96

as the cradle

41

extends into an upward position as depicted in FIG.

7

.

The exemplary latch member

96

is generally has an upper portion which includes a latch surface that engages the cradle

41

and a lower portion having a latch surface which engages a latch shaft assembly

100

. The center portion of the latch member

96

is angled with respect to the upper and lower portion and includes two tabs which provide a pivot edge for the latch member

96

when it is inserted into the latch frame

92

. As shown in

FIGS. 5-7

, the latch member

96

is coupled to a torsion latch spring

102

which is mounted on the latch shaft

104

. The torsion latch spring

102

biases the latch member

96

toward the cradle

41

while at the same time biasing the latch shaft assembly

100

into a position which engages the lower surface of the latch member

96

. The latch shaft assembly

100

pivots in a clockwise direction about an axis, responsive to a force exerted by a trip mechanism

60

, during, for example, a long duration overcurrent condition. As latch shaft assembly

100

rotates, the operations surface

118

on the center portion

110

of the shaft

104

disengages the latch surface on the latch member

96

. When this latch surface of the latch member

96

is disengaged, the latch member

96

rotates in a under the force of the operating mechanism

40

, exerted through a cradle

41

by the latch roller

94

. In the exemplary circuit breaker, this force is provided by a tension spring

50

. Tension is applied to the spring when the breaker handle

14

is moved from the open position to the closed position. More than one tension spring

50

may be utilized.

As the latch member

96

rotates responsive to the upward force exerted by the cradle

41

, it releases the latch member on the operating mechanism

40

, allowing the cradle

41

to rotate. When the cradle

41

rotates, the operating mechanism

40

is released and the cross bar

55

rotates to move the movable contact arms

45

away from the stationary contact

44

.

A latch shaft assembly

100

is rotatably mounted in the latch frame

92

and selectively engages with the latch member

96

. The latch member

96

is held in place by the operating surface

118

of the center portion

110

of the latch shaft assembly

100

. When the latch shaft assembly

100

rotates it will disengage the latch shaft assembly

100

from the latch member

96

with the latch member

96

rotating to the right (counter-clockwise) as illustrated in

FIG. 7

to release the cradle

41

which causes the operating mechanism

40

to move the movable contact arm

45

in an upward motion which separates the movable contact

42

from stationary contact

44

which in turn breaks the electrical circuit in which the circuit breaker

10

is placed.

A latch spring

102

is coupled to the latch shaft

100

and the latch member

96

. The latch spring

102

biases the latch shaft assembly

100

as well as the latch member

96

as described above. The latch spring

102

can be a torsion spring which is wound around the shaft

104

of a latch shaft assembly

100

.

As shown in

FIGS. 8 and 8

a

, the latch shaft assembly

100

includes a metal shaft

104

with a center portion

110

. A first molded member

114

is mounted on at least one end

106

of the shaft

104

with the first molded member

114

including an operating surface

118

configured to engage a device

80

associated with the circuit breaker

10

. The illustrated embodiment shows a molded member on each end of the shaft.

Another embodiment provides that the shaft

104

includes a second molded member

116

on another end

108

of the shaft

104

. The second molded member

116

includes an operating surface

118

configured to engage another device

80

associated with the circuit breaker

10

. The center portion

110

of the latch shaft assembly

100

is configured in a D-shape as shown in

FIG. 8

a

. The D-shape portion

110

can be a molded element

112

mounted on the shaft

104

. The shaft

104

can be metal or other suitable material that is configured to withstand the forces and temperatures typically experienced by a circuit breaker

10

. The operating surface

118

of the center portion

110

of the latch shaft assembly

100

engages the operating surface of the latch member

96

and holds it in a “cocked” condition. When the trip mechanism

60

of the circuit breaker

10

senses an overload, a kicker member

122

moves a kicker extension

124

which contacts the trip arm

120

which is mounted in the center portion

110

of the latch

104

of the latch shaft assembly

100

. (See FIGS.

8

and

7

).

The trip arm

120

is aligned with the trip mechanism

60

associated with the circuit breaker

10

and is configured to be acted upon by the trip mechanism

60

to trip the circuit breaker

10

. The trip mechanism

60

also includes the above mentioned kicker member

122

which is pivotally mounted in the trip mechanism

60

and is configured to act upon the trip arm

120

. The kicker member

122

and specifically a kicker extension

124

is configured to be moved to a reset position by the handle

14

of the circuit breaker. Movement of the handle

14

against the extension

124

of the kicker member

122

moves the kicker back into alignment with the trip mechanism

60

as can be seen in

FIGS. 6 and 7

.

The latch frame

92

is the means for supporting the latch member

96

within the circuit breaker housing

12

. The apparatus for operating the circuit breaker

90

allows the circuit breaker to be operated during a condition other than an overload condition. As mentioned above, the trip mechanism

60

of the circuit breaker

10

will trip the circuit breaker when it senses an overload condition either through a bi-metal element

62

or a magnetic amplifier which is part of the trip mechanism

60

in the trip housing

61

. However, various devices associated with the circuit breaker

80

can also trip the circuit breaker

10

. Such devices

80

are placed in accessory pockets

22

and align with the various operating surfaces

118

located on the latch shaft assembly

100

through various accessory pocket openings

24

in the cover

20

of the circuit breaker. A signal can be sent to one of the accessory devices

80

which will then act upon one of the operating surfaces

118

of the latch shaft assembly

100

. The shaft in turn will rotate the latch shaft assembly

100

and disengage the latch member

96

allowing the cradle

41

to rotate up and cause the movable contact arm

45

to break the electrical circuit. The cradle is biased in an upward direction by the spring

50

as previously described. The latch spring

102

maintains the proper rotational relationship between the latch member

96

and the latch shaft assembly

100

.

While the embodiments illustrated in the figures and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. Invention is not intended to be limited to any particular embodiment, but it is intended to extend to various modifications that nevertheless fall within the scope of the intended claims. For example, it is also contemplated that the trip mechanism having a bi-metal trip unit or an electronic trip unit with a load terminal be housed in a separate housing capable of mechanically and electrically connecting to another housing containing the operating mechanism and line terminal, thereby providing for a quick and easy change of current rating for an application of the circuit breaker contemplated herein. Modifications will be evident to those with ordinary skill in the art.