DESC:Trip Indication Mechanism for Circuit Breaker

Field of the invention

The present invention relates to circuit breakers and more particularly, to a trip indication mechanism for the circuit breaker.

Background of the invention

Normally, molded case circuit breakers (herein after ‘the MCCB’) have three stable conditions: ON, OFF and Trip. During ON condition, contacts are closed and an operating mechanism is latched. During OFF condition, the contacts are open and the operating mechanism is latched. During Trip condition, the contacts are open and the operating mechanism is de-latched.

Conventional MCCBs include a trip auxiliary contact, alternatively a trip alarm contact or a trip alarm lever or a trip alarm switch to indicate a transition to the Trip condition from any other condition. The trip auxiliary contact (herein after ‘the TAC’) is generally a micro-switch with three terminals Common (C), Normally Closed (NC) and Normally Open (NO). During normal conditions, C and NC are connected (closed) and when the TAC is actuated by an actuator, C and NC opens thereby connecting C and NO.

A US patent number ‘5036303’ discloses a mechanism latch along with an actuator component to actuate the trip alarm contact. Upon delatching, the mechanism latch rotates in an anticlockwise direction along with a component attached thereto. This component actuates the actuator component on a cover by a cam joint. Then, the actuator component actuates the trip alarm contact by a cam arrangement. Once the breaker is reset, the component on the mechanism latch rotates along with the latch which allows the actuator component on the cover to come to its designed position with the help of a spring.
Another US patent number ‘5714940’ discloses a lower actuating member (latch member) which is latched to an upper actuating lever member annular shoulder (cam surface). The lower lever member is actuated by a plunger (mechanism) causing the lower lever to rotate and disengage with the upper lever member. On complete disengagement, a flat surface of the upper lever member actuates a trip alarm switch. Both the levers are attached by a lever spring for retaining them to their original positions. The force required to actuate the trip alarm switch is given by this lever spring.

Yet another US patent number ‘6882258 B2’ discloses a mechanical bell alarm assembly for a circuit breaker and a mechanism assembly with a latch, a primary latch, a secondary latch (latch bracket), a lever which is connected with the latch and a compliant component that acts in tandem to actuate a trip alarm switch. During ON condition, the main latch does not allow the lever to rotate at the same time one free end of the compliant component assembled in a cover pushes the micro switch lever during ON-OFF condition. Upon de-latching from the primary latch through the secondary latch, the latch rotates counter clockwise allowing the lever to rotate clockwise thereby allowing the compliant component to rotate and release the lever of the switch.

The above mentioned conventional designs involve several drawbacks as summarized below:
• Need of extra components to actuate the TAC lever.
• Need of an extra margin to actuate the TAC lever as there are more components involved to actuate the TAC lever.
• The process of assembling of the TAC actuator with the latch link is tedious.
• Less reliable as more components are involved.
• In conventional breakers, the TAC actuator is mounted on a latch link hinge point or it forms a rigid assembly with the latch link. By this virtue, the movement of the TAC actuator is dependent upon the latch link movement.

Accordingly, there is a need of a trip indication mechanism for a circuit breaker that overcomes the above mentioned drawbacks of the prior art.

Objects of the invention

An object of the present invention is to actuate a trip auxiliary contact (TAC) lever directly without requiring extra components.

Another object of the present invention is to provide more reliable and fast actuation of the TAC lever.

Yet another object of the present invention is to provide a hardware free assembly of a tripping mechanism that is easy to assemble.

Summary of the invention

Accordingly, the present invention provides a trip indication mechanism for a circuit breaker. The trip indication mechanism comprises a trip auxiliary contact, a latch bracket, a latch link and a trip plate.

The trip auxiliary contact is mounted on a chassis of the circuit breaker. The trip auxiliary contact includes an auxiliary actuator configured thereon. The auxiliary actuator is capable of being actuated for indicating a transition of the circuit breaker to a trip condition from any of ON and OFF conditions.

The latch bracket is capable of undergoing rotation to cause the transition of the circuit breaker to the trip condition from any of ON and OFF conditions. The latch bracket is mounted through two pivot holes and includes a latching profile and at least two latching surfaces configured thereon. Each latching surface defines a cam surface thereon.

The latch link is capable of removably engaging to the latching profile of the latch bracket during an ON-OFF operation of the circuit breaker.

The trip plate is mounted through a pivot axis thereof. The trip plate includes a latching surface and an actuation limb configured thereon. The latching surface is capable of removably engaging to at least two latching surfaces on the latch bracket thereby keeping the latch bracket engaged with the latch link during the ON-OFF operation of the circuit breaker. The latching surface defines a cam surface thereon. The actuation limb is adapted to actuate the auxiliary actuator of the trip auxiliary contact for indicating the trip condition of the circuit breaker.

During the transition of the circuit breaker to the trip condition, a first degree of rotation of the trip plate in an anticlockwise direction causes disengagement thereof from the latch bracket resulting in rotation of the latch bracket in the anticlockwise direction and disengagement thereof from the latch link thereby causing rotation of the latch link in a clockwise direction resulting in tripping of the circuit breaker followed by an extra / a second degree of rotation of the trip plate in the anticlockwise direction due to the cam surfaces thereby rotating the actuation limb therewith causing the actuation of the auxiliary actuator to indicate the trip condition of the circuit breaker.

Brief description of the drawings

Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:
Figures 1 and 1a show a trip indication mechanism for a circuit breaker, in accordance with the present invention;
Figure 2 shows a trip auxiliary contact of the trip indication mechanism figure 1;

Figure 3 shows the trip indication mechanism of figure 1;

Figure 3a shows an exploded view of the trip indication mechanism of figure 1;

Figure 4a shows the trip indication mechanism of figure 1 with a trip plate latched;

Figure 4b shows the trip indication mechanism of figure 1with the trip plate delatching initially;

Figure 4c shows the trip indication mechanism of figure 1with the trip plate delatched;

Figure 4d shows the trip indication mechanism of figure 1with the trip plate relatched;

Figure 5a shows a side perspective view of the trip plate of the trip indication mechanism of figure 1;

Figure 5b shows another side perspective view of the trip plate of the trip indication mechanism of figure 1;

Figure 6 shows a latch bracket of the trip indication mechanism of figure 1;

Figure 6a - 6c show various views of the latch bracket, the latch link and the trip plate of the trip indication mechanism of figure 1;

Figure 7a shows of the trip indication mechanism of figure 1 with the trip plate and a TAC lever position during on-off, in accordance with the present invention; and

Figure 7b shows the operating mechanism with the trip plate and the TAC lever during a trip position in accordance with the present invention.

Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.

The present invention provides a trip indication mechanism for a circuit breaker. The trip indication mechanism actuates a trip auxiliary contact (TAC) lever directly by means of a trip plate without extra/ hardware components. The trip indication mechanism is a hardware free assembly that is easy to assemble and provides more reliable and fast actuation of the TAC lever. The trip indication mechanism trips the circuit breaker once it de-latches bringing a knob in the center of circuit breaker to indicate the trip condition.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.

Referring to figures 1-7b, a trip indication mechanism (100) for a circuit breaker (150) in accordance with the present invention is shown. The trip indication mechanism (100) is adapted for actuation of tripping and indication of tripping in the circuit breaker (150). Specifically, the circuit breaker (150) is a molded case circuit breaker. The trip indication mechanism (100) rests on slots (110) of a housing (121) of the circuit breaker (150) as shown in figures 1 and 1a. The trip indication mechanism (100) comprises a trip auxiliary contact (10), a latch link (50), a latch bracket (30) and a trip plate (70).

The trip auxiliary contact (10) (herein after ‘the TAC (10)’) is a micro-switch mounted on a chassis (120) of the circuit breaker (150). The TAC (10) includes a first terminal (2), a second terminal (4), a third terminal (6) and an auxiliary actuator/ TAC lever (8) configured thereon. The three terminals (2, 4 and 6) of the TAC (10) are Common (herein after ‘C’), Normally Closed (herein after ‘NC’) and Normally Open (herein after ‘NO’). During normal conditions, C and NC are connected electrically. The auxiliary actuator (8) is capable of being actuated for indicating a transition of the circuit breaker (150) to a trip condition from any of ON and OFF conditions. The actuation of the auxiliary actuator (8) causes C and NC to open thereby connecting C and NO electrically.

The latch bracket (30) is mounted on the assembly of the trip indication mechanism (100) through two pivot holes (25) configured thereon. The latch bracket (30) is capable of undergoing rotation to cause the transition of the circuit breaker (150) to the trip condition from any of ON and OFF conditions. The latch bracket (30) includes a latching profile (22) and at least two latching surfaces (24) configured thereon. Each latching surface (24) defines a cam surface (23) thereon.

The latch link (50) is capable of removably engaging to the latching profile (22) of the latch bracket (30) during an ON-OFF operation of the circuit breaker (150). The reference numeral ‘A’ indicates a latching point between the latch link (50) and the latch bracket (30) as shown in figure 4a.

The trip plate (70) is mounted on the assembly of the trip indication mechanism (100) through a pivot axis (65) thereof. The trip plate (70) includes a latching surface (64) and an actuation limb (66) configured thereon. The latching surface (64) is capable removably engaging to the at least two latching surfaces (24) on the latch bracket (30) at a point indicated by reference numeral ‘B’ in figure 4a. The latching surface (64) engages to the at least two latching surfaces (24) for keeping the latch bracket (30) engaged with the latch link (50) during the ON-OFF operation of the circuit breaker (150). The latching surface (64) defines a cam surface (63) thereon. The cam surface (63) is adapted for extra rotation of the trip plate (70). The actuation limb (66) is adapted to actuate the auxiliary actuator (8) of the TAC (10) for indicating the trip condition of the circuit breaker (150).

In ON condition of the circuit breaker (150), contacts (not shown) are closed, the operating mechanism is latched and the latch link (50) is latched with the latch bracket (30) that in turn is latched with the trip plate (70). Specifically, the latching surface (24) of the latch bracket (30) is latched with the latching surface (64) of the trip plate (70) in ON condition of the circuit breaker (150). During ON-OFF condition, the latch link (50) and the latch bracket (30) remains in latched condition because of the trip plate (70) that does not allow the latch bracket (30) to rotate. Once the trip plate (70) rotates clockwise direction, the latch bracket (30) rotates and de latches the latch link (50) that in turn rotates anti clockwise to trip the circuit breaker (150).The transition of the circuit breaker (150) to the trip condition is illustrated in further detail below:

During the transition of the circuit breaker (150) to the trip condition wherein the contacts are open and the operating mechanism is de-latched, a first degree of rotation (a1 rotation ) of the trip plate (70) in an anticlockwise direction causes disengagement thereof from the latch bracket (30). Specifically, the trip plate (70) rotates to disengage the latching surface (64) thereof from the latching surface (24) of the latch bracket (30). The force required to delatch the trip plate (70) is very less compared to force required to move a breaker fork of the prior art from ON to OFF condition. Also, the transition from ON condition to Trip condition is faster than ON to OFF. This process of rotating the trip plate (70) and de-latching the circuit breaker (150) is called as tripping of the circuit breaker (150).
The complete disengagement of the trip plate (70) from the latch bracket (30) (indicated by reference numeral ‘C’ in figure 4c) results in rotation of the latch bracket (30) in the anticlockwise direction and disengagement thereof from the latch link (50) thereby causing rotation of the latch link (50) in a clockwise direction resulting in tripping of the circuit breaker (150). The latch link (50) after rotation, keeps the latch bracket (30) in de-latched condition till it is reset again. This is followed by an extra / a second degree of rotation of the trip plate (70) in the anticlockwise direction by an additional angle a2 from a1. The second degree of rotation of the trip plate (70) is caused by the cam surfaces (23, 63) on the latch bracket (30) and the trip plate (70). The trip plate rotation is transmitted and amplified by the actuation limb (66). The second degree of rotation of the trip plate (70) results in rotation of the actuation limb (66) therewith. The actuation limb (66) rotates to actuate the auxiliary actuator (8). Specifically, the cam profile on the actuation limb (66) actuates the auxiliary actuator (8) that indicates the trip condition of the circuit breaker (150).

Thus, during this tripping actuation, till a1 rotation, the trip plate (70) will not actuate the TAC (10) since the latching surfaces (64 and 24) have not disengaged. After a2 rotation, the latching surfaces (64 and 24) disengage and de-latch the trip plate (70) and the latch bracket (30) as well as the latch bracket (30) and the latch link (50). This angle a2 rotation the trip plate (70) actuates the auxiliary actuator (8) fully to give trip indication on transition of the circuit breaker (150). Thus, direct actuation of the trip plate (70) gives fast actuation of the TAC (10) by involving only one component (the trip plate (70) itself) and still taking the forces from mechanism through the cam arrangement to actuate TAC (10) (Cam based tripping actuation).

Where,
a = Total rotation of trip plate for Trip condition
a 1= Rotation of the trip plate (70) to de-latch the mechanism
a 2= Actuation zone of the auxiliary actuator (8)

To reset the circuit breaker (150) to ON condition, the latch link (50) is moved back forcing the latch bracket (30) to go in latched condition with the trip plate (70) again.

Advantages of the invention

• No need of extra hardware component to actuate the auxiliary actuator (8) of the TAC (10). This gives rigidity to parts as well as to the assembly of the trip indication mechanism (100).
• Ease of manufacturing/assembly and cost effective as there is no extra component such as spring which is required in prior art mechanisms.
• The trip indication mechanism (100) does not take actuation signal from the latch link (50) but rather takes actuation signal from the trip plate (70) directly. While tripping the breaker (1), the latch bracket (30) will de-latch from the trip plate (70) which allows the latch link (50) to rotate clockwise. Conventional breakers use this movement of latch link (50) to actuate the auxiliary actuator (8). In this design the trip indication is actuated by the trip plate (70) directly. This gives fast and more reliable actuation of the auxiliary actuator (8) without involvement of mechanism components.
• The auxiliary actuator (8) is actuated by the component which started rotating initially (i.e. the trip plate (70)). During the initial angle of rotation of trip plate until de-latching, it moves closer to the auxiliary actuator (8) but does not actuate it. After de-latching, now the auxiliary actuator (8) is actuated by the trip plate (70). The force required for actuating the auxiliary actuator (8) is given by the main mechanism through cam action between the trip plate (70) and the latch bracket (30) but not by a trip plate-latch bracket connecting spring (lever spring).
• Provision of a pivot axis in the main cover.
• Same rotating axis of actuation: axes of rotation of the trip plate (70) and the actuation limb (66) are one and the same.
• Single component push button

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.

,CLAIMS:We claim:

1. A trip indication mechanism (100) for a circuit breaker (150), the trip indication mechanism (100) comprising:
• a trip auxiliary contact (10) mounted on a chassis (120) of the circuit breaker (150), the trip auxiliary contact (10) having an auxiliary actuator (8) configured thereon, the auxiliary actuator (8) capable of being actuated for indicating a transition of the circuit breaker (150) to a trip condition from any of ON and OFF conditions;
• a latch bracket (30) being capable of undergoing rotation to cause the
transition of the circuit breaker (150) to the trip condition from any of ON and OFF conditions, the latch bracket (30) having a latching profile (22) and at least two latching surfaces (24) configured thereon, each latching surface (24) defining a cam surface (23) thereon;
• a latch link (50) capable of removably engaging to the latching profile
(22) of the latch bracket (30) during an ON-OFF operation of the circuit breaker (150); and
• a trip plate (70) having a latching surface (64) and an actuation limb (66) configured thereon, the latching surface (64) capable of being removably engaging to the at least two latching surfaces (24) on the latch bracket (30) thereby keeping the latch bracket (30) engaged with the latch link (50) during the ON-OFF operation of the circuit breaker (150), the latching surface (64) defining a cam surface (63) thereon, the actuation limb (66) adapted to actuate the auxiliary actuator (8) of the trip auxiliary contact (10) for indicating the trip condition of the circuit breaker (150),

wherein, during the transition of the circuit breaker (150) to the trip condition, a first degree of rotation of the trip plate (70) in an anticlockwise direction causes disengagement thereof from the latch bracket (30) resulting in rotation of the latch bracket (30) in the anticlockwise direction and disengagement thereof from the latch link (50) thereby causing rotation of the latch link (50) in a clockwise direction resulting in tripping of the circuit breaker (150) followed by an extra / a second degree of rotation of the trip plate (70) in the anticlockwise direction due to the cam surfaces (23, 63) thereby rotating the actuation limb (66) therewith causing the actuation of the auxiliary actuator (8) to indicate the trip condition of the circuit breaker (150).

2. The trip indication mechanism (100) as claimed in claim 1, wherein the trip plate (70) is mounted through a pivot axis (65) thereof.

3. The trip indication mechanism (100) as claimed in claim 1, wherein the latch bracket (30) is mounted through two pivot holes (25) configured thereon.