Title of Invention	AN IMPROVED CONTACT LATCH ASSEMBLY FOR A MOLDED CASE CIRCUIT BREAKER
Abstract	An improved contact latch assembly for a molded case circuit breaker comprising of a latch configured for establishing contact with the upper contact of a molded case circuit breaker; a base provided with means for mounting the said latch; a tensile spring for coupling said latch with the casing and a cup for providing signals for latching and/or delatching of the said assembly onto said upper contact of said molded case circuit breaker. The cup is configured to operate in the overdrive mode to enable latching and/or delatching of the latch assembly only subsequent to the movement of the cup. Further the contact latch assembly as provided in the invention reduces the arcing of the contacts of the molded case circuit breaker, prevents automatic opening of contacts due to repulsive forces and enhances the life of the contacts.

Title of Invention

AN IMPROVED CONTACT LATCH ASSEMBLY FOR A MOLDED CASE CIRCUIT BREAKER

Abstract

An improved contact latch assembly for a molded case circuit breaker comprising of a latch configured for establishing contact with the upper contact of a molded case circuit breaker; a base provided with means for mounting the said latch; a tensile spring for coupling said latch with the casing and a cup for providing signals for latching and/or delatching of the said assembly onto said upper contact of said molded case circuit breaker. The cup is configured to operate in the overdrive mode to enable latching and/or delatching of the latch assembly only subsequent to the movement of the cup. Further the contact latch assembly as provided in the invention reduces the arcing of the contacts of the molded case circuit breaker, prevents automatic opening of contacts due to repulsive forces and enhances the life of the contacts.

Full Text	AN IMPROVED CONTACT LATCH ASSEMBLY FOR A MOLDED CASE CIRCUIT BREAKER Field of the invention [001] The present invention relates to circuit breakers. More particularly, embodiments of the invention relates to an improved contact latch for a molded case circuit breaker. PRIOR ART [002] The Molded Case Circuit Breaker (MCCB) is designed to protect systems against overload and short circuits with the full range of accessories. The MCCB is designed to be trip-free. This applies when the breaker contacts open under overload and short circuit conditions and even if the breaker handle is held at the ON position. To eliminate single phasing, should an overload or short circuit occur on any one phase, a common trip mechanism disconnects al! phase contacts of a multiple breaker. [003] There are broadly two utilization categories in MCCB, namely category A (CAT A) and utilization category B (CAT B) breakers. These breakers are i expected to break during abnormal conditions to prevent high current damaging the system. [004] In a known mode of trip mechanism of the circuit breaker, the release senses the abnormal conditions and gives the mechanical trip signal to the trip plate, which in turn opens the upper contact and thus breaks the circuit. In another known mode, the contacts itself senses the abnormal condition where high current are involved and the free to move contact preferably the upper contact opens. This is achieved by redefining the shape of the contacts. In this condition, there is no conversion of electrical signal to mechanical signal, which results in a large reduction of time. The contact promoted tripping of the circuit is at a faster time when compared with the release promoted trip of the circuit by the circuit breaker. [005] CAT A breakers have instantaneous opening during short circuit conditions. If the current is high enough to repel open the contacts then the contact promoted tripping occurs and in other conditions trip signal is driven by the release promoted trigger. CAT A breakers are normally employed in the lower end of the distribution network i.e., near the load. [006] CAT B, also called as conventional breakers is capable of tripping only through the release promoted trigger mode. CAT B breakers are normally employed in the branches of a distribution network.The time delay in tripping needed as a fault in one branch of distribution system near the consumer end should not disturb the whole distribution system or other healthy branches in the network. [007] However, the time delay onset occurring in both CAT A and CAT B circuit breakers results in generation of arc due to the rapid breaking and making of in a circuit breaker. The generation of arc causes wearing of the contacts buttons and reduction of the effective life of the contact systems in a circuit breaker. Hence, there is a need for a mechanism that effectively reduces the arc formation by controlled opening and closing of the upper contact in a circuit breaker. OBJECT OF THE INVENTION [008] It is an object of the invention to provide an improved contact latch assembly for a molded case circuit breaker for controlled opening and closing of the upper contact [009] It is another object of the invention to provide an improved contact latch assembly that effectively reduces the arc formation at the contacts through controlled opening and closing of the upper contact. [0010] It is a further object of the invention to provide an improved contact latch assembly that is capable of holding contacts in its place for currents occurring during short circuits. BRIEF DESCRIPTION OF THE DRAWINGS [0011] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. [0012] FIGURE 1 represents a schematic diagram of the upper contact assembly according to an embodiment of the invention. [0013] FIGURE 2 represents a schematic diagram of the latch according to an embodiment of the invention. [0014] FIGURE 3 represents a schematic diagram of the spring in spring grove of latch and its attachment with external casing. [0015] FIGURE 4 represents a schematic diagram of the latch assembly along with the contact assembly of a molded case circuit breaker according to an embodiment of the invention. DETAILED DESCRIPTION OF INVENTION [0016] The invention provides an improved contact latch assembly for a molded case circuit breaker for controlled opening and closing of the upper contact by repulsive forces. More particularly embodiments of the invention provide a contact latch assembly that effectively reduces the arc formation at the contacts through controlled opening and closing of the upper contact. The invention will be described in detail herein below by providing illustrations and examples of the invention. [0017] Figure 1 shows a molded case circuit breaker with a pair of upper contacts (movable contacts) (1); a pair of upper contact buttons (2); a cup (3) along with two pairs of pins (4) according to an embodiment of the invention. The cup is capable of moving along with the movable contact namely the upper contact during making and/or breaking of the circuit breaker. The upper contact (1) is capable of moving along with the cup. Further, the said cup (3) is enabled to undergo overdrive motion to provide contact pressure to the movable contact, i.e., upper contact. The overdrive motion of the cup enabled by the shafts provided shall be explained in detail herein. [0018] Figure 2 shows a schematic diagram of the latch assembly according to an embodiment of the invention. The improved contact latch assembly for a molded case circuit breaker comprises of a latch (5) configured to form a latch head for establishing contact with the upper contact (1) of molded case circuit breaker and a tail region (7) to establish contact with the lower contact (2). Further, the said latch head is provided with a groove (6) for establishing connection with a tensile spring. A base (8) provided acts as a supporting member for the latch and has means for mounting the said latch (5). In an example of the invention, the said latch along with the latch head and the tail region is mounted onto the base with a rivet arrangement. The latch is connected to the base by a pin. [0019] A tensile spring (10) is provided for coupling latch with the casing (11) of the said molded case circuit breaker. Figure 3 shows a schematic representation of the coupling of the latch with the casing of the MCCB. Further the said latch assembly also comprises of said cup (3) with said pins (4) for latching and/or delatching of the latch assembly onto upper contact of molded case circuit breaker, [0020] Operation of the Latch Assembly during ON condition of the circuit breaker: In the closed position of said circuit breaker, the said cup (3) along with said pins (4] is configured to operate in overdrive mode. In the overdrive mode, the cup provided move through a distance of at least 5mm more than the distance of movement of said contact system of the molded case circuit breaker, [n an example of the invention, if the contacts move through a distance of 30mm, the cup along with the pins are configured to move through a distance of 35mm. The operation of the cup along with the pins in overdrive mode during closed position provides the required force by pushing the tail region as indicated in the arrow (14) of Figure 4. The downward movement of the tail region pushes the head of latch in the direction (12) of Figure 4 to enable latching of the latch assembly onto upper contact of molded case circuit breaker. The additional movement of the cup forces the latch head to latch on tightly to the upper contact and this forced latching effectively reduces the arc forming during the closing of the contacts [0021] Operation of the Latch Assembly during OFF condition and/or TRIP condition of the circuit breaker: During the operation at open condition of the circuit breaker, the cup moves prior to the movement of upper contact due to cup capable of operating in overdrive mode. The movement of the cup enables the tensile spring to bring the latching assembly to normal position. Further, due to the movement of the cup, the tensile spring holding the latch through the spring groove provided on the latch head enables the release of the latch subsequent to the movement of the cup thereby separating the upper contact as indicated by the direction (13) of Figure 4. This controlled opening or delatching of the latch assembly during the open condition of the circuit breaker effectively reduces the arcing of contact and enhances the life of contact assembly of molded case circuit breaker. [0022] During ON and OFF of the Circuit breaker there is a generation of repulsive forces due to the constriction force between upper and lower contact buttons. The repulsive force pushes the movable upper contact upwards and hence causing undesired opening. The latch assembly as provided herein and as described in the invention, keeps the upper contact in its place even if there is any repulsion force. [0023] Further, the latch is configured to sense the position of the upper contact at every operation and produces latching. As the tail region is pushed down by the Cup, the head portion of the latch moves till it hits the upper contact. Thus by this way, the upper contacts' position is sensed and latched at its position. On the other hand, if the upper contact moves down when it is latched, due to the wearing down of the contact buttons, the latch still follows the upper contact du to the tail region being constantly under pressure by the Cup to move downwards. The downward movement of the Cup and in turn the tail region of the latch is stopped because the head region is stopped by the upper contact. So as the upper contact moves down the latch also follows the upper contact and it is latched at any point. [0024] Thus, both during the open and close condition of the circuit breaker, the latching and delatching of the contact latch assembly as described in detail herein above advantageously reduces the arc formation on the contacts and increases the current withstanding capabilities of the circuit breaker. [0025] The invention, as described herein and as illustrated by diagrams provide an improved contact latch assembly for a molded case circuit breaker. [0026] The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. We claim: 1. An improved contact latch assembly for a molded case circuit breaker comprising of a latch configured for establishing contact with the upper contact of a molded case circuit breaker; a base provided with means for mounting the said latch; a tensile spring for coupling said latch with the casing and a cup with a plurality of pins for providing signals for latching and/or delatching of the said assembly onto said upper contact of said molded case circuit breaker. 2. An improved contact latch assembly of Claim 1, wherein the said latch is provided with a spring groove for coupling said tensile spring and further wherein the said latch is provided with a slot to mount said latch onto said base. 3. An improved contact latch assembly of Claim 1, wherein during the closed position of said circuit breaker the said cup with the said plurality of the pinss is configured to operate in overdrive mode. 4. An improved contact latch assembly of Claim 1, wherein during the said overdrive mode the said cup moves through a distance of at least 5mm more than the distance of movement of said contact system of the said molded case circuit breaker. 5. An improved contact latch assembly of Claim 1, wherein the said overdrive movement of the said shaft position provides the required force for latching of the said latch assembly onto the said upper contact 6. An improved contact latch assembly of Claim I, wherein the said repulsion force is achieved by downward motion of the said tail region of the said latch and further wherein the said downward motion of the said tail region pushes the head of said latch to enable latching of the said latch assembly onto said upper contact of said molded case circuit breaker. 7. An improved contact latch assembly of Claim 1, wherein during the open condition of the said circuit breaker the said cup moves prior to the movement of said upper contact due to said cup capable of operating in said overdrive mode. 8. An improved contact latch assembly of Claim I, wherein the said open condition of the said molded case circuit breaker is an OFF position and/or TRIP position. 9. An improved contact latch assembly of Claim I, wherein said movement of the said cup enables the said tensile spring to bring the said latching assembly to normal position and further wherein the release of the said latch subsequent to the said movement of the said cup enables the separation of said upper contact. 10. An improved contact latch assembly of Claim 1, wherein the operation of the said assembly as claimed in claims I - 9 reduces the arcing of said contacts and enhances the life of said contact assembly of said molded case

Full Text

AN IMPROVED CONTACT LATCH ASSEMBLY FOR A MOLDED CASE
CIRCUIT BREAKER
Field of the invention
[001] The present invention relates to circuit breakers. More particularly, embodiments of the invention relates to an improved contact latch for a molded case circuit breaker.
PRIOR ART [002] The Molded Case Circuit Breaker (MCCB) is designed to protect systems against overload and short circuits with the full range of accessories. The MCCB is designed to be trip-free. This applies when the breaker contacts open under overload and short circuit conditions and even if the breaker handle is held at the ON position. To eliminate single phasing, should an overload or short circuit occur on any one phase, a common trip mechanism disconnects al! phase contacts of a multiple breaker.
[003] There are broadly two utilization categories in MCCB, namely category A
(CAT A) and utilization category B (CAT B) breakers. These breakers are
i expected to break during abnormal conditions to prevent high current damaging
the system.
[004] In a known mode of trip mechanism of the circuit breaker, the release
senses the abnormal conditions and gives the mechanical trip signal to the trip
plate, which in turn opens the upper contact and thus breaks the circuit. In another
known mode, the contacts itself senses the abnormal condition where high current
are involved and the free to move contact preferably the upper contact opens. This
is achieved by redefining the shape of the contacts. In this condition, there is no
conversion of electrical signal to mechanical signal, which results in a large
reduction of time. The contact promoted tripping of the circuit is at a faster time
when compared with the release promoted trip of the circuit by the circuit breaker.
[005] CAT A breakers have instantaneous opening during short circuit
conditions. If the current is high enough to repel open the contacts then the contact

promoted tripping occurs and in other conditions trip signal is driven by the release promoted trigger. CAT A breakers are normally employed in the lower end of the distribution network i.e., near the load.
[006] CAT B, also called as conventional breakers is capable of tripping only through the release promoted trigger mode. CAT B breakers are normally employed in the branches of a distribution network.The time delay in tripping needed as a fault in one branch of distribution system near the consumer end should not disturb the whole distribution system or other healthy branches in the network.
[007] However, the time delay onset occurring in both CAT A and CAT B circuit breakers results in generation of arc due to the rapid breaking and making of in a circuit breaker. The generation of arc causes wearing of the contacts buttons and reduction of the effective life of the contact systems in a circuit breaker. Hence, there is a need for a mechanism that effectively reduces the arc formation by controlled opening and closing of the upper contact in a circuit breaker.
OBJECT OF THE INVENTION
[008] It is an object of the invention to provide an improved contact latch
assembly for a molded case circuit breaker for controlled opening and closing of
the upper contact
[009] It is another object of the invention to provide an improved contact latch
assembly that effectively reduces the arc formation at the contacts through
controlled opening and closing of the upper contact.
[0010] It is a further object of the invention to provide an improved contact latch
assembly that is capable of holding contacts in its place for currents occurring
during short circuits.
BRIEF DESCRIPTION OF THE DRAWINGS [0011] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be

noted, however, that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0012] FIGURE 1 represents a schematic diagram of the upper contact assembly
according to an embodiment of the invention.
[0013] FIGURE 2 represents a schematic diagram of the latch according to an
embodiment of the invention.
[0014] FIGURE 3 represents a schematic diagram of the spring in spring grove of
latch and its attachment with external casing.
[0015] FIGURE 4 represents a schematic diagram of the latch assembly along with
the contact assembly of a molded case circuit breaker according to an embodiment
of the invention.
DETAILED DESCRIPTION OF INVENTION [0016] The invention provides an improved contact latch assembly for a molded case circuit breaker for controlled opening and closing of the upper contact by repulsive forces. More particularly embodiments of the invention provide a contact latch assembly that effectively reduces the arc formation at the contacts through controlled opening and closing of the upper contact. The invention will be described in detail herein below by providing illustrations and examples of the invention.
[0017] Figure 1 shows a molded case circuit breaker with a pair of upper contacts (movable contacts) (1); a pair of upper contact buttons (2); a cup (3) along with two pairs of pins (4) according to an embodiment of the invention. The cup is capable of moving along with the movable contact namely the upper contact during making and/or breaking of the circuit breaker. The upper contact (1) is capable of moving along with the cup. Further, the said cup (3) is enabled to undergo overdrive motion to provide contact pressure to the movable contact, i.e., upper contact. The overdrive motion of the cup enabled by the shafts provided shall be explained in detail herein.
[0018] Figure 2 shows a schematic diagram of the latch assembly according to an embodiment of the invention. The improved contact latch assembly for a molded

case circuit breaker comprises of a latch (5) configured to form a latch head for establishing contact with the upper contact (1) of molded case circuit breaker and a tail region (7) to establish contact with the lower contact (2). Further, the said latch head is provided with a groove (6) for establishing connection with a tensile spring. A base (8) provided acts as a supporting member for the latch and has means for mounting the said latch (5). In an example of the invention, the said latch along with the latch head and the tail region is mounted onto the base with a rivet arrangement. The latch is connected to the base by a pin. [0019] A tensile spring (10) is provided for coupling latch with the casing (11) of the said molded case circuit breaker. Figure 3 shows a schematic representation of the coupling of the latch with the casing of the MCCB. Further the said latch assembly also comprises of said cup (3) with said pins (4) for latching and/or delatching of the latch assembly onto upper contact of molded case circuit breaker, [0020] Operation of the Latch Assembly during ON condition of the circuit breaker: In the closed position of said circuit breaker, the said cup (3) along with said pins (4] is configured to operate in overdrive mode. In the overdrive mode, the cup provided move through a distance of at least 5mm more than the distance of movement of said contact system of the molded case circuit breaker, [n an example of the invention, if the contacts move through a distance of 30mm, the cup along with the pins are configured to move through a distance of 35mm. The operation of the cup along with the pins in overdrive mode during closed position provides the required force by pushing the tail region as indicated in the arrow (14) of Figure 4. The downward movement of the tail region pushes the head of latch in the direction (12) of Figure 4 to enable latching of the latch assembly onto upper contact of molded case circuit breaker. The additional movement of the cup forces the latch head to latch on tightly to the upper contact and this forced latching effectively reduces the arc forming during the closing of the contacts [0021] Operation of the Latch Assembly during OFF condition and/or TRIP condition of the circuit breaker: During the operation at open condition of the circuit breaker, the cup moves prior to the movement of upper contact due to cup capable of operating in overdrive mode. The movement of the cup enables the

tensile spring to bring the latching assembly to normal position. Further, due to the movement of the cup, the tensile spring holding the latch through the spring groove provided on the latch head enables the release of the latch subsequent to the movement of the cup thereby separating the upper contact as indicated by the direction (13) of Figure 4. This controlled opening or delatching of the latch assembly during the open condition of the circuit breaker effectively reduces the arcing of contact and enhances the life of contact assembly of molded case circuit breaker.
[0022] During ON and OFF of the Circuit breaker there is a generation of repulsive forces due to the constriction force between upper and lower contact buttons. The repulsive force pushes the movable upper contact upwards and hence causing undesired opening. The latch assembly as provided herein and as described in the invention, keeps the upper contact in its place even if there is any repulsion force.
[0023] Further, the latch is configured to sense the position of the upper contact at every operation and produces latching. As the tail region is pushed down by the Cup, the head portion of the latch moves till it hits the upper contact. Thus by this way, the upper contacts' position is sensed and latched at its position. On the other hand, if the upper contact moves down when it is latched, due to the wearing down of the contact buttons, the latch still follows the upper contact du to the tail region being constantly under pressure by the Cup to move downwards. The downward movement of the Cup and in turn the tail region of the latch is stopped because the head region is stopped by the upper contact. So as the upper contact moves down the latch also follows the upper contact and it is latched at any point. [0024] Thus, both during the open and close condition of the circuit breaker, the latching and delatching of the contact latch assembly as described in detail herein above advantageously reduces the arc formation on the contacts and increases the current withstanding capabilities of the circuit breaker.
[0025] The invention, as described herein and as illustrated by diagrams provide an improved contact latch assembly for a molded case circuit breaker.

[0026] The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

We claim:
1. An improved contact latch assembly for a molded case circuit breaker
comprising of
a latch configured for establishing contact with the upper contact of a molded case circuit breaker;
a base provided with means for mounting the said latch; a tensile spring for coupling said latch with the casing and a cup with a plurality of pins for providing signals for latching and/or delatching of the said assembly onto said upper contact of said molded case circuit breaker.
2. An improved contact latch assembly of Claim 1, wherein the said latch is provided with a spring groove for coupling said tensile spring and further wherein the said latch is provided with a slot to mount said latch onto said base.
3. An improved contact latch assembly of Claim 1, wherein during the closed position of said circuit breaker the said cup with the said plurality of the pinss is configured to operate in overdrive mode.
4. An improved contact latch assembly of Claim 1, wherein during the said overdrive mode the said cup moves through a distance of at least 5mm more than the distance of movement of said contact system of the said molded case circuit breaker.
5. An improved contact latch assembly of Claim 1, wherein the said overdrive movement of the said shaft position provides the required force for latching of the said latch assembly onto the said upper contact
6. An improved contact latch assembly of Claim I, wherein the said repulsion force is achieved by downward motion of the said tail region of the said latch and further wherein the said downward motion of the said tail region pushes the head of said latch to enable latching of the said latch assembly onto said upper contact of said molded case circuit breaker.
7. An improved contact latch assembly of Claim 1, wherein during the open condition of the said circuit breaker the said cup moves prior to the

movement of said upper contact due to said cup capable of operating in said overdrive mode.
8. An improved contact latch assembly of Claim I, wherein the said open condition of the said molded case circuit breaker is an OFF position and/or TRIP position.
9. An improved contact latch assembly of Claim I, wherein said movement of the said cup enables the said tensile spring to bring the said latching assembly to normal position and further wherein the release of the said latch subsequent to the said movement of the said cup enables the separation of said upper contact.
10. An improved contact latch assembly of Claim 1, wherein the operation of
the said assembly as claimed in claims I - 9 reduces the arcing of said
contacts and enhances the life of said contact assembly of said molded case

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=hNSOjxkEqfFeGF4dJFSw8g==&loc=egcICQiyoj82NGgGrC5ChA==

« Previous Patent

Next Patent »

Patent Number

277229

Indian Patent Application Number

1866/CHE/2008

PG Journal Number

48/2016

Publication Date

18-Nov-2016

Grant Date

16-Nov-2016

Date of Filing

04-Aug-2008

Name of Patentee

LARSEN & TOUBRO LIMITED

Applicant Address

LARSEN & TOUBRO LIMITED KIADB INDUSTRIAL AREA HEBBAL - HOOTAGALLI MYSORE- 570 018.

Inventors:

#	Inventor's Name	Inventor's Address
1	V. SENTHIL KUMAR	LARSEN & TOUBRO LIMITED KIADB INDUSTRIAL AREA HEBBAL - HOOTAGALLI MYSORE- 570 018.

PCT International Classification Number

H01H3/20

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA