CLIAMS:We claim:

1. A braidless contact system (100) for a modular circuit breaker, the
braidless contact system (100) being enclosed between a pair of cassettes (10A, 10B), the braidless contact system (100) comprising:
• an incoming terminal (30) and a braidless outgoing terminal (50), the
braidless outgoing terminal (50) having at least two limbs (40, 42), each limb of the at least two limbs (40, 42) having a groove configured thereon;
• a moving contact assembly having
a moving contact (70) adapted to rest between the at least two
limbs (40, 42) thereby forming an assembly with the outgoing terminal (50), the moving contact (70) being capable of separating from the incoming terminal (30) acting as a fixed contact, the moving contact (70) having a first slot and a second slot configured thereon,
a first pin (65) inserted into the moving contact (70) through the
first slot, the first pin (65) having at least two holders (63) fitted on each side thereof, each holder of the at least two holders (63) enclosing and compressing a contact spring (62) there between through a slot configured thereon, and
a second pin (60) inserted into the moving contact (70) through
the second slot, the second pin (60) adapted to rest on the grooves of the at least two limbs (40, 42), the second pin (60) having a braidless joint spring (55) coiled on each side thereof; and
• a two-part shaft assembly (90) having a first shaft (80) and a second
shaft (82), each shaft (80, 82) having a third slot (78) and a fourth slot (74), the shafts (80, 82) being assembled to enclose the assembly of the moving contact (70) and the outgoing terminal (50) such that the second pin (60) gets inserted into the third slot (78),

wherein, during a normal current condition, the compressed contact springs (62, 65) apply a force on the moving contact (70) that being greater than the electromagnetic repulsive force developed between the moving contact (70) and the incoming terminal (30) results in contact force establishment between the moving contact (70) and the incoming terminal (30),

wherein, during an abnormal current condition, the electromagnetic repulsive force developed between the moving contact (70) and the incoming terminal (30) being greater than the force offered by the compressed contact springs (62) acting on the moving contact (70) results in a clockwise rotation of the moving contact (70) about an axis of the second pin (60) thereby separating the moving contact (70) from the incoming terminal (30).

2. The braidless contact system (100) as claimed in claim 1, wherein the
braidless joint springs (55) are coiled on each side of the second pin (60) through a pair of plain washers (53).

,TagSPECI:Field of the invention

The present invention relates to low voltage circuit breakers and more particularly, to a braidless contact system for a modular circuit breaker in which each pole of the breaker with a single break philosophy is constructed as a module.

Background of the invention

A circuit breaker is a switching device capable of making, breaking and carrying normal currents and making and breaking currents under specified abnormal circuit conditions such as that of a short circuit or overload. A typical modular circuit breaker comprises of the following as modules: an electrical contact system, an operating mechanism, a release mechanism, a termination block and accessories. In a multi-pole modular circuit breaker, each pole in the electrical contact system is further constructed as a module. Modular pole construction has housing units called cassettes which enclose a fixed contact, an outgoing terminal and a shaft which is a rotating unit consisting of a moving contact and contact springs. The arrangement of the moving contact and the contact springs in the shaft results in the establishment of contact force between the contacts during which the moving contact rests on the fixed contact.

Current breaking techniques in the electrical contact system are single break and double break. Each pole of the single break contact system as disclosed in US patent number 5319166 comprises the fixed contact which is the incoming terminal, the moving contact and the outgoing terminal with a flexible braid which is used for establishment of electrical connection between the moving contact and the outgoing terminal irrespective of the moving contact position. The moving contact repels away from the fixed contact whenever there is an excess current flowing in the system either because of short circuit or overload condition.
During such opening of contacts, the braid gets stiffened because of exposure to the arcing gas called as fraying of the braid. Hence, the final position of the moving contact will never be achieved after successive opening and closing of the circuit breaker thereby resulting in loss of electrical continuity. Thus, the single break modular contact system uses the braid which results in problems of fraying and requires fixing of the braid to the moving contact by a process of brazing.

The double break contact system comprises the fixed contact, the moving contact and the outgoing terminal without the braid. Here, the moving contact repels away from the fixed contact and also from the outgoing terminal whenever there is an excess current flowing in the system either because of short circuit or overload condition. Unequal erosion in the contacts because of arcing during opening of the moving contact will result in the loss of electrical continuity after successive opening and closing of the breaker.

Most of the braidless contact inventions are not suitable for implementation in the cassette-shaft construction of a pole and thus are widely used in the housing type construction of the circuit breaker. Efforts have been made for implementation of braidless contact in a few cassette-shaft constructions. Reference may be made to US4484164, US4733033, US5302778 and EP2323155 A1 that disclose that the establishment of braidless joint force between the moving contact and the braidless terminal is not by direct action at the hinged area of the moving contact and there is no provision of locking of the moving contact when it repels.

Accordingly, there is a need for a braidless contact system for a modular circuit breaker with a single break technique that overcomes the drawbacks of the prior art.

Objects of the invention
An object of the present invention is to eliminate a braid in a modular electrical contact system with a single break technique without compromising on functionalities of the contact system.

Another object of the present invention is to provide braidless arrangement in a cassette-shaft construction of a modular pole along with a moving contact locking through a shaft assembly.

Yet another object of the present invention is to provide direct joint pressure establishment at joint of the moving contact and parallel limbs of a braidless outgoing terminal by making a shaft into a two-part component and using axial braidless joint springs.

Summary of the invention

Accordingly, the present invention provides a braidless contact system for a modular circuit breaker. The braidless contact system is enclosed between a pair of cassettes. The braidless contact system comprises an incoming terminal, a braidless outgoing terminal, a moving contact assembly and a two-part shaft assembly.

The incoming terminal acts as a fixed contact. The braidless outgoing terminal includes at least two limbs. Each limb of the at least two limbs includes a groove configured thereon.

The moving contact assembly includes a moving contact, a first pin and a second pin. The moving contact is adapted to rest between the at least two limbs thereby forming an assembly with the outgoing terminal. The moving contact is capable of separating from the incoming terminal. The moving contact includes a first slot and a second slot configured thereon.

The first pin is inserted in the moving contact through the first slot. The first pin includes at least two holders fitted on each side thereof. Each holder of the at least two holders enclose and compress a contact spring there between through a slot configured thereon. The second pin is inserted in the moving contact through the second slot. The second pin rests on the grooves of the at least two limbs. The second pin includes a braidless joint spring coiled on each side thereof through a pair of plain washers.

The two-part shaft assembly includes a first shaft and a second shaft. Each shaft includes a third slot and a fourth slot configured thereon. The shafts are assembled to enclose the assembly of the moving contact and the outgoing terminal such that the second pin gets inserted into the third slot.

During a normal current condition, the compressed contact springs apply a force on the moving contact that being greater than the electromagnetic repulsive force developed between the moving contact and the incoming terminal results in contact force establishment between the moving contact and the incoming terminal.

During an abnormal current condition, the electromagnetic repulsive force developed between the moving contact and the incoming terminal being greater than the force offered by the compressed contact springs acting on the moving contact results in a clockwise rotation of the moving contact about an axis of the second pin thereby separating the moving contact from the incoming terminal.

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:

Figure 1 shows a braidless contact system of a single pole assembly of a modular circuit breaker, in accordance with the present invention;

Figure 2 shows components and subassemblies of the braidless contact system of figure 1;

Figure 3 shows an exploded view of a two-part shaft assembly, in accordance with the present invention;

Figure 4 shows an assembly of pins in a moving contact, in accordance with the present invention;

Figure 5 shows an exploded view of an assembly of a braidless outgoing terminal with the moving contact, in accordance with the present invention;

Figure 6 shows an exploded view of an assembly of braidless joint springs and shafts with the assembly of figure 5;

Figure 7 shows an exploded view of fixing the two-part shaft assembly by rivets, in accordance with an embodiment of the present invention;

Figure 8 shows a riveted two-part shaft assembly of figure 7;

Figure 9 shows an exploded view of an assembly of contact springs in the riveted two-part shaft assembly of figure 8;

Figure 10 shows a cross sectional view of the two-part shaft assembly of figure 8;

Figure 11 shows another cross-sectional side view of the two-part shaft assembly of figure 8; and

Figure 12 shows moving contact locking and contact pressure establishment in the braidless contact system of figure 1.

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 braidless contact system (herein after ‘the system’) for a modular circuit breaker. The system eliminates a braid by incorporating all the braid functionality in an outgoing terminal and in a shaft assembly. The system is arranged in a cassette-shaft construction through the shaft assembly. The system uses a single break technique and provides moving contact locking and establishes direct joint pressure at joint of a moving contact and parallel limbs of a braidless outgoing terminal by making a shaft into two-part components and using axial braidless joint springs.

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 1-12, a braidless contact system (100) (herein after ‘the system (100)’) for a modular circuit breaker (not shown) in accordance with the present invention is shown. Specifically, the system (100) is used in a single pole assembly (not shown) of the modular circuit breaker. The system (100) is enclosed between a pair of cassettes (10A, 10B) such that any one of the pair of cassettes (10A, 10B) includes the system (100) assembled thereon and the other cassette covers the system (100). The system (100) comprises an incoming terminal (30), an outgoing terminal (50), a moving contact assembly (not numbered) and a two-part shaft assembly (90). The above mentioned components are assembled together on any one of the cassette (10A/10B) and enclosed/covered by the other cassette (10B/10A).

The incoming terminal (30) acts as a fixed contact. The outgoing terminal (50) is a braidless outgoing terminal. The outgoing terminal (50) includes at least two parallel limbs (40, 42) (herein after ‘the limbs (40, 42). Each limb (40, 42) includes a groove (not numbered) configured thereon.

The moving contact assembly is capable of forming an assembly (not numbered) with the outgoing terminal (50) as shown in figure 5. The moving contact assembly includes a moving contact (70), a first pin (65) and a second pin (60) as shown in figure 4.

The moving contact (70) is adapted to rest between the limbs (40, 42) thereby forming the assembly with the outgoing terminal (50). The moving contact (70) is capable of joining and separating from the incoming terminal (30) by rotating about an axis (not numbered) of the second pin (60) in any of a clockwise and anti-clockwise direction. The moving contact (70) includes a first slot (not numbered) and a second slot (not numbered) configured thereon.

The first pin (65) is inserted into the moving contact (70) through the first slot. In an embodiment, the first pin (65) is a moving pin. The first pin (65) includes at least two holders (63) fitted on each side (not numbered) thereof. Each of the at least two holders (63) enclose and compress a contact spring (62) there between through a slot (not numbered) configured thereon and guide the contact spring (62) to move smoothly for undergoing compression. Thus, the contact spring (62) is compressed inside respective holder of the at least two holders (63)

The second pin (60) is inserted into the moving contact (70) through the second slot. In an embodiment, the second pin (60) is a hinge pin. The second pin (60) is adapted to rest on the grooves of the limbs (40, 42). The second pin (60) includes a braidless joint spring (55) coiled on each side (not numbered) thereof through a pair of plain washers (53). The braidless joint spring (55) when compressed acts axially on the respective limbs (40, 42) at the hinge area to achieve joint force for good electrical conduction between the limbs (40, 42) of the outgoing terminal (50) and the moving contact (70) thereby substituting braid brazing joint. The pair of plain washers (53) distributes the force uniformly at the braidless joint area.

The two-part shaft assembly (90) encloses the assembly of the moving contact assembly and the outgoing terminal (50) therein. The two-part shaft assembly (90) and the outgoing terminal (50) are constructed by incorporating all the features of braid functionality thus eliminating braid and the process of brazing. The two-part shaft assembly (90) includes a first shaft (80) and a second shaft (82) as shown in figure 6. Each shaft (80, 82) includes a third slot (78) and a fourth slot (74) configured thereon.

The shafts (80, 82) are assembled to enclose the assembly of the moving contact assembly and the outgoing terminal (50) such that the second pin (60) along with the braidless joint spring (55) gets axially inserted into the third slot (78) and the slot on the at least two holders (63) gets aligned with the fourth slot (74). The second pin (60) inserted into the third slot (78) is fixed to the shafts (80, 82) using rivets (72). A third pin (71) for example a spring pin is inserted through the fourth slot (74) of the first shaft (80) and then through the slots in the at least two holders (63) and finally through the fourth slot (74) of the second shaft (82). However, it is understood that any other connecting means such as screws, nuts and the like can be used for assembling the shafts (80, 82). The insertion of the second pin (60) into the third slot (78) of the shafts (80, 82) causes compression of the braidless joint spring (55) that establishes the braidless joint force at the hinge area between the moving contact (70) and the limbs (40, 42) of the outgoing terminal (50). The moving contact (70) experiences the clockwise torque or anticlockwise torque about the axis of the second pin (60) depending on the orientation of the first pin (65) and the third pin (71) with respect to the alignment of the second pin (60) and the third pin (71) as illustrated in figure 11.

In accordance with the present invention, for assembling the system (100), firstly, the second pin (60) and the first pin (65) are inserted into the moving contact (70) as shown in figure 4. Then, the second pin (60) is inserted into the grooves of the limbs (40, 42) of the outgoing terminal (50) thereby fitting the moving contact (70) between the limbs (40, 42) of the outgoing terminal (50). The at least two holders (63) are then inserted into the first pin (65) from both directions. The assembly of the moving contact assembly and the outgoing terminal (50) is then assembled with the shafts (80, 82). The braidless joint springs (55) are inserted into the second pin (60) from both directions through the pair of plain washers (53). The shafts (80, 82) are assembled over the braidless joint springs (55) from both directions such that the extreme ends (not numbered) of the braidless joint spring (55) rest on the third slot (78) of the shafts (80, 82) and the second pin (60) is also inserted into the third slot (78).

The assembled shafts (80, 82) are fixed with each other enclosing the assembly of the moving contact assembly and the outgoing terminal (50) by inserting the rivets (72) as shown in figure 7. The complete riveted two-part shaft assembly (90) is shown in figure 8. Then, the contact springs (62) are inserted into the slots of the at least two holders (63). Another pair of the at least two holders (63) is placed on the free end of the contact springs (62). The contact springs (62) are compressed by pressing down the at least two holders (63) to match the slot on the at least two holders (63) with the fourth slot (74) of the shafts (80, 82). Once the slots are aligned, the third pin (71) is inserted into the second shaft (82) then through the at least two holders (63) and finally through the first shaft (80). The complete assembly of the contact springs (62) with two-part shaft assembly (90) is depicted in figures 9 and 10.

Figure 11 depicts the moving contact assembly in different positions and respective lines of force acting thereon depending on the orientation of the first pin (65) and the third pin (71). The system (100) is constructed such that when the moving contact (70) rests on the incoming terminal (30) in closed / ON state at position ‘A’ and carries a current, an electromagnetic repulsive force develops between the conductors that means between the moving contact (70) and the incoming terminal (30) because of anti-parallel current flow in the conductors. Since, the incoming terminal (30) is fixed, repulsive force results in the clockwise torque acting on the moving contact (70) about the axis of the second pin (60).

When the compressed contact springs (62) apply force on the moving contact (70), the force results in anticlockwise torque acting on the moving contact (70) from position ‘A’ until before position ‘B’ because line of action of force is on the left to the second pin (60). The clockwise torque acts on the moving contact (70) after position ‘B’ upto position ‘C’ because line of action of force is right to the second pin (60). At position ‘B’ called as dead centre, line of action of force FB is aligned to the second pin (60) hence torque is zero (TB = 0) and the direction of torque reverses at the position ‘B’.

During a normal current condition at position ‘A’, the compressed contact springs (62) apply force on the moving contact (70) which is greater than the electromagnetic repulsive force developed between the moving contact (70) and the incoming terminal (30). Hence, the moving contact (70) continues to remain in contact with the incoming terminal (30) and leads to establishment of contact force therebetween.

During an abnormal current condition at position ‘A’, the electromagnetic repulsive force developed between the moving contact (70) and the incoming terminal (30) overcomes the contact force offered by the compressed contact springs (62) acting on the moving contact (70) thereby resulting in the clockwise rotation of the moving contact (70) about the axis of the second pin (60) thereby separating the moving contact (70) from the incoming terminal (30). Once the repelled moving contact (70) crosses position ‘B’, the torque due to the compressed contact spring (62) reverses its direction and becomes clockwise which aids with the torque due to the electromagnetic repulsion. Hence, the moving contact (70) reaches position ‘C’ and gets stopped/locked thereon by the third pin (71). Thus, the locking of the moving contact (70) is achieved in the two-part shaft assembly (90).

Advantages of the invention

1. The system (100) overcomes the problems associated with the ageing of braids, fraying of braids after short circuit and the sluggish response of the system (100) during repulsion of the moving contact (70).
2. The system (100) results in increased joint force during current carrying because electrical current through the limbs (40, 42) of the braidless outgoing terminal (50) introduces electromagnetic attractive force between the limbs (40, 42). This attractive force is high during short circuit condition. Despite all this, the friction offered by the braidless joint to the repulsion of the moving contact (70) from the incoming terminal (30) during the short circuit is less when compared to the electromagnetic repulsion torque developed. Hence, the repulsion of the moving contact (70) also ensured here during the short circuit and effect of sluggish movement of the braid is eliminated.
3. The system (100) results in effective establishment of the braidless joint without compromising on functions like contact force and contact locking due to the high current flowing through the limbs (40, 42) that result in the attraction of the limbs (40, 42).
4. The system (100) results in effective area of contact at the braidless joint due to the axial force applied at the hinge point rather than away from the hinge point that results in better thermal performance of the system (100).
5. The system (100) achieves the locking of the moving contact (70) in the two-part shaft assembly (90).

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.