CLIAMS:We Claim:

1. A plug-in contact system (100) for a molded case circuit breaker (200), the molded case circuit breaker (200) having a movable part (120) and a fixed part (140), the movable part (120) having a plurality of conducting terminals (105) configured on a rear frame (110) thereof and the fixed part (140) having a plurality of base terminals (125) configured thereon, the plug-in contact system (100) comprising:
a moving component (10) mounted on the plurality of conducting terminals (105);
a fixed component (20) mounted on the plurality of base terminals (125);
a tulip contact (30); and
a pair of garter springs (40) placed over the tulip contact (30) from either side, characterized in that
the tulip contact (30) is a single component hollow tube having a plurality of slits (26) equally cut thereon from a top portion (22) and a bottom portion (24) such that remaining part in the hollow tube acts as an individual leaf of the tulip contact (30) thereby reducing an insertion force and providing a surface finish to ensure uniform distribution of force of the pair of the garter spring (40) thereon.

2. The plug-in contact system (100) as claimed in claim 1, wherein the movable component (10) is inserted into the top portion (22) of the tulip contact (30).

3. The plug-in contact system (100) as claimed in claim 1, wherein the fixed component (20) is inserted into the bottom portion (24) of the tulip contact (30).

4. The plug-in contact system (100) as claimed in claim 1, wherein the moving component (10) is a movable copper stud.

5. The plug-in contact system (100) as claimed in claim 1, wherein the tulip contact (30) is made from a single hollow copper tube.

,TagSPECI:Field of the invention

The present invention relates to a switching device and more particularly, to a plug-in contact system for a molded case circuit breaker.

Background of the invention

In general, a molded case circuit breaker is an electrical device that protects electrical loads and power systems by breaking an electrical circuit in case of an abnormal condition such as overloads, short circuit or ground fault. The molded case circuit breakers are connected to an electrical source and to loads by means of cables at the terminals. Termination is carried either by lugs, box clamps and extended spreader terminals or by direct cable terminations. However, installation and removal of the circuit breaker in such termination is not an easy task and hence, plug-in terminals are employed as an alternative for the same.

Plug-in terminals for the circuit breakers provide an easy means of termination as they offer quick, safe and easy installation, maintenance and replacement of the circuit breakers without disturbing the power connections. It consists of a movable conducting terminal directly obtained from a rear frame of the fixed circuit breaker and a stationary part assembled directly on a base of the plug-in cubicle where the circuit breaker is to be installed.

In the prior art system, the stationary part acts as a female part of a tulip contact system which consists of a number of copper fingers coupled together by means of a garter spring or a conducting circular ring. This tulip contact system is then assembled to a plug-in base. A moving terminal or a male component protruding out of the circuit breaker is a copper stud connected to the base of the circuit breaker terminals. As the cylindrical male contact is inserted into the female contact, the tulip contact fingers extend radially in a circumference of the male contact stud. Each of the fingers bends axially inward with respect to the stud such that an internal diameter of the female contact sleeve is shorter than an external diameter of the cylindrical male contact so that a proper electrical and mechanical contact is formed between them.

However, during insertion process in the prior art tulip system, the frictional force between the female contact fingers and the male stud is very high as the assembly of contact fingers around a circular frame is not an uniform outcome process as the alignment of the components is not at all guaranteed. Also, during disengagement, the probability of extensive wear and tear of contact surfaces becomes very high due to the high frictional force.

Moreover, manufacturing of the tulip contact fingers by maintaining the required shape for proper contact joints is quite a complex engineering process. Manufacturing (bending) of the tulip contacts is another mammoth task as one has to maintain the desired radius and surface finish for proper contact surface mating. In the prior art, one has to make a fine blank and then make desired bend in it. This process requires higher level of precision as one has to maintain the same radius in all the leaves which are to be assembled together to make the tulip contact system.

Figure 1 shows a prior art assembly of tulip leaves having a lower contact and a male component. In this kind of tulip contact assembly, there are number of individual tulip leaves assembled together with the help of the garter spring or the circular ring. In terms of electrical performance, the reliability of such tulip contact system is lower as it is very difficult to maintain the same radius in all the leaves for proper contact mating and maintain uniform contact pressure. The area of contact mating surface mainly depends upon the mating radius of the individual tulip contact finger.

Due to the manufacturing process limitations, the mating radius of every individual tulip contact finger is not maintained uniform. This reduces the actual contact mating surface area and results in formation of heat spot at the contact joints during service. Whatever the contact pressure is generated between the moving contact and the fixed contact with the tulip system is only because of the garter spring which may not be uniformly distributed on account of the non-symmetrical tulip design and surface finish. Owing to this, problems like high insertion force, heavy wear and tear and high temperature rise results during service.

Accordingly, there exists a need to provide a plug-in contact system for a molded case circuit breaker that overcomes the drawbacks of the prior art.

Objects of the invention

An object of the present invention is to provide a single component tulip contact that gives higher mechanical strength to a plug-in contact system.

Another object of the present invention is to provide good surface finish and uniform spring force at all contact mating points.

Summary of the invention

Accordingly, the present invention provides a plug-in contact system for a molded case circuit breaker. The molded circuit breaker comprises a movable part and a fixed part. The movable part includes a plurality of conducting terminals configured on a rear frame thereof. The fixed part includes a plurality of base terminals configured thereon. The plug-in contact system comprises a moving component, a tulip contact, a fixed component and a pair of garter springs.

The moving component is mounted on the plurality of conducting terminals and inserted into a top portion of the tulip contact. The moving component is a movable copper stud. The fixed component is mounted on the plurality of base terminals and inserted into a bottom portion of the tulip contact. The pair of garter springs is placed over the tulip contact from either side.

The tulip contact is made from a single hollow copper tube. The tulip contact is a single component hollow tube and comprises a plurality of slits equally cut thereon from the top portion and the bottom portion such that remaining part in the hollow tube acts as an individual leaf of the tulip contact thereby reduces an insertion force and provides a surface finish and ensures uniform distribution of force of the pair of the garter spring thereon.

Brief description of the drawings

Figure 1 shows an assembly of tulip leaves, in accordance with a prior art;

Figures 2a and 2b show a molded case circuit breaker assembly, in accordance with the present invention;

Figure 3a shows a plug-in contact system, in accordance with the present invention;

Figure 3b shows a sectional view of the plug-in contact system of figure 3a;

Figure 4 shows an exploded view of the plug-in contact system of figure 3a;

Figure 5 shows an assembly view of the plug-in contact system of figure 3a; and

Figure 6 shows a tulip contact of the plug-in contact system of figure 3a.

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 embodiments.

The present invention provides a plug-in contact system (hereinafter “the system”) for a molded case circuit breaker. The system comprises a single component tulip contact with provision of a plurality of slits thereon. Each remaining part/non-cut part of the tulip contact acts as a leaf spring that further increases a contact pressure and contact mating and provides higher mechanical strength to the system.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.

Referring to figures 2a and 2b, a molded case circuit breaker assembly (200) (hereinafter “the assembly (200)”) in accordance with the present invention is shown. The assembly (200) comprises a movable part (120) and a fixed part (140). The movable part (120) includes a plurality of conducting terminals (105) configured on a rear frame (110) thereof. The fixed part (140) includes a plurality of base terminals (125) configured thereon. The plurality of conducting terminals (105) is inserted into the plurality of base terminals (125) as shown in figure 2b.

Now referring to figures 3a-6, a plug-in contact system/electrical contact system (100) (hereinafter “the system (100)”) for the assembly (200) in accordance with the present invention is shown. Specifically, the system (100) is designed for the molded case circuit breaker. However, it is understood that the system (100) may be suitably used for any other type of the circuit breaker.

The system (100) comprises a moving component (10), a fixed component (20), a tulip contact (30) and a pair of garter springs (40). The moving component (10) is mounted on the plurality of conducting terminals (105) and inserted into a top portion (22) of the tulip contact (30). In an embodiment, the moving component (10) is a movable copper stud. However, it is understood that the movable stud may be made of any other conducting material. The fixed component (20) is mounted on the plurality of base terminals (125) and inserted into a bottom portion (24) of the tulip contact (30). The pair of garter springs (40) is placed over the tulip contact (30) from either side thereby forming a firm contact mating.

As shown in figure 6, the tulip contact (30) is a single hollow tube (not numbered) of a fixed thickness. In an embodiment, the tulip contact (30) is made from single hollow copper tube. The tulip contact (30) includes a plurality of slits (26) cut thereon. The plurality of slits (26) is equally cut all over the tulip contact (30) from the top portion (22) and the bottom portion (24). In an embodiment, the plurality of slits (26) is made alternately in the hollow tube such that each remaining part in the hollow tube acts as an individual leaf of the tulip contact (30).

If four slits are cut on each top and bottom side of the tulip contact (30) then eight leaf springs are obtained from the single tulip contact. This kind of arrangement ensures concentricity of the leaves. The insertion force required is reduced drastically by maintaining symmetricity and a surface finish in the tulip (leaves) radius. Furthermore, such design also enhances uniform distribution of the force of the pair of garter springs (40) all over a diameter of the tulip contact (30). The tulip contact (30) connected to the plurality of base terminals (125) is further connected to a power source (not shown) and to loads.

Again referring to figures 2a-6, during insertion of the movable part (120) into the fixed part (140) of the assembly (200), each moving component (10) gets inserted into the tulip contact (30) and held in place by the fixed component (20) mounted on the plurality of base terminals (125).

The plurality of slits (26) provided in the hollow tube of the tulip contact (30) gives spring action and increases the contact pressure during a service condition. This simpler process of manufacturing makes the tulip contact (30) cheaper, gives higher yield and more efficient performance.

The plurality of slits (26) cut in the tulip contact (30) themselves act as leaf springs which further add to the contact pressure between the tulip contact (30) and the moving component (10). Therefore, the resultant contact pressure increases and offers less contact resistance and higher conductivity so as to lower the heat generation. So, this double benefit of spring action from within makes the system (100) more reliable as mating is made mechanically as well as electrically.

Advantages of the invention

1. The single component tulip contact (30) provides higher mechanical strength to the system (100) thereby increases capacity of withstanding higher electrodynamics forces generated during short circuit fault.
2. The system (100) provides higher contact mating surface area between the moving component (10) and the tulip contact (30) thereby helping in reducing the contact joint resistance.
3. The system (100) provides high quality surface finish that reduces thermal losses.
4. The moving component (10) experiences less wear and tear and opposing insertion force on account of the tulip’s singular nature with good surface finish and uniform spring force at all contact mating points.
5. Plurality of contact fingers is eliminated and hence, an improper alignment and the improper contact mating are highly reduced.
6. Ease of assembly as the number of components is reduced. Also, the time required for assembly and cost involved for manufacture is reduced.
7. With provision of the plurality of slits (26) in the tulip contact (30), each remaining part acts as leaf spring which further increases the contact pressure and contact mating.
8. Proper contact mating reduces the resistance between the contact joints and hence, lowers heat generation.
9. The provision of the plurality of slits (26) given in the tulip contact (30) help in maintaining adequate air gap which enforces proper air circulation and reduces heat generation.
10. The system (100) facilitates easy installment, stronger structure and higher reliability.

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.