DESC:Contact System for Molded Case Circuit Breaker

Field of the invention

The present invention relates to electrical switches and more particularly, to a contact system for a low voltage molded case current limiting circuit breaker.

Background of the invention

In a molded case current limiting circuit breaker of the prior art, the making and breaking operation is performed by a moving contact which in turn is connected to a terminal by a flexible conductor (braid). The moving contact starts moving apart from a fixed contact due to the current loop formation. The current loop is formed such as from the moving contact-arc-fixed contact, due to which a self created magnetic field pushes the arc in to an arc chamber and hence the arc gets extinguished due to multiple splitting. The braids in the prior art have following disadvantages:
• Stiffness increase due to high temperature.
• Since braids are made of thin strands, at higher currents the braid always exerts a longitudinal force.
• Braid consumes high volume for accommodation.

Earlier attempts to avoid braid are found in U.S. Patent Numbers 4733033 and 3023292. According to these patents, when the moving contact repel opens, the mechanism initiates a shaft rotation before the moving contact starts closing again to avoid reclosing of the moving contact. So, the mechanism trip signal should be quick enough for successful fault interruption.

Another U.S. Patent Number 4484164 discloses that the moving contact is held at the open position after it has completely opened by providing CAM joint between the moving contact and a stationary element thereby enhancing the breaking capacity. But, the CAM joint of the prior art has drawbacks like:
• Friction
• Wear and tear
• Possibility of slip
• Manufacturing difficulties of CAM profile

In U.S. Patent Number 5146194, a contact pressure between the moving contact and a stationary component to which the moving contact is pivoted is adjusted by a screw tightening. However, the criticality should be maintained while tightening the screw for achieving a definite contact pressure between the moving contact and the stationary component to which the moving contact is pivoted.

Accordingly, there is a need for a contact system/arm for a molded case circuit breaker that uses a spring flip mechanism avoiding slip possibility and prevents manufacturing difficulties of a complex CAM profile of the prior art.

Objects of the invention

An object of the present invention is to provide a reliable and efficient flip action that ensures holding of a moving contact at open position after complete opening thereof until a mechanism operates.

Another object of the present invention is to prevent manufacturing difficulties of a complex CAM profile of the moving contact.

Yet another object of the present invention is to provide easier manufacturability.
Still another object of the present invention is to provide reliable functionality avoiding possibility of slipping.

Further object of the present invention is to increase mechanical life of the moving contact.

Summary of the invention

Accordingly, the present invention discloses a contact system for a molded case circuit breaker. The contact system comprises a fixed contact, a braid-less moving contact pivoted on a holder and a spring assembly operatively mounted between a wall of a shaft and the holder. The braid-less moving contact includes a spring configured on a side thereof. The spring configured on the side of the moving contact is a Belleville spring. The spring ensures a seamless current flow between the holder and the moving contact. When the current flowing through the molded case circuit breaker increases more than a threshold value, electrodynamic forces between the moving contact and the fixed contact overcomes the force of the spring assembly and allows the moving contact to rotate about the pivot on the holder. The spring assembly crosses a dead centre making the moving contact to flip and held in an open position until a circuit breaker mechanism operates.

Brief description of 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 front view of a contact system for a molded case circuit breaker, in accordance with the present invention;
Figure 2 shows an assembly of a spring providing contact pressure between a moving contact and a holder, in accordance with the present invention;

Figure 3a shows a symmetrical sectional view of the contact system of figure 1 in ON condition;

Figure 3b shows a symmetrical sectional view of the contact system of figure 1 when the moving contact is opening and crossing a dead center of the spring assembly, in accordance with the present invention; and

Figure 3c shows a symmetrical sectional view of the contact system of figure 1 after the moving contact has completely opened and flipped, 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 embodiments.

The present invention provides a contact system for a molded case circuit breaker. The contact system comprises a braid-less moving contact that after completely repelling reaches an open position, avoiding re-closure until a mechanism operates. The contact system uses reliable and efficient flip action of a spring assembly thereby increasing an electrical life of the molded case circuit breaker.

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 1-3c, a contact system (100) for a molded case circuit breaker (hereinafter referred as “circuit breaker”) in accordance with the present invention is shown. The contact system (100) comprises a moving contact (10), a fixed contact (20), a holder (30), a shaft (40) and a spring assembly (50).

The moving contact (10) is a single member pivoted on the holder (30) as shown in figure 1. In an embodiment, the moving contact (10) is a braid-less moving contact. When a current loop is formed, the moving contact (10) after completely repelling reaches an open position. The opening of the moving contact (10) avoids re-closure thereof until a mechanism (not shown) of the circuit breaker (not shown) operates.

The holder (30) is a stationary component of the circuit breaker. The moving contact (10) includes a spring (4) configured on a side thereof as shown in figure 2. In an embodiment, the spring (4) is a Belleville spring that ensures a seamless current flow between the holder (30) and the moving contact (10). In an embodiment, the moving contact (10), the fixed contact (20) and the holder (30) forms a copper path of the circuit breaker. The entire copper path provides an unbridled access for the current flow. The contacts (10, 20) are designed in such a way that during short circuit conditions, an electromagnetic force acts between the moving contact (10) and the fixed contact (20).

The moving contact (10) at one end (not numbered) is pivoted to the shaft (40) and has an independent rotation for certain degree that is exploited by the electromagnetic forces to open a circuit, in such situation the shaft (40) remains in a closed position until being steered to an open position by the mechanism of the circuit breaker. In an embodiment, the moving contact (10) along with the spring (4) is housed inside the shaft (40). The shaft (40) is a rotating shaft. The shaft (40) is capable of making or breaking the current path based on the operation of the mechanism of the circuit breaker.

The spring assembly (50) is operatively mounted between a wall (not numbered) of the shaft (40) and the holder (30). The distance between the shaft (40) and the holder (30) is designed in such a way that there is sufficient spring force to overcome the electrodynamic force between the moving contact (10) and the holder (30) at very high fault currents thereby ensuring proper electrical connection therebetween.

The spring assembly (50) ensures a contact pressure between the moving contact (10) and the fixed contact (20) at ON condition as shown in fig 3a. The spring assembly (50) is designed in such a way that when the current passing through the circuit breaker increases more than a threshold value, the electrodynamic forces between the contacts (10, 20) overcome the spring force and allow the moving contact (10) to rotate about the pivot on the holder (30). During this course of time, the spring assembly (50) crosses a dead centre as shown by an arrow “X” in fig 3b thereby making the moving contact (10) to flip. Once the spring assembly (50) crosses the dead centre, the moving contact (10) is held in the open position until the circuit breaker mechanism operates as shown in fig 3c.

Advantages of the invention

1. The contact system (100) provides reliable and efficient flip action of the moving contact (10) that ensures holding of the moving contact (10) in the open position after complete opening thereof until the mechanism operates.
2. The contact system (100) is easy to manufacture.
3. The contact system (100) provides reliable functionality avoiding possibility of slipping.
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 contact system (100) for a molded case circuit breaker, the contact system (100) comprising:
a fixed contact (20), a braid-less moving contact (10) pivoted on a holder (30) and a spring assembly (50) operatively mounted between a wall of a shaft (40) and the holder (30), characterized in that,
the braid-less moving contact (10) includes a spring (4) configured on a side thereof, the spring (4) being capable of ensuring a seamless current flow between the holder (30) and the moving contact (10),
wherein, when the current flowing through the molded case circuit breaker increases more than a threshold value, electrodynamic forces between the moving contact (10) and the fixed contact (20) overcomes the force of the spring assembly (50) and allows the moving contact (10) to rotate about the pivot on the holder (30), the spring assembly (50) then crosses a dead centre thereby making the moving contact (10) to flip and held in an open position until a circuit breaker mechanism operates.

2. The contact system (100) as claimed in claim 1, wherein the spring (4) configured on the side of the moving contact (10) is a Belleville spring.