Claims:We claim:

1. A miniature circuit breaker (MCB) with improved circuit breaking mechanism, the miniature circuit breaker having a magnetic trip unit which provides a trip signal to an operating mechanism, a thermal release unit, magnetic release unit, terminals, a box clamp arranged in a common housing, din clips to mount miniature circuit breaker on a din rail, a moving contact along with a with fixed contact for current continuity, an arc chute for quenching arc, and an arc runner for giving a magnetic force to pull the arc towards arc chute, the miniature circuit breaker comprising:
a fixed runner configured for improving the arc initiation and immobility phases, the fixed runner held behind the fixed contact for containing orthogonal flux therein, the fixed runner having a base, a slanting surface extending upward from the base and a flat surface extending horizontally from the slanting surface;
a runner aid configured for improving the arc running and quenching phases, the arc runner held in parallel along the arc runner, the runner aid having a slot configured on rear surface thereof for accommodating the runner aid in the common housing; and
a permanent magnet slot motor for low current breaking, the permanent magnet slot motor configured parallely above the arc runner and in proximity to the moving contact and fixed runner, the permanent magnet slot motor having a first member and a second member extending from the first member in slanted configuration.

2. The miniature circuit breaker as claimed in claimed 1, wherein the base of the fixed runner rests on the common housing, the slanting surface aligns to the fixed contact and the flat surface rests on the magnetic core.

3. The miniature circuit breaker as claimed in claimed 1, wherein the slot configured on rear surface of runner aid restricts the movement of the runner aid in X and Y axis.

4. The miniature circuit breaker as claimed in claimed 1, wherein the fixed runner and the runner aid are made of magnetic material.

, Description:Field of the invention

The present invention relates miniature circuit breaker with improved circuit breaking mechanism, and more particularly, to a miniature circuit breakers and circuit breakers operating on both alternating and direct current source, where faster arc quenching and breaking at low currents are required.

Background of the invention

In low voltage distribution system, circuit breakers provide rapid and reliable protection against both overload and short-circuit currents. The overload protection module consist of a bimetallic element as an actuator and the short-circuit protection module consist of a coil and an armature as an actuator. Signal from both these modules are given to the mechanism for opening the contacts, thereby interrupting the circuit during abnormal condition.

When a circuit breaker is subjected to short circuit fault, the contacts start separating and an arc is struck across its contacts. Specifically, contact opening is facilitated by the repulsion forces acting on the contacts and the armature actuator force exerted by the short circuit protection module through the mechanism. The electromagnetic forces and gas dynamic forces developed by the arc pushes the arc towards an arcing chamber and finally quenching the arc. The time taken by the contacts to sense the fault and to the instant final quenching occurs is generally called as arcing time. The total arcing time can be divided into four phases such as initiation time, immobility time, running time and splitting time. Efficient contact system design and improved breaking can be achieved if total arcing time and energy let through is very less.

Various patent and patent application such as PCT/GB2010/001669, CN 203456404 and CN203553410 have been directed towards improving performance of a circuit breaker depends by reducing magnitude of the fault current it allows and the time up to which it is flowing through the breaker. Specifically, Chinese patent application CN 203456403 discloses an arc extinction promoting device for a circuit protection device. The arc extinction promoting device is near the moving contact of the circuit protection device and is arranged in the circuit protection device. The device disclosed in CN 203456403 uses permanent magnet and set of MS components placed on either side of the contact for higher blow out force. However, their mechanism of working is complex and requires many additional components.

Accordingly, there exists a need to provide a circuit breaker device with improved circuit breaking capacity which overcomes abovementioned drawbacks.

Objects of the invention

An object of the present invention is to provide a circuit breaker which sense fault in an earlier stage and quench the arc at lower current with lesser time.

Another object of the present invention is to operate miniature circuit breaker at higher fault currents of the order of10kA (both AC and DC) and low currents of the order of 0.5A (More significant in DC).

Summary of the invention

Accordingly, the present invention provides a miniature circuit breaker (MCB) with improved circuit breaking mechanism. The miniature circuit breaker includes a magnetic trip unit which provides a trip signal to an operating mechanism, a thermal release unit, magnetic release unit, terminals, a box clamp arranged in a common housing, din clips to mount miniature circuit breaker on a din rail, a moving contact along with a with fixed contact for current continuity, an arc chute for quenching arc, a permanent magnet slot motor and an arc runner for giving a magnetic force to pull the arc towards arc chute.

Specifically, the miniature circuit breaker comprises a fixed runner for improving the arc initiation and immobility phases. The fixed runner is held behind the fixed contact for containing orthogonal flux therein. The fixed runner comprises a base, a slanting surface extending upward from the base and a flat surface extending horizontally from the slanting surface.

Further, the miniature circuit breaker comprises a runner aid for improving the arc running and quenching phases. The arc runner is held in parallel along the arc runner. The runner aid includes a slot configured on rear surface thereof for accommodating the runner aid in the common housing of the circuit breaker.

Furthermore, the miniature circuit breaker comprises a permanent magnet slot motor configured parallely above the arc runner and in proximity to the moving contact and fixed runner, the permanent magnet slot motor having a first member and a second member extending from the first member in slanted configuration.

Brief description of the drawings

Figure 1 shows a miniature circuit breaker arrangement in ON condition;

Figure 2 shows a single break contact system having components for improved circuit breaking in accordance with the present invention;

Figure 3 shows a contact system of a circuit breaker;

Figure 4 shows isometric views of a fixed runner, a fixed contact and a magnetic core of a circuit breaker, in accordance with the present invention;

Figure 5 shows an isometric view of a runner aid and an arc runner of a circuit breaker, in accordance with the present invention;

Figure 6 show a slot motor of the prior art; and

Figure 6A shows a permanent magnet slot motor of the contact system of a circuit breaker, 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 miniature circuit breaker (MCB) with improved circuit breaking mechanism. The miniature circuit breaker operates at higher fault currents of the order of 10 kA (both AC and DC) and low currents of the order of 0.5A (DC).

Referring now to figure 1, there is shown a miniature circuit breaker MCB (100) in ON condition. The MCB (100) includes a magnetic trip unit (10), a mechanism (12), a thermal release unit (14), a magnetic core (16), terminals (18, 20), a box clamp (22, 24) arranged in a common housing (26), Din clips (28, 30) to mount the MCB in din rail system. The MCB (200) further includes a moving contact (32) which makes contact with a fixed contact (34) for current continuity. The MCB (100) furthermore includes arc chute (36) for quenching the arc, and a arc runner (40) which gives magnetic force to pull the arc towards arc chute (42).

The magnetic trip unit (10) gives tripping signal to a mechanism (12) in case of short circuit fault condition. The contact system (50) of the MCB (100) is designed in such a way that, when fault current exceeds the rated value of the circuit breaker, Lorentz forces are developed which pulls the moving contact (32) and a fixed contact (34) apart leading to arc formation. By this, first two phases of arcing, initiation and immobility are addressed in conventional circuit breakers.

The arc being developed need to be quenched at the earliest. This is addressed in the next two phases of arcing (running and quenching) in the conventional circuit breaker. This is achieved by introducing arc runner (40) for arc to shift its root and also a proper arc chamber (40a) where arc is deionized fully. However, for achieving better arc running and quenching time, the forces developed across the arc column should be high enough to pull the arc towards arc chute (42).

Accordingly, the present invention provides then MCB (100) which provides mechanism for better arc running and quenching time. Figure 2 shows a single break contact system of the miniature circuit breaker (MCB) of figure 1, with improved circuit breaking mechanism. Figure 2 is described in conjunction with the components of miniature circuit breaker as shown in figure 1. As shown in figure 2, the miniature circuit breaker (100) with single break contact system comprises a fixed runner (44) and a runner aid (46) configured for improving the arc running and quenching phases. The miniature circuit breaker (100) also comprises a permanent magnet slot motor (38).

The fixed runner (44) is held behind the fixed contact (34) for containing orthogonal flux therein. During the normal short circuit conditions, the required electromagnet force for the arc is achieved by the rotating flux developed across magnetic core, the permanent magnet slot motor (38), arc runner (40), and the arc chute (42). The flux developed due to the current flow in fixed contact (34) gets reduced due to current reversal. The fixed runner (44) held behind fixed contact (34) is capable of containing the orthogonal flux developed due to current reversal which drastically improve the arc force during the initial arcing phases. In a preferred embodiment, the fixed runner (44) is made of magnetic material.

The fixed runner (44) includes a base (44a), a slanting surface (44b) extending upward from the base (44a) and a flat surface (44c) extending horizontally from the slanting surface (44b). Specifically, the base (44a) of the fixed runner (44) rests on the common housing (26), the slanting surface (44b) aligns to the fixed contact (34) and the flat surface (44c) rests on the magnetic core of the MCB (100). The fixed runner (44) offers the flux, a lower reluctance path until the arc reaches the arc chute (42) and also enhance the repulsion force acting on the contacts (32,34) which aids in faster contact opening.

Further, the runner aid (46) is held in parallel along the arc runner (40). The runner aid (46) is a strip like structure held in position at base of the housing (26) and upper face (46a) of the runner aid (46) is aligned to the arc runner (40). The runner aid (46) includes a slot (46b) configured on rear surface thereof for accommodating the runner aid (46) in the common housing (26). In a preferred embodiment, the runner aid (46) is made of magnetic material.

In an embodiment, the runner aid (46) is a magnetic strip material folded and bended to create the required geometry for accommodating the runner aid (46) in common housing (26). Specifically, the slot (46b) configured on rear surface of runner aid (46) restricts the movement of the runner aid (46) in X and Y axis.

The runner aid (46) acts as an open core magnet which increases the magnetic intensity along the arc running path, which causes more orthogonal flux to act on the arc. This significantly improves the arc blow out force, which reduces the arc running time and hence the arc is pulled towards arc chute (42) where the arc splits into a number of short arcs and finally gets extinguished.

The runner aid (46) and the fixed runner (44) significantly contribute for the arc pull force, which leads to better circuit interruption.

The permanent magnet slot motor (30) is configured parallely above the arc runner (40) and in proximity to the moving contact (32) and fixed runner (44). Specifically, the permanent magnet slot motor (38) has an improved profile for low current breaking. The permanent magnet slot motor (38) includes a first member (38a) and a second member (38b) extending from the first member (38a) in slanted configuration. The profile the permanent magnet slot motor (38) has been optimized for shapes and checked the EMF at F1 & F2 position which gives higher force compared to MS component of the prior art having a hook shaped profile. Further, thickness the permanent magnet slot motor (38) is increased to 1.6mm and made of ALNICO as compared to MS of the prior art. Specifically, the permanent magnet slot motor (38) profile optimized to accommodate in the existing Housing & cover. Also, by changing the slot motor into permanent Magnet, the EMF has been increased. Figure 6 shows the slot motor of the prior art, whereas figure 6A shows the permanent magnet slot motor (38) in accordance with the present invention.

In case of direct currents, breaking the circuit during low currents is equally significant to breaking during short circuit conditions. Due to the non-availability of natural current zero phenomena, as in alternating currents (AC), the arc quenching becomes extremely difficult even at low currents. This is because the Lorentz and the magnetic armature force, at low currents, are not significant to drive the arc away from the contacts. So arc root is struck between the fixed button (34a) of the fixed contact (34) and the moving contact (32), called as standing arcs, and which eventually lead to contact erosion.

In case of miniature circuit breaker (100), to be suitable for direct current applications, the breaker has to be subjected, manually, for breaking at low currents (as low as 1A). This is because at such low currents neither the thermal release (14) nor the magnetic release (16) issue trip signals to the mechanism (12).

Hence, the miniature circuit breaker (100) is subjected for make-break operations, at rated voltage, for 1A, 2A, 4A, 8A, 16A, 32A, 63A and 150A respectively and the total arcing time is monitored. Of the above current rating, the rating which has a maximum arcing time is considered as the critical current. The arcing time, at critical current, may be of the order of several milliseconds. This is where the role of permanent magnet slot motor (38) becomes significant. The profile and orientation of the permanent magnet slot motor (38) are in such a way that, aided by the fixed runner (44) and the runner aid (46), the total arcing time, at critical current, has been significantly reduced to 10 milliseconds.

As discussed earlier, when the contacts (32 and 34) are opened at low currents, the arc is struck between the fixed button (34a) and the moving contact (32). Here, both the Lorentz and magnetic armature forces are insignificant to drive the arc roots away. With the use of the permanent magnet slot motor (38), the forces generated due to magnetic field quickly displaces the arc root away from fixed button (34a) and the moving contact (32) towards the arc chute (42), where the arc gets split into several shorter arcs and eventually die out.

With the introduction of permanent magnet, the MCB (100) become polarity dependent. Hence the shape and orientation of the permanent magnet slot motor (38) enhances the low current performance of the MCB (100).

Advantages of the invention

1. The miniature circuit breaker (100) of the present invention sense fault in an earlier stage and quench the arc at lower current with lesser time.

2. The miniature circuit breaker (100) operate at higher fault currents of the order of10kA (both AC and DC) and low currents of the order of 0.5A (More significant in DC).

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.