WO2003017302A1

WO2003017302A1 - Circuit breaker for low-voltage currents

Info

Publication number: WO2003017302A1
Application number: PCT/EP2002/008214
Authority: WO
Inventors: Bianc Giuseppe Bertolotto; Davide Malacalza
Original assignee: Abb Service S.R.L.
Priority date: 2001-07-23
Filing date: 2002-07-23
Publication date: 2003-02-27
Also published as: CN100470698C; CN1465080A; ATE373867T1; DE60222560T2; ITMI20011573A0; EP1412956B1; ITMI20011573A1; DE60222560D1; EP1412956A1

Abstract

A circuit breaker for low-voltage currents, comprising an enclosure that contains moving contact means and fixed contact means, the moving contact means comprising at least one moving contact, the fixed contact means comprising at least one fixed contact, a kinematic chain that comprises a plurality of levers that move the moving contact between an open position, in which the contacts are separated, and a closed position, in which they are coupled, and a mechanism that ensures a substantially constant force between the contacts in the closed position, its particularity consisting of the fact that the mechanism comprises a single body that has a first rigid element, which is associated with at least one of the fixed and moving contacts, and a second rigid element, which is arranged adjacent to the first rigid element and is connected thereto by virtue of a flexible hinge constituted by a first elastic and resilient element.

Description

CIRCUIT BREAKER FOR LOW-VOLTAGE CURRENTS

DESCRIPTION

The present invention relates to a circuit breaker for low-voltage currents having improved characteristics; more particularly, the invention relates to an automatic low- voltage circuit breaker in which the contact force between the moving contact and the fixed contact of the circuit breaker is kept constant over time by virtue of a solution that is structurally simple and functionally effective. As is known, circuit breakers are protective devices which, when an electrical fault occurs in the circuit in which they are inserted, trip and interrupt the flow of current; for this purpose, they are provided with electrical contacts constituted by two conducting metallic parts, one of which is fixed and termed fixed contact or stationary contact, the other one being movable and being termed moving contact. The moving contact is actuated by a kinematic chain that allows its coupling or separation with respect to the corresponding fixed contact, accordingly closing or opening the circuit.

A very important parameter for correct operation of the circuit breaker is constituted by the contact force, i.e., the force that occurs between the contacts when they are mutually coupled. The value of this force, which in the closed condition must ensure adequate pressure between the coupled parts, on the one hand is inversely proportional to the contact resistance, i.e., to the electrical resistance produced by physical contact between the conducting parts, and on the other hand is directly proportional to the contact opening time, i.e., the time that elapses between the beginning of the separation of the contacts and their complete separation. Since a fundamental requirement of circuit breakers is contact separation speed, which must be as high as possible, due to the above explained reason it is necessary to have a low contact force; this leads to a high contact resistance, for which a small value is instead desirable. It is therefore evident that during the design of the circuit breaker it is necessary to pay particular attention in deciding the value of this contact force, taking into account the contrasting requirements of short opening time and low contact resistance.

In current circuit breakers, the contact force is obtained by means of the action of the kinematic chain, whose components are designed specifically to ensure that it has a predefined value; moreover, in order to maintain the performance of the circuit breaker, said force must remain constant and equal to the intended value throughout the useful life of the circuit breaker. Unfortunately, during the normal operating cycle the components of the circuit breaker are subject to variations with respect to the initial design conditions; in particular, the electrical contacts are subjected to significant wear and erosion, due mainly to the presence of electrical arcs generated during opening and closure operations. These effects are so important that the shape of the contacts changes over the useful life of the circuit breaker and can lead to an insufficient electrical coupling between the parts in contact.

In order to obviate this at least partially and ensure adequate electrical coupling, even in the presence of worn contacts, the kinematic chain must be able to compensate for the variations that have occurred. This compensation is usually performed by using one or more springs. Accordingly, even though it is possible to have an adequate contact between the electrical parts, the contact force does not remain constant throughout the useful life of the circuit breaker, thus affecting directly the opening time and the resistance of the contacts and ultimately causing a general degradation of the electrical performance of the circuit breaker. One solution to the problem cited above is currently to act on the configuration of the kinematic chains, but although this allows partial improvements, it usually leads to greater complexity of the circuit breaker, with a consequent increase in production and assembly costs. The aim of the present invention is to provide a low-voltage automatic circuit breaker in which the contact force between the moving contact and the fixed contact can be kept substantially constant throughout the useful life of the circuit breaker. Within the scope of this aim, an object of the present invention is to provide a circuit breaker for low-voltage currents in which the contact opening time and the electrical resistance of the contacts do not vary over the useful life of the circuit breaker. Another object of the present invention is to provide a circuit breaker for low- voltage currents whose performance is substantially invariant over time.

Another object of the present invention is to provide a circuit breaker for low- voltage currents in which a constant contact force is maintained throughout the life of the circuit breaker without affecting negatively the complexity of the kinematic chain that is used. Another object of the present invention is to provide a circuit breaker for low- voltage currents that is highly reliable, relatively simple to manufacture and at competitive costs.

This aim, these objects and others that will become apparent hereinafter are achieved by a circuit breaker for low-voltage currents, comprising an enclosure that contains moving contact means and fixed contact means, the moving contact means comprising at least one moving contact, the fixed contact means comprising at least one fixed contact, a kinematic chain that comprises a plurality of levers that move the moving contact between an open position, in which the contacts are separated, and a closed position, in which they are coupled, and a mechanism that ensures a substantially constant force between the contacts in the closed position, characterized in that said mechanism comprises a single body that has a first rigid element, which is associated with at least one of said fixed and moving contacts, and a second rigid element, which is arranged adjacent to said first rigid element and is connected thereto by virtue of a flexible hinge constituted by a first elastic and resilient element. Further characteristics and advantages of the invention will become apparent from the description of preferred but not exclusive embodiments of the automatic low-voltage circuit breaker according to the present invention, illustrated by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a schematic view of a portion of an automatic low-voltage circuit breaker, illustrating in particular the moving and fixed contacts, according to a known type of configuration;

Figure 2 is a view of a first embodiment of the fixed and moving contacts that can be used in the circuit breaker according to the present invention; Figure 3 is a view of a second embodiment of the fixed and moving contacts that can be used in the circuit breaker according to the present invention; and Figure 4 is a view of a third embodiment of the fixed and moving contacts that can be used in the circuit breaker according to the present invention. Figure 1 partially illustrates an automatic circuit breaker for low-voltage currents of a per se known type, which comprises an enclosure 9 that contains moving contact means and fixed contact means. In the illustrated embodiment, the fixed contact means comprise at least one fixed contact 1 that has a conducting body la on which a contact plate lb is fixed; in turn, the moving contact means comprise a moving contact 2 that has a contoured conducting body 2a on which a contact plate 2b, suitable for electrical coupling to the corresponding plate lb, is fixed. The moving contact 2 is actuated by an appropriate kinematic chain, generally designated by the reference numeral 15 in Figure 1, which comprises, according to embodiments that are widely known in the art and are therefore not described in detail, multiple levers that move the moving contact 2 between an open position, in which the contacts are separated, and a closed position, in which they are coupled and the plates lb and 2b are in physical contact with each other.

Furthermore, the circuit breaker is provided with a suitable constant-force mechanism, i.e., a mechanism that is suitable to generate a substantially constant force in response to a stress in the form of a linear and/or rotational movement.

Generally, these mechanisms are provided by using rigid elements that are mutually connected by appropriate hinges, with which springs, usually of the torsion type, are associated. A conventional constant-force mechanism is constituted, for example, by two rigid link rods connected by means of a rotational hinge; the end of a first link rod is pivoted to a fixed part by means of an additional rotational hinge and the end of the second link rod is connected to a slider by virtue of another rotational hinge. A torsion spring acts on the rotational hinge that connects the second link rod to the slider. In this configuration, as a consequence of a movement of the slider that tends for example to move it toward the link rod connected to the fixed element, the mechanism reacts by generating a substantially constant force. In the circuit breakers currently in use, mechanisms of this kind are suitable to ensure a substantially constant force between the contacts in the closed position, and this function is generally entrusted to the components of the kinematic chain.

Advantageously, in the embodiment of the circuit breaker according to the present invention, said mechanism suitable to generate a substantially constant force comprises a single body that has a first rigid element, which is associated with at least one of the fixed or moving contacts 1 and 2, and a second rigid element, which is arranged adjacent to the first rigid element and is connected thereto by virtue of a flexible hinge constituted by an elastic and resilient element. Preferably, said single body is made of an electrically conducting material and the flexible hinge is provided by reducing the thickness of one part of said body with respect to the thickness of the adjacent parts that constitute the rigid elements. In this manner, the mechanism suitable to generate a constant force between the contacts is provided by using a single body in which the flexible hinge, by virtue of its resiliency and elasticity characteristics, fully replaces in functional terms the rotational hinge and the corresponding torsion spring; the appropriate choice of the thickness of the elastic and resilient element in fact corresponds to the choice of a torsion spring having a preset elastic constant.

Furthermore, as mentioned, the single body can be associated with the fixed contact or with the moving contact, with the great advantage of being able to simplify the kinematic chain 15 or in any case of not having to act thereon in order to obtain a constant force over the useful life of the circuit breaker; furthermore, the single body, by virtue of its elasticity and resiliency characteristics, is capable of compensating for any variations with respect to the ideal design behavior, for example due to contact wear.

Figure 2 illustrates a preferred embodiment of the constant-force mechanism in which the single body is associated with the moving contact 2 of the circuit breaker. In particular, in the illustrated embodiment, said single body, generally designated by the reference numeral 20, is integrated in the structure of the contoured body 2a of the moving contact 2, at its region for coupling to the fixed contact 1, and comprises a first rigid element 3 and a second rigid element 5, which are mutually connected by virtue of a first flexible hinge 6. The first rigid element 3 is connected to the remaining part of the body 2a by virtue of a second flexible hinge 4; in turn, the second rigid element 5 is connected, by virtue of a third flexible hinge 8, to an additional conducting element 7 that is suitable for electrical coupling to the fixed contact 1 and in particular to the plate lb. Said element 7, which can be constituted by the plate 2b itself or in any case replaces it functionally, abuts, when the circuit breaker is closed, against the end of the fixed contact 1, so that under the action of the body 20 there is a constant contact force between the coupled parts. As an alternative, the body 20 can be integrated into the structure of the contoured body 2a at a certain distance from the plate 2b or can be used as a component that is structurally separate from the moving contact and is operatively associated therewith by virtue of an appropriate connection. Figure 3 illustrates a second embodiment, in which the body 20 that constitutes the mechanism for maintaining the contact force is associated with the structure of the fixed contact 1.

In this configuration, too, the body 20 is integrated in the structure of the body la of the fixed contact 1 and comprises a first rigid element, which is connected to the remaining part of the body la by virtue of a flexible hinge 4, and a second rigid element 5, which is connected to the first element 3 by virtue of a flexible hinge 6; in turn, the second rigid element 5 is connected to an additional conducting element 7 by virtue of a third flexible hinge 8. Like the previous embodiment, the conducting element 7 can be constituted by said plate lb or in any case by an element that is part of the body 20 and replaces it functionally, coupling electrically to the moving contact 2.

In this case also, as an alternative to the embodiment shown in Figure 3, the body 20 can be integrated into the structure of the contoured body la at a certain distance from the region of contact with the moving contact 3, or can be used as a component that is structurally separate from the fixed contact and is operatively associated therewith by virtue of an appropriate connection.

Finally, Figure 4 illustrates a third embodiment of the mechanism suitable to ensure a constant contact force between the fixed contact 1 and the moving contact 2. In this case, the body 20 is substantially Y-shaped and is fixed to one end of the fixed contact 1 at the region where the contact plate lb is provided. In particular, the body 20 comprises a first rigid element 10, which is connected to the body la of the fixed contact 1 and lies along a reference axis 16, and a second rigid element, which has a first rigid portion 11 and a second rigid portion 12 that are arranged symmetrically to each other with respect to the reference axis 16 and are connected to the rigid element 10 by virtue of a flexible hinge 13. In the specific case, the hinge 13 is substantially fork-shaped; the element 10 can be preferably fixed to the body of the fixed contact 1, as shown in Figure 3, or can be connected thereto by virtue of an additional flexible hinge.

In this configuration, the two rigid portions 11 and 12 functionally replace the plate lb and are suitable to make contact with the moving contact 2, which can have, in the contact region, a hemispherical portion 14. In this manner, when the rigid parts 11 and 12 are coupled to the moving contact 2, the body 20 as a whole ensures that the force applied along the axis of symmetry 16 is constant for a wide range of axial movements.

As an alternative, and in a manner that is fully similar from the functional standpoint, the body 20 in the configuration of Figure 4 can be associated with the moving contact 2, optionally adopting a spherical configuration for the fixed contact 1 and particularly for its plate lb; furthermore, the shape of the elements that constitute the body 20 can be changed, so long as it is changed in a manner that is compatible with the application.

In practice it has been found that the circuit breaker according to the invention fully achieves the intended aim and objects, providing a series of advantages with respect to the known art. By virtue of the adoption of the body 20, the contact force between the fixed contact and the moving contact is substantially constant over the useful life of the circuit breaker, regardless of the variations in the behavior of the various components and in particular of the wear to which the contacts are inevitably subjected. This leads to an improvement in performance with respect to known kinds of circuit breaker, with the simultaneous advantage of reducing the complexity and high costs of improved kinematic chains. The circuit breaker thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; thus, for example, the shape of the contacts can be changed in various manners with respect to what is shown in the figures. All the details may furthermore be replaced with other technically equivalent elements. In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims

CLAIMS 1. A circuit breaker for low- voltage currents, comprising an enclosure that contains moving contact means and fixed contact means, the moving contact means comprising at least one moving contact, the fixed contact means comprising at least one fixed contact, a kinematic chain that comprises a plurality of levers that move the moving contact between an open position, in which the contacts are separated, and a closed position, in which they are coupled, and a mechanism that ensures a substantially constant force between the contacts in the closed position, characterized in that said mechanism comprises a single body that has a first rigid element, which is associated with at least one of said fixed and moving contacts, and a second rigid element, which is arranged adjacent to said first rigid element and is connected thereto by virtue of a flexible hinge constituted by a first elastic and resilient element.

2. The circuit breaker according to claim 1, characterized in that said single body is made of electrically conducting material, said flexible hinge having a reduced thickness with respect to said first and second rigid elements.

3. The circuit breaker according to claim 1 or 2, characterized in that said single body is integrated in the structure of the moving contact.

4. The circuit breaker according to claim 3, characterized in that said single body comprises a first rigid element and a second rigid element, which are mutually connected by means of said first flexible hinge, said first rigid element being connected to a portion of the moving contact by means of a second flexible hinge and said second rigid element being connected, by means of a third flexible hinge, to an additional conducting element that is suitable for electrical coupling to said fixed contact.

5. The circuit breaker according to claim 1 or 2, characterized in that said single body is integrated in the structure of the fixed contact.

6. The circuit breaker according to claim 5, characterized in that said single body comprises a first rigid element and a second rigid element that are mutually connected by means of said first flexible hinge, said first rigid element being connected to a portion of the fixed contact by means of a second flexible hinge, said second rigid element being connected, by means of a third flexible hinge, to an additional conducting element suitable for electrical coupling to said moving contact.

7. The circuit breaker according to claim 1 or 2, characterized in that said single body comprises a first rigid element, which is connected to said fixed contact or to said moving contact, and a second rigid element, which has a first rigid portion and a second rigid portion that are arranged symmetrically with respect to each other relative to a reference axis, said first rigid part being arranged along said axis of symmetry and being connected to said first and second portions by means of said first flexible hinge.