Protection device for an automatic circuit breaker and automatic circuit breaker comprising this device

The present invention relates to a magnetic protection device, in particular for an automatic circuit breaker or a disconnecting switch, preferably for use in low voltage systems. The invention also relates to an automatic circuit breaker comprising this device. The protection device (1) according to the invention comprises a low voltage circuit breaker comprising an air gap magnetic circuit (T), provided with a first portion (10) forming a first surface (11) of said air gap (T) and a second portion (20) forming a second surface (21) of the air gap (T). The first portion (10) constitutes a fixed section of the magnetic circuit, while the second portion (20) constitutes a moving section of the magnetic circuit. The magnetic circuit also comprises a flexible portion (30) that connects the first portion (10) to the second portion (20) with continuity, forming an intermediate section of magnetic circuit interposed between the fixed section and the moving section. The third flexible portion (30) advantageously allows a relative movement of the second surface (21) of the air gap (T) with respect to said first surface (11). In its essential form, the protection device (1) comprises an actuation element (50) associated with the second portion (20) of the magnetic circuit for the purpose of contacting a trip device of a circuit breaker to which the protective device is applied.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT/EP2007/062070 filed Nov. 8, 2007 which in turn claims priority from Italian Application BG2006A000065 filed Dec. 21, 2006, the entire contents of which are incorporated herein by reference.

The present invention relates to a magnetic protection device, in particular for an automatic circuit breaker or a disconnecting switch, preferably for use in low voltage systems. The invention also relates to an automatic circuit breaker comprising this device.

Automatic circuit breakers, hereinafter simply called circuit breakers, are devices capable of protecting an electrical network from possible faults (such as overloads and short-circuits) by automatic opening of the circuit.

Automatic circuit breakers comprise an outer case, at least one pair of main contacts, reciprocally couplable with/decouplable from each other, an actuator device to cause said main contacts to open and close, a protection device and one or more automatic trip devices. Protection devices, hereinafter called relays, are normally of the thermal, magnetic, thermomagnetic or electronic type. The main object of relays, which are also available in varied combinations of the aforesaid types, is to cause operation of the automatic trip device of the circuit breaker when undesirable events occur.

The automatic trip device is normally part of the circuit breaker. To cause operation of the trip device, relays generate a signal, normally of the mechanical type, which is transmitted to the trip device. This signal is normally generated and transmitted by levers or solenoids which, for example, cause rotation of the trip shaft of the circuit breaker, which causes the release of the potential energy contained in specific driving devices (i.e. springs). This energy is suitably conveyed, by means of kinematic chains, to the main contacts of the circuit breaker which at the end of the trip operation must be reciprocally separated, in the open or tripped position.

In particular, magnetic relays are often used to produce instant protection. These relays are based on the principle of electromagnetic induction and make use variously of the physical phenomena linking the current circulating in a conductor to the magnetic field that is established in the surrounding area.

Magnetic relays are in practice transducers which, in predetermined conditions, convert a current (i.e. the current circulating in one of the phases of the circuit breaker) into a signal useful to trip the circuit breaker.

Magnetic relays are normally constituted by an electric induction circuit supplied by a significant current of the current to be detected (i.e. a branch winding, or simply a length of main electrode in which one of the phase currents circulates), and by a magnetic circuit which in turn comprises an armature, and a moving keeper capable of taking at least two positions, de-energized and energized respectively.

In the presence of a current of predetermined level in one of the phases of the circuit breaker (i.e. a short circuit current), the magnetic field established in the magnetic circuit of the relay generates forces on the moving keeper, capable of attracting it towards an energized position, usually in contact with the armature. Ultimately, magnetic relays make use of the movement of the keeper during switching between the de-energized and energized positions, to cause operation of the trip unit. During movement of the keeper, a lever integral therewith intercepts a cam keyed onto the trip shaft and causes it to rotate to trip the circuit breaker.

A magnetic relay of this first type, of recent conception, is described for example in U.S. Pat. No. 6,842,096 (FIG. 1).FIG. 1shows, for example, the pivot hinge of the moving keeper and the return spring. Conceptually similar magnetic relays can also comprise additional elements, such as adjustment means, screws, return levers; or alternative elements such as sliding guides of the moving keeper.

Prior art solutions are relatively effective, but are subject to a series of drawbacks. The choice of materials used in conventional types of magnetic relays does not generally cause particularly critical states. To ensure generic operation of the relay, it is in fact sufficient to use materials that respectively have average magnetic (magnetic circuit) or elastic (return springs) characteristics, generally found in mid-range commercial products. Instead, the most critical aspect is the stability of the kinematic behaviour of moving components during the entire useful life required of the circuit breaker.

The first drawback thus consists in the lack of stability of the moving joints that allow reciprocal movement of the keeper with respect to the armature, i.e. the hinges. It is in fact known that both constructional or assembly faults and the effect of heat, the deposit of debris and wear can cause progressive phenomena of slackening of constraints, seizure of moving joints or even total block in prior art magnetic relays.

It is also evident that the general efficiency of a circuit breaker is closely linked to the efficiency of the relays. As slackening of constraints, seizure of moving joints or blocking of a relay tends to translate into premature, delayed or even non-operation of the trip unit in the event of a short circuit, these potential faults can be extremely dangerous.

Another drawback of prior art solutions consists in the high number of parts required and in the corresponding risk of erroneous assembly or imperfect reciprocal interaction.

Practice has shown that the complex configuration of prior art protection devices makes them significantly bulky with respect to the dimensions of the circuit breaker in which they are installed. This aspect considerably complicates the design and assembly of automatic circuit breakers, with an evident increase in final production costs.

On the basis of these considerations the main aim of the present invention is to provide a protection device for an automatic circuit breaker that allows the aforesaid drawbacks to be overcome.

Within this aim, an object of the present invention is to provide a protection device of magnetic type, the components of which have stable and reliable kinematic behaviour.

Another object of the present invention is to provide a protection device of magnetic type with relatively short tripping times as a result of high operating efficiency.

A further object of the present invention is to provide a protection device with an extremely compact structural configuration, or made with a limited number of parts, of simple configuration and simple to assemble.

Yet another object of the present invention is to provide a protection device that is reliable and easy to produce at competitive costs.

This aim, and said and other relative objects which will be more apparent below, are achieved by a protection device for an automatic circuit breaker as claimed in claim1.

The protection device according to the invention has an extremely compact configuration, i.e. defined by an extremely limited number of components distinguished by stable and reliable kinematic behaviour. In particular, this advantage is achieved as a result of the physical continuity between the portions respectively defining the armature and the moving keeper of the protection device, or the magnetic circuit it forms.

With reference to the aforesaid figures, the protection device1according to the invention comprises an armature and a moving keeper made of ferromagnetic material, which form an air gap magnetic circuit T, operatively intended to surround a section of one or more conductors2in each of which a phase current circulates. The expression conductor indicates any section of an electric circuit supplied by a significant current to be detected, such as a phase current. In particular, this conductor could be a branch winding or a section of main electrode of a circuit breaker.

The armature comprises a first portion10connectable to a fixed part8of a circuit breaker to which the protection device1is applied. This fixed part8can, for example, be constituted by a wall of the case containing the circuit breaker or by any other fixed part provided inside this case. The first portion10defines a fixed section of the magnetic circuit and comprises a first11of the two surfaces that form the air gap T. The armature also comprises a second portion20facing the first portion10defining a moving section of the magnetic circuit. The second portion20also comprises a second surface21facing the first surface11of the first portion10to completely define the air gap T.

The armature is completed by a flexible portion30that connects the first portion10to the second portion20with continuity, in practice forming an intermediate section of magnetic circuit interposed between the fixed section and the moving section respectively defined by the first10and by the second20portion indicated above. As can be seen in the figures, the portions10,20,30T (air gap) of the magnetic circuit in substance define an open loop48inside which at least one conductor2is operatively positioned so that the magnetic circuit defined by the portions10,20,30, T (air gap) feels the effects of the current circulating in the conductor.

The protection device1according to the invention also comprises an actuating element50operatively associated with the second portion20. It must be understood that the expression “associated” is intended both as the possibility of producing the actuation device50in one piece with the second portion20and as the possibility of connecting this element to said portion using suitable connection means66.

The actuation element50is prearranged to contact, following movement of the second portion20, a trip device90of the circuit breaker2in order to move the relative kinematic chains thereof provided to cause opening of the contacts of the circuit breaker. This trip device90can be constituted by a trip shaft commonly used in automatic circuit breakers or alternatively by any other functionally equivalent element that can be used for the same purposes.

With reference toFIG. 2, the operating principle of the protection device1is immediately understood. Any faulty operating conditions, such as those generated by a short circuit, cause a variation in the phase current circulating in the conductor2. This translates into a variation in the intensity of the magnetic field that hits the magnetic circuit and consequently into the creation of a system of forces that reciprocally attracts the surfaces of the air gap T. As a result of the elasticity distinguishing the flexible portion30, the second surface21of the air gap T (formed by the second portion20) moves towards the first surface11defined by the first portion10. The movement of the second portion20determines the movement of the actuation element50which in turn actuates the trip device90of the circuit breaker to which the protection device1is applied.

From the above, it is clear how the kinematic behaviour of the protection device1is absolutely stable and reliable for the entire useful life required of the circuit breaker. As a result of the simple configuration thereof, the flexible portion30in fact ensures physical continuity between the first10and the second20portion, allowing totally repeatable and reliable motion of the latter with respect to the former.

FIGS. 2 and 3are perspective views respectively of a first and of a second embodiment of the protection device1according to the present invention applied to an automatic circuit breaker. In particular, by comparing the two figures it is possible to see, with the same configuration of the armature, a different orientation of the actuation element50, for the purpose of satisfying different constructional requirements. This highlights how the configuration of the protection device1and the constructional principle underlying it make the device extremely versatile, that is, capable of serving different installation requirements.

According to a preferred embodiment of the invention, the first10, the second20and the flexible portion30are advantageously produced in one piece. This is possible as a result of the particular configuration of the portions of magnetic circuit that allows the number of components forming the protection device1to be reduced to a minimum. As explained in greater detail below, the actuation element50can also advantageously be produced in one piece with the second portion20so that the protection device1is in fact formed of a single element.

FIGS. 4 and 5are views respectively of a first and of a second embodiment of the protection device according to the invention. As shown, the first portion10comprises a flat base13defining a supporting surface13A for the armature. This supporting base is advantageously connectable to a fixed part of the circuit breaker8, for example through conventional fixing means, not shown in the figures.

The flexible portion30extends from a first side16of the flat base13toward a first end part28of the second portion20. A lower surface26of the latter faces an inner surface13B of the flat base13substantially opposite the supporting surface13A. The lower surface26of the second portion20forms the aforesaid second surface21of the air gap T, in proximity of a second end part29opposite the first end part28.

In the solution shown in the last mentioned figures, the first portion10comprises a shoulder15extending from the flat base13at a second side substantially opposite the first side16from which the flexible portion30extends. The shoulder15comprises an end part15A forming the first surface11of the air gap T.

As shown, the flexible portion30is constituted by a flexible joint substantially bent in a U-shape connecting the first10and the second20portion so that the latter is disposed in a raised position with respect to the former. As can be seen from the viewpoint of construction, the conductor2is disposed operatively in the open loop48defined by the ferromagnetic elements and by the air gap T, that is, so as to be surrounded by the magnetic circuit.

In the solutions shown inFIGS. 3 to 9, the ferromagnetic elements10,20,30have a substantially prismatic configuration preferably extending along a main direction of reference100. In particular, the first10and the second20portion have a prismatic configuration with a rectangular section. From a viewpoint of operative positioning, the ferromagnetic elements extend so that the conductor2is, for example, disposed in a position substantially orthogonal to the position of reference100.

FIG. 6is a view relative to a third embodiment of the protection device1according to the invention which differs in particular from the preceding embodiments in the shape of the flexible portion30. In fact, this portion comprises a first31and a second32flexible brace extending separately from the flat base13toward a first end part28of the second flat portion20. The use of this pair of braces substantially bent in a U-shape allows a different distribution of the magnetic and elastic parameters to be obtained. Through the use of these braces31,32, suitably dimensioned, it is for example possible to obtain, with the same material, a different elasticity of the flexible portion. This allows the protection device1to be more or less sensitive to the electromagnetic effects induced by the phase current passing through the conductor2, i.e. to improve configuration of various calibration requirements. The braces31,32can be obtained directly during manufacture, or produced with subsequent machining operations in order to provide the overall conditions required.

With reference toFIGS. 4,5and6, the actuation element50according to the invention can be produced in one piece with said second portion20. Alternatively, the actuation element50can be produced separately from the second portion20and subsequently connected thereto with the use of suitable connection means66. In particular, in the solution shown inFIG. 5, the actuation element50extends as an extension of one side of the second portion20which has a trapezoidal configuration provided with an end part55that is bent in order to facilitate contact with the trip device90. In an alternative solution (seeFIG. 6), the actuation element50extends from an upper surface26A of the second portion20substantially opposite the lower surface26that forms the second surface12of the air gap T. In particular, the actuation element50extends according to a substantially hook-shaped configuration defined by a first connection part51and by a second hooking part52extending in a position raised with respect to the upper surface26A.

The embodiments of the actuation element50described above are obviously only to be considered as two examples of embodiment which do not limit any functionally equivalent solutions that can be used for the same object and which must undoubtedly be considered as falling within the scope of the present invention.

FIGS. 7,8and9each show an embodiment of the armature5of the present invention distinguished by the fact that it comprises a series of openings62provided on the second portion20. These openings have the function of allowing connection of the actuation element50to said second portion20cooperating with the connection means used for this object. For this purpose, the connection means66can include screws, rivets, pins or other functionally equivalent means.

With reference toFIG. 7, these openings62are disposed according to a first pre-established direction71to allow a corresponding first orientation of the actuation element50with respect to the second portion20or with respect to the armature5. In the solutions shown inFIGS. 8 and 9, the openings62are also disposed at least according to a second pre-established direction72. This advantageously allows the actuation element50to be oriented according to different constructional needs with obvious advantages, for example, from the viewpoint of design.

FIGS. 10,11,12and13show a further possible embodiment of the protection device1according to the present invention, applied to a circuit breaker. More precisely, the first portion10(armature) comprises a first41and a second42side which extend on opposite sides of the flat base13so as to define a seat for connection of a portion of at least one conductor2of the circuit breaker. In this solution, the first surface11of the air gap T is constituted by a first41A and by a second42A end surface respectively of the first41and of the second42side. The flexible portion30is formed so as to allow the lower surface26of the second portion20to face the first41A and the second42A end surface of the two sides41and42so as to form the second surface of the air gap T.

In particular, the flexible portion30comprises a first46and a second flexible elbow47extending from opposite sides of a first side16of the flat base13. The two flexible elbows46and47are mutually spaced apart and extend so as to define an open loop48which is completed by said first side16of the flat base13and by the first end part28of the second portion20.

FIG. 11is a side view of the application shown inFIG. 10and allows the function of the open loop48described above to be observed. As shown, the protection device1is applied to the conductor2so that the latter is housed partially in the seat defined between the two sides41and42and in the frame48defined between the two flexible elbows47,48. From the viewpoint of installation, it can be seen that in this embodiment the conductor2is disposed according to the same direction100in which the protection device1extends.

Again inFIG. 11, other characteristics of this further embodiment of the protection device can also be observed. In particular, it can be seen that the two end surfaces41A and41B of the two sides41,42of the first portion10extend according to a first plane substantially inclined with respect to the flat base13of the same portion. Likewise, the second portion20, by means of the two flexible elbows46and47, faces the end surfaces41A and42A of the two sides41,42being disposed according to a second plane also substantially inclined with respect to the flat base13.

FIGS. 12 and 13show two possible variants of the embodiment of the invention described above. Similarly to the description above for the armature inFIGS. 1 to 8, the actuation element50can be connected to the second portion20through connection means66or alternatively produced in one piece with said portion20.

From the viewpoint of construction, the protection device according to the invention can obviously be provided with further return and/or adjustment and/or calibration devices for the purpose of making the characteristics (elastic and magnetic) adjustable. For example, by making use of prior art solutions, it is possible to associate elastic elements (such as springs), the effect of which contributes to that of the flexible portion30, with the second portion20. Alternatively, retaining and/or adjustment screws could be associated with the flexible portion30and/or with the second portion20. In other words, without prejudice to the reliability and various advantages deriving from the protection device1, this can therefore advantageously be integrated with all the adjustment/calibration elements already known and already applied to prior art magnetic protection devices.

The protection device1according to the invention can be produced in various materials, such as silicon plate. An alternative could be constituted by the use of amorphous ferromagnetic alloys, of non-crystalline type, processed according to a fusion process with a very fast cooling rate to maintain the physical properties of the amorphous material.

The protection device according to the invention could also be produced using an injection moulding process. In particular, this could be produced from metal powders (elemental or pre-alloyed) with the addition of mouldable binders such as thermoplastics, polymer waxes. The granular feedstock thus formed can in fact be injected into a cavity to produce the desired shape, taking account of shrinkage due to removal of the binder. This removal can, for example, be performed with chemical methods (solvents or catalytic reactions), thermal methods (heating) or according to other different known systems. The subsequent technological step involves sintering to seal the particles together and obtain the finished part. Other finishing steps could follow subsequently, such as coining, heat or surface treatment, mechanical machining to reach the desired final shape. It has been seen that a material particularly suitable for this process is represented, for example, by Carbonyl Iron (Fe with 2/8% Ni).

It must be understood that the above must be considered solely as examples of technological processes and of materials that can be used to produce the protection device according to the present invention. For this reason other known processes could nonetheless be employed in alternative to those indicated.

The present invention also relates to a single-pole and multi-pole low voltage circuit breaker to be used for low voltage systems. The circuit breaker according to the invention comprises an outer case, inside which there is located at least one pair of main contacts couplable with and decouplable from each other through an actuator device. Inside the outer case, the circuit breaker comprises an automatic trip device90operatively connected to the actuator device to allow automatic opening of the pair or pairs of main contacts.

The automatic circuit breaker according to the invention is characterized in that it comprises a protection device1as defined in the present invention. In particular, the protection device1allows actuation of the trip device90and is operatively positioned at one or more conductors in which a phase current circulates. More precisely, the armature of the protection device is connected, through the flat base13thereof, to a fixed part of the circuit breaker which can, for example, be a wall of the containing case. This positioning of the protection device can be direct, in the sense that the armature is connected directly to the fixed part, or can be mediated by a positioning template9as shown in the applications indicated inFIGS. 2,3,9and10.

The technical solutions adopted for the protection device according to the invention allow the aims and objects set to be fully achieved. The protection device as conceived is constituted by a minimum number of components, easy to produce and easily assembled together. Moreover, the protection device is particularly reliable and efficient as a result of the innovative structural configuration thereof.

In practice, the materials used, the dimensions and contingent shapes can be any according to requirements and to the state of the art.