HK1094089B - Switching device - Google Patents

Description

Switching device

The invention relates to a switchgear according to the preamble of claim 1. In this case, it is of great interest, in particular for its use as a circuit breaker, to provide a switchgear with additional means for increasing the current carrying capacity and accelerating the dynamic opening of the contacts.

Such switching devices usually have a translatory contact opening movement, wherein the contacts are arranged on a contact bridge and a bridge carrier and a contact force spring are provided for the translatory movement. In addition, however, the switching device may also have a rotary contact-breaking movement, as is also relevant to the invention.

In order to protect electrical devices, but also to operate electrical consumers, electrical switching devices are required which conduct a current within a predetermined value without failure and which are able to interrupt excessive currents, for example short-circuit currents, in the shortest possible time. For this purpose, the switching device has a switching device drive (mechanical switch lock and/or electromagnetic drive) which closes the contacts with a predetermined contact pressure, and a tripping mechanism (e.g., an n-type trip or an electronically actuated actuator) which causes rapid opening of the switching contacts and thus rapid establishment of a current-limiting arc voltage.

Since the electrodynamic forces act earlier than the momentum of the tripping mechanism, which is transmitted to the movable contact, when extremely high short-circuit currents (for example I-50 kA) may occur, the short-circuit switching behavior can be improved by an optimized design of the drive magnetic field. However, the magnetic field strength, which is dependent on the current intensity, may already be in the operating current range, for example when the motor starting current is reached, leading to reduced contact pressure and thus to a disturbance of the current-carrying behavior. In order to eliminate these problems, the force provided by the switchgear drive can be increased. However, this results in a drive of larger dimensions, which increases the outlay on equipment and the construction volume. Both of these results are undesirable for economic reasons and a solution is therefore needed which eliminates the above-mentioned disadvantages.

In order to use dynamic breaking forces in an electrical switchgear, the current path between the moving contact and the stationary contact is guided in a narrow circuit and/or the magnetic field around the moving contact, through which the current flows, is distorted by ferromagnetic means (e.g. deep-slot motors), thereby causing strong lorentz forces.

DE 4216080 a1 discloses a device for increasing the contact pressure for a relay contact, in which the current path to the movable contact is guided in a loop-like manner in order to utilize the loop force as an additional contact pressure. In this case, an iron plate is additionally assigned to the current path at a slight distance in order to obtain additional magnetic forces for increasing the contact pressure. Furthermore, it is known from DE 19912713 a1 to provide a blocking element with good electrical conductivity for the case of a switching contact through which current flows. The movement of the contacts is prevented by the parallel shunt current in the blocking element and the movable contact for such a long time that the current and the magnetic force exceed a predetermined minimum value. Finally, on the basis of the "switchgear technology" numbered ISBN3-540-) "the general characteristics of switchgear, in particular contactors, are described in the literature (Berlin Springer Press 1975), especially pages 257 to 274.

The known devices described above do not make it possible to: provides the desired high dynamic electromotive force and does not sensitively attenuate the contact pressure even at high operating currents (motor starting currents). The drive and the contact pressure must therefore be designed to be greater.

Furthermore, a contactor with a switching bridge consisting of two contact pairs having the characteristics of an interrupter contact is known from US 4454490, wherein two ferromagnetic yokes surround the contact rails of the two contact pairs and generate a contact opening force. Between these two yokes, a further yoke is fastened to the bridge carrier, which produces a contact closing force. Means for increasing the current carrying capacity and accelerating the dynamic opening of the contacts are thereby said to be provided.

The object of the present invention is therefore to provide a further improved switching device in which the contact pressure does not undergo an impermissible weakening, in particular in the case of operating currents.

The above object is achieved according to the invention by a switching device comprising a switching box having at least one stationary contact and at least one movable contact, to which at least two ferromagnetic U-shaped yokes are assigned for generating at least two electrodynamic magnetic forces which are opposite to one another with respect to their force vectors, wherein the at least two ferromagnetic U-shaped yokes are each positioned relative to the at least one movable contact in such a way that the force vector generated by one of the ferromagnetic yokes acting on the at least one movable contact is directed toward the at least one stationary contact and the force vector of the other ferromagnetic yoke is directed away from the at least one stationary contact, wherein the two yokes are dimensioned in such a way that the yoke of smaller dimensions can be at least partially accommodated in the air gap of the yoke of larger dimensions, for this purpose, the outer dimension width of the smaller yoke is smaller than the air gap width of the larger yoke.

In the present invention, a U-shaped yoke made of a ferromagnetic material, preferably a general steel plate, is used in order to enhance the magnetic force. Such a yoke is previously known per se from the prior art. In the present invention, however, the outer dimension width of the smaller yoke is smaller than the air gap width of the larger yoke.

The invention provides for the design of the magnet yoke to enable the electromagnetic force acting on the moving contact to switch signs in a targeted manner in the process of increasing the current from a small current value (i.e. in a standard operating state) to a very high current value (i.e. in a short-circuit operating state). This means in particular that in the case of low currents an increased contact pressure effect is produced and in the case of high currents a reduced contact pressure effect is produced, whereby a dynamic opening force is obtained. According to the invention, by appropriately designing the ferromagnetic component, a changing magnetic force curve with changing sign or almost even magnetic force curve can be formed.

In order to realize the switching device according to the invention, a first U-shaped plate for generating a magnetic closing force and a second U-shaped plate for generating a magnetic opening force are used as magnetic yokes, which are positioned in a suitable manner on the contact device.

Further details and advantages of the invention are given in the following description of embodiments according to the invention with the aid of the figures in conjunction with the claims. All the figures are schematic diagrams. Wherein:

fig. 1 shows a switchgear with a switching bridge (or "moving bridge contact") and an auxiliary drive;

fig. 2 shows a portion taken from fig. 1 in order to clearly illustrate the two ferromagnetic yokes associated with the switching bridge;

fig. 3 is a perspective view showing the respective positioning directions of the two yokes;

fig. 4 shows a contact arrangement with a switching bridge and a correspondingly associated partial yoke;

fig. 5 shows a contact arrangement with a partial magnet yoke mounted thereon and two plate elements assigned to the partial magnet yoke.

The functional components of a known contactor are schematically represented in fig. 1: the contactor essentially consists of a switching box containing switching elements and an electromagnetic drive 10, by means of which electromagnetic drive 10 the switching contacts are mechanically actuated in an electromagnetically actuated manner.

In fig. 1, the stationary contacts 3a and 3b in the switch cabinet 1 are arranged on stationary contact supports 2a and 2b and the movable contacts 5a and 5b associated with these stationary contacts are arranged on a moving switch bridge 4. The contact arrangement with the contacts 3a, 5a and 3b, 5b lying opposite one another is provided in a known manner with quenching bars 9a and 9b, these quenching bars 9a and 9b usually being part of a quenching bar arrangement with a running rail or guide 32. The moving switching bridge 4 is connected to a bridge carrier 8 in a relatively movable manner by means of a contact force spring 7, and the bridge carrier 8 is moved together with the armature 13 into the switched-on or switched-off position by the electromagnetic drive 10.

Other elements that can be moved relative to one another and which can be acted upon by an actuator and which can trigger the bridge movement can be contained in the bridge carrier.

The electromagnetic drive 10 is composed in particular of a magnetic yoke 11 with a magnetic coil 12 and an armature 13 associated therewith, which armature 13 is connected to the bridge carrier 8 via a support plate 14. A tripping spring 15 acts on the magnet yoke 11, which ensures that the bridge carrier is in the tripping position in the closed state of the electromagnetic drive 10.

In the switching device described above, ferromagnetic parts are provided for controlling the contact pressure, to be precise in particular in the switching box, two yokes 20 and 30, the function of which is discussed further in detail below. Only the yoke 30 is visible in fig. 1 and is connected to the slide or rail 32.

Fig. 2 shows the arrangement of the two magnetic yokes 20 and 30 relative to the contact arrangement consisting of the stationary contact and the contact carrier and the movable contact and the switching bridge. The geometry of the two U-shaped yokes 20 and 30 can be derived from fig. 1 to 3. In particular, fig. 3 shows the geometrical differences between the two yokes that are important with regard to magnetization.

According to the arrangement shown in fig. 2, the U-shaped contact-pressure generating element 20 reacts more sensitively to the current in the switching bridge 4 than the U-shaped opening-force generating element 30, on the basis of its geometry and its positioning on the switching bridge 4. This means in particular that the U-shaped plate element 20 is charged more quickly than the U-shaped plate element 30 due to its compact size and reaches magnetic saturation earlier due to its thin plate thickness.

The U-shaped plate element 30, which generates the opening force, covers the movable contacts or the switching bridges 4 with the movable contacts 5a and 5b almost or completely over their entire length and has a greater clear width and a greater plate thickness. Thus, its magnetic saturation is only reached at higher current conditions than in the U-shaped plate element 20 which generates the contact pressure.

In the case of a mechanical switching device drive, the U-shaped plate element 20, which generates the contact pressure, is fastened either to a switching lock part or to the switch housing. In the case of an electromagnetic drive corresponding to that shown in fig. 1, the U-shaped plate element 20, which generates the contact pressure, is fastened to the bridge carrier 8 and encloses the switching bridge 4, wherein the bridge carrier connects the switching bridge 4 to the drive 10 shown in fig. 1.

As shown in a further example, the possibilities of positioning and fixing the U-shaped plate element 20 generating the contact pressure are not limited to the two cases described above.

The U-shaped plate element 30 generating the tripping force is expediently fastened to the switch cabinet 1, to the housing or to a stationary mechanical part located on the housing in both cases.

In the above-described fig. 1 and 2, the switching bridge executes a translational movement, but a rotational movement can also be realized in a corresponding configuration of the switching device. In the case of a rotary movement of a switching bridge, U-shaped plates 20 and 20 'and U-shaped plates 30 and 30' are arranged in a point-symmetrical arrangement on both sides of the axis of rotation, respectively, for the switching bridge. For this purpose, the two U-shaped plate elements 30 and 30' are fixedly connected to the housing or to stationary mechanical parts in the housing. The two U-shaped plate elements 20 and 20' can likewise be fixedly connected to the housing or to a switching bridge carrier which is in force-transmitting engagement with the switching device drive (mechanical and/or electromagnetic drive) and rotates together with the switching bridge in the open position during the opening process.

The U-shaped plate members 20 and 20 'and the U-shaped plate members 30 and 30' are positioned at a predetermined interval from each other, and thus, magnetic short circuits are prevented from occurring between the U-shaped plate members 20 and 20 'and between the U-shaped plate members 30 and 30'. For example, the clear width of the U-shaped gaps is predefined as the distance.

Only one U-shaped plate element 20 and one U-shaped plate element 30 can be associated with a rotary movable contact that can be easily opened, in which case, as shown in fig. 2 and/or fig. 3, by suitable arrangement of the two U-shaped plate elements, a contact opening magnetic force and a contact closing magnetic force are respectively generated on the movable contact through which the current flows, the resultant forces of which can change sign or direction during the transition of the current from a low current value to a high short-circuit current value.

When the contacts are disconnected dynamically, the movable contact or the moving contact bridge is moved out of the gap of the U-shaped plate generating the contact pressure and falls into the gap of the U-shaped plate generating the disconnection force due to large electrodynamic force. Whereby the force of the first U-shaped plate element 20 is lost and the breaking force of the second U-shaped plate element 30 is applied without loss.

In the transition region of the dynamic disconnection movement of the contacts, i.e. before the movable contact or the moving contact bridge can leave the gap of the U-shaped plate 20 generating the contact pressure, the magnetic flux acting on the movable contact can be regarded as the difference between the magnetic fluxes of the second U-shaped plate and the first U-shaped plate. The respective saturation flux can be formed approximately in dependence on the plate thickness on the basis of the different plate thicknesses. The thickness of the U-shaped plate element 20 generating the contact pressure is about 10% to 20% of the thickness of the U-shaped plate element 30 generating the breaking force, so that the resultant magnetic field in the transition region is reduced by aboutAs little as 80% to 90% of the magnetic field of the second U-shaped plate member 30. The resulting magnetic force that contributes to the opening of the contacts is reduced in the same way.

In fig. 3 it is shown that the second U-shaped plate element 30 may be part of a slide or rail 32 as is commonly found in such switchgear.

An example of the design dimensions for the U-shaped plate elements 20 and 30 is given in the following diagram. The values may vary within predetermined limits while still substantially ensuring that the design dimensions of the U-shaped plate members 20 and 30 are compatible with each other.

The length of the U-shaped plate element generating contact pressure in the bracket is 8.5mm, and the plate thickness is 0.1mm	The U-shaped plate element used as a part of the slide rail for generating the breaking force has the length of 19.5mm and the plate thickness of 0.8mm
		Complete coverage (i.e. switching bridge in the U-shaped slot) S with a clear width of 5mm≈5mm(SAir travel of magnetic line of force) K＝μ*i*8.5/S＝μ*i*1.7	A clear width of 10mm covering-2 mm (i.e. a switch bridge in front of the U-shaped slot) S≈13mm(SAir travel of magnetic line of force) K＝μ*i*19.5/S＝μ*i*1.5

It can be seen from the graph that the force component that forms the contact pressure is only slightly greater than the force component that forms the opening force before the first U-shaped plate element 20 reaches magnetic saturation.

The magnetic force component forming the contact pressure and the magnetic force component forming the opening force can be adjusted within a larger range by designing the length and the clear width of the U-shaped plate elements 20 and 30 and by selecting the range covering the switch bridge.

In a further embodiment shown in fig. 4, instead of the small magnet yoke 20, which is inserted in place in the bridge carrier 8, two small magnet yokes 21 and 22 are mounted on a stationary part of the switch cabinet 1 or on the switch housing in a force-transmitting manner on the sides of the bridge carrier 8. These two yokes are positioned between the bridge carrier 8 and the switch contacts 3a, 5a and 3b, 5b, respectively. The two yokes 21 and 22 do not hinder the translational movement of the switch bridge carrier 8 by their predetermined spacing relative to the bridge carrier 8 in the millimeter or sub-millimeter range.

When the yoke 20 is replaced by two yokes 21 and 22, the two yokes 21 and 22 are positioned in such a way that the moving switching bridge 4 completely or partially penetrates into the U-shaped slots of the two yokes 21 and 22 when the switching contacts 3a, 5a and 3b, 5b are in the closed state. For this purpose, the magnetic yokes 21 and 22 are mounted in force-transmitting fashion in suitable positions on a stationary part of the switch cabinet 1 or on the switch housing.

In this latter variant, in particular in contrast to the one shown in fig. 2, the magnetic force generated by the two small yokes 21 and 22 is not supported on the electromagnetic drive of the switching device. The function of the drive is thus not impaired.

In a further preferred embodiment shown in fig. 5, instead of the two small yokes, two plate elements 25, 26 are provided, which with their planar sides approximately occupy the position of the transverse sections of the yokes 21 and 22 shown in fig. 4 and which are correspondingly force-transmitting mounted on a stationary part of the switch cabinet 1 or on the switch housing.

When the switching contacts 3a, 5a and 3b, 5b are in the closed state, the moving contact carrier has a minimum predetermined spacing, i.e. a spacing in the range of submillimeters to millimeters, relative to the two plate parts 25, 26. Two U-shaped plate elements 28, 29 are mounted on the moving contact carrier, which with their side leg sections each face one of the two plate elements 25, 26, thus forming two magnetic circuits which are charged by the current in the moving bridge carrier, thereby generating a magnetic attraction force on the moving contact carrier.

The yoke or U-shaped plate elements 20 or 21, 22 or the plate elements 25, 26 with the associated U-shaped plate elements 28, 29, respectively, are made of a ferromagnetic material and generate a magnetic attraction force acting in the opposite direction on the switching bridge 4 with respect to the magnetic force of the large yoke 30 made of the ferromagnetic material.

The invention described with the aid of the figures is particularly applicable in switchgear in which the movable contact performs a translational movement. Which may be a contactor as in the embodiment shown in fig. 1. The invention is not limited to circuit breakers having mechanical or electromechanical drives.

As already explained above, the invention can also be applied in switching devices with rotary switching movement, in which case the first yoke or U-shaped plate 20 engages the moving rotary contact from the front side of the contact carrier facing the contact, while the second yoke or U-shaped plate 30 engages the opening region of the rotary contact at the rear side of the contact carrier.

Claims (13)

1. A switching device comprising a switching box having at least one stationary contact and at least one movable contact, in association with which at least two ferromagnetic U-shaped yokes (20, 30; 21, 22; 25, 26, 28, 29) are associated for generating at least two electrodynamic magnetic forces which are opposite to one another with respect to their force vectors, wherein the at least two ferromagnetic U-shaped yokes (20, 30; 21, 22; 25, 26, 28, 29) are each positioned relative to the at least one movable contact (5a and 5b) in such a way that the force vector generated by one of the ferromagnetic yokes acting on the at least one movable contact (5a and 5b) is directed toward the at least one stationary contact (3a and 3b) and the force vector of the other ferromagnetic yoke is directed away from the at least one stationary contact (3a and 3b), wherein the two yokes (20, 30) are dimensioned such that the yoke (20) of smaller dimensions can be at least partially inserted into the air gap of the yoke (30) of larger dimensions, for which purpose the outer dimensional width of the smaller yoke (20) is smaller than the air gap width of the larger yoke (30).

2. A switching apparatus as claimed in claim 1, wherein: the side leg sections of at least one of the larger yokes (30) and at least one of the smaller yokes (20) are directed opposite to each other, so that the side leg sections of the smaller yokes (20) are oriented towards the transverse sections of the larger yokes (30).

3. A switching apparatus as claimed in claim 2, wherein: the smaller U-shaped yoke (20) is connected in a force-transmitting manner to a bridge (8).

4. A switching apparatus as claimed in claim 2, wherein: the small U-shaped yoke (20) is formed by two partial yokes (21, 22) which are associated with the moving contacts (5a and 5b) and are fastened to the stationary part of the switch cabinet (1).

5. A switching apparatus as claimed in claim 1, wherein: a means for generating a closing force of at least one magnetic contact is formed by two small U-shaped yokes (28, 29) and iron plates (25, 26) associated with them.

6. The switching apparatus as defined in claim 5, wherein: the small U-shaped magnetic yokes (28, 29) are associated with the movable contacts (5a and 5b) and are connected in a force-transmitting manner to a switching bridge (4).

7. The switching apparatus as defined in claim 5, wherein: iron plates (25, 26) associated with the two smaller U-shaped yokes (28, 29) are fixed to a stationary part of the switch cabinet (1).

8. A switching apparatus as claimed in claim 2, wherein: a large U-shaped magnet yoke (30) is connected to the switch cabinet (1) in a force-transmitting manner and is used to generate a magnetic breaking force.

9. A switchgear apparatus as claimed in claim 2, wherein a guide rail is provided on said switch box, characterized in that: the larger U-shaped yoke (30) is connected to the guide rail (32).

10. A switching apparatus as claimed in claim 9, wherein: the guide rail (32) is made of iron.

11. A switching device according to claim 9 or 10, characterized in that: the guide rail (32) and the larger U-shaped yoke (30) are composed of one piece.

12. A switching device according to claim 2 or 8, characterized in that: the smaller yoke (20) is significantly smaller than the larger yoke (30).

13. A switching apparatus as claimed in claim 12, wherein: the length dimension of the larger yoke (30) is three times the length dimension of the smaller yoke (20).