DE20116400U1 - Overload protection for an electric motor using a controlled power relay circuit - Google Patents

Abstract

The switching relay used to control an electric motor [7] has a pair of mechanically interlocked coils [2a,2b] that control movement of an armature that operates motor supply contacts [3a,3b]. Included in the coil circuit is an overload current detector [6]. When a set value is exceeded the relay responds and shuts down the motor.

Description

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KÖNIG ■ PALGEN ■ SCWuMACRHR ■ K3iUfN* DÜSSELDORF■ESSEN PATENT ATTORNEYS

OUR SIGN: 101 169 M/Hg Essen, 05 October 2001

Society for Drive Technology Dr. Ing. Günther Hammann GmbH & Co. Wiesenstrasse 81 D - 40549 Dusseldorf Switching device, especially contactor

The invention relates to a switching element, in particular a contactor, according to the preamble of claim 1.

The aforementioned contactors are generally understood to be pushbutton switches whose switching elements are held in the switched-on position by means of a current-carrying magnetic coil. When the switching force of the current-carrying coil ceases, a restoring force, usually caused by a spring element, returns the switching element to its original position and the contactor switches off.

Such contactors, in particular so-called reversing contactor combinations, are known from the state of the art, for example from the European patent application EP 0 363 523 A1. These reversing contactor combinations are usually used to control motors in order to change their running direction. The reversing contactor combination has primarily

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the task of preventing a phase short circuit between the two outer conductors of the motors' power supply. The switching elements known as contactors have, in addition to the switching element, the electromagnetically actuated coil described above with a movable armature to actuate the switching element. In order to avoid the coils of both contactors of the reversing contactor combination being attracted together and thus the phase short circuit described above between the two outer conductors, the armatures of the coils can be locked against one another using a mechanical locking device. This mechanical locking device essentially consists of a movable articulation point for the two switching elements designed as hinged armatures, so that when the first switching element is actuated and moved in one direction, the second switching element cannot close due to the displaced articulation even when it is actuated.

Furthermore, in order to deal with the problem of the simultaneous attraction of both coils of a switching element designed as a reversing contactor combination, European patent EP 0 455 534 B1 proposes, in addition to the mechanical locking described above, to provide two additional interrupter switching elements which additionally interrupt the control circuit of the coil which is not in operation.

Nevertheless, it can happen that in reversing contactor combinations with a mechanical locking of the two armatures, the second coil also receives a pull-in signal, although the armature of the first coil is already pulled. If this state of control of both coils lasts for a longer period, the current of the additionally controlled coil with the non-pulled armature increases very quickly. This high current in the coil causes a rapidly increasing field strength of the coil, which is not converted into active power to move the armature, but into heat. The coils usually have a plastic winding body for the coil wire, in which the armature is guided so that it can move. The strong heating of the coil can

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This can lead to the plastic winding body becoming deformed and the armature no longer being guided optimally within the plastic body. This can result in the switching element failing or not working reliably.
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The present invention is based on the object of creating a switching element, in particular a contactor, whose reliability is optimized.

This object is achieved by a switching element having the features of claim 1. Advantageous embodiments of this invention are specified in the further claims 2 to 7.

According to the invention, in a switching device, in particular a contactor, with a switching element and a coil with a movable armature for electromagnetic actuation of the switching element, a fault current monitoring element is assigned to the coil, which switches off the coil when a presettable switching current is exceeded. This reliably prevents the coil and thus its plastic winding body, in which the movable armature is arranged, from overheating when the movable armature is blocked or jammed.

The above invention can be used particularly advantageously for so-called reversing contactor combinations for controlling electric motors with reversible rotation direction. These reversing contactor combinations have two switching elements with corresponding switching elements and coils, each with a movable armature. In addition, the movable armatures of the two coils are mechanically locked against each other so that the electric motor connected to the reversing contactor combination cannot be switched incorrectly with regard to its direction of rotation. In the event of incorrect control of the coils, however, the mechanical locking of the two armatures against each other can lead to an overload of the coil which is later switched on incorrectly. To avoid this, the two coils are provided with the common

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Residual current monitoring element is assigned. The preset maximum tripping current of the residual current monitoring element is approximately 10% above the holding current of a coil in normal operation.

Advantageously, the residual current monitoring element resets itself so that after the control current has been switched off, the previously switched-on coil can be automatically put back into operation. This reset time is advantageously in the range of 1 to 5 seconds and is therefore very short so that the operation of the respective electric motor drive only needs to be interrupted insignificantly despite the incorrect control of the reversing contactor combination. The coils usually have a winding body for the winding, which is made of plastic and in which the armature is guided.

With the previously described switching device with the residual current monitoring element, it is possible to achieve the longevity of the reversing contactor combination despite the occurrence of incorrect activations, since the switched-on coil is not damaged by switching off the control current in the event of incorrect activations.

The components to be used according to the invention as mentioned above, as well as those claimed and described in the exemplary embodiment, are not subject to any special exceptional conditions in terms of their size, shape, choice of material and technical conception, so that the selection criteria known in the field of application can be applied without restriction.

Further details, features and advantages of the subject matter of the invention emerge from the subclaims and from the following description of the associated drawing, in which - by way of example - a preferred embodiment of the switching element according to the invention, in particular a contactor, is shown.

The drawing shows a basic circuit diagram of a control circuit of a reversing contactor combination. This reversing contactor combination consists of two switching elements 1a and 1b. These switching elements 1a and 1b have coils 2a and 2b, which essentially consist of a plastic winding body (not shown), the actual winding and an armature guided within a hole in the winding body for actuating the switching elements 3a and 3b, via which an electric motor 7 is controlled. The armatures of the coils 2a and 2b are connected to one another via a mechanical lock 4, which is only indicated schematically. Such mechanical locks are generally state of the art and essentially consist of a combination of levers, switching pawls and guide surfaces, which prevent the second switching elements 3b from closing when the first switching elements 3a are already closed. The coils 2a and 2b are controlled via a control current and corresponding push-button switching elements 8a, 8b to actuate the switching elements 3a and 3b. A residual current monitoring element 6 is arranged in the line 5 of the control current to the coils 2a and 2b, which interrupts the control current supply and thus switches off the coils 2a and 2b together. The residual current monitoring element 6 is selected so that if the control current exceeds a predetermined value in the common supply line 5, the control current supply to the two coils 2a and 2b is interrupted. This value is approximately 10% above the usual holding current of the coils 2a, 2b. The residual current monitoring element 6 is preferably designed as a self-resetting fuse.

The fault current monitoring element 6 is associated with a reset element integrated therein, via which the normal operation of the electric motor can be automatically resumed in the desired direction of rotation after a fault current has been detected and the coils 2a, 2b have dropped out and after a certain time has elapsed. The time here is approximately between 1 and 5 seconds and is therefore very short to ensure almost continuous operation.

of the electric motor drive despite a previously occurring fault.

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List of reference symbols

1a, 1b Switching devices 2a, 2 B Kitchen sink 3a, 3b Switching element 4 mechanical locking 5 Control current line 6 Residual current monitoring element 7 Electric motor 8a. 8b Pushbutton switch element

N neutral conductor

L1, L2, L3 conductors

Claims (7)

1. Switching device, in particular a contactor, with a switching element and a coil with a movable armature for electromagnetic actuation of the switching element, characterized in that the coil ( 2 a, 2 b) is assigned a residual current monitoring element ( 6 ), via which the coil ( 2 a, 2 b) can be switched off when a presettable switching current is exceeded. 2. Switching device according to claim 1, characterized in that two switching devices ( 1 a, 1 b) with corresponding switching elements ( 3 a, 3 b) and coils ( 2 a, 2 b), each with a movable armature, are connected to one another in the manner of a reversing contactor combination in such a way that the switching-on movements of the respective movable armatures of the coils ( 2 a, 2 b) are mechanically locked against one another. 3. Switching device according to claim 2, characterized in that the two coils ( 2 a, 2 b) are assigned a common fault current monitoring element ( 6 ), via which both coils ( 2 a, 2 b) can be switched off when the presettable switching current is exceeded. 4. Switching device according to one of claims 1 to 3, characterized in that the presettable switching current is approximately 10% above the holding current of a coil ( 2 a, 2 b) in normal operation. 5. Switching device according to one of claims 1 to 4, characterized in that the residual current monitoring element ( 6 ) has a reset element ( 8 ) via which, after previous switching off, the control current of the previously switched on coil ( 2a , 2b ) can be switched on again after a presettable time. 6. Switching device according to claim 5, characterized in that the presettable time is in the range between 1 and 3 s. 7. Switching device according to one of claims 1 to 6, characterized in that each of the coils ( 2 a, 2 b) has a winding body made of plastic in which the armature is guided.