EP1911059B1 - Short-circuiting device for use in low-voltage and medium-voltage systems for the protection of parts and personnel - Google Patents

Abstract

Device has a switching element (9) actuated by the tripping signal of a fault detection device, two mutually opposite contact electrodes (2,6), and a sacrificial element (5) acting as spacer between contact electrodes. Electrical connection is provided between sacrificial element and switching element and between the sacrificial element and one contact electrode to bring about thermal destruction of the sacrificial element in a targeted manner owing to current flow. The sacrificial element may be provided in the form of a thin-walled hollow cylinder made of high-melting metallic material. The sacrificial element may also be provided in the form of a wire or rod made of conductive material having low melting integral. The sacrificial element in wire or rod form is under mechanical prestress under tension in contrast to the sacrificial element in hollow cylinder form. Contact can be made with the contact electrodes at a circuit having connections of different potentials. The contact electrodes, under mechanical prestress, perform relative movement in relation to one another in the event of a shirt-circuit assisted by spring force. A further part is provided to move with respect to the contact electrodes for short-circuiting the contact electrodes. An independent claim is included for the short-circuiting method using the short-circuiting device.

Description

The invention relates to a further developed short-circuiting device for use in low and medium voltage equipment for property and personal protection, comprising a switching element which is actuated by the trigger signal of a fault detection device, two opposing contact electrodes with means for supplying power, which to a circuit with terminals of different Potential are contactable, continue the contact electrodes under mechanical bias standing in the case of short circuit spring assisted perform a relative movement to each other, a sacrificial element as a spacer between the contact electrodes and an electrical connection between the sacrificial element and the switching element on the one hand and one of the contact electrodes on the other hand, a current flow induced thermal destruction of the Targeting element to bring about specifically, according to the preamble of claim 1.

Furthermore, the invention relates to a method for initiating a short circuit in low and medium voltage installations with a short-circuiting device.

Various electrical faults can occur in electrical switchgear and distribution systems, which do not lead directly to the response or only to a delayed response of existing overcurrent protection devices. By way of example, arcing arcs may be mentioned here. Similar problems occur, in particular with regard to the protection of persons due to operational or error-related potential differences. Such errors can lead to extreme property damage, but also personal injury. To limit the damage in addition to a very quick detection of the error and its rapid shutdown is required.

Various solutions are state of the art for fast detection of various error cases.
Reference is made, for example, to the DE 43 31 992 A1 , a cell-like switchgear secured against arcs for the distribution of electrical Energy revealed. Also in the DE 43 45 170 A1 an arc fault protection device for switchgear is described, where the actual switching or protection device is actuated by a signal from an AND operation of at least one light-sensitive sensor and a light-insensitive sensor. The actual short-circuiter comprises a coil, wherein the short-circuiter generates a metallic short circuit between the parts to be short-circuited as a result of the forces which are produced by the induction current in cup-shaped metal parts under a vacuum. The energy storage source and the coil should be dimensioned so that the mentioned metallic short circuit takes place in a time between 0.1 ms and 2 ms.

For a short-circuiter for use in electrical energy distribution installations according to DE 197 46 815 A1 is provided directly driven by a gas generator short-circuiting element with a short-circuiting piston. The local short-circuiting piston should perform regardless of manufacturing tolerances optimal shock movement and at the same time be transport-secured.

Other typical short circuiters of the prior art, for example, in the DE 94 19 141 U1 . DE 197 46 815 A1 such as DE 42 35 329 C2 described. Here, a distinction is made between reusable and single-acting devices. Reusable short circuiters are very expensive and expensive. In the case of single-acting short-circuiters, an explosive charge or a gas generator is generally used to move the electrodes towards each other, which understandably involves special protective measures during manufacture, transport and use.

According to the DE 42 35 329 A1 includes a short-circuit device to the prior art, which consists of at least one switching element which is actuated with a trigger signal of an error detection device. The short-circuiter provided there comprises at least two electrodes receiving the switching element between them and has current-carrying parts or regions. As a result of the current flowing directly in both the switching element and the short-circuiter in the current-carrying parts is at least a movable or deformable current-carrying region pressed against the electrodes and thus generates a metallic short circuit. In this known short-circuit device, the response times are insufficient and it is the overall design arrangement from a manufacturing point of view very expensive.

In teaching according to the patent DE 103 13 045 B3 a short-circuiting device for use in low and medium voltage systems is presented, which also includes a switching element which is actuated by a trigger signal of an error detection device. According to the local invention, the switching element is a triggerable overvoltage protection device, which can be brought to a response by a current or voltage pulse and destructible in the event of an error. At least one of the surge arrester receiving electrodes is under mechanical bias and is movable toward the opposite electrode, the overvoltage protector forming an electrode spacer which, in the event of destruction, allows the electrodes to contact the short circuit.
The aforementioned switching element may be a series circuit of a triggerable overvoltage protection device and a device with adjustable or defined melting integral. In this series connection, only the device with the defined melt integral can be destroyed in the event of a fault. In one embodiment, the aforementioned device is a glass tube fuse, a linear or non-linear resistor, a varistor, a low-melting metal or a metal alloy, a semiconductive or conductive ceramic, such a glass, or the like. To generate the mechanical bias and the relative electrode movement is in accordance with DE 103 13 045 B3 used a tension or compression spring. Also, according to the related teaching of the prior art, an embodiment of the electrodes as a pot with a counter electrode is common, which has a plunging into the pot die.

However, it has been found as a result of further investigations that the execution and optimization of the sacrificial element for the functional properties of the short-circuiter has a great and extraordinary importance. Fundamental goal of the optimization of a short-circuit device is it is to achieve the fastest possible closing movement of the main contacts and a very low load on the switching element, wherein the sacrificial element significantly influences these two parameters.

From the FR-A-1514214 a cylinder of a refractory metallic material is previously known, which is used as a sacrificial element. Furthermore, from this document, a fusible element in the form of a spiral wire is previously known.

From the foregoing, it is therefore an object of the invention to provide an advanced short-circuiting device for use in low and medium voltage equipment for property and personal protection, said short-circuiting device should have a cost-effective to manufacture sacrificial element, which leads to a minimized loading of the switching element and the has the highest possible electrical conductivity to minimize the commutation with simultaneous high mechanical strength to use a high spring force with the aim of reducing the movement time.

The object of the invention is achieved with a short-circuiting device according to the combination of features according to claim 1, wherein reference is additionally made to an inventive method for initiating a short circuit in low-voltage systems using the short-circuiting device according to the invention.

In the inventive short-circuiting device according to the invention for use in low and medium voltage systems for property and personal protection, this includes a switching element which can be actuated by the trigger signal of an error detection device. Furthermore, two opposing contact electrodes are provided with means for supplying power, wherein the contact electrodes can be contacted to a circuit with terminals of different potential.

Furthermore, the contact electrodes, under mechanical bias standing, spring-assisted in case of short circuit, a relative movement from each other.

The sacrificial element, which is provided as a spacer between the contact electrodes, is in electrical connection with the switching element, on the one hand, and one of the contact electrodes, on the other hand, in order to bring about thermal destruction caused by thermal flow.

According to the invention the sacrificial element is designed as a thin-walled hollow cylinder made of a refractory metallic material.

In one embodiment of the invention, it is possible to receive an electrically conductive substance in the hollow cylinder. The hollow cylinder is a structure of a pressure-resistant material, wherein the aforementioned filling is designed as a low-melting metal, for example. To avoid too high a melting integral value, an insulating layer with little mechanical or even low temperature resistance can be arranged between the hollow cylinder and the actual conductive substance instead of accompanying partial filling.

Upon the desired destruction of the sacrificial element, i. of the hollow cylinder, the substance located in the interior is released and can already realize an electrically conductive short circuit or support such a short circuit even before closing or complete contact without mechanical movement of the main contacts.

The hollow cylinder can be inserted and guided in recesses of the contact electrodes, so that a low contact resistance is given.

In a variant of the invention, an insulating body and an auxiliary electrode are located in the stationary contact electrode, wherein the auxiliary electrode is in communication with the sacrificial element.

The opposing sides of the contact electrodes and the opposing surfaces may have a complementary conical shape with resulting centering effect in the case of short circuit contact.

According to the invention, the ratio between the diameter and the wall thickness of the hollow cylinder is selected to be greater than 10: 1.

Defined structures or changes in wall thickness in the hollow cylinder can form current paths, with the result of uneven heating under current load and deformation with concomitant loss of mechanical strength. It remains in this case advantageously the conductive connection between the contact electrodes, but decreases the mechanical resistance of the hollow cylinder, so that under the action of the spring force of the short-circuiter can be quickly converted into a closed state.

A cavity can be formed between the contact electrodes in order to receive parts of the destroyed sacrificial element, without the desired low-resistance contact connection being impaired in the event of a short circuit.

Between the contact electrodes, a venting channel or a venting bore effective in the closed state can be effective in order to prevent forces arising due to an increase in pressure in the event of a short circuit, in particular when an arc arises, which counteract the movement of the contact electrodes towards one another.

The device for generating the biasing force can be designed as a compression spring, disc spring or the like spring arrangement.

The invention will be explained below with reference to exemplary embodiments and with the aid of figures.

Fig. 1

eine Ausführungsform der Kurzschließeinrichtung mit druckbelasteter beweglicher Kontaktelektrode und hohlzylindrischem Opferelement;

Fig. 2

eine Ausführungsform analog Fig. 1, jedoch mit einem hohlzylindrischen Opferelement, welches mindestens teilweise mit einer leitfähigen Substanz gefüllt ist, und

Fig. 3

ein Blockschaltbild zur Erläuterung des Verfahrens zum Einleiten eines Kurzschlusses in Niederspannungsanlagen mit gestaffelter Zuschaltung.

Hereby show:

Fig. 1

an embodiment of the short-circuiting device with pressure-loaded movable contact electrode and hollow cylindrical sacrificial element;

Fig. 2

an embodiment analog Fig. 1 but with a hollow cylindrical sacrificial element which is at least partially filled with a conductive substance, and

Fig. 3

a block diagram for explaining the method for initiating a short circuit in low-voltage systems with staggered connection.

In the following embodiments, the same reference numerals are used for the same or equivalent elements.

According to the embodiments, the sacrificial element 5 has a special significance with respect to the effective operation of the short-circuiting device. The aim of optimizing the short-circuiting device is to achieve the fastest possible closing movement of the main contacts and a very low load on the switching element. The speed of the closing movement of the main contacts is in addition to the contact distance, the mass of the moving contact, the effective counter forces also determined substantially by the force-displacement characteristic of the spring 4 used. The higher the initial force in the tensioned state and the higher the residual force in the closed state of the short-circuiter, the shorter the closing time of the main contacts.

The mass of the moving contact and the spring force in the stressed state permanently act on the sacrificial element and require a certain mechanical strength.

On the other hand, the sacrificial element should be overloaded as possible as a result of a low power supply and cause the desired movement of the corresponding main contact, ie the respective contact electrode. Until the current commutation of the fault current to the main contacts, the switching element is loaded with the fault current. The lower this load, the lower the cost of the switching element can be kept. In addition to the costs and the protection of the switching element is a rapid overload of the sacrificial element and a rapid reduction in the impedance of the Kurzschlusspfads serve, since after closing the main contacts a purely metallic short circuit is realized. Thus, the impedance of the switching element and possibly the existing impedance of the arc and the substantially ohmic resistance of the sacrificial element is eliminated from the fault circuit.

The sacrificial elements according to the invention have the following properties. There is a low melting integral (I ² t value) of the material to minimize stress on the switching element. The sacrificial elements have a high electrical conductivity to minimize the commutation time and have a high mechanical strength to use a high spring force in view of a desired reduction in the movement time of the contact electrodes. Furthermore, there is only a low arc voltage in the destruction of the sacrificial element for the realization of a short commutation time. Forces, which counteract the mechanical movement, such as a resulting increase in pressure, are avoided or reduced. The destruction behavior of the particular hollow cylindrical material is designed so that there is no impairment of the mechanical movement of the contact electrodes.

As in the Fig. 1 and 2 shown, the sacrificial element 5 is designed as a thin-walled hollow cylinder. As a material for the hollow cylinder are particularly suitable due to the high mechanical strength steels or iron alloys. Materials with high specific melting integral values, such as copper or silver, lead with sufficient mechanical strength to a comparatively higher load on the switching element.

The thin-walled hollow cylinder geometry is chosen so that the ratio of diameter to wall thickness is substantially greater than 10: 1. This geometry has a much higher mechanical strength compared to a solid cylinder of the same material at the same melt integral. This makes it possible to specify higher spring forces and ensures faster closing times of the contact electrodes.

Compared with solid material, the hollow cylinder according to the invention has a further advantage explained below, in particular at diameters of several millimeters.
As a result of low asymmetries in the current distribution on or in the hollow cylinder, the hollow cylinder heats and melts unevenly even at high current loads and short melting times. This effect can consciously by the current transfer at the contact points or by structuring be promoted of the cylinder. In principle, structural material influences or even the use of composite material are conceivable.

This uneven heating leads to small and medium current loads (melting times of a few minutes to a few milliseconds) to the deformation of the hollow cylinder. The hollow cylinder thus loses its mechanical strength in this process almost abruptly, causing the compression of the cylinder and the closing of the main contacts of the short-circuiter. This type of closing process is very advantageous because the process takes place even without a significant arc in the short-circuiter. There is therefore no additional impedance and no pressure wave, which possibly counteracts the contact closure in the embodiment of the invention.

At higher currents, the hollow cylinder also does not melt or evaporate uniformly, as a result of which individual metallic bridges remain and thus the arc-free behavior of the short-circuiter is maintained far into the kA range.

An arc arises quasi only when the hollow cylinder is completely evaporated and the main contacts may not have been completely closed.

In the case of an arc ignition at high currents, a larger cavity or in addition a vent may be provided which limits the pressure build-up and thus the resulting counter forces.

The arrangement of the sacrificial element, the main contacts and the gas flow is chosen or designed so that in an arc ignition of the arc commutes immediately from the auxiliary path with the switching element 9 on the two contact electrodes 2 and 6. As a result, in this case, the switching element 9 can already be relieved of the flow of current before closing the contact electrodes.

In order to ensure the absence of arcing even at high currents, in addition, another stage of the current transfer before closing the Main contacts are realized. Here, the use of a sliding contact or a low-melting material is possible.

According to the representations after Fig. 1 and 2 Accordingly, an electrically conductive housing 1 with a movable contact electrode element 2 is present, which is biased under the action of a spring 4. The movable contact electrode 2 is insulated from the electrically conductive housing 1 by means of an insulation 3. In the center of the fixed contact electrode 6 is an auxiliary contact 8 for the switching element 9 and a terminal for the switching element 9. Furthermore, here is an insulation 7, to the electrically conductive housing 1 and the contact electrode 6 is present.

Reference numeral 10 symbolizes a conductive substance that can be used as a complete or partial filling of the hollow cylinder sacrificial element 5.

According to this embodiment Fig. 2 For example, the conductive substance 10 may be embodied as a low melting point metal or conductive liquid.

The inventive principle of the method for initiating a short circuit is based on a staggered connection of the short-circuiter with the following timing.

After the detection of a fault, e.g. an arc fault in the system, the switching element of the short-circuiter is briefly actuated. The possible short-circuit current through the switching element is limited by the sacrificial element and the impedance of the terminal and of the switching element. The current commutes from the fault location to the short circuiter. After an adjustable time, the switching element interrupts the short-circuit current and the system and the fault location are again loaded with mains voltage. In the case of a wiper and a sufficient reconsolidation of the fault remains the supply of the system. The short-circuiter reports the error that has occurred and thus indicates a necessary system check.

If the error persists, the switching element of the short-circuiter is controlled again and permanently. The sacrificial element of the short-circuiter is in overloaded in this case and generates a permanent metallic short circuit, which forces a shutdown of the plant.

In the proposed solution, the sacrificial element is designed so that a metallic short circuit can already be achieved after the lowest current loads (low I ² t values). The switching elements used in this case must thus have only a very low current carrying capacity or a low switching capacity.

For an application of the described method, while maintaining the construction, a differentiated design of the sacrificial element and the switching element is recommended. As an alternative to an almost opposite optimization of the presented short-circuiting device, however, this can be improved by a parallel path for the described method. Thus, an inexpensive and needs-based extension of the simple short-circuiter is always possible to use the explained method.

Fig. 3 shows a schematic diagram relating to the parallel connection of another path. The additional parallel path consists essentially of a controllable switching element 17 with medium to high current carrying capacity and breaking capacity. In addition, an impedance 16 may be provided. With the help of the impedance, it is possible to influence the magnitude of the short-circuit current or the value of the square-wave current pulse, for example with non-linear impedances. On the one hand, this can be useful in order to avoid a response of possible overcurrent or undervoltage protection devices of the network during the first time-limited switching of the switching element and, on the other hand, not to exceed the maximum load with regard to current carrying capacity and extinguishing capability for less powerful switching elements.

However, the height of the impedance 16 should not exceed a few 100 mΩ, since otherwise a commutation of the fault current to the overall device (short circuit path 1 and 2) is severely hindered. Preferably, the impedance should be less than a few mΩ.

As the switching element 17, semiconductor switches, e.g. Thyristors or IGBTs, but also triggerable vacuum switch and spark gaps suitable.

Claims (11)

1. Short-circuiting device for use in low-voltage and medium-voltage systems for the protection of parts and personnel, comprising
   a switching element (9), which can be actuated by the trigger signal of a fault detection device,
   two mutually opposite contact electrodes (2, 6) having power supply means, wherein said contact electrodes (2, 6) can be contacted with an electric circuit having connections of different potentials, wherein further the contact electrodes (2, 6), being under a mechanical preload, carry out in the event of a short-circuit a relative movement in relation to one another assisted by a spring force,
   a sacrificial element (5) as spacer between the contact electrodes (2, 6) and having an electrical connection between the sacrificial element (5) and the switching element (9) on the one hand, and one of the contact electrodes (2, 6) on the other hand, in order to bring about in a targeted manner a thermal destruction of the sacrificial element (5) in response to the current flow,
   characterized in that
   the sacrificial element (5) is a thin-walled hollow cylinder consisting of a high-melting metallic material, with a ratio of diameter to wall thickness of the hollow cylinder greater than 10:1.
2. Short-circuiting device according to claim 1,
   characterized in that
   an electrically conductive substance (10) is received in the hollow cylinder.
3. Short-circuiting device according to claim 2,
   characterized in that
   an insulating layer is provided between the conductive substance (10) and the hollow cylinder, the mechanical stability and temperature resistance of which are lower than those of the material of the hollow cylinder.
4. Short-circuiting device according to one of the preceding claims,
   characterized in that
   the hollow cylinder is inserted into and guided in recesses of the contact electrodes (2, 6).
5. Short-circuiting device according to one of the preceding claims,
   characterized in that
   an insulating body (7) and an auxiliary electrode (8) are located in the stationary contact electrode (6), wherein the auxiliary electrode (8) communicates with the sacrificial element (5).
6. Short-circuiting device according to one of the preceding claims,
   characterized in that
   the opposite sides of the contact electrodes (2, 6) have a complementary conical shape.
7. Short-circuiting device according to one of the preceding claims,
   characterized in that
   the hollow cylinder comprises structures distributed over the wall thickness for defining current paths, resulting in a non-uniform heating in the case of a current load and a deformation along with a loss of mechanical stability.
8. Short-circuiting device according to one of the preceding claims,
   characterized in that
   a hollow space is defined between the contact electrodes (2, 6) in order to receive parts of the destroyed sacrificial element.
9. Short-circuiting device according to one of the preceding claims,
   characterized in that
   a vent channel or a vent hole between the contact electrodes (2, 6) are active also in the closed state.
10. Short-circuiting device according to one of the preceding claims,
    characterized in that
    the device for producing the preloading force is a compression spring (4).
11. Method for initiating a short circuit in low-voltage systems by using a short-circuiting device according to one of the preceding claims,
    characterized by
    switching in the short-circuiting device in a staggered manner, comprising the following steps:

    - actuating the switching element (9) for a short time after a fault event was detected;

    - limiting the short-circuit current through the switching element (9) by means of the sacrificial element (5) and by the impedance of the connection and the impedance of the switching element (9) itself, and commuting the current from the fault location to the short-circuiting device;

    - interrupting the short-circuit current after a predetermined time by the switching element (9) and loading the system anew with supply voltage;

    - if the fault event remains, if necessary, actuating the switching element (9) again, now-permanently;

    - destroying the sacrificial element (5) and generating a permanent short circuit including the shutdown of the system.

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