Switch device and method for operating a switch device

Abstract

The invention relates to a switch device (1) for controlling a flow of electric energy from an energy source (4) to a load (2), having: - n outer conductor inputs (E1, E2, E3) for electrically connecting to the energy source (4), - n outer conductor outputs (A1, A2, A3) for electrically connecting to the load (2), - n outer conductor current paths (6) which electrically connect the n outer conductor inputs (E1, E2, E3) to the n outer conductor outputs (A1, A2, A3) in a bijective manner within the switch device (1), - n switch elements (S1, S2, S3), wherein each of the n switch elements (S1, S2, S3) is arranged in a respective outer conductor current path of the n outer conductor current paths (6), said switch element being capable of switching a current flow through the outer conductor current path (6), and - n overvoltage limiting elements (OV1, OV2, OV3), each of which is connected in parallel to the n switch elements (S1, S2, S3), a respective overvoltage limiting element (OV1, OV2, OV3) being paired with each switch element (S1, S2, S3), and - a control unit (8) for actuating the switch elements (S1, S2, S3). The invention is characterized by - short-circuiting switches (SCS1, SCS2, SCSPE, SCSPE1, SCSPE2, SCSPE3, SCSN1, SCSN2, SCSN3) which can be actuated by the control unit (8) and which are arranged such that, in a current-conducting state, the short-circuiting switches connect the n outer conductor outputs (A1, A2, A3) of the switch device a) to each other and / or b) to a ground conductor (10) or a neutral conductor (11) of the energy source (4) in an electrically conductive manner.

Description

[0001] Description

[0002] Switching device and method for operating a switching device

[0003] The present invention relates to a switching device for controlling an electrical energy flow from an electrical energy source to an electrical load. The present invention also relates to a method for operating such a switching device.

[0004] Switching devices are used to supply electrical consumers with electrical energy from an electrical power source in a controlled manner. Electrical current paths run within a switching device via which electrical current is conducted from an input of the switching device to an output of the switching device, thus conducting electrical energy from the electrical power source to the load. The current paths contain switching elements for switching the electrical current on and off. The fast switching capacity of modern electronic switching elements such as MOSFET transistors can be used to switch off a rapidly rising current in the output circuits, e.g. as a result of a short circuit, after a very short time.

[0005] When currents are switched off quickly, inductances in the circuits can lead to very high voltage stress on the electronic switching elements, which would destroy them without suitable protective measures. To protect the electronic switching elements, overvoltage limiting elements, also known as surge limiters, are arranged in parallel with them. The voltage limiting effect of the overvoltage limiting elements is achieved because they become electrically conductive above a predetermined voltage limiting value, so that the voltage across them can only increase slightly. The voltage limiting value is selected so that a maximum permissible voltage on the electronic switching elements is not exceeded during the limiting process.The surge suppression elements must be dimensioned so that they can completely convert the magnetic energy of the inductors in the short-circuit into heat without causing damage. The dimensioning of the surge suppression elements is critical because it depends on the size of the inductors in the overall electrical arrangement and thus on several parameters.

[0006] One problem for the dimensioning of the surge limiting elements is that suitable assumptions must be made for the length of the load connection cables and the type of load, and the most unfavorable switching events must be identified in order to be able to dimension the surge limiting elements to a reasonable size.

[0007] A further challenge for the dimensioning of surge suppression elements is the normal switching off of an asynchronous motor. The interaction of load output terminal voltages and the voltages of the three-phase network leads to increased voltages at the switching elements. While these voltages do not damage them, they can trigger the surge suppression elements, as their voltage limiting value must be lower than the maximum permissible switching element voltage. This is due to tolerances in the surge suppression elements and their non-ideal limiting function.

[0008] Due to the relatively wide tolerance bands and the non-ideal limiting characteristic, determining the voltage limiting value of the overvoltage limiting elements is not easy in practice and is further complicated by the temperature dependence of the voltage limiting value, so that the selection of the voltage limiting value often represents a compromise with gray areas in which the limiting function functions only suboptimally. The object of the present invention is improved protection of electronic switching elements against overvoltage.

[0009] This object is achieved according to the invention by a switching device having the features specified in claim 1. This object is also achieved according to the invention by a method having the features specified in claim 10.

[0010] The switching device according to the invention is used to control an electrical energy flow from an energy source to a load. The energy source is also referred to as a current source. The energy source can be a single-phase or multi-phase, generally: n-phase, current source. The load is also referred to as a current load. The load can be a motor load, e.g. an induction motor, or a non-motor load, e.g. an electric heater or a lighting device. The switching device has n outer conductor inputs for electrically connecting to the energy source; the outer conductor inputs are also referred to as phase inputs. The switching device has n outer conductor outputs for electrically connecting to the load; the outer conductor outputs are also referred to as phase outputs.The switching device has n outer conductor current paths which, within the switching device, bijectively electrically connect the n outer conductor inputs of the switching device to the n outer conductor outputs of the switching device. The outer conductor current paths thus form supply lines which connect the outer conductor inputs and the outer conductor outputs for transmitting power from the energy source to the load, with each supply line corresponding to a phase of the power load. The energy source can provide a single- or multi-phase power supply; for example, the energy source can be a three-phase network or three-phase system from which one current phase is transmitted to the load via an outer conductor current path of the switching device or from which three current phases are each transmitted to the load via one of three outer conductor current paths of the switching device. The energy source can also be designed as any other single- or multi-phase voltage source, e.g.based on galvanic elements. The switching device has n switching elements, each of which can switch an electric current flowing through an outer conductor current path. One of the n switching elements is arranged in each of the n outer conductor current paths. The switching device has n overvoltage limiting elements, each of which is connected in parallel to one of the n switching elements; each switching element is assigned an overvoltage limiting element. The overvoltage limiting elements have a voltage-limiting effect by becoming conductive and carrying current above a defined voltage value, which is referred to as the voltage limiting value, so that the voltage across them can only increase relatively little. The voltage limiting value is selected such that a maximum permissible voltage that may be applied to the switching elements is not exceeded during the limiting process.The switching device has a control unit for controlling the switching elements. The switching device also has short-circuiting switches that can be controlled by the control unit and are arranged in the switching device such that, in a current-conducting state, they electrically connect the n phase conductor outputs of the switching device a) to each other and / or b) to an earth conductor or a neutral conductor of the energy source. Thus, three variants can be distinguished:

[0011] Variant i ): The short-circuiting switches are arranged in the switching device and are controlled by the control unit in such a way that the short-circuiting switches, in their current-conducting state, electrically connect the n outer conductor outputs of the switching device to one another.

[0012] Variant ii): The short-circuiting switches are arranged in the switching device and are controlled by the control unit in such a way that the short-circuiting switches, in their current-conducting state, electrically connect the n phase conductor outputs of the switching device to another conductor, wherein the another conductor is an earth conductor or a neutral conductor of the energy source.

[0013] Variant iii): The short-circuiting switches are arranged in the switching device and are controlled by the control unit in such a way that the short-circuiting switches, in their current-conducting state, electrically connect the n phase conductor outputs of the switching device to one another and to another conductor, the another conductor being an earth conductor or a neutral conductor of the energy source.

[0014] The combination of phase conductors, neutral conductors and earth conductors is called a wiring system.

[0015] The switching device according to the invention can be connected to an electrical supply line of an electrical load, i.e. a so-called load feeder, and used to switch and / or protect the electrical load; therefore, the switching device according to the invention can alternatively also be referred to as a switching and protection device. The protection of the electrical load by the switching device serves to protect the electrical load and the supply line leading to the electrical load from impermissibly high currents. A supply line of an electrical load is an electrical line via which the load is supplied with electrical energy. Examples of the use of a switching device are applications as a circuit breaker, contactor, relay and motor starter, i.e. a switching device for starting an electric motor.

[0016] The method according to the invention serves to operate a switching device which controls an electrical energy flow from an energy source to a load. Arranged within the switching device are n outer conductor current paths, in each of which a parallel connection of a switching element and an overvoltage limiting element is arranged. The switching element can be controlled in such a way that it changes from a current-conducting switching state to a current-blocking switching state or that it changes from a current-blocking switching state to a current-conducting switching state. The n outer conductor current paths bijectively connect n outer conductor inputs of the switching device to n outer conductor outputs of the switching device. The n outer conductor inputs are suitable for electrical connection to the energy source and the n outer conductor outputs are suitable for electrical connection to the load.The method comprises a step in which the switching elements are controlled such that the switching elements assume a current-conducting switching state and a current flow through the respective outer conductor current paths is possible. The method comprises a further step in which the current flow through the outer conductor current paths is interrupted by controlling the switching elements such that they change from their current-conducting switching state to their current-blocking switching state.The method comprises a further step in which, after the switching elements have changed to their current-blocking state, short-circuiting switches in the switching device are controlled in such a way that they change to a current-conducting switching state. The short-circuiting switches are arranged in the switching device in such a way that, in their current-conducting switching state, they electrically connect the n phase conductor outputs of the switching device a) to one another and / or b) to an earth conductor or a neutral conductor of the energy source. The short-circuiting switches are also referred to as output short-circuiters or simply as short-circuiters.

[0017] The invention is based on the finding that by means of short-circuiting switches in the switching device, which short-circuit the outer conductor outputs of the switching device after switching off a short circuit or after a normal, operational switching off with each other and / or with a neutral or earth conductor, it is possible to reduce the magnetic energy of inductances which are present in a power network comprising the connecting lines between the energy source and the switching device and comprising the connecting lines between the switching device and the load, in two circuits, only one of which runs through the overvoltage limiting elements.Compared to switching off without output short-circuiters, the current flow duration through the surge suppression elements is considerably shorter when switching off with output short-circuiters, since only the magnetic energy of the inductances of the input connection cables and the electrical power source needs to be dissipated. The magnetic energy on the load side, which can be very large depending on the cable length and load type, no longer needs to be converted into heat by the surge suppression elements. The surge suppression elements can therefore be considerably smaller, since they only need to be designed for the comparatively small inductances of the input connection cables and the electrical power source.

[0018] Voltages generated by the load during switching off are short-circuited by the short-circuiters and do not affect the switching elements. The surge suppression elements are therefore only active for a short time and therefore heat up relatively little.

[0019] In conventional solutions that operate without the short-circuiters according to the invention, the surge suppression elements must be dimensioned for a wide inductance range determined by the length of the load connection cables and the type of load. This requires large, bulky, and therefore more expensive surge suppression elements, which significantly increase the installation space of the switching device. Alternatively, limiting specifications must be made for the length of the load connection cables and the type of load, which must then be listed in the operating instructions and restrict universal use.

[0020] By simultaneously switching off the switching elements and switching on the short-circuiters, the functionality is the same for all short circuits that can occur between any two electrical phases; even in the case of a simultaneous short circuit of all three electrical phases, the function of relieving the surge limiting elements is retained.

[0021] In addition to the function of relieving the overvoltage limiting elements when a current in the load circuit is switched off, the short-circuiters can also be switched on after a normal switch-off process, as soon as the output currents have fallen to zero. During normal switch-off, the voltage generated by the load, particularly if it is a motor, can lead to increased voltage stress on the switching elements, which must be designed to cope with this. The short-circuiters prevent voltages generated by the load after switch-off from having a feedback effect on the switching elements. In the case of an asynchronous motor, these are the voltages at its output terminals, which can no longer build up, so that increased voltage stress on the switching elements caused by the motor can no longer occur.This allows electronic switching elements with a lower blocking voltage to be selected, while simultaneously alleviating the tolerance problems when selecting the voltage limiting value of the surge suppression elements. The switching elements can be dimensioned smaller in terms of their dielectric strength, which offers cost advantages. Furthermore, switching elements with a lower dielectric strength have lower electrical losses when conducting electrical current, so less heat needs to be dissipated. This reduces cooling requirements and allows for smaller housings for the switching devices.

[0022] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0023] According to a preferred embodiment of the invention, the switching device has an (n+l)th input for electrically connecting to an earth conductor or a neutral conductor of the energy source. One or more of the short-circuiting switches are arranged such that, in a current-conducting state, they electrically connect the n outer conductor outputs to the (n+l)th input. The advantage of this embodiment is that the solution according to the invention works in the event of any short circuits and earth faults in the entire load circuit, i.e. both in the load connection lines and within the load: short circuits can therefore occur between individual or multiple electrical phases, earth faults from one or more electrical phases to an earthed metallic conductor, without the described functioning of the invention being impaired.

[0024] According to a preferred embodiment of the invention, the switching device has an (n+l)th output for electrically connecting to an earth conductor or a neutral conductor of the load, as well as an (n+l)th current path which electrically connects the (n+l)th input to the (n+l)th output within the switching device and thus represents an earth or neutral conductor connection within the switching device. Because the earth conductor is led through the switching device, the current through the earth conductor can be measured and used to monitor the electrical insulation state of the load side, consisting of load connection lines and the load.

[0025] Another advantage of monitoring the current in the earth conductor is that the short-circuiter to the earth conductor is only activated when necessary—that is, only when a ground fault occurs—along with the other short-circuiters between the current-carrying current paths, and can otherwise remain switched off at all times. This minimizes leakage currents from the electrical phases to the earth conductor.

[0026] A switching device with a neutral conductor connection makes it possible to control loads with different energy consumption in each of the three electrical phases during normal operation. The neutral conductor ensures that the same voltage is applied to each of the individual loads in the three electrical phases. This enables separate, independent control of the three loads in the electrical phases. This means that each of the three loads can be switched on and off at different time intervals; the switching elements are also switched on and off independently of one another. In order to keep the voltage generated by the load away from the switching element when an electrical phase is switched off, a short-circuiter is connected to the neutral conductor from each output of the switching device. This means that each switching element is assigned a short-circuiter, so that each switching element is protected when switched off regardless of the switching state of the other two switching elements.

[0027] According to a preferred embodiment of the invention, a short-circuiting switch leads from each of said n phase conductor outputs to the (n+l)th input. The fact that each of the short-circuiters present leads to the earth conductor, so that the three short-circuiters have a common connection point, can be advantageous when controlling the short-circuiters, since, due to the common connection point, a single control voltage can be used for all three short-circuiters simultaneously.

[0028] According to a preferred embodiment of the invention, the switching device has a current measuring device for measuring the current in the earth or neutral conductor connection. The input-side earth fault current subsides quickly after the short-circuiter is switched on, whereas the load-side earth fault current flows for considerably longer before it reaches zero. The surge limiting element is only slightly loaded and can again be made small, as described above. Because the earth conductor is passed through the switching device, the current through the earth conductor can be measured and used to monitor the electrical insulation state of the load side, consisting of the load connection cables and the load.In contrast to the case where the earth-fault current can be measured directly in the earth conductor and only flows in the event of a fault, earth-fault measurement with a connected neutral conductor is only possible indirectly and is therefore subject to greater inaccuracy. The earth-fault current must be determined by summing the four currents flowing out of the switching device. Ideally, if there is no earth fault, the sum of these four currents is zero.

[0029] According to a preferred embodiment of the invention, the control unit is designed to determine the electrical insulation state of the load based on the measured current in the earth conductor connection. Because the earth conductor is routed through the switching device, the current through the earth conductor can be measured and used to monitor the electrical insulation state of the load side, consisting of the load connection cables and the load. This allows for early detection of insulation faults and notification to the operator of the switching device.

[0030] According to a preferred embodiment of the invention, the control unit is designed to calculate an earth fault current based on the measured current in the neutral conductor connection, together with the other measured currents flowing to the phase conductor outputs. This earth fault current is used to monitor the electrical insulation status of the load. In embodiments in which the neutral conductor passes through the switching device, the current in the neutral conductor can be measured, and from this, the electrical insulation status of the connected load can be assessed. This allows early detection of insulation faults and notification to the operator of the switching device.

[0031] According to a preferred embodiment of the invention, the switching device has current sensors for detecting measured values ​​of the current intensity in at least one of the current paths and transmission means for transmitting the measured values ​​to the control unit.

[0032] According to a preferred embodiment of the invention, the short-circuiting switches are electronic components. This is advantageous because electronic components can be switched on much more quickly and precisely than mechanical switching elements. In this way, the time interval between the switching element currents becoming zero and the short-circuiters being switched on can be minimized and thus also the time during which the overvoltage limiting elements are subjected to thermal stress. The short-circuiting switches are electronic switches which implement the function of an electromechanical switch but do not have any moving parts. The short-circuiting switches can be switched to a high-resistance state to prevent current flow or to a low-resistance state to enable current flow in a current path; for this purpose, semiconductor-based switching elements such as field-effect transistors (FETs) and MOSFETs (e.g.Based on silicon, gallium nitride, silicon carbide), IGBTs, bipolar transistors, or diodes. In addition to a semiconductor switch, an electronic switching element may also have a protective element for the semiconductor switch.

[0033] According to a preferred embodiment of the invention, the short-circuiting switching elements are electronic components of the MOSFET, IGBT, thyristor, triac or transistor components. Thyristors and triacs are very suitable as electronic components for the short-circuiting switches when the electrical energy source generates alternating voltages, since thyristors and triacs automatically interrupt the flow of current when the current has dropped below a certain threshold. Furthermore, these components have a high short-time current carrying capacity. This means that the maximum short-circuit current values ​​in the range of 300 to 600 A can be carried by inexpensive components in the lower power range without being damaged. However, electronic components such as MOSFET or IGBT are just as possible. These are particularly suitable when the electrical energy source generates direct voltages.

[0034] According to a preferred embodiment of the invention, the method comprises the following steps: A current and / or a voltage is measured in at least one of the outer conductor current paths. The measured values ​​are sent to a control unit of the switching device. The control unit sends control commands to the switching elements and short-circuiting switches based on the measured values ​​measured in the outer conductor current paths.

[0035] According to a preferred embodiment of the invention, the method comprises the following step: The switching elements are switched into their current-blocking state if an overcurrent such as a short-circuit current occurs in an outer conductor current path or if an operational switching off of the load is to take place.

[0036] According to a preferred embodiment of the invention, the method comprises the following step: By means of one or more of the short-circuiting switches, the n outer conductor outputs of the switching device are electrically connected to an (n+1) -th input which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source.

[0037] According to a preferred embodiment of the invention, the method comprises the following step: From each of said n outer conductor outputs, an electrical connection is established by means of a short-circuiting switch to the (n+l)th input of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source.

[0038] According to a preferred embodiment of the invention, the method comprises the following step: by means of an (n+l)th current path within the switching device, the (n+l)th input of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source, is electrically connected to an (n+l)th output of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the load, and thus an earth or neutral conductor connection is generated within the switching device.

[0039] According to a preferred embodiment of the invention, the switching elements are electronic components. This is advantageous because electronic components can be switched on much more quickly and precisely than mechanical switching elements. In this way, the time interval between the switching element currents becoming zero and the short-circuiters being switched on can be minimized and thus also the time during which the overvoltage limiting elements are subjected to thermal stress. The switching elements are electronic switches which implement the function of an electromechanical switch but do not have any moving parts. The switching elements can be switched to a high-resistance state to prevent current flow or a low-resistance state to enable current flow in the current path; for this purpose, semiconductor-based switching elements such as field-effect transistors (FETs), MOSFETs (e.g.Silicon, gallium nitride, silicon carbide), IGBTs, bipolar transistors, or diodes can be used. An electronic switching element can have a semiconductor switch as well as a protective element for the semiconductor switch.

[0040] According to a preferred embodiment of the invention, the switching elements are electronic components of the MOSFET (metal oxide semiconductor field-effect transistor) or IGBT (insulated-gate bipolar transistor) type. Suitable electronic components for the switching elements are electronic components such as MOSFET or IGBT.

[0041] According to a preferred embodiment of the invention, the electrical energy source comprises one or more voltage sources that generate an alternating voltage. According to a preferred embodiment of the invention, the electrical energy source comprises voltage sources that generate a direct voltage. The present invention functions with both direct and alternating voltage. The choice of alternating or direct voltage is made depending on what is more appropriate for the particular application.

[0042] According to a preferred embodiment of the invention, the short-circuiting switches remain switched on during the period after the switching elements are switched off until the switching elements are switched on again. This allows overvoltages induced in the load circuit, e.g., by other circuits located nearby or by indirect lightning strikes, to be kept away from the semiconductor switches and the switching device.

[0043] In the following, the invention is explained with the aid of the accompanying drawing. It shows schematically and not to scale

[0044] Fig. 1 shows a conventional switching device;

[0045] Fig. 2 shows the conventional switching device from Fig. 1 with a short circuit within the load between two electrical phases;

[0046] Fig. 3: Current and voltage curves in the event of a short circuit as shown in Fig. 2;

[0047] Fig. 4 shows a conventional switching device with overvoltage limiting elements above the switching elements, wherein a short circuit occurs within the load between two electrical phases;

[0048] Fig. 5: Current and voltage curves in the event of a short circuit as shown in Fig. 4;

[0049] Fig. 6 shows a conventional switching device with overvoltage limiting elements above the switching elements, wherein an earth fault occurs within the load from one electrical phase to a metallic housing of the load; Fig. 7 shows a switching device according to the invention with two internal short-circuiters, wherein a short circuit occurs within the load between two electrical phases;

[0050] Fig. 8: Current and voltage curves in the event of a short circuit as shown in Fig. 7;

[0051] Fig. 9 shows a switching device according to the invention with two internal short-circuiters, in which an earth fault occurs;

[0052] Fig. 10 shows a switching device according to the invention with three internal short-circuiters, one of which can be connected to an earth conductor;

[0053] Fig. 11 shows the switching device according to the invention from Fig. 10, wherein the earth fault current paths are shown after the closing of the three internal short-circuiters;

[0054] Fig. 12 shows a switching device according to the invention with three internal short-circuiters, each of which can short-circuit one output of a current path to the earth conductor;

[0055] Fig. 13 shows a switching device according to the invention with three internal short-circuiters, each of which can short-circuit an output of a current path to a neutral conductor;

[0056] Fig. 14 shows a switching device according to the invention with three internal short-circuiters, each of which can short-circuit an outer conductor output of an outer conductor current path with an input to an earth conductor;

[0057] Fig. 15 shows a switching device according to the invention with three internal short-circuiters, two of which can each short-circuit two outer conductor current paths with each other and the third short-circuiter can short-circuit an outer conductor output of an outer conductor current path with an input to an earth conductor; and

[0058] Fig. 16 a tree diagram with an overview of different constellations of the piping system.

[0059] Fig. 1 shows an electrical switching device 1. Electrical switching devices are used to connect electrical consumers to the electrical power grid and to supply them with electrical energy in a controlled manner.

[0060] For this purpose, the switching device 1 has input terminals E1, E2, E3, to which input connection cables 3 are connected, which connect an electrical energy source 4, here for example a three-phase system with the phase voltages UQ1, UQ2, UQ3, to the switching device 1. Load connection cables 5 are connected to output terminals A1, A2, A3 of the switching device 1, which lead to a load 2 and are connected there to load connection terminals K1, K2, K3, so that the load 2 is electrically connected to the switching device 1.

[0061] Within the switching device 1, each of the inputs El, E2, E3 leads via an electrical current path 6 to exactly one of the outputs Al, A2, A3, whereby the first input El typically leads to the first output Al, the second input E2 to the second output A2, and the third input E3 to the third output A3. Via each current path 6, the electrical current is conducted from one input El, E2, E3 to a corresponding output Al, A2, A3, thus conducting electrical energy from the electrical energy source 4 to the load 2.

[0062] Within each current path 6 there is an electrical switching element SI, S2, S3, e.g. in the current path 6 from the first input El to the first output Al there is a first switching element SI. The electrical switching elements SI, S2, S3 influence the electrical current il, 12, 13 through the current paths 6 in order to supply the load 2 with the required electrical energy at predetermined times. For influencing the current by means of the switching elements SI, S2, S3, the switching device 1 has a control input 7 which is electrically connected to a control unit 8 of the switching device 1. The control unit 8 takes over the targeted control of the electrical switching elements SI, S2, S3 in order to supply the load 2 with the appropriate energy. In addition to the control input 7, other electrical variables can bethe currents iMl, iM2, iM3 measured by sensors 9, in particular current measuring devices, are led in the current paths 6 to the control unit 8 so that the control unit 8 can perform additional functions, such as protecting the load 2 against overload.

[0063] The electrical switching elements S1, S2, and S3 are often designed as mechanical switching contacts, which allow for easy switching of load 2. By using modern electronic power components, such as silicon carbide-based MOSFET transistors, electronic switching elements can be manufactured that can switch electrical current on and off very quickly. This fast switching capability can be used to switch off a rapidly rising current in output-side circuits, e.g., as a result of a short circuit, after a very short time. The energy dissipated in this process is orders of magnitude smaller than with mechanical switching devices, so the damage at a short circuit point is significantly reduced.

[0064] A very rapidly rising current occurs, for example, in the event of a short circuit between the load connection lines 5 or in the load 2. As an example, a short circuit SCI within the load 2 is shown in Fig. 2. A short-circuit current iSCl forms in the first electrical phase Phi and in the second electrical phase Ph2, shown in dashed lines in Fig. 2, which flows through two input connection lines 3, two load connection lines 5, parts of the load 2 and the AC voltage sources UQ1 and UQ2 of the electrical energy source 4.

[0065] Fig. 3 shows the time course of the voltage uSl across the switching element S1 (upper part of the diagram in Fig. 3) and the current il for the first electrical phase Phi (lower part of the diagram in Fig. 3) in the event of a short circuit. The time intervals are not to scale. Starting from a current flow in normal operation 31 (t < t30), in which the switching element S1 carries the current il, a short circuit SCI occurs at time t30: t30 = time at which the short circuit begins. The current il becomes the short-circuit current iSCl and increases very quickly in the period 33 until it is detected after a few microseconds at time t31 and the switch-off process of the short-circuit current is initiated. The switch-off process is initiated by the switch-off of the electronic switching elements S1 and S2 at time t31: t31 = time of switch-off. The current il through the switching element S1 orthe current 12 through the switching element S2 now begins to fall very rapidly, so that after a very short time, typically 30 to 200 nanoseconds, it would fall to the value zero.

[0066] Due to the very rapid change in current il, which is equal to the short-circuit current iSCl, very high voltages USl develop at the inductors of the short-circuit circuit, LQ1, LEI, LAI, LL1 and LQ2, LE2, LA2, LL2, which then appear as very high voltage stress at the current-interrupting switching elements S1 and S2, so that after a very short time, at time t32, the electronic switching elements S1 and S2 are destroyed 32: t32 = time of the switching element failure due to overvoltage. The switching elements often become very low-resistance, so that the short-circuit current iSCl begins to rise again in time 34.

[0067] Another operating scenario involving high voltage stress on the electronic switching elements can occur during the normal switching off of an asynchronous motor. After switching off, the asynchronous motor generates electrical, sinusoidal voltages at its output terminals for a short period of time, from a few hundred milliseconds to several seconds, comparable to those of the three-phase network from which it is powered.

[0068] At the beginning of the period, the level of the sinusoidal output terminal voltages almost reaches the level of the sinusoidal voltages of the three-phase network and then drops to zero at the end of the period. The frequency of the motor terminal voltages changes proportionally to the speed of the rotor of the asynchronous motor and gradually decreases in line with the load on the motor. If the rotor speed and thus the frequency of the motor terminal voltages change quickly, the sinusoidal motor terminal voltages come into phase opposition to the sinusoidal voltages of the three-phase network after a few network periods, i.e. the voltage maxima of the motor terminal voltages coincide with the voltage minima of the three-phase network and vice versa. For the switched off electronic switching elements this briefly means that the voltage stress is almost doubled.

[0069] When the currents il , 12 , 13 are switched off quickly, the inductances in the circuits result in very high voltage stress on the electronic switching elements SI , S2 , S3, which would destroy them without suitable protective measures.

[0070] Fig. 4 shows a solution developed for this purpose, in which overvoltage limiting elements OV1, OV2, OV3 are arranged in parallel to the electronic switching elements SI, S2, S3 to protect the electronic switching elements SI, S2, S3, namely the overvoltage limiting element OV1 in parallel to the switching element SI, the overvoltage limiting element OV2 in parallel to the switching element S2 and the overvoltage limiting element OV3 in parallel to the switching element S3. The voltage limiting effect of the overvoltage limiting elements OV1, OV2 and OV3 arises from the fact that above a certain voltage value US1, US2, US3, which is referred to as the voltage limiting value, they become conductive and carry current iOV1, iOV2, iOV3, so that the voltage across them can only increase relatively little.The voltage limiting value US 1 , US2 , US3 is selected so that the maximum permissible voltage of the electronic switching elements SI , S2 , S3 is not exceeded during the limiting process.

[0071] Fig. 5 serves to explain the temporal relationships during switching off, whereby a short circuit SCI within the load 2 is assumed for the switching element S 1 as an example of a current to be switched off, as shown in Fig. 4.

[0072] Starting from a current flow in normal operation 51 (t < t50), in which the switching element S 1 carries the current il, a short circuit SCI occurs at time t50: t50 = start of the short circuit. The current il becomes the short-circuit current iSCl and increases very quickly in the period 53 until it is detected after a few microseconds at time t51 and the switch-off process of the short-circuit current is initiated. The switch-off process is initiated by the switching off of the electronic switching elements S 1 and S2 at time t51: t51 = time of switch-off. The current iS l through the switching element S 1 now begins to fall very quickly, so that after a very short period 54, typically 30 to 200 nanoseconds, it reaches the value zero.

[0073] Since the current decay rate of the switching element currents iS l and iS2 when they are switched off is so high that a voltage u far above the voltage limiting value Un m of the overvoltage limiting elements OV1 and OV2, the overvoltage limiting elements OV1 and OV2 are active almost immediately after the currents iS l and iS2 begin to fall at time t51 and limit the voltage uS l and uS2 at the electronic switches S 1 and S2 to the voltage limiting value Uiim. The voltage curve across the switching element S 1 is shown in the upper part of the diagram in Fig. 5. The overvoltage limiting elements 0V1 and 0V2 carry a current iOVl or iOV2 which is equal to the difference between the short-circuit current iSCl and the rapidly falling current iS l through the first switching element S 1 or the current iS2 through the second switching element S2.

[0074] If the switching element currents iS l and iS2 have become zero at time t52, the short-circuit current iSCl flows completely through the overvoltage limiting elements OV1 and OV2 during the period 55, which can last from many hundreds of microseconds to several milliseconds. The short-circuit current iSCl has thus switched from the first switching element S 1 to the parallel overvoltage limiting element OV1 and from the second switching element S2 to the parallel overvoltage limiting element OV2 during the switching-off of the switching elements SI, S2.

[0075] As the circuit continues, the short-circuit current iSCl decreases as the magnetic energy of the inductances of the short-circuit circuit is converted into heat in the ohmic resistors of the short-circuit circuit and in the overvoltage limiting elements OV1, OV2. The magnetic energy E present in the inductances mag is proportional to the square of the current flowing through it .

[0076] If the magnetic energy in the inductances has been completely converted into heat, the short-circuit current iSCl has dropped to zero at time t53, thus ending the short-circuit process 56. No more current flows from the electrical energy source 4 to the load 2, and the switching device 1 has shut off the current flow.

[0077] A voltage is now applied to the electronic switching elements SI, S2, S3 which is predetermined by the voltage sources UQ1, UQ2 and UQ3 of the electrical energy source 4. The overvoltage limiting elements OV1 and OV2 must be dimensioned such that they can completely convert the magnetic energy of the inductances LQ1, LEI, LAI, LL1 and LQ2, LE2, LA2, LL2 in the short-circuit circuit into heat without suffering damage. The energy converted into heat in the ohmic resistors RA1, RL1, RA2, RL2 is negligible compared to the energy converted in the overvoltage limiting elements OV1 and OV2 and can therefore be disregarded.

[0078] The dimensioning of the surge limiting elements 0V1 and 0V2 is critical because it depends on the size of the inductances in the entire electrical arrangement and thus on several parameters. While the inductances LQ1 and LQ2 of the electrical energy source 4 can be estimated relatively easily, the inductances of the input connection cables, which are proportional to their cable length, are a first variable due to the unknown cable length. However, for the sake of simplicity, it can be assumed that electrical distribution boards incorporating switching devices are normally located close to the electrical energy source, meaning that the cable lengths tend to be shorter: typical cable lengths are in the range of 3 to 30 m.

[0079] On the output side of switching device 1 towards load 2, the range of values ​​in which the inductances can lie increases considerably. Firstly, the length of the load connection cable can vary greatly, from a few meters up to several hundred meters. Secondly, load 2 itself can display very different inductive behavior. For example, an asynchronous motor has an inductive component that depends on its operating state, i.e. it is greater during the start-up phase than during nominal operation. In contrast, heating elements, for example, have a predominantly resistive character with only a small inductive component. In order to dimension surge limiting elements, realistic lengths of the load connection cables and the load properties must be defined. These parameters must then also be listed in the operating instructions for the device.

[0080] A variant of the short circuit shown in Fig. 2 is the earth fault, which represents an electrically conductive connection from an electrical element of the circuit to an earthed electrical conductor, this connection being caused in most cases by an insulation defect in an electrical element.

[0081] Fig. 6 shows an example of an earth fault. Here, the earth fault SCPE1 occurs in the first electrical phase Phi within the load 2, the electrical behavior of which is described by the series connection of a resistor and an inductance; this series connection can be implemented, for example, by a motor winding. As a result of an insulation defect within the motor winding, current transfers to the iron sheets of the motor, which are electrically connected to the earthed motor housing 20. The earth fault circuit shown in dashed lines is formed with the earth fault current iSCPE1, which flows through the electrical components of the first electrical phase Phi, the metallic motor housing 20 and an earth conductor PE, 10 (PE = Protective Earth).

[0082] The location of the insulation defect within the motor winding has a strong influence on the course and magnitude of the earth fault current iSCPEl . If the insulation defect is located close to the load terminal Kl , the winding inductance L Lia and the winding resistance R Lia small, so that the earth fault current iSCPEl can very quickly reach high values. However, if the insulation defect is close to the winding star point WSP of the motor, the winding inductance LLia and the winding resistance R Lia almost as high as in the fault-free case. The resulting earth-fault current iSCPEl will then be small. Depending on the location of the insulation defect, all intermediate stages of earth-fault current development are possible, lying between these two extremes.

[0083] This variability in the earth fault current level and the effective inductance L Lia, which together significantly influence the magnetic energy of the earth-fault circuit, must be taken into account when dimensioning the surge suppression elements, since it is in these that the magnetic energy is essentially converted into heat. The difficulty lies in identifying the worst-case scenario in order to be able to design the surge suppression elements appropriately.

[0084] The problem of the high voltage stress on electronic switching elements during normal switching off of an asynchronous motor, due to the superposition of the three-phase mains voltages with the motor terminal voltages, is solved by ensuring that the switching elements have a sufficiently high dielectric strength. To achieve this, the switching elements must be designed for approximately twice the voltage value that can occur as the maximum value in the three-phase mains during normal operation in the worst case scenario.

[0085] In summary, it can be stated that the problem outlined below exists: Switchgear with semiconductor-based switching elements, which can switch off electrical currents relatively quickly, must switch off currents in the event of a fault, e.g. in the event of a short circuit. During such a switching-off process, high overvoltages arise at the switching elements, which must be limited to safe values ​​by overvoltage limiting elements. The overvoltages are caused by the inductances in the circuits. The magnetic energy stored in the inductances at the time of switching off must essentially be absorbed by the overvoltage limiting elements during the switching-off process and converted into heat without overloading them. The dimensioning of the overvoltage limiting elements depends primarily on the size of the inductance values ​​and the currents to be switched off in the circuits.The inductance values ​​and the level of the currents to be switched off depend heavily on the length of the load connection cables, the type of load and the reason for switching off.

[0086] One problem is that suitable assumptions must be made for the length of the load connection cables and the type of load, and the most unfavorable tripping events must be identified in order to be able to dimension the surge limiting elements at a reasonable size. The length of the load connection cables and the load types must then be included as specifications in the operating instructions. With regard to short-circuit or tripping events, there remains a relatively small residual risk of not having considered the worst-case scenario, which could lead to device defects in the field. For mechanical switching devices, such specifications mentioned above are not required in the operating instructions due to their greater robustness.

[0087] A further challenge for the dimensioning of surge limiting elements is the normal switching off of an asynchronous motor. The interaction of the motor output terminal voltages and the voltages of the three-phase network leads to increased voltages at the switching elements. While these voltages do not damage them, they can trigger the surge limiting elements, as their limiting value must be lower than the maximum permissible switching element voltage. This is due to tolerances in the surge limiting elements and their non-ideal limiting function.

[0088] The limiting value must be selected such that, when positioned at the lower tolerance band, the overvoltage limiting elements do not respond, or at least do not respond excessively, after switching off and thus heat up. However, when positioned at the upper tolerance band, the voltage at the switching elements is limited to acceptable values ​​even at the maximum expected current switching value. Due to the relatively wide tolerance bands and the non-ideal limiting characteristic, specifying the limiting value of the overvoltage limiting elements is not easy in practice and is made even more difficult by the temperature dependence of the limiting value. The choice of limiting value therefore often represents a compromise with certain gray areas in which the limiting function only functions suboptimally.

[0089] Fig. 7 shows the principle of the solution to the problem on which the present invention is based. In the switching device 1, short-circuiting switching elements SCS I and SCS2 are installed between the switching elements S1, S2, S3 and the output terminals A1, A2, A3. These short-circuiting switching elements can also be referred to as "short-circuiting switches" or simply as "short-circuiters". The short-circuiter SCS I can short-circuit the two output terminals A1 and A2 or the two switching elements S1 and S2, and the short-circuiter SCS2 can short-circuit the output terminals A2 and A3 or the two switching elements S2 and S3.

[0090] To explain the mode of operation, an unintentional short circuit SCI within the load 2 from the first electrical phase Phi to the second electrical phase Ph2 is assumed in Fig. 7. Until the short circuit SCI is detected and a current shutdown is initiated, the short-circuit current iSCl, which is shown in dashed lines in Fig. 7, develops.

[0091] In Fig. 8, which shows the time courses of the currents (lower part of the diagram in Fig. 8) and the voltage (upper part of the diagram in Fig. 8) for the switching element S1 and the overvoltage limiting element 0V1, this is the period 86, which typically lasts a few microseconds, between t80, the start of the short circuit, and t81, the start of the switch-off.

[0092] After switching elements S1 and S2 are turned off at time t81 in Fig. 8, the currents iS1 and iS2 drop very rapidly; however, due to the inductances LI, LEI, LAI, LL1 and LQ2, LE2, LA2, LL2, the voltage uS1, uS2 at switching elements SI, S2 rises very rapidly, up to the voltage limiting value Uiim of the overvoltage limiting elements 0V1 and 0V2. At time t82, which is a period 87 of typically 30 to 200 nanoseconds after the start of the turn-off, the currents iS1 and iS2 have dropped to zero.

[0093] At time t83, which is a relatively short period 88 of typically 5 to 50 microseconds after time t82, the short-circuiter SCSI is switched on. As shown in Fig. 7, two circuits are formed: a first, load-side circuit with the current iSC1 through the load connection lines 5, through a portion of the load 2, and through the short-circuiter SCSI; and a second, source-side circuit with the current iSC2 through the input connection lines 3, through the electrical energy source 4, through the two surge suppression elements OV1 and OV2, and, like the first circuit, through the short-circuiter SCSI. The term "load-side" refers to an object such as an electrical element or an electrical phenomenon such as a current flow that is closer to the load 2 than to the power source 4 with respect to the switching device 1, whereas the term "source-side" refers to a position closer to the power source 4 than to the load 2.

[0094] The source-side current iSC2 decays much faster than the load-side current iSCl, since the magnetic energy of the inductances of the input connection lines 3 and the electrical energy source 4 is quickly converted into heat in the overvoltage limiting elements OV1 and OV2, while the magnetic energy of the load connection lines 5 and the inductance of the load 2 located upstream of the short circuit is only slowly converted into heat in the low-ohmic resistors RA1, RA2. The source-side current iSC2, as well as the current iOVl through the first overvoltage limiting element 0V1 and the current il through the first current path 6, becomes zero at time t84, while the load-side current iSCl only at time t85.The time period 89 between the time t83 at which the short-circuiter SCS I is electrically switched on and the time t84 at which the source-side current iSC2 has dropped to zero is typically in the range of a few hundred microseconds, while the corresponding time period 90 for the load-side current iSCl can last up to several hundred milliseconds.

[0095] As long as the source-side current iSC2 flows, it generates heat in the overvoltage limiting elements OV1, OV2. However, compared with switching off without short-circuiters, which is shown in Fig. 4, when switching off with short-circuiters the current flow time through the overvoltage limiting elements OV1, OV2 is considerably shorter, since only the magnetic energy of the inductances of the input connection lines 3 and the electrical energy source 4 needs to be dissipated. The magnetic energies on the load side, which can be very large depending on the line length and load type, no longer need to be converted into heat by the overvoltage limiting elements OV1, OV2. The overvoltage limiting elements OV1, OV2 can therefore be made considerably smaller, since they only need to be designed for the comparatively small inductances of the input connection lines 3 and the electrical voltage source 4.

[0096] The basic function of the invention was described with reference to Fig. 7 in the case of a short circuit from the first electrical phase Phi to the second electrical phase Ph2 within the load 2, without going into detail about the third electrical phase Ph3.Since the current from the normal operation preceding the short circuit is still flowing in the non-faulty third electrical phase Ph3, the third switching element S3 is also switched off together with the other two switching elements S1 and S2 and, together with the short-circuiter SCS1 for the outputs A1 and A2, the short-circuiter SCS2 for the outputs A2 and A3 is also activated, since otherwise the output current iA3, which flows in the third current path from the third output A3 in the direction of the load 2, flows back to the energy source 4 via the first and second electrical phases Phi and Ph2 and in the process additionally heats up not only the third overvoltage limiting element OV3 of the third switching element S3, but also the other two overvoltage limiting elements OV1 and OV2.

[0097] By simultaneously switching off all three switching elements SI, S2, S3 and simultaneously switching on the two short-circuiters SCSI and SCS2, the functioning is the same for all other unintentional short-circuits that may occur between any two other electrical phases; even in the case of a simultaneous short-circuit of all three electrical phases, the function of relieving the overvoltage limiting elements OV1, OV2, OV3 is retained.

[0098] The short-circuiting switches SCS I and SCS2 are preferably made from electronic components because these can be switched on much faster and with greater precision than mechanical switching elements. This means that the time interval between the switching element currents iS l, iS2, iS3 becoming zero and the short-circuiters SCS I and SCS2 switching on can be minimized and with it the time during which the overvoltage limiting elements OV1, OV2, OV3 are thermally stressed. Thyristors and triacs are very suitable as electronic components for the short-circuiting switches if the electrical energy source generates alternating voltage because thyristors and triacs automatically interrupt the flow of current as soon as the current has dropped below a certain threshold.Furthermore, these components have a high short-time current carrying capacity; thus, the maximum short-circuit current values ​​in the range of 300 to 600 A can be handled by cost-effective components in the lower power range without damage. MOSFETs or IGBTs are also possible electronic components; these are particularly suitable when the electrical energy source generates direct current.

[0099] In addition to the function of relieving the overvoltage limiting elements 0V1, 0V2, 0V3 when switching off a current in the load circuit, the short-circuiters SCSI and SCS2 can also be switched on after a normal switching-off process as soon as the output currents iAl, iA2, iA3, ie the currents from the output terminals Al, A2, A3 of the switching device 1 to the load 2, have become zero.

[0100] By short-circuiting the load connection terminals K1, K2, K3 after switching off, feedback from load 2 to switching device 1 is prevented. In the case of an asynchronous motor, this is the voltage at its output terminals A1, A2, A3, which can no longer develop, so that increased voltage stress on the switching elements S1, S2, S3 caused by motor 2 can no longer occur. This allows electronic switching elements to be selected with a lower blocking voltage, while simultaneously eliminating the tolerance problem when selecting the voltage limiting value Ui. im the overvoltage limiting elements 0V1, 0V2, 0V3 are attenuated.

[0101] The solution shown in Fig. 7 for relieving the surge limiting elements 0V1, 0V2, 0V3 with the two short-circuiters SCSI and SCS2 works for all short circuits between the electrical phases Phi, Ph2, Ph3. However, in the case of a short circuit to earth and occurring from one or more electrical phases to a grounded conductor PE, 10, short-circuiting with the short-circuiters SCSI and SCS2 does not work.

[0102] For the purpose of clarification, Fig. 9 shows the earth fault SCPE1 within the load 2 in the first electrical phase Phi towards the earthed housing 20 of the load 2. The dashed earth fault current iPEl is formed and flows via the earthed housing 20 of the load 2, the earth conductor PE, 10, the voltage source uQl and the first switching element S1 back to the earth fault point SCPE1. The previously described switching off sequence for the short circuit case has no effect on the earth fault current iPEl because the earth fault current iPEl flows via the earth conductor PE, 10 and thus bypasses the short-circuiters SCS1 and SCS2. The overvoltage limiting element OV1 is loaded to a comparable extent as if there were no short-circuiter. A smaller dimensioning of the overvoltage limiting elements OV1, OV2, OV3 is therefore not possible.

[0103] Fig. 10 and Fig. 11 represent a possible solution to this problem. The switching device 1 is expanded to include the input EPE and the output APE. The earth conductor PE, which comes from the electrical energy source 4, is connected to the input EPE. The earth conductor 10, which leads to the metallic housing 20 of the load 2 and is there electrically connected to the housing 20, is connected to the output APE. The input EPE and the output APE are electrically connected to one another in the switching device 1. In addition, a further short-circuiter SCSPE is installed in the switching device 1. This short-circuiter is electrically connected on one side to one of the existing short-circuiters SCS1, SCS2, here to the short-circuiter SCS2, and on the other side is electrically connected to the connection leading through the switching device 1 from the input EPE to the output APE.

[0104] Fig. 10 shows, in dashed lines, the current path of the earth fault current iSCPEl when the earth fault occurs within the load 2 in the first electrical phase Phi to the metallic casing 20 of the load 2. If the earth fault is detected and switched off, two currents form, as shown in Fig. 11: on the one hand, a load-side earth fault current iSCPEl and, on the other hand, a source-side earth fault current 1SCPE2. The processes here are analogous to the short circuit case according to Fig. 7.

[0105] Since the inductances of the earth conductor PE, 10 on both the input side PE and the output side 10 are comparable to those of the input connection lines 3 and the load connection lines 5, the temporal characteristics of current i and voltage u also behave analogously to Fig. 8, which shows the case of a short circuit within the load 2 between the first electrical phase Phi and the second electrical phase Ph2. The source-side earth fault current 1SCPE2 decays quickly, while the load-side earth fault current iSCPEl flows for considerably longer before dropping to zero. The overvoltage limiting element 0V1 is only slightly loaded and can again be dimensioned small, as previously described.

[0106] By passing the earth conductor PE, 10 through the switching device 1, the current iPE through the earth conductor PE, 10 can be measured by means of a current sensor 90. Measured values ​​iMPE of the current iPE through the earth conductor PE, 10 recorded in this way can be transmitted from the current sensor 90 to the control unit 8, where they can be used to monitor the electrical insulation state of the load side 2, consisting of load connection lines 5 and the load 2.

[0107] The advantage of the solution shown in Fig. 11 is that, by monitoring the current iPE1 in the ground conductor PE, 10 using a current sensor 90, the short-circuiter SCSPE to the ground conductor PE, 10 is only activated when necessary, i.e., only when a ground fault occurs, together with the two other short-circuiters SCSI and SCS2, i.e., it is switched to electrically conducting, and can otherwise remain switched off, i.e., electrically non-conductive. This minimizes leakage currents from the electrical phases Phi, Ph2, Ph3 to the ground conductor PE, 10.

[0108] Fig. 12 shows a variant of a three-phase Phi, Ph2, Ph3 switching device 1, in which each of the three short-circuiters SCSPE1, SCSPE2, SCSPE3 leads to a current path 60 of the earth conductor connection, which connects a fourth input EPE of the switching device 1, to which an earth conductor PE of the energy source is connected, with a fourth output APE of the switching device 1, to which an earth conductor 10 of the load is connected, wherein the three short-circuiters SCSPE1, SCSPE2, SCSPE3 have a common connection point 12. This can be advantageous when controlling the short-circuiters SCSPE1, SCSPE2, SCSPE3, since due to the common connection point 12, a single control voltage can be used for all three short-circuiters SCSPE1, SCSPE2, SCSPE3 simultaneously. A disadvantage may be that the leakage currents via the earth conductor PE, 10 are somewhat higher than in the variant according to Fig. 10.

[0109] Fig. 13 shows a further variant of switching device 1. Switching device 1 is expanded by the input EN and the output AN for connecting an N-conductor 11 (N-conductor = neutral conductor). The neutral conductor 11, which comes from the electrical energy source 4, is connected to the input EN. The neutral conductor 11, which leads to the neutral conductor connection of the load 2, is connected to the output AN. In switching device 1, the input EN and the output AN are electrically connected to one another by a current path 60 of the N-conductor connection. Each of the three outputs A1, A2, A3 can be connected to the current path 60 of the N-conductor connection using a short-circuiter SCSN1, SCSN2, SCSN3.

[0110] A switching device 1 with neutral conductor connection EN, AN makes it possible to control loads 2 with different energy consumption in each of the three electrical phases Phi, Ph2, Ph3 during normal operation. The neutral conductor 11 ensures that the same voltage is applied to each of the individual loads 2 in the three electrical phases Phi, Ph2, Ph3. This enables separate, independent control of the three loads 2 in the electrical phases Phi, Ph2, Ph3. This allows each of the three loads 2 to be switched on and off at different time intervals, i.e. the switching elements SI, S2, S3 are also switched on and off independently of one another. In order to keep the voltage generated by the load 2 away from the switching element 1 when an electrical phase Phi, Ph2, Ph3 is switched off, a short-circuiter SCSN1, SCSN2, SCSN3 is electrically connected to the neutral conductor 11 from each output of the switching device 1. This provides each switching element

[0111] 51 , S2 , S3 are each assigned a short-circuiter SCSN1 , SCSN2 , SCSN3 , so that each switching element SI , S2 , S3 is protected when switching off, regardless of the switching state of the other two switching elements. In the event of a detected short-circuit or earth fault, the switching elements S l ,

[0112] 52 , S3 is switched off and then the short-circuiters SCSN1 , SCSN2 , SCSN3 are switched on .

[0113] As an example, Fig. 13 shows an earth fault SCPE1 in the first electrical phase Phi in load 2 leading to the metal housing 20. The earth fault current iSCPE1 that develops before switching off is marked with a dashed line. It flows through the metal housing 20 of load 2, via the earth conductor 10, via the electrical energy source 4 and the input connection line 3, through the switching element S1, and through the output of switching device 1 back to the earth fault point SCPE1.

[0114] After switching element S1 is switched off and short-circuiter SCSN1 is subsequently switched on, two current paths are formed: In a first current path, the earth fault current iSCPE1 flows via the earth conductor 10 to the energy source 4 and then via the input-side neutral conductor 11 into the switching device 1, from there via the short-circuiter SCSN1 to the output A1 and back to the earth fault point SCPE1. In the other, second current path, a current 1SCPE2 flows, also via the input-side neutral conductor 11, the short-circuiter SCSN1, through the first overvoltage limiting element OV1 to the input E1 and back to the energy source 4.

[0115] The electrical conditions are very similar to those in the case of an earth fault with earth conductors PE, 10 connected to the switching device 1 according to Fig. 10 and Fig. 11, so that the current and voltage curves are also very similar.

[0116] In contrast to Fig. 10 and Fig. 11, where the earth fault current iPE can be measured directly in the earth conductor PE, 10 and only flows in the event of a fault, an earth current measurement in the case of a connected neutral conductor 11 according to Fig. 13 is only possible indirectly and is therefore subject to greater inaccuracy. The earth fault current iSCPEl must be determined here by summing the measured values ​​iMl, iM2, iM3, iMN of the four currents il, 12, 13, and IN flowing out of the switching device 1 in the control unit 8. If there is no earth fault, the sum of these four currents il, 12, 13, and IN is ideally zero.

[0117] Fig. 14 shows a design in which only one additional connection point is necessary on switching device 1: Only one input connection point EPE is provided, to which the earth conductor PE coming from the energy source 4 is connected. The short-circuiters SCSPE1, SCSPE2, SCSPE3 are connected to one side of this input connection EPE in switching device 1. In the event of an earth fault, after the switching elements SI, S2, S3 are switched off and the short-circuiters SCSPE1, SCSPE2, SCSPE3 are subsequently switched on, two current paths are formed, both of which lead via the input connection point EPE via the short-circuiters SCSPE1, SCSPE2, SCSPE3 through the switching device 1. The current paths are completely analogous to the current paths in Fig. 13. However, with this solution, it is not possible to measure the current in the earth conductor PE during normal operation and therefore also not to continuously monitor the electrical insulation state of the load.

[0118] Fig. 15 also shows an embodiment with only one additional connection point, namely an input connection point EPE, on the switching device 1, wherein the embodiment differs from Fig. 14 only in the arrangement of the short-circuiters. In this embodiment, two short-circuiters SCSI, SCS2 are arranged between the three output connections A1, A2, A3 of the switching device 1, and a short-circuiter SCSPE leads from any one of the output connections A1, A2, A3 to the earth conductor connection EPE. The advantage of the two embodiments in Figs. 14 and 15 lies in the elimination of a device connection terminal and thus in a structurally simpler device design.

[0119] The solution to the problem underlying this invention was illustrated on the one hand by means of a short circuit in a load 2 from a first electrical phase Phi to a second electrical phase Ph2 and on the other hand by means of an earth fault within a first electrical phase Phi to an earthed, metallic housing 20 of the load 2. The solutions according to Fig. 10 to Fig. 15, however, work with any short circuits and earth faults in the entire load circuit. The short circuits can therefore occur between individual or more electrical phases, and the earth faults from one or more electrical phases to an earthed metallic conductor, without the described functions being impaired. Short circuits and earth faults can occur in the entire load circuit, i.e. both in the load connection lines and within the load.

[0120] There are several possibilities for the state of the short-circuiting switches in the period after switching off until the next switching on:

[0121] - This allows the short-circuiting switches to be switched off after the switch-off process, as soon as the current flowing through them has dropped to zero, i.e., they become current-blocking. This eliminates the need to provide the control energy required for the short-circuiting switches, which somewhat reduces the energy consumption of the switching device in the off state.

[0122] - Alternatively, the short-circuiting switches can remain switched on, i.e., conducting current, so that overvoltages induced in the load circuit, e.g., by other nearby circuits or by indirect lightning strikes, are kept away from the semiconductor switches and the switching device. - Another possibility would be to temporarily switch the short-circuiting switches on while the switching device is off, if an overvoltage load on the switching device is to be expected at certain times.

[0123] In any case, the short-circuiting switches must be switched off immediately before the switching device is switched on again.

[0124] The key difference between the inventive solution and conventional solutions is the integration of short-circuiting switches into the switching device, which short-circuit the switching device's outputs after a short circuit has been cleared or after normal, operational shutdown. This allows for significantly smaller overvoltage limiting elements, which are always required for the switching elements in this arrangement.

[0125] Without the short-circuiters provided by the invention, the surge suppression elements must be dimensioned for a wide inductance range, which is determined by the length of the load connection cables and the type of load. This requires large, bulky, and expensive surge suppression elements, which significantly increase the installation space of the switching device. Alternatively, limiting specifications would have to be set for the length of the load connection cables and the type of load, which would then have to be listed in the operating instructions and restrict universal application.

[0126] During normal switching off, the voltage generated by the load, particularly if it is a motor, can lead to increased voltage stress on the switching elements, which must be designed accordingly. The short-circuiters provided according to the invention prevent voltages generated by the load after switching off from acting on the switching elements. The switching elements can be dimensioned smaller in terms of their dielectric strength, which offers cost advantages on the one hand. On the other hand, switching elements with a lower dielectric strength have lower electrical losses when conducting the electrical current, so that less heat needs to be dissipated. This reduces the cooling effort and allows smaller housings for the switching devices.

[0127] In the exemplary embodiments shown in Fig. 10, Fig. 12, and Fig. 13, in which the earth conductor or the neutral conductor passes through the switching device, the current in the earth conductor or the neutral conductor can be measured, and from this, the electrical insulation status of the connected load can be assessed. This allows early detection of insulation faults and a warning message to the operator of the switching device.

[0128] Fig. 16 shows a tree diagram with an overview of the various constellations 160a to 160X which, starting from the "construction" elements 160: "n phase conductors", "neutral conductors" and "earth conductors", can exist in a line system which is protected by the switching device. The constellations are initially differentiated according to the number n of outer conductors "Ph" of the power supply. In a first 1-phase branch 161 there is only a single outer conductor: n=1 . In an alternative n-phase branch 162 there are several outer conductors: n>1 .

[0129] If the 1-phase case 161 (only 1 phase conductor Ph) exists, there are two possible branches: either the phase conductor Ph and a neutral conductor N exist in a first branch 163 of the 1-phase branch 161, or the phase conductor Ph, a neutral conductor N and an earth conductor E exist in an alternative branch 164 of the 1-phase branch 161.

[0130] - If the first branch 163 is present, only the constellation 160a exists, that a short-circuiter electrically connects the outer conductor Ph with the neutral conductor N.

[0131] - If the second branch 164 is present, there is either the constellation 160 ß that a short-circuiter electrically connects the outer conductor Ph with the neutral conductor N or the constellation 1 60Y that a short-circuiter electrically connects the outer conductor Ph with the earth conductor E.

[0132] If the n-phase case 162 (n outer conductors Phi , Phn, where n is an integer greater than 1) applies, there are four possible branches: in a first branch 165 of the n-phase branch 162 there are only the outer conductors Ph, in a second branch 166 of the n-phase branch 162 there are the outer conductors Ph and a neutral conductor N, in a third branch 167 of the n-phase branch 162 there are the outer conductors Ph and an earth conductor E, and in a fourth branch 168 of the n-phase branch 162 there are the outer conductors Ph, a neutral conductor N and an earth conductor E.

[0133] - If the first branch 165 is present, the only constellation 1605 exists, that one or more short-circuiters electrically connect the outer conductors Ph to each other.

[0134] - If the second branch 166 is present, there is either the constellation 160 s that one or more short-circuiters electrically connect the outer conductors Ph to one another, or the constellation 160 ^ that one or more short-circuiters electrically connect the outer conductors Ph to the neutral conductor N.

[0135] - If the third branch 167 is present, there is either the constellation 160r| that one or more short-circuiters electrically connect the outer conductors Ph to one another, or the constellation 1600 that one or more short-circuiters electrically connect the outer conductors Ph to the earth conductor E.

[0136] - If the fourth branch 168 is present, there is firstly the constellation 160 L , in which one or more short-circuiters electrically connect the outer conductors Ph to one another, secondly the constellation 160 K , in which one or more short-circuiters electrically connect the outer conductors Ph to the neutral conductor N, and thirdly the constellation 160 X , in which one or more short-circuiters electrically connect the outer conductors Ph to the earth conductor E.

Claims

Patent claims 1. Switching device (1) for controlling an electrical energy flow from an energy source (4) to a load (2), comprising: - n outer conductor inputs (El, E2, E3) for electrical connection to the energy source (4) , - n phase conductor outputs (Al, A2, A3) for electrical connection to the load (2), - n outer conductor current paths (6) which electrically connect the n outer conductor inputs (El, E2, E3) bijectively with the n outer conductor outputs (Al, A2, A3) within the switching device (1), - n switching elements (SI, S2, S3), wherein in each of the n outer conductor current paths (6) one of the n switching elements (SI, S2, S3) is arranged, which can switch a current flow through the outer conductor current paths (6), and - n overvoltage limiting elements (OV1, OV2, OV3) which are each connected in parallel to one of the n switching elements (SI, S2, S3), with each switching element (SI, S2, S3) being assigned an overvoltage limiting element (OV1, OV2, OV3), - a control unit (8) for controlling the switching elements (SI, S2, S3), characterized by - short-circuiting switches (SCSI, SCS2, SCSPE, SCSPE1, SCSPE2, SCSPE3, SCSN1, SCSN2, SCSN3) which can be controlled by the control unit (8) and are arranged such that, in a current-conducting state, they electrically connect the n outer conductor outputs (A1, A2, A3) of the switching device a) to one another and / or b) to an earth conductor (10) or a neutral conductor (11) of the energy source (4).

2. Switching device (1) according to claim 1, comprising: - an (n+l)-th input (EPE, EN) for electrical connection to the earth conductor (10) or the neutral conductor (11) of the energy source (4), wherein one or more of the short-circuiting switches (SCSI, SCS2, SCSPE, SCSPE1, SCSPE2, SCSPE3, SCSN1, SCSN2, SCSN3) are arranged such that, in a current-conducting state, they electrically connect the n outer conductor outputs (A1, A2, A3) to the (n+l)-th input (EPE, EN).

3. Switching device (1) according to claim 2, comprising: - an (n+l)th output (APE, AN) for electrical connection to an earth conductor (10) or a neutral conductor (11) of the load (2), and - an (n+l)-th current path (60) which electrically connects the (n+l)-th input (EPE, EN) to the (n+l)-th output (APE, AN) within the switching device (1) and thus forms an earth or neutral conductor connection within the switching device (1).

4. Switching device (1) according to one of claims 2 or 3, wherein from each of said n outer conductor outputs (A1, A2, A3) a short-circuiting switch (SCSPE1, SCSPE2, SCSPE3) leads to the (n+l)-th input (EPE, EN).

5. Switching device (1) according to one of claims 2 to 4, comprising a current measuring device (iMPE, iMN) for measuring the current in the earth or neutral conductor connection.

6. Switching device (1) according to claim 5, wherein the control unit (1) is designed to, on the basis of the measured current (iMPE) in the earth conductor connection to determine an electrical insulation state of the load (2).

7. Switching device (1) according to claim 5, wherein the control unit (8) is designed to determine an earth fault current based on the measured current (iMN) in the neutral conductor connection together with the other measured currents (iMl, iM2, iM3) flowing to the phase conductor outputs (A1, A2, A3). (iSCPEl) which is used to monitor an electrical insulation state of the load (2).

8. Switching device (1) according to one of the preceding claims, comprising: - current sensors for detecting measured values ​​(iMl, iM2, iM3) of the current intensity in at least one of the current paths (6, 60), and - transmission means for transmitting the measured values ​​(iMl, iM2, iM3) to the control unit (8).

9. Switching device according to one of the preceding claims, wherein the short-circuiting switches are electronic components.

10. A method for operating a switching device (1) which controls an electrical energy flow from an energy source (4) to a load (2), wherein n outer conductor current paths (6), in each of which a parallel circuit of a switching element (S1, S2, S3) and an overvoltage limiting element (OV1, OV2, OV3) is arranged, electrically connect n outer conductor inputs (E1, E2, E3) of the switching device (1) within the switching device (1), which are suitable for electrical connection to the energy source (4), bijectively to n outer conductor outputs (A1, A2, A3) of the switching device (1), which are suitable for electrical connection to the load (2), comprising the following steps: - controlling the switching elements (SI, S2, S3) in such a way that the switching elements (SI, S2, S3) assume a current-conducting switching state and a current flow through the respective current path (6) is possible; - interrupting the current flow through the current paths (6) by controlling the switching elements (SI, S2, S3) so that they change to their current-blocking switching state, and - After the switching elements (SI, S2, S3) have changed into their current-blocking state, actuating short-circuiting switches of the switching device (1) in such a way that they change into a current-conducting switching state, wherein the short-circuiting switches in the switching device (1) are arranged in such a way that in their current-conducting switching state they Electrically connect the outputs of the switching device a) to each other and / or b) to an earth conductor (10) or a neutral conductor (11) of the energy source (4).

11. Method according to claim 10, comprising the following steps: - measuring a current and / or a voltage in at least one of the outer conductor current paths (6); - sending the measured values ​​to a control unit (8) of the switching device (1); - Sending, by the control unit (8), control commands to the switching elements (SI, S2, S3) and short-circuiting switches based on the measured values.

12. Method according to one of claims 10 or 11, wherein the switching elements (SI, S2, S3) are switched to their current-blocking state if a short-circuit current occurs in one of the outer conductor current paths (6) or if an operational switching off of the load is to take place.

13. Method according to one of claims 10 to 12, wherein by means of one or more of the short-circuiting switches the n outer conductor outputs of the switching device are electrically connected to an (n+l)-th input (EPE, EN) of the switching device which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source (4).

14. Switching device according to claim 13, wherein an electrical connection is established from each of said n phase conductor outputs by means of a short-circuiting switch to the (n+l)th input (EPE, EN) of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source.

15. Method according to one of claims 13 or 14, wherein by means of an (n+l)-th current path (6) within the switching device (1) the (n+l)-th input (EPE, EN) of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the energy source, is connected to a (n+l)-th output (APE, AN) of the switching device, which is suitable for electrical connection to an earth conductor or a neutral conductor of the load (2), is electrically connected and thus an earth or neutral conductor connection is created within the switching device.

Images