Electrical switch with overvoltage protection

Abstract

The invention relates to an electrical switch (1) having at least one switchable semiconductor switch (2, 21, 22), wherein the electrical switch (1) has a capacitor (3) and a varistor (4), wherein the capacitor (3) and the varistor (4) are arranged in a first series circuit (10), and wherein the first series circuit (10) formed by the capacitor (3) and the varistor (4) is connected in parallel with the switchable semiconductor switch (2, 21, 22). In order to improve the electrical switch (1), especially in terms of its switching behavior, it is proposed that the electrical switch (1) has a switch (5) and a resistor (6), wherein the switch (5) and the resistor (6) are arranged in a second series circuit (11), and wherein the second series circuit (11) formed by the switch (5) and the resistor (6) is connected in parallel with the switchable semiconductor switch (2, 21, 22) and with the first series circuit (10). The invention also relates to a method for operating such an electrical switch (1), wherein the switch (5) is switched on before the switchable semiconductor switch (2, 21, 22) is switched on.

Description

Field of the Invention

[0001] The present invention relates to an electrical switch having at least one turn-off semiconductor switch, wherein the electrical switch has a capacitor and a varistor, wherein the capacitor and the varistor are arranged in a first series circuit, and wherein the first series circuit composed of the capacitor and the varistor is connected in parallel with the turn-off semiconductor switch. The present invention also relates to a method for operating such an electrical switch. Background Art

[0002] Today, the supply of electrical energy is mainly achieved via an AC power grid. The advantage of an AC power grid is that different voltage levels can be generated by means of transformers. Since semiconductors available on the market are becoming increasingly cheaper, different voltage levels can also be generated in a simple manner for a direct current (DC) power grid, making it particularly economical to supply energy via a DC power grid, especially within industrial networks.

[0003] Here, the DC power grid should reduce losses in future industrial equipment, ensure direct energy exchange between converters, memories, and motors, and improve stability. Here, for example, a small DC power grid with different cable lengths between different load outlets and feed-in points can be operated. Short cable lengths result in very small longitudinal inductances in the feeder lines, such that fault currents can have a very sharp current increase. This requires very fast fault identification and shutdown in the event of a fault. Usually, mechanical switches cannot meet this requirement. Therefore, so-called electrical switches with semiconductor switches are introduced. Semiconductor switches are also known as solid-state circuit breakers. The characteristic of this switch is a particularly fast switching compared to mechanical switches, typically occurring in the order of 100 ns.

[0004] A device for introducing a high-voltage current into a chemical solution is known from DE 37 18 941 A1. The device consists of a storage device, a receiving device, a detection device, and a guiding device including a high yoke switch.

[0005] A switching device for separating a current path is known from EP 3 367 567 A1. This document relates to a switching device for separating a current path in a DC power grid, including source-side and load-side inductances. The switching device includes at least two series-connected switch modules, wherein each switch module includes at least one controllable semiconductor switch element, and a series circuit composed of a resistor and a capacitor is connected in parallel with the semiconductor switch element.

[0006] A method for controlling a DC switch is proposed in WO 2018 / 172134 A1, which was published after the priority date. Here, the DC switch has a first turn-off semiconductor switch and a second turn-off semiconductor switch, wherein the first and second turn-off semiconductor switches are arranged between a first terminal and a second terminal, so that a current with a first polarity can be conducted through the first turn-off semiconductor switch, and a current with a polarity opposite to the first polarity can be conducted through the second turn-off semiconductor switch, and one of the turn-off semiconductor switches is turned off according to a current measurement value.

[0007] An electrical switch is proposed in WO 2019 / 011642 A1, which was published after the priority date. The electrical switch has at least one turn-off semiconductor switch, a varistor and a capacitor. Here, the electrical switch has a first terminal and a second terminal, and a conductive connection can be established or interrupted between the terminals by means of at least one turn-off semiconductor switch according to the switching state of the turn-off semiconductor switch. It is proposed here that a series circuit composed of a varistor and a capacitor is connected to the first terminal by means of a first diode and to the second terminal by means of a second diode respectively. Summary of the Invention

[0008] The basic object of the present invention is to provide an electrical switch that is improved especially in terms of the switching performance of the electrical switch.

[0009] This object is achieved by an electrical switch having at least one turn-off semiconductor switch, a capacitor and a varistor, wherein the capacitor and the varistor are arranged as a first series circuit, wherein the first series circuit composed of the capacitor and the varistor is connected in parallel with the turn-off semiconductor switch, wherein the electrical switch has a switch and a resistor, wherein the switch and the resistor are arranged as a second series circuit, and wherein the second series circuit composed of the switch and the resistor is connected in parallel with the turn-off semiconductor switch and in parallel with the first series circuit. This object is also achieved by a method for operating such an electrical switch, wherein the switch is turned on before the turn-off semiconductor switch is turned on.

[0010] Other advantageous designs of the present invention are given in the dependent claims.

[0011] The present invention is based on the recognition that if a series circuit composed of a varistor and a capacitor is connected in parallel with a turn-off semiconductor switch, the switching performance of the electrical switch can be improved. The series circuit can protect the turn-off semiconductor switch from voltage peaks formed during switching, thereby ensuring interference-free operation and at the same time increasing its service life.

[0012] The turn-off power semiconductor switch can be a switch that can only turn off the current in one direction. This switch is particularly suitable for loads that cannot feed back and thus only conduct current in one direction. Similarly, it can be a turn-off power semiconductor switch that can turn off the current in both directions.

[0013] The turn-off semiconductor switch is sensitive to the voltage peaks that occur during current switching, especially during its turn-off. Due to the inductance present in the DC grid, for example, the current change caused by the parasitic inductance of the cable, especially the current interruption, results in a high voltage. This high voltage then partially drops across the turn-off semiconductor switch and can damage the semiconductor switch or reduce its service life. By the parallel arrangement of the first series circuit consisting of a varistor and a capacitor, the turn-off semiconductor switch can be reliably protected from the formed overvoltage and voltage peaks.

[0014] Here, the transition from the cut-off state to the conducting state of the switch is called switching on, and the transition from the conducting state to the cut-off state of the switch is called switching off or turn-off.

[0015] According to its current-voltage characteristic curve, a part of the voltage formed when turning off the turn-off semiconductor switch drops across the varistor, while the other part drops across the capacitor. Here, it is advantageous that the design of the varistor becomes simpler from now on because it no longer has to bear the entire cut-off voltage.

[0016] The energy from the inductance in the load and the relevant branch of the DC grid is now also absorbed by the capacitor. Thereby, a voltage is established in the capacitor, and this voltage is added to the voltage of the varistor. Here, it is particularly helpful that when the load current drops, the capacitor voltage rises and compensates for the smaller reverse voltage of the varistor. The load current drops according to the equation u(t) = L * di / dt due to the applied reverse voltage of the capacitor, and due to the capacitor behavior of i(t) = C * du / dt, more and more reverse voltage is established across the capacitor. In any case, a reverse voltage greater than the driven DC voltage is thereby generated because the reverse voltage is established by the current passing through the capacitor, and the reverse voltage compulsorily and reliably suppresses the current after a certain time.

[0017] In other words, the energy of one or more inductors located in the branch to be turned off or already turned off is transferred from the one or more inductors to the capacitor, and the voltage of the capacitor thus increases. When the turn-off-capable semiconductor switch is turned off, a voltage peak is formed due to the large current change. The voltage peak causes the varistor to break down and transition to the conducting state, and the current flowing from the inductor to the capacitor is realized. Therefore, the voltage existing at the capacitor and only integrated via the current flowing through the capacitor, and the small voltage at the varistor in the conducting state is also applied to the turn-off-capable semiconductor switch, and the semiconductor switch is in parallel with the first series circuit composed of the varistor and the capacitor. Thus, the voltage at the turn-off-capable semiconductor switch is also small, and the semiconductor switch is reliably protected from voltage peaks. This ensures its function even when the high current or high inductance in the relevant turn-off-capable branch is turned off. In addition, when the turn-off-capable semiconductor switch is turned off, a moderate voltage increases its service life.

[0018] If a short circuit now occurs in the load in the DC grid, the DC power supply can be separated from the fault point by turning off the electrical switch. The current passing through the load inductor has no freewheeling path, and thus the following voltage is established across the semiconductor switch, which is applied to the semiconductor switch or even damages the semiconductor switch. The voltage-limiting network in the form of the first series circuit composed of the varistor and the capacitor can be used not only in the electrical switch schematically shown here with the turn-off-capable semiconductor switch, but also in any configured DC voltage switch in the DC grid.

[0019] Here, the electrical switch has a switch and a resistor, where the switch and the resistor are arranged as a second series circuit, and the second series circuit composed of the switch and the resistor is in parallel with the turn-off-capable semiconductor switch and in parallel with the first series circuit. By expanding the use of the switch and the resistor for the electrical switch, the reconnection can be implemented with particularly low losses after the turn-off process. The energy absorbed by the capacitor from the inductor during the turn-off process is the load when the switch is reconnected, because this energy suddenly discharges via the turn-off-capable semiconductor switch when the electrical switch is turned on. The discharge current is preset by the current / voltage characteristic curve of the varistor and can be set to a relatively large value. This is particularly applicable when there is only a short time period between the disconnection and the reconnection. During the short time period, the capacitor can only be discharged slightly and the stored energy causes a load on the turn-off-capable semiconductor switch. A resistor is used to reduce this load caused by the discharge current. When the switch is turned on, the resistor discharges. This occurs when the capacitor voltage reaches a value higher than the trigger voltage of the varistor. The capacitor does not need to be discharged when the voltage is lower than the trigger voltage, because the turn-on via the turn-off-capable semiconductor switch does not generate any discharge current either.

[0020] In addition, the resistor can be used to pre-charge a load that causes a high turn-on current with a moderate current. An example of such a load is an inverter, and the intermediate circuit capacitor of the inverter causes a large charging current. Such a load is therefore usually charged via a pre-charge resistor. When using an electrical switch having a switch and a resistor, the current limiting can be performed via the resistor by means of the electrical switch. Thereby, a separate pre-charge circuit can be omitted. A synergistic effect is produced because, on the one hand, the switch is turned on with particularly low load by means of the resistor, and at the same time the following feasibility is provided for the load: connecting to the DC power grid in a current-limiting manner. This saves components and thereby increases the reliability and economy of the DC power supply because such a device can be manufactured particularly inexpensively.

[0021] The switch can be inexpensively implemented as a mechanical switch here because the requirements for the switching speed are low. It is also feasible that, since a control unit for controlling the semiconductor switch already exists, the switch is also constructed by means of a semiconductor. Then, depending on the implementation of the semiconductor, the switch can also be constructed in anti-parallel or anti-series, so that the switch ensures the discharge of the capacitor regardless of the voltage polarity. If the electrical switch is only provided for interrupting the current with one polarity, it is also implemented in the switch that the switch is only provided for one polarity because the capacitor can only be supplied with a voltage of one polarity.

[0022] The semiconductor can be a turn-off semiconductor, such as an IGBT or a MOSFET, or it can be a non-turn-off semiconductor, such as a thyristor. Since a current through the switch and the resistor occurs with the turn-on of the turn-off semiconductor switch of the electrical switch, the ability to turn off the current is not required for this application. The use of a thyristor is particularly advantageous here because the discharge current or the pre-charge current of the load is a short-term large current and the thyristor has a particularly high overload capacity. The overload capacity is understood as a short-term load of the current, which, although short-term, cannot be sustained. Therefore, especially when the switch is implemented by means of a semiconductor or a thyristor, the electrical switch can be manufactured particularly inexpensively.

[0023] Then, it is advantageous to turn on the switch before turning on one or more turn-off semiconductor switches of the electrical switch again, so that the voltage at the capacitor is small enough or even zero at the time point of turning on one or more turn-off semiconductor switches. Then, the discharge current through one or more turn-off semiconductor switches is no longer a high load thereby, so that the electrical switch has a higher service life.

[0024] In an advantageous design of the present invention, the electrical switch has at least two turn-offable semiconductor switches, wherein a first turn-offable semiconductor switch of the two turn-offable semiconductor switches is arranged to be able to turn off the current from the first terminal of the electrical switch to the second terminal of the electrical switch, and a second turn-offable semiconductor switch of the two turn-offable semiconductor switches is arranged to be able to turn off the current from the second terminal of the electrical switch to the first terminal of the electrical switch, and the capacitor is designed as a bipolar capacitor. Commercially available turn-offable semiconductor switches can generally only turn off the current in one direction. Typical representatives of such turn-offable semiconductor switches are IGBTs or MOSFETs. If it is desired to turn off the current in both directions through such a turn-offable semiconductor switch, two of these turn-offable semiconductor switches are used. Thereby, the current of both polarities is turned off by the electrical switch. Here, the switch is arranged such that the current from the first terminal of the electrical switch to the second terminal of the electrical switch can be conducted and turned off by the first semiconductor switch of the two turn-offable semiconductor switches, and the current from the second terminal of the electrical switch to the first terminal of the electrical switch can be conducted and turned off by the second semiconductor switch of the two turn-offable semiconductor switches. For the case where a diode is arranged in parallel with the switching element of the semiconductor switch, the two semiconductor switches are arranged in a series circuit, wherein the diode enables the turn-offable semiconductor switch to conduct in the reverse direction. Since the switching elements of the two semiconductor switches can respectively conduct and turn off currents with different polarities, this series circuit is also referred to as being reverse-connected in series. Here, the two semiconductor switches are inverted relative to each other with respect to the collector and emitter or drain and source terminals. For the case where the turn-offable semiconductor switch cannot conduct in the reverse direction, the first and second turn-offable semiconductor switches are arranged in a parallel circuit, wherein the first turn-offable semiconductor switch can conduct and turn off the current with a first polarity, and the second turn-offable semiconductor switch can conduct and turn off the current with a different polarity. Such a parallel circuit is also referred to as a reverse parallel circuit, or such an arrangement is called reverse parallel.

[0025] By using two such turn-offable semiconductor switches, a switch that can turn off currents with different polarities can be implemented in a simple manner by using standard components.

[0026] In another advantageous design of the present invention, a discharge resistor is connected in parallel with the capacitor. The discharge resistor ensures that the voltage is continuously discharged via the capacitor. Thereby, the voltage formed at the capacitor can be reduced during the turn-off process of the electrical switch. In this context, a deterministic discharge of the capacitor is involved. If there is a sufficient time period related to the selection of the resistance value of the discharge resistor between the turn-off process and the reconnection process, the use of a switch with a resistor can be dispensed with. Optionally feasible is to expand the circuit with a switch and a resistor to use the discharge resistor, so that the function of the electrical switch is also provided without limitation for a short time period between turn-off and reconnection. Therefore, the load on the turn-offable semiconductor switch and the existing switch is further reduced by the discharge resistor, thereby further increasing the service life of the switch in a simple manner.

[0027] In another advantageous design of the present invention, an additional capacitor is connected in parallel with the varistor. By means of the additional capacitor, the capacitance value of which is advantageously at least one order of magnitude smaller than the capacitance value of the capacitor, the inductive response behavior of the varistor is compensated, and thus the overvoltage is further reduced when the current commutates from one or more turn-offable semiconductor switches to the first series circuit composed of the varistor and the capacitor. This also reduces once again the load formed at one or more turn-offable semiconductor switches, which load is formed by the voltage applied there.

[0028] In another advantageous design of the present invention, an additional discharge resistor is connected in parallel with the varistor. If now, as another advantageous design, it is proposed to arrange an additional discharge resistor in parallel with the varistor, which additional discharge resistor has a resistance value significantly lower than that of the discharge resistor, then the voltage drop across the varistor is thus further significantly reduced both in normal operation, i.e., in the state where the electrical switch is open, and in the state where the electrical switch is closed. Thereby, the service life of the varistor is increased because its load is significantly reduced during operation. Advantageously, the resistance value of the additional discharge resistor is at least one order of magnitude smaller than the resistance value of the discharge resistor.

[0029] Now, in the state where the electrical switch is open, the voltage drop across the varistor is determined by the voltage divider of the discharge resistor and the additional discharge resistor, so that the selection of the above resistance value is particularly advantageous. In the state where the electrical switch is closed, the capacitor is discharged via the varistor and the additional discharge resistor. This provides the feasibility of dispensing with the first series circuit and nevertheless achieving a rapid reconnection after the turn-off process without unduly loading the turn-offable semiconductor switch with a high load. It is also feasible to supplement the electrical switch with the specification of the first series circuit with an additional discharge resistor in order to thereby further reduce the load during operation, especially when the electrical switch is reconnected.

[0030] In another advantageous design of the present invention, the switch is opened when the voltage at the capacitor is below a voltage threshold. If it is ensured that the load obtained for one or more turn-offable semiconductor switches due to the discharge current of the capacitor is small enough, the discharge of the capacitor can be ended. This is the case when the voltage at the capacitor is below a preset voltage threshold. Thereby, even when the capacitor has not been fully discharged, a smooth reconnection of the capacitor can be achieved. In addition, the time during which the load is connected to the DC power supply via the resistor is further reduced. Even if a small current value can be formed thereby, since the current is limited via the resistor, in particular in the case of a load-side short circuit, the current between the DC power supply and the load can be advantageously prohibited quickly to avoid possible damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Hereinafter, the present invention will be described and explained in more detail based on the embodiments shown in the drawings. The drawings show:

[0032] Figure 1 show a DC power grid with an electrical switch, and

[0033] Figures 2 to 4 show an embodiment of an electrical switch with overvoltage protection. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Figure 1 A DC power grid 33 is shown, which is also referred to as a DC voltage power grid. The DC power grid supplies power to a load 31 from a DC power supply 30 (also referred to as a DC voltage source). The load can be, for example, a drive with an inverter, where the inverter is connected to the DC power supply 30 via an intermediate circuit by means of an electrical switch 1. The line between the DC power supply 30 and the load 31 can exhibit completely different characteristics in terms of its inductance performance. The inductance performance is shown in the view by means of an inductor 32. The inductor can take on very small values because there is no transformer whose inductance acts in a current-limiting manner. On the other hand, the inductor can also take on very large values due to the large cable length, which is allowed due to the energy transfer with direct current. For the electrical switch, the following requirements result therefrom: Due to the small inductance and the resulting large current changes, especially the large current changes during a short circuit, the electrical switch should have a very fast switching performance so that inadmissible large currents, such as those formed during a short circuit, can be reliably controlled. In addition, the switch must also be able to work reliably at high inductances. Thus, although the inductor causes a high voltage resulting from the current change during turn-off, an excessive current rise is not a problem. The high voltage must also be reliably controlled and must not damage the electrical switch 1 and the components therein.

[0035] Here, Figure 1Shows the basic structure of the electrical switch 1. It has at least one turn-offable semiconductor switch 2 in the power path between its first terminal 12 and its second terminal 13, which can turn off the current passing through the switch. Depending on the type of turn-offable semiconductor switch 2, the semiconductor switch can turn off the current between the first terminal 12 and the second terminal 13 in only one direction or in both directions. Advantageously, two turn-offable semiconductor switches 2 are used, and each semiconductor switch can disconnect the current in one direction. If the semiconductor switch is reverse-blocking, it is arranged in an anti-parallel circuit. For the case where the turn-offable semiconductor switch can conduct in the reverse direction, it can be recognized at the diode connected in parallel with the switching elements of the turn-offable semiconductor switches 2, 21, 22, so as to Figure 1 be arranged in a series circuit as shown in, where the first turn-offable semiconductor switch 21 and the second turn-offable semiconductor switch 22 among the two turn-offable semiconductor switches are connected in series in the reverse direction.

[0036] Figure 2 Shows an embodiment of the electrical switch 1 with overvoltage limitation. To avoid repetition, reference is made to the description of Figure 1 and the reference numerals introduced there. A first series circuit 10 is connected in parallel with the first turn-offable semiconductor switch 21 and the second turn-offable semiconductor switch 22. The first series circuit 10 has a capacitor 3 and a varistor 4 that form a series circuit. If one of the two turn-offable semiconductor switches 21, 22 turns off the current between the terminals 12, 13 of the electrical switch 1, the current driven by the inductor is commutated onto the first series circuit 10. Due to the voltage formed, the varistor becomes conductive, which is also referred to as the breakdown of the varistor, and the capacitor 3 absorbs energy from the inductor. Thereby, the voltage formed at the switch is reduced and switch damage is avoided, and the voltage is derived from the large current drop by turning off. At the same time, the service life of the switch is increased because the turn-offable semiconductor switch is not loaded with too high a voltage.

[0037] Reconnecting the electrical switch 1 causes the capacitor 3 to discharge via the turn-offable semiconductor switches 2, 21, 22. This is especially the case if the time period between turning off and reconnecting the electrical switch is so small that self-discharge of the capacitor has not yet occurred or has not occurred sufficiently. To avoid this, in the embodiment of the electrical switch 1 in Figure 3 , a second series circuit 11 composed of a switch 5 and a resistor 6 is connected, and the second series circuit is connected in parallel with the first series circuit. To avoid repetition, reference is made to Figure 1 and Figure 2description and the reference signs introduced therein. By means of the second series circuit 11, the capacitor 3 can be discharged by closing the switch 5 before the turn-on of the turn-offable semiconductor switches 2, 21, 22. At the same time, the resistor 6 can be used as a precharging resistor for the load 31 which, due to the large turn-on current, is usually connected to the DC power supply via a precharging resistor. As an example of such a load, an inverter can be used, the intermediate circuit capacitor of which is usually charged via a precharging resistor.

[0038] Here, the switch can be implemented as a mechanical switch or by means of semiconductors. Here, turn-offable semiconductors or non-turn-offable semiconductors, such as thyristors, can be used.

[0039] In Figure 4 the embodiment, other measures for voltage limitation are shown, which can be used individually or in combination. To avoid repetition, reference is made to Figures 1 to 3 the description and the reference signs introduced therein. Here, as a first measure, a discharge resistor 7 can be connected in parallel with the capacitor 3. The discharge resistor ensures that, after the electrical switch 1 is turned off, the capacitor 3, which absorbs energy from the inductor 32, is discharged smoothly again and can also be reconnected without having to connect the resistor 6 beforehand.

[0040] As a second measure, a further capacitor 8 is connected in parallel with the varistor 4. When the current commutates from the turn-offable semiconductor switch to the current path through the capacitor 3, the further capacitor improves the response behavior of the inductance of the varistor 4. Thus, short-term voltage peaks at the turn-offable semiconductor switch can also be avoided. This also has a positive effect on the service life of the electrical switch 1.

[0041] As a third measure, a further discharge resistor 9 can be connected in parallel with the varistor 4. By means of the voltage divider formed by the discharge resistor 7 and the further discharge resistor 9, the voltage drop across the varistor 4 is reduced. This takes place when the electrical switch 1 is turned on and off and increases the service life of the varistor 4 and thus also the service life of the electrical switch 1. At the same time, when the electrical switch 1 is reconnected, the further discharge resistor 9 causes the capacitor 3 to be discharged moderately. Thereby, the second series circuit 11 can also be dispensed with. When used together with the second series circuit 11, the voltage load on the electrical switch 1 during switching can be further reduced, and thus its service life can be further increased.

[0042] Here, these three measures can be carried out individually or in any combination in order to improve the switching behavior of the electrical switch 1.

[0043] In summary, the present invention relates to an electrical switch having at least one switchable semiconductor switch, wherein the electrical switch has a capacitor and a varistor, wherein the capacitor and the varistor are arranged in a first series circuit, and the first series circuit composed of the capacitor and the varistor is connected in parallel with the switchable semiconductor switch. In order to improve the electrical switch, especially in terms of its switching performance, it is proposed that the electrical switch has a switch and a resistor, wherein the switch and the resistor are arranged in a second series circuit, and the second series circuit composed of the switch and the resistor is connected in parallel with the switchable semiconductor switch and with the first series circuit. The present invention also relates to a method for operating such an electrical switch, wherein the switch is turned on before the switchable semiconductor switch is turned on.

Claims

1. An electrical switch (1), comprising: - at least one turn-offable semiconductor switch (2, 21, 22), - a capacitor (3), and - a varistor (4), Among them, The capacitor (3) and the varistor (4) are arranged in a first series circuit (10), wherein the first series circuit (10) formed by the capacitor (3) and the varistor (4) is connected in parallel with the turn-offable semiconductor switch (2, 21, 22). It is characterized in that the electrical switch (1) has a switch (5) and a resistor (6), wherein the switch (5) and the resistor (6) are arranged in a second series circuit (11), and the second series circuit (11) formed by the switch (5) and the resistor (6) is connected in parallel with the turn-offable semiconductor switch (2, 21, 22) and in parallel with the first series circuit (10). A discharge resistor (7) is connected in parallel with the capacitor (3), another capacitor (8) is connected in parallel with the varistor (4), and another discharge resistor (9) is connected in parallel with the varistor (4). The voltage drop across the varistor (4) can be reduced by a voltage divider formed by the discharge resistor (7) and the other discharge resistor (9).

2. The electric switch (1) according to claim 1, wherein, The electrical switch (1) has at least two turn-offable semiconductor switches, wherein the first turn-offable semiconductor switch among the two turn-offable semiconductor switches (2, 21, 22) is configured to be able to turn off the current from the first terminal (12) of the electrical switch (1) to the second terminal (13) of the electrical switch (1), and the second turn-offable semiconductor switch among the two turn-offable semiconductor switches is configured to be able to turn off the current from the second terminal (13) of the electrical switch (1) to the first terminal (12) of the electrical switch (1), and the capacitor (3) is designed as a bipolar capacitor.

3. A method for operating an electrical switch (1) according to any one of claims 1 to 2, wherein, The switch (5) is turned on before the turn-offable semiconductor switch (2, 21, 22) is turned on.

4. The method according to claim 3, wherein, The switch (5) is turned off when the voltage at the capacitor (3) is lower than a voltage threshold.

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