The invention relates to a device for the permanently secure disconnection of an electric circuit with high currents at high voltages with an inductive load. The device has a first and a second switch/switch group, which are connected to each other in series and can be transferred from a closed state into a separated state for disconnecting the electric circuit, wherein none of the switches/switch groups is formed such that it is capable of reliably and permanently disconnecting the electric circuit by itself, and a control unit, which actuates the second switch/switch group and which is formed such that the second switch/switch group is transferred from the closed state into the separated state after the first switch/switch group. Equally, the present invention also relates to an electric circuit, which in addition to the device according to the invention also has a voltage source, a load resistance and an inductive load, as well as to a method using the device according to the invention.

A disconnection of electric circuits with high currents at high voltages is often possible only with switches which tolerate a high energy input without being destroyed. Until now, switches which have a separation region which is present within an extinguishing agent or is in contact with the at least one extinguishing agent have often been used for this. Through the extinguishing agent, an electric arc which forms after the separation of the separation region is to be extinguished, depleted or at least disrupted. The cause of the formation of an electric arc is the energy stored in the circuit inductance in the form of a magnetic field at the moment that the current is disconnected, which energy is introduced into the switch immediately after the disconnection. This means that a high-energy electric arc occurs in particular when electric circuits with a high inductive load are disconnected. Because most extinguishing agents and plastics contain carbon atoms, these atoms are broken down in the extreme heat of the electric arc of well above 2000° C. and then form an electrically conductive carbon layer on cooling, or the heat of the electric arc makes the extinguishing agent completely or partially electrically conductive. Although such switches can actively or passively shut off electric circuits at high source voltage and high current strengths, here the inductance of the electric circuit to be shut off determines whether this switch is and remains highly insulating after the current interruption or becomes more or less conductive again later. The same applies to materials used in the switch, which mostly contain halides such as chlorine or fluorine—here too, after the current has been shut off, although the electrical conductivity of the highly-heated plasma still present in the switch is very low, it becomes extremely high when the plasma cools once the disconnection of the electric circuit is complete. Here, a few milliseconds are already sufficient for the cooling time. Consequently, although at first it is possible to interrupt the electric circuit with such switches, a permanently secure disconnection with a high insulation resistance always required cannot be guaranteed. Some of the switches currently used are already suitable for shutting off a voltage of 450 V to 850 V usual in motor vehicles and currents in the electric circuit of up to 20 kA at the moment of the disconnection. However, in the case of currents to be disconnected up to 30 kA, voltages of 1250 V, and in the case of buses and HGVs even over 2000 V, are expected in future in this field, with the result that the switches used until now can no longer permanently and securely shut off such electric circuits as an individual assembly.

The object of the present invention is therefore to provide a possibility for permanently and securely disconnecting electric circuits with high currents and high voltages with a high inductive load, in the case of which previous high-current/high-voltage switches fail. It is intended to securely prevent such a switch from becoming conductive again within a short time after the disconnection. Furthermore, it is intended to prevent the switch from being destroyed after the tripping operation by high steady currents flowing in the case of insufficient insulation resistance.

This object is achieved through the provision of a device according to the present specification, an electric circuit according to the present specification, as well as a method according to the present specification.

The device for disconnecting an electric circuit with an inductive load according to the invention has a first and a second switch/switch group, which are connected to each other in series and can be transferred from a closed state into a separated state for disconnecting the electric circuit, wherein none of the switches/switch groups is formed such that it is capable of permanently disconnecting the electric circuit by itself. Furthermore, the device according to the invention has a control unit, which actuates the second switch/switch group and which is formed such that the second switch/switch group is transferred from the closed state into the separated state after the first switch/switch group.

In the following, the term “switch” is intended to represent an individual switch, but also a switch group.

Also included here are switches/switch groups in which more than two switches or individual assemblies are actuated one after the other. The tripping principle or protective principle is the same, for the sake of simplicity only two switches/switch groups are ever described here.

When the electric circuit is disconnected by the first switch, the energy stored in the circuit inductance is introduced into the first switch. This energy leads to an electric arc between the two separated ends of a separation element of the switch. In the process, an amount of energy is introduced into the first switch, which would lead to the first switch becoming conductive again or being destroyed after the actual separation operation. Through the time-delayed tripping of the second switch, the amount of energy which is introduced into the first switch can be reduced since some of the energy to be dissipated is introduced into the second switch, which moreover additionally encounters or must tolerate only a considerably lower tripping load with regard to current and voltage via its connecting element at the moment of its actuation. This also enables the electric circuit to be interrupted before a circuit inductance, which the second switch would not tolerate, can build up again due to the first switch becoming conductive again. Each switch could not tolerate all of the energy stored in the circuit inductance by itself, it would either be destroyed or become conductive again and thus would not be capable of permanently and securely disconnecting the electric circuit. In this way, electric circuits with such a high inductive load, for which one switch alone would not be sufficient, can be permanently and securely disconnected.

A special type of actuation or tripping of the two switches/switch assemblies is the simultaneous actuation of the two switches. The voltage dropping across each of the two switches would thus be halved; the energy flowing into the individual switches would thus likewise be halved. Both switches would thus be loaded equally, assuming an identical design of the two switches. For lower circuit inductances, this may still be acceptable, but at higher circuit inductances there is the danger that both assemblies become conductive again after the disconnection, which would not be acceptable at all. It would thus also not be possible to utilize the very high separability of the individual switches because it would be necessary here to have the insulation resistance after the separation in mind in the case of both switches, and it would not be possible to use the second switch only with/at an extremely low tripping load.

Also, different types of switch could only be combined with each other if actuation and separation operations are staggered one after the other in time. Thus, for example, a switch with high separability at high voltage and high current at the moment of its actuation, like the so-called power fuse (seeFIG. 5), can be used as first switch, whereas a conventional battery cut off switch which could not trip a high current at high voltage by itself can be used as second switch in the electric circuit because, at that point in time, thus after the separation operation of the first switch, this must only separate a low voltage at a low current and in this connection also need not use an extinguishing agent.

According to the invention, as first switch, one which is a high-current/high-voltage switch, i.e. is capable of reliably disconnecting electric circuits with high currents at high voltages, is preferably used. As a rule, such high-current/high-voltage switches can reliably and permanently disconnect electric circuits with currents up to 30 kA and voltages up to 2000 V. Such high-current/high-voltage switches are known for example from DE 10 2014 107 853 A1, DE 10 2014 110 825 A1, DE 20 2015 100 525 U1, DE 10 2015 112 141 A1, DE 10 2015 114 279 A1, DE 10 2015 114 894 A1, DE 10 2016 124 176 A1 and DE 10 2017 123 021 A1. If the switch is a switch group, then it preferably comprises or preferably consists of a parallel circuit consisting of one or more safety fuses and a conventional battery cut off switch. This is preferably a battery cut off switch as is known, for example, for the battery or cable circuitry of conventional vehicle batteries up to 56 V. Both systems mentioned are suitable for the primary power shutoff at high switching voltages and high switching currents. Particularly preferably, the first switch/switch group has an extinguishing agent inside in the region of the separation element, through the separation of which the circuit is disconnected. The extinguishing agent guarantees that a higher energy can be absorbed by the switch at the moment of disconnection of the electric circuit, since the energy of the electric arc is used to vaporize the extinguishing agent and to break it down into its constituents. Switches without such extinguishing agents are not suitable to such an extent for disconnecting electric circuits with high switching voltages at high switching currents. However, as mentioned further above, the disadvantageous effect of the chemical conversion of the extinguishing agent into a conducting material results in the switch very quickly becoming electrically conducting again from a particular energy input after the actual separation operation.

The extinguishing agent can be a solid, powdery or liquid medium. The extinguishing agent is preferably a vaporizable medium. The extinguishing agent is preferably a liquid or gel-like medium, which passes entirely or partially into a gaseous state when the boiling or vaporization temperature is reached. At the same time, it is preferred for the extinguishing agent to also have electrically insulating properties, in order that the electric arc can be extinguished after the two separated parts of the separation region have been moved away from each other sufficiently and there is thereafter a sufficient insulation from a current flow, which is then undesired here, between the separated contacts. The extinguishing agent is preferably an oil, for example silicone oil, with or without thickening agent, or a silane or polysiloxane, for example hexasilane or pentasilane with as little as possible, or even better without, carbon atom content.

According to the invention, as second switch, one can be used which tolerates only a smaller energy input than the first switch, since a large proportion of the energy from the circuit inductance has already been consumed in the first switch. The second switch is preferably one which is capable of reliably and permanently disconnecting electric circuits with currents up to 100 A at voltages at the moment of actuation up to 100 V and, after the disconnection thereof, of being able to insulate voltages up to 1000 V or 2000 V without breakdown. Since the high energy of the electric arc quickly leads, in the first switch, to it becoming conductive again, the second switch is preferably formed such that its switching delay lies in the range of from 1 ms to 10 ms.

By switching delay is meant here the time lag in which the first and the second switch disconnect the electric circuit or are transferred from the closed state into the separated state. However, a second switch with a longer switching delay would also be conceivable, if, for example, the second switch has already been triggered before an electric arc forms in the second switch, but, for example, only shortly thereafter passes from the closed state into the separated state. However, the latter is only possible if the time interval between the tripping of the first and of the second switch necessary for the secure and permanent disconnection of the electric circuit can be defined in advance on the basis of all of the parameters of the electric circuit. The systems which are mentioned above for the first switch can also be used as second switch. Furthermore, however, a conventional battery cut off switch without a safety fuse connected in parallel can also be used, since, in the untriggered state, although this battery cut off switch cannot trip the high currents to be disconnected occurring, it can conduct them very well. Furthermore, after the power has been shut off by the first switch, the second switch only has to be able to trip a current in the range of from 0 A to 100 A at a switching voltage across the switching contacts of the second switch of less than 100 V. Relays or electromagnetic contactors are not very suitable as second switch because the relays or contactors in the automotive field used for the usual operating currents of from 400 A to 1000 A already explode between 0.5 ms and 2 ms at the high currents of over 10 kA that can be supplied for example by lithium ion batteries (the huge and heavy contactors which are used for this purpose in railway train engines are not considered here because they cannot be used at all in the automotive field, as is also the case with electric aircraft, for weight, size and cost reasons).

The high-current/high-voltage switch or battery cut off switch which can be used according to the invention preferably has a casing which surrounds a contact unit/a connecting element defining the current path through the high-current/high-voltage switch or battery cut off switch, which has a first and second connection contact and a separation region. The contact unit is preferably formed such that a current can be supplied to it via the first connection contact and can be discharged from it via the second connection contact, or vice versa. The separation region is preferably formed such that, when it is separated, the current path between the first connection contact and the second connection contact is interrupted. The separation region is preferably arranged inside a reaction chamber. The reaction chamber is preferably filled with an extinguishing agent. If the switch is a high-current/high-voltage switch, the contact unit can have a sabot or be connected to a sabot or a plunger, which is formed such that it can be moved from a starting position into an end position through exposure to pressure, wherein in the end position of the sabot the separation region is separated and an insulation spacing between the first and the second connection contact is achieved.

Through the described arrangement of the series connection of the first and the second switch, electric circuits with considerably greater circuit inductance can be shut off than would be possible with only a single switch. Here, the first switch dissipatively takes on the main proportion of the magnetic energy stored in the circuit inductance at the moment of the separation, while the second switch only has to take on a very small portion of any magnetic energy still present in the circuit inductance during the development thereof. Therefore, the second switch need not necessarily be one which has an extinguishing agent in the vicinity of its separation element. However, if electric circuits with extremely high circuit inductances are involved, for safety reasons the second switch should also be one which has an extinguishing agent in the vicinity of its separation element. Possible extinguishing agents for this are named further above.

In the case of the switches to be used according to the invention, within the meaning of the present invention adiabatic systems can be taken as the starting point as the tripping operations are so quick that a heat exchange with the surroundings is negligible, at least during the separation operation.

The property that the first and the second switch are not formed such that they are capable of permanently and securely disconnecting the electric circuit by themselves is to be attributed to the fact that known high-current/high-voltage switches become conductive again after the actual separation operation in the case of very high switching voltages and very high switching currents. By a permanent and secure disconnection of the electric circuit is meant according to the invention that the switch or switches insulate(s) permanently and thus do not become conductive again.

The device according to the invention can be used both for AC and also for DC electric circuits. Thus, although the current always crosses zero in the case of AC electric circuits, it can never be predicted when the electric circuit is to be shut off. If tripping has to take place at maximum current, effectively the DC current shutoff state exists.

The separation element in the switches can be hollow cylindrical or in the form of an elongate hollow body with a cross-sectional footprint deviating from a circle, with the result that it is ruptured by an internal pressure but, for the so-called battery cut off switch, can also be formed as a solid rod-shaped conductor, which is broken open at one or more points by a plunger or a projectile. In both cases, materials and also extinguishing agents are usually used which can become electrically conductive during or after contact with an electric arc with a correspondingly large energy exposure.

In a design of the device according to the invention, the control unit is preferably formed such that the second switch is transferred from the closed state into the separated state at the earliest when so much energy has been absorbed in the first switch that the remaining amount of energy, which is introduced into the second switch, does not lead to the destruction of the second switch.

In a design of the device according to the invention, the control unit is preferably formed such that the second switch is transferred from the closed state into the separated state at the latest before an amount of energy introduced into the second switch is reached which leads to the destruction thereof.

By the destruction of the switch is meant according to the invention that the switch casing breaks open or the switch explodes as a result of the energy introduced and the formation of the electric arc.

In a design of the device according to the invention, the first and the second switch can preferably be actively transferred from the closed state into the separated state by an actuatable drive. By “actively” is meant any type of mechanical or pyrotechnic energy which can separate the separation region (separation element) of a switch on command. Thus, for example, the separation region can be separated by the action of a pulling or pushing movement. Or a pyrotechnic material, such as for example an igniter (EED) or a mini detonator, is used, which is either located in a reaction chamber or is attached outside the reaction chamber such that it can act on the separation region through a pulling or pushing movement or a shock wave and causes the separation thereof.

In a design of the device according to the invention, the first switch can be passively transferred from the closed state into the separated state when a particular threshold amperage is exceeded, and the second switch can be actively transferred from the closed state into the separated state by an actuatable drive. This passive triggering can be effected, for example, by melting the material forming the separation region, for example on reaching a particular current integral. The passive triggering can also be supported by the action of pyrotechnic explosives and priming compositions, as well as merely by thermal action of decomposing substances, such as for example tetrazene. Devices which move these two ends further away from each other, for example through an existing tensile load which can act after separation of the separation region, can also be attached to one or to both separated parts of the separation region. A tensile load by a pre-stressed spring can be named here by way of example.

In a design of the device according to the invention, the control unit is preferably formed such that it transfers the second switch from the closed state into the separated state as a function of a particular measured current or a particular measured voltage, which is applied to the first switch.

In a design of the device according to the invention, the control unit is preferably formed such that the second switch is transferred from the closed state into the separated state when the current flowing through both switches has fallen to a value in the range of from 25% to 40% of the current present at the start of the separation of the first switch.

In a design of the device according to the invention, the control unit is preferably formed such that the second switch is transferred from the closed state into the separated state when the current flowing through both switches has fallen to a value in the range of from 5% to 15% of the current present at the start of the separation of the first switch.

In a design of the device according to the invention, the control unit is preferably formed such that it transfers the second switch from the closed state into the separated state as a function of a particular measured drop in current in the electric circuit.

The present invention also relates to an electric circuit which, in addition to a device according to the invention, also has a voltage source and an inductive load. In addition to the inductive load, a load resistance can also be present in the electric circuit. All preferred embodiments or designs of the device according to the invention also apply to the electric circuit according to the invention.

The present invention also relates to a method for disconnecting an electric circuit with an inductive load with a first and a second switch, which are connected to each other in series and are transferred from a closed state into a separated state for disconnecting the electric circuit, wherein none of the switches is formed such that it is capable of permanently disconnecting the electric circuit by itself, wherein the second switch is transferred from the closed state into the separated state after the first switch.

In a design of the method according to the invention it is preferred for the second switch to be transferred from the closed state into the separated state at the earliest when so much energy has been absorbed in the first switch that the remaining amount of energy, which is introduced into the second switch, does not lead to the destruction thereof.

In a design of the method according to the invention, the second switch is preferably transferred from the closed state into the separated state at the latest before an amount of energy introduced into the second switch is reached which leads to the destruction thereof.

In a design of the method according to the invention it is preferred for the first and the second switch to be actively transferred from the closed state into the separated state by an actuatable drive.

In a design of the method according to the invention it is preferred for the first switch to be passively transferred from the closed state into the separated state when a particular nominal value is exceeded, and the second switch to be actively transferred from the closed state into the separated state by an actuatable drive. For this purpose, the actuatable drive is preferably connected to a control unit which actuates the drive and, in this way, can transfer the second switch from the closed state into the separated state.

In a design of the method according to the invention it is preferred for the second switch to be transferred from the closed state into the separated state as a function of a particular measured current or a particular measured voltage through the first switch.

In a design of the method according to the invention it is preferred for the second switch to be transferred from the closed state into the separated state when the current flowing through both switches has fallen to a value in the range of from 25% to 40% of the current present at the start of the separation of the first switch.

In a design of the method according to the invention, the control unit is preferably formed such that the second switch is transferred from the closed state into the separated state when the current flowing through both switches has fallen to a value in the range of from 5% to 15% of the current present at the start of the separation of the first switch.

In a design of the method according to the invention, the control unit is preferably formed such that it transfers the second switch from the closed state into the separated state as a function of a particular measured drop in current in the electric circuit.

A device according to the invention or an electric circuit according to the invention is preferably used in the method according to the invention. Thus, all preferred embodiments and designs which are mentioned further above in connection with the device according to the invention are also intended to apply to the method according to the invention. For transferring the second switch from the closed into the separated state, a control unit as mentioned further above is preferably also used. The same also applies to the second switch, if it is actuated by the control unit.

