Surge protection device with monitoring function and arrangement with the like

Abstract

Overvoltage protection device with monitoring function (1), comprising a parallel connection of two current branches (A, B), wherein the first current branch (A) has a first overvoltage protection device (Ü1) and a second overvoltage protection device (Ü2) which are connected in series, wherein the second current branch (B) has a third device (E3) and a fourth device (E4) which are connected in series, wherein the first overvoltage device (Ü1) and the third device (E3) have a first common voltage potential (P1) during operation, and wherein the second overvoltage device (Ü2) and the fourth device (E4) have a second common voltage potential (P2) during operation,wherein a first measuring tap (M1) is provided between the first overvoltage protection device (Ü1) and the second overvoltage protection device (Ü2), and wherein a second measuring tap (M2) is provided between the third device (E3) and the fourth device (E4), wherein a signal (S1, S2) is derived from the voltage between the first measuring tap (M1) and the second measuring tap (M2), which provides a status statement with regard to the first overvoltage protection device (Ü1) and the second overvoltage protection device (Ü2), wherein an evaluation circuit (C) is further provided, wherein the evaluation circuit (C) evaluates a differential voltage between the first measuring tap (M1) and the second measuring tap (M2), wherein the third device (E3) and the fourth device (E4) are overvoltage protection devices.

Description

The invention relates to an overvoltage protection device with a monitoring function and an arrangement with the like.Overvoltage protection devices use, for example, varistors or transient voltage suppressor diodes (TVS diodes).Varistors are used, for example, in overvoltage protection for limiting overvoltage. The power range extends from measurement control control loops with small signals to applications in the high voltage range. It is known that varistors are subject to aging which is strongly dependent on the mounting conditions and the frequency and intensity of the stresses with overvoltage pulses, and therefore the aging behavior of varistors is not reliably predictable.Transient voltage suppressor diodes (TVS diodes) are used for limiting overvoltage preferably in the field of measurement control regulation technology (MSR), in information technology (IT) and generally in circuits of lower electrical power, i.e. typically in a range which is referred to as fine protection. It is known that TVS diodes are damaged in different ways in the event of overloading (for example due to high surge current amplitudes). In addition to the so-called forward alloying into the short circuit, damage also occurs in which the diodes remain relatively high-ohmic, up to the case in which the junction capacitance of the diode is changed in a relevant manner.In order to overcome this problem, varistor devices typically have cut-off devices that cut off the respective varistor. These separating devices use heat of the varistor in order to separate the varistor when a temperature predetermined by the manufacturer is reached.On the other hand, TVS diodes are only rarely monitored or even separated from the electrical circuit by separating devices in the event of a fault. DE 10 2010 038 066 A1 and DE 10 2010 036 909 B3 already disclose thermal separation devices for monitoring TVS diodes. These separating devices are likewise based on the principle of component heating. For this purpose, however, the already flowing "leakage current" must have a certain magnitude in order to cause the necessary component heating.Especially in MSR and IT applications with (very) low-energy systems, the energy (the flowing leakage current) may not be sufficient to ensure reliable isolation.In other solutions (e.g. raycap), the varistors are provided with solid housings in which the overloaded varistor can go into short circuit and be destroyed without consequences for the environment. That is, a shutdown is dispensed with and the destruction is accepted. In this case, particularly pressure- and temperature-resistant housings must be provided, which are on the one hand large-volume and on the other hand expensive.The thermal separation mechanisms react to the energy conversion (temperature increase) which arises from fault currents / leakage currents. Depending on the degree of damage, the leakage current can increase very quickly.However, how fast the thermal separators operate depends on a variety of factors. The thermal mass which each mechanical separating device has is generally critical. The mechanism generally has to be of relatively massive design, since it has to be suitable for carrying the desired surge currents and, in turn, has to have sufficient mechanical energy stored for the triggering situation in order to reliably move the separating contacts. This is made more difficult by the fact that the critical region of a varistor, at which the impermissible heating is formed (so-called hotspot), may be located further away from the thermal separation devices, so that the heat transfer to the separation point is poor.This can lead to a greatly delayed reaction of the thermal separation devices. This gives rise to the risk that the damage to the varistor or to a TVS diode will proceed more quickly than the thermal cut-off device can (or can) react. In this case, there is the risk that the disconnection device no longer switches off the leakage current, which can develop up to the short-circuit current of the network. Complete, explosive destruction of the varistor or of the TVS diode can occur.Systems which do not monitor the thermal aging of the active overvoltage protection elements, but merely limit the effect of the short-circuit current through the arrester by means of solid metallic housings are comparatively large and generate strong feedback effects on the network, up to the failure as a result of tripping system fuses.A further disadvantage of the known monitoring methods is that it is not the actual damage of the varistors or diodes themselves that is detected, but rather only the consequence of damage is detected or the consequences of the total failure are diminished. The monitoring of the temperature thus makes use of a secondary, time-delayed effect, which only occurs when damage has already substantially advanced and thus there is a direct risk.Predictive detection by measurement technology of the damage to varistors and TVS diodes is associated with high outlay, since for a measurement the component or the overvoltage protection component must generally be disconnected from the supply network, so that its electrical parameters can be measured and compared with defined limit values.This is firstly complicated and secondly generally also associated with an interruption of the supply voltage of the device to be protected.DE 34 23 444 A1 discloses a device for limiting or protecting against occurring over-voltages. In this case, for example, two varistors are connected in series. A tap between the varistors is connected to a measuring bridge in which a lamp is arranged in the shunt arm. In this arrangement, however, it is not possible to provide a state statement regarding the first varistor and the second varistor.From DE 10 2012 022 399 A1 of the applicant, an ignition circuit is known. Furthermore, the document discloses multicontact transistors.The object of the invention is to provide an overvoltage protection device with a monitoring function which avoids one or more disadvantages from the prior art.The object is achieved according to the invention by the features of the independent claims. Advantageous embodiments of the invention are specified in the dependent claims.The invention is explained in more detail below with reference to the attached drawing on the basis of preferred embodiments.They show FIG. 1 shows a first schematic diagram of a device according to the invention according to a first embodiment, FIG. 2 shows a second basic circuit diagram of a device according to the invention according to a second embodiment, FIG. 3 shows the use of a multi-contact varistor in a circuit according to FIG. 2, FIG. 4 shows the use of a further multi-contact varistor in a circuit according to FIG. 2, FIG. 5 shows the use of a further multi-contact varistor in a circuit according to FIG. 2, FIG. 6 shows the use of a further multi-contact varistor in a circuit according to FIG. 1, FIG. 7 shows an arrangement with a spark gap and a circuit according to FIG. 1.The figures show an overvoltage protection device with a monitoring function 1.The overvoltage protection device with monitoring function 1 has a parallel connection of two current branches A, B. The first current branch A has a first overvoltage protection device Ü 1 and a second overvoltage protection device Ü 2 which are connected in series. Although, as a rule, varistors are shown as overvoltage protection device in the figures, this is not limiting, but rather can be seen merely as an example of overvoltage protection devices of a general type.Furthermore, the second current branch B has a third device E 3 and a fourth device E 4 which are likewise connected in series.The first overvoltage device Ü 1 and the third device E 3 have a first common voltage potential P 1 during operation, while the second overvoltage device Ü 2 and the fourth device E 4 have a second common voltage potential P 2 during operation. A first measurement tap M 1 is provided between the first overvoltage protection device Ü 1 to the second overvoltage protection device Ü 2 and a second measurement tap M 2 is provided between the third device E 3 to the fourth device E 4 and a signal S 1, S 2 is derived from the voltage between the first measurement tap M 1 and the second measurement tap M 2, providing a state indication with respect to the first overvoltage protection device Ü 1 and the second overvoltage protection device Ü 2.In this case, as shown in FIG. 1 and in FIGS. 6 and 7, the third device E 3 and the fourth device E 4 can be, for example, a series circuit of complex resistors, for example capacitors, coils, resistors or a combination thereof, or else the third device E 3 and the fourth device E 4 are themselves designed as third overvoltage protection device Ü 3 and fourth overvoltage protection device Ü 4 as shown in FIGS. 2-5. Unless it is explicitly stated below that a specific design has to be used exclusively, the description of one design must always be taken to include the other design as including.With the embodiments described above, it is now possible to identify the state of the overvoltage protection devices immediately in time in a simple manner. If damage occurs to one of the overvoltage protection devices, this has a direct effect on the impedance. Due to the arrangement in an arrangement similar to the Wheatstone bridge, a voltage now occurs between the measurement taps M 1 and M 2 due to the changed impedance conditions.That is to say, the voltage between the first measurement tap M 1 of the current branch A and the second measurement tap M 2 of the current branch B is compared. If one of the components changes, this can be detected very easily by means of the voltage change between the first measurement tap M 1 of the current branch A and the second measurement tap M 2 of the current branch B. In this case, it may be possible under certain circumstances to draw a conclusion from the (sign of the) signal about the corresponding current branch A or B in which the fault occurs. Since this change can be registered very early, corresponding measures can be initiated very early.For status control, alternatively or additionally a temporary (also periodically recurring measurement, e.g. in power plants) can take place or also a permanent measurement. Both measurements can be realized during operation in the simplest possible way, with the mains voltage applied. In the most general form, it can be assumed here that, in the case of a voltage measurement not equal to zero, there is a defect in one of the overvoltage protection devices. From the measurements, given appropriate evaluation and further processing, fault reporting signals and switching commands (switching off or disconnecting, etc.) can be generated.In an advantageous embodiment, an evaluation circuit C can now be provided, for example as shown in FIGS. 1 to 6, wherein the evaluation circuit C evaluates a differential voltage between the first measurement tap M 1 and the second measurement tap M 2. Such an evaluation circuit can be constructed, for example, by means of an operational amplifier, wherein, for example, a switch-off is initiated when a specific differential voltage is reached and / or a local or remote signaling S 1 is provided. Local signaling can be provided, for example, by an optical and / or acoustic signal and / or a local display, e.g., an e-paper display, for the state signaling or for the signaling of measured values. Remote signaling can be provided, for example, by remote communication via a signaling and / or automation bus or generally by means of telecommunication.The evaluation unit C can be used via different algorithms for excluding errors and for adjustability of the sensitivity. Different switching and reporting thresholds can be generated without problems, in particular in the case of varistors, so that, for example, a detected low differential voltage can be used as an indicator of an beginning degradation of one of the overvoltage devices, so that, for example, a corresponding component is replaced in the event of a ready revision.It is particularly advantageous that the measurement can be carried out during operation, so that it is not necessary to shut down or remove the overvoltage protection devices.Furthermore, in embodiments of the invention, it can be provided that the derived signal S 2 is used as a switching signal for a switch-off device SW.For example, the switch-off device can be a contactor or otherwise suitable switches or else it is an externally triggerable fuse, as have likewise been invented by the applicant and is the subject matter of other applications.Although in the introduction the present invention is directed to varistors and transient voltage suppressor diodes, the invention is not limited thereto, but in principle the operating principles can also be used for other suitable overvoltage protection devices Ü 1, Ü 2. The same applies with respect to the third device E 3 and the fourth device E 4 in terms of their configuration as overvoltage protection devices Ü 3, Ü 4.In a particularly compact embodiment, multicontact transistors M-MOV are used, as will now be described below with reference to various embodiments in connection with FIGS. 3 to 6.For example, in these, the first overvoltage protection device Ü 1 and the second overvoltage protection device Ü 2 are each designed as a partial varistor of a multicontact varistor M-MOV, and the first measuring tap M 1 is in electrical contact with a (central) contact of the multicontact varistor M-MOV. Although the partial transistors are shown as being similar, this is not absolutely necessary.For example, as in FIGS. 3 to 6, the multicontact varistor M-MOV can be provided by different measures. For example, in FIG. 3, two similar taps are provided in the ceramic of a varistor for contacting the measurement taps, so that two (virtual) current branches A, B are formed. A measure corresponding to this is shown using the example of a single tap for the case in which overvoltage protection devices are provided only in one current branch.To improve the separation of the measuring taps in the multicontact varistor M-MOV, it can be provided that, for example, a first varistor ceramic is arranged on a further varistor ceramic, the measuring taps M 1 M 2 being arranged between the varistor ceramics, these being additionally insulated in the interspace, in order thus to separate the current flow in the branches A and B.Furthermore, as shown in FIG. 5, a complete separation of the ceramics can also be provided.In an advantageous arrangement, which is shown in FIG. 7, an overvoltage protection device 1 is arranged with a spark gap FS with one or more auxiliary electrodes H 1, H 2. The overvoltage protection device 1 and the spark gap FS are connected in parallel and the first measuring tap M 1 of the overvoltage protection device 1 is connected to a first ignition auxiliary electrode H 1 of the spark gap FS.An example of simply monitoring a varistor bridge in such a way that, in the event of relevant damage to a varistor, the device 1 is protected from destruction is the ignition of the parallel spark gap FS, which provides a short circuit, so that a series-connected fuse (not shown) responds and disconnects the entire overvoltage protection device from the operating voltage. In this case, for example, a resisiively assisted ignition filed by the applicant can be used for igniting the spark gaps FS.In the overvoltage protection devices with monitoring function of the invention, for example, the impedance ratio (complex resistance ratio) of the first overvoltage protection device U 1 to the second overvoltage protection device U 2 can correspond to the impedance ratio (complex resistance ratio) of the third device E 3 to the fourth device E 4 in the normal operation. Particularly simple evaluation circuits can thereby be provided. As shown in FIGS. 1, 6 and 7 at the devices E 3 and E 4, it may be advantageous that one or both devices E 3 and E 4 can be detuned, so that the impedance ratios are the same during normal operation. Such a setting can be carried out, for example, during production or during startup. Alternatively or additionally, other measures, such as a matching network, may also be used.Alternatively, it can of course also be provided that the impedance conditions are not identical in normal operation. Here too, a suitable circuit can be used to ensure that, for example, only deviations from a (measured or previously set) standard value are detected as a malfunction. For this purpose, for example, suitable threshold switches or matching networks or also an (electrically reliable) comparison with one or more previously determined / set values of the voltage between the first measurement tap M 1 and the second measurement tap M 2 can be used.Although the above elements of the invention have been described as individual elements, it is understood that they may also be part of a saleable device, for example, united in a housing.The system proposed here enables a constant, very precise monitoring of the overvoltage protection components. Even minor changes can be detected and corresponding information and measures can be initiated on the basis of a downstream evaluation unit. On the one hand, the measurement method can be used to carry out an actual analysis, i.e. to provide technical data, and on the other hand, direct mechanisms can be initiated from the measurement, which mechanisms lead, for example, to the disconnection of the arrester from the power supply network.By continuous or cyclical evaluation of the obtained data, a prognosis for the further development of the arrester can be made. In particular for installations whose accessibility is not always given and whose revision is associated with particular effort (e.g. wind power offshore), such monitoring is of particular importance (smart SPD).Furthermore, the voltage signal between the first measurement tap M 1 of the current branch A and the second measurement tap M 2 of the current branch B can also be used directly for actuating actuators. This means that at the same time, from the fault which forms, an actuator for disconnection, short-circuiting or bridging SW can be actuated. This eliminates the time-critical bypass via the detection of heating, so that it is possible to react much earlier to errors.As a result, damage which may progress "quickly" and which could lead to the flow of the short-circuit current and the associated explosion of the arrester can also be absorbed so early that comparatively simple switching devices are still sufficient to switch off the fault.List of reference characters1 Overvoltage protection device with monitoring function A, B current branch Ü 1, 2, Ü 3, Ü 4 overvoltage protection device E 3, E 4 device P 1, P 2 voltage potential M 1, M 2 measuring tap S1, S2signal C evaluation circuit SW switch-off device M-MOV multicontact varistor FS spark gap H1, H2 ignition auxiliary electrode

Claims

Overvoltage protection device with monitoring function (1), comprising a parallel connection of two current branches (A, B), wherein the first current branch (A) comprises a first overvoltage protection device (Ü 1) and a second overvoltage protection device (Ü 2) which are connected in series, wherein the second current branch (B) comprises a third device (E 3) and a fourth device (E 4) which are connected in series, wherein the first overvoltage device (Ü 1) and the third device (E 3) comprise a first common voltage potential (P 1) in operation, and wherein the second overvoltage device (Ü 2) and the fourth device (E 4) have a second common voltage potential (P 2) during operation, wherein a first measurement tap (M 1) is provided between the first overvoltage device (Ü 1) and the second overvoltage device (Ü 2) and wherein a second measurement tap (M 2) is provided between the third device (E 3) to the fourth device (E 4), wherein a signal (S 1, S 2) is derived from the voltage between the first measuring tap (M 1) and the second measuring tap (M 2) and provides a state statement with respect to the first overvoltage protection device (Ü 1) and the second overvoltage protection device (Ü 2) wherein an evaluation circuit (C) is also provided, wherein the evaluation circuit (C) evaluates a differential voltage between the first measuring tap (M 1) and the second measuring tap (M 2), wherein the third device (E 3) and the fourth device (E 4) are overvoltage protection devices.Overvoltage protection device (1) according to claim 1, characterized in that a measurement takes place during operation.Overvoltage protection device (1) according to one of the preceding claims, characterized in that the derived signal (S 2) is used as a switching signal for a switch-off device (SW).Overvoltage protection device (1) according to one of the preceding claims, characterized in that the first overvoltage protection device (Ü 1) and the second overvoltage protection device (Ü 2) are selected from the group comprising varistors and transient voltage suppressor diodes.Overvoltage protection device (1) according to one of the preceding claims, characterized in that the first overvoltage protection device (Ü 1) and the second overvoltage protection device (Ü 2) are partial transistors of a multicontact varistor (M-MOV), and in that the first measurement tap (M 1) is a contact of the multicontact varistor (M-MOV).Overvoltage protection device (1) according to one of the preceding claims, characterized in that the impedance ratio of the first overvoltage protection device (Ü 1) to the second overvoltage protection device (Ü 2) in normal operation corresponds to the impedance ratio of the third device (E 3) to the fourth device (E 4).Arrangement of an overvoltage protection device (1) according to one of the preceding claims, having a spark gap (FS) with auxiliary electrodes (H1, H2), wherein the overvoltage protection device (1) and the spark gap (FS) are connected in parallel and wherein the first measuring tap (M 1) of the overvoltage protection device (1) is connected to a first ignition auxiliary electrode (H 1) of the spark gap (FS).

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