OVERVOLTAGE PROTECTION APPARATUS WITH MONITORING FUNCTION

Abstract

The object of the invention is an overvoltage protection apparatus with monitoring function having a parallel circuit of two branch circuits, wherein the first branch circuit has a first overvoltage protection device and a second overvoltage protection device that are connected in series, wherein the second branch circuit has a third device and a fourth device that are connected in series, wherein the first overvoltage device and the third device have a first shared voltage potential during operation, and wherein the second overvoltage device and the fourth device have a second shared voltage potential during operation, wherein a first measuring tap is provided between the first overvoltage protection device and the second overvoltage protection device and wherein a second measuring tap is provided between the third device and the fourth device, with a signal being derived from the voltage between the first measuring tap and the second measuring tap that provides state information in relation to the first overvoltage protection device and the second overvoltage protection device.

Claims

1. An overvoltage protection apparatus with monitoring function having a parallel circuit of two branch circuits, wherein the first branch circuit has a first overvoltage protection device and a second overvoltage protection device that are connected in series, wherein the second branch circuit has a third device and a fourth device that are connected in series, wherein the first overvoltage device and the third device have a first shared voltage potential during operation, and wherein the second overvoltage device and the fourth device have a second shared voltage potential during operation, wherein a first measuring is provided between the first overvoltage protection device and the second overvoltage protection device and wherein a second measuring tap is provided between the third device and the fourth device, with a signal being derived from the voltage between the first measuring tap and the second measuring tap that provides state information in relation to the first overvoltage protection device and the second overvoltage protection device.

2. The overvoltage protection apparatus as set forth in claim 1, wherein an evaluation circuit is also provided, with the evaluation circuit evaluating a differential voltage between the first measuring tap and the second measuring tap.

3. The overvoltage protection apparatus as set forth in claim 1, wherein the measurement is performed during ongoing operation.

4. The overvoltage protection apparatus as set forth in claim 1, wherein the derived signal is used as a switch signal for a shutoff device.

5. The overvoltage protection apparatus as set forth in claim 1, wherein the first overvoltage protection device and the second overvoltage protection device are selected from the group consisting of varistors and transient voltage suppressor diodes.

6. The overvoltage protection apparatus as set forth in claim 1, wherein the third device and the fourth device are overvoltage protection devices.

7. The overvoltage protection apparatus as set forth in claim 1, wherein the first overvoltage protection device and the second overvoltage protection device are subvaristors of a multicontact varistor and that the first measuring tap is a contact of the multicontact varistor.

8. The overvoltage protection apparatus as set forth in claim 1, wherein the impedance ratio of the first overvoltage protection device to the second overvoltage protection device corresponds during normal operation to the impedance ratio of the third device the fourth device.

9. An arrangement of an overvoltage protection apparatus as set forth in claim 1, with a spark gap with auxiliary electrodes, wherein the overvoltage protection apparatuses and the spark gap are connected in parallel and wherein the first measuring tap of the overvoltage protection apparatus is connected to a first auxiliary ignition electrode of the spark gap.

Description

[0018] In the following, the invention is explained in further detail with reference to the enclosed drawing on the basis of preferred embodiments.

[0019] FIG. 1 shows a first block diagram of an apparatus according to the invention according to a first embodiment;

[0020] FIG. 2 shows a second block diagram of an apparatus according to the invention according to a second embodiment;

[0021] FIG. 3 shows the use of a multi-contact varistor in a circuit according to FIG. 2;

[0022] FIG. 4 shows the use of another multi-contact varistor in a circuit according to FIG. 2;

[0023] FIG. 5 shows the use of another multi-contact varistor in a circuit according to FIG. 2;

[0024] FIG. 6 shows the use of another multi-contact varistor in a circuit according to FIG. 1;

[0025] FIG. 7 shows an arrangement with a spark gap and a circuit according to FIG. 1.

[0026] The figures show an overvoltage protection apparatus with monitoring function 1.

[0027] The overvoltage protection apparatus with monitoring function 1 has a parallel circuit of two branch circuits A, B. The first branch circuit A has a first overvoltage protection device Ü.sub.1 and a second overvoltage protection device Ü.sub.2, which are connected in series. Even though varistors are generally depicted in the figures as an overvoltage protection device, this is not limitative and is to be regarded merely as an example of overvoltage protection devices of the general type.

[0028] Furthermore, the second branch circuit B has a third device E.sub.3 and a fourth device E.sub.4, which are also connected in series.

[0029] During operation, the first overvoltage device Ü.sub.1 and the third device E.sub.3 have a first shared voltage potential P.sub.1, whereas the second overvoltage device Ü.sub.2 and the fourth device E.sub.4 have a second shared voltage potential P.sub.2 during operation. A first measuring tap M.sub.1 is provided between the first overvoltage protection device Ü.sub.1 and the second overvoltage protection device Ü.sub.2, and a second measuring tap M.sub.2 is provided between the third device E.sub.3 and the fourth device E.sub.4, with a signal S.sub.1, S.sub.2 being derived from the voltage between the first measuring tap M.sub.1 and the second measuring tap M.sub.2 that makes state information available in relation to the first overvoltage protection device Ü.sub.1 and the second overvoltage protection device Ü.sub.2 .

[0030] As shown in FIG. 1, FIG. 6, and FIG. 7, the third device E.sub.3 and the fourth device E.sub.4 can, for example, be a series circuit of complex resistances such as capacitors, coils, resistors, or a combination thereof, or the third device E.sub.3 and the fourth device E.sub.4 are themselves embodied as the third overvoltage protection device Ü.sub.3 and fourth overvoltage protection device Ü.sub.4, as shown in FIGS. 2-5. Insofar as it is not explicitly indicated below that a specific design must be used exclusively, a description of one design must always be assumed to cover the other design as well.

[0031] With the embodiments described above, it is not possible to immediately identify the state of the overvoltage protection devices in a simple manner. To wit, if one of the overvoltage protection devices is damaged, this has an immediate effect on the impedance. Due to the arrangement in a configuration similar to a Wheatstone bridge, a voltage now occurs between measuring taps M.sub.1 and M.sub.2 due to the altered impedance ratios.

[0032] That is, the voltage between the first measuring tap M.sub.1 of the branch circuit A and the second measuring tap M.sub.2 of the branch circuit B is compared. If one of the components changes, this can be detected very easily on the basis of the change in voltage between the first measuring tap M.sub.1 of the branch circuit A and the second measuring tap M.sub.2 of the branch circuit B. In some circumstances, it is possible to determine the branch circuit A or B in which the fault occurs from the (sign of the) signal. Since this change can be registered very early on, appropriate measures can be initiated very promptly.

[0033] For the status check, a temporary or periodic measurement (such as those performed in power plants) or a continuous measurement can be performed. Both measurements can be carried out during operation with the greatest of ease while the line voltage is connected. In the most general of terms, it can be assumed that a voltage measurement not equal to zero indicates that a defect is present in one of the overvoltage protection devices. With appropriate evaluation and further processing, fault indication signals and switch commands (open or disconnect, etc.) can be generated from the measurements.

[0034] In one advantageous embodiment, it is now possible, as shown in FIGS. 1 to 6, for example, to provide an evaluation circuit C, with the evaluation circuit C evaluating a differential mode voltage between the first measuring tap Mi and the second measuring tap M.sub.2. Such an evaluation circuit can be constructed by means of an operational amplifier, for example, in which case disconnection is initiated and/or a local or remote signaling S.sub.1 is provided when a certain differential voltage is reached, for example. Local signaling can be provided, for example, by means of an optical and/or acoustic signal and/or a local display, e.g., an e-paper display, for status signaling or for the signaling of measurement values. Remote signaling can be provided, for example, in the form of remote reporting of an indication, and/or by means of an automation bus, or generally by means of telecommunication.

[0035] The evaluation unit C can be utilized on the basis of different algorithms in order to rule out errors and enable the sensitivity to be adjusted. Different switching and reporting thresholds can easily be generated particularly with varistors, so a low differential voltage that is detected can be taken as an indication of the onset of degradation in one of the overvoltage devices, thus enabling a corresponding component to be replaced during a shift inspection.

[0036] It is particularly advantageous that the measurement can be performed during ongoing operation, so that it is not necessary to switch off or remove the overvoltage protection devices.

[0037] Moreover, a provision can be made in embodiments of the invention for the derived signal S.sub.2 to be used as a switch signal for a shutoff device SW.

[0038] For example, the shutoff device can be a contactor or an otherwise suitable switch, or an externally triggerable fuse such as those which have already been invented by the applicant and constitute the subject matter of other applications.

[0039] Even though the focus was placed on varistors and transient voltage suppressor diodes in the introduction, the invention is not limited to these; rather, the operating principles can also be used for other suitable overvoltage protection devices Ü.sub.1, Ü.sub.2. The same applies with respect to the third device E.sub.3 and the fourth device E.sub.4 in their implementation as overvoltage protection devices Ü.sub.3, Ü.sub.4.

[0040] In one especially compact embodiment, multicontact varistors M-MOV are used, as will now be described below in relation to various embodiments in conjunction with FIGS. 3 to 6.

[0041] In these embodiments, for example, the first overvoltage protection device Ü.sub.1 and the second overvoltage protection device Ü.sub.2 are each embodied as a subvaristor of a multicontact varistor M-MOV, and the first measuring tap M.sub.1 is in electrical contact with a (center) contact of the multicontact varistor M-MOV. Although the subvaristors are depicted as being identical, this is not absolutely necessary.

[0042] For example, the multicontact varistor M-MOV can be provided by various means, as shown in FIGS. 3 to 6. In FIG. 3, for example, two similar taps for contacting the measuring taps are provided in the ceramic of a varistor, thereby forming two (virtual) branch circuits A, B. A commensurate measure is shown using the example of a single tap for a case in which overvoltage protection devices are provided in only one branch circuit.

[0043] To enable better separation of the measuring taps in the multicontact varistor M-MOV, a provision can be made, for example, that a first varistor ceramic is arranged on another varistor ceramic, with the measuring taps M.sub.1 M.sub.2 being arranged between the varistor ceramics, and with the latter being additionally insulated in the interspace in order to separate the current flow into branches A and B.

[0044] Furthermore, a complete separation of the ceramics can also be provided for as shown in FIG. 5.

[0045] In an advantageous arrangement, which is shown in FIG. 7, an overvoltage protection apparatus 1 is arranged with a spark gap FS with one or more auxiliary electrodes H1, H2. The overvoltage protection apparatus 1 and the spark gap FS are connected in parallel, and the first measuring tap M.sub.1 of the overvoltage protection apparatus 1 is connected to a first auxiliary ignition electrode H.sub.1 of the spark gap FS.

[0046] One example of monitoring a varistor bridge in a simple manner such that, in the event of relevant damage to a varistor, the apparatus 1 is protected from destruction, is the ignition of the parallel spark gap FS, which produces a short circuit, so that an upstream fuse (not shown) is triggered and the entire overvoltage protection device is disconnected from the operating voltage. A resistively supported ignition filed by the applicant can be used to ignite the spark gaps FS, for example.

[0047] In overvoltage protection apparatuses with monitoring function according to the invention, the impedance ratio (complex resistance ratio) of the first overvoltage protection device Ü.sub.1 to the second overvoltage protection device Ü.sub.2 can correspond during normal operation to the impedance ratio (complex resistance ratio) of the third device E.sub.3 to the fourth device E.sub.4, for example. Especially simple evaluation circuits can be provided in this way. As shown in FIGS. 1, 6, and 7 for the devices E3 and E4, it can be advantageous for one or both devices E3 and E4 to be detuned so that the impedance ratios are the same during normal operation. Such a configuration can be used during production or startup, for example. Alternatively or in addition, other measures, such as a matching network, for example, can also be used.

[0048] Alternatively, a provision can of course also be made for the impedance ratios not to be identical during normal operation. Here, too, it can be achieved through appropriate wiring that only deviations from a (measured or preset) standard value are identified as a malfunction, for example. Suitable threshold switches or matching networks, for example, or even an (electronic) comparison with one or more previously-detected or previously-set values of the voltage between the first measuring tap M.sub.1 and the second measuring tap M.sub.2, can be used for this purpose.

[0049] Even though the elements of the invention were described above as individual elements, it will readily be understood that they can also be components of a marketable apparatus combined in a housing, for example.

[0050] The system proposed herein enables the constant, very precise monitoring of overvoltage protection components. Even slight changes can be detected and appropriate reporting and measures initiated by means of a downstream evaluation unit. First, the measuring method can be utilized to perform an actual analysis, that is, to obtain technical data; second, direct mechanisms can be set in motion by the measurement that result in the disconnection of the arrester from the power supply network, for example.

[0051] Through the constant or cyclical evaluation of the data obtained, a forecast can be made regarding the further development of the arrester. For systems that are not always accessible and the checking of which is associated with a high degree of effort (e.g., offshore wind power), such monitoring is of particular importance (Smart SPD).

[0052] Moreover, the voltage signal between the first measuring tap M.sub.1 of the branch circuit A and the second measuring tap M.sub.2 of the branch circuit B can also be used directly to operate actuators. This means that an actuator SW for disconnecting, short-circuiting, or bridging can be controlled simultaneously in response to the developing fault. This eliminates the time-critical detour via the detection of heating, making it possible to respond much earlier to faults.

[0053] As a result, even “rapidly” progressing damage that might lead to a short-circuit current and the associated explosion of the arrester can be caught so early that even relatively simple switching devices are sufficient to isolate the fault.

List of Reference Symbols

[0054] Overvoltage protection apparatus with monitoring function 1 [0055] Branch circuit A, B [0056] Overvoltage protection device Ü.sub.1, Ü.sub.2, Ü.sub.3, Ü.sub.4 [0057] Device E.sub.3, E.sub.4 [0058] Voltage potential P.sub.1, P.sub.2 [0059] Measuring tap M.sub.1, M.sub.2 [0060] Signal S.sub.1, S.sub.2 [0061] Evaluation circuit C [0062] Shutoff device SW [0063] Multi contact varistor M-MOV [0064] Spark gap FS [0065] Auxiliary ignition electrode H.sub.1, H.sub.2