Monitoring device and method for detecting a leakage current in an overvoltage protection device, and assembly

Abstract

The invention relates to a monitoring device (14) for detecting a leakage current in an overvoltage protection device (12). The monitoring device (14) has a connection (15) for connecting to the overvoltage protection device (12) in series. The monitoring device (14) has a component (20) with a short-circuit-current-extinction and / or overvoltage-switching capability, and the monitoring device (14) has a detection circuit (22) which is connected in parallel with the component (20) with the short-circuit-current-extinction and / or overvoltage-switching capability. The detection circuit (22) comprises at least one measuring capacitor (24) with a measuring capacitance, said capacitor being connected to the overvoltage protection device (12) in series, and the detection circuit (22) comprises measuring electronics (26) which are designed to detect a parameter that is relevant to a leakage current. The invention further relates to an assembly (16) and to a method for detecting a leakage current in an overvoltage protection device (12).

Description

[0001] Monitoring device and method for detecting a leakage current in a surge protection device and assembly

[0002] The invention relates to a monitoring device for detecting a leakage current in a surge protection device. Furthermore, the invention relates to a method for detecting a leakage current in a surge protection device using a monitoring device. Furthermore, the invention relates to an assembly comprising a surge protection device and a monitoring device of the aforementioned type.

[0003] Surge protection devices are well-known and used in a wide variety of applications. A primary application for surge protection using such devices is at electrical power feed-in points in buildings or in branched power distribution systems.

[0004] Surge protection devices (SPDs) generally operate by switching to low impedance in the event of a transient or temporary overvoltage in order to dissipate the energy of a surge pulse. Overloads and operating conditions outside the specified ratings of the surge protection devices can cause the device to fail. Typically, the failure of a surge protection device results in permanent low impedance behavior, causing upstream protective devices (overcurrent protection - OCP) such as fuses or miniature circuit breakers (MCBs) to trip. To prevent a complete power failure due to overcurrent shutdown in the power distribution system, additional (pre-)fuses are installed downstream of the branch to the surge protection device if necessary.

[0005] However, dimensioning these (pre-)fuses is complicated, as two criteria must be met that make correct dimensioning difficult. Firstly, the (pre-)fuses must not be dimensioned too small to prevent impulse currents from triggering them. Secondly, the respective (pre-)fuses must not be dimensioned too large to prevent the destruction of a defective surge protection device due to high thermal stress. Such (pre-)fuses are generally designed to trigger at currents in the kiloampere range.

[0006] Surge protective devices contain surge protection elements, which can be designed differently depending on their intended use or application. These include, for example, varistors (MOVs) for type 2 and 3 surge protection, whereas gas discharge tubes or spark gaps are typically used for type 1 surge protection. However, the respective surge protection elements of the surge protective devices can degrade over time, i.e., be subject to aging effects, resulting in leakage current. This degradation therefore results in the surge protective device, which, when delivered or new, has a high internal electrical resistance when operated on mains voltage, having a lower internal electrical resistance due to the degradation.The decreasing electrical resistance and the associated increase in leakage current lead to increasing power dissipation in the surge protection device, which in turn can accelerate the degradation of the surge protection element. As a result, thermal destruction due to high leakage currents, known as thermal runaway, can occur.

[0007] This degradation effect of the surge protection device, in particular of the surge protection elements, is typically counteracted today by providing a (thermal) disconnection device which detects a slow aging of the surge protection device, in particular of a surge-limiting protective element (surge protection element), and switches off the associated low leakage currents, i.e. currents in the order of milliamperes up to tens of amperes.

[0008] If the leakage current increases due to the degrading surge protection element, the user only becomes aware of it after the (thermal) disconnector has disconnected or the (pre-)fuse has blown. This is not insignificant, however, because the (thermal) disconnector is designed for currents in the range of milliamperes to single-digit amperes, whereas the (pre-)fuse only blows in the kiloampere range. The surge protection device is no longer functional once these devices have been triggered, which means that the electrical system is no longer protected against surges until the surge protection device is replaced. For this reason, so-called monitoring systems are also used today. These inform the user about the current status of the surge protection device, in particular its very finely detectable degradation. However, the solutions known from the state of the art are complex and / ortechnically complex and therefore cause high costs.

[0009] The object of the invention is to provide a cost-effective and easy-to-implement possibility to detect a leakage current in a surge protection device in order to inform the user accordingly about a degree of degradation of the surge protection device.

[0010] The object is achieved according to the invention by a monitoring device for detecting a leakage current in a surge protection device. The monitoring device has a connection for series connection with the surge protection device. The monitoring device has a short-circuit current-quenching and / or overvoltage-switching component. The monitoring device has a detection circuit connected in parallel with the short-circuit current-quenching and / or overvoltage-switching component. The detection circuit comprises at least one measuring capacitor with a measuring capacitance, which is connected in series with the surge protection device. The detection circuit comprises measuring electronics configured to detect a leakage current-relevant parameter.

[0011] The problem is further solved by a method for detecting a leakage current in a surge protection device using a monitoring device. The monitoring device has a short-circuit current-quenching and / or overvoltage-switching component. The monitoring device is connected in series with the surge protection device, so that the leakage current is conducted by a detection circuit of the monitoring device, which is connected in parallel with the short-circuit current-quenching and / or overvoltage-switching component. A leakage-current-relevant parameter is detected by the detection circuit.

[0012] The basic idea of ​​the invention is to detect leakage currents occurring in a degraded surge protection device of any technology using a simple and cost-effective monitoring device. If the surge protection device is degraded, a leakage current flows through the monitoring device and the monitoring device connected in series with it, in particular its detection circuit. The leakage current is thus conducted via the detection circuit, which contains the measuring capacitor with the measuring capacitance. Depending on the degradation of the surge protection device, a different leakage current results, which results in a different voltage across the measuring capacitor.This is because the degradation is associated with the surge protection device's internal electrical resistance, so the voltage applied to the measuring capacitor allows a conclusion to be drawn about the surge protection device's internal electrical resistance, i.e., the surge protection device's degradation. The voltage applied to the measuring capacitor with the measuring capacitance is therefore a resistance-dependent voltage, namely a voltage dependent on the surge protection device's internal electrical resistance.

[0013] The voltage applied to the measuring capacitor can be directly recorded as a leakage-current-relevant parameter. Alternatively or additionally, an oscillator frequency can be recorded by the detection circuit, particularly by the measuring electronics. For this purpose, an oscillating circuit (RC element) of the monitoring device is set into oscillation, with the resulting frequency depending on the internal resistance of the surge protection device. The oscillating circuit includes the measuring capacitor with the measuring capacitance. Thus, the measuring capacitor is integrated into the determination of the leakage-current-relevant parameter, regardless of whether the voltage applied to the measuring capacitor is recorded directly or an oscillator frequency is recorded as the leakage-current-relevant parameter.

[0014] The measurement electronics are therefore configured to include the measuring capacitor when measuring the leakage current-relevant parameter. In other words, the measurement electronics are configured to measure the leakage current-relevant parameter while taking the measuring capacitor into account.

[0015] Since the measuring capacitor is connected in series with the surge protection device and simultaneously arranged in parallel with the short-circuit current-quenching and / or overvoltage-switching component, two branches are created, which are provided between a terminal of the monitoring device, via which the monitoring device is connected to a potential, e.g., a phase, and the surge protection device, in particular a terminal of the monitoring device to which the surge protection device is connected. The short-circuit current-quenching and / or overvoltage-switching component is arranged in a first of the two branches, whereas the measuring capacitor is arranged in the second of the two branches.

[0016] The surge protection device is arranged, for example, between the monitoring device and a protective conductor potential, PE, or a neutral conductor potential N.

[0017] The measuring electronics, which are configured to detect the leakage current-relevant parameter, can comprise a microcontroller (PC) which initiates the corresponding measurement of the leakage current-relevant parameter.

[0018] In principle, the measurement electronics, in particular the microcontroller, can be configured to execute a measurement algorithm, for example, periodically. This can be done in firmware. Between measurement phases, the firmware can put the measurement electronics, in particular the microcontroller, into sleep mode, thereby saving energy.

[0019] In general, the monitoring device is a (back-up fuse for the surge protection device, whereby the monitoring device and the surge protection device are connected in series. It can therefore be intended that the monitoring device replaces a previously used (back-up fuse. Consequently, the monitoring device can also be regarded as a (back-up fuse.

[0020] This is important because the monitoring device also solves the aforementioned problem of correctly dimensioning the surge protection device's (pre-)fuse. The monitoring device can also be adapted to the different surge protection device technologies and configured accordingly. This is preferably done by the manufacturer.

[0021] The monitoring device enables early detection of degradation of the surge protection device, which also offers the advantage of reducing any downtime, as the surge protection device can be replaced before it fails due to excessive degradation or a defect.

[0022] Since the monitoring device has the short-circuit current extinguishing and / or overvoltage switching component, the monitoring device is basically designed to extinguish or interrupt a fault and / or short-circuit current from a few amperes up to the maximum short-circuit current.

[0023] The following cases must be distinguished:

[0024] The surge protection device is essentially intact. When a surge occurs, the short-circuit current-quenching and / or surge-switching component forwards the incoming surge pulse to the downstream surge protection device. The surge protection device then properly discharges the surge.

[0025] The surge protection device is old and / or defective. When an overvoltage occurs, the surge pulse is sent to the

[0026] The surge protection device is then passed on. As the surge protection device ages or is defective, the current increases, activating the short-circuit current-quenching and / or surge-switching component. The overvoltage pulse is then quenched or diverted by the short-circuit current-quenching and / or surge-switching component. As explained above, in the event of an overvoltage, the short-circuit current-quenching and / or surge-switching component can switch simultaneously with the surge protection device to divert a pulse or surge current.

[0027] The short-circuit current-quenching and / or overvoltage-switching component is therefore particularly useful when the downstream surge protection device is degraded, for example, to quench a follow-on current. If the surge protection device is not degraded, the corresponding function can still be performed by the surge protection device, so that only a low-impedance path for the pulse current discharge is provided via the short-circuit current-quenching and / or overvoltage-switching component.

[0028] The detection circuit, which is connected in parallel to the short-circuit current-quenching and / or overvoltage-switching component, ensures that an aged, but not yet defective, surge protection device is detected early, namely during normal operation or at a normal operating voltage, i.e., when no overvoltage pulse is present. This is achieved by the monitoring device, in particular its detection circuit, detecting the leakage current flowing to earth through the surge protection device during normal operation or at a normal operating voltage. The leakage current is not large enough to activate or trigger the short-circuit current-quenching and / or overvoltage-switching component. Furthermore, the leakage current is not large enough to trigger an optional upstream (thermal) disconnect device.

[0029] The monitoring device therefore has a parallel circuit comprising the short-circuit current-quenching and / or overvoltage-switching component and the detection circuit. In this respect, the short-circuit current-quenching and / or overvoltage-switching component and the detection circuit are connected in parallel. However, the short-circuit current-quenching and / or overvoltage-switching component and the detection circuit are each connected in series with the surge protection device. The leakage current that occurs during degradation of the surge protection device during normal operation is conducted via the detection circuit, since the short-circuit current-quenching and / or overvoltage-switching component is in a non-conductive state during normal operation.

[0030] The monitoring device can be implemented cost-effectively because the detection circuit is connected in parallel with the short-circuit current-quenching and / or overvoltage-switching component, meaning the detection circuit only needs to be designed up to the protection level of the short-circuit current-quenching and / or overvoltage-switching component. Furthermore, the monitoring device, especially the detection circuit, can be designed compactly and space-savingly.

[0031] One aspect provides that the detection circuit is configured to evaluate the leakage current-relevant parameter in order to determine degradation of the surge protection device. The detection circuit is thus not only intended to detect or record the leakage current-relevant parameter, but also to evaluate it in order to determine degradation of the surge protection device.

[0032] Alternatively, it could be provided that the detection circuit merely records the leakage current-relevant parameter and transmits it via a communication interface of the monitoring device to an external evaluation unit, which processes the recorded leakage current-relevant parameter externally, i.e. outside the monitoring device, in order to detect a degradation of the surge protection device.

[0033] According to a further aspect, the detection circuit is configured to detect a leakage current in a timely manner that enables an operator to replace the surge protection device before an electrical system protected by the surge protection device must be operated without surge protection. In other words, it is ensured that the operator is informed early, allowing the operator to replace the surge protection device before the electrical system is unprotected. The leakage current is thus detected in a timely manner, allowing the operator to carry out the replacement. Timely detection by the detection circuit means that detection occurs at lower current intensities and thus before a disconnection device built into the surge protection device is activated.In other words, the leakage current is detected before the disconnecting device is activated, which would result in the electrical system operating without surge protection. In principle, the monitoring device can indicate and / or remotely signal the presence of a leakage current to inform the operator accordingly.

[0034] In particular, the detection circuit is configured to compare the detected leakage current-relevant parameter with at least one threshold value and / or a limit value. Using the threshold value, the degree of degradation of the surge protection device can be determined, for example, low degradation (aging), medium degradation (aging), or high degradation (aging). For each of the different degradation degrees that can be determined, a corresponding threshold value is provided, resulting in a total of several threshold values.

[0035] In addition, the detection circuit can compare the detected leakage current-relevant parameter with a threshold value. The threshold value represents an absolute limit that is relevant to the functioning of the surge protection device. If the threshold value is exceeded, the surge protection device is considered defective. If the threshold value is exceeded again unexpectedly, the monitoring device can initiate appropriate measures to deactivate the surge protection device, for example, by disconnecting it.

[0036] The at least one threshold value and the limit value can be stored in a memory of the monitoring device, which the measuring electronics can access.

[0037] A further aspect provides that the detection circuit comprises at least one indicator that indicates the presence of a leakage current in the surge protection device. In particular, the at least one indicator is a light, for example an LED. In this respect, it is possible for the user to be directly informed about the degradation of the surge protection device at the (upstream) monitoring device, since a corresponding display is displayed on the monitoring device. In this respect, the monitoring device is a warning device that warns the user early on of a detected degradation of the surge protection device. This can prompt the user to initiate appropriate countermeasures, for example, replacing the degraded surge protection device with a new one in a timely manner before the degraded surge protection device fails.

[0038] The detection circuit can be configured to control a display mode dependent on the degradation of the surge protection device. A color, brightness, and / or flashing frequency can be controlled. The different display modes ensure that the user is informed about the degradation level of the surge protection device in a comprehensible manner, allowing them to quickly and intuitively recognize how severely the surge protection device has degraded. The colors green, yellow, and red are typical indicator colors for color-coded representations of the degradation level. Likewise, a flashing speed can intuitively provide information about the degree of degradation, for example, slow flashing for a low degree of degradation or fast flashing for a high degree of degradation. A continuous light can then indicate a defective surge protection device, i.e., when the limit value has been exceeded.

[0039] Furthermore, the monitoring device can have a disconnecting device that can be controlled by the detection circuit. The disconnecting device ensures that the downstream surge protection device is disconnected. This can be the case if the limit value has been exceeded, i.e., if a defective surge protection device has been detected, so that the detection circuit, in particular the measuring electronics, controls the disconnecting device accordingly. However, the disconnecting device can also be controlled if the last threshold value, which indicates a high degradation of the surge protection device, has been exceeded. This depends in particular on the area of ​​application or the stored threshold values.

[0040] The short-circuit current-quenching and / or overvoltage-switching component, together with a limiting resistor at the input of the detection circuit and the timing of the measuring electronics to significantly reduce or interrupt the leakage current or any potential follow-on current during pulsed loads, also offers the advantage of significantly reducing the switching capacity of the disconnecting device, allowing the monitoring device's disconnecting device to be switched off with virtually no current. Therefore, the disconnecting device can be designed compactly and cost-effectively, as there is no significant breaking capacity.

[0041] Furthermore, the monitoring device can have a manual bypass configured to bridge a line interrupted by the disconnecting device. The user can thus manually bridge an isolating gap opened by the disconnecting device in order to detect the leakage current flowing through the degraded surge protective device. The manual bypass is therefore provided in parallel with the disconnecting device. The manual bypass can be easily implemented as a mechanical momentary contact that is manually pressed by the operator to temporarily bridge the isolating gap.

[0042] A further aspect provides that the short-circuit current-quenching and / or overvoltage-switching component can comprise a spark gap, a gas discharge tube, and / or a power electronic component. In particular, the power electronic component is a thyristor, a TRIAC ("Triode for Alternating Current"), or a DIAC ("Diode for Alternating Current"). Typically, a spark gap is used as the short-circuit current-quenching and / or overvoltage-switching component. If the monitoring device serves solely to monitor the surge protection device, the short-circuit current-quenching and / or overvoltage-switching component can also be designed as a gas discharge tube and / or a power electronic component.

[0043] In addition, the detection circuit can include a diode bridge circuit, a Zener diode connected in parallel with the measuring capacitor and the measuring capacitance, and / or a switchable or adjustable load resistor connected in parallel with the measuring capacitor and the measuring capacitance. The leakage current is rectified via the diode bridge circuit to charge the measuring capacitor and the measuring capacitance. The Zener diode connected in parallel with the measuring capacitor ensures that the voltage across the measuring capacitor is limited to a maximum value. The switchable or adjustable load resistor is used to adapt the monitoring device to different technologies or variants of surge protection devices. This can be adjusted via the measuring electronics. In other words, the effective load resistance can be easily adapted to different types of surge protection devices via the measuring electronics, for example via firmware.

[0044] Furthermore, the monitoring device can have a power supply block for at least the measuring electronics, which includes a buffer capacitor, so that the measuring electronics are powered by the leakage current of a degraded surge protection device into a buffer capacitance of the buffer capacitor. The at least one indicator can also be powered via the power supply block. The buffer capacitor of the power supply block is decoupled from the measuring capacitor via a blocking diode. The measuring electronics and / or the at least one indicator can therefore be powered by the leakage current of the degraded surge protection device into a buffer capacitance of the buffer capacitor, thus eliminating the need for an additional external power supply for the measuring electronics and / or the at least one indicator.

[0045] According to a further aspect, the monitoring device has a communication interface via which the monitoring device can be communicatively connected to a monitoring system. The monitoring system can be an electronic operational monitoring system for the building's power supply, so that the building is informed accordingly about the status of the surge protection device. In principle, it can be provided that the monitoring device also transmits further data via the communication interface.

[0046] Furthermore, an assembly is provided that includes a surge protection device and a monitoring device of the aforementioned type, which is connected in series with the surge protection device. As already explained above, the leakage current of the surge protection device is passed through the detection circuit of the monitoring device, whereby parameters relevant to the leakage current can be detected by the monitoring device. It is possible that the voltage applied to the measuring capacitor can be measured and evaluated in both loaded and unloaded conditions. Depending on the internal electrical resistance of the surge protection device, different voltages or voltage differences result. A new surge protection device with a high internal electrical resistance will result in low voltages applied to the measuring capacitor.A degraded surge protection device with a low electrical internal resistance, on the other hand, will result in high voltages across the measuring capacitor.

[0047] Alternatively or additionally, the oscillator frequency can be measured and evaluated. The resonant circuit (RC circuit) containing the measuring capacitor can be set into oscillation by a flip-flop on the load switch. The resulting frequency depends on the internal electrical resistance of the surge protection device being monitored.

[0048] In principle, if degradation of the surge protection device or a leakage current is detected, the monitoring device can issue a warning and / or disconnect the surge protection device. Thus, the monitoring device can be used as a warning and / or disconnect device.

[0049] Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. In the drawings:

[0050] Figure 1 is a schematic representation of a system in which an assembly according to the invention is used with a monitoring device according to the invention

[0051] Figure 2 shows a detailed representation of the monitoring device according to the invention when used in an assembly according to the invention, and

[0052] Figure 3 shows an overview of the internal electrical resistance of a new surge protection device and a degraded surge protection device. Figure 1 shows a system 10 used, for example, at an electrical power feed-in point in a building. In the present illustration, the system 10 comprises a multiphase feed-in 11 with three phases L1, L2, L3 and a neutral conductor N, as well as several surge protection devices 12, i.e., "surge protection devices" (SPDs).

[0053] In the embodiment shown, a surge protection device 12 is provided between a protective conductor potential (PE) and a respective phase L1, L2, L3, so that initially three surge protection devices 12 are present. Additionally, a fourth surge protection device 12 is provided, which is arranged between the neutral conductor N and the protective conductor potential (PE) and is connected in series with the three surge protection devices 12 assigned to the three phases L1, L2, L3.

[0054] The surge protection devices 12 assigned to the three phases L1, L2, and L3 are each connected in series with a monitoring device 14 ("SSD") via a corresponding connection 15 on the monitoring device 14. Specifically, a monitoring device 14 is connected upstream of each surge protection device 12.

[0055] This results in a total of three modules 16, each comprising a surge protection device 12 and a monitoring device 14 connected in series with the surge protection device 12.

[0056] In Figure 2, one of these assemblies 16 is shown in detail, in particular the monitoring device 14, which is connected in series with the surge protection device 12.

[0057] The monitoring device 14 is basically used to detect a leakage current in the surge protection device 12, which may occur due to a degradation of the surge protection device 12.

[0058] The monitoring device 14 comprises a housing 18 in which a short-circuit current-quenching and / or surge-switching component 20 is arranged, which in the present embodiment comprises a spark gap ("FS"). In the event of an overvoltage, the short-circuit current-quenching and / or surge-switching component 20 generally switches simultaneously with the actual surge protection device 12 and diverts the pulse / surge current. When the surge protection device 12 is intact, the short-circuit current-quenching and / or surge-switching component 20 is not subjected to the functions of the surge protection device 12, such as follow-current quenching, but rather merely forms a low-impedance path for the pulse current diversion. However, if the surge protection device 12 degrades, the follow-current-quenching capability of the short-circuit current-quenching and / or surge-switching component 20 comes into play in the event of an overvoltage.

[0059] The monitoring device 14 also has a detection circuit 22, which is provided in parallel with the short-circuit current-quenching and / or overvoltage-switching component 20. Therefore, nodes 23 are provided before and after the short-circuit current-quenching and / or overvoltage-switching component 20.

[0060] This also results in the detection circuit 22 and the short-circuit current extinguishing and / or overvoltage switching component 20 being connected in series with the overvoltage protection device 12.

[0061] However, in normal operation or at a normal operating voltage, the short-circuit current-extinguishing and / or overvoltage-switching component 20 is not electrically conductive, so that any leakage current of the overvoltage protection device 12 is conducted via the detection circuit 22, as is also indicated in Figure 2.

[0062] The detection circuit 22 comprises at least one measuring capacitor 24 with a measuring capacitance, so that the measuring capacitor 24 is connected in series with the surge protection device 12.

[0063] The leakage current conducted through the detection circuit 22 thus charges the measuring capacitor 24, resulting in a voltage across the measuring capacitor 24 that depends on the internal electrical resistance of the surge protection device 12, which in turn is related to the degree of degradation of the surge protection device 12. The value of the internal electrical resistance of the surge protection device 12 decreases with increasing degradation of the surge protection device 12.

[0064] By evaluating the voltage applied to the measuring capacitor 24, conclusions can be drawn about the degree of degeneration of the surge protection device 12.

[0065] For this purpose, the detection circuit 22 has measuring electronics 26 configured to detect a leakage current-relevant parameter, for example, the voltage applied to the measuring capacitor 24. In this case, the measuring electronics 26 is embodied as a microcontroller (PC).

[0066] The measuring electronics 26 is also configured to evaluate the leakage current-relevant parameter in order to determine a degradation of the surge protection device.

[0067] For this purpose, the detected leakage current-relevant parameter can be compared with at least one threshold value representative of a specific degree of degradation of the surge protection device 12. This means that the measuring electronics 26 can, for example, determine how severely the surge protection device 12 is degraded, for example, low, medium, or high. For this purpose, three different threshold values ​​would then be available, for example, representative of low degradation, medium degradation, or high degradation.

[0068] Depending on the use of the monitoring device 14, the measuring electronics 26 can then control at least one indicator 28 which indicates the presence of a leakage current in the surge protection device 12, in particular the degree of degradation of the surge protection device 12.

[0069] The indicator 28 can, as shown in the embodiment, be a light, for example an LED, which is controlled accordingly by the measuring electronics 26. Alternatively, a display or other optical display element can be provided as the indicator 28.

[0070] The indicator can be operated by the measuring electronics 26 in a specific display mode, which is unique to the degree of degradation of the surge protection device 12. The corresponding display mode can be characterized by a color, a brightness, and / or a flashing frequency. Thus, a slightly degraded surge protection device 12 can be indicated by slow flashing, whereas a high degree of degradation of the surge protection device 12 is indicated by rapid flashing. If the indicator 28, in particular the light, is continuously illuminated, this can indicate a defect in the surge protection device 12.

[0071] However, a value can also be displayed by indicator 28, for example a percentage value that indicates the degradation, e.g. 46% or 100% in the case of a defect.

[0072] For the different degradation levels or display modes, the detection circuit 22 can compare the detected leakage current-relevant parameter with one or more threshold values ​​in order to determine the corresponding degradation level of the surge protection device 12, as already explained above.

[0073] To determine a defect in the surge protection device 12, the detection circuit 22 can compare the leakage current-relevant parameter with a limit value representative of the defect in the surge protection device 12. If the limit value is exceeded, a corresponding display mode can be triggered, for example, a continuous illumination state in the case of a light, in particular an LED, as indicator 28.

[0074] Alternatively or additionally, the monitoring device 14 may comprise a disconnecting device 30 which is controlled by the detection circuit 22, in particular the measuring electronics 26, if the leakage current-relevant parameter is above the limit value which is representative of the defect of the surge protection device 12.

[0075] The disconnect device 30 can then disconnect the surge protection device 12 to interrupt the path for the leakage current through the surge protection device 12.

[0076] In particular, the separation occurs between the surge protection device 12 and the detection circuit 22, i.e., below the node 23 associated with the surge protection device 12. Alternatively, the separation device 30 can also be provided between a phase connection point and the node 23, which is remote from the surge protection device 12.

[0077] Optionally, the monitoring device 14 can have a manual bypass 32, for example in the form of a push-button element, which is configured to bypass a line interrupted by the disconnecting device 30, so that it is still possible to (briefly) detect the existing leakage current of the surge protection device 12. The leakage current can thus be measured even if the leakage-relevant parameter associated with the leakage current is above the limit value that results in automatic disconnection of the surge protection device 12 using the disconnecting device 30.

[0078] In addition, the monitoring device 14 can have a communication interface 34 via which the monitoring device 14 can communicate with a separately designed monitoring system 36 in order to transmit, for example, information or the detected degree of degradation of the surge protection device 12.

[0079] The communication interface 34 can be configured wirelessly, as indicated by way of example in Figure 2. However, the communication interface 34 can also be configured as a wired communication interface.

[0080] Furthermore, the detection circuit 22 includes a limiting resistor 38 at the input of the detection circuit 22, i.e., after the node 23, which faces away from the surge protection device 12. The limiting resistor 38 limits the leakage current in the event that the surge protection device 12 has a very low resistance. The limiting resistor 38 can consist of one or more resistance elements connected in series. Furthermore, the limiting resistor 38 can also be arranged on the output side with respect to the detection circuit 22, i.e., before the node 23, which faces the surge protection device 12. In the case of several resistance elements connected in series, these can be arranged on the input and output sides. Furthermore, the detection circuit 22 has a diode bridge circuit 40, which serves to rectify the leakage current.

[0081] Furthermore, a Zener diode 42 connected in parallel with the measuring capacitor 24 with the measuring capacitance can be provided in the reverse direction, which limits the voltage applied to the measuring capacitor 24 to a maximum value.

[0082] In addition, the detection circuit 22 includes a switchable or adjustable load resistor 44, which is connected in parallel with the measuring capacitor 24 with the measuring capacitance. This allows the monitoring device 14 to be adapted to different technologies or variants of surge protection devices 12. This can be adjusted accordingly via the measuring electronics 26.

[0083] In addition, the monitoring device 14 has a voltage supply block 46 ("VDD") for the measuring electronics 26, which includes a buffer capacitor (not shown in detail) that is decoupled from the measuring capacitor 24 via a blocking diode. The measuring electronics 26 can therefore be operated by the leakage current of a degraded surge protection device 12 into a buffer capacitance of the buffer capacitor.

[0084] The voltage curves over time shown in Figure 3 for a new surge protection device 12 with a high internal electrical resistance (100 kOhm) and for a degraded surge protection device 12 with a lower internal electrical resistance (10 kOhm) illustrate the different voltages present at the measuring capacitor 24, particularly in the passive and active load conditions, i.e., in the unloaded and loaded conditions. The power-up behavior is also different.

[0085] In principle, it can be provided that the monitoring device 14 uses an oscillator frequency as a leakage current-relevant parameter instead of the voltage applied to the measuring capacitor 24 in order to determine the degree of degradation of the surge protection device 12.

[0086] For this purpose, an oscillating circuit (RC element) comprising the measuring capacitor 24 can be set into oscillation by means of a flip-flop, with the resulting oscillator frequency being evaluated to obtain conclusions about the degree of degradation of the surge protection device 12. This fundamentally ensures that the leakage current can be detected by the monitoring device 14 in such a timely manner that an operator is able to replace the surge protection device 12 before an electrical system protected by the surge protection device 12 must be operated without surge protection.

[0087] The operator is thus notified early by the monitoring device 14, allowing the surge protection device 12 to be replaced before the electrical system is exposed. The leakage current is detected in a timely manner, i.e., even at lower currents and thus before the leakage current is detected by a disconnecting device (built into the surge protection device 12).

[0088] In principle, the monitoring device 13 can indicate this via the at least one indicator 28 and / or report it remotely via the communication interface 34 in order to inform the operator accordingly.

Claims

Patent claims 1. A monitoring device (14) for detecting a leakage current in a surge protection device (12), wherein the monitoring device (14) has a connection (15) for connecting in series with the surge protection device (12), wherein the monitoring device (14) has a short-circuit current-quenching and / or overvoltage-switching component (20), wherein the monitoring device (14) has a detection circuit (22) connected in parallel to the short-circuit current-quenching and / or overvoltage-switching component (20), wherein the detection circuit (22) comprises at least one measuring capacitor (24) with a measuring capacitance, which is connected in series with the surge protection device (12), and wherein the detection circuit (22) comprises measuring electronics (26) configured to detect a leakage current-relevant parameter.

2. Monitoring device (14) according to claim 1, characterized in that the detection circuit (22) is configured to evaluate the leakage current-relevant parameter in order to determine a degradation of the overvoltage protection device (12).

3. Monitoring device (14) according to claim 1 or 2, characterized in that the detection circuit (22) is configured to detect a leakage current in such a timely manner that an operator is able to replace the surge protection device (12) before an electrical system protected by the surge protection device (12) has to be operated without surge protection.

4. Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (22) is configured to compare the detected leakage current-relevant parameter with at least one threshold value and / or one limit value.

5. Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (22) comprises at least one indicator (28) which indicates the presence of a leakage current in the surge protection device (12), in particular wherein the at least one indicator (28) is a light, for example an LED.

6. Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (22) is configured to control a display mode dependent on a degradation of the overvoltage protection device (12), in particular a color, a brightness and / or a flashing frequency.

7. Monitoring device (14) according to one of the preceding claims, characterized in that the monitoring device (14) has a separating device (30) which can be controlled by the detection circuit (22).

8. Monitoring device (14) according to one of the preceding claims, characterized in that the monitoring device (14) has a manual bridging device (32) which is designed to bridge a line interrupted by the disconnecting device (30).

9. Monitoring device (14) according to one of the preceding claims, characterized in that the short-circuit current-extinguishing and / or overvoltage-switching component (20) comprises a spark gap, a gas discharge tube and / or a power electronic component, in particular a thyristor, a TRIAC or a DIAC.

10. Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (22) comprises a diode bridge circuit (40), a Zener diode (42) connected in parallel to the measuring capacitor (24) with the measuring capacitance and / or a switchable or adjustable load resistor (44) connected in parallel to the measuring capacitor (24) with the measuring capacitance.

11. Monitoring device (14) according to one of the preceding claims, characterized in that the monitoring device (14) has a voltage supply block (46) for at least the measuring electronics (16), which comprises a buffer capacitor, so that the measuring electronics (16) is operated by the leakage current of a degraded overvoltage protection device (12) into a buffer capacitance of the buffer capacitor.

12. Monitoring device (14) according to one of the preceding claims, characterized in that the monitoring device (14) has a Communication interface (34) via which the monitoring device (14) can be communicatively connected to a monitoring system (36).

13. An assembly (16) comprising an overvoltage protection device (12) and a monitoring device (14) according to any one of the preceding claims, wherein the overvoltage protection device (12) and the monitoring device (14) are connected in series.

14. Method for detecting a leakage current in a surge protection device (12) using a monitoring device (14) which has a short-circuit current-extinguishing and / or overvoltage-switching component (20) and is connected in series with the surge protection device (12), so that the leakage current is conducted by a detection circuit (22) of the monitoring device (14), which is connected in parallel to the short-circuit current-extinguishing and / or overvoltage-switching component (20), and wherein a leakage current-relevant parameter is detected by the detection circuit (22).

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