Monitoring device and method for monitoring a surge protection device and assembly

Abstract

The invention relates to a monitoring device (14) for monitoring a surge protection device (12). The monitoring device (14) has a connection (20) for series connection with the surge protection device (12) and an overload protection device (22) comprising a spark gap (24). Furthermore, the monitoring device (14) has a detection circuit (26) configured to detect a degradation-relevant parameter. The monitoring device (14) includes an arc detection unit (30) associated with the spark gap (24) of the overload protection device (22) and configured to detect an arc. A module (10) and a method for monitoring a surge protection device (12) are also described.

Description

The invention relates to a monitoring device for monitoring a surge protection device, in particular for detecting degradation, especially leakage current, in a surge protection device. Furthermore, the invention relates to a method for monitoring a surge protection device by means of a monitoring device, in particular for detecting degradation or leakage current in a surge protection device. The invention also relates to an assembly comprising a surge protection device and a monitoring device. Surge protection devices are well-known and used in a wide variety of applications. One major area of ​​application for surge protection using such devices is at electrical power supply points in buildings or in branched power distribution systems. Surge protection devices (SPDs), also known as surge protection devices, function by becoming low-impedance in the event of a transient or temporary overvoltage to dissipate the energy of the surge pulse. Overloads and operating conditions outside the specified ratings of the surge protection devices can lead to their failure. Typically, a failed surge protection device results in a permanently low-impedance condition, causing upstream protective devices (overcurrent protection - OCP) such as fuses or miniature circuit breakers (MCBs) to trip. To prevent a complete power outage due to overcurrent tripping in the power distribution system, additional (pre-)fuses are installed downstream of the surge protection device if necessary. However, dimensioning these (pre-)fuses is complicated because two criteria must be met, which make correct dimensioning difficult. On the one hand, the (pre-)fuses must not be too small, so that impulse currents do not cause them to trip; on the other hand, the respective (pre-)fuses must not be too large, so that a defective surge protection device is not destroyed by high thermal stress. Generally, such (pre-)fuses are designed to trip at currents in the kiloampere range. Surge protection devices incorporate surge protection elements, which can vary in design depending on the application. For example, varistors (MOVs) are used for surge protection types 2 and 3, while gas discharge tubes or spark gaps are typically used for surge protection type 1. Over time, however, the surge protection elements in these devices can degrade, meaning they are subject to aging effects or become defective, resulting in leakage current. This degradation means that the surge protection device, which initially exhibits a high internal resistance when operating at mains voltage, will have a lower internal resistance due to the degradation process.The decreasing electrical resistance and the associated increase in leakage current lead to increased power dissipation in the surge protection device, which in turn can accelerate the degradation of the surge protection element. As a consequence, thermal destruction can occur due to high leakage currents, a phenomenon known as thermal runaway. This degradation effect of the surge protection device, in particular the surge protection elements, is typically countered nowadays by providing a (thermal) disconnect device which detects a slow aging of the surge protection device, in particular of a surge limiting protection element (surge protection element), and switches off the associated small leakage currents, i.e. currents in the order of milliamperes to double-digit amperes. The user only becomes aware of the increasing leakage current through the degrading surge protection element after the (thermal) disconnect device has tripped or the (pre-)fuse has blown. This is significant because the (thermal) disconnect device is designed for currents in the milliampere to single-digit ampere range, whereas the (pre-)fuse only trips in the kiloampere range. Once these components have tripped, the surge protection device is no longer functional, meaning the electrical system is unprotected against surges until the device is replaced. Therefore, monitoring systems are now used to inform the user about the current status of the surge protection device, particularly its highly detectable degradation. However, existing solutions are complex and / or...They are technically complex and therefore incur high costs. Regardless of the type of monitoring system, it must also be ensured that the system functions correctly. From DE 20 2012 002 281 U1 a monitoring device for monitoring a surge protection device is known, wherein an arc of a surge arrester is detected. In WO 2019 / 122 041 A1 a procedure for monitoring a surge protection device is described. DE 10 2016 011 076 A1 shows a monitoring device for monitoring a surge protection device. A device for recording degradation-relevant parameters of surge protection devices is known from AU 2017 202 441 A1. The object of the invention is to provide a cost-effective and easy-to-implement way to monitor the degradation, i.e., aging or defect, of a surge protection device and to record the condition of a monitoring device provided for this purpose. The problem is solved according to the invention by a monitoring device for monitoring a surge protection device. The monitoring device has a connection for series connection with the surge protection device. The monitoring device has an overload protection element that includes a spark gap. The monitoring device has a detection circuit configured to detect a degradation-relevant parameter. The monitoring device has an arc detection unit that is associated with the spark gap of the overload protection element and configured to detect an arc. Furthermore, the object of the invention is achieved by a method for monitoring a surge protection device using a monitoring device. A degradation-relevant parameter is recorded to detect aging and / or a defect of the surge protection device, i.e., degradation. An arc in a spark gap of an overload protection element of the monitoring device is detected. The status of the surge protection device and / or the status of the monitoring device is displayed. Alternatively or additionally, the monitoring device is switched off and / or the surge protection device is disconnected when the arc has been detected. The basic idea of ​​the invention is to create a two-stage monitoring system for the surge protection device. For this purpose, the surge protection device is continuously monitored to detect leakage currents occurring in a degraded (i.e., a deteriorated, aged, or defective) surge protection device and to activate arc detection via the arc detection unit, so that any arcing occurring at the monitoring device can be detected. The arc only occurs when an overvoltage event is present and the monitoring device is protecting the surge protection device or assisting in dissipating the overvoltage. For this purpose, the detection circuit of the monitoring device is configured to detect the degradation-relevant parameter, in particular the degradation-relevant parameter of the surge protection device with which the monitoring device is connected in series. In principle, the monitoring device can therefore protect the surge protection device being monitored, and the monitoring device is simple in design and inexpensive to manufacture, especially compared to monitoring systems known from the state of the art. The monitoring is based, for example, on the fact that a leakage current flows through the surge protection device and the monitoring device connected in series with it, particularly the detection circuitry of the monitoring device, if the surge protection device is degraded. Depending on the degree of degradation of the surge protection device, a different leakage current results, allowing conclusions to be drawn about the degree of degradation of the surge protection device. In other words, the degradation-relevant parameter can be a leakage current that flows due to the degradation of the surge protection device and is accordingly detected by the monitoring device's detection circuit, since the monitoring device is connected in series with the surge protection device. In general, the monitoring device is therefore a monitoring and protection device for the surge protection device, with the monitoring device and the surge protection device being connected in series, specifically the surge protection device and the overload protection of the monitoring device. It is thus possible that the monitoring device replaces a previously used (pre-)fuse. Consequently, the monitoring device can also be considered a (pre-)fuse. This is important because the monitoring device also solves the aforementioned problem of correctly sizing the (pre-)fuse of the surge protection device. Furthermore, the monitoring device can be adapted to or configured for different surge protection device technologies. This is preferably done by the manufacturer. The surge protection device can therefore be of any technology, i.e., it can use a metal oxide varistor (MOV), a gas discharge tube, or a spark gap. The early detection of degradation of the surge protection device made possible by the monitoring device also offers the advantage of reducing potential downtime, as the surge protection device can be replaced before it fails due to excessive degradation. Since the monitoring device has overload protection, which can also be described as a 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 of a few amperes up to the maximum short-circuit current. The following cases must be distinguished: The surge protection device is fundamentally intact. When an overvoltage occurs, the overload protection device forwards the incoming overvoltage pulse to the downstream surge protection device. The surge protection device then properly dissipates the overvoltage. The surge protection device is aged and / or defective. When a surge occurs, the surge pulse is forwarded to the surge protection device. Because the surge protection device is aged or defective, the current increases, activating the overload protection, which generates an arc along the spark gap of the overload protection device. The surge pulse is then extinguished or diverted by the overload protection device. As explained above, in the event of an overvoltage, the overload protection can switch simultaneously with the surge protection device in order to dissipate an impulse or surge current. Overload protection is therefore particularly relevant when the downstream surge protection device is disabled, for example, to extinguish a follow current. If the surge protection device is not disabled, it can still perform this function, so that the overload protection simply provides a low-impedance path for the impulse current discharge. The detection circuit now ensures that an aged surge protection device, which is not yet defective, is detected early, namely during normal operation or at a normal operating voltage, i.e., when there is no overvoltage pulse. This is achieved, for example, by the fact that the leakage current flowing to earth through the surge protection device is detected by the monitoring device, in particular its detection circuit, during normal operation or at a normal operating voltage. Alternatively or additionally, a change in voltage drop across the surge protection device and / or the overload protection can be detected, which is associated with the leakage current or degradation of the surge protection device. The leakage current is not large enough to activate or trigger the overload protection, i.e., the short-circuit current-extinguishing and / or overvoltage-switching component. Furthermore, the leakage current is not large enough to trigger an optional upstream (thermal) disconnect device. The monitoring device can therefore have a parallel circuit comprising the overload protection and the detection circuit in parallel branches. In this respect, the overload protection and the detection circuit are connected in parallel to each other. However, the overload protection and the detection circuit are each connected in series with the surge protection device. The leakage current present during normal operation due to degradation of the surge protection device is routed through the detection circuit, since the short-circuit current-quenching and / or surge-switching component is in a non-conductive state during normal operation. The monitoring device can be implemented cost-effectively because the detection circuit is connected in parallel to the overload protection, meaning the detection circuit only needs to be designed up to the protection level of the overload protection. Furthermore, the monitoring device, and especially the detection circuit, can be designed to be compact and space-saving. The additional arc detection unit then ensures that the triggering of the overload protection can be detected, since an arc occurs across the spark gap when the overload protection is triggered, which is detected accordingly. Therefore, two criteria are used: the degradation-relevant parameter, which allows a conclusion to be drawn about the condition of the surge protection device, and the occurrence of the arc across the spark gap of the monitoring device. In general, degradation of a surge protection device can refer to a deterioration of the device due to age or wear. Degradation can also include a defect in the device, resulting from aging or wear, or from a single event. As explained above, the degradation of the surge protection device can be detected by a leakage current. In other words, the leakage current corresponds to the degradation-relevant parameter. The leakage current can be caused by a reduced impedance of the surge protection device, for example, due to aging of the device, but also by an (impulse) overload, i.e., an impedance jump, which permanently puts the surge protection device into an undefined, non-reactive state. One aspect stipulates that the detection circuit is configured to activate the arc flash detection unit after the degradation-relevant parameter reaches a threshold. This aspect therefore stipulates that an arc flash detection unit is only activated to detect an arc flash if the degradation-relevant parameter has exceeded a threshold. The continuous monitoring of the surge protection device ensures that it is detected in a timely manner whether the device is still functional, i.e., neither defective nor deteriorating. For this purpose, the detected degradation-relevant parameter is compared with a predefined threshold. As soon as the detected degradation-relevant parameter reaches the threshold, it can be assumed that the surge protection device has aged and / or is defective.Since an overvoltage would activate the overload protection, generating an arc along the spark gap of the overload protection device, the arc detection unit is activated to detect an overvoltage only if the surge protection device is no longer functioning. If the degradation-relevant parameter has not yet reached the threshold value, the surge protection device can still dissipate the overvoltage, which is why the arc detection unit does not need to be active to detect an overvoltage event if the surge protection device is functioning correctly. In particular, the detection circuit is configured to compare the detected degradation-relevant parameter with at least one threshold value and / or a limit value. Using the at least one threshold value, the degree of degradation of the surge protection device can be determined, for example, low degradation (slight aging), medium degradation (moderate aging), or high degradation (significant aging). For the different degrees of degradation that can be detected, a corresponding threshold value is provided for each, resulting in a total of several threshold values. Furthermore, the detection circuit can compare the detected degradation-relevant parameter with a limit value. This limit value represents an absolute boundary that is relevant to the operation of the surge protection device. If the limit value is exceeded, the surge protection device is considered defective. Should the limit value be exceeded unexpectedly, the monitoring device can initiate appropriate measures to disable the surge protection device, for example, by disconnecting it from the overload protection of the monitoring device, so that the monitoring device cannot become active even in the event of an overvoltage. This can also occur as soon as the threshold value is reached, if desired. The at least one threshold value and the limit value can be stored in a memory of the monitoring device, which the detection circuit can access. In particular, the at least one threshold value and / or the limit value can be set to adapt the behavior of the monitoring device. Another aspect stipulates that the monitoring device has a shutdown device that can be controlled by the detection circuit and / or the arc fault detection unit, particularly after the arc fault detection unit has detected an arc fault. In other words, the monitoring device can be switched off and / or the surge protection device disconnected when the arc fault has been detected. The shutdown device can switch off the monitoring device and / or disconnect the surge protection device from the overload protection of the monitoring device. If the monitoring device is switched off, the overload protection only provides emergency operation protection. This emergency operation protection can include follow current extinguishing capability, which is still ensured by the overload protection, particularly the spark gap.Switching off the monitoring device can consist, among other things, of deactivating a trigger circuit that serves as a trigger aid for the spark gap of the overload protection. The shutdown device can be controlled via the detection circuit, provided it receives feedback from the arc detection unit that an arc has been detected. Alternatively, the shutdown device can also be controlled directly by the arc detection unit, provided an arc has been detected. In particular, the shutdown device comprises a disconnect device, an electrode actuator, an isolator actuator, and / or a trigger actuator. The trigger actuator can be used to deactivate the trigger circuit. For example, a trigger electrode is moved by means of the trigger actuator, so that triggering of the spark gap is no longer possible. Alternatively or additionally, at least one electrode of the spark gap can be moved via the electrode actuator to change the response behavior of the spark gap. This can also be achieved by introducing an insulator, for example, by means of the isolator actuator. The disconnect device can be assigned to a connecting line to the surge protection device in order to disconnect it, whereby the surge protection device is permanently disconnected from the overload protection of the monitoring device when the connecting line is disconnected. According to another aspect, the arc detection unit features a photodiode that switches to an electrically conductive state upon detection of an arc. This generates a detection signal that can be used, for example, to control the shutdown device. In its initial state, the photodiode has a high resistance, which decreases upon detection of the arc. Basically, the arc is detected optically by the arc detection unit. According to one embodiment, the arc detection unit is arranged on a circuit board that is mounted in a recess of a housing surrounding the spark gap. The housing thus has a slot for the arc detection unit, specifically the circuit board of the arc detection unit, which is inserted into the recess. The housing can also have a stop for the circuit board, ensuring that the circuit board or the arc detection unit is positioned correctly within the housing. In particular, the photodiode of the arc detection unit is then optimally aligned with respect to the spark gap to reliably detect any arcing. According to another embodiment, the arc detection unit is arranged on a circuit board which is mounted externally to a housing surrounding the spark gap via an adapter. This ensures that the arc detection unit is not exposed to thermal stresses from the spark gap, as it is protected by the housing. The housing may include a viewing window and / or a recess, i.e., an area with reduced material thickness, to ensure that the arc detection unit, and in particular the photodiode, detects the arc. In other words, the brightness of the arc makes it possible to detect it even through the housing material. In particular, the arc flash detection unit is galvanically isolated from the overload protection. This galvanic isolation ensures the operational reliability of the arc flash detection unit. The monitoring device features a status indicator and / or a communication interface. This allows the monitoring device itself to display the status of the surge protection device and / or the monitoring device. The status indicator is designed, among other things, to show the presence of a leakage current in the surge protection device. It is also designed to show the status of the monitoring device, specifically an arc flash detected by the arc flash detection unit. The status indicator typically includes a light, such as an LED, or a screen. Therefore, the user can be directly informed about the degradation of the surge protection device at the (upstream) monitoring device, as a corresponding indicator is displayed there.The monitoring device is therefore a warning device that alerts the user at an early stage to any detected degradation of the surge protection device. This allows the user to take appropriate countermeasures, such as replacing the degraded surge protection device with a new one in good time before it fails. The detection circuit can be configured to control a display mode that depends on the degradation of the surge protection device. This mode can involve controlling a color, brightness, and / or flashing frequency. These different display modes ensure that the user is clearly informed about the degree of degradation, allowing them to quickly and intuitively recognize the extent of the device's degradation. Green, yellow, and red are typical indicator colors used to visually represent the degree of degradation. Similarly, the flashing speed can intuitively indicate the level of degradation, for example, slow flashing for low degradation and fast flashing for high degradation. A continuous light indicates a defective surge protection device, i.e., when the limit has been exceeded. Alternatively or additionally, the relevant information can be forwarded to a device specifically designed for monitoring by transmitting the information via the communication interface. This device, specifically designed for monitoring, can be a control center that receives information from multiple devices and processes it centrally. It is also possible for the detection circuit to merely record the degradation-relevant parameter and transmit it via the monitoring device's communication interface to an external evaluation unit. This evaluation unit processes the recorded degradation-relevant parameter externally, i.e., outside the monitoring device, to detect degradation of the surge protection device. The separately designed evaluation unit can therefore include the memory in which at least one threshold value is stored. In principle, the monitoring device can indicate and / or remotely report the presence of degradation of the surge protection device in order to inform the operator accordingly. One embodiment provides that the detection circuit is connected in parallel to the overload protection device, wherein the detection circuit includes measuring electronics configured to detect the degradation-relevant parameter. In particular, the detection circuit includes at least one measuring capacitor with a measuring capacitance, which can be connected in series with the surge protection device. The leakage current is thus passed through the detection circuit, which includes the measuring capacitor with the measuring capacitance. The leakage current results in a variable voltage being applied to the measuring capacitor. This is because the degradation is associated with an internal electrical resistance of the surge protection device, so the voltage applied to the measuring capacitor therefore allows a conclusion to be drawn about the internal electrical resistance of the surge protection device, i.e., the degradation of the surge protection device.The voltage applied to the measuring capacitor with the measuring capacitance is therefore a resistance-dependent voltage, namely a voltage dependent on the electrical internal resistance of the surge protection device. The detection circuit, which is set up to detect the degradation-relevant parameter, may include a microcontroller (µC) which initiates the corresponding measurement of the degradation-relevant parameter. In principle, the detection circuit, especially the microcontroller, can be configured to execute a measurement algorithm, for example, periodically. This can be implemented in the firmware. Between measurement phases, the firmware can put the detection circuit, especially the microcontroller, into a sleep mode, thus making the detection circuit energy-efficient. Another embodiment provides that the detection circuit includes an evaluation unit connected by a line between the overload protection device and the terminal to detect and evaluate a voltage drop across the overload protection device in order to determine the degradation-relevant parameter. The degradation of the surge protection device can also be detected by a change in the voltage drop across the surge protection device and / or across the overload protection device, in particular the change in the voltage distribution across these components, which are connected in series. For this purpose, the detection circuit can include a bridge circuit with a corresponding tap both before the overload protection device, between the overload protection device and the surge protection device, and after the surge protection device, in order to detect the voltage drop across the overload protection device and / or the voltage drop across the surge protection device. The evaluation unit can be a microcontroller (µC). In general, the detection circuit is designed to detect leakage current or voltage drop changes in such a timely manner that an operator is able to replace the surge protection device before an electrical system protected by the device has to be operated without surge protection. In other words, it is ensured that the operator is informed in a timely manner, allowing them to replace the surge protection device before the electrical system becomes unprotected. The timely detection by the detection circuit means that the detection takes place before the shutdown device is activated, which would result in the electrical system being operated without full overvoltage protection. The voltage across the measuring capacitor can be directly measured as a degradation-relevant parameter. Alternatively or additionally, an oscillator frequency can be measured by the detection circuit, particularly by the measuring electronics. For this purpose, a resonant 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 resonant circuit includes the measuring capacitor with its measuring capacitance. Therefore, the measuring capacitor is involved in determining the degradation-relevant parameter, regardless of whether the voltage across the measuring capacitor is measured directly or an oscillator frequency is measured as the degradation-relevant parameter.Furthermore, the degradation-relevant parameter can be the voltage drop across the overload protection and / or the voltage drop across the surge protection device, since the corresponding voltage drop also depends on the leakage current through the surge protection device, i.e., on the degradation of the surge protection device. In principle, a three-stage approach can therefore be followed, since in the first stage the condition of the surge protection device is continuously monitored, i.e., the degradation-relevant parameter is recorded. This degradation-relevant parameter can then be compared with at least one threshold value. If the threshold has been reached, the second stage can be activated. In the second stage, the arc detection unit is activated, enabling the detection of an arc along the spark gap. Typically, the arc occurs during a pulse (8 / 20 pulse), a lightning pulse (10 / 350 pulse), or a follow current, which can then be detected by the arc detection unit. If the activated arc detection unit detects the arc, the third stage is activated. In the third stage, a mains follow current is extinguished and the detection circuit controls the shutdown device to switch off the monitoring device and / or disconnect the surge protection device. The activation of the respective stages, especially the second and third stages, can be displayed directly via the status indicator and / or indirectly via the communication interface. Furthermore, in the second stage, the respective degree of degradation can be displayed via the status indicator, i.e., a low, medium, or high degree of degradation. Furthermore, a module comprising a surge protection device and a monitoring device of the aforementioned type is provided. The surge protection device and the monitoring device are connected in series. The aforementioned advantages apply analogously to the module. The assembly may be designed so that the surge protection device and the monitoring device are two separately designed devices, each with its own housing. Alternatively, the surge protection device and the monitoring device can be housed in a single enclosure. In this case, the surge protection device and the monitoring device together form a single protective device. In other words, the assembly then corresponds to a protective device that has an enclosure enclosing both the surge protection device and the monitoring device. Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. The drawings show: - Fig. 1 a schematic overview of an assembly according to the invention with a monitoring device according to a first illustration, - Fig. 2 a further schematic overview of an assembly according to the invention with a monitoring device according to a second illustration, - Fig. 3 a subordinate unit of the monitoring device according to the invention, comprising the arc detection unit and the spark gap, - Fig. 4 a first embodiment of the subordinate unit from Fig. 3, - Fig. 5 a second embodiment of the subordinate unit from Fig. 3, - Fig. 6 a detailed illustration of the monitoring device according to the invention when used in an assembly according to a first embodiment.7 a detailed representation of the monitoring device according to the invention when used in an assembly according to a second embodiment, and- Fig. 8 an overview of the method according to the invention for monitoring a surge protection device by means of a monitoring device. Figure 1 shows an assembly 10 comprising a surge protection device 12 (SPD) and a monitoring device 14. In the illustrated embodiment, the surge protection device 12 and the monitoring device 14 are shown as two separate devices. Alternatively, the assembly 10 can also have a housing in which the surge protection device 12 and the monitoring device 14 are contained. In this case, the assembly 10 represents a single device, namely a protection device. The monitoring device 14 is connected to a phase or live conductor (L) via an input 16, whereas the surge protection device 12 is connected to a neutral conductor (N) or a protective conductor (PE) via an output 18. The monitoring device 14 has a connection 20 through which it is connected in series with the surge protection device 12. The assembly 10 therefore consists of a series connection of the monitoring device 14 and the surge protection device 12, arranged between the phase or live conductor (L) and the neutral conductor (N) or the protective conductor (PE). The monitoring device 14 has an overload protection device 22 which includes a spark gap 24. Therefore, the overload protection device 22 is a component capable of extinguishing short-circuit currents and / or overvoltage switching. Furthermore, the monitoring device 14 has a detection circuit 26 which is set up to detect a degradation-relevant parameter of the surge protection device 12. For this purpose, the detection circuit 26 is arranged, for example, in parallel with the overload protection 22, as shown in Fig. 1. The detection circuit 26 can include measuring electronics 28, which are configured to detect the degradation-relevant parameter. If the surge protection device 12 is degraded, for example due to (age-related) wear or a defect, a leakage current flows through the surge protection device 12 and the monitoring device 14 connected in series with it, in particular the detection circuit 26 of the monitoring device 12. The leakage current can represent the degradation-relevant parameter, which is detected by the detection circuit 26, in particular by the measuring electronics 28 of the detection circuit 26. Furthermore, the monitoring device 14 includes an arc detection unit 30, which is assigned to the spark gap 24 in order to detect any arc along the spark gap 24. The arc can occur if the spark gap 24 is exposed to a pulse (8 / 20 pulse) or a lightning pulse (10 / 350 pulse) or if a mains follow current is present. Furthermore, the monitoring device 14 has a shutdown device 32 which, in the embodiment shown, can be directly controlled by the arc detection unit 30 and is configured to switch off the monitoring device 14 or to disconnect the surge protection device 12 from the overload protection 22 of the monitoring device 14. The shutdown device 32 can, as shown in the embodiment according to Fig. 1, include a disconnecting device 34 with which the surge protection device 12 can be disconnected from the overload protection 22 of the monitoring device 14. It is also possible, in principle, for the detection circuit 26 to control the shutdown device 32, particularly after the detection circuit 26 has received feedback from the arc detection unit 30 indicating that an arc has been detected. The detection circuit 26 then constitutes the central electronic unit of the monitoring device 14. Fig. 2 shows the assembly 10 in more detail, in particular the detection circuit 26. The detection circuit 26 includes an evaluation unit 36, which is designed, for example, as a microcontroller (µC). The recorded degradation-relevant parameter is transmitted to the evaluation unit 36, which compares the degradation-relevant parameter with at least one threshold value, which is stored, for example, in a memory 37. If the threshold value is reached, the evaluation unit 36 ​​outputs an activation signal to the arc detection unit 30 to activate it. Therefore, the evaluation unit 36 ​​also includes an activation unit 38. The arc detection unit 30, which includes a photodiode 40, is thus activated, so that an arc occurring in the spark gap 24 can be detected by the photodiode 40, resulting in a detection signal. The photodiode 40 is typically non-conducting or high-resistance, so that only when the arc occurs does the photodiode 40 switch to a conductive state, i.e., become low-resistance, in order to generate or transmit the detection signal. If the arc detection unit 30 detects an arc in the spark gap 24 during operation of the assembly 10, the detection signal is forwarded to the shutdown device 32 in the illustrated embodiment. Alternatively, the arc detection unit 30 can output the detection signal to the detection circuit 26, which in turn controls the shutdown device 32. As explained above, the shutdown device 32 can include the disconnecting device 34, which allows the surge protection device 12 to be disconnected from the overload protection 22 of the monitoring device 14. Furthermore, the shutdown device 32 can switch off the monitoring device 14. Switching off the monitoring device 14 can be accomplished in various ways, for example, by means of an actuator 41 such as an electrode actuator, an insulator actuator, and / or a trigger actuator. The actuator 41 influences the spark gap 24, in particular its response behavior. The electrode actuator can change the position of at least one electrode of the spark gap 24, whereas the insulator actuator can insert an insulator, thereby changing the properties of the spark gap 24, which is equivalent to switching off the monitoring device 14. Similarly, the trigger actuator can extend a trigger electrode of a trigger circuit, thus preventing the spark gap 24 from being triggered, which is also equivalent to switching off the monitoring device 14. In principle, the detection circuit 26, the arc detection unit 30 and / or the shutdown device 32 can be arranged on a circuit board 42, which can therefore include the electronics of the monitoring device 14. Fig. 3 shows by way of example that the circuit board 42 includes the arc detection unit 30, in particular the photodiode 40. The arc detection unit 30 is positioned in relation to the spark gap 24 also shown in Fig. 3 such that the photodiode 40 can detect an arc forming at the spark gap 24. As can be clearly seen in Fig. 3, the spark gap 24 comprises two electrodes 44, 46, which are spaced apart from each other so that an arc can form between the two electrodes 44, 46. In addition, an quenching chamber 48 is provided into which the arc can flow to be quenched. The electrodes 44, 46 and the quenching chamber 48 are arranged in a housing 50, which therefore surrounds the spark gap 24. The arc is detected by the arc detection unit 30, in particular the photodiode 40, which triggers the shutdown device 32 (directly or indirectly via the detection circuit 26) to switch off the monitoring device 14 and / or to disconnect the surge protection device 12 from the overload protection 22 of the monitoring device 14. In principle, the arc detection unit 30 can be arranged in different ways in relation to the housing 50, which surrounds the spark gap 24. Figure 4 shows that the housing 50 has a receptacle 52 for the circuit board 42, on which at least the arc detection unit 30 is provided. The arc detection unit 30 is thus arranged in the housing 50. Figure 5 shows an alternative embodiment in which the arc detection unit 30 is arranged externally on the housing 50 via an adapter 54. The adapter 54 has a corresponding holder for the circuit board 42 of the arc detection unit 30. The arc detection unit 30 is therefore able to detect the arc generated inside the housing 50 even through the housing material of the housing 50. For this purpose, a viewing window can be provided in the housing 50 or an area with reduced housing material, to which the photodiode 40 is assigned. Basically, the monitoring of the surge protection device 12 by means of the monitoring device 14 provides for three-stage monitoring, as can be seen from Fig. 8. In a first stage, the surge protection device 12 is continuously monitored by the monitoring device 14. This means that the degradation-relevant parameter is continuously detected by the detection circuit 26. In particular, the detected degradation-relevant parameter is continuously compared with at least one threshold value to determine whether the threshold value has been reached or not. If the threshold value has been reached, the surge protection device 12 is no longer fully functional, which is why a second stage of monitoring is activated. The second stage is characterized by the fact that the arc detection unit 30 is activated, i.e. only after a degradation of the surge protection device 12 has been detected, which is accompanied by reaching at least one threshold value. Since the arc detection unit 30 has been activated, an arc forming in the spark gap 24 can now be detected. This occurs when an overvoltage occurs, for example due to a pulse or a lightning impulse, or when a mains follow current is present. The detection of the arc during the second stage triggers the activation of the third stage, in which the surge protection device 12 is disconnected and / or the monitoring device 14 is switched off. For this purpose, the shutdown device 32 can be controlled, for example, a corresponding actuator 31. The monitoring device 14 then only has an emergency operating function, for example, a follow current extinguishing capability. Fig. 2 further shows that the monitoring device 14 has a status indicator 56 which is configured to display the status of the surge protection device 12 and / or the status of the monitoring device 14. In other words, the current monitoring level can be displayed: first, second, or third level. Specifically, the second level can also display the degree of degradation of the surge protection device 12, provided the degradation-relevant parameter has reached a corresponding threshold. This informs the user that the surge protection device 12 has aged or is defective, meaning that surge protection is (only or primarily) now provided by the monitoring device 14, in particular the overload protection device 22. It can also be indicated when the third stage has been activated, i.e., when the monitoring device 14 has been switched off or the surge protection device 12 has been disconnected, so that only an emergency running function is available, for example, a follow current extinguishing capability. The user of assembly group 10 is therefore also informed about this. Alternatively or additionally, the information can be output via a communication interface 58, so that the information is also available at another location, in particular at a control center. Fig. 6 shows an exemplary embodiment of the monitoring device 14, in which the detection circuit 26 according to a first embodiment is shown in detail. The detection circuit 26 includes at least one measuring capacitor 60 with a measuring capacitance, which is connected in series with the overvoltage protection device 12. The leakage current passed through the detection circuit 26 thus charges the measuring capacitor 60, resulting in a voltage across the measuring capacitor 60 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. For example, the value of the internal electrical resistance of the surge protection device 12 decreases with increasing degradation of the surge protection device 12. By evaluating the voltage applied to the measuring capacitor 60, it is therefore possible to deduce the degree of degeneration of the surge protection device 12. For this purpose, the detection circuit 26 has measuring electronics 28 or an evaluation unit 36 ​​to detect the degradation-relevant parameter, for example the voltage applied to the measuring capacitor 60, and to evaluate it in order to determine a degradation of the overvoltage protection device 12. Furthermore, as shown in the embodiment according to Fig. 6, the monitoring device 14 optionally has a manual bypass 62, for example in the form of a push button, which is configured to bypass a line interrupted by the disconnecting device 34, so that it is still possible to (briefly) detect the leakage current of the surge protection device 12. The leakage current can therefore be measured even if the third stage of monitoring has been activated, which results in the automatic disconnection of the surge protection device 12 from the overload protection 22 of the monitoring device 14. Alternatively, in the embodiment shown in Fig. 6, it can be provided that the monitoring device 14 uses an oscillator frequency as the degradation-relevant parameter instead of the voltage applied to the measuring capacitor 60 in order to determine the degree of degradation of the overvoltage protection device 12. For this purpose, a resonant circuit (RC element) comprising the measuring capacitor 60 can be set into oscillation by means of a flip-flop circuit, whereby the resulting oscillator frequency is evaluated in order to obtain conclusions about the degree of degradation of the overvoltage protection device 12. Figure 7 shows another embodiment in which the degradation-relevant parameter is determined by means of a voltage drop, in particular by means of a voltage drop across the overload protection 22 and / or a voltage drop across the overvoltage protection device 12. For this purpose, the monitoring device 14 includes a bridge circuit 64, which has a tap 66 leading from a line 68, connecting the overload protection device 22 to terminal 20, to the evaluation unit 36. The evaluation unit 36 ​​is connected via the bridge circuit 28 to terminal 16 (serving as input) and terminal 18 (serving as output). The evaluation unit 36 ​​can detect and evaluate the voltage distribution across the series connection of the overload protection device 22 and the surge protection device 12 by means of the bridge circuit 64, which represents the degradation-relevant parameter. The evaluation unit 36 ​​can compare the detected voltage drop with an assigned threshold value to determine whether the predefined threshold has been reached in order to activate the second stage, as explained above, i.e., to activate the arc detection unit 30. If the arc detection unit 30 detects an arc after activation, the third stage is activated, in which the shutdown device 32 is controlled, which in this case controls a switch 70, thereby activating a current path. If current flows through the activated current path, the actuator 41 can be controlled accordingly to switch off at least the monitoring device 14. As previously explained, the current status or monitoring level can be displayed via status indicator 56. Alternatively or additionally, the relevant information can be transmitted via the communication interface. In principle, it is ensured that the change in the degradation-relevant parameter, i.e. the changed leakage current or the changed voltage drop, is detected by the monitoring device 14 in such a time that a user 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.

Claims

Monitoring device (14) for monitoring a surge protection device (12), wherein the monitoring device (14) has a connection (20) for series connection with the surge protection device (12), wherein the monitoring device (14) has an overload protection (22) comprising a spark gap (24), wherein the monitoring device (14) has a detection circuit (26) configured to detect a degradation-relevant parameter, and wherein the monitoring device (14) has an arc detection unit (30) associated with the spark gap (24) of the overload protection (22) and configured to detect an arc. Monitoring device (14) according to claim 1, characterized in that the detection circuit (26) is configured to activate the arc detection unit (30) after the degradation-relevant parameter has reached a threshold value. Monitoring device (14) according to claim 1 or 2, characterized in that the monitoring device (14) has a shutdown device (32) which can be controlled by the detection circuit (26) and / or the arc detection unit (30), in particular after the arc detection unit (30) has detected an arc. Monitoring device (14) according to claim 3, characterized in that the shutdown device (32) comprises a disconnecting device (34), an electrode actuator, an insulator actuator and / or a trigger actuator. Monitoring device (14) according to one of the preceding claims, characterized in that the arc detection unit (30) has a photodiode (40) which transitions into an electrically conductive state upon detection of an arc. Monitoring device (14) according to one of the preceding claims, characterized in that the arc detection unit (30) is arranged on a circuit board (42) which is received in a receptacle (52) of a housing (50) surrounding the spark gap (24), or is arranged externally on a housing (50) surrounding the spark gap (24) via an adapter (54). Monitoring device (14) according to one of the preceding claims, characterized in that the arc detection unit (30) is galvanically isolated from the overload protection (22). Monitoring device (14) according to one of the preceding claims, characterized in that the monitoring device (14) has a status indicator (56) and / or a communication interface (58). Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (26) is connected in parallel to the overload protection (22), wherein the detection circuit (26) comprises measuring electronics (28) which is configured to detect the degradation-relevant parameter, in particular wherein the detection circuit (26) comprises at least one measuring capacitor (60) with a measuring capacitance which can be connected in series with the overvoltage protection device (12). Monitoring device (14) according to one of the preceding claims, characterized in that the detection circuit (26) has an evaluation unit (36) which is connected to a line (68) between the overload protection (22) and the terminal (20) in order to detect and evaluate a voltage drop across the overload protection (22) in order to detect the degradation-relevant parameter. Assembly (10) comprising a surge protection device (12) and a monitoring device (14) according to one of the preceding claims, wherein the surge protection device (12) and the monitoring device (14) are connected in series. Method for monitoring a surge protection device (12) by means of a monitoring device (14), comprising the steps of: - capturing a degradation-relevant parameter to detect aging and / or a defect of the surge protection device (12), and - detecting an arc in a spark gap (24) of an overload protection of the monitoring device (14), characterized in that a status of the surge protection device (12) and / or a status of the monitoring device (14) is displayed and / or that the monitoring device (14) is switched off and / or the surge protection device (12) is disconnected when the arc has been detected. Method according to claim 12, characterized in that an arc detection unit (30) is only activated to detect the arc if the degradation-relevant parameter has exceeded a threshold value.

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