DE102019132071A1 - Device for monitoring a supply network - Google Patents

Abstract

A device (20) for monitoring a supply network (10) with active conductors (L1, L2, L3, N; HOT1, HOT2) and a protective conductor (PE) has a first connection (21), a second connection (22), a third connection (25), a current regulator (44) and a signal detection arrangement (31), which current regulator (44) is designed to enable a current flow in a first current loop (81, 84) when the supply network (10) is connected the first current loop (81, 84) comprises the current controller (44), the third connection (25), the supply network (10), the first connection (21) and again the current controller (44), which device (20) is designed to Generate an alternating current signal (I_I) in the first current loop (81, 84) via the current regulator (44), which signal detection arrangement (31) is designed to generate a first signal (SIG1) at a predetermined first point of the first current loop (81, 84) ) and which evaluation device (3 0) is designed to generate an evaluation signal (OUT) as a function of the first signal (SIG1), which evaluation signal is dependent on the impedance of the first current loop (81, 84).

Description

The invention relates to a device and a method for monitoring a supply network. Such devices are also referred to as PE monitors.

The DE 10 2011 101 530 A1 shows a method in which a loop impedance of a circuit is determined and the charging device is decoupled from the energy supply system as a function of the determined loop impedance.

The EP 0 881 500 A1 shows a loop current measurement for a supply network with a neutral conductor.

The EP 2 869 075 A1 relates to a method for detecting a leak between the power connections and earth, in which the impedance between the power connections and earth is determined.

The US 2014/0340092 A1 shows a monitoring apparatus in which the loop resistance of the battery charging and discharging system is measured.

The US 2016/0327615 A1 shows a method and an apparatus for a portable vehicle charging arrangement which is used for testing charging stations.

It is an object of the invention to provide a new device for monitoring a supply network.

This object is achieved by the subject matter of claim 1.

A device for monitoring a supply network with active conductors and a protective conductor has a first connection, a second connection, a third connection, a current regulator and a signal detection arrangement, which first connection can be connected to a first active conductor of the supply network, which third connection can be connected to the Protective conductor of the supply network can be connected, and which current controller is designed to enable a current flow in a first current loop when the supply network is connected, which first current loop comprises the current controller, the third connection, the supply network, the first connection and again the current controller, which device is designed to generate an alternating current signal in the first current loop via the current regulator, which signal acquisition arrangement is designed to acquire a first signal at a predetermined first point of the first current loop and the evaluation before direction to supply a signal acquisition arrangement signal, which first signal has first information about the impedance of the first current loop, which signal acquisition arrangement signal is dependent on the first signal, and which evaluation device is designed to generate an evaluation signal as a function of the signal acquisition arrangement signal which is dependent on the impedance of the first current loop. The use of an alternating current signal enables good evaluation and the risk of a residual current circuit breaker being triggered is lower than with a direct current signal.

According to a preferred embodiment, the signal acquisition arrangement is designed to acquire a signal characterizing the voltage at the first connection as the first signal. The voltage at the first connection contains information about the impedance of the supply network and is therefore well suited for evaluation. The signal characterizing the voltage at the first connection can also be detected, for example, if a resistor is provided at the first connection and measurement is only taken after the resistor.

According to a preferred embodiment, the first current loop has at least one capacitor, the first connection of which is connected in the direction of the first connection and the second connection of which is connected in the direction of the current regulator.

According to a preferred embodiment, the first current loop has at least one resistor which is connected in parallel to the capacitor. The resistance allows the generation of a potential suitable for the power controller.

According to a preferred embodiment, the second connection can be connected to a second active conductor of the supply network, and the current regulator is designed to enable a current flow in a second current loop when the supply network is connected, which second current loop is the Power controller, the third connection, the supply network, the second connection and again includes the power controller. The measurement in the second current loop increases the accuracy of the measurement, since the effect of the alternating current signal can be detected well even with unequal impedances in the first current loop and the second current loop. In supply networks with only two active conductors, such as the US split phase supply network, both active conductors are measured with one current loop each, and a good result is obtained for the impedances.

According to a preferred embodiment, the second current loop has at least one capacitor, the first connection of which is connected in the direction of the second connection and the second connection of which is connected in the direction of the current regulator.

According to a preferred embodiment, the signal acquisition arrangement is designed to acquire a second signal at a predetermined second point of the second current loop, which second signal has second information about the impedance of the second current loop, and the signal acquisition arrangement signal is dependent on the first signal and the second signal . This enables the evaluation device to evaluate both the first signal and the second signal.

According to a preferred embodiment, the signal acquisition arrangement has an adder which is designed to form the signal acquisition arrangement signal as a sum signal of the first signal and the second signal. The sum signal contains the effect of the alternating current signal on both current loops. In addition, the phases HOT1 and HOT2 with the mains frequency, which have a phase shift of 180 ° to one another, are at least partially averaged by the adder to a lower voltage or, ideally, to a mains voltage of 0 V.

According to a preferred embodiment, the adder has a voltage divider. The voltage divider enables simple addition. However, adders with operational amplifiers are also possible, for example.

According to a preferred embodiment, the signal acquisition arrangement is designed to supply a first signal acquisition arrangement signal and a second signal acquisition arrangement signal to the evaluation device as a signal acquisition arrangement signal, which first signal acquisition arrangement signal is dependent on the first signal and which second signal acquisition arrangement signal is dependent on the second signal. As a result of the separate supply of the first signal acquisition arrangement signal and the second signal acquisition arrangement signal, the evaluation device can evaluate the current loops individually and thus receives the full information of the measurement.

According to a preferred embodiment, the device has a current measuring device for detecting a measurement signal characterizing the current generated by the current regulator, and the evaluation device is designed to generate the evaluation signal as a function of the measurement signal. According to a preferred embodiment, the evaluation device is designed to generate an error signal as the evaluation signal when the measurement signal corresponds to an alternating current signal that is too low. The measurement of the current actually generated is advantageous since the signal detection arrangement signal is dependent on it. If the measurement current is too low, this can be a sign of too high an impedance in the respective current loop, and this provides information for the evaluation signal.

According to a preferred embodiment, the alternating current signal has a measuring frequency which is in the range 75 Hz to 625 Hz, preferably in the range 100 Hz to 590 Hz. The measuring frequency influences the impedance generated by capacitances and / or inductances. The range mentioned has proven to be advantageous for the measurement and evaluation.

According to a preferred embodiment, the alternating current signal has a measurement frequency which is not equal to an odd multiple of the network frequency. Investigations have shown that harmonics occur at the odd multiples of the network frequency, which can lead to a disruption of the measurement.

According to a preferred embodiment, the device has a frequency measuring device, which frequency measuring device is designed to determine a frequency measurement value characterizing the network frequency, and which device is designed to determine the measurement frequency as a function of the frequency measurement value. A measurement frequency that is well suited for the measurement can be selected from the information on the measured frequency value.

According to a preferred embodiment, the current regulator is designed as a current regulator. The use of a current regulator allows the reaction to changing impedances in the measuring loops.

According to a preferred embodiment, the evaluation device is designed to filter the signal acquisition arrangement signal through a bandpass filter in order to effect an attenuation in the range of the network frequency. The band-pass filter enables low attenuation in the area around the measurement frequency, the so-called band, but at the same time strong attenuation above and below it. The network frequency can be damped well in this way, and this facilitates the evaluation in the frequency range of the measurement frequency.

According to a preferred embodiment, the bandpass filter is designed as an active filter. The use of active filters enables a narrow band range and a large attenuation outside the band range. This is advantageous because the network frequency and the measurement frequency are relatively close to one another.

According to a preferred embodiment, the device has a phase locked loop, which phase locked loop is designed to generate a phase locked loop signal through a closed control loop in such a way that the phase deviation between the phase locked loop signal and a phase of the supply voltage is constant. The generation of the phase locked loop signal provides a good reference for the behavior of the phase.

According to a preferred embodiment, the evaluation device is supplied with a value characterizing the network frequency and a value characterizing the measurement frequency.

According to a preferred embodiment, the device is designed to influence the alternating current signal as a function of the phase locked loop signal. The alternating current signal can thereby be synchronized with the phase-locked loop signal, and the quality of the evaluation is improved, in particular in connection with a Fourier transformation that may be carried out.

According to a preferred embodiment, the device is designed to synchronize the alternating current signal with a predetermined frequency factor with the phase locked loop signal. By this measure, the frequencies of the phase and the alternating current signal are set in a fixed ratio, and there is no phase shift in addition to the phase shift due to the different frequencies.

According to a preferred embodiment, the evaluation device has an adder which is designed to sum the signal arrangement signal with a phase signal, which phase signal has a frequency which corresponds to the network frequency of the power supply in order to reduce the frequency component of the network frequency in the signal arrangement signal. The amplitude of the voltage in the range of the network frequency is significantly greater than the voltage amplitude generated by the alternating current signal. A reduction in the amplitude of the network frequency therefore facilitates the evaluation.

According to a preferred embodiment, the evaluation device is designed to carry out a Fourier transformation of the signal arrangement signal in order to determine the frequency component of the measurement frequency. The frequency component of interest can be determined well through the Fourier transformation.

According to a preferred embodiment, the device can be connected to a supply network without a neutral conductor. The device therefore does not require the presence of a neutral conductor; in particular, in the relevant circuit part it does not have any components that require the connection of a neutral conductor.

According to a preferred embodiment, the first connection and the second connection are connected to a phase as an active conductor. This advantageously enables the device to be operated on a US split phase supply network, for example.

According to a preferred embodiment, the first connection is connected to a neutral conductor as an active conductor, and the second connection is connected to a phase as an active conductor. According to a further preferred embodiment, the current loop comprises the first connection in order to enable a measurement on the neutral conductor.

According to a preferred embodiment, the evaluation device is designed to respond to an increase in impedance above a predetermined limit value within a response time of less than 40.0 ms to generate corresponding information in the evaluation signal. If there is a very short wait, for example 0.5 ms, a false alarm can occur, in which an excessively high impedance of the current loop is indicated, although this is not the case. If, on the other hand, the measurement signal is observed for too long, an actual increase in impedance can result in a risk of poor protective conductor connection. The 40 ms turned out to be a good value. More preferably, the response time is more than 1.0 ms.

The object is also achieved by the subject matter of claim 24.

1. A) Durch den Stromsteller wird ein Wechselstromsignal in der ersten Stromschleife erzeugt,
2. B) Durch die Signalerfassungsanordnung wird ein erstes Signal an einem vorgegebenen ersten Punkt der ersten Stromschleife erfasst und der Auswertevorrichtung ein Signalerfassungsanordnungssignal zugeführt, welches erste Signal eine erste Information über die Impedanz der ersten Stromschleife aufweist, welches Signalerfassungsanordnungssignal abhängig ist vom ersten Signal,
3. C) Durch die Auswertevorrichtung wird in Abhängigkeit vom Signalerfassungsanordnungssignal ein Auswertesignal erzeugt, welches abhängig ist von der Impedanz der ersten Stromschleife.

A method for monitoring a supply network with active conductors and a protective conductor by means of a device which has a first connection, a second connection, a third connection, a current regulator and a signal detection arrangement, which first connection can be connected to a first active conductor of the supply network, which third connection can be connected to the protective conductor of the supply network, and which current controller is designed to enable a current flow in a first current loop when the supply network is connected, which first current loop is the current controller, the third connection, the supply network, the first connection and again the current controller includes the following steps:

1. A) The current controller generates an alternating current signal in the first current loop,
2. B) The signal detection arrangement detects a first signal at a predetermined first point of the first current loop and the evaluation device is supplied with a signal detection arrangement signal, which first signal has first information about the impedance of the first current loop, which signal detection arrangement signal is dependent on the first signal,
3. C) The evaluation device generates an evaluation signal as a function of the signal acquisition arrangement signal, which evaluation signal is dependent on the impedance of the first current loop.

• 1 eine Vorrichtung zum Überwachen eines Versorgungsnetzes mit einem Stromsteller und einer Signalerfassungsanordnung,
• 2 das Frequenzspektrum eines Signalerfassungsanordnungssignals,
• 3 das Frequenzspektrum des Signalerfassungsanordnungssignals von 2 nach Anwendung eines Tiefpass-Filters,
• 4 ein Tiefpass-Filter,
• 5 ein Blockschaltbild einer ersten Ausführungsform der Vorrichtung von 1,
• 6 ein Blockschaltbild einer zweiten Ausführungsform der Vorrichtung von 1,
• 7 ein Blockschaltbild einer dritten Ausführungsform der Vorrichtung von 1,
• 8 ein Bild eines Oszilloskops bei einer ersten Messung,
• 9 ein Bild eines Oszilloskops bei einer zweiten Messung,
• 10 eine Ausführungsform eines Netzteils und eines Stromstellers,
• 11 eine weitere Ausführungsform der Vorrichtung von 1, und
• 12 eine weitere Ausführungsform einer Vorrichtung zum Überwachen eines Versorgungsnetzes mit einem Stromsteller und einer Signalerfassungsanordnung,

Further details and advantageous developments of the invention emerge from the exemplary embodiments described below and shown in the drawings, which are in no way to be understood as limiting the invention, as well as from the subclaims. It shows

• 1 a device for monitoring a supply network with a power controller and a signal detection arrangement,
• 2 the frequency spectrum of a signal acquisition arrangement signal,
• 3rd the frequency spectrum of the signal acquisition array signal from 2 after applying a low-pass filter,
• 4th a low pass filter,
• 5 a block diagram of a first embodiment of the device of FIG 1 ,
• 6th a block diagram of a second embodiment of the apparatus of FIG 1 ,
• 7th a block diagram of a third embodiment of the apparatus of FIG 1 ,
• 8th an image of an oscilloscope during a first measurement,
• 9 a picture of an oscilloscope during a second measurement,
• 10 an embodiment of a power supply unit and a power controller,
• 11 another embodiment of the device of FIG 1 , and
• 12th a further embodiment of a device for monitoring a supply network with a current regulator and a signal detection arrangement,

In the following, identical or identically acting parts are provided with the same reference numerals and are usually only described once. The description builds on each other across all figures in order to avoid unnecessary repetitions.

1 shows an apparatus 20th for monitoring a supply network 10 .

The device 20th has a connection 21 (or. 21 ' ) with one line 51 , a connection 24 (or. 24 ' ) with one line 54 as well as a protective conductor connection 25th (or. 25 ' ) with one line 55 . The Protective conductor connection 25th is with a protective conductor symbol 99 connected, which is also used elsewhere in the circuit as a symbol for a conductive connection with the protective conductor connection 25th is used.

The device 20th is an example of a supply network 10 of the type US split phase connected, as it is used in particular in the USA. Such a supply network is also referred to as a single-phase three-wire network. The supply network 10 has a point 13th , which has a first AC voltage source 11 with the connector 21 (HOT1) and an AC voltage source 12th with the connector 24 (HOT2) is connected. The point 13th is via a ground connection 199 grounded and with the protective conductor connection 25th (PE) connected. The AC voltage sources 11 , 12th are for example the secondary of a transformer, and the point 13th is a center tap on the secondary side. The ladder 51 , 54 are referred to as active conductors, as the current usually flows through them. In the present case, the active conductors are 51 , 54 connected to HOT1 or HOT2 of the US split phase supply network. For example, in a European network, the conductors 51 , 54 be connected to the terminals L1 and N, respectively.

A consumer 15th is an example of cables at the connections 21 , 24 and 25th as well as additional connections 22nd , 23 connected and can take power from the supply network 10 can be removed or fed from the supply network. Over the lines 22nd , 23 For example, the phases L2, L3 can be connected to a European three-phase supply network with the active connections L1, L2, L3, N.

The device 20th has a resistance 60 and a resistor 62 . The administration 51 is about the resistance 60 with a point 61 connected, and the point 61 is about the resistance 62 with the line 54 connected. The resistances 60 and 62 each is a capacitor 63 or. 64 connected in parallel. The point 61 is via a power controller 44 with a point 42 connected, and the point 42 is about a resistance 40 with the connector 25th connected. In other words, the first current loop 81 the capacitor 63 on, its first connection in the direction of the first connection 21 is connected and its second connection in the direction of the power controller 44 is connected. The resistance 60 is in parallel with the capacitor 63 interconnected. In the same way, the second current loop 84 the capacitor 64 on, its first connection in the direction of the second connection 24 is connected and its second connection in the direction of the power controller 44 is connected. The resistance 62 is in parallel with the capacitor 64 interconnected. The resistances 60 , 62 cause a voltage divider.

A power supply 46 is with the line 51 and the line 54 connected, and the output voltages of the power supply 46 are via lines 65 , 66 the power controller 44 fed. On the line 65 is the voltage of the power supply 46 e.g. + 15 V, and on the line 66 e.g. - 15 V.

An analysis device 28 has a difference generator 32 and an evaluation device 30th .

A signal detection arrangement 31 is designed, for example, to generate a first signal SIG1 on the line 51 to capture a second signal SIG2 on the line 54 to detect and the evaluation device 30th a signal detection arrangement signal SIG3 to feed. The signal detection arrangement 31 has an adder as an example 67 , 68 , which is designed to provide the signal detection arrangement signal SIG3 as the sum signal of the first signal SIG1 and the second signal SIG2 to build. In the exemplary embodiment, the adder has 67 , 68 a resistance 67 over which the line 51 with a point 69 connected, and a resistor 68 over which the line 54 with the point 69 connected is. The resistances 67 , 68 act as a voltage divider and generate at the point 69 in the case of the connection of a supply network of the type US split phase, a low potential. This can also be referred to as a virtual neutral conductor. The low potential can also be generated in other ways, for example by a voltage regulator.

The evaluation device 30th is with the point 69 connected and gets over this point 69 the signal detection arrangement signal SIG3 .

The difference maker 32 is over a line 71 with the line 51 connected and one line 72 with the line 54 connected. The output signal of the difference calculator 32 characterizes the difference U21 - U24 the tension U21 at the connection 21 and the tension U24 at the connection 24 and becomes the evaluation device 30th over a line 33 fed. It can, for example, be used as a difference generator 32 a comparator can be used, or a subtracter. The difference maker 32 can also be designed as a measuring circuit, which the mains voltage for the evaluation device 30th processed both in terms of level and interference.

The evaluation device 30th has a frequency measuring device 348 , which is designed to determine a frequency measurement value f_N_M characterizing the network frequency f_N. The measurement frequency f_M is preferably determined as a function of the frequency measurement value f_N_M.

The evaluation device 30th is over a line 73 with the power controller 44 connected, and over the line 73 can the power controller 44 a signal I_S as a setpoint for the current controller 44 generated electricity can be supplied. The point 42 is over a line 74 with the evaluation device 30th connected. At the point 42 lies because of the resistance 40 a voltage which is dependent on the voltage generated by the current controller 44 generated amperage. The tension drops at the point 42 opposite to the protective conductor PE. The resistance 40 thus acts as a current measuring device and detects the through the current regulator 44 generated current I_I characterizing measurement signal l_l_M, which over the line 74 to the evaluation device 30th is transmitted.

The power controller 44 is preferably designed as a current regulator.

The following are exemplary values for some of the components of the circuit arrangement: Resistors 60, 62, 67, 68 44 kOhm Capacitors 63, 64 1 µF Resistance 40 510 ohms

functionality

The one from the power controller 44 generated electricity can be in a first current loop 81 about the resistance 40 , the connection 25th , the AC power source 11 , the connection 21 and the resistance 60 or the capacitor 63 to the power controller 44 flow.

Because the impedance of the capacitor 63 for the measuring current I_I that is an alternating current is lower than the resistance 60 , the measuring current flows I_I mainly through the capacitor 63 . The resistor divider with the resistors 60 , 62 generates a virtual neutral conductor or at least one point with low voltage in a US split phase power grid with symmetrical amplitudes and resistances. This allows the current to flow through the current regulator 44 can be easily embossed.

Another current loop 84 is possible with the from the power controller 44 generated current through the resistor 40 , the connection 25th , the AC power source 12th , the connection 24 , the resistance 62 or the capacitor 64 back to the power controller 44 can flow.

A resistance is schematic 14th in the supply network 10 between the connection 25th and the point 13th drawn. While the connections 21 and 24 via the AC voltage sources 11 , 12th are usually connected with low resistance, this is not always the case with the protective conductor PE. This can be due to a defective line. There are also supply networks 10 where the protective conductor PE is not present at all or is connected with a high resistance. Since the protective conductor PE at the connection 25th usually for the grounding of metallic housings of the consumer 15th is used, the protective effect or protection class caused by the grounding cannot be achieved if there is no low-resistance connection of the connection 25th with the protective conductor PE is present. For this reason, the device 20th be checked whether on the side of the supply network 10 the resistance 14th is low or high resistance. This monitoring can be done by the current flowing in the current loops 81 or. 84 flows, depends on the resistance 14th and from the other resistances 60 , 40 or. 62 , 40 . Because the resistance 14th on the side of the supply network 10 it cannot be measured directly. The voltage drop across the resistor 60 or. 62 and the voltage drop across the resistor 14th however, are dependent on the resistance 40 , and the voltage or current on the line 51 and also on the line 54 contain information about the influence of the resistance 14th depending on the power controller 44 generated electricity.

In the exemplary embodiment, the lines are 51 and 54 with the signals SIG1 or. SIG2 via the voltage divider from the resistors 67 and 68 connected together, and the signal SIG3 at the point 69 becomes the evaluation device 30th fed.

A first problem with monitoring the supply network 10 is that, for example, the consumer 15th an EMC filter with Y capacitances, which has a capacitive connection between the connection 25th and the connection 21 or between the connection 25th and the connection 24 cause. This has the consequence that with the current loops 81 and 84 an alternating current can also flow in a parallel path via the Y capacitances. One by the power controller 44 The constant direct current generated would not flow through the Y capacitances, as these only conduct with alternating currents or changing direct currents. With direct currents, however, there is the problem that they can lead to a fault current that would trigger a possibly existing fault current circuit breaker. The one from the power controller 44 generated currents may therefore only be relatively low.

This leads to the next problem because of the active conductors 51 and 54 high voltages of several hundred volts can be present, caused by the power controller 44 The electricity generated, on the other hand, has to be in the milliampere range and therefore only influences the voltage on the lines 51 or. 54 leads in the mV range. This results in a very poor signal-to-noise ratio and evaluation is difficult.

Tests have shown that the generation of a direct current signal by the current controller 44 for measuring the resistance of the current loops 81 , 84 is difficult to evaluate in terms of measurement technology. Residual current circuit breakers have a tripping limit value of, for example, 20 mA fault current. As almost every consumer 15th For example, fault currents generated by the Y capacitances could be caused by the current controller 44 generated electricity amount to at most a few milliamperes.

There were therefore attempts with one by the power controller 40 generated alternating current carried out. The frequency of the supply network is usually 50 Hz or 60 Hz. For the smallest possible influence on the measurement by the network frequency, it is advantageous if the measurement frequency is significantly lower or significantly higher than the network frequency. If the measuring frequency f_M is very low, the risk of a residual current circuit breaker being triggered by the alternating current increases. Residual current circuit breakers trigger, for example, when the residual current is above a specified maximum value over two periods of the mains frequency. At frequencies that are higher than the mains frequency, the residual current caused by the measuring current I_I is largely averaged out over the individual periods, and triggering of the residual current circuit breaker is avoided. Another effect results from the Y capacitors, which are, for example, in the consumer 15th are provided. The impedance is proportional to the reciprocal of the frequency of the alternating current. As the frequency increases, the impedance decreases. Because the current loops 81 or. 84 via the supply network 10 should run and not across the Y capacitors, it is advantageous if the Y capacitors have as high an impedance as possible. Because then the current I_I flows mainly via the supply network 10 . As a result, the lowest possible frequency is advantageous.

The observation shows that each frequency range has an advantage and a disadvantage. The range between 75 Hz and 625 Hz has proven to be an advantageous frequency range for the measurement, more preferably the range 100 Hz to 590 Hz. Another point to be taken into account is that the measurement frequency should not correspond to an odd multiple of the mains frequency, since with these Frequencies Harmonics of the mains frequency can occur. Measurement frequencies in the range 175 ± 23 Hz, 225 Hz ± 23 Hz, 275 ± 23 Hz, 325 Hz ± 23 Hz and 375 ± 23 Hz have proven to be particularly advantageous.

The resistance 14th on the side of the supply network 10 is, for example, 2-3 ohms, and as a threshold for a resistance that is too high 14th a resistance of 200 ohms or 250 ohms can preferably be assumed.

The signal detection arrangement 31 can be the first signal SIG1 or the second signal SIG2 at different points on the first current loop 81 or second current loop 84 capture. The points are preferably in the area of the device 20th between that of the port 25th remote side of the power controller 44 and the connection 21 for the signal SIG1 and in the area of the device 20th between that of the port 25th remote side of the power controller 44 and the connection 24 for the signal SIG2 . The signals SIG1 and SIG2 thus characterize the voltage at the first connection 21 .

The signal acquisition order signal SIG3 is by merging the signal SIG1 and SIG2 at the point 69 both depending on the signal SIG1 as well as from the signal SIG2 and contains the information about the impedance of the respective current loop 81 and 84 .

It can also use both signals SIG1 and SIG2 as separate signals from the evaluation device 30th are supplied and evaluated separately. This enables a possible asymmetry of the resistance to be determined 14th towards the connector 21 or. 24 . The individual evaluation units of the Evaluation device 30th but in such a case must at least partially be provided twice in order to carry out the evaluation of the separate signals.

The evaluation device 30th is designed to be dependent on the signal acquisition arrangement signal SIG3 to generate an evaluation signal OUT, which is dependent on the impedance of the first current loop 81 and / or second current loop 84 . The evaluation signal OUT can either be internal to the evaluation device 30th used or passed on to other devices. In a vehicle, the evaluation signal OUT can be made available via a CAN bus, for example, and the connection to the power supply can be made available as a function of the evaluation signal OUT 10 interrupted, and / or an error display can be made depending on the evaluation signal OUT.

• - Qualitative Angabe, ob die Impedanz im zulässigen Bereich ist oder nicht
• - Quantitative Angabe der Impedanz des Widerstands 14
• - Quantitative Angabe der Gesamtimpedanz einer der Stromschleifen 81, 84 oder beider Stromschleifen 81, 84
• - Information auf Grund des Messsignals I_I_M, ob das Messsignal gemäß der Vorgabe erzeugt ist

The evaluation signal OUT can include, for example, one or more of the following items of information:

• - Qualitative indication of whether the impedance is in the permissible range or not
• - Quantitative indication of the impedance of the resistor 14
• - Quantitative indication of the total impedance of one of the current loops 81 , 84 or both current loops 81 , 84
• - Information on the basis of the measurement signal I_I_M as to whether the measurement signal has been generated according to the specification

When evaluating the signal acquisition arrangement signal SIG3 it is beneficial to the effect of the capacitor 63 or. 64 and possibly an additional winding in the power supply 10 , for example a secondary winding of the AC voltage sources 11 , 12th with a US split phase supply network 10 to consider. This can lead to a phase shift of the signal acquisition arrangement signal SIG3 lead with respect to the measuring current I_I. The device is preferably calibrated 20th .

Both the resistance (real part) and the capacitive part (in general: imaginary part) are preferably determined.

2 shows an example of the dynamic range of the signal acquisition arrangement signal SIG3 at the point 69 . The level of the signal detection arrangement signal is shown SIG3 at the point 69 , plotted against the frequency. The representation of the level over the frequency is obtained, for example, by Fourier transformation of the signal detection arrangement signal SIG3 , and such a Fourier transformation is preferred in the evaluation device 30th carried out, for example by an FFT (Fast Fourier Transformation). The power controller 44 used a measurement frequency f_M of 300 Hz, and the total capacitance of the Y capacitors was assumed to be relatively large _{with C y = 2 µF.} In addition, an asymmetry of the voltages between the terminals HOT1 and HOT2 of 20 Vp was assumed. At the network frequency f_N the level is approx. 16 dB, and at the measurement frequency f_M the level is -20 dB. The level spacing of the signal detection arrangement signal SIG3 to the network asymmetry is thus -36 dB. A good analog / digital converter has, for example, a resolution of 12 bits. This gives 4096 possible different values. A measurement of the signal at the point 69 and modulation of the analog / digital converter to the maximum occurring asymmetry of the mains voltage leads to the additional through the current I_I caused effect with the analog / digital converter is not or only very poorly resolvable. Analog / digital converters with a higher resolution of 24 bits may also have resolution difficulties with such a signal-to-noise ratio. In addition, such high-resolution analog / digital converters are comparatively expensive.

3rd shows the dynamic range of a filtered signal SIG3 " after using a bandpass filter (cf. 4th ) to the signal acquisition arrangement signal SIG3 at the point 69 . The bandpass filter is designed to measure the frequency range of the signal detection arrangement signal SIG3 to pass in a frequency range (band) around 300 Hz, but in the frequency range above and below the measurement frequency f_M the signal acquisition arrangement signal SIG3 to dampen. The bandpass filter was designed as an analog bandpass filter, and it has a level reduction of -18 dB in the range of the network frequency f_N. The frequency scale is opposite the scale of 2 shifted, but the grid frequency is as in 2 for example at 50 Hz, and the measuring frequency at 300 Hz. The level of the signal SIG3 in the range of the network frequency f_N has decreased from approx. 16 dB to approx. -3 dB, and the measurement frequency f_M is approx. -21 dB. With a level difference between the signal and the phase of -21 dB (or -18 dB), a direct measurement is possible using a standard analog / digital converter.

4th shows a bandpass filter 300 , which in the evaluation device 30th is usable. The signal SIG3 will have a resistor 301 one point 303 fed. The point 303 is about a resistance 302 with GND 99 connected and through a resistor 304 with the plus input of an operational amplifier 305 connected. The output of the operational amplifier 305 is to the minus input of the operational amplifier 305 connected and through a resistor 306 with a point 307 connected. The point 307 is through a capacitor 308 with a point 312 connected and through a capacitor 309 with a point 310 connected. The point 312 is about a resistance 326 with the point 310 connected, and the point 310 is to the minus input of an operational amplifier 311 connected. The output of the operational amplifier 311 is with the point 312 connected. The point 312 is about a resistance 313 with a point 315 connected, and the point 315 is about a resistance 314 with GND 99 and connected to the plus input of the operational amplifier 311 connected. The point 312 is about a resistance 327 with a point 316 connected. The point 316 is through a capacitor 317 with a point 319 connected and through a capacitor 318 with a point 320 connected. The points 319 and 320 are about a resistance 328 connected with each other. The point 320 is to the minus input of an operational amplifier 321 connected, and the point 319 is with a point 322 connected. The output of the operational amplifier 321 is with the point 322 connected, and the point 322 is about a resistance 323 with a point 324 connected. The point 324 is to the plus input of the op amp 321 connected and through a resistor 325 with GND 99 connected. At the point 322 is a signal as a result of the bandpass filtering SIG3 ' generates a level corresponding to the diagram of 3rd having.

The bandpass filter 300 has, for example, a center frequency of 320 Hz, and the level reduction at a network frequency f_N of 60 Hz is, for example, -18 dB. Depending on the supply network, other values can of course also be selected.

The bandpass filter 300 is preferably designed as an active filter. The bandpass filter 300 is preferably of the second order or higher, and preferably has an enhancer. A higher-order filter can be created, for example, by connecting several lower-order filters ( 1 . and 2nd order).

5 shows a block diagram for the evaluation by the device 20th of 1 .

The power controller 44 received from the evaluation device 30th the current setpoint I_S, which is the level of the current controller 44 generated current I_I determined. The current setpoint I_S is, for example, as a voltage across the line 73 (see. 1 ) specified. By the power controller 44 the actual current I_I is generated, and via the line 74 of 1 the measuring signal I_I_M characterizing the actual current I_I is sent to an analog / digital converter 340 supplied, for example as the voltage characterizing the actual current. A measuring section 45 corresponds to the current loops 81 , 84 of 1 , and as a result the signal becomes SIG3 recorded and the analog / digital converter 340 fed. The analog / digital converter 340 converts the signal SIG3 and the signal I_I_M into digital signals. The digital signals are from the analog / digital converter 340 to the evaluation device 30th passed, which is formed, for example, by a microcontroller. The evaluation device 30th preferably also determines the current setpoint I_S for the current controller 44 .

6th shows a further block diagram with an embodiment for the measurement and evaluation of the device 20th . The evaluation of the signal SIG3 does not take place directly, but a signal characterizing the mains voltage is also recorded and sent to the evaluation device 30th supplied, for example. The difference signal U21 - U24 . The evaluation device 30th contains a phase locked loop 344 , which is referred to as phase-locked loop (PLL), and the phase-locked loop 344 generates another signal 346 . The signal SIG3 and the signal 346 become a totalizer 342 fed, and the result SIG3 ' becomes the evaluation device 30th fed. The totalizer 342 realizes, for example, level adjustment of high input voltages via a resistor network. In other words, the line frequency component is given by the adder 342 actively withdrawn. This determines the absolute size of the signal SIG3 reduced, and this enables a better resolution by the analog / digital converter and thus a better evaluation.

The evaluation device is preferred 30th a value characterizing the network frequency and a value characterizing the measurement frequency are supplied.

The signals mentioned in the description SIG3 , SIG3 ' and SIG3 " can all be referred to as signal acquisition array signals, as is common with filters, as they still contain the relevant information. When multiple filters on the signal acquisition arrangement signal SIG3 are applied, in some cases the order is not relevant, in other cases it may be relevant.

The phase locked loop 44 is designed to generate a phase-locked loop signal PLL_SIG by a closed control loop in such a way that the phase deviation between the phase-locked loop signal PLL_SIG and a phase HOT1, HOT2 or L1 of the supply voltage 10 is constant.

The evaluation device is preferred 30th designed to influence the alternating current signal I_I as a function of the phase locked loop signal PLL_SIG. For this purpose, for example, the phase-locked loop signal PLL_SIG is used by a setpoint generating device 352 supplied, and the setpoint generating device 352 generates the setpoint I_S as a function of the phase locked loop signal PLL_SIG. The alternating current signal I_I is thus also synchronized with the phase locked loop signal PLL_SIG. Although the alternating current signal I_I and the mains voltage with the mains frequency f_N have different frequencies, a fixed ratio can be set by using the phase-locked loop signal PLL_SIG, and this improves the Fourier transformation.

The device is preferred 20th designed to synchronize the alternating current signal I_I with a predetermined frequency factor with the phase locked loop signal PLL_SIG, for example with a frequency factor of 6.5, 5.5 or 6.

The evaluation device preferably has the adder 342 which is designed to be the signal arrangement signal SIG3 with the phase signal 346 to sum up. The phase signal 346 has a frequency which is preferably the network frequency f_N of the power supply 10 corresponds to at the signal arrangement signal SIG3 to bring about a reduction in the frequency component of the network frequency f_N. To generate the phase signal 346 the evaluation device preferably has a phase signal generating device 350 , and the phase signal generating device 350 generates the phase signal 346 preferably based on the phase locked loop signal PLL_SIG.

7th shows a block diagram with a further embodiment for the measurement and evaluation of the device 20th . The evaluation device 30th has like in 6th the phase locked loop 344 and the totalizer 342 . As in the embodiment of 5 be the signal SIG3 and the signal I_I_M characterizing the actual current I_I to the analog / digital converter 340 fed, and the digital signals are the evaluation device 30th fed. In addition, the signal SIG3 the bandpass filter 300 fed through the bandpass filter 300 generated signal SIG3 " becomes the evaluation device 30th fed.

The evaluation accordingly 5 leads to a good result, the evaluation accordingly 6th with the additional phase locked loop 344 leads to an improvement in the device 20th , and the embodiment of 7th with the bandpass filter 300 and possibly also the phase locked loop leads to an additional improvement in the evaluation.

8th shows the image of an oscilloscope with signals of an actual measurement on the device 20th . In the upper area the size of the actual current I_I can be seen in the form of a sinusoidal signal. The signal SIG is in the lower area 3rd to see which example. With the device 20th of 7th after applying the bandpass filter 300 is produced. The resistance 14th of the supply network 10 , which can be set by a supply network simulator (not shown), is 38 ohms up to time t1, and the resistance jumps at time t1 14th to infinity (open), which corresponds to an interruption of the protective conductor PE. Since the power controller 44 voltage to use when increasing resistance 14th increases, the signal also increases SIG3 or its amplitude. A limit value SIG3_MAX is drawn in, and if this limit value is exceeded several times, a state signal STATE changes its state from LOW to HIGH at time t2. It is thus determined at time t2 that the resistance 14th the power supply 10 has become too big and grounding through the protective conductor PE is no longer guaranteed. The duration t2-t1 is 16 ms in the exemplary embodiment. That despite the resistance 14th A measuring current can flow from infinity is due to the Y capacitances that are present in the system, for example in the consumer. If, on the other hand, there were no or only very low Y capacitances, the power controller could 44 do not generate a measuring current, and in this case it can be determined by evaluating the signal I_I_M that the protective conductor connection PE is very poor or not available. The evaluation signal OUT is thus preferably generated as a function of the measurement signal I_I_M. For example, an error signal can be output as the evaluation signal OUT if the measurement signal I_I_M corresponds to an alternating current signal I_I that is too low. Whether the measurement signal I_I_M is too low can be determined, for example, by comparing the amplitude of the measurement signal I_I_M with a limit value, or the area of the positive and negative half-waves of the measurement signal can be determined by integration or summation and the area compared with a limit value . The limit value can, for example, be in It can be determined as a function of the setpoint signal I_S, or it can be predefined with a fixed amplitude of the setpoint signal I_S.

In the present evaluation, symmetrical Y capacitances were assumed, and this means that the mains voltage at the point is averaged 69 of 1 off when the amplitudes of the phases at the terminals 21 and 24 are of the same size and the phases also have a phase shift of 180 °.

The decision as to when the protective conductor PE is too high can be made by comparing the signal SIG3 with the limit value SIG3_MAX. To increase security and to reduce the risk of wrong decisions, it can be required, for example, that a certain number of overshoots has occurred before the status signal STATE changes. This can be done, for example, by a microcontroller in the evaluation device 30th be done arithmetically, or a capacitor with an upstream comparator can be provided to add up the excesses.

Multiple strategies are also possible in which both exceeding a higher limit value over a shorter number of periods and exceeding a lower limit value over a longer number of periods lead to a change in the status signal STATE. The evaluation device reacts as a result 30th at a high resistance 14th fast, and with increased resistance 14th In the limit range, there is a longer wait until the status signal STATE is changed. The status signal STATE can be used as an evaluation signal OUT.

9 shows another image of an oscilloscope for a measurement in which the Y capacitances were assumed to be asymmetrical, namely 1,360 nF between the connections 21 and 25th of 1 , and 1 .680 nF between the terminals 24 and 25th of 1 . At time t1, the resistance increases 14th of the supply network 10 from 137 ohms to 400 ohms.

The one from the power controller 44 (see. 1 ) generated current I_I is shown in the upper area.

The asymmetrical Y capacitances lead to the signal SIG 2 is superimposed by a beat frequency. The beat frequency is 25 Hz and thus half of the mains frequency f_N = 50 Hz. With a mains frequency f_N = 60 Hz, the beat frequency is correspondingly 30 Hz.

For a reliable evaluation, it is advantageous to carry out the evaluation over at least 2 network periods. However, this increases the response time. The detection time between times t1 and t2 was 46 ms in the exemplary embodiment.

The voltage U_PE across the resistor is in the lower area 14th plotted, which can be measured with the supply network simulator, in an ordinary supply network 10 though not. By increasing the resistance 14th drops at the same measuring current at the resistor 14th a higher voltage, and the increase in resistance 14th at time t1 can be clearly seen.

10 shows a specific exemplary embodiment for the power supply unit 46 and the power controller 44 of 1 . The administration 51 is over a line 501 with a point 508 connected. The point 508 is about a diode 507 with the line 65 and via a diode 509 with the line 66 connected. The administration 54 is over a line 502 with a point 511 connected. The point 511 is about a diode 510 with the line 65 and via a diode 512 with the line 66 connected. The cathodes of the diodes 507 , 510 point towards the administration 65 , and the anodes of the diodes 509 , 512 point towards the administration 66 . This makes a bridge rectifier. The administration 61 that are also in 1 is present is via a zener diode 505 with the line 65 and a zener diode 506 with the line 66 connected. The Zener diodes 505 , 506 cause a voltage limitation on the lines 65 , 66 relative to the potential on the line 61 . The administration 61 is through a capacitor 503 with the line 65 and through a capacitor 504 with the line 66 connected, and the capacitors 503 , 504 smooth the tensions on the lines 65 , 66 . The administration 61 is about a resistance 520 to the minus input of an operational amplifier 522 connected. The operational amplifier 522 is at the plus input with the line 73 connected, via which the setpoint signal I_S is supplied. The output of the operational amplifier 522 is over a line 524 to the minus input of the operational amplifier 522 connected, and this forms the current control loop.

The administration 65 serves for the positive power supply of the operational amplifier 522 , and the line 66 to negative power supply.

11 shows a further embodiment in which the signals SIG1 and SIG2 not by the signal detection arrangement 31 summed and as a common signal acquisition arrangement signal SIG3 are fed to the evaluation device, but there are a first signal detection arrangement signal SIG3 .1 and a second signal detection arrangement signal SIG3.2 supplied as separate signals. The first signal acquisition order signal SIG3 .1 depends on the first signal SIG1 and the second signal detection arrangement signal SIG3.2 depends on the second signal SIG2 .

12th shows a further embodiment of the device 20th for monitoring a supply network 10 . The supply network 10 in the exemplary embodiment has at least one phase L1 that is connected to the connection 21 is connected, possibly phases L2, L3, as well as a neutral conductor N, which is connected to the connection 24 connected. The neutral conductor N usually has a low voltage or a voltage of 0 V.

The power controller 44 is about the resistance 62 with the line 54 connected, and it can when connected to the supply network 10 a current loop from the current regulator 44 about the resistance 40 , the connection 25th , the supply network 10 , the connection 24 and the resistance 62 back to the power controller 44 flow.

The evaluation of the phase via the difference generator 32 works like in 1 described.

The neutral conductor N or the line 54 is about the resistance 68 with a point 469 connected. The point 469 is about a resistance 410 with a point 411 connected. The point 411 is about a resistance 412 with the protective conductor 99 connected and through a resistor 414 with the point 69 connected. The point 69 is with the evaluation device 30th connected.

The resistances 68 and 410 one hand and the resistance 412 on the other hand cause a level adjustment for the evaluation device 30th , and the resistance 414 causes a current limitation.

The signal detection arrangement 31 is designed to send the first signal SIG1 on the line 54 to detect and the evaluation device 30th the signal detection arrangement signal SIG3 to feed.

Measurements have shown that the signal SIG3 in practice has a line frequency component. This comes from the capacitive coupling via the Y capacitors. By applying the band pass filter 300 of 4th or another bandpass filter, the line frequency component can be reduced, and an evaluation can be carried out with the evaluation device 30th of 1 - as described - take place.

Since usually the supply network 10 If there is a comparatively low-resistance connection between the neutral conductor N and the protective conductor PE, further current loops do not need to be measured, but can be done in addition.

A wide variety of alterations and modifications are of course possible within the scope of the present invention.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102011101530 A1 [0002]
• EP 0881500 A1 [0003]
• EP 2869075 A1 [0004]
• US 2014/0340092 A1 [0005]
• US 2016/0327615 A1 [0006]

Claims (24)

Device (20) for monitoring a supply network (10) with active conductors (L1, L2, L3, N; HOT1, HOT2; L1, N) and a protective conductor (PE), which device (20) has a first connection (21), has a second connection (22), a third connection (25), a current regulator (44) and a signal detection arrangement (31), which first connection (21) can be connected to a first active conductor (L1; HOT1; N) of the supply network (10), which third connection (25) can be connected to the protective conductor (PE) of the supply network (10), and which current controller (44) is designed to enable a current flow in a first current loop (81, 84) when the supply network (10) is connected, which first current loop (81, 84) is the current controller (44), the third connection (25 ), the supply network (10), the first connection (21) and again the power controller (44), which device (20) is designed to generate an alternating current signal (I_I) in the first current loop (81, 84) via the current regulator (44); to detect the first point of the first current loop (81, 84) and to supply the evaluation device (30) with a signal detection arrangement signal (SIG1; SIG3), which first signal (SIG1) has first information about the impedance of the first current loop (81, 84) which Signal acquisition arrangement signal (SIG1; SIG3) is dependent on the first signal (SIG1), and which evaluation device (30) is designed to generate an evaluation signal (OUT) as a function of the signal acquisition arrangement signal (SIG1; SIG3), which evaluation signal is dependent on the impedance of the first current loop (81, 84). Device (20) after Claim 1 , in which the signal acquisition arrangement (31) is designed to acquire a signal characterizing the voltage at the first connection (21) as the first signal (SIG1). Device (20) after Claim 1 or 2 , in which the first current loop (81, 84) has at least one capacitor (63, 64), the first connection of which is connected in the direction of the first connection (21) and the second connection of which is connected in the direction of the current controller (44). Device (20) after Claim 3 , in which the first current loop (81, 84) has at least one resistor (60; 62) which is connected in parallel to the capacitor (63, 64). Device (20) according to one of the preceding claims, in which the second connection (24) can be connected to a second active conductor (N; HOT2; L2) of the supply network (10), and which current controller (44) is designed to do so when connected of the supply network (10) to enable a current flow in a second current loop (81, 84), which second current loop (81, 84) the current controller (44), the third connection (25), the supply network (10), the second connection ( 24) and again includes the power controller (44). Device (20) after Claim 5 , in which the signal acquisition arrangement (31) is designed to acquire a second signal (SIG2) at a predetermined second point of the second current loop (81, 84), which second signal (SIG2) provides second information about the impedance of the second current loop ( 81, 84), and in which the signal detection arrangement signal (SIG3) is dependent on the first signal (SIG1) and on the second signal (SIG2). Device according to Claim 6 , in which the signal acquisition arrangement (31) has an adder (67, 68) which is designed to form the signal acquisition arrangement signal (SIG3) as a sum signal of the first signal (SIG1) and the second signal (SIG2). Device according to Claim 7 , in which the adder (67, 68) has a voltage divider. Device according to Claim 6 , in which the signal acquisition arrangement (31) is designed to supply a first signal acquisition arrangement signal (SIG3.1) and a second signal acquisition arrangement signal (SIG3.2) to the evaluation device (30) as a signal acquisition arrangement signal (SIG3), which first signal acquisition arrangement signal is dependent on the first signal ( SIG1) and which second signal detection arrangement signal is dependent on the second signal (SIG2). Device (20) according to one of the preceding claims, which comprises a current measuring device (40) for detecting a measurement signal characterizing the current (I_I) generated by the current regulator (44) (I_I_M), and in which the evaluation device (30) is designed to generate the evaluation signal (OUT) as a function of the measurement signal (I_I_M). Device (20) after Claim 10 , in which the evaluation device (30) is designed to generate an error signal as an evaluation signal (OUT) when the measurement signal (I_I_M) corresponds to an alternating current signal (I_I) that is too low. Device (20) according to one of the preceding claims, in which the alternating current signal (I_I) has a measuring frequency (f_M) which is in the range 75 Hz to 625 Hz, preferably in the range 100 Hz to 590 Hz. Device (20) according to one of the preceding claims, in which the alternating current signal (I_I) has a measuring frequency (f_M) which is not equal to an odd multiple of the network frequency (f_N). Device (20) according to one of the preceding claims, which has a frequency measuring device (348), which frequency measuring device (348) is designed to determine a frequency measurement value (f_N_M) characterizing the network frequency (f_N), and which device (20) is designed to do so to determine the measurement frequency (f_N) depending on the frequency measurement value (f_N_M). Device (20) according to one of the preceding claims, in which the current regulator (44) is designed as a current regulator. Device (20) according to one of the preceding claims, in which the evaluation device (30) is designed to filter the signal detection arrangement signal (SIG1; SIG3) through a bandpass filter (300) in order to add attenuation in the range of the network frequency (f_N) cause. Device (20) after Claim 16 , in which the bandpass filter (300) is designed as an active filter. Device (20) according to one of the preceding claims, which has a phase-locked loop (344), which phase-locked loop (44) is designed to generate a phase-locked loop signal (PLL_SIG) through a closed control loop in such a way that the phase deviation between the phase-locked loop signal (PLL_SIG) and a phase (HOT1; HOT2; L1) of the supply voltage (10) is constant. Device (20) after Claim 18 which is designed to influence the alternating current signal (I_I) as a function of the phase locked loop signal (PLL_SIG). Device (20) after Claim 18 or 19th , which is designed to synchronize the alternating current signal (I_I) with a predetermined frequency factor with the phase-locked loop signal (PLL_SIG). Device (20) according to one of the preceding claims, in which the evaluation device (30) has an adder (342) which is designed to sum the signal arrangement signal (SIG1; SIG3) with a phase signal (346), which phase signal (346) has a frequency which corresponds to the network frequency of the power supply (10) in order to bring about a reduction in the frequency component of the network frequency (f_N) in the signal arrangement signal (SIG1; SIG3). Device according to one of the preceding claims, in which the evaluation device is designed to carry out a Fourier transformation of the signal arrangement signal (SIG1; SIG3) in order to determine the frequency component of the measurement frequency (f_M). Device according to one of the preceding claims, which can be connected to a supply network (20) without a neutral conductor. Method for monitoring a supply network (10) with active conductors (L1, L2, L3, N; HOT1, HOT2; L1, N) and a protective conductor (PE) by means of a device (20) which device (20) has a first connection ( 21), a second connection (22), a third connection (25), a current regulator (44) and a signal detection arrangement (31), which first connection (21) with a first active conductor (L1; HOT1; N) of the supply network (10) is connectable, which third connection (25) can be connected to the protective conductor (PE) of the supply network (10), and which current controller (44) is designed to enable a current to flow in a first current loop (81, 84) when the supply network (10) is connected , which first current loop (81, 84) comprises the current controller (44), the third connection (25), the supply network (10), the first connection (21) and again the current controller (44), which method comprises the following steps: A) The current controller (44) generates an alternating current signal (I_I) in the first current loop (81, 84), B) The signal detection arrangement (31) generates a first signal (SIG1) at a predetermined first point on the first current loop (81 , 84) and the evaluation device (30) is supplied with a signal acquisition arrangement signal (SIG1; SIG3), which first signal (SIG1) has first information about the impedance of the first current loop (81, 84), which signal acquisition arrangement signal (SIG1; SIG3) is dependent on the first signal (SIG1), C) The evaluation device (30) generates an evaluation signal (OUT) as a function of the signal acquisition arrangement signal (SIG1; SIG3), which is dependent on the impedance of the first current loop (81, 84) .

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