Device for monitoring a supply network

Abstract

A device (20) for monitoring a supply network (10) with live conductors (L1, L2, L3, N; HOT1, HOT2; L1, N) and a protective conductor (PE) has a first connection (21), a second connection (22), a third connection (25), a current controller (44), a current measuring device (252; 246) and a signal acquisition arrangement (31), which first connection (21) is connectable to a first live conductor (L1; HOT1; N) of the supply network (10), which third connection (25) is connected to a line (55) and is connectable to the protective conductor (PE) of the supply network (10), and which current controller (44) is configured to generate a current flow (I_I), which current flow (I_I) flows when the supply network (10) is connected with a first component (I_PE) in at least a first current loop (81, 84) and proportionally in at least a second current loop (83), which device (20) is configured to generate the current flow (I_I) with an alternating current signal via the current controller (44), wherein the evaluation is carried out depending on the current measuring device (252; 246) and the signal acquisition arrangement (31).

Description

[0001] The invention relates to a device for monitoring a supply network. Such devices are also known as PE monitors.

[0002] DE 10 2011 101 530 A1 discloses a method in which a loop impedance of a circuit is determined and, depending on the determined loop impedance, the charging device is decoupled from the power supply system.

[0003] DE 10 2020 124 143 A1 shows an electrical measuring arrangement for monitoring a protective conductor resistance.

[0004] DE 10 2015 207 456 B3 shows an insulation monitoring device.

[0005] DE 10 2018 121 320 A1 discloses a method for controlling a vehicle-external charging device.

[0006] DE 10 2020 130 764 A1 shows a method for controlling a charging process.

[0007] DE 198 26 410 A1 describes a method for insulation and fault current monitoring.

[0008] DE 10 2019 132 071 A1 discloses a device for monitoring a supply network with live conductors and a protective conductor, wherein the device has a first connection, a second connection, a third connection, a current controller and a signal acquisition arrangement, wherein the current controller is configured to enable a current flow in a first current loop comprising the supply network when the supply network is connected, wherein the device is configured to generate an alternating current signal in the first current loop via the current controller, wherein the signal acquisition arrangement is configured to detect a first signal at a predetermined first point of the first current loop, and wherein the evaluation device is configured to generate an evaluation signal depending on the first signal, which depends on the impedance of the first current loop.

[0009] DE 10 2020 119 106 B3 discloses a device for generating a compensation current, wherein a differential current sensing device is provided for measuring the differential current in the supply lines of the phases to a consumer and for generating a differential current measurement signal, the differential current characterizing the leakage currents. A compensation current setpoint signal is determined from the differential current measurement signal, which characterizes the magnitude of the required compensation current.

[0010] One object of the invention is to provide a new device for monitoring a supply network.

[0011] This problem is solved by the subject matter of claim 1.

[0012] A device for monitoring a supply network with live conductors and a protective conductor has a first connection, a second connection, a third connection, a current controller, a current measuring device, and a signal acquisition arrangement, which first connection is connectable to a first live conductor of the supply network, which third connection is connected to a first conductor and is connectable to the protective conductor of the supply network, and which current controller is configured to generate a current flow, which current flow, when the supply network is connected with a first component, flows in at least a first current loop and partially in at least a second current loop, which at least one first current loop includes the supply network, which at least one second current loop does not include the supply network, which device is configured toto generate the current flow with an alternating current signal via the current controller, which signal acquisition arrangement is configured to acquire a first signal at a predetermined first point of the at least one first current loop and to supply a signal acquisition arrangement signal to the evaluation device, which first signal provides first information about the impedance of the at least one first current loop, which signal acquisition arrangement signal depends on the first signal, which current measuring device is configured to acquire a second signal, which second signal provides second information about the first component of the current flow generated by the current controller in the at least one first current loop, and which evaluation device is configured to generate an evaluation signal depending on the signal acquisition arrangement signal and the second signal.which depends on the impedance of at least one first current loop. The current generated by the current controller can flow proportionally in at least one first current loop and in at least one second current loop. Since only the current through the at least one first current loop is relevant for evaluating the impedance of the power grid, the impedance evaluation can be performed more accurately using the second signal, which provides information about the current level. The current level, in turn, is proportional to the influence of the voltage on the impedance. Therefore, the impedance can be analyzed more precisely using the second signal, and improved absolute calculations can be performed. The second signal can either provide information about the first component of the current flow from each of the at least one first current loop, or it can provide information about the first component of the current flow from multiple first current loops.

[0013] According to a preferred embodiment, the current measuring device includes a resistor which is arranged in the at least one first current loop and not in the at least one second current loop, and the current measuring device is configured to detect the first signal via the voltage drop across the resistor. This results in a direct measurement of the relevant current at the appropriate point.

[0014] According to a preferred embodiment, the current measuring device has a first winding, which is arranged in the at least one first current loop and not in the at least one second current loop around the first conductor, in order to detect the current flowing through the first conductor to the third terminal. Here, too, a direct measurement of the relevant current can be carried out at the appropriate point.

[0015] According to a preferred embodiment, the current measuring device has a second winding, which is arranged around the active conductors and is configured to detect the sum of the currents flowing through the active conductors. Such a current measuring device is also referred to as a sum current measuring device, and it is also used to enable compensation of leakage currents. Therefore, the additional use of this potentially present current measuring device reduces the circuit complexity.

[0016] The alternating current signal has at least one first frequency, and the evaluation device is designed to evaluate the current flow in the frequency range of the at least one first frequency when evaluating the second signal. This allows the relevant current flow to be isolated, and in particular, current flow in other frequency ranges caused by leakage currents can be eliminated.

[0017] According to a preferred embodiment, the evaluation device is configured to perform a Fourier analysis of the second signal and generate a frequency spectrum, and, during the evaluation of the second signal, to evaluate the frequency spectrum in the region of at least one first frequency. This enables a comparatively accurate analysis of predefined frequency ranges.

[0018] According to a preferred embodiment, the at least one first current loop comprises a current loop which includes the current controller, the third connection, the supply network, the first connection and again the current controller.

[0019] According to a preferred embodiment, the signal acquisition arrangement is configured to first acquire a signal characterizing the voltage at the first terminal. This type of acquisition requires comparatively little circuitry.

[0020] According to a preferred embodiment, the second terminal can be connected to a second active conductor of the supply network. The at least one first current loop has an additional current loop comprising the current controller, the third terminal, the supply network, the second terminal, and again the current controller. The signal acquisition arrangement is configured to acquire a third signal at a predetermined second point of the additional current loop. This third signal provides third information about the impedance of the additional current loop, and the signal acquisition arrangement signal depends on the first and third signals. In supply networks without a neutral conductor, this device enables advantageous evaluation.

[0021] According to a preferred embodiment, the AC signal has a measurement frequency in the range of 75 Hz to 625 Hz, preferably in the range of 100 Hz to 590 Hz. These measurement frequencies have proven advantageous because interference from mains frequencies is comparatively low.

[0022] According to a preferred embodiment, the current controller is designed as a current regulator. This enables very precise current setting.

[0023] According to a preferred embodiment, the evaluation device is configured to filter the signal from the signal acquisition arrangement using a bandpass filter to cause attenuation in the mains frequency range. This improves the evaluation because the bandpass filter results in strong attenuation in the mains frequency range.

[0024] According to a preferred embodiment, the bandpass filter is designed as an active filter. Active filters can be designed with comparatively sharp cutoff frequencies.

[0025] According to a preferred embodiment, the device is designed to allow connection to a load. Second current loops can occur, particularly with loads.

[0026] According to a preferred embodiment, the device is connected to a consumer.

[0027] Further details and advantageous embodiments of the invention will become apparent from the exemplary embodiments described below and illustrated in the drawings, which are in no way to be understood as limiting the invention, as well as from the dependent claims. It shows Fig. 1 a device for monitoring a supply network comprising a current controller and a signal acquisition arrangement, Fig. 2 the frequency spectrum of a signal acquisition arrangement signal, Fig. 3 the frequency spectrum of the signal acquisition arrangement signal from Fig. 2 after applying a low-pass filter, Fig. 4 a low-pass filter, and Fig. 5 another embodiment of a device for monitoring a supply network comprising a current controller and a signal acquisition arrangement,

[0028] In the following, identical or equivalent parts are designated with the same reference symbols and are usually described only once. The description builds upon itself across figures to avoid unnecessary repetition.

[0029] Fig. Figure 1 shows a device 20 for monitoring a supply network 10.

[0030] The device 20 has a terminal 21 (or 21') with a conductor 51, a terminal 24 (or 24') with a conductor 54, and a protective conductor terminal 25 (or 25') with a conductor 55. The protective conductor terminal 25 is connected to a protective conductor symbol 99, which is also used elsewhere in the circuit as a symbol for a conductive connection with the protective conductor terminal 25.

[0031] The device 20 is connected, by way of example, to a US split-phase power supply network 10, as is commonly used in the USA. Such a power supply network is also referred to as a single-phase three-wire network. The power supply network 10 has a point 13, which is connected via a first AC voltage source 11 to terminal 21 (HOT1) and via an AC voltage source 12 to terminal 24 (HOT2). Point 13 is grounded via an earthing terminal 199 and connected to the protective earth (PE) terminal 25. The AC voltage sources 11 and 12 are, for example, the secondary side of a transformer, and point 13 is a center tap on the secondary side. The conductors 51 and 54 are referred to as live conductors, since the current typically flows through them. In this case, the live conductors 51 and 54 are connected to HOT1 and HOT2, respectively, of the US split-phase power supply network.In a European network, for example, conductors 51 and 54 could be connected to terminals L1 and N respectively.

[0032] For example, a consumer 15 is connected via lines 151, 154, 155 to terminals 21, 24 and 25 or 25', and via lines 152, 153 to additional terminals 22, 23, and can draw power from or be supplied to the supply network 10. Lines 22, 23 can, for example, be used to connect phases L2, L3 in a European three-phase supply network with the active terminals L1, L2, L3, N. The protective earth conductor (PE), however, is not considered an active terminal, as current should not normally flow through it.

[0033] Device 20 has a resistor 60 and a resistor 62. Line 51 is connected via resistor 60 to a point 61, and point 61 is connected via resistor 62 to line 54. A capacitor 63 and 64 are connected in parallel to resistors 60 and 62, respectively. Point 61 is connected via a current controller 44 to a point 42, and point 42 is connected via a resistor 40 and a resistor 240 to terminal 25. Resistors 60 and 62 form a voltage divider.

[0034] A power supply 46 is connected to line 51 and line 54, and the output voltages of the power supply 46 are fed to the current controller 44 via lines 65 and 66. For example, the voltage of the power supply 46 at line 65 is +15 V, and at line 66 it is -15 V.

[0035] An analysis device 28 has a difference former 32 and an evaluation device 30.

[0036] A signal acquisition arrangement 31 is configured, by way of example, to acquire a first signal SIG1 on line 51, to acquire a second signal SIG2 on line 54, and to supply a signal acquisition arrangement signal SIG3 to the evaluation device 30. The signal acquisition arrangement 31 has, by way of example, an adder 67, 68, which is configured to form the signal acquisition arrangement signal SIG3 as the sum signal of the first signal SIG1 and the second signal SIG2. In the exemplary embodiment, the adder 67, 68 has a resistor 67, through which line 51 is connected to a point 69, and a resistor 68, through which line 54 is connected to the point 69. The resistors 67, 68 act as voltage dividers and generate a low potential at point 69 in the case of connection to a US split-phase power supply network. 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.

[0037] Resistor 240 is located closer to terminal 25 than resistor 40, and line 155 branches off from line 55 between resistors 240 and 40. Resistor 240 is connected to line 55 between points 241 and 242, and points 241 and 242 are connected via lines 243 and 244 to a current measuring device 246, which detects the current, for example, by measuring the voltage. The current measuring device 246 outputs a signal SIGI2, which provides information about the current flowing through resistor 240. Alternatively, the current measuring device 246 could measure the current through a winding around line 55, cf. Fig. 5.

[0038] A current measuring device 252 has a winding 251 around the conductors 51, 54, 152, and 153 of terminals 21, 22, 23, and 24 of the live conductors. The winding 251 does not enclose the conductor 55 of the protective conductor terminal 25, as schematically indicated. The current measuring device 252 is configured to generate a signal SIGI2 characterizing a first sum of the currents flowing through the live conductors. This sum corresponds to a differential current and occurs in particular when current does not flow between the live conductor terminals 21, 22, 23, and 24, but rather between one or more of the live conductor terminals 21, 22, 23, and 24 and the protective conductor terminal 25. Such currents arise, for example, from filter capacitors or capacitances. If no leakage currents occur, the differential current or, equivalently, the total current is zero, and no resulting voltage is induced in winding 251.If, on the other hand, leakage currents occur and are not compensated by compensating currents, the differential current is not zero. Therefore, the measured differential current corresponds in magnitude to the current to the protective conductor terminal 25, but possibly with the opposite sign, depending on the winding direction of winding 251.

[0039] Both the current measuring device 252 and the current measuring device 246 contain information about the current flowing through the terminal 25.

[0040] The evaluation device 30 is supplied with the signals SIGI1 and / or SIGI2.

[0041] The evaluation device 30 is connected to point 69 and receives the signal acquisition arrangement signal SIG3 via this point 69.

[0042] The signals SIGI1 and SIGI2 contain, on the one hand, an effect of the current flow generated by the current controller 44 in the form of an alternating current signal with at least a specified frequency, and on the other hand, possibly additional leakage currents that flow via the terminal 25.

[0043] Preferably, the evaluation device 30 is configured to evaluate the proportional current flow in the frequency range of at least one predetermined frequency when evaluating the signals SIGI1 and SIGI2, since this allows the effect of the component of the signals SIGI1 and SIGI2 generated by the current controller 44 to be isolated and separated from the leakage currents. This enables a more precise evaluation.

[0044] Preferably, the evaluation device 30 is configured to perform a Fourier analysis of the signal SIGI1, SIGI2 and to generate a frequency spectrum. During the evaluation of the signal SIGI1, SIGI2, the frequency spectrum can be evaluated in the range of at least one predetermined frequency, and thereby the magnitude of the current generated by the current controller 44 at the predetermined frequency can be determined.

[0045] The differential generator 32 is connected to line 51 via line 71 and to line 54 via line 72. The output signal of the differential generator 32 characterizes the difference U21 - U24 between the voltage U21 at terminal 21 and the voltage U24 at terminal 24 and is supplied to the evaluation device 30 via line 33. For example, a comparator or a subtractor can be used as the differential generator 32. The differential generator 32 can also be designed as a measuring circuit that conditions the mains voltage for the evaluation device 30, both in terms of level and interference.

[0046] The evaluation device 30 has a frequency measuring device 348, which is configured to determine a frequency measurement value f_N_M that characterizes the mains frequency f_N. Preferably, the measurement frequency f_M is determined as a function of the frequency measurement value f_N_M.

[0047] The evaluation device 30 is connected to the current controller 44 via a line 73, and a signal I_S, representing the setpoint for the current to be generated by the current controller 44, can be supplied to the current controller 44 via line 73. Point 42 is connected to the evaluation device 30 via a line 74. Due to the resistor 40, a voltage is present at point 42, which depends on the current generated by the current controller 44. This voltage is applied at point 42 relative to the potential at the protective conductor symbol 99. The resistor 40 thus acts as a current measuring device and detects a measurement signal I_I_M, which characterizes the current I_I generated by the current controller 44 and is transmitted to the evaluation device 30 via line 74.

[0048] The current controller 44 is preferably designed as a current regulator.

[0049] The following are example values ​​for some of the components of the circuit arrangement: Widerstände 60, 62, 67, 68 44 kOhm Kondensatoren 63, 64 1 µF Widerstand 40 510 Ohm How it works

[0050] The current I_I generated by the current controller 44 can flow in a first current loop 81 via the resistor 40, the resistor 240, the terminal 25, the AC source 11, the terminal 21 and the resistor 60 or the capacitor 63 to the current controller 44.

[0051] Since the impedance of capacitor 63 for the measuring current I_I, which is an alternating current, is lower than that of resistor 60, the measuring current I_I flows mainly through capacitor 63. The resistor divider with resistors 60 and 62 creates a virtual neutral conductor, or at least a point of low voltage, in a US split-phase power grid with symmetrical amplitudes and resistances. This allows the current to be easily impressed by the current controller 44.

[0052] Another current loop 84 is possible, in which the current I_I generated by the current controller 44 can flow back to the current controller 44 via the resistor 40, the resistor 240, the terminal 25, the AC source 12, the terminal 24, the resistor 62 or the capacitor 64.

[0053] In other words, the first current loop 81 includes the capacitor 63, whose first terminal is connected towards the first terminal 21 and whose second terminal is connected towards the current controller 44. The resistor 60 is connected in parallel to the capacitor 63.

[0054] Similarly, the second current loop 84 includes the capacitor 64, whose first terminal is connected to the second terminal 24 and whose second terminal is connected to the current controller 44. The resistor 62 is connected in parallel to the capacitor 64.

[0055] A resistor 14 is schematically shown in the supply network 10 between terminal 25 and point 13. While terminals 21 and 24 are usually connected with low resistance via the AC voltage sources 11 and 12, this is not always the case for the protective conductor PE. This can be due to a defective line. Furthermore, there are supply networks 10 in which the protective conductor PE is either not present at all or is connected with high resistance. Since the protective conductor PE at terminal 25 is usually used for grounding the metallic housings of the consumer 15, the protective effect or protection class provided by the grounding cannot be achieved if there is no low-resistance connection between terminal 25 and the protective conductor PE. For this reason, the device 20 is intended to check whether the resistor 14 on the supply network 10 side is low-resistance or high-resistance.This monitoring can be achieved by considering the current flowing in current loops 81 and 84 as a function of resistance 14 and the other resistances 60, 40 and 62, 40. Since resistance 14 is on the supply network side 10, it cannot be measured directly. However, the voltage drop across resistance 60 and 62, as well as the voltage drop across resistance 14, depend on resistance 40. The voltage and current at line 51 and line 54, respectively, provide information about the influence of resistance 14 on the current generated by the current controller 44.

[0056] In the exemplary embodiment, the lines 51 and 54 with the signals SIG1 and SIG2 respectively are connected to each other via the voltage divider from the resistors 67 and 68, and the signal SIG3 at point 69 is supplied to the evaluation device 30.

[0057] A first problem in monitoring the supply network 10 is that, for example, the consumer 15 has an EMC filter with Y-capacitances, which create a capacitive connection between terminal 25 and terminal 21, and between terminal 25 and terminal 24. This means that in current loops 81 and 84, alternating current can also flow in a parallel path via the Y-capacitances. A constant direct current generated by the current controller 44 would not flow through the Y-capacitances, as these only conduct alternating currents or changing direct currents. However, with direct currents, there is the problem that they can lead to a fault current, which would trip a residual current device (RCD) if one is present. Therefore, the currents generated by the current controller 44 must be relatively small.

[0058] This leads to the next problem, since high voltages of several hundred volts can be present on the active conductors 51 and 54, while the current generated by the current controller 44 must be in the milliampere range and therefore only affects the voltage on conductors 51 and 54 in the mV range. This results in a very poor signal-to-noise ratio, and evaluation is difficult.

[0059] Tests have shown that generating a DC signal by the current controller 44 to measure the resistance of the current loops 81, 84 is technically difficult to evaluate. Residual current circuit breakers have a tripping threshold of, for example, 20 mA fault current. Since almost every load 15 generates fault currents, for example, through the Y-capacitances, a current generated by the current controller 44 could at most amount to a few milliamperes.

[0060] Therefore, tests were carried out using an alternating current generated by the current controller 40. The frequency of the supply network is typically 50 Hz or 60 Hz. To minimize the influence of the mains frequency on the measurement, it is advantageous for the measurement frequency to be significantly lower or higher than the mains frequency. At a very low measurement frequency f_M, the risk of a residual current device (RCD) being tripped by the alternating current increases. RCDs trip, for example, if the fault current exceeds a predefined maximum value for two periods of the mains frequency. At frequencies higher than the mains frequency, the fault current caused by the measurement current I_I largely averages out over the individual periods, and tripping of the RCD is avoided. A further effect results from the Y-capacitors, which are provided, for example, in the load 15.The impedance is proportional to the inverse of the frequency of the alternating current. Therefore, the impedance decreases with increasing frequency. Since the current loops 81 and 84 are to run via the supply network 10 and not via the Y-capacitors, it is advantageous for the Y-capacitors to have the highest possible impedance. This ensures that the current I_I flows primarily through the supply network 10. Consequently, a low frequency is also advantageous.

[0061] The analysis reveals that each frequency range has its advantages and disadvantages. The range between 75 Hz and 625 Hz has proven advantageous for measurement, with the range from 100 Hz to 590 Hz being even more preferred. Another point to consider is that the measurement frequency should not be an odd multiple of the mains frequency, as harmonics of the mains frequency can occur at these frequencies. Measurement frequencies in the ranges of 175 ± 23 Hz, 225 Hz ± 23 Hz, 275 ± 23 Hz, 325 Hz ± 23 Hz, and 375 ± 23 Hz have proven particularly advantageous.

[0062] The resistance 14 on the side of the supply network 10 is, for example, 2-3 ohms, and a resistance of 200 ohms or 250 ohms can preferably be assumed as the threshold for a resistance 14 that is too high.

[0063] The signal acquisition arrangement 31 can acquire the first signal SIG1 or the second signal SIG2 at different points of the first current loop 81 or the second current loop 84, respectively. Preferably, these points are located in the region of the device 20 between the side of the current controller 44 facing away from terminal 25 and terminal 21 for signal SIG1, and in the region of the device 20 between the side of the current controller 44 facing away from terminal 25 and terminal 24 for signal SIG2. Signals SIG1 and SIG2 thus characterize the voltage at the first terminal 21.

[0064] The signal acquisition arrangement signal SIG3 is dependent on both signal SIG1 and signal SIG2 by combining signals SIG1 and SIG2 at point 69 and contains information about the impedance of the respective current loops 81 and 84.

[0065] Both signals SIG1 and SIG2 can also be fed to the evaluation device 30 as separate signals and evaluated separately. This allows for the determination of any possible asymmetry of the resistance 14 in the direction of terminal 21 or 24. However, in such a case, the individual evaluation units of the evaluation device 30 must be at least partially duplicated in order to perform the evaluation of the separate signals.

[0066] Measurements and investigations have shown that the current I_I generated by the current controller 44 does not flow exclusively through terminal 25, but a current loop 83 can also be formed via the load 15, in which the current I_I flows from the current controller 44 via the resistor 40, the line 155, the load 15, the line 154, and the capacitor 64 back to the current controller 44. In the load 15, for example, filter capacitors or coils can lead to a possible current flow between lines 154 and 155. If the load 15 is, for example, a charger in a vehicle, the impedance of the load 15 between lines 154 and 155 is usually unknown and not constant.

[0067] In practice, the current generated by the current controller 144 is distributed proportionally among the current loops 81, 84, and 83. The actual current flowing through terminal 25 is therefore less than the current I_I generated by the current controller 144. For a more precise evaluation of the impedance of the current loops 81 and / or 84, it is therefore advantageous to determine the actual current flowing through the respective current loop, i.e., the fraction of the current I_I that flows through the corresponding current loop. As described above, this is possible using the current measuring devices 252 and / or 246. Therefore, the signals SIGI1 and / or SIGI2 are fed to the evaluation device 30. Measurements have shown that by additionally considering the signal from the current measuring devices 252 and / or 246, the accuracy of the evaluation can be improved by up to 20%.

[0068] The evaluation device 30 is configured to generate an evaluation signal OUT, dependent on the signal acquisition arrangement signal SIG3 and the signals SIGI1 and / or SIGI2. This evaluation signal OUT depends on the impedance of the first current loop 81 and / or the second current loop 84. The evaluation signal OUT can either be used internally within the evaluation device 30 or transmitted to other devices. In a vehicle, for example, the evaluation signal OUT can be provided via a CAN bus. Depending on the evaluation signal OUT, the connection to the power supply 10 can be interrupted, and / or an error message can be displayed.

[0069] The evaluation signal OUT can, for example, include one or more of the following information: - Qualitative indication of whether the impedance is within the permissible range or not - Quantitative specification of the impedance of the resistor 14 - Quantitative specification of the total impedance of one or both current loops 81 and 84. - Information based on the measurement signal I_I_M, indicating whether the measurement signal was generated according to the specification.

[0070] When evaluating the signal acquisition device signal SIG3, it is advantageous to consider the effect of the capacitor 63 or 64 and, if applicable, an additional winding in the power supply 10, for example, a secondary winding of the AC voltage sources 11, 12 in a US split-phase power supply network 10. These can lead to a phase shift of the signal acquisition device signal SIG3 relative to the measuring current I_I. Preferably, the device 20 is calibrated.

[0071] Preferably, both the resistance (real part) and the capacitive component (generally: imaginary part) are determined.

[0072] Fig. Figure 2 shows an example of the dynamic range of the signal acquisition system signal SIG3 at point 69. The level of the signal acquisition system signal SIG3 at point 69 is plotted against frequency. This frequency-based level plot can be obtained, for example, by Fourier transformation of the signal acquisition system signal SIG3, and such a Fourier transformation is preferably performed in the evaluation device 30, for example, by an FFT (Fast Fourier Transform). The current controller 44 used a measurement frequency f_M of 300 Hz, and the total capacitance of the Y capacitors was determined to be C. yThe capacitor value of 2 µF was assumed to be relatively large. Furthermore, a voltage asymmetry of 20 Vp between terminals HOT1 and HOT2 was assumed. At the mains frequency f_N, the level is approximately 16 dB, and at the measurement frequency f_M, the level is -20 dB. The level difference between the signal acquisition arrangement signal SIG3 and the mains asymmetry is therefore -36 dB. A good analog-to-digital converter (ADC) has, for example, a resolution of 12 bits. This results in 4096 possible different values. Measuring the signal at point 69 and driving the ADC to the maximum occurring asymmetry of the mains voltage means that the additional effect caused by the current I_I cannot be resolved, or can only be resolved very poorly, with the ADC. Even ADCs with a higher resolution of 24 bits may have resolution difficulties with such a signal-to-noise ratio. Furthermore, such high-resolution analog-to-digital converters are comparatively expensive.

[0073] Fig. Figure 3 shows the dynamic range of a filtered signal SIG3" after the application of a bandpass filter (see Figure 3). Fig. 4) on the signal acquisition system signal SIG3 at point 69. The bandpass filter is designed to allow the frequency range of the signal acquisition system signal SIG3 to pass through within a frequency range (band) around 300 Hz, but to attenuate the signal acquisition system signal SIG3 in the frequency range above and below the measurement frequency f_M. The bandpass filter is designed as an analog bandpass filter and has a level attenuation of -18 dB in the range of the mains frequency f_N. The frequency scale is different from the scale of Fig. 2 shifted, however the network frequency is as in Fig. Example 2: 50 Hz, and the measurement frequency is 300 Hz. The level of the SIG3 signal in the range of the mains frequency f_N has dropped from approximately 16 dB to approximately -3 dB, and the measurement frequency f_M is approximately -21 dB. With a signal-to-phase level difference of -21 dB (or -18 dB), a direct measurement using a standard analog-to-digital converter is possible.

[0074] Fig. Figure 4 shows a bandpass filter 300, which can be used in the evaluation device 30. The signal SIG3 is fed to a point 303 via a resistor 301. Point 303 is connected to GND 99 via a resistor 302 and to the positive input of an operational amplifier 305 via a resistor 304. The output of the operational amplifier 305 is connected to the negative input of the operational amplifier 305 and to a point 307 via a resistor 306. Point 307 is connected to a point 312 via a capacitor 308 and to a point 310 via a capacitor 309. Point 312 is connected to point 310 via a resistor 326, and point 310 is connected to the negative input of an operational amplifier 311. The output of operational amplifier 311 is connected to point 312.Point 312 is connected to point 315 via resistor 313, and point 315 is connected to GND 99 via resistor 314 and to the positive input of operational amplifier 311. Point 312 is connected to point 316 via resistor 327. Point 316 is connected to point 319 via capacitor 317 and to point 320 via capacitor 318. Points 319 and 320 are connected to each other via resistor 328. Point 320 is connected to the negative input of operational amplifier 321, and point 319 is connected to point 322. The output of operational amplifier 321 is connected to point 322, and point 322 is connected to point 324 via resistor 323. Point 324 is connected to the positive input of the operational amplifier 321 and to GND 99 via a resistor 325.At point 322, a signal SIG3' is generated as a result of the bandpass filtering, which has a level corresponding to the diagram of . Fig. 3.

[0075] The bandpass filter 300, for example, has a center frequency of 320 Hz, and the level reduction at a mains frequency f_N of 60 Hz is, for example, -18 dB. Depending on the power supply network, other values ​​can of course be selected.

[0076] The bandpass filter 300 is preferably designed as an active filter. The bandpass filter 300 is preferably of the second order or a higher order, and preferably has an amplifier. A higher-order filter can be created, for example, by combining several lower-order filters (1st and 2nd order).

[0077] Fig. Figure 5 shows a further embodiment of the device 20 for monitoring a supply network 10. In this embodiment, the supply network 10 has at least one phase L1, which is connected to terminal 21, and optionally phases L2 and L3, as well as a neutral conductor N, which is connected to terminal 24. The neutral conductor N typically has a low voltage or a voltage of 0 V.

[0078] The current controller 44 is connected to the line 54 via the resistor 62, and when the supply network 10 is connected, a current loop 84 can flow from the current controller 44 via the resistor 40, the terminal 25, the supply network 10, the terminal 24 and the resistor 62 back to the current controller 44.

[0079] Additionally, a current loop 83 can flow from the current controller 44 via the resistor 40, the line 155, the consumer 15, the line 154 and the resistor 62 back to the current controller 44.

[0080] The current I_I generated by the current controller 44 is thus divided proportionally into a partial current I_PE in current loop 84 and a partial current I_V in current loop 83. Only the partial current I_V in current loop 84 is suitable for measuring the impedance of the supply network 10 via the protective conductor PE. Therefore, it is advantageous, as in Fig. 1. The current measuring device 252 is used to measure the current I_PE flowing through the current loop 84. In the exemplary embodiment, the current measuring device 252 has a winding 253 around the line 55 leading to the terminal 25, wherein the winding 253 is provided between the terminal 25 and the terminal of the line 155 to the consumer 15, in order not to measure the partial current I_V flowing from the current controller 44 via the line 55 and the line 155 to the consumer. However, the current measuring device 252 can also be configured as shown in Fig. 1 or as the current measuring device 246 of Fig. 1 be trained, or several current measuring devices 246, 252 may be provided and evaluated.

[0081] The evaluation of the phase via the difference generator 32 can be carried out as in Fig. 1 described below.

[0082] The neutral conductor N, or line 54, is connected via resistor 68 to point 469. Point 469 is connected via resistor 410 to point 411. Point 411 is connected via resistor 412 to the protective conductor 99 and via resistor 414 to point 69. Point 69 is connected to the evaluation device 30.

[0083] Resistors 68 and 410 on the one hand and resistor 412 on the other hand provide level adjustment for the evaluation device 30, and resistor 414 provides current limiting.

[0084] The signal acquisition arrangement 31 is designed to acquire the first signal SIG1 on line 54 and to supply the signal acquisition arrangement signal SIG3 to the evaluation device 30.

[0085] Measurements have shown that the SIG3 signal exhibits a mains frequency component in practice. This arises from capacitive coupling via the Y-capacitors. By applying the 300 bandpass filter from Fig. The mains frequency component can be reduced by using a bandpass filter (4) or another bandpass filter, and an evaluation can be performed with the evaluation device 30. Fig. 1 - as described.

[0086] Since the supply network 10 usually has a comparatively low-resistance connection between the neutral conductor N and the protective conductor PE, a measurement of further current loops is not necessary, but it can be carried out additionally.

[0087] Naturally, various variations and modifications are possible within the scope of the present invention.

Claims

[1] 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 terminal (21), a second terminal (22), a third terminal (25), a current controller (44), a current measuring device (252; 246) and a signal detection arrangement (31), which first terminal (21) is connectable to a first active conductor (L1; HOT1; N) of the supply network (10), which third terminal (25) is connected to a first line (55) and can be connected to the protective conductor (PE) of the supply network (10), and which current controller (44) is designed to generate a current flow (I_I), which current flow (I_I) flows when the supply network (10) is connected with a first portion (I_PE) in at least one first current loop (81, 84) and proportionally in at least one second current loop (83), which at least one first current loop (81, 84) includes the supply network (10), which at least one second current loop (83) does not include the supply network (10), which device (20) is designed to generate the current flow (I_I) with an alternating current signal via the current controller (44), which signal detection arrangement (31) is designed to detect a first signal (SIG1) at a predetermined first point of the at least one first current loop (81, 84) and to supply a signal detection arrangement signal (SIG1; SIG3) to the evaluation device (30), which first signal (SIG1) has first information about the impedance of the at least one first current loop (81, 84), which signal detection arrangement signal (SIG1; SIG3) is dependent on the first signal (SIG1), which current measuring device (252; 246) is designed to detect a second signal (SIGI1; SIGI2), which second signal (SIGI1; SIGI2) has a second item of information about the first portion of the current flow generated by the current controller (44) in the at least one first current loop (81, 84), and which evaluation device (30) is designed to generate an evaluation signal (OUT) as a function of the signal detection arrangement signal (SIG1; SIG3) and the second signal (SIGI1; SIGI2), which evaluation signal is dependent on the impedance of the at least one first current loop (81, 84), wherein the alternating current signal (I_I) has at least one first frequency, and wherein the evaluation device (30) is designed to evaluate the current flow in the frequency range of the at least one first frequency when evaluating the second signal (SIGI1, SIGI2). [2] Device (20) according to claim 1, wherein the current measuring device (246) comprises a resistor (240), which resistor (240) is arranged in the at least one first current loop (81, 84) and not in the at least one second current loop, and the current measuring device (246) is designed to detect the second signal (SIGI2) via the voltage drop across the resistor (240). [3] Device (20) according to claim 1 or 2, wherein the current measuring device (252) has a first winding (253), which first winding is arranged in the at least one first current loop (81, 84) and not in the at least one second current loop (83) around the first line (55) in order to detect the current (I_PE) flowing through the first line (55) to the third terminal (25). [4] Device (20) according to one of the preceding claims, in which the current measuring device (252) has a second winding (251), which second winding (251) is arranged around the active conductors (L1, L2, L3, N; HOT1, HOT2; L1, N) and is designed to detect the sum current of the currents flowing through the active conductors (L1, L2, L3, N; HOT1, HOT2; L1, N). [5] Device (20) according to one of the preceding claims, in which the evaluation device (30) is designed to carry out a Fourier analysis of the second signal (SIGI1, SIGI2) and to generate a frequency spectrum, and to evaluate the frequency spectrum in the range of the at least one first frequency when evaluating the second signal (SIGI1, SIGI2). [6] Device (20) according to one of the preceding claims, wherein the at least one first current loop (81, 84) comprises a current loop (81) which comprises the current controller (44), the third terminal (25), the supply network (10), the first terminal (21) and again the current controller (44). [7] Device (20) according to claim 6, wherein the signal detection arrangement (31) is designed to detect, as the first signal (SIG1), a signal characterizing the voltage at the first terminal (21). [8] Device (20) according to claim 6 or 7, in which the second terminal (24) is connectable to a second active conductor (N; HOT2; L2) of the supply network (10), in which the at least one first current loop (81, 84) has an additional current loop (84) which comprises the current controller (44), the third terminal (25), the supply network (10), the second terminal (24) and again the current controller (44), and in which the signal detection arrangement (31) is designed to detect a third signal (SIG2) at a predetermined second point of the additional current loop (84), which third signal (SIG2) has third information about the impedance of the additional current loop (81, 84), and in which the signal detection arrangement signal (SIG3) is dependent on the first signal (SIG1) and the third signal (SIG2). [9] Device (20) according to one of the preceding claims, wherein 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. [10] Device (20) according to one of the preceding claims, in which the current controller (44) is designed as a current regulator. [11] 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 effect an attenuation in the range of the mains frequency (f_N), wherein the bandpass filter (300) is preferably designed as an active filter.

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