Method and device for determining the resistive component of the leakage current impedance in an AC power network

Abstract

The invention relates to a method for determining the resistive component of the leakage current impedance (R iso ) of a downstream branch (2) of an alternating current network, the alternating current network having a phase (L), a neutral conductor (N) and a protective conductor (PE). The method comprises the steps of: measuring a differential current I LN between the phase (L) and the neutral conductor (N) by scanning using a differential current sensor; measuring a voltage U between the phase (L) and the neutral conductor (N) or between the phase (L) and the protective conductor (PE) by scanning; correcting a phase shift between the differential current I LN and the voltage U; determining a plurality of individual differential current values I LN,I and a plurality of individual voltage values U i , the differential current values I LN,I being phase-corrected with respect to the voltage values U i ; determining an active power P from the plurality of individual differential current values I LN,I and the plurality of individual voltage values U i ; determining an effective voltage U i using the voltage value U Eff ; and determining the resistive component of the leakage current impedance (R Eff ) using the effective voltage U iso and the active power P.

Description

Technical Field

[0001] The present invention relates to a method and a device for determining the resistive component of the leakage current impedance in an alternating current network. Background Art

[0002] In order to prevent personal injury caused by electrical accidents, it is necessary to inspect electrical devices and facilities regarding insulation resistance and fault current. The insulation resistance R between the active conductors (phase L and neutral conductor N) and the protective conductor PE in an alternating current network and / or the electrical appliances connected thereto iso is an important quality and safety feature. The inspection of the insulation resistance R iso is specified in many standards. The limit value of the insulation resistance R iso is usually higher than 1 MOhm.

[0003] However, the insulation resistance R iso can only be directly measured without network voltage. As a result, the insulation of components arranged behind a switch or a contactor separating all poles cannot be detected. As an alternative to directly measuring the insulation resistance R iso , the differential current measurement method is used during operation, which determines the differential current between the phase L and the neutral conductor N. This differential current roughly corresponds to the leakage current between the active conductors (phase L and neutral conductor N) and the protective conductor PE when the alternating current network is switched on. Due to the system-related capacitive filter elements usually built into the alternating current network and / or the electrical appliances for EMC reasons, the limit value for the maximum allowable differential current in the standard is relatively high, for example 3.5 mA, which corresponds to an AC impedance of only 66 kOhm in a 230 V network. A high differential current results in a high risk. At 3.5 mA, it is far from high impedance. It can be seen from this that the insulation resistance R iso as an indicator of contamination or aging of the electrical appliance cannot be detected as being above 1 MOhm. When determining the insulation resistance R iso by determining only the pure differential current, this limits the test accuracy.

[0004] DE 198 26 410 A1 describes methods and devices for insulation and fault current monitoring in an alternating current network. Here, the differential current between at least two network conductors is detected. The alternating current component of the differential current is detected as a first network variable, and the transformed network voltage between at least two network conductors or between a network conductor and a protective conductor or a neutral conductor is detected as a second network variable. The product of the amplitude of the alternating current component of the differential current and the cosine of the phase angle Φ between the two detected network variables is a measure of the resistive fault current. When the determined product exceeds a certain response value, load shutdown is performed. However, the provisions for resistive fault current in DE 198 26 410 A1 only apply to sinusoidal voltages and currents.

[0005] US 6,922,643 B2 also shows methods and devices for determining fault current in an alternating current network.

[0006] DE 103 55 086 A1 describes a method for determining the ohmic insulation resistance of a grounded, single-phase or polyphase, operating and working alternating current network, in which in particular the differential current is measured and evaluated.

[0007] EP 3 136 115 A1 discloses devices and methods for determining the resistive component of the leakage current impedance. For this purpose, the voltage between the phase and neutral conductors, the differential current, the active power, and the effective voltage are determined. No discussion is made of the phase correction between the voltage and the differential current.

[0008] EP 2 571 128 A2 describes an electrical monitoring device and a method for ensuring the protection function of a fault current safety device. The monitoring device is connected in series with the fault current safety device. The differential current is detected by measuring the current transformer circuit in the monitoring device, and the differential current is evaluated by an evaluation unit in the monitoring device. If a functionally hazardous residual current is identified, the evaluation unit generates a shutdown signal.

[0009] US 2003 / 0112015 A1 discloses devices and methods for determining the resistive component of the leakage current impedance. Here, the voltage and the differential current are measured. Fourier analysis is performed on the voltage and the differential current. Using the third harmonic, the phase between the voltage and the differential current is calculated, the active power is calculated, and finally the resistive component of the leakage current impedance is calculated.

[0010] DE 10 2015 218 911 A1 describes a fault current circuit breaker for an electrical circuit. If a first differential current limit value is exceeded, the electrical circuit is interrupted by a tripping unit. Summary of the Invention

[0011] The present invention is based on the object of providing a method which can improve insulation and fault current monitoring. Another object of the present invention is to provide a device which can improve insulation and fault current monitoring.

[0012] This object is achieved by the subject matter of the present invention. Advantageous embodiments of the method according to the present invention are the subject matter of the present invention and emerge from the following description of the present invention. The device according to the present invention is described in the present invention.

[0013] Accordingly, a method for determining the resistive component of the leakage current impedance to a downstream branch of an alternating current network having a phase conductor, a neutral conductor and a protective conductor is described. The method comprises the following steps:

[0014] - Measuring the differential current I between the phase conductor and the neutral conductor by scanning using a differential current sensor LN ,

[0015] - Measuring the voltage U between the phase conductor and the neutral conductor or between the phase conductor and the protective conductor by scanning,

[0016] - Correcting the phase shift between the differential current I LN and the voltage U,

[0017] - Determining a number of individual differential current values I LN,i and a number of individual voltage values U i , wherein the differential current values I i are phase-corrected with respect to the voltage values U LN,i ,

[0018] - Determining the active power P from the number of individual differential current values I LN,i and the number of individual voltage values U i ,

[0019] - Using the voltage value U i to determine the effective voltage U Eff , and

[0020] - Using the effective voltage U Eff and the active power P to determine the resistive component of the leakage current impedance.

[0021] Measuring the differential current I LN and the voltage U by scanning also enables digital detection of the active power of the leakage current. Accordingly, the resistive component of the leakage current impedance can also be determined for a non-sinusoidal network voltage and a non-sinusoidal current.

[0022] When measuring the differential current I LNAt that time, individual differential current scan values are measured at mutually predetermined time intervals, and when measuring the voltage U by means of a scan, individual voltage scan values are measured at mutually predetermined time intervals.

[0023] The voltage U is measured between the phase and neutral conductor by means of a scan (i.e., the voltage U is measured LN ). Alternatively, the voltage U is measured between the phase and protective conductor by means of a scan (i.e., the voltage U is measured LPE ).

[0024] The correction of the phase shift is preferably carried out digitally.

[0025] According to one embodiment of the method, the AC power network is a TN AC power network. Alternatively, the AC power network can also be a TT AC power network or an IT AC power network.

[0026] According to another embodiment of the method, in order to adjust the device for determining the resistive component of the leakage current impedance, first the value for correcting the phase shift is determined by connecting a downstream branch with a purely capacitive load, a purely inductive load or a purely resistive load to the AC power network. Then, the voltage U and the differential current I are determined by means of this downstream branch LN . Advantageously, by means of such a downstream branch with a purely capacitive load, a purely inductive load or a purely resistive load, the value for the phase shift can be determined, which can be used in a later measurement for correcting the downstream branch to be measured.

[0027] According to another embodiment of the method, when measuring the differential current I by means of a scan LN , individual differential current scan values are measured. When measuring the voltage U by means of a scan, individual voltage scan values are measured. In addition, a time differential current curve is obtained from the interpolation of the differential current scan values, and a time voltage curve is obtained from the interpolation of the voltage scan values in order to improve the correction of the phase shift between the differential current I LN and the voltage U. Advantageously, the phase shift can be accurately determined by means of the interpolation of the differential current samples and the interpolation of the voltage samples.

[0028] According to another embodiment of the method, when measuring the differential current I by means of a scan LN , the differential current sensor includes a compensating conductor. Thereby, the error of the differential current sensor is compensated by means of the compensating conductor. For this purpose, the compensating conductor, the phase and the neutral conductor pass through the core of the compensating conductor. The compensating conductor can be used to compensate for the fact that the phase and the neutral conductor do not pass through the core exactly symmetrically. Thus, the compensating conductor compensates for the asymmetry of the unit composed of the core, the phase and the neutral conductor. For this purpose, a compensating current proportional to the current flowing through the phase is sent through the compensating conductor.

[0029] According to another embodiment of the method, the current flowing through the compensating conductor is proportional to the current flowing through the phase or neutral conductor. Therefore, a compensating circuit for causing current to flow through the compensating conductor can be easily constructed. Then, the current flowing through the phase or neutral conductor only has a constant factor.

[0030] According to another embodiment of the method, a factor Kp is calculated by measuring the variable current of the phase and / or the variable current of the neutral conductor, and for each measured differential current value I LN,i the value Kp*I is subtracted LN,i , to compensate for the error of the differential current sensor. Therefore, the compensation of the error of the differential current sensor is performed digitally. Preferably, the variable current of the measured phase, or the variable current of the measured neutral conductor and the differential current I LN are detected. Then the differential current I LN is corrected digitally using the current of the phase (or the current of the neutral conductor). The factor Kp is calculated from the variable current of the measured phase (or the variable current of the measured neutral conductor). Then for each measured differential current value I LN,i , the value Kp*I is subtracted LN,i .

[0031] According to another embodiment of the method, if the resistance component of the leakage current impedance drops below a predetermined value, the AC power network is turned off and / or a message is sent to a higher-level system. The lower the resistance component of the leakage current impedance, the higher the leakage current can be. Since a high leakage current can be dangerous, it is not desirable for the resistance component of the leakage current impedance to be too low. Therefore, if the resistance component of the leakage current impedance is too low, the AC power network can be turned off. In this context, "turning off" can mean that the AC power network is turned off or the AC power network is completely disconnected from the downstream branch on all poles.

[0032] The higher-level system should be understood to mean, for example, a cloud system or a monitoring system. A cloud system is a system that can be accessed via the Internet. A monitoring system is a local system suitable for monitoring individual parameters.

[0033] As an alternative to, or in addition to, the resistance component of the leakage current impedance, other network parameters can also be monitored. If the detected other network parameters are exceeded or not reached, a message can be sent to a higher-level system and / or the AC power network can be turned off. For example, the other network parameter can be the differential current I LN .

[0034] Furthermore, a device is provided for determining the resistive component of the leakage current impedance of a downstream branch to an alternating current network having a phase, a neutral conductor, and a protective conductor. The device includes the following components: a voltage sensor adapted to measure the voltage U between the phase and the neutral conductor or between the phase and the protective conductor by scanning; a differential current sensor adapted to measure the differential current I between the phase and the neutral conductor by scanning LN ; and an evaluation unit adapted to correct the phase shift between the differential current I LN and the voltage U, adapted to determine a number of individual differential current values I LN,i and a number of individual voltage values U i , where the differential current values I i are phase-corrected with respect to the voltage values U LN,i , adapted to determine the active power P from the number of individual differential current values I LN,i and the number of individual voltage values U i , adapted to determine the effective voltage U i using the voltage values U Eff , and adapted to determine the resistive component of the leakage current impedance using the effective voltage U Eff and the active power P.

[0035] Advantageously, the device is suitable for performing the method.

[0036] According to an embodiment of the device, the differential current sensor includes a core and a compensating conductor. Here, the phase, the neutral conductor, and the compensating conductor pass through the core. Due to the asymmetric arrangement of the phase and the neutral conductor with respect to the core, there may be a symmetry error in the differential current measurement. This symmetry error can be compensated using the compensating conductor. Thus, the compensating conductor compensates for the asymmetry of the unit composed of the core, the phase, and the neutral conductor. For this purpose, a compensating current proportional to the current flowing through the phase is sent through the compensating conductor.

[0037] Alternatively, the error of the differential current sensor can also be compensated digitally. In this case, no compensating conductor is required.

[0038] According to another embodiment of the device, the device includes a monitoring system connected to the evaluation unit to monitor the resistive component of the leakage current impedance. The monitoring system can display the resistive component of the leakage current impedance so that the user can decide whether the alternating current network should be switched off. As an alternative or in addition, the monitoring system can also electronically check the resistive component of the leakage current impedance and independently make a decision on whether the alternating current network should be switched off.

[0039] Additionally, the device can alternatively or additionally forward the measurement data to a cloud system for analysis and processing.

[0040] In addition, a distribution box is provided that includes at least one device as described above. One or more than one device can be very easily installed, clamped or inserted into the distribution box.

[0041] At least one device measures the network parameters differential current I LN , voltage U and insulation resistance (i.e., the resistance component of the leakage current impedance R iso ). Here, the distribution box can measure other network parameters. Such network parameters are, for example, the active power of the electrical appliance and the current of the electrical appliance. The distribution box can also include an energy meter. Additionally, current measurement of the neutral conductor using harmonic analysis and energy analysis can provide information related to arc faults.

[0042] According to one embodiment of the distribution box, at least one device is designed as a terminal block. Here, the terminal block can be a flat terminal block. A number of terminal blocks can be arranged in a larger quantity on the mounting rail. For this purpose, the distribution box can include a mounting rail. Among other things, the terminal block can also be used for the detachable connection or connection of wires, strands and lines within the distribution box.

[0043] According to another embodiment of the distribution box, the distribution box includes at least one other device. In this case, the measured values of at least one device are exchanged with at least one other device. The distribution box is advantageously suitable for enabling the exchange of measured values between devices. Advantageously, it is not necessary to perform the same measurement again in each individual device.

[0044] The embodiments and features described for the proposed method apply accordingly to the proposed device and the proposed distribution box, and vice versa.

[0045] Other possible implementations of the present invention also include combinations of features not explicitly mentioned above or below. Individual aspects can also be added as improvements or additions to the various basic forms of the present invention. Description of the Drawings

[0046] The present invention will be explained in more detail below with reference to the drawings. These are shown as:

[0047] Figure 1 is a schematic diagram of a device for determining the resistance component of the leakage current impedance of a downstream branch of a TN alternating current network,

[0048] Figure 2 is a flowchart of a method for determining the resistance component of the leakage current impedance of a downstream branch of a TN alternating current network,

[0049] Figure 3 is Figure 1 a schematic diagram of the differential current sensor shown in

[0050] Figure 4 is Figure 3 a block diagram of a differential current sensor as shown in

[0051] Figure 5 is a circuit diagram for controlling Figure 3 a compensating conductor of the differential current sensor as shown in

[0052] In the drawings, identical or functionally identical elements are provided with the same reference numerals. It should also be noted that the representations in the drawings are not necessarily to scale. DETAILED DESCRIPTION

[0053] Figure 1 shows a schematic diagram of a device 1 for determining the resistive component of the leakage current impedance R iso to a downstream branch 2 of a TN alternating current network 3. The TN alternating current network 3 has a phase L, a neutral conductor N, and a protective conductor PE.

[0054] The device 1 includes a voltage sensor 4, a differential current sensor 5, and an evaluation unit 6. The voltage sensor 4 measures the voltage U LN between the phase L and the neutral conductor N. Alternatively, the voltage sensor 4 can also measure the voltage U LPE between the phase L and the protective conductor PE.

[0055] The active conductor phase L and the neutral conductor N pass through the differential current sensor 5. The differential current sensor 5 adds the current in the phase L and the current in the neutral conductor N. If no leakage current flows, the sum is zero. When there is a leakage current, a part of the current does not flow back through the neutral conductor N. Therefore, the differential current I LN between the phase L and the neutral conductor N is measured.

[0056] The evaluation unit 6 is used to correct the phase shift between the differential current I LN and the voltage U LN ; to determine a number of individual differential current values I LN,i and a number of individual voltage values U LN,i , where the differential current values I LN,i are phase-corrected with respect to the voltage values U LN,i ; to determine the active power P from the number of individual differential current values U LN,i and the number of individual voltage values U LN,i ; to determine the effective voltage U LN,i using the voltage values U Eff ; and to determine the resistive component of the leakage current impedance R Eff using the effective voltage U iso and the active power P.

[0057] If the resistance component of the leakage current impedance R iso is less than a limit value of, for example, 1 MOhm, the downstream branch 2 can be disconnected (completely) from the TN AC power network 3 at all poles by means of a switch ( Figure 1 not shown in the figure).

[0058] The downstream branch 2 includes a first branch having a resistance R iso . This first branch results in a purely resistive leakage current. The downstream branch 2 also includes a second branch having a capacitance C1. This second branch results in a purely capacitive leakage current. The downstream branch 2 also includes a third branch having an inductance L1, a resistance R1, a capacitance C3, and a capacitance C2. This third branch results in a leakage current, where the resistance R1 generates a resistance component. However, this current is not detected in a DC insulation resistance measurement because it is decoupled via the capacitance C2 in the DC measurement method. This example shows that the AC measurement method can specify a resistance value, which, however, does not result in a lower insulation resistance value in the DC measurement method.

[0059] By detecting the resistance component of the leakage current impedance R iso to the downstream branch 2 of the TN AC power network 3, the insulation of the downstream branch 2 in the operating state can be evaluated. The measurement results are distorted by the resistance components present in series with the capacitance components. These are also measured but not taken into account when determining the insulation resistance. However, resistance components (see resistance R1) in series with a capacitance (see capacitance C2), which significantly affect the result of the typical insulation resistance limit value of 1 MOhm, are not common.

[0060] The device 1 can include a monitoring system ( Figure 1 not shown in the figure) connected to the evaluation unit 6. The monitoring system can be used to monitor the resistance component of the leakage current impedance R iso . That is, the resistance component of the leakage current impedance R iso can be monitored manually and / or by machine using the monitoring system.

[0061] Furthermore, the distribution box can include a number of devices 1. Here, the device 1 can be designed in particular as a junction box. Additionally, the individual devices can be designed in such a way that they exchange individual measurement values with another device 1 (i.e., the measurement values from one device 1 are transmitted to another device 1).

[0062] Figure 2 A flowchart of a method for determining the resistance component of the leakage current impedance R iso to the downstream branch 2 of the TN AC power network 3 is shown.

[0063] In a first alternative step S1, the downstream branch with a purely capacitive load is connected to the TN AC power network 3. Then, the voltage U is measured between the phase L and the neutral conductor NLN In addition, a differential current I is measured between the phase L and the neutral conductor N. LN By comparing the phase curve of the voltage U LN with the phase curve of the differential current I LN , the value of the phase shift of the voltage U LN relative to the differential current I LN can be determined. Alternatively, a downstream branch with a purely inductive load or a purely resistive load can also be connected. Other adjustment options are also conceivable, such as using a dual-channel oscilloscope.

[0064] In the second step S2, instead of the downstream branch with a purely capacitive load, the downstream branch 2 to be measured is connected to the TN AC power network 3. In addition, a voltage U is measured between the phase L and the neutral conductor N. LN Furthermore, a differential current sensor 5 is used to measure the differential current I between the phase L and the neutral conductor N. LN Here, the voltage U LN and the differential current I LN are both measured by scanning. Thus, a digitized voltage curve and a digitized differential current curve are obtained.

[0065] As Figures 3 to 5 shown, the differential current I LN can be measured, for example, with a differential current sensor 5.

[0066] In the third step S3, the phase shift between the differential current I LN determined in the second step and the voltage U LN determined in the second step is corrected. This is done, for example, by correcting the phase of the differential current I LN determined in the second step with the value of the phase shift determined in the first step. This correction is preferably done digitally.

[0067] In the fourth step S4, a number of individual differential current values I LN,i and a number of individual voltage values U LN,i are determined. As described above, the differential current values I LN,i have been phase-corrected relative to the voltage values U LN,i . In summary, the number of n values in each case is determined.

[0068] In the fifth step S5, the active power P is determined. In principle, the following formula is used to calculate the active power:

[0069]

[0070] Here, T is the duration of a network cycle. In particular, at least a quarter of the period is used as the integration time. Preferably, the integration is carried out over one or several network cycles. In the present case, the following formula is used to determine the active power P from a number of individual residual current values I LN,i and a number of individual voltage values U LN,i :

[0071]

[0072] In the sixth step S6, the following formula is used to determine the effective voltage U LN,i using the voltage value U Eff :

[0073]

[0074] In the seventh step S7, the following formula is used to determine the resistive component of the leakage current impedance R Eff using the effective voltage U iso and the active power P

[0075]

[0076] Here, the resistive component of the leakage current impedance R iso corresponds approximately to the insulation resistance of the downstream branch 2 and is thus a measure of the insulation quality of the downstream branch 2

[0077] In another step, if the resistive component of the leakage current impedance R iso drops below a predetermined value, the TN alternating current network 3 can be switched off

[0078] The correction of the phase shift between the differential current I LN and the voltage U LN can be improved by determining the voltage curve by interpolation from the individual voltage scan values and by determining the differential current curve by interpolation from the individual differential current scan values. The phase shift of the curves determined in this way can be determined better

[0079] Figure 1 The TN alternating current network 3 shown has a phase L. Alternatively, the TN alternating current network 3 can also have two or three phases L. In this case, the resistive component of the leakage current impedance R iso can be determined separately for each phase L

[0080] Figure 3 shows Figure 1Schematic diagram of the differential current sensor 5 shown in. The differential current sensor 5 includes a core 7 and a compensation conductor 8. The phase L, the neutral conductor N, and the compensation conductor 8 pass through the core 7. In particular, the phase L, the neutral conductor N, and the compensation conductor 8 can each be wound around the core 7 a number of times. The core 7 can be designed as a closed, particularly circular structure with a through-hole 9. The differential current ILN can be detected using a measuring winding 10.

[0081] The error of the differential current sensor 5 can be compensated using the compensation conductor 8. The error is caused by the imperfect symmetry of the phase L and the neutral conductor N with respect to the core 7. This asymmetry error can be compensated using the current flowing through the compensation conductor 8.

[0082] In addition, the differential current sensor 5 can include an ammeter 11 and a control unit 12. The current intensity measured by the ammeter 11 is particularly in the range of 0 to 20 A. However, the current intensity can also be higher than 20 A. The current signal of the phase L is measured using the ammeter 11. The ammeter 11 is connected to the control unit 12 such that the control unit 12 can further process the current signal. The control unit 12 controls the current flowing through the compensation conductor 8 to compensate for the asymmetry error.

[0083] In particular, the current flowing through the compensation conductor 8 can be proportional to the current flowing through the phase L.

[0084] Alternatively, the current of the neutral conductor N can also be measured using the ammeter 11 to compensate for the asymmetry error.

[0085] In addition, as will be further described below, the compensation of the asymmetry error can also be carried out digitally alternatively.

[0086] Figure 4 Shows Figure 3 The block diagram of the differential current sensor 5 shown in. The current measured using the ammeter 11 can be fed into the differential current sensor 5 together with the phase L and the neutral conductor N via the control unit 12 and the compensation line 8. The measured differential current I LN can be forwarded via an amplifier circuit 13 and an analog-to-digital converter 14.

[0087] Due to the asymmetric structure of the differential current sensor 5, an error linearly proportional to the current flowing in the circuit appears. The linear error can be compensated analogously using the compensation line 8 by appropriate amplification feedback of the current signal of the ammeter 11 in the sensor circuit.

[0088] Figure 5 Shows for controlling Figure 3Circuit diagram of the compensation conductor 8 of the differential current sensor 5 shown. The phase L, the circuit diagram, the circuit diagram 15 for the galvanometer 11, the circuit diagram 16 for the control unit 12, the shunt 17 for the current measurement of the galvanometer 11, and the connector 18 for the compensation conductor 8 are shown. Using an amplifier circuit and a voltage divider, the current signal of the galvanometer 11 is appropriately amplified for compensation. The connector 18 is connected to the compensation conductor 8.

[0089] Since the phase L and the neutral conductor N form an electrical consumer circuit, the current can also be measured alternatively (instead of the phase L) at the neutral conductor N.

[0090] Alternatively, the compensation of the asymmetry error of the differential current sensor 5 can also be implemented digitally. For this purpose, the measured variable current of the phase L (or the current of the neutral conductor N) and the differential current I LN are detected. Then the current of the phase L is used to digitally correct the differential current I LN . For example, the factor Kp is calculated from the measured variable current of the phase L. For each measured differential current value I LN,i , the value Kp * I LN,i is subtracted.

[0091] List of reference numerals:

[0092] 1 Device

[0093] 2 Downstream branch

[0094] 3 TN AC power network

[0095] 4 Voltage sensor

[0096] 5 Differential current sensor

[0097] 6 Evaluation unit

[0098] 7 Core

[0099] 8 Compensation conductor

[0100] 9 Through hole

[0101] 10 Measuring winding

[0102] 11 Galvanometer

[0103] 12 Control unit

[0104] 13 Amplifier circuit

[0105] 14 Analog-to-digital converter

[0106] 15 Circuit diagram

[0107] 16 Circuit diagram

[0108] 17 Shunt

[0109] 18 Connector

[0110] Phase L

[0111] N Neutral Conductor

[0112] PE Protective Conductor

[0113] R iso Resistance Component of Leakage Current Impedance

Claims

1. A method for determining the resistive component of the leakage current impedance (R iso ) to a downstream branch (2) of an alternating current network, the alternating current network having a phase (L), a neutral conductor (N) and a protective conductor (PE), the method Comprising the following steps: Using a differential current sensor (5), the differential current I between the phase (L) and the neutral conductor (N) is measured by scanning LN ; Measuring the voltage U between the phase (L) and the neutral conductor (N), or between the phase (L) and the protective conductor (PE) by scanning; Correct the phase shift between the differential current I LN and the voltage U; Determine a plurality of individual differential current values I LN,i and a plurality of individual voltage values U i , wherein the differential current value I LN,i is phase-corrected with respect to the voltage value U i ; From the plurality of individual differential current values I LN,i and the plurality of individual voltage values U i , determine the active power P; Using the voltage value U i to determine the effective voltage U Eff ; and Using the effective voltage U Eff and the effective power P to determine the resistance component of the leakage current impedance (R iso ).

2. The method according to claim 1, wherein, The alternating current network is a TN alternating current network (3).

3. The method according to claim 1 or 2, wherein, In order to adjust the device (1) for determining the resistive component of the leakage current impedance (R iso ), first, a value for correcting the phase shift is determined by connecting a downstream branch (2) having a purely capacitive load, a purely inductive load, or a purely resistive load to the AC power network, and then the voltage U and the differential current I LN are determined using this downstream branch (2).

4. The method according to claim 1 or 2, wherein, When measuring the differential current I by scanning LN individual differential current scan values are measured, when measuring the voltage U by scanning individual voltage scan values are measured, a time differential current curve is obtained by interpolation of the differential current scan values, and a time voltage curve is obtained by interpolation of the voltage scan values to improve the correction of the phase shift between LN the differential current I and the voltage U.

5. The method according to claim 1 or 2, wherein, When measuring the differential current I by scanning LN the differential current sensor (5) includes a compensation conductor (8), and wherein the error of the differential current sensor (5) is compensated by using the compensation conductor (8).

6. The method according to claim 5, wherein, The current flowing through the compensation conductor (8) is proportional to the current flowing through the phase (L) or the neutral conductor (N).

7. The method according to claim 1 or 2, characterized in that, Compensate for the error of the differential current sensor (5) by calculating a factor Kp from the measured varying current of the phase (L) and / or from the measured varying current of the neutral conductor (N), and wherein, for each measured differential current value I LN,i , subtract the value Kp*I LN,i .

8. The method according to claim 1 or 2, wherein, If the resistance component of the leakage current impedance (R iso ) drops below a predetermined value, the AC power network is turned off and / or a message is sent to a higher-level system.

9. A device (1) suitable for determining the resistive component of the leakage current impedance (R iso ) to a downstream branch (2) of an alternating current network by using the method according to any one of claims 1 to 8, the alternating current network having a phase (L), a neutral conductor (N) and a protective conductor (PE), the device Comprising: A voltage sensor (4) adapted to measure the voltage U between the phase (L) and the neutral conductor (N), or between the phase (L) and the protective conductor (PE) by scanning; Differential current sensor (5), adapted to measure the differential current I between said phase (L) and said neutral conductor (N) by scanning LN ; and An evaluation unit (6) is adapted to evaluate the differential current I LN and the phase shift between the voltage U and is suitable for determining several individual differential current values ​​I LN,i and several individual voltage values ​​U i , applies to the differential current values ​​I LN,i and the several individual voltage values ​​U i Determine the effective power P for the voltage value U i To determine the effective voltage U Eff , and is suitable for utilizing the effective voltage U Eff and the effective power P to determine the leakage current impedance (R iso ) of the resistance component, wherein the differential current value I LN,i Relative to the voltage value U i is phase corrected.

10. The device according to claim 9, wherein, The differential current sensor (5) comprises a core (7) and a compensation conductor (8), and wherein the phase (L), the neutral conductor (N) and the compensation conductor (8) pass through the core (7).

11. A distribution box comprising at least one device (1) according to claim 9 or 10.

12. The distribution box according to claim 11, wherein, The device (1) is designed as a junction box.

13. The distribution box according to claim 11 or 12, wherein, The distribution box comprises at least one other device and exchanges at least one measured value of the device (1) with the at least one other device.

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