Fault current monitoring device and method

Abstract

The invention relates to the process of monitoring fault currents in an electric low-voltage current circuit for alternating currents. The level of a differential current (IΔ1, IΔ2) of two conductors of the low-voltage current circuit is ascertained, and the level of the voltage (UL1N, UL2N) of the two conductors of the low-voltage current circuit is ascertained. A differential active current (IΔ,WIRK) or a differential reactive current (IΔ, BLIND) is ascertained from the level of the voltage and the level of the differential current, and the level of the differential active current or the differential reactive current is displayed.

Description

[0001]202312391 1 Description Residual current monitoring device and method Regardless of the grammatical gender of a particular term, persons with male, female, or other gender identity are included. The invention relates to the technical field of a residual current monitoring device for monitoring the level of residual currents in an electrical low-voltage AC circuit, and to a method for residual current monitoring of an electrical low-voltage AC circuit. The term residual current monitoring device refers to low-voltage residual current monitoring devices. These are also referred to as residual current monitoring devices (RCM devices). With this residual current monitoring device (RCM device), in particular operational,Residual currents are measured and displayed (monitored). This is used to monitor (earth) fault currents in a low-voltage AC circuit or, in general, in an electrical system. Residual current monitoring devices display the measured residual currents in various ways. Low voltage refers to voltages up to 1000 volts AC or 1500 volts DC. Low voltage refers specifically to voltages greater than extra-low voltage, with values ​​of 50 volts AC or 120 volts DC. Low-voltage circuits refer to circuits for currents up to 6300 amperes, more specifically for currents up to 1600 amperes, 1200 amperes, 630 amperes, 125 amperes, 63 amperes, 40 amperes, 32 amperes, 16 amperes, 10 amperes, or 6 amperes. The current values ​​mentioned refer in particular to rated currents (formerly nominal and / or breaking currents).i.e., currents that the circuit or a residual current monitoring device can carry continuously, i.e., without damage, under standardized conditions (such as 202312391 2 connection cross-sections of the copper conductors and their length) at a defined ambient temperature (such as 40°C). Such conditions are specified in relevant product standards (e.g., DIN EN 60947-2 or 60898-1). This means, colloquially, the maximum current that is normally carried through the circuit or at which the electrical circuit is usually interrupted, such as a miniature circuit breaker or a power switch. Residual current monitoring devices are used primarily for rated current ranges of or up to 16, 25, 32, 40, 63, 80, or 125 amperes. Residual current monitoring devices for electrical low-voltage AC circuits or systems,are generally known. Residual current monitoring devices determine the current sum (i.e., a total current or, depending on the current direction / power flow direction, a differential current) between two or more conductors in an electrical circuit, which is normally zero. The magnitude of the current sum / differential current is displayed in order to monitor it. Almost all previous residual current monitoring devices have a summation current transformer, the primary windings of which are formed by the conductors of the circuit and the secondary winding of which outputs the current sum or the differential current or an equivalent of the current sum / differential current, e.g., in the form of a voltage (or current), which is used directly or indirectly to display the magnitude. For this purpose, two or more conductors, usually forward and return conductors or phase conductors (= outer conductors) and neutral conductors in a single-phase alternating current network,All three phase conductors (= outer conductors) or all three phase conductors (= outer conductors) and the neutral conductor in a three-phase alternating current network are passed through a current transformer, usually having a ring-shaped core made of ferromagnetic material. Only the differential current, i.e., a current that differs from the forward and return current, from the conductors is converted (or transferred to the secondary winding). The sum of the currents in an electrical circuit is usually zero. This allows the magnitude of a fault current to be determined. If, for example, a current flows to earth on the energy sink side or the consumer side, this is referred to as a fault current (or leakage current to earth). This is the case, for example,when a person touches a live phase conductor. In this case, this current to earth is referred to as a fault current. In contrast, electrical equipment (such as power supplies or frequency converters) can also discharge a current to earth due to, for example, so-called Y capacitors. This current is typically referred to as a leakage current. A fault occurs, for example, when there is an electrically conductive connection from a phase conductor or outer conductor of the electrical circuit to earth. For example, when a person touches the phase conductor. In this case, part of the electrical current does not flow back via the neutral conductor or neutral conductor as usual, but rather via the person and the earth. This fault current can now be detected using the summation current transformer.because the recorded sum of incoming and returning current is not equal to zero. The main function of residual current monitoring devices is to monitor electrical systems with regard to their residual current behavior. In this way, emerging residual currents can be detected and eliminated at an early stage, whereby early detection and planned elimination can ensure high system availability. 202312391 4 In general, operational (technically caused) leakage currents (especially at the mains frequency (fundamental frequency) (e.g., 50 Hz in Europe)) and fault currents (e.g., caused by people) cannot be distinguished. The response of a residual current monitoring device is the same for both (operational, technically caused leakage currents or fault currents caused by people). When using electronic equipment,which often use capacitors connected to the protective conductor for interference suppression (EMC interference suppression) (this EMC measure is also referred to in the specialist literature as a Y capacitor), unwanted (technically caused) fault currents (leakage currents) can occur. The object of the present invention is to improve a residual current monitoring device. More specifically, to enable a distinction between fault currents caused, in particular, by people or insulation faults and technically caused fault currents (leakage currents). This object is achieved by a residual current monitoring device with the features of patent claim 1 and a method with the features of patent claim 15. According to the invention, a residual current monitoring device for monitoring fault currents for electrical low-voltage AC circuits is proposed,comprising: - a housing with at least one first input for connecting a first external unit, wherein the external unit (external, i.e. outside the housing): (brackets related to the first external unit) a differential current sensor unit for determining the level of a differential current of a (first) conductor pair, in particular of a (first) low-voltage circuit, wherein the (first) conductor pair in particular has a phase conductor and a neutral conductor (alternatively two phase conductors), and a voltage sensor unit for determining the level of a 202312391 5 voltage of the (first) conductor pair, that the residual current monitoring device receives the level of a (first) differential current and the level of a (first) voltage by means of the first input, - an internal or external display unit (particularly suitable for displaying the level of the differential current), - a control unit,which is connected to the first input and the display unit, - that the residual current monitoring device, in particular the control unit, is designed such that a (first) differential active current or (first) differential reactive current of the first input is determined from the obtained level of the (first) differential current and level of the (first) voltage of the first input, that the level of the (first) differential active current or (first) differential reactive current of the first input is displayed on the display unit. This means that the (first) differential active current or (first) differential reactive current of the first input is displayed, for example, on an internal display unit or (or / and) reported to an external display unit and displayed there. Differential active current refers to the active current component in the differential current, i.e., the ohmic current component (real component) in the differential current, i.e., the current component,which, together with the voltage, results in active electrical power. Active power is the electrical power available for conversion into other power (e.g., mechanical, thermal, or chemical). It must be distinguished from reactive power, which cannot be used for this conversion. Furthermore, terms such as active power, reactive power, or apparent power are generally known from the fundamentals of AC voltage technology. An ohmic resistor as a load or consumer converts its absorbed power completely into heat. This is called active power. This power is expressed in the unit watt (W). If a consumer has inductive and capacitive components in addition to the ohmic resistance, a time shift occurs between the temporal (especially sinusoidal) course of current and voltage.also called phase shift. In addition to the active power, there is therefore also reactive power (volt-amperes reactive (VAr)), which is not converted into heat. Instead, the reactive power is shifted back and forth at twice the frequency of the alternating voltage. This reactive power is also referred to as oscillating power or displacement reactive power. This type of reactive power should not be confused with the so-called distortion reactive power, which in turn is caused by different frequency components in current and voltage. The reactive power is not consumed (unused "blind" power). If the power consumption of a load / consumer includes reactive power in addition to the active power, the total power is referred to as apparent power. According to DIN 40110-1, the apparent power is specified in volt-amperes (VA). Volt-amperes (VA) are intended to expressthat in addition to the active power, reactive power is also included in the power. In the case of AC and AC voltage consumers, we usually speak of apparent power. Apparent power is generally greater than the active power. The current component relating to the reactive power is referred to as reactive current. In the differential current according to the present invention, this current component is referred to as differential reactive current. The current relating to the apparent power is the total current, in this example the total current is the differential current. The differential current is composed of the differential active current (real part: resistive component, active power) and the differential reactive current (imaginary part: capacitive or inductive component,Reactive power). 202312391 7 The apparent power S is defined as the product of the effective value of the total current and the effective value of the voltage U. In the example related to the differential current, the apparent power is the product of the effective value of the differential current and the effective value of the voltage U, i.e., a differential apparent power. The apparent power S is composed of the actually converted active power P and the additional reactive power Q. In electrical engineering, the effective value is understood to be the root mean square of a time-varying physical quantity. The term is preferably applied to alternating quantities, generally to quantities in stationary processes. The effective value of the variable quantity (in the example, voltage or current) is as large as the value of a constant quantity,which converts the same electrical power to a resistive load or converts the same electrical energy in a representative period of time as the time-varying quantity. The effective value depends on both the peak value and the curve shape. In English, the effective value is referred to as RMS (abbreviation for Root Mean Square). The present invention relates in particular to low-voltage circuits with an alternating voltage, usually with a time-dependent sinusoidal alternating voltage with the frequency f. The time dependence of the instantaneous voltage value u(t) of the alternating voltage is described by the equation: u(t) = Ua * sin (2π * f * t). Where: u(t) = instantaneous voltage value at time t Ua = amplitude of the voltage 202312391 8 A harmonic alternating voltage can be represented by the rotation of a phasor,whose length corresponds to the amplitude (Ua) of the voltage. The instantaneous deflection is the projection of the pointer onto an axis of the coordinate system (typically the abscissa). One oscillation period corresponds to one full revolution of the pointer, and its full angle is 2π (2Pi) or 360°. The angular frequency is the rate of change of the phase angle of this rotating pointer. The angular frequency of a harmonic oscillation is always 2π times its frequency, i.e.: ω = 2π*f = 2π / T = angular frequency of the alternating voltage (T = period of the oscillation). The angular frequency (ω) is often preferred over the frequency (f), since many formulas in oscillation theory differ due to the occurrence of trigonometric functions whose period is, by definition, 2π.can be represented more compactly using the angular frequency: u(t) = Ua * sin(ωt) In the case of angular frequencies that are not constant over time, the term instantaneous angular frequency is also used. For a sinusoidal, in particular time-constant, alternating voltage, the time-dependent value from the angular velocity ω and the time t corresponds to the time-dependent angle φ(t), which is also referred to as the phase angle φ(t). This means that the phase angle φ(t) periodically passes through the range 0…2π or 0°…360°. This means that the phase angle periodically assumes a value between 0 and 2π or 0° and 360° (φ = n*(0…2π) or φ = n*(0°…360°), due to periodicity; in short: φ = 0…2π or φ = 0°…360°). With instantaneous voltage value u(t) or instantaneous current value or instantaneous differential current value i(t) is therefore the 202312391 9 instantaneous value of the voltage / current / differential current at time t,i.e. for a sinusoidal (periodic) alternating voltage, the value of the voltage / current / differential current at the phase angle φ is meant (φ = 0…2π or φ = 0°…360°, of the respective period). An effective value of the voltage U can be calculated from instantaneous voltage values ​​u(t), and an effective value of the differential current I can be calculated from instantaneous differential current values ​​i(t). The calculation is usually carried out over at least one period of the voltage or differential current. In the patent application, instantaneous values ​​(e.g. instantaneous voltage value u(t), instantaneous differential current value i(t), instantaneous differential power p(t)) are designated with lower case letters (u, i, …) and effective values ​​(e.g. effective value of the voltage U, effective value of the differential current I, …) are designated with capital letters (U, I, …). State-of-the-art residual current monitoring devices use the residual current, more precisely the effective value of the residual current I,for display or message. The effective value of the differential current can contain both active and reactive components (differential active current and differential reactive current components). For example, the effective value of the differential current can consist only of differential active current components; alternatively, the effective value of the differential current can consist only of differential reactive current components; alternatively, or generally, the effective value of the differential current can consist of differential active current components and differential reactive current components. This means that regardless of whether active or reactive current components are included in the differential current,According to the state of the art, a residual current monitoring device "rigidly" (or "stupidly") displays or reports the effective value of the residual current. Especially for residual currents with the fundamental frequency (the mains voltage), no distinction is possible today. 202312391 10 According to the invention, it is now advantageous (especially for the 50 Hz part of the residual current) to use not the (effective value of the) residual current, but only the differential active current, i.e., the active power component of the residual current, or (alternatively) the differential reactive current, i.e., the reactive power component of the residual current. This allows a distinction to be made between ohmic-induced fault currents caused by defective insulation or persons, since persons usually resemble an ohmic resistance (or always contain an ohmic component). The IEC 60479-1 standard describes the effect of electric current on the human body.and, on the other hand, capacitive or inductive induced fault currents (leakage currents), i.e., technically induced fault currents or leakage currents (which are not critical for personal protection). This allows for faster searches for the causes and more specific maintenance, thereby saving costs. A voltage sensor unit is advantageously provided in the residual current monitoring device to determine the voltage level, as well as a control unit,to determine the differential active current or (alternatively) the differential reactive current from the determined voltage level and the determined differential current level. In this context, the effective value of the differential active current or the effective value of the differential reactive current is advantageously used. Specifically, the differential active current refers to the active current component in the differential current at the (mains) voltage frequency in the low-voltage circuit. This means, for example, that at an alternating voltage frequency of 50 Hz (as is common in Europe), the differential active current relative to 50 Hz,i.e., the fundamental component. 202312391 11 In alternating current technology, harmonic oscillations are considered as a first approximation. This means that a voltage is considered a harmonic alternating voltage u(t) = Ua * sin(ωt) (see above), and a current in the same circuit is considered a harmonic alternating current i(t) = I * sin(ωt – phi), where phi is the phase shift between (alternating) voltage and (alternating) current (0° to 360° or -180° and +180°, etc.). The alternating current i(t) = I * sin(ωt – phi) can be decomposed (related to the phase angle phi) into two orthogonal components, according to the well-known alternating current theory: a first component in phase with the voltage (phase shift = phase difference 0°) and a second component with a 90° phase shift with the voltage. Bronstein,Pocket book of mathematics: sin(α – β) = cos(β) * sin(α) + sin(-β) * cos(α) i(t) = I * sin(ωt – phi) α = ωt β = phi i(t) = I * (cos(phi) * sin(ωt) + sin(-phi) * cos(ωt)) The component cos (phi) * sin (ωt) is the alternating current component (decomposed alternating current component) that is in phase (phase shift 0°) with the (alternating) voltage (sin (ωt)) and is referred to as the active current component (active current component). 202312391 12 The component sin (-phi) * cos (ωt) is the alternating current component (decomposed alternating current component) orthogonal (phase shift 90°) to the (alternating) voltage (sin (ωt)) and is referred to as the reactive current component (reactive current component), i.e., the reactive current component with the fundamental frequency (= fundamental oscillation) (e.g., 50 Hz). This applies, as already mentioned in the introduction, to a harmonic oscillation / harmonic alternating voltage / harmonic alternating current with a phase shift Phi between voltage and current (between 0° and 360°). For the general case,In particular for sampled, time-varying variables (instantaneous value curves): - the active current component is the component in the current that transmits active power with the (mains) voltage, - the active current component has the same frequency as the (mains) voltage, in particular the same fundamental frequency (fundamental oscillation) as the (mains) voltage (e.g. 50 Hz), - the active current component has the same phase (or phase position) as the (mains) voltage, in particular the phase shift between the active current component and the fundamental oscillation of the (mains) voltage is 0°. The reactive power is shifted back and forth at twice the frequency of the alternating voltage; this is referred to as oscillating power or displacement reactive power. For the general case, especially for sampled, time-varying quantities (instantaneous value curves), the following is: -the reactive current component is the component in the current that transmits reactive power with the (mains) voltage,-The reactive current component (also called displacement reactive current component) has the same frequency as the (mains) voltage, in particular the same fundamental frequency (fundamental oscillation) as the (mains) voltage (e.g. 50 Hz). -The reactive current component (displacement reactive current) has a (+ / -) 90° phase shift (or phase position) to the (mains) voltage. 202312391 13 The differential reactive current is the differential reactive current component with the fundamental frequency of the voltage in the low-voltage circuit. This reactive power should not be confused with the so-called distortion reactive power, which in turn is caused by different frequency components in the current, in particular higher frequency components (relative to the fundamental frequency (fundamental oscillation) of the (mains) voltage) in the current. More specifically, the third, fourth, fifth,... harmonic of the current (relative to the fundamental frequency of the (mains) voltage). More generally, higher (relative to the fundamental frequency) frequency components of the current that are different from the fundamental frequency of the alternating voltage ((mains) voltage). For the purposes of the present invention, reactive power does not mean distortion reactive power. For the general case, especially for sampled, time-varying quantities (instantaneous value curves), the following is: - the distortion reactive current component is the component in the current that transmits reactive power with the (mains) voltage, - the distortion reactive current component has a higher frequency compared to the (mains) voltage,in particular to the fundamental frequency (fundamental oscillation) of the (mains) voltage (e.g., 50 Hz). Advantageous embodiments of the invention are specified in the subclaims. In an advantageous embodiment of the invention, the magnitude of the differential current of the first input is (additionally) displayed. This has the particular advantage that, in addition to the display or signaling of the (first) differential active current or (first) differential reactive current of the first input, the (first) differential current of the first input is also displayed or signaled. 202312391 14 This has the particular advantage thatthat a realization analogous to classic residual current monitoring devices is provided. In an advantageous embodiment of the invention, the external display unit receives the level of the (first) differential active current or (first) differential reactive current of the first input via wired or wireless communication. In particular, the external display unit receives the level of the (first) differential current of the first input. This has the particular advantage that, by transmitting the values, they can be displayed and / or stored in a central device. In an advantageous embodiment of the invention, a communication unit connected to the control unit is provided for wired or wireless communication in order to report the level of the (first) differential active current or (first) differential reactive current of the first input, in particular also the level of the (first) differential current of the first input.to enable, for example, a display on an external display unit (or a central monitoring or management system). This has the particular advantage that the data evaluation, monitoring, and data storage of the occurring differential currents can be carried out in a central management system. In an advantageous embodiment of the invention, the residual current monitoring device is designed such that the (first) differential current sensor unit of the (first) external unit determines instantaneous (first) differential current values ​​of the magnitude of the (first) differential current, that the (first) voltage sensor unit of the (first) external unit determines instantaneous (first) voltage values ​​of the magnitude of the (first) voltage, that an effective value of the (first) voltage (in particular over half aone or more periods of the alternating voltage - 202312391 15 generally over a multiple of half the period of the alternating voltage), that an instantaneous (first) differential power is determined from the instantaneous (first) voltage values ​​and the instantaneous (first) differential current values; that a (first) differential active power is determined from the instantaneous (first) differential power, in particular by averaging (in particular over half, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), that from the (first) differential active power, which was determined over half, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), by dividing it by the effective value of the (first) voltage (over the same half,one or more (half) periods of the alternating voltage – generally determined over the same multiple of half the period of the alternating voltage), an (effective value of the) (first) differential active current is determined, that the (effective value of the) (first) differential active current is displayed or reported, in particular that a report is issued when the level of a (first) active current limit value is exceeded. This has the particular advantage of demonstrating a simple possibility for determining the differential active current. In an advantageous embodiment of the invention, the instantaneous (first) voltage values ​​u(t) (alternatively also: u, LN ) and the instantaneous (first) differential current values ​​i(t) (alternatively: i ∆) by averaging the product of the instantaneous (first) voltage values ​​u(t) and the instantaneous (first) differential current values ​​i(t) (over half, one or more (half) periods of the alternating voltage – generally over a multiple of half the period of the alternating voltage) the (first) differential active power Pd (alternatively also: P ∆ ) is determined. 202312391 16 Ie from the instantaneous (first) difference power pd(t) (alternatively: p ∆ ) is determined by (especially arithmetic) averaging (ie by integrating the instantaneous (first) difference power pd(t) and dividing by the integration time (t b - t a ); the integration period is half, one or more (half) periods of the alternating voltage – generally over a multiple of half the period of the alternating voltage) a (first) differential active power Pd is determined. From the (first) differential active power Pd (= P∆ ) can be calculated by dividing by the effective value of the (first) voltage U (alternatively: ^^ ^ே,^^^ ) the effective value of the (first) differential current I (alternatively: ^^ ௱,௪^^^ ) can be determined. This has the particular advantage that specific possibilities for determining the (first) differential active power (the (effective value of the) (first) differential active current) are provided, which can be implemented in particular by a control unit having a microprocessor. In an advantageous embodiment of the invention, the (first) differential current sensor unit of the (first) external unit determines instantaneous (first) differential current values ​​of the magnitude of the (first) differential current. From the instantaneous (first) differential current values, an effective value of the (first) differential current is determined (over half, one or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage). The (first) voltage sensor unit of the (first) external unit determines instantaneous (first) voltage values ​​of the magnitude of the 202312391 17 (first) voltage.From the instantaneous (first) voltage values, an effective value of the (first) voltage (over half, one, or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage) is determined, and from the effective value of the (first) voltage and the effective value of the (first) differential current, a (first) differential apparent power is determined. This has the particular advantage that a determination of the (first) differential apparent power is provided for further embodiments of the invention. In an advantageous embodiment of the invention, a (first) differential reactive power is determined from the (first) differential apparent power and the (first) differential active power. The (first) differential reactive current is determined from the (first) differential reactive power. This has the particular advantage thatthat a possibility for determining the (first) differential reactive current is demonstrated. In an advantageous embodiment of the invention, the square root of the difference from the square of the (first) differential apparent power S (alternatively also ^^, ௱ ) and the square of the (first) difference active power Pd (alternatively ^^ ௱ ) the (first) difference reactive power ^^ ௱ determined. From the (first) differential reactive power ^^ ௱ (over half, one or more periods of the alternating voltage – generally over a multiple of half the period of the alternating voltage) is determined by dividing by the effective value of the (first) voltage U (alternatively: ^^ ^ே,^^^ ) (over the same half, one or more periods of the alternating voltage – generally over the same multiple of half the period of the alternating voltage) an effective value of the (first) differential reactive current The effective value of the (first) differential reactive current ^^ ௱,^^^^ௗ is displayed or (alternatively and) reported; in particular, if the level 202312391 18 of a (first) (differential) reactive current limit is exceeded, a message is issued. S = U * I (alternatively also: S ^ ^U LN , rms ^ I ^ , rms ) This has the particular advantage of providing a specific way of determining the (effective value of the) (first) differential reactive current, which can be implemented in particular by a control unit having a microprocessor. In an advantageous embodiment of the invention, a second input is provided for connecting a second external unit. The control unit is connected to the second input. From the obtained level of the (second) differential current and the level of the (second) voltage of the second input, a (second) differential active current or (second) differential reactive current of the second input is determined. The level of the (second) differential active current or (second) differential reactive current of the second input is displayed on the display unit.The second external unit can be assigned to a second conductor pair of the (first) low-voltage circuit or to a second low-voltage circuit. The second conductor pair can in turn have a phase conductor and a neutral conductor (alternatively two phase conductors). This has the particular advantage that two circuits can be monitored (with one residual current monitoring device). 202312391 19 In an advantageous embodiment of the invention, the level of the (second) differential current of the second input is displayed. In an advantageous embodiment of the invention, the receipt, reporting, display or (and) determination of the (second) differential active current or (second) differential reactive current of the second input is carried out in a manner analogous to the aforementioned embodiments. (Therefore, first / first is often placed in parentheses.) This has the particular advantage that a simple parallel evaluation is provided for two circuits. In an advantageous embodiment of the invention, an additional input or additional inputs are provided for the connection of an additional external unit or additional external units. The control unit is connected to the additional input or additional inputs. From the received level of the differential current and level of the voltage of the additional input or additional inputs, a (respective) differential active current or (respective) differential reactive current of the additional input or inputs is determined. The level of the (respective) differential active current or (respective) differential reactive current of the additional input or inputs is shown on the display unit. This has the particular advantage that several circuits can be monitored.In an advantageous embodiment of the invention, the level of the differential current of the additional input or the additional inputs is displayed. In an advantageous embodiment of the invention, the receipt, reporting, display or (and) determination of the (respective) differential active current or (respective) differential reactive current of the additional input or the additional inputs is carried out in a similar manner to the aforementioned embodiments. (Therefore, first / firster is often placed in parentheses.) 202312391 20 This has the particular advantage of providing a simple parallel evaluation for several circuits. In an advantageous embodiment of the invention, the determination of the (first) differential active current or (alternatively and) the (first) differential reactive current of the (first, second, additional input or the additional inputs) is carried out continuously (periodically).This has the particular advantage of providing continuous periodic monitoring of the low-voltage circuit. In an advantageous embodiment of the invention, an external mechanical isolating contact unit is provided, which has a closed state of the contacts for a current flow in the conductors of the low-voltage circuit or an open state of the contacts for a current-preventing galvanic isolation of the conductors of the low-voltage circuit, or (alternatively and) an external electronic interruption unit, which, through semiconductor-based switching elements, has a high-resistance state of the switching elements to prevent a current flow or a low-resistance state of the switching elements for current flow in the low-voltage circuit. If the first differential active current exceeds a current limit value or current-time limit value (ieIf the current limit is exceeded for an initial period of time, the contacts are open for galvanic isolation to prevent current flow, or the switching elements are in a high-impedance state to prevent current flow. The external mechanical isolating contact unit or (alternatively) external electronic interruption unit can be part of the external unit. This has the particular advantage that, in addition to monitoring the fault current, the low-voltage circuit is interrupted in the event of fault currents (differential active currents) that are hazardous to personnel, so that in addition to monitoring, a protective effect is also achieved (similar to conventional residual current circuit breakers, but not with the differential current, but with the differential active current).According to the invention, an external unit is claimed, comprising a differential current sensor unit for determining the magnitude of a differential current of a conductor pair of a low-voltage circuit, wherein the conductor pair has, in particular, a phase conductor and a neutral conductor, and a voltage sensor unit for determining the magnitude of a voltage of the conductor pair, such that the external unit is connectable to a residual current monitoring device. According to the invention, a corresponding method for residual current monitoring for electrical low-voltage AC circuits, specifically for a residual current monitoring device, with the same and further advantages is claimed.The inventive method for monitoring fault currents for low-voltage electrical circuits for alternating voltage: determines the magnitude of a differential current between two conductors of a low-voltage circuit, determines the voltage of the two conductors of the low-voltage circuit, a differential active current or differential reactive current is determined from the voltage and the differential current, the magnitude of the differential active current or differential reactive current is displayed (in particular, reported in order to be displayed at the location receiving the message, in particular, if the magnitude of a (differential) active current limit value or (differential) reactive current limit value is exceeded, a message is issued in order to be displayed at the location receiving the message). 202312391 22 In particular, the magnitude of the differential current is additionally displayed (in particular, reported in order to be displayed at the location receiving the message).According to the invention, a corresponding computer program product for a residual current monitoring device is claimed. The computer program product comprises instructions which, when the program is executed by a microprocessor, cause the microprocessor to carry out or support the inventive embodiments or methods of the residual current monitoring device. In particular, the differential active current or (alternatively) differential reactive current is used for the display or message. The microprocessor is part of the residual current monitoring device, in particular the control unit. According to the invention, a corresponding computer-readable storage medium on which the computer program product is stored is claimed. According to the invention, a corresponding data carrier signal which the computer program product transmits is claimed. All embodiments, both in dependent form and referring back to patent claim 1 or15, as well as referring back to individual features or combinations of features of patent claims, in particular also a reference back of the dependent arrangement claims to the independent method claim, bring about an improvement in a residual current monitoring device. In general, a new concept for a residual current monitoring device is provided. The described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.The drawing shows: Figure 1 shows a first representation with a residual current monitoring device, Figure 2 shows a second representation with a residual current monitoring device, Figure 3 shows a third representation with a residual current monitoring device, Figure 4 shows a fourth representation with a residual current monitoring device, Figure 5 shows a fifth representation with a residual current monitoring device, Figure 6 shows a first block diagram for a calculation unit, Figure 7 shows a representation of a display, Figure 8 shows a first test setup with a residual current monitoring device, Figure 9 shows a second test setup with a residual current monitoring device. Figure 1 shows a representation of a residual current monitoring device SG for monitoring an electrical low-voltage circuit for alternating voltage. It has a housing 103 with at least one first input E1 for connecting a first external unit sensor1. 202312391 24 The first external unit sensor1 (external, ieoutside the housing) has a first differential current sensor unit (not shown) for determining the level of a first differential current i. ∆1 (i ∆1 =i L1 -i N1 ) of a first conductor pair LP1, for example, a first low-voltage circuit or partial low-voltage circuit. The first conductor pair LP1 comprises, in particular, a first conductor pair phase conductor LP1L1 and a first conductor pair neutral conductor LP1N (alternatively, it could comprise two phase conductors). The first external unit sensor1 further comprises a first voltage sensor unit (not shown) for determining the level of a first voltage u L1Nof the first conductor pair LP1. The first external unit sensor1 is connected to the first input E1 via a wired or wireless first connection V1. The residual current monitoring device SG receives the level of the first differential current i via the first connection V1 / the first input E1. ∆1 and the level of the first voltage u L1N the first external unit sensor1. The first external unit sensor1 determines the level of the (first) voltage and the level of the (first) differential current of the first conductor pair LP1. The first conductor pair LP1 is, for example, a first branch A1 of a first phase conductor L1 and a neutral conductor N. The first phase conductor L1 and the neutral conductor N are connected to a first energy source EQ1. The first energy source EQ1 has a first voltage source SQ1 with a generator voltage u G, such as a nominal voltage of 230 volts (effective value) AC voltage (phase conductor to neutral conductor) (or 400 volts between two phase conductors). This means that on the one hand, the first conductor pair phase conductor LP1L1 is connected to the first phase conductor L1 and the first conductor pair neutral conductor LP1N is connected to the neutral conductor N. On the other hand, the first conductor pair LP1 is connected to a first (energy) consumer Load1. The first consumer 202312391 25 Load1, for example, has a first resistance or resistance value RL1. Between the connection of the first conductor pair LP1 to the first phase conductor L1 and neutral conductor N on the one hand and the first consumer Load1 on the other hand, the first external unit sensor1 is arranged, as shown in Figure 1. According to Figure 1, for example, a second conductor pair LP2 is provided, which is, for example, a second branch A2 of the first phase conductor L1 and the neutral conductor N. This meansFor example, on the one hand, the second conductor pair phase conductor LP2L1 is connected to the first phase conductor L1 and the second conductor pair neutral conductor LP2N is connected to the neutral conductor N. On the other hand, the second conductor pair LP2 is connected to a second (energy) consumer Load2. The second consumer Load2 has, for example, a second resistance or resistance value RL2. Between the connection of the second conductor pair LP2 to the first phase conductor L1 and neutral conductor N on the one hand and the second consumer Load2 on the other hand, a second external unit sensor2 is arranged, as shown in Figure 1. In this example, the housing 103 has a second input E2 for connecting the second external unit sensor2. Analogous to the first external unit sensor1, the second external unit sensor2 has a second differential current sensor unit (not shown) for determining the level of a second differential current i. ∆2(i ∆2 =i L2 -i N2 ) of the second conductor pair LP2, for example, a second low-voltage circuit or partial low-voltage circuit. The second external unit sensor2 further comprises a second voltage sensor unit (not shown) for determining the level of a second voltage u L2N of the second conductor pair LP2. 202312391 26 The second external unit sensor2 is connected to the second input E21 via a wired or wireless second connection V2. The residual current monitoring device SG receives the level of the second residual current i via the second connection V2 / the second input E2. ∆2 and the level of the second voltage u L2Nthe second external unit sensor2. The second external unit sensor2 determines the level of the (second) voltage and the level of the (second) differential current of the second conductor pair LP2. The first input E1 of the residual current monitoring device SG is connected to an (internal) control unit SE. The control unit SE is connected to an internal or external display unit DISP, particularly suitable for displaying the level of a differential current. In the example according to Figure 1, an internal display unit DISP is shown. The residual current monitoring device SG, in particular the control unit SE, is designed such that a (first) differential active current or (first) differential reactive current of the first input E1 is determined from the obtained level of the differential current and the voltage level of the first input E1.The magnitude of the (first) differential active current or (first) differential reactive current of the first input E1 is displayed on the display unit DISP. In addition, the magnitude of the (first) differential current of the first input E1 can be displayed. In a similar manner, a second input E2 (if provided) of the residual current monitoring device SG can be connected to the (internal) control unit SE. The residual current monitoring device SG, in particular the control unit SE, is designed such that a (second) differential active current or (second) differential reactive current of the second input E2 is determined from the obtained magnitude of the differential current and the voltage of the second input E2. The magnitude of the (second) differential active current or (second) differential reactive current of the second input E2 is displayed on the display unit DISP.In addition, the level of the differential current of the second input E2 can be displayed. In a similar way, another input or inputs can be provided for connecting another external unit or units. The control unit SE is connected to the additional input or inputs. From the received level of the differential current and voltage of the additional input or inputs, a differential active current or differential reactive current of the additional input or inputs is determined. The level of the differential active current or differential reactive current of the additional input or inputs is shown on the display unit DISP. In addition, the level of the differential current of the additional input or inputs can be displayed.The residual current monitoring device SG, in particular the control unit SE, is designed in such a way that the level of the instantaneous voltage u. L1N , and L2N and the magnitude of the instantaneous differential current i ∆1 , i ∆2 a determination of an effective value of the differential active current I ∆,wirk of the respective input. Alternatively (or additionally), an effective value of the differential reactive current ^^ is determined. ௱,^^^^ௗ of the respective input. In a circuit, the magnitude of the phase conductor current i L1 the level of the neutral conductor current i N1 (relative to the first conductor pair LP1), ie the level of the differential current i ∆1 = i L1 – i N1(relative to the first conductor pair LP1) is normally equal to or almost zero in 202312391 28 normal operation. The display unit DISP can display further information on the residual current monitoring device. In particular, the level of the residual active current or residual reactive current of the respective input is displayed. In addition, the level of the residual current of the respective input can be displayed. In one embodiment, the level of the residual active current and the level of the residual reactive current (and, if applicable, also the level of the residual current) can be displayed. The control unit can be connected to a communication unit COM, for example for (further) external display or reporting of the level of the residual active current or residual reactive current of the respective input. In addition, the level of the residual current can be reported. In these cases, for example, the internal display unit DISP can be omitted.In one embodiment, the level of the differential active current and the level of the differential reactive current (and, if necessary, also the level of the differential current) can be reported. In these cases, the internal display unit DISP can also be omitted, for example. Alternatively or additionally, the report can only be issued when an active current limit or reactive current limit is exceeded. The level of the active current limit can be, for example, 5 mA, 6 mA, 10 mA, 20 mA, 30 mA, 50 mA, 100 mA, or 300 mA. The level of the reactive current limit is typically greater (e.g., 2, 3, 5, or 10 times) or equal to the level of the active current limit. The communication unit COM can provide wired or wireless communication to report the level of the residual active current or residual reactive current, especially the level of the residual current, especially for an external display. A message or transmission is provided.The current level can be transmitted (reported) to an external display unit. The external display unit can be part of a higher-level monitoring or management system, or it can be reported to other units, particularly for display purposes. The (effective value of the) differential active current I. ∆,wirk or (alternatively and) differential reactive current ^^ ௱,^^^^ௗof the respective input is displayed on an internal or external display unit (e.g. by means of a message). Alternatively or additionally, a display (message) can be issued if the active current limit value (or (alternatively and) reactive current limit value) is exceeded. In one embodiment, signaling contacts can be provided on the residual current monitoring device SG. The signaling contacts can be controlled, for example, by the control unit SE. If a certain first active current limit value (or (alternatively and) first reactive current limit value) or (alternatively and) first current limit value of the differential current is exceeded, the exceedance of a critical value can be reported or signaled by closing (alternatively opening) the contacts. This message via the signaling contacts can also be used to switch external switching devices (contactors, relays).The residual current monitoring device can be used to inform a user that there is a fault in the low-voltage circuit (in a system) ((partial circuit, branch A1)) before the shutdown threshold of a protective switching device is reached. This means that measures can be taken before the system is shut down if values ​​​​are slowly deteriorating, for example due to aging insulation. The (effective value) of the differential active current is determined in relation to the frequency of the alternating voltage in the low-voltage circuit. This means that for an alternating voltage frequency of 50 Hz, for example, the first differential active current is determined in relation to 50 Hz. 202312391 30 The same applies to the second input E2 and the associated second differential active current or second differential reactive current or second differential current. The differential current sensor unit has, in particular, a (classic) summation current transformer.The conductor pair of the low-voltage circuit is, for example, passed through the differential current sensor unit, in particular the summation current transformer. This means that they form the primary winding of the summation current transformer, for example with a number of turns of 0.5 to 1. Figure 2 shows a representation according to Figure 1, with the difference that a second energy source EQ2 is provided. The second energy source EQ2 is connected on the one hand to the first energy source EQ1 and its neutral conductor N. The second energy source EQ2 is also connected to a second phase conductor L2. Analogous to the first energy source, the second energy source EQ2 can be a second voltage source SQ2 with a generator voltage u. Ghave, for example, a nominal voltage of 230 volts (effective value) alternating current (phase conductor to neutral conductor) (or 400 volts between two phase conductors). In the example according to Figure 2, the second phase conductor L2 is also connected to the second conductor pair phase conductor LP2L2 (reference symbol adapted) of the second conductor pair LP2. (Ie. not to the first phase conductor L1.) Ie. the second conductor pair LP2 is a second branch A2 of the second phase conductor L2 and the neutral conductor NDh the second conductor pair phase conductor LP2L2 is connected to the second phase conductor L2 and the second conductor pair neutral conductor LP2N is connected to the neutral conductor N. Figure 3 shows a representation according to Figure 2, with the following differences and explanations. 202312391 31 The neutral conductor of the first / second energy source EQ1, EQ2 is grounded on the energy source side, which is indicated by an earth symbol. This earthing has an earth impedance Z (not shown). PEThe earth-side neutral conductor connection is provided as a protective earth connection PE (Protective Earth) according to Figure 3. In Figure 3, the first load Load1 has a metal housing MG with a first impedance or resistance RL1. In the example, the metal housing MG of the first load Load1 is connected via a protective conductor SL to the protective conductor connection PE of the energy source EQ. Alternatively, the housing could also be grounded. The protective conductor SL has a protective conductor impedance Z SL as indicated in Figure 3. Depending on the device type, a so-called operational current i flows on the protective conductor SL SL, such as a leakage current. This can be the case, for example, with a power supply unit containing Y capacitors. Figure 4 shows a diagram according to Figure 3, with the difference that a first fault case FF1 is shown. In the example according to Figure 4, there is an electrical connection from the first conductor pair phase conductor LP1L1 to the protective conductor SL, whereby this connection is made on the one hand between the first external unit sensor1 and the first consumer Load1. This would be the case, for example, if a person touches the first conductor pair phase conductor LP1L1 and, on the other hand, simultaneously has contact with the protective conductor SL (e.g., via a metal housing MG). This means that an electrical fault current i RE1 flow (to the first energy source EQ1), so that in the first external unit sensor1 the current in the first conductor pair phase conductor i L1 and the current in the first pair of conductors - neutral conductor i N1is no longer identical, since a fault current i RE1 via the protective conductor SL, here as protective conductor current i SL marked, to the protective conductor terminal PE of the first energy source 202312391 32 EQ1. The first fault case FF1 has a resistance value RE1, which can consist of fault resistances (e.g., resistance of a person). The first fault case FF1 is shown separately in Figure 4 (for explanation). The first fault case FF1 can also occur in an analogous manner in the first consumer Load1 or otherwise. In the example according to Figure 4, the resulting fault current i RE1 the differential current i determined in the first external unit sensor1 ∆1 (i RE1 = i PE = i ∆1 ) (the impedance Z SLof the protective conductor SL is not taken into account in this example; it can be taken into account in an analogous manner). Figure 5 shows a representation according to Figure 3 or 4, with the difference that a second fault case FF2 is shown. In the example according to Figure 5, there is an electrical connection from the first conductor pair phase conductor LP1L1 to earth, whereby this connection is connected on one side between the first external unit sensor1 and the first consumer Load1. This is the case, for example, if a person touches the first conductor pair phase conductor LP1L1 (between the first external unit sensor1 and the first consumer Load1). This means that an electrical fault current i RE2 flow (to the first energy source EQ1), so that in the first external unit E1 the current in the first conductor pair phase conductor i L1 and the current in the first pair of conductors - neutral conductor i N1is no longer identical, since a fault current i RE2 to earth and via it to the energy source EQ or its earth. The second fault case FF2 has a resistance value RE2, which can consist of fault resistances and (if applicable) earth resistances. The second fault case FF2 is shown separately in Figure 5 (for explanation). The second fault case FF2 can also occur in an analogous manner at / in the first consumer Load1 or otherwise. 202312391 33 In the example according to Figure 5, the resulting fault current i RE2 the differential current i determined in the first external unit sensor1 ∆1 (i RE2 = i ∆1 ). Figure 6 shows a functional block diagram of functions executed in the control unit SE, which are represented as units. The control unit SE receives - from the external unit (or its differential current sensor unit) the level of the differential current (i ∆1 ) = i ∆(= i(t)) of the (first / respective) input, in particular the instantaneous level of the differential current (instantaneous differential current values), and - from the external unit (or its voltage sensor unit) the level of the voltage u LN (= u(t)) of the (first / respective, e.g. = u L1N / = u L2N ) input, in particular the instantaneous voltage level (instantaneous voltage values). Both are fed, for example, to a calculation unit BE (which is part of the control unit SE). From the (instantaneous) voltage level u LN (e.g. = u L1N / = u L2N ) and the (instantaneous) level of the differential current i ∆ (e.g. = i ∆1 / = i ∆2 ) (i ∆ = i L – i N / i ∆1 = i L1 – i N1 / i ∆1 = i L1 – i N1 ) of the (first / respective) input, a differential active current I ∆,wirk(RMS value) or (and) differential reactive current I ∆,blind (effective value) of the (first / respective) input. (The same applies to the differential current / voltage of the (second / respective) input; therefore, the corresponding terminology and formulas have been simplified, in particular, the first or the index 1 have been omitted or placed in parentheses for clarity.) The magnitude of the (first) differential active current I ∆,wirk (RMS value) or (and) (first) differential reactive current I ∆,blind (RMS value) is used for display on an internal or external display unit. (The level of the differential active current I ∆,wirk (effective value) can be used to prevent current flow in the monitored circuit.) 202312391 34 In the example according to Figure 6, the determination of the (effective value of the) differential active current I ∆,wirk The magnitude of the (instantaneous) differential current i ∆, specifically according to Figure 6, the instantaneous level of the differential current (instantaneous differential current values), and the level of the voltage u LN (e.g. = u L1N / = u L2N ), specifically according to Figure 6 the instantaneous voltage level (instantaneous voltage values), is fed to a multiplication unit ME, which is calculated by (in-phase) multiplication of the two supplied quantities (differential current i ∆ and tension u LN ) a momentary difference power p ∆ (= pd) is determined or calculated. The instantaneous difference power p ∆ is fed to a first integration unit INT1 to determine the differential active power P ∆ , which is obtained by integrating or averaging the instantaneous difference power p ∆ over a multiple of half the period of the alternating voltage, e.g. over half, one, one and a half, ... or several periods of the alternating voltage, a differential active power P ∆determined or calculated. The level of voltage u LN , specifically according to Figure 6 the instantaneous level of voltage u LN (= u(t)), is fed to an effective value unit, which, according to Figure 6, is calculated from the instantaneous level of the voltage u LN an effective value of the voltage U LN,rms determined or calculated. The effective value unit according to Figure 6 consists of three series-connected units: a squaring unit QQ, a second integration unit INT2, and a square root unit QW. The squaring unit QQ squares the instantaneous voltage level u. LNThe squared instantaneous voltage level is fed to the second integration unit INT2, which calculates an average value by integrating or, in particular, averaging (the squared instantaneous voltage level) over a multiple of half the period of the alternating voltage, e.g., over half, one, one and a half, ... or more periods of the alternating voltage (integration unit INT2 alternatively also means or includes a 202312391 35 unit for averaging). The square root unit QW extracts the square root of the average value, so that the effective value of the voltage U LN,rmsdetermined or calculated (root mean square, the calculation of an effective value is usually known). It is important that the first integration unit INT1 (= mean value unit 1) and the second integration unit INT2 (mean value unit 2) (each) integrate over the same multiple of half the period of the alternating voltage, e.g., over the same half, one, one and a half, ... or several periods of the alternating voltage. The differential active power P determined by the first integration unit INT1 ∆ and the effective value of the voltage U determined by the three series-connected units (squaring unit QQ, second integration unit INT2, square root unit QW) LN,rms is fed to a division unit DIV, which is calculated by dividing the difference active power P ∆ by the effective value of the voltage U LN,rms the effective value of the differential active current I ∆,wirk determined or calculated. This means that from the instantaneous voltage values ​​an effective value of the voltage U is calculated. LN,rms (over a multiple (1, 2, … n) of half the period of the alternating voltage). From the instantaneous voltage values ​​and the instantaneous differential current values, a differential active power P ∆ (over the same multiple of half the period of the alternating voltage). The differential active power P ∆ (over the multiple (1, 2, … n) of half the period of the alternating voltage) is determined by dividing by the effective value of the voltage U LN,rms (over the same multiple (1, 2, … n) of half the period of the 202312391 36 alternating voltage) an effective value of the differential active current I ∆,wirk The effective value of the differential active current I ∆,wirkof the respective input can be displayed by the internal (external) display unit DISP or (and) reported by the communication unit COM for display on an external display unit. The effective value of the differential active current I ∆,wirk can only be reported (displayed) when an active current limit is exceeded. The same applies to the residual reactive current. An external display unit can be, for example, a web browser. Technically speaking, there can be some kind of data storage / database from which the collected data is loaded and displayed. This process, as well as the subsequent processes, can be implemented by a method, algorithm, or computer program product that runs on a microprocessor in the control unit SE. This means that the units are, for example, functions that are executed. The instantaneous power p determined from the instantaneous voltage values ​​and the instantaneous residual current values ∆, from which by integration (over a multiple (such as 1, 2, 3, 4, … n) of half the period of the alternating voltage) the differential active power P ∆is determined, can alternatively also be determined in another way. The control unit can, in an analogous manner, determine an effective value of the differential current (over a multiple of half the period of the alternating voltage) from the instantaneous differential current values. A differential apparent power is determined by multiplying the effective value of the voltage and the effective value of the differential current (equal times / (multiples of) the period durations are considered in each case). A differential reactive power is determined from the differential apparent power and the differential active power. The differential reactive current is determined from the 202312391 37 differential reactive power. More specifically, the differential reactive power is determined from the square root of the difference between the square of the differential apparent power and the square of the differential active power.The differential reactive power (over a multiple of half the period of the alternating voltage) is divided by the effective value of the voltage (over the same multiple of half the period of the alternating voltage) to obtain an effective value of the differential reactive current. The effective value of the differential reactive current I ∆,blind can be displayed by the internal (external) display unit DISP or reported by the communication unit COM for display on an external display unit. The effective value of the differential reactive current I ∆,blind can only be reported (displayed) when a reactive current limit is exceeded. S ^ ^U LN , rms ^ I ^ , rms The differential reactive current determined from the instantaneous voltage values ​​and the instantaneous differential current values ​​can alternatively be determined by other means. The determination of the differential active current, in particular the differential reactive current, is advantageously carried out continuously (periodically), for example, with microprocessor support. The residual current monitoring device can also be designed or expanded such that, in addition to the differential active or reactive current, the level of the differential current (effective value) is displayed by the internal (external) display unit DISP 202312391 38 or reported by the communication unit COM for (storage and / or) display on an external display unit. The effective value of the differential current can only be reported (displayed) when a limit value is exceeded. The level of the current limit values ​​or current time limit values ​​can be fully or partially adjustable, e.g.by means of an input unit or the communication unit on the residual current monitoring device. With the invention, differential active currents or differential reactive currents (or also differential currents) of several (particularly independent) circuits can be determined and displayed separately. This means that the residual current monitoring device according to the invention behaves, for example, as shown below. Figure 7 shows how the level of the differential active current or differential reactive current can be displayed on the (internal) display unit DISP (a corresponding display can also be made on an external display unit). In the example according to Figure 7, the differential current I. ∆ Figure 7 shows a digital display on the left side, where the differential current I ∆ is displayed, in the example according to Figure 7 a differential current I ∆ of 227 mA, in the lower range the differential active current I ∆,wirkdisplayed, represented as active differential current I ∆,active , in the example according to Figure 7 a (differential active current I ∆,wirk =) active differential current I ∆,active of 4 mA. Figure 7 shows a corresponding display in the right part as a bar chart, where the type of current, ie differential current I ∆ or (differential active current I ∆,wirk =) active differential current I ∆,active, and the current level (logarithmic) in milliamperes (mA) is plotted on the vertical Y-axis. 202312391 39 Figure 8 shows a test setup (measurement setup) with a residual current monitoring device SG. The first external unit E1 sensor1 is connected on the mains side to the first energy source EQ1 via a two-pole first switch S1. On the first external unit E1, the load-side phase conductor connection LP1L1 is connected to the (mains-side = energy source-side) neutral conductor N via an adjustable resistor R, a second switch S2 and an ammeter AM. The load-side neutral conductor connection LP1N is not connected in the example. A voltmeter VM is (optionally) connected between the mains-side first phase conductor L1 and neutral conductor N. The first external unit E1 is connected to the first input E1 of the residual current monitoring device SG.The residual current monitoring device can have a power supply that is connected, for example, to the (first) phase conductor and the neutral conductor. A conventional residual current monitoring device, as well as a residual current monitoring device according to the invention, behaves in such a way that when the first and second switches S1, S2 are closed and the residual current I is set with the adjustable resistor R. ∆,R (= differential current in the test setup via the first external unit E1), which in this case flows through the ammeter AM, of, for example, 30 mA, both residual current monitoring devices would display this value. The residual current monitoring device according to the invention would display this current (30 mA) as the differential active current I ∆,wirk (active differential current I ∆,active ). In one embodiment of the residual current monitoring device according to the invention, in which the differential current I ∆is displayed, this value (30 mA) would also be displayed. The residual current monitoring device according to the invention would, when displaying the residual reactive current I ∆,blind do not display this value (ideally ~ 0 mA). 202312391 40 Ohmic test fault currents I ∆,R Different levels can be set using the adjustable resistor R, allowing the residual current monitoring device SG to be tested for its display behavior. Figure 9 shows a structure / arrangement according to Figure 8, with the difference that instead of the adjustable resistor R, a particularly adjustable capacitive or inductive component is provided, in the example a capacitor C with a specific capacitance (advantageously variably adjustable). If the capacitance of the capacitor C is dimensioned such that a (capacitive) residual current of I ∆,Cof 30 mA in the example (effective value, note tolerance ranges), a conventional residual current monitoring device (according to the state of the art) will display this current value. A residual current monitoring device SG according to the invention will display the differential active current I ∆,wirk (active differential current I ∆,active ) do not display this value (ideally ~ 0 mA). In an embodiment of the residual current monitoring device according to the invention, in which the residual current I ∆ is displayed, this value (30 mA) would also be displayed. The residual current monitoring device according to the invention would, when displaying the residual reactive current I ∆,blind display this value (30 mA). Using the test setup mentioned, the effectiveness of the invention can be easily demonstrated. The capacitance of capacitor C would only need to be dimensioned for corresponding fault currents (depending on the frequency of the low-voltage AC circuit). 202312391 41 ^^. ^^. U LN= 230 Volt, f=50 Hz The invention is briefly explained again below in other words. The curve of an instantaneous differential power is determined from the instantaneous values ​​of the measured differential current and the instantaneous values ​​of the measured voltage. This instantaneous value curve can be converted into an active power (by averaging) and then a differential active current can be determined from this (by dividing by the (50 Hz) effective value of the voltage). This determined differential active current is an effective value that relates to 50 Hz (or the fundamental frequency of the mains voltage). In addition to the active current calculation, the 50 Hz reactive current can be calculated using the same principle. The information can be displayed to the user via an (internal or external) display unit or transmitted via a communication unit (interface), in particular for a (further) external display.Today, it is not possible to split the 50 Hz differential current into active and reactive components because only a current measurement is available and it is physically impossible to separate the 50 Hz component into active and reactive components from the exclusive analysis of the current curve. The method presented here therefore enables new information and new device functions. Active and reactive components can be detected and analyzed. For example, the active and reactive current values ​​can be used to determine the ohmic and capacitive impedance components in an electrical system. 202312391 42 The solution according to the invention requires a voltage determination (measurement) that can be implemented cost-effectively. Only a small amount of calculation is required because only multiplication and averaging are required.An external unit (sensor unit) contains a differential current sensor unit, for example a conventional summation current transformer, and a voltage sensor unit. The external unit is connected to the residual current monitoring device SG. The residual current monitoring device contains the functions for evaluation and, if necessary, display. The external unit can be inserted into a line to one or more consumers. If necessary, a contactless differential current sensor unit (e.g., summation current transformer) or (alternatively: and) a voltage sensor unit (e.g., resistive voltage divider) can be used. Although the invention has been illustrated and described in detail by the exemplary embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

202312391 43 Patent Claims 1. Residual current monitoring device (SG) for monitoring residual currents for electrical low-voltage circuits for alternating voltage, comprising: - a housing with at least one first input E1 for connecting a first external unit (sensor1), wherein the external unit (sensor1) has a differential current sensor unit for determining the level of a differential current of a conductor pair of the low-voltage circuit, and a voltage sensor unit for determining the level of a voltage of the conductor pair, that the residual current monitoring device receives the level of a differential current and the level of a voltage by means of the first input, - an internal or external display unit (DISP), - a control unit (SE) which is connected to the first input (E1) and the display unit (DISP), - that the residual current monitoring device (SG), in particular the control unit (SE), is designed such thatthat a determination of a differential active current or differential reactive current of the first input (E1) is carried out from the obtained level of the differential current and the level of the voltage of the first input, that the level of the differential active current or differential reactive current of the first input (E1) is displayed on the display unit (DISP).

2. Residual current monitoring device (SG) according to claim 1, characterized in that the differential reactive current is the differential reactive current component with the fundamental frequency of the voltage in the low-voltage circuit.

3. Residual current monitoring device (SG) according to one of the preceding claims, characterized in that 202312391 44 that the magnitude of the differential current of the first input (E1) is displayed.

4. Residual current monitoring device (SG) according to one of the preceding claims, characterized in that the external display unit (DISP) receives the magnitude of the differential active current or differential reactive current, in particular also receives the magnitude of the differential current, by means of wired or wireless communication.

5. Residual current monitoring device (SG) according to claim 4, characterized in that a communication unit (COM) connected to the control unit (SE) is provided for wired or wireless communication in order to report the magnitude of the differential active current or differential reactive current, in particular also the magnitude of the differential current. 6.Residual current monitoring device (SG) according to one of the preceding claims, characterized in that the differential current sensor unit determines instantaneous differential current values ​​of the magnitude of the differential current, that the voltage sensor unit determines instantaneous voltage values ​​of the magnitude of the voltage, that an effective value of the voltage is determined from the instantaneous voltage values, that a differential active power is determined from the instantaneous voltage values ​​and the instantaneous differential current values; that an effective value of the differential active current is determined from the differential active power by dividing by the effective value of the voltage, that the effective value of the differential active current is displayed on the display unit. 202312391 45 7. Residual current monitoring device (SG) according to claim 6, characterized in that the differential effective power is determined from the instantaneous voltage values ​​and the instantaneous differential current values ​​by averaging the product of the instantaneous voltage values ​​and the instantaneous differential current values.

8. Residual current monitoring device (SG) according to one of the preceding claims, characterized in that the differential current sensor unit determines instantaneous differential current values ​​of the magnitude of the differential current, that an effective value of the differential current is determined from the instantaneous differential current values, that the voltage sensor unit determines instantaneous voltage values ​​of the magnitude of the voltage, that an effective value of the voltage is determined from the instantaneous voltage values, that a differential apparent power is determined from the effective value of the voltage and the effective value of the differential current,that a differential active power is determined from the instantaneous voltage values ​​and the instantaneous differential current values, that a differential reactive power is determined from the differential apparent power and the differential active power, that the differential reactive current is determined from the differential reactive power, that the differential reactive current is displayed on the display unit.

9. Residual current monitoring device (SG) according to claim 8, characterized in that the differential reactive power is determined from the square root of the difference between the square of the differential apparent power and the square of the differential active power, that an effective value of the differential reactive power is determined from the differential reactive power by dividing it by the effective value of the voltage, 202312391 46 reactive current is determined, that the effective value of the differential reactive current is displayed on the display unit.

10. Residual current monitoring device (SG) according to one of the preceding claims, characterized in that a second input (E2) is provided for connecting a second external unit (sensor2), that the control unit (SE) is connected to the second input (E2), that a determination of a differential active current or differential reactive current of the second input (E2) is carried out from the obtained level of the differential current and level of the voltage of the second input (E2), that the level of the differential active current or differential reactive current of the second input (E2) is displayed on the display unit (DISP).

11. Residual current monitoring device (SG) according to claim 10, characterized in that the level of the differential current of the second input (E2) is displayed. 12.Residual current monitoring device (SG) according to claim 10 or 11, characterized in that a further input or further inputs are provided for the connection of a further external unit or further external units, that the control unit (SE) is connected to the further input or further inputs, that from the received level of the differential current and level of the voltage of the further input or further inputs a determination of a differential active current or differential reactive current of the further input or the further inputs is carried out, that the level of the differential active current or differential. 202312391 47 reactive current of the further input or the further inputs is displayed on the display unit.

13. Residual current monitoring device (SG) according to claim 12, characterized in that the magnitude of the differential current of the further input or the further inputs is displayed.

14. External unit (E1, E2) comprising a differential current sensor unit for determining the magnitude of a differential current of a conductor pair of a low-voltage circuit, and a voltage sensor unit for determining the magnitude of a voltage of the conductor pair, that the external unit (E1, E2) is connectable to a residual current monitoring device (SG). 15.Method for monitoring fault currents for low-voltage electrical circuits for alternating current, in that the magnitude of a differential current between two conductors of a low-voltage circuit is determined, characterized in that the voltage level of the two conductors of the low-voltage circuit is determined, that a differential active current or differential reactive current is determined from the voltage level and the differential current level, and that the magnitude of the differential active current or differential reactive current is displayed.

16. Method according to claim 15, characterized in that the magnitude of the differential current is displayed.

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