Fault current monitoring apparatus and method

Abstract

A fault current monitoring apparatus and method. The invention relates to monitoring of fault currents in low voltage circuits for alternating voltages. The magnitude () of the differential current of the two conductors (L, N) of the low-voltage circuit is determined. The magnitude (ULN) of the voltage of the two conductors of the low voltage circuit is determined. The difference value active current () or the difference value reactive current () is determined according to the magnitude of the voltage and the magnitude of the difference current. And displaying the magnitude of the difference value active current or the difference value reactive current.

Description

[0001] Regardless of the grammatical gender of a particular term, individuals with either male or female gender identity are included. Technical Field

[0002] This invention relates to the field of fault current monitoring equipment for monitoring the magnitude of fault current in low-voltage AC circuits, and to a method for monitoring fault current in low-voltage AC circuits. Background Technology

[0003] Fault current monitoring equipment refers to low-voltage fault current monitoring equipment. It is also called residual current monitoring (RCM) equipment. This type of fault current monitoring equipment (RCM) can be used to measure and display (monitor) fault currents (differential currents), particularly those caused by operation. This is used to monitor (grounding) fault currents in low-voltage AC circuits or, more generally, electrical equipment. The measured differential current is displayed in different ways using fault current monitoring equipment. Low voltage refers to voltages up to 1000 volts AC or 1500 volts DC. Low voltage specifically refers to voltages greater than a value of 50 volts AC or 120 volts DC.

[0004] Circuits used for low voltage refer to circuits used for currents up to 6300 amps, particularly those up to 1600 amps, 1200 amps, 630 amps, 125 amps, 63 amps, 40 amps, 32 amps, 16 amps, 10 amps, or 6 amps. The current values ​​mentioned specifically refer to the design current (formerly known as the rated current and / or breaking current), i.e., the current that the circuit or fault current monitoring device can continuously carry under standard conditions (e.g., the cross-sectional area and length of the copper conductor joint) at a defined ambient temperature (e.g., 40°C) without damage. Such matters are specified in relevant product standards (e.g., DIN EN 60947-2 or 60898-1). In simpler terms, it is the maximum current that the circuit can carry under normal conditions, or the current at which the circuit would typically be interrupted, for example, by a line protection switch or circuit breaker.

[0005] Fault current monitoring equipment is specifically designed for rated current ranges starting from or up to 16, 25, 32, 40, 63, 80, or 125 amps.

[0006] Fault current monitoring devices for low-voltage AC circuits or low-voltage AC equipment are generally known.

[0007] Fault current monitoring devices determine the sum of currents between two or more conductors in a circuit (i.e., determine the total current, or the differential current based on the current direction / power flow direction), which is normally zero. The magnitude of the total current / differential current is displayed for monitoring.

[0008] Almost all fault current monitoring devices to date have a total current transformer, whose primary winding consists of conductors of a circuit, and whose secondary winding outputs, for example, a voltage (or current) equivalent to the sum of currents or differential currents, or the sum of currents / differential currents, which is used directly or indirectly to display magnitude.

[0009] For this purpose, two or more conductors, typically the outgoing and returning conductors or phase conductors (= external conductors) and neutral conductor in a single-phase AC power grid, and all three phase conductors (= external conductors) or all three phase conductors (= external conductors) and neutral conductor in a three-phase AC power grid, are guided through a current transformer, which typically has a toroidal core made of ferromagnetic material. Only the differential current in the conductors, i.e., the current that deviates from the outgoing and returning currents, is converted (or only transferred to the secondary winding). Typically, the sum of the currents in the circuit is equal to zero. Therefore, the magnitude of the fault current can be determined.

[0010] For example, if current flows to ground on the energy absorption side or the equipment side, it is called a fault current (or leakage current to ground) in this context. This is the case, for example, when a person comes into contact with a live conductor. In particular, in this situation, this current to ground is called a fault current.

[0011] Conversely, electrical operating equipment (such as power supply units or frequency converters) may also generate current to ground due to so-called Y capacitors. This current is usually referred to as leakage current.

[0012] For example, a fault occurs when there is a conductive connection from a phase conductor or external conductor in the circuit to ground, such as when a person touches a phase conductor. Consequently, some current will not flow back through the neutral or zero conductor as it would normally, but instead through the person and ground. This fault current can now be collected using a total current transformer because the sum of the outflow and return currents collected is not equal to zero in magnitude.

[0013] The main function of fault current monitoring equipment is to monitor the fault current behavior of electrical equipment. Therefore, it can identify and interrupt fault currents as early as possible. Through early identification and planned elimination, a high level of equipment availability can be ensured.

[0014] Generally, it is impossible to distinguish between leakage current (technically caused) that meets operating conditions and fault current (e.g., caused by personnel or insulation failure). Fault current monitoring equipment reacts the same to both (technically caused leakage current that meets operating conditions or fault current caused by personnel).

[0015] When using electronic operating equipment that frequently utilizes capacitors connected to the protective conductor to eliminate interference (EMV (electromagnetic compatibility) interference elimination) (in technical literature, this EMV measure is referred to as Y capacitor), undesirable (technically caused) fault currents (leakage currents) may occur. Summary of the Invention

[0016] The technical problem to be solved by this invention is to improve fault current monitoring equipment. More specifically, it enables the differentiation between fault currents caused, particularly by personnel or insulation faults, and fault currents (leakage currents) caused by technical reasons.

[0017] The above-mentioned technical problem is solved by a fault current monitoring device having the features of claim 1 and a method having the features of claim 15.

[0018] According to the present invention, a fault current monitoring device for monitoring fault current in a low-voltage circuit using AC voltage is provided, the fault current monitoring device having:

[0019] - A differential current sensor unit used to determine the magnitude of the differential current between two conductors in a low-voltage circuit (specifically, the differential current between the phase conductor and the neutral conductor of the low-voltage circuit, i.e., the differential current between the phase conductor and the neutral conductor, or alternatively, the differential current between the two phase conductors of the low-voltage circuit)).

[0020] - An internal or external display unit suitable for displaying the magnitude of differential current.

[0021] According to the present invention, the fault current monitoring device is extended to include a voltage sensor unit for determining the magnitude of the voltage between the two (or alternatively, the two) conductors of the low-voltage circuit (i.e., particularly the voltage between the phase conductor and the neutral conductor (or alternatively, the voltage between the two phase conductors)).

[0022] It is equipped with a control unit, which is connected to the differential current sensor unit, the voltage sensor unit, and the display unit.

[0023] The fault current monitoring device, especially the control unit, is designed to be...

[0024] The difference in active or reactive current is determined by the magnitude of the voltage and the magnitude of the difference current.

[0025] The display unit shows the magnitude of the differential active current or differential reactive current.

[0026] That is, for example, the differential active current or differential reactive current is displayed on an internal display unit or (or / and) notified to an external display unit, and displayed there.

[0027] Differential current sensor units, in particular, have (conventional) summation current transformers.

[0028] Two conductors of the low-voltage circuit are guided, for example, through the differential current sensor unit, particularly the total current transformer. That is, they form the primary winding of the total current transformer, which, for example, has 0.5 to 1 turns.

[0029] The fault current monitoring device may have a housing with at least two grid-side connectors for two conductors used in the low-voltage circuit. The two grid-side connectors are connected to a voltage sensor unit.

[0030] Furthermore, the fault current monitoring device may have at least two load-side connectors for the two conductors of the low-voltage circuit. These at least two load-side connectors are connected to at least two grid-side connectors. That is, for example, a first grid-side connector for the phase conductor is connected to a first load-side connector, and a second grid-side connector for the neutral conductor is connected to a second load-side connector.

[0031] According to the design of the differential current sensor unit, these connections between the grid-side connector and the load-side connector are connected to or guided through the differential current sensor unit.

[0032] Differential active current refers to the active current component of the differential current, that is, the ohmic current component (real part) of the differential current, which is the current component that generates active power together with the voltage.

[0033] Active power is electrical power that can be converted into other forms of power, such as mechanical, thermal, or chemical power. It is distinct from reactive power, which cannot be used for such conversion. Furthermore, terms such as active power, reactive power, or apparent power are generally known based on the fundamental principles of AC voltage technology.

[0034] An ohmic resistor acting as a load or electrical appliance converts all the power it receives into heat. This is called active power. This power is given in watts (W). If the electrical appliance has inductive and capacitive components in addition to its ohmic resistance, a time offset, also known as phase offset, occurs between the current and voltage (especially sinusoidal ones) in time. Therefore, in addition to active power, there exists reactive power (reactive volt-amperes (VAr)) that is not converted into heat. Instead, reactive power moves back and forth at twice the frequency of the AC voltage. This reactive power is also called oscillating power or moving reactive power. This reactive power should not be confused with so-called distorted reactive power (Verzerrungs-Blindleistung), which is caused by different frequency components in the current and voltage. Reactive power is not consumed (unconsumed "reactive" power).

[0035] If, during power reception by a load / equipment, there is reactive power in addition to active power, the total power is referred to as apparent power. According to DIN 40110-1, apparent power is given in volt-amperes (VA). The volt-ampere (VA) should indicate that reactive power is included in the power measurement. Apparent power is typically referred to in both AC current and AC voltage applications.

[0036] Apparent power is usually greater than active power.

[0037] The portion of the current related to reactive power is called reactive current. In the differential current according to the present invention, this portion of the current is called differential reactive current.

[0038] The current associated with apparent power is the total current, which in this example is the total current of the differential current.

[0039] The differential current consists of the differential active current (real part: ohmic part, active power) and the differential reactive current (imaginary part: capacitive or inductive part, reactive power).

[0040] 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 this example concerning differential current, apparent power is the product of the effective value of the differential current and the effective value of the voltage U, i.e., the differential apparent power.

[0041] Apparent power S consists of the actual active power P and the additional reactive power Q.

[0042] In electrical engineering, the effective value should be understood as the square mean of a physical parameter that varies over time. This term is preferably applied to alternating parameters, and generally to parameters in steady-state processes. The effective value of a variable parameter (voltage or current in this example) is as large as the value of an equivalent parameter that converts the same electrical power as the time-varying parameter on an ohmic electrical device, or converts the same electrical energy as the time-varying parameter over a representative time interval.

[0043] The effective value is related to the peak value and the shape of the curve. In English, the effective value is represented by RMS (an abbreviation for Root Mean Square, or quadratic average).

[0044] This invention particularly relates to a low-voltage circuit utilizing alternating current (AC) voltage, typically a time-dependent sinusoidal AC voltage with frequency f. The instantaneous voltage value of the AC voltage... The time correlation is described by the following equation:

[0045] .

[0046] in:

[0047] = Instantaneous voltage value with respect to time t

[0048] = Voltage amplitude

[0049] Harmonic AC voltage can be represented by the rotation of a pointer, with the pointer's length corresponding to the voltage amplitude. Here, the instantaneous deflection is the projection of the pointer onto the axes of the coordinate system (usually the horizontal axis). The oscillation period corresponds to a complete revolution of the pointer, and its full angle is... (2Pi) or 360°. The circumferential frequency is the rate of change of the phase angle of the rotating pointer. The circumferential frequency of a harmonic oscillation is always 1 / 3 of its frequency. times, that is:

[0050] Circular frequency of alternating voltage

[0051] (T = Duration of the oscillation period)

[0052] Circular frequency ( The given value of is often superior to that of frequency (f) because many formulas in oscillation theory are derived from the definition of period as... The emergence of trigonometric functions allows for a more compact representation using circumferential frequencies:

[0053]

[0054] The term "instantaneous circumferential frequency" is also used when the circumferential frequency is not constant over time.

[0055] In the case of sinusoidal, especially time-constant alternating voltage, the angular velocity... The time-dependent value formed by the sum of time and time t corresponds to the time-dependent angle. It is also called the phase angle. In other words, the phase angle Periodically traverse the range 0... Or 0°...360°. That is, the phase angle periodically takes the values ​​of 0 and... Or a value between 0° and 360° (due to periodicity). or ;in short: or ).

[0056] Therefore, instantaneous voltage value Or instantaneous current value or instantaneous difference current value It refers to the instantaneous value of voltage / current / differential current at time point t; that is, in the case of sinusoidal (periodic) alternating voltage, it refers to the phase angle. The voltage / current / differential current values ​​at the corresponding period or ).

[0057] It can be determined by instantaneous voltage value To calculate the effective value U of the voltage, and it can be obtained from the instantaneous difference current value. This is used to calculate the effective value I of the differential current. The calculation is typically performed over at least one cycle duration of either the voltage or the differential current.

[0058] In this patent application, instantaneous values ​​(e.g., instantaneous voltage values) Instantaneous difference current value Instantaneous difference power The effective values ​​(e.g., the effective value of voltage U, the effective value of differential current I, etc.) are represented by lowercase letters (u, i, ...), while the effective values ​​(e.g., the effective value of voltage U, the effective value of differential current I, ...) are represented by uppercase letters (U, I, ...).

[0059] According to existing fault current monitoring devices, differential current, more precisely, the effective value (I) of the differential current, is used for display or notification. The effective value of the differential current can include both active and reactive components (differential active current and differential reactive current). For example, the effective value of the differential current can consist only of the differential active current component; alternatively, it can consist only of the differential reactive current component; or, more generally, it can consist of both the differential active and differential reactive current components. That is, regardless of whether the differential current contains an active or reactive current component, existing fault current monitoring devices "invariably" (or "foolishly") display or notify the effective value of the differential current. This is particularly applicable to the 50 Hz component of the differential current or differential current flowing at the grid frequency of the voltage.

[0060] According to the invention, it is now advantageous (particularly for the 50 Hz portion of the differential current) not to use the effective value of the differential current, but only to use the differential active current, i.e., the active power portion of the differential current, or (alternatively) the differential reactive current, i.e., the reactive power portion of the differential current. Therefore, it is advantageous to distinguish between fault currents caused by defective insulation or personnel, which are ohmic (since personnel are generally analogous to ohmic resistance (or always contain an ohmic component), and fault currents caused by capacitive or inductive faults (leakage current), i.e., technically caused fault currents or leakage currents (less critical for personnel protection).

[0061] Therefore, the cause can be found more quickly, and the corresponding maintenance can be performed more specifically, thereby saving costs.

[0062] For this purpose, it is advantageous to include a voltage sensor unit for determining the magnitude of the voltage and a control unit in the fault current monitoring device, the control unit being used to determine the differential active current or (alternately) the differential reactive current from the determined magnitude of the voltage and the determined magnitude of the differential current.

[0063] In this context, it is advantageous to use the effective value of the differential active current or the effective value of the differential reactive current.

[0064] In particular, differential active current refers to the active current component of the differential current at the (grid) frequency of the voltage in a low-voltage circuit. That is, in the case of, for example, an AC voltage frequency of 50 Hz (a frequency commonly seen in Europe), the differential active current is related to 50 Hz, which is the fundamental oscillation component.

[0065] In AC technology, harmonic oscillations are assumed in the first-order approximation. That is, the voltage is considered as a harmonic AC voltage as follows (see above):

[0066] ,

[0067] And in the same circuit, the current is considered as a harmonic alternating current as follows:

[0068] ,

[0069] Where phi is the phase offset between (AC) voltage and (AC) current (0° to 360° or -180° and +180°, etc.).

[0070] Based on known alternating current theory, alternating current can be... (Regarding the phase angle phi) it is decomposed into two orthogonal components, namely, a first part that is in phase with the voltage (phase offset = phase difference of 0°) and a second part that has a phase offset of 90° from the voltage.

[0071] Bronstein, *Taschenbuch der Mathematik* (Handbook of Mathematics):

[0072]

[0073]

[0074]

[0075]

[0076] Part of it is related to (alternating) voltage ( The in-phase (phase offset of 0°) AC current component (decomposed AC current component) is referred to as the active current component (active current component).

[0077] Part of it is related to (alternating) voltage ( The orthogonal (phase offset of 90°) alternating current component (decomposed alternating current component) is called the reactive current component (reactive current component), which is the reactive current component with a fundamental frequency (= fundamental oscillation) (e.g., 50 Hz).

[0078] As mentioned at the beginning, this applies to harmonic oscillations / harmonic AC voltage / harmonic AC current with a phase offset Phi between voltage and current (between 0° and 360°).

[0079] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0080] - The active current component is the portion of the current that carries active power along with the (grid) voltage.

[0081] - The active current component has the same frequency as the (grid) voltage, especially the same fundamental frequency (basic oscillation) as the (grid) voltage (e.g., 50 Hz).

[0082] - The active current component has the same phase (or phase) as the (grid) voltage, and in particular, the phase offset between the active current component and the fundamental oscillation of the (grid) voltage is 0°.

[0083] Reactive power moves back and forth at twice the frequency of AC voltage, and is called oscillating power or moving reactive power.

[0084] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0085] - The reactive current component is the portion of the current that carries reactive power along with the (grid) voltage.

[0086] - The reactive current component (also known as the moving reactive current component) has the same frequency as the (grid) voltage, especially the same fundamental frequency (basic oscillation) as the (grid) voltage (e.g., 50 Hz).

[0087] - The reactive current component (moving reactive current) has a phase offset (or phase) of 90° relative to the (grid) voltage.

[0088] Differential reactive current is the portion of the reactive current that is differential to the fundamental frequency of the voltage in a low-voltage circuit.

[0089] This reactive power should not be confused with so-called distorted reactive power, which is caused by different frequency components in the current, especially the higher frequency components of the current (relative to the fundamental frequency of the (grid) voltage). In particular, these are the third, fourth, fifth, and so on harmonics of the current (relative to the fundamental frequency of the (grid) voltage). More generally, it is not equal to the fundamental frequency of the AC voltage ((grid) voltage), but rather to the higher frequency components of the current (relative to the fundamental frequency).

[0090] In the context of this invention, reactive power specifically does not refer to distorted reactive power.

[0091] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0092] - The distorted reactive current component is the portion of the current that transmits reactive power along with the (grid) voltage.

[0093] - The distorted reactive current component has a higher frequency compared to the (grid) voltage, especially compared to the fundamental frequency (basic oscillation) of the (grid) voltage (e.g., 50 Hz).

[0094] Advantageous designs of the invention are given in the dependent claims.

[0095] In an advantageous embodiment of the invention, the magnitude of the differential current is (additionally) displayed.

[0096] This has the particular advantage that, in addition to displaying or notifying the differential active current or differential reactive current, it also displays or notifies the differential current.

[0097] This has the particular advantage of providing an implementation similar to that of conventional fault current monitoring devices.

[0098] In an advantageous embodiment of the invention, the external display unit obtains the magnitude of the differential active current or differential reactive current via wired or wireless communication. In particular, the external display unit also obtains the magnitude of the differential current.

[0099] This has the particular advantage that, by transmitting these values, they can be displayed in the central device and / or stored in the central device.

[0100] In an advantageous embodiment of the invention, a communication unit connected to the control unit is provided for wired or wireless communication to notify the magnitude of the differential active current or differential reactive current, and in particular the magnitude of the differential current, so that it can be displayed, for example, on an external display unit (or a central monitoring or management system).

[0101] This has the particular advantage that differential currents can be evaluated, monitored, and stored in a central management system.

[0102] In an advantageous embodiment of the invention, the fault current monitoring device is designed to be,

[0103] The differential current sensor unit determines the instantaneous differential current value that determines the magnitude of the differential current.

[0104] The voltage sensor unit determines the instantaneous voltage value that represents the magnitude of the voltage.

[0105] The effective value of the voltage (especially over half, one, or multiple AC voltage cycles, generally over multiple times the half-cycle duration of the AC voltage) is determined from the instantaneous voltage value.

[0106] The instantaneous difference power is determined by the instantaneous voltage value and the instantaneous difference current value;

[0107] The differential active power is determined by averaging the instantaneous differential power, particularly over half, one, or more (half) cycle durations of AC voltage, and generally over multiple times the half-cycle duration of AC voltage.

[0108] The effective value of the differential active current is determined by dividing the effective value of the voltage (over the same half-cycle duration of one or more AC voltages, or generally over the same multiple half-cycle duration of AC voltages) by the effective value of the voltage (over the same half-cycle duration of one or more AC voltages, or generally over the same multiple half-cycle duration of AC voltages).

[0109] Display or notify the difference in active current (effective value), especially when it exceeds the active current limit.

[0110] This has the particular advantage of revealing a simple possibility for determining differential active current.

[0111] In an advantageous design of the invention, the instantaneous voltage value... (The alternative location can also be:) and instantaneous difference current value (The alternative location can also be:) ), by analyzing the instantaneous voltage value With instantaneous difference current value The difference in active power is determined by averaging the products (over half, one, or multiple (half) cycle durations of AC voltage, generally over multiple times the half cycle duration of AC voltage). (The alternative location can also be:) In other words, it is determined by the instantaneous difference power. (The alternative location can also be:) ), by (especially arithmetically) averaging (i.e., by averaging the instantaneous difference power) Integrate and divide by the integration duration ( The integral duration is half, one, or multiple times the (half) cycle duration of the AC voltage; generally speaking, it is multiple times the half-cycle duration of the AC voltage to determine the differential active power. .

[0112]

[0113] From the difference in active power It can be calculated by dividing by the effective value of the voltage U (or alternatively, by: To determine the effective value I of the differential current (which can also be: ).

[0114]

[0115] This has the particular advantage of providing specific possibilities for determining the differential active power (the effective value of the differential active current), which can be realized in particular by a control unit with a microprocessor.

[0116] In an advantageous embodiment of the invention, the differential current sensor unit determines the instantaneous differential current value that determines the magnitude of the differential current.

[0117] These instantaneous difference current values ​​determine the effective value of the difference current (over half, one, or multiple AC voltage cycle durations; generally, over multiple times the half-cycle duration of the AC voltage).

[0118] The voltage sensor unit determines the instantaneous voltage value that represents the magnitude of the voltage.

[0119] These instantaneous voltage values ​​determine the effective value of the voltage (over half, one, or multiple AC voltage cycle durations; generally, over multiple times the half-cycle duration of the AC voltage).

[0120] The apparent power difference is determined by the effective value of the voltage and the effective value of the differential current (especially by multiplication).

[0121] This has the particular advantage that it provides a determination of the difference apparent power for further design of the present invention.

[0122] In an advantageous embodiment of the invention, the differential reactive power is determined from the differential apparent power and the differential active power. The differential reactive current is then determined from the differential reactive power.

[0123] This has the particular advantage of revealing a possibility for determining differential reactive current.

[0124] In an advantageous design of the invention, the difference in apparent power... (The alternative location can also be) The square of the difference between the active power and the active power (The alternative location can also be) The square root of the difference between the squares of the two values ​​is used to determine the reactive power difference. The difference in reactive power The effective value U of the voltage (over half, one, or more AC voltage cycle durations, generally speaking, over multiple times the half-cycle duration of the AC voltage) is obtained by dividing by the effective value U of the voltage (over the same half, one, or more AC voltage cycle durations, generally speaking, over the same multiple times the half-cycle duration of the AC voltage). (Alternatively, it can also be:) Determine the effective value of the differential reactive current. Display or (alternatively) notify the effective value of the differential reactive current. In particular, a notification will be issued when the reactive current exceeds the limit value (the reactive current limit value refers to the differential reactive current limit value). The reactive current limit value specifically refers to the differential reactive current limit value at the fundamental frequency (basic oscillation).

[0125]

[0126] (The alternative location can also be:) )

[0127]

[0128]

[0129] This has the particular advantage that it provides a specific possibility for determining the differential reactive current (effective value), which can be achieved, in particular, by a control unit with a microprocessor.

[0130] In an advantageous design of the invention, the determination of differential active current or (alternatively) differential reactive current is performed continuously (periodically).

[0131] This has the particular advantage of providing continuous and periodic monitoring of the low-voltage circuit.

[0132] In an advantageous embodiment of the invention, a mechanically separating contact unit is provided, which has a closed contact state or a closed contact state. The closed contact state is used for current flow in the conductor of the low-voltage circuit, and the open contact state is used to prevent current flow and separation of current in the conductor of the low-voltage circuit.

[0133] Alternatively, an electronic interruption unit may be provided, which has a high-ohmic state for preventing current flow or a low-ohmic state for preventing current flow in low-voltage circuits via semiconductor-based switching elements. When the differential active current exceeds the current limit or the current-time limit (i.e., when the current limit is exceeded for a first duration), the disconnection state of the current-separated contacts for preventing current flow or the high-ohmic state of the switching elements for preventing current flow is initiated.

[0134] This has the following particular advantage: in addition to monitoring the fault current (differential active current) that poses a danger to personnel, it also interrupts the low-voltage circuit, thereby achieving a protective effect in addition to monitoring (similar to a conventional fault current protection switch, but instead of using differential current, it uses differential active current).

[0135] According to the present invention, a method for monitoring fault current in low-voltage circuits for AC voltage, and in particular for a corresponding fault current monitoring device, is claimed, which has the same and additional advantages.

[0136] A method for monitoring fault current in a low-voltage circuit for AC voltage according to the present invention:

[0137] Determine the magnitude of the differential current between the two conductors in a low-voltage circuit.

[0138] Determine the magnitude of the voltage between the two conductors in a low-voltage circuit.

[0139] The difference in active or reactive current is determined by the magnitude of the voltage and the magnitude of the difference current.

[0140] Display the magnitude of the difference in active current or reactive current (especially to notify the magnitude of the difference in active current or reactive current so that it can be displayed at the location where the notification is received, especially when the active current limit or reactive current limit is exceeded).

[0141] In particular, the magnitude of the differential current is displayed (especially the magnitude of the differential current is notified so that it can be displayed at the location where the notification is received).

[0142] According to the present invention, a corresponding computer program product for a fault current monitoring device is claimed. This computer program product includes instructions that, when executed by a microprocessor, cause the microprocessor to perform or support a design scheme or method for the fault current monitoring device according to the present invention.

[0143] In particular, differential active current or (alternatively ground and) differential reactive current can be used for display or notification.

[0144] The microprocessor is part of the fault current monitoring device, and in particular, it is part of the control unit.

[0145] According to the present invention, a corresponding computer-readable storage medium storing a computer program product is claimed.

[0146] According to the present invention, a data carrier signal corresponding to a computer program product is claimed.

[0147] Not only does the reference to claim 1 or claim 15 in a dependent form, but all design schemes that refer to individual features or combinations of features of the claims, especially the reference of dependent device claims to independent method claims, also lead to improvements in fault current monitoring devices.

[0148] Overall, this presents a new concept for fault current monitoring devices. Attached Figure Description

[0149] The features, characteristics, advantages, and implementations of the present invention described herein will become clearer and more readily understood in conjunction with the following detailed description of the embodiments in conjunction with the accompanying drawings.

[0150] Here, in the attached diagram:

[0151] Figure 1 A first illustration is shown, featuring a fault current monitoring device.

[0152] Figure 2 A second illustration is shown, featuring a fault current monitoring device.

[0153] Figure 3 A third illustration shows a device with fault current monitoring.

[0154] Figure 4 A fourth illustration shows a device with fault current monitoring.

[0155] Figure 5 A first block diagram of the computing unit is shown.

[0156] Figure 6 The illustration shown is shown.

[0157] Figure 7 The first test structure utilizing a fault current monitoring device is shown.

[0158] Figure 8 A second test structure utilizing a fault current monitoring device is shown. Detailed Implementation

[0159] Figure 1 A diagram is shown of a fault current monitoring device SG for monitoring low-voltage circuits using AC voltage, which has:

[0160] - Housing 103, which has two terminals on the grid side 101 for the two conductors L and N of the low-voltage circuit, particularly the phase conductor L and neutral conductor N of the low-voltage circuit, and two terminals on the load side 102.

[0161] according to Figure 1 The housing 103 is provided with a neutral conductor connector NG on the grid side, a phase conductor connector LG on the grid side, a neutral conductor connector NL on the load side, and a phase conductor connector LL on the load side for two conductors L and N of the low voltage circuit.

[0162] Typically, an energy source EQ is connected to the grid side 101.

[0163] Typically, electrical equipment ES is connected on the load side 102 (Load);

[0164] - Differential current sensor unit ZCT, which is used to determine the magnitude of the differential current between two conductors L and N (connected to the fault current monitoring device) in the low-voltage circuit. ,

[0165] That is, especially the instantaneous differential current ,

[0166] in, It refers to the magnitude of the phase conductor current (in phase conductor L), that is, the magnitude of the current flowing between the phase conductor terminal LG on the grid side and the phase conductor terminal LL on the load side.

[0167] and It is the magnitude of the neutral conductor current, that is, the magnitude of the current flowing between the neutral conductor joint NG on the grid side and the neutral conductor joint NL on the load side.

[0168] In the circuit, the magnitude of the phase conductor current (in the fault current monitoring device) The magnitude of the neutral conductor current (corresponding to the fault current monitoring device) In other words, the magnitude of the differential current Under normal circumstances, it is usually zero.

[0169] This arrangement will essentially correspond to traditional fault current monitoring equipment.

[0170] According to the present invention, Figure 1 The fault current monitoring device SG is expanded to,

[0171] A voltage sensor unit SUA is provided, which is used to determine the magnitude (especially instantaneous) of the voltage between the two conductors L and N (connected to the fault current monitoring device) of the low-voltage circuit. That is, determining the magnitude of the voltage between the neutral conductor terminal and the phase conductor terminal. According to Figure 1 In this example, the voltage sensor unit SUA is arranged on or in the region of the grid-side connector 101; that is, in this example, it determines the magnitude of the voltage between the grid-side neutral conductor connector NG and the grid-side phase conductor connector LG. .

[0172] (According to existing technology, fault current monitoring equipment does not have a voltage sensor unit (voltage is determined).)

[0173] In addition, a control unit SE is provided, which is connected to the differential current sensor unit ZCT and the voltage sensor unit SUA. The fault current monitoring device SG, especially the control unit SE, is designed to detect the magnitude of the (instantaneous) voltage. The magnitude of the sum (instantaneous) difference current To perform differential active current (RMS value) calculation. The determination.

[0174] The alternative ground (or additional ground) performs differential reactive current (RMS value). The determination.

[0175] According to Figure 1 In the example, the control unit is connected to the internal display unit DISP to display information, particularly the magnitude of the differential active current or differential reactive current, on the fault current monitoring device. The magnitude of the differential current can also be displayed.

[0176] In a design scheme, the magnitude of the differential active current and the magnitude of the differential reactive current can be displayed (and the magnitude of the differential current can be displayed additionally if necessary).

[0177] The control unit is connected to the communication unit (COM) for externally displaying or notifying the magnitude of the differential active current or differential reactive current. The magnitude of the differential current can also be notified.

[0178] In a design scheme, the magnitude of the differential active current and the magnitude of the differential reactive current can be notified (and the magnitude of the differential current can be notified additionally if necessary).

[0179] Alternative or additional grounding may only notify when the active or reactive current limits are exceeded. Active current limits can be, for example, 5mA, 6mA, 10mA, 20mA, 30mA, 50mA, 100mA, or 300mA. Reactive current limits are generally greater than (e.g., 2, 3, 5, or 10 times) or equal to the active current limit.

[0180] The communication unit (COM) can provide wired or wireless communication to notify the magnitude of differential active or reactive current, particularly the magnitude of differential current, especially for external display. It provides notification or transmission. The corresponding current magnitude can be transmitted (notified) to an external display unit. The external display unit can be part of a higher-level monitoring or management system, or it can notify other units, particularly for display purposes.

[0181] The effective value of the differential active current is displayed on an internal or external display unit (e.g., via notification). Or (replace ground and) the effective value of the differential reactive current. .

[0182] The alternative ground or additional ground can display (notify) when the active current limit (or (alternate ground and) reactive current limit) is exceeded.

[0183] In one design, notification contacts can be installed on the fault current monitoring device SG. These notification contacts can be controlled, for example, by the control unit SE. When a specific active current limit (or (alternate ground and) reactive current limit) or (alternate ground and) differential current limit is exceeded, notification can be sent by closing the contacts (alternate ground opening) or by signaling that the critical value has been exceeded. This notification via notification contacts can also be used to switch external switching devices (contactors, relays). The fault current monitoring device can be used to notify the user of a fault in the low-voltage circuit (within the equipment) before the tripping threshold of the protective switching device is reached. Therefore, measures can be taken before disconnecting the equipment when the value deteriorates slowly, for example, due to insulation aging.

[0184] The effective value of the differential active current is determined with respect to the frequency of the AC voltage in the low-voltage circuit. That is, if the frequency of the AC voltage is, for example, 50 Hz, the differential active current is determined with respect to 50 Hz.

[0185] about Figure 2 Description based on Figure 1 Further details regarding the energy source EQ and energy absorber ES.

[0186] Figure 2 It shows that according to Figure 1 The illustrations have the following differences or explanations. Figure 2 In the fault current monitoring device SG, there is a (two-pole) mechanically disconnecting contact unit MK, which has a closed state for the current flow of the conductors in the low-voltage circuit, or an open state for the current separation of the conductors in the low-voltage circuit to prevent current flow. The mechanically disconnecting contact unit MK can also be implemented as a single-pole mechanically disconnecting contact unit, i.e., having a single contact, wherein the contact is preferably arranged in the phase conductor, i.e., between the phase conductor joint LG on the grid side and the phase conductor joint LL on the load side.

[0187] Alternatively, an electronic interruption unit can be provided, which has a high-ohmic state for the switching element to prevent current flow or a low-ohmic state for the switching element to allow current flow in low-voltage circuits via a semiconductor-based switching element.

[0188] Fault current monitoring devices can be designed to, when the differential active current exceeds the current limit or the current-time limit (i.e., when the current limit is exceeded for a first duration), (according to the design) achieve an open state of the (current-on) disconnecting contacts to prevent current flow or a high-ohmic state of the switching elements to prevent current flow.

[0189] In particular, when there is a differential reactive current, the contact is not in an open state or the switching element is in a high-ohmic state (i.e., the current continues to flow).

[0190] The energy source EQ basically has a voltage source SQ that provides an AC voltage, such as an effective value of 230 volts from the phase conductor to the neutral conductor or 400 volts between two phase conductors (not shown) in Europe.

[0191] The neutral conductor is grounded on the energy source side, as indicated by the grounding symbol. This grounding has a grounding impedance. .

[0192] according to Figure 2 It serves as a protective earth (PE) connector to provide a neutral conductor connector on the grounding side.

[0193] The energy source EQ is connected to connectors 101 on both grid sides, according to... Figure 1 and Figure 2 It is connected to the neutral conductor joint NG on the grid side and the phase conductor joint LG on the grid side.

[0194] exist Figure 2The diagram also shows an electrical device ES on the load side. It has a load, in this example a resistor RL. It is connected to connector 102 on the load side, according to... Figure 1 and Figure 2 It is connected to the neutral conductor connector NL on the load side and the phase conductor connector LL on the load side.

[0195] Typically, protective conductor connections are installed in electrical equipment with a metal casing (or similar casing).

[0196] In this example, for instance, the metal casing of the electrical device ES is connected to the protective conductor PE of the energy source EQ via the protective conductor SL. Alternatively, the casing can also be grounded.

[0197] The protective conductor SL has a protective conductor impedance ,like Figure 2 As shown.

[0198] Depending on the type of equipment, a so-called operating current will flow through the protective conductor SL. For example, leakage current. This might be the case, for instance, in a power supply unit that includes a Y capacitor.

[0199] Figure 3 It shows that according to Figure 2 The difference in the diagram is that it depicts the first fault condition, FF1. Based on... Figure 3 In the example, at the output terminal 102 on the load side of the fault current monitoring device SG, that is, between the output terminal 102 on the load side of the fault current monitoring device SG and the electrical equipment ES, there is an electrical connection from the phase conductor to the protective conductor SL. This would be the case, for example, when a person touches the phase conductor and simultaneously (e.g., through a metal casing) touches the protective conductor. In other words, a fault current may flow from the phase conductor connection LL on the load side. (Flowing to the energy source EQ), thereby monitoring the current in the phase conductors in the fault current monitoring device. and current in a neutral conductor No longer the same, because of the fault current through the protective conductor SL. This is marked as a protective conductor current. This could flow to the protective conductor joint PE of the energy source EQ. This fault condition has a resistance value RE1, which may be composed of fault resistance (such as the resistance of a person).

[0200] (For illustrative purposes) in Figure 3 Fault condition FF is shown separately. Fault condition FF may also appear in a similar manner in the electrical equipment ES or other locations.

[0201] According to Figure 3In the example, the generated fault current Corresponding to the differential current determined in the differential current sensor unit ZCT (In this example, the impedance of the protective conductor SL is not considered.) Impedance can be considered in a similar way. ).

[0202] Figure 4 It shows that according to Figure 2 or Figure 3 The difference in the diagram is that it depicts the second fault condition, FF2. Based on... Figure 4 In the example, at the output terminal 102 on the load side of the fault current monitoring device SG, that is, between the output terminal 102 on the load side of the fault current monitoring device SG and the electrical equipment ES, there is an electrical connection from the phase conductor to ground. This is, for example, when a person touches the phase conductor. That is, fault current may flow from the phase conductor connection LL on the load side. (Flowing to the energy source EQ), thereby monitoring the current in the phase conductors in the fault current monitoring device. and current in a neutral conductor No longer the same, because of the fault current It may flow to ground, and via it to the energy source EQ or its ground. This second fault condition FF2 has a resistance value RE2, which may consist of a fault resistance and (possibly) a ground resistance.

[0203] (For illustrative purposes) in Figure 4 The second fault condition FF2 is shown separately. The second fault condition FF2 may also occur in a similar manner at the electrical equipment ES or other locations.

[0204] According to Figure 4 In the example, the generated fault current Corresponding to the differential current determined in the differential current sensor unit ZCT .

[0205] Figure 5 A functional block diagram is shown, illustrating the functions performed in the control unit SE, as illustrated as individual units. Control Unit SE

[0206] - Obtain the magnitude of the differential current from the differential current sensor unit ZCT Especially the instantaneous magnitude of the differential current (instantaneous differential current value), and

[0207] - Obtain the voltage magnitude from the voltage sensor unit SUA In particular, the instantaneous magnitude of the voltage (instantaneous voltage value).

[0208] For example, these two components are fed into the computing unit BE (which, during operation, is part of the control unit SE). The magnitude of the (instantaneous) voltage... The instantaneous magnitude of the sum and difference currents Perform differential active current (RMS value) or (and) difference reactive current Determination of (effective value).

[0209] Differential active current (RMS value) or (and) difference reactive current The magnitude of the (RMS value) is used for display on internal or external display units. (Differential active current) The magnitude of the effective value can be used to avoid current flow in the monitored circuit.

[0210] According to Figure 5 The example shows the effective value of the differential active current. The determination of the magnitude of the (instantaneous) difference current. Specifically, according to Figure 5 The instantaneous magnitude of the differential current (instantaneous differential current value) and the magnitude of the voltage. Specifically, according to Figure 5 The instantaneous magnitude of the voltage (instantaneous voltage value) is fed to the multiplication unit ME, which processes the two parameters fed in (differential current) into a multiplication unit ME. and voltage Multiply (in a phase-correct manner) to determine or calculate the instantaneous difference power. .

[0211] Instantaneous difference power The feed is sent to the first integration unit INT1 to determine the differential active power. It measures the instantaneous difference power over multiple times the half-cycle duration of the AC voltage, such as over the half-cycle duration of the AC voltage, one cycle duration, one half-cycle duration, ... or multiple cycle durations. Integrating or averaging is used to determine or calculate the difference in active power. .

[0212] The magnitude of the voltage Specifically, according to Figure 5 The instantaneous magnitude of voltage Feed to the effective value unit, according to Figure 5 The effective value unit is determined by the instantaneous magnitude of the voltage. Determine or calculate the effective value of the voltage .according to Figure 5The effective value unit consists of three units connected sequentially: the square unit QQ, the second integration unit INT2, and the square root unit QW.

[0213] The instantaneous magnitude of the square unit QQ relative to the voltage The square is then applied. The instantaneous magnitude of the squared voltage is fed into a second integrator unit INT2, which calculates an average value by integrating or, in particular, averaging the squared voltage over multiple times the half-cycle duration of the AC voltage, such as over half-cycle duration, one cycle duration, one half-cycle duration, ..., or multiple cycle durations. (Alternatively, integrator unit INT2 also refers to or includes units for averaging.) The square root unit QW takes the square root of the average value to determine or calculate the effective value of the voltage. (The root mean square and effective values ​​are usually known.) Importantly, in the first integration unit INT1 (= average value unit 1) and the second integration unit INT2 (average value unit 2), integration is performed (respectively) over the same multiple of the half-cycle duration of the AC voltage, i.e., over the same half-cycle duration of the AC voltage, one cycle duration, one half-cycle duration, ... or multiple cycle durations.

[0214] The difference in active power determined by the first integration unit INT1 The effective value of the voltage determined by three sequentially connected units (square unit QQ, second integration unit INT2, and square root unit QW). The power is fed to the division unit DIV, which divides the active power difference by passing it through the division unit DIV. Divide by the effective value of the voltage To determine or calculate the effective value of the differential active current. .

[0215]

[0216]

[0217] In other words, the effective value of the voltage (over a multiple (1, 2, ... n times) half-cycle duration of the AC voltage) is determined by the instantaneous voltage value. .

[0218] The difference in active power (over half-cycle duration of AC voltage of the same multiple) is determined by the instantaneous voltage value and the instantaneous difference current value. .

[0219] The active power difference over the half-cycle duration of the AC voltage (multiple times (1, 2, ... n times)). Divide by the effective value of the voltage (at the same multiple (1, 2, ... n times) of the half-cycle duration of the AC voltage). To determine the effective value of the differential active current. .

[0220] The effective value of the differential active current can be displayed via the internal display unit DISP or notified via the communication unit COM. This is used for (storing) and / or displaying on an external display unit. The effective value of the differential active current can be notified (displayed) only when the active current limit is exceeded. This similarly applies to differential reactive current.

[0221] The external display unit could be, for example, a web browser. Technically, a data storage / database could be provided in some way from which the collected data is loaded and displayed.

[0222] This process, along with other processes, can be implemented using methods, algorithms, or computer program products that run on a microprocessor within the control unit SE. In other words, these units are, for example, the functions performed.

[0223] Alternatively, the instantaneous power determined by the instantaneous voltage value and the instantaneous difference current value can be determined in other ways. From that instantaneous power The differential active power is determined by integrating over multiples (e.g., 1, 2, 3, 4, ... n times) the half-cycle duration of the AC voltage. .

[0224] The control unit can determine the effective value of the differential current (over a multiple of the half-cycle duration of the AC voltage) from the instantaneous differential current value in a similar manner.

[0225] The apparent power difference is determined by multiplying the effective value of the voltage with the effective value of the differential current (with the same time / (multiple) of the cycle duration taken into account accordingly).

[0226] The differential reactive power is determined by the differential apparent power and differential active power. The differential reactive current is determined by the differential reactive power.

[0227] More specifically, the differential reactive power is determined by the square root of the difference between the square of the differential apparent power and the square of the differential active power. The effective value of the differential reactive current is determined by dividing this differential reactive power (over a multiple of the half-cycle duration of the AC voltage) by the effective value of the voltage (over the same multiple of the half-cycle duration of the AC voltage). .

[0228] The effective value of the differential reactive current can be displayed through the internal display unit DISP or notified through the communication unit COM. This is used for (storing) and / or displaying on an external display unit. The effective value of the differential reactive current can be notified (displayed) only when the reactive current limit is exceeded. .

[0229]

[0230]

[0231]

[0232] Alternatively, the differential reactive current determined by the instantaneous voltage value and the instantaneous differential current value can also be determined in other ways.

[0233] The determination of differential active current, and especially differential reactive current, can be advantageously carried out continuously (periodically), for example, with the assistance of a microprocessor.

[0234] Furthermore, the fault current monitoring device can be designed or expanded to serve as an addendum to the differential active or reactive current monitoring, displaying the magnitude (RMS value) of the differential current via an internal display unit (DISP) or notifying it via a communication unit (COM), for storage and / or display on an external display unit. The RMS value of the differential current can be notified (displayed) only when a limit value is exceeded.

[0235] The current limit or current-time limit can be set fully or partially, for example, by means of an input unit or communication unit on the fault current monitoring device.

[0236] In other words, the behavior of the fault current monitoring device according to the present invention is as follows.

[0237] Figure 6 This demonstrates how the magnitude of differential active current or differential reactive current can be displayed on the (internal) display unit DISP (or correspondingly on an external display unit). Based on... Figure 6 The example also shows differential current. .

[0238] Figure 6 The left side shows a digital display, on which the differential current is displayed in the upper area. According to Figure 6 In the example, differential current It is 227 mA; the differential active current is shown in the area below. It acts as an active differential current. As shown, in accordance with Figure 6 In the example, (differential active current) =)Active differential current It is 4 mA.

[0239] Figure 6 The corresponding display is shown as a bar chart in the right-hand section, where the type of current, i.e., differential current, is shown on the horizontal X-axis. Or (differential active current) =)Active differential current The current magnitude was plotted in milliamperes (mA) on the vertical Y-axis (logarithmically).

[0240] Figure 7 The test setup (measurement setup) using the fault current monitoring device SG is shown. The fault current monitoring device SG is connected to the energy source EQ on the grid side via a first switch S1 with two poles. On the load side, the phase conductor terminal LL on the load side is connected to the neutral conductor terminal NG on the grid side via an adjustable resistor R, a second switch S2, and a current measuring device AM.

[0241] In this example, the neutral conductor connector NL on the load side is not connected.

[0242] A voltage measuring device VM is optionally connected between the two grid-side connectors NG and LG of the fault current monitoring device SG.

[0243] The conventional fault current monitoring device and the fault current monitoring device SG according to the present invention behave as follows: when the first and second switches S1 and S2 are closed, and a fault current of, for example, 30 mA is set using an adjustable resistor R... (= Differential current in the test structure of the fault current monitoring device) When this current flows through the current measuring device AM, the two fault current monitoring devices display these values.

[0244] The fault current monitoring device according to the present invention will use the differential active current. (Active differential current) The current is displayed as 30 mA.

[0245] The fault current monitoring device according to the invention also displays differential current. The design scheme will also display this value (30 mA). For differential reactive current... The fault current monitoring device according to the present invention will not display this value (ideally ~0 mA).

[0246] The fault current can be tested by setting different values ​​of the adjustable resistor R. Therefore, the display behavior of the fault current monitoring device SG can be tested.

[0247] Figure 8 It shows that according to Figure 7 The structure / arrangement differs in that, instead of an adjustable resistor R, a particularly adjustable capacitive or inductive component is provided, in this example, a capacitor C with a specific capacitance (advantageously which can be set in a variable manner).

[0248] If the capacitance of capacitor C is designed to provide a (capacitive) fault current of 30 mA in this example. If the current flows through (RMS value, note the tolerance range), then conventional fault current monitoring equipment (according to existing technology) will display this current value.

[0249] For differential active current (Active differential current) The fault current monitoring device SG according to the present invention will not display this value (ideally ~0 mA).

[0250] The fault current monitoring device according to the invention also displays differential current. The design scheme will also display this value (30 mA). For differential reactive current... The fault current monitoring device according to the present invention will display this value (30 mA).

[0251] The effectiveness of the invention can be easily demonstrated using the aforementioned test structure. The capacitance of capacitor C must be determined solely based on the frequency of the low-voltage AC circuit and the corresponding fault current.

[0252]

[0253] For example,

[0254]

[0255] = 230 volts, f = 50 Hz

[0256] The invention will now be briefly described again using other terms.

[0257] The instantaneous difference power change is determined by measuring the instantaneous values ​​of the differential current and voltage. This instantaneous change can be converted into active power (by averaging), and then the differential active current is determined from this (by dividing by the effective value of the (50 Hz) voltage). The determined differential active current is an effective value related to 50 Hz (or the fundamental frequency of the grid voltage). In addition to active current calculation, the 50 Hz reactive current can be calculated using the same principle. This information can be displayed to the user via an internal or external display unit, or transmitted to the user via a communication unit (interface), particularly for external display.

[0258] Currently, it is impossible to decompose the 50 Hz differential current into active and reactive components because only current measurement exists, and physically it is not possible to decompose the 50 Hz component into active and reactive components solely by analyzing current changes. The method shown here therefore enables the realization of new information and the functionality of the equipment. Thus, the active and reactive components can be identified and analyzed. For example, conclusions about the ohmic and capacitive impedance components in electrical equipment can be derived from the values ​​of active and reactive currents.

[0259] The solution according to the invention requires voltage determination (measurement), which can be achieved in a cost-effective manner. Because only multiplication and averaging are required, only minimal computational overhead is needed.

[0260] Although the present invention has been further described and illustrated with reference to the embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A fault current monitoring device (SG) for monitoring fault current in a low-voltage circuit for AC voltage, the fault current monitoring device comprising: - Differential current sensor unit (ZCT), which is used to determine the magnitude of the differential current between the two conductors of the low-voltage circuit. - An internal or external display unit suitable for displaying the magnitude of differential current. Its features are, A voltage sensor unit (SUA) is provided to determine the magnitude of the voltage between the two conductors of the low-voltage circuit. A control unit (SE) is provided, which is connected to the differential current sensor unit (ZCT), the voltage sensor unit (SUA), and the display unit. The fault current monitoring device (SG), and in particular the control unit (SE), is designed to be, The difference in active current or the difference in reactive current is determined based on the magnitude of the voltage and the magnitude of the difference in current. The display unit displays the magnitude of the differential active current or differential reactive current.

2. The fault current monitoring device (SG) according to claim 1. Its features are, The differential reactive current is the portion of the differential reactive current having the fundamental frequency of the voltage in the low-voltage circuit.

3. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The differential current sensor unit (ZCT) specifically has a total current transformer. The two conductors of the low-voltage circuit are guided through the differential current sensor unit (ZCT).

4. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The fault current monitoring device has a housing with at least two grid-side connectors (LG, NG) for the two conductors of the low-voltage circuit. The two grid-side connectors (LG, NG) are connected to the voltage sensor unit.

5. The fault current monitoring device (SG) according to claim 4. Its features are, The fault current monitoring device has at least two load-side connectors (LG, NG) for the two conductors of the low-voltage circuit. Wherein, the at least two load-side connectors are connected to the at least two grid-side connectors. The connection between the load-side connector and the grid-side connector is connected to or guided through the differential current sensor unit.

6. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, This indicates the magnitude of the differential current.

7. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The external display unit obtains the magnitude of the differential active current or differential reactive current via wired or wireless communication, and in particular, also obtains the magnitude of the differential current.

8. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, A communication unit connected to the control unit is provided for wired or wireless communication to notify the magnitude of the differential active current or differential reactive current, and in particular the magnitude of the differential current.

9. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The differential current sensor unit (ZCT) determines the instantaneous differential current value that determines the magnitude of the differential current. The voltage sensor unit (SUA) determines the instantaneous voltage value of the voltage magnitude. The effective value of the voltage is determined from the instantaneous voltage value. The difference active power is determined from the instantaneous voltage value and the instantaneous difference current value; The effective value of the differential active current is determined by dividing the differential active power by the effective value of the voltage. The effective value of the differential active current is displayed on the display unit.

10. The fault current monitoring device (SG) according to claim 9. Its features are, The difference active power is determined by averaging the product of the instantaneous voltage value and the instantaneous difference current value.

11. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The differential current sensor unit (ZCT) determines the instantaneous differential current value that determines the magnitude of the differential current. The effective value of the difference current is determined by the instantaneous difference current value. The voltage sensor unit (SUA) determines the instantaneous voltage value of the voltage magnitude. The effective value of the voltage is determined from the instantaneous voltage value. The apparent power difference is determined from the effective value of the voltage and the effective value of the differential current. The difference active power is determined from the instantaneous voltage value and the instantaneous difference current value; The difference in reactive power is determined from the difference in apparent power and the difference in active power. The differential reactive current is determined from the differential reactive power. The differential reactive current is displayed on the display unit.

12. The fault current monitoring device (SG) according to claim 11. The reactive power difference is determined by the square root of the difference between the square of the apparent power difference and the square of the active power difference. The effective value of the differential reactive current is determined by dividing the differential reactive power by the effective value of the voltage. The effective value of the differential reactive current is displayed on the display unit.

13. The fault current monitoring device (SG) according to any one of the preceding claims. Its features are, The circuit includes a mechanically disconnecting contact unit (MK) connected to the control unit (SE), which has a closed contact state or a closed contact state. The closed contact state allows current flow in the conductors of the low-voltage circuit, while the open contact state prevents current flow and separation of current from the conductors of the low-voltage circuit. When the differential active current exceeds the current limit or the current-time limit, the contact that is used to prevent current flow is disconnected.

14. The fault current monitoring device (SG) according to any one of claims 1 to 12. Its features are, An electronic interruption unit (EU) connected to the control unit (SE) is provided, which has a high-ohmic state for preventing current flow or a low-ohmic state for current flow in the low-voltage circuit via a semiconductor-based switching element. When the differential active current exceeds the current limit or the current-time limit, the current-disconnected contact for preventing current flow is opened or the switching element for preventing current flow is in a high-ohm state.

15. A method for monitoring fault current in a low-voltage circuit for AC voltage. Determine the magnitude of the differential current between the two conductors of the low-voltage circuit. Its features are, Determine the magnitude of the voltage between the two conductors in the low-voltage circuit. The difference in active current or the difference in reactive current is determined based on the magnitude of the voltage and the magnitude of the difference in current. Displays the magnitude of the difference in active current or the difference in reactive current.

16. The method according to claim 15, Its features are, This indicates the magnitude of the differential current.

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