Protection switching device and method

Abstract

The invention relates to fault current protection of a low-voltage AC circuit using a differential current sensor unit (ZCT) for determining the magnitude of the differential current of two conductors of the low-voltage circuit. A voltage sensor unit (SUA) is provided for determining the magnitude of the voltage of the two conductors of the low-voltage circuit. A control unit (SE) is provided, which is connected to the differential current sensor unit (ZCT) and the voltage sensor unit (SUA). And determining the difference value active current according to the magnitude of the voltage and the magnitude of the difference current. The differential active current is compared with a first current limit value or a first current-time limit value. Avoidance of the current flow in the low-voltage circuit is initiated when the first current limit value or the first current-time limit value is exceeded.

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 protective switching devices for protecting low-voltage AC circuits, particularly in the field of fault current protection switching technology, and to a method for fault current protection of low-voltage circuits. Background Technology

[0003] Protective switchgear refers to low-voltage protective switchgear, especially fault current protection switches. Low voltage refers to voltages up to 1000 volts AC or 1500 volts DC. Low voltage specifically refers to voltages greater than a small voltage 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 protective switching 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 protective switching devices such as line protection switches or circuit breakers.

[0005] Fault current protection switches are specifically designed for rated current ranges starting from or up to 6, 10, 16, 25, 32, 40, 63, 80 or 125 amps.

[0006] Fault current protection switches are generally known for use in circuits, especially in low-voltage circuits or low-voltage equipment. Fault current protection switches are also called FI protection switches or residual current devices (RCDs). Fault current protection switches according to the prior art are known from the following patent applications: DE 10 2013 219292 A1; DE 10 2015 224 890 A1; DE 10 2015 225 423 A1; DE 10 2015 225 910 A1; DE10 2015 218 911 A1; DE 10 2015 215 456 A1; DE 10 2016 213 875 A1; DE 10 2016 205101 A1; DE 10 2017 217 040 A1; DE 10 2017 217 267 A1; DE 10 2017 217 411 A1; DE10 2018 200 714 A1.

[0007] A fault current protection switch determines the sum of currents between two or more conductors in a circuit (i.e., determines the total current, or the differential current based on the current direction / power flow direction), which is zero under normal conditions. The fault current protection switch (differential current protection switch) interrupts the circuit when the sum of currents exceeds the differential current value, i.e., exceeds a specific differential current-current limit (differential current threshold, response current value, fault current value, or fault response current value). This is also called triggering. Typical differential current thresholds are, for example, 30 mA for personnel protection and 300 mA for fire protection (IEC standard, 230V / 400V rated voltage network). For special requirements regarding personnel protection, differential current thresholds are typically 10 mA or 6 mA.

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

[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, fault currents can be identified.

[0010] For example, if current flows to ground on the energy absorption side or the equipment side, it is called a fault current 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. This can happen 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 zero in magnitude. The circuit is interrupted, for example, by a holding magnet trigger (= self-holding magnet) or a relay or trigger coil, generally speaking, by an interrupting unit, such as a holding magnet trigger with connecting mechanical devices and contacts; this interruption can result in at least one, part, or all of the circuit being interrupted.

[0013] The main function of a fault current protection switch is to protect people from electric shock and to protect equipment, machinery or buildings from fires caused by electrical insulation faults.

[0014] When a fault current protection switch or its total current transformer is configured such that the energy on the secondary side is sufficient to operate the triggering unit, interrupting unit, or trigger, this type of fault current protection switch is called... Independent of The mains voltage; otherwise, it is called dependent on the mains voltage.

[0015] If the power supply is configured to provide energy for the fault current identification device, it involves fault current protection switches that depend on the mains voltage. These fault current protection switches are needed, for example, to identify fault currents in DC mains and hybrid DC / AC mains, or in circuits with high frequencies.

[0016] Fault current protection switches exist in different implementations, which are referred to as types and represented by letters or letter combinations, such as AC, A, F, G, K, S, B, B+. Each type collects a specific type of fault current. Currently, known fault current protection switches are 2-pole switches for phase conductors and neutral conductors (L+N), 3-pole switches for three phase conductors (L1, L2, L3), and 4-pole switches for three phase conductors and neutral conductors (L1, L2, L3, N).

[0017] For example, Type AC only collects pure sinusoidal fault current. Type A collects both pure sinusoidal AC current and pulsed DC fault current. Type F is a mixed frequency-sensitive fault current protection device. Like Type A, it collects all types of fault current, and is also suitable for collecting fault currents consisting of frequency mixtures up to 1 kHz. Type S is a selective fault current protection switch, which can be graded in terms of design differential current and triggering time. Type B fault current protection switches (= fault current protection devices) are used to collect smooth DC fault currents in addition to those of Type F. Furthermore, they are suitable for fault currents with frequencies up to 2 kHz. For Type B+ fault current protection switches, the same conditions apply as for Type B fault current protection switches. The frequency range for collecting fault current only is suitable for an extended range up to 20 kHz. Type K fault current protection switches contain the characteristics of Type A, but have a short time delay in their disconnection behavior. Type K is also referred to as a superresistent fault current protection switch. Because it is generally impossible to distinguish between leakage current and fault current that meet operating conditions (typically in fault current protection switches), type K fault current protection switches are used. Fault current protection switches react identically to both (leakage current or fault current that meet operating conditions). When leakage current is large for a short period, it is neither necessary nor desirable to disconnect the electrical equipment. When using electronically operated equipment that frequently uses capacitors connected to the protective conductor to eliminate interference, undesirable triggering of the fault current protection switch (= FI protection switch) may occur upon connection. To avoid these disconnections, the use of a super-resistant fault current protection switch (= fault current protection device) is recommended. For this purpose, it has a short time delay in its disconnection behavior (and is referred to as type K).

[0018] Product standards DIN EN 61008-1 (FI protection switches) and DIN EN 61009-1 (FI / LS switches) describe the behavior of fault current protection switches, particularly the limits of their disconnection time. In the sense of this standard, the super-resistant fault current protection switch (FI protection switch) is an implementation with no delay. Type K super-resistant FI protection switches utilize the maximum permissible triggering range of this standard. They have minimal time delay. That is, short-duration leakage currents and large inrush currents are ignored within this time period (thus the fault current protection switch will not trigger accidentally). Disconnection only begins when the fault current flow exceeds the delay time. Protection against electric shock is still achieved through this FI protection device. Unwanted disconnections are eliminated, significantly improving equipment availability.

[0019] In the case of equipment with frequency converters, high equipment availability should be ensured. This means that false triggering, such as due to leakage current caused by technical reasons, should be avoided. Furthermore, personnel protection should be guaranteed. Summary of the Invention

[0020] The technical problem this invention aims to solve is to improve protective switching equipment, particularly fault current protection switches. More specifically, it aims to ensure personnel protection while minimizing the magnitude of the fault current, and to maintain high equipment availability, i.e., especially to avoid false triggering caused by leakage current due to technical reasons.

[0021] The aforementioned technical problem is solved by a protective switchgear having the features of claim 1 and a method having the features of claim 12.

[0022] According to the present invention, a protective switching device, particularly a fault current protection switch, for protecting low-voltage circuits using AC voltage is provided, which has the following features:

[0023] - A housing having at least two terminals on the grid side and at least two terminals on the load side for at least two conductors for low-voltage circuits, particularly phase conductors and neutral conductors for low-voltage circuits (or alternatively, for the two phase conductors of low-voltage circuits).

[0024] - A differential current sensor unit used to determine the magnitude of the differential current (i.e., the differential current between the phase conductor and the neutral conductor, or alternatively, the differential current between the two phase conductors) of a low-voltage circuit.

[0025] - A mechanically separating contact unit having a closed contact state or a closed contact state. The closed contact state is used for the current flow of conductors in a low-voltage circuit, and the open contact state is used to prevent the current flow and to separate the current in conductors of a low-voltage circuit.

[0026] According to the present invention, the protection of switchgear, particularly fault current protection switches, is extended to include,

[0027] A voltage sensor unit is provided to determine the magnitude of the voltage between two conductors (connected to the protective switching device) in the low-voltage circuit (i.e., the voltage between the phase conductor and the neutral conductor (or alternatively, the voltage between the two phase conductors)).

[0028] It is equipped with a control unit, which is connected to the differential current sensor unit, the voltage sensor unit, and the mechanical separation contact unit.

[0029] Protective switchgear, especially control units, is designed to,

[0030] The differential active current is determined by the magnitude of the voltage and the magnitude of the differential current.

[0031] The difference in active current is compared with the first current limit or the first current-time limit.

[0032] When the first current limit or the first current-time limit is exceeded, current flow prevention in the low-voltage circuit is initiated. (The first current limit or the first current-time limit is, for example, a differential current threshold based on a relevant standard.)

[0033] The avoidance of current flow in low-voltage circuits is preferably initiated by the open state of the contacts.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] Apparent power is usually greater than active power.

[0039] 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.

[0040] The current associated with apparent power is the total current, which in this example is the total current of the differential current.

[0041] 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).

[0042] 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.

[0043] Apparent power S consists of the actual active power P and the additional reactive power Q.

[0044] 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.

[0045] 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).

[0046] 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:

[0047] .

[0048] in:

[0049] = Instantaneous voltage value with respect to time t

[0050] = Voltage amplitude

[0051] 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:

[0052] Circular frequency of alternating voltage

[0053] (T = Duration of the oscillation period)

[0054] 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:

[0055]

[0056] The term "instantaneous circumferential frequency" is also used when the circumferential frequency is not constant over time.

[0057] 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 ).

[0058] 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 ).

[0059] 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.

[0060] 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, ...).

[0061] According to existing technology, fault current protection switches use differential current, more precisely, the effective value (I) of the differential current, for triggering. That is, a fault current protection switch with a differential current threshold of, for example, 30 mA, will interrupt the low-voltage circuit when the effective value of the differential current exceeds 30 mA. 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 differential active and differential reactive current components. In other words, regardless of whether the differential current contains an active or reactive current component, according to existing technology, the fault current protection switch "invariably" (or "foolishly") interrupts the circuit when its differential current threshold is exceeded. Therefore, triggering occurs regardless of the type of differential current (active or reactive). Especially in the case of differential current with a base frequency (of the grid voltage), it is currently impossible to distinguish between them.

[0062] According to the present invention, it is now advantageous not to use the differential current (RMS value), but only the differential active current, i.e., the active power portion of the differential current, is used. Therefore, on the one hand, reliable personnel protection can be advantageously provided, since personnel are typically analogous to ohmic resistors (or always contain an ohmic component), and the IEC 60479-1 standard describes the effects of current on the human body; on the other hand, robustness is provided against leakage currents that are technically induced and typically capacitive in nature (which are less critical for personnel protection). Thus, false triggering due to technically induced (capacitive) leakage currents can be avoided.

[0063] Therefore, it is advantageous to provide a voltage sensor unit for determining the magnitude of the execution voltage and a control unit in the protective switchgear / fault current protection switch, the control unit being used to determine the differential active current from the determined magnitude of the voltage and the determined magnitude of the differential current.

[0064] The magnitude of the first current limit or the first current-time limit is advantageously set, for example, on the protective switching device. The current-time limit means that the low-voltage circuit must be interrupted only if the current exceeds the current limit for a specific period of time.

[0065] In this situation, it is advantageous to use the effective value of the differential active current when the first current limit or the first current-time limit is exceeded.

[0066] 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.

[0067] 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):

[0068] ,

[0069] And in the same circuit, the current is considered as a harmonic alternating current as follows:

[0070] ,

[0071] Where phi is the phase offset between (AC) voltage and (AC) current (0° to 360° or -180° and +180°, etc.).

[0072] 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.

[0073] Bronstein, *Taschenbuch der Mathematik* (Handbook of Mathematics):

[0074]

[0075]

[0076]

[0077]

[0078] 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).

[0079] 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).

[0080] 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°).

[0081] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0082] - The active current component is the portion of the current that carries active power along with the (grid) voltage.

[0083] - 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).

[0084] - 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°.

[0085] Reactive power moves back and forth at twice the frequency of AC voltage, and is called oscillating power or moving reactive power.

[0086] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0087] - The reactive current component is the portion of the current that carries reactive power along with the (grid) voltage.

[0088] - 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).

[0089] - The reactive current component (moving reactive current) has a phase offset (or phase) of 90° relative to the (grid) voltage.

[0090] 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.

[0091] 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).

[0092] In the context of this invention, reactive power specifically does not refer to distorted reactive power.

[0093] In general, especially for sampled, time-varying parameters (instantaneous value trends):

[0094] - The distorted reactive current component is the portion of the current that transmits reactive power along with the (grid) voltage.

[0095] - 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).

[0096] Advantageous designs of the invention are given in the dependent claims.

[0097] In an advantageous embodiment of the invention, the magnitude of the differential current is compared with a second current limit or a second current-time limit. When the second current limit or the second current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

[0098] This has the particular advantage that, in addition to interrupting when the differential active current exceeds the limit, it also interrupts when the differential current exceeds the limit.

[0099] In an advantageous embodiment of the invention, for this purpose, the second current limit value or the second current-time limit value is greater than the first current limit value or the first current-time limit value, particularly up to 10 times, 20 times, or 100 times the first current limit value or the first current-time limit value. In particular, this factor is related to the portion on the current limit value side (the current limit value portion) (the magnitude of the current) (i.e., this factor is particularly independent of the time limit value portion).

[0100] This has the following particular advantages: it provides similar safety as a traditional fault current protection switch, and also interrupts the low-voltage circuit when the corresponding differential reactive current is exceeded.

[0101] The magnitude of the second current limit or the second current-time limit is advantageously set, for example, it can be set on the protective switching device.

[0102] In this context, the effective value of the differential current is advantageously used when exceeding the second current limit or the second current-time limit. For example, the first current limit for the differential active current could be 30 mA, 10 mA, or -6 mA to ensure a high level of personnel protection, while the second current limit for the effective value of the differential current could be 300 mA to avoid high robustness against false triggering due to leakage current caused by operation.

[0103] In an advantageous embodiment of the invention, the differential reactive current is determined based on the magnitude of the voltage and the magnitude of the differential current. The differential reactive current is compared to a third current limit or a third current-time limit. If the third current limit or the third current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

[0104] This has the particular advantage that, in addition to interrupting when the differential active current exceeds the limit, it also interrupts when the differential reactive current exceeds the limit.

[0105] In an advantageous embodiment of the invention, the third current limit value or the third current-time limit value is greater than the first current limit value or the first current-time limit value, particularly up to 10, 20, or 100 times the first current limit value or the first current-time limit value. In particular, this factor is related to the portion on the current limit value side (the current limit value portion) (the magnitude of the current) (i.e., this factor is particularly independent of the time limit value portion).

[0106] This has the particular advantage of providing safety even when the differential reactive current is large. When the corresponding differential reactive current exceeds the limit, the low-voltage circuit is interrupted.

[0107] The magnitude of the third current limit or the third current-time limit is advantageously set, for example, it can be set on the protective switching device.

[0108] In this context, it is advantageous to use the effective value of the differential reactive current when the third current limit or the third current-time limit is exceeded.

[0109] In particular, differential reactive current refers to the portion of reactive current obtained at the frequency of the AC voltage in the low-voltage circuit after subtracting the differential active current from the total current. That is, it is the differential reactive current obtained after subtracting the differential active current when the AC voltage frequency is, for example, 50 Hz (common in Europe). Differential reactive current is the portion of reactive current with the fundamental frequency of the voltage in the low-voltage circuit (e.g., 50 Hz in Europe).

[0110] In an advantageous embodiment of the invention, the first current limit or first current-time limit is a fault current limit in personnel protection. Specifically, it has a value of 30 mA or less on the current limit side (with respect to the first current limit or first current-time limit). Alternatively, it may also have a value of 6 mA or less.

[0111] This has the particular advantage that low-voltage circuits can be interrupted only in the case of differential active current, i.e., in the case of ohmic differential current (fault current) caused, for example, due to personnel, provided that applicable personnel protection regulations are observed.

[0112] In an advantageous embodiment of the invention, the protective switching device is designed as follows:

[0113] The differential current sensor unit determines the instantaneous differential current value that determines the magnitude of the differential current.

[0114] The voltage sensor unit determines the instantaneous voltage value that represents the magnitude of the voltage.

[0115] 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.

[0116] The instantaneous difference power is determined by the instantaneous voltage value and the instantaneous difference current value;

[0117] The differential active power is determined by averaging the instantaneous differential power (especially over half, one, or multiple half-cycle durations of AC voltage; generally, over multiple times the half-cycle duration of AC voltage).

[0118] 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.

[0119] The effective value of the differential active current is compared with a first current limit or a first current-time limit to initiate current flow avoidance in the low-voltage circuit when the first current limit or the first current-time limit is exceeded.

[0120] This has the particular advantage of revealing a simple possibility for determining differential active current.

[0121] 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. .

[0122]

[0123] 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: ).

[0124]

[0125] 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.

[0126] 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.

[0127] 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).

[0128] The voltage sensor unit determines the instantaneous voltage value that represents the magnitude of the voltage.

[0129] 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).

[0130] The apparent power difference is determined by the effective value of the voltage and the effective value of the differential current.

[0131] This has the particular advantage that it provides a determination of the difference apparent power for further design of the present invention.

[0132] 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.

[0133] This has the particular advantage of revealing a possibility for determining differential reactive current.

[0134] 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. The effective value of the differential reactive current. It is compared with a third current limit or a third current-time limit to initiate the avoidance of current flow in the low-voltage circuit when the third current limit or the third current-time limit is exceeded.

[0135]

[0136] (The alternative location can also be:) )

[0137]

[0138]

[0139] 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.

[0140] In an advantageous design of the invention, the determination of differential active current, and in particular differential reactive current, is performed continuously (periodically).

[0141] This has the particular advantage of providing continuous and periodic monitoring of the low-voltage circuit.

[0142] According to the present invention, a method for fault current protection of low-voltage circuits for AC voltage, particularly for a corresponding fault current protection switch, is claimed, which has the same and additional advantages.

[0143] The method for fault current protection of low-voltage AC circuits according to the present invention includes:

[0144] - Differential current sensor unit, which is used to determine the magnitude of the differential current between two conductors in a low-voltage circuit.

[0145] - A voltage sensor unit used to determine the magnitude of the voltage between two conductors in a low-voltage circuit.

[0146] - Control unit, which is connected to the differential current sensor unit and the voltage sensor unit.

[0147] The differential active current is determined based on the magnitude of the voltage and the magnitude of the differential current. This differential active current is then compared to a first current limit or a first current-time limit. If the first current limit or the first current-time limit is exceeded, current flow prevention is initiated in the low-voltage AC circuit (between the two conductors).

[0148] In an advantageous design of the method, the magnitude of the differential current is compared with a second current limit or a second current-time limit. If the second current limit or the second current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

[0149] In an advantageous design of the method, the differential reactive current is determined by the magnitude of the voltage and the magnitude of the differential current. The differential reactive current is compared with a third current limit or a third current-time limit. If the third current limit or the third current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

[0150] According to the present invention, a corresponding computer program product for protecting switchgear, particularly fault current protection switches, is claimed. This computer program product includes instructions that, when executed by a microprocessor, cause the microprocessor to perform or support a design or method for protecting switchgear according to the present invention.

[0151] In particular, the differential active current is used for comparison with the current limit or the current-time limit. Furthermore, especially when the current limit or the current-time limit is exceeded, current flow prevention in the low-voltage circuit is initiated.

[0152] Microprocessors are part of the protection switching equipment, and in particular, they are part of the control unit.

[0153] According to the present invention, a corresponding computer-readable storage medium storing a computer program product is claimed.

[0154] According to the present invention, a data carrier signal corresponding to a computer program product is claimed.

[0155] Not only does the reference to claim 1 or claim 12 in a dependent form, but also all design schemes applicable only to individual features or combinations of features of the claims, particularly the reference of dependent device claims to independent method claims, also result in improvements to protective switching equipment, especially fault current protection switches. In particular, it ensures personnel protection even when the fault current is small, and improves equipment availability by avoiding false triggering, for example, due to leakage current caused by technical reasons.

[0156] Overall, this paper presents a new concept for protecting switchgear, and in particular, provides a fault current protection switch. Attached Figure Description

[0157] 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.

[0158] Here, in the attached diagram:

[0159] Figure 1 A first illustration showing a protective switchgear is shown.

[0160] Figure 2 A second illustration showing a protective switchgear is provided.

[0161] Figure 3 A third illustration shows a protective switchgear.

[0162] Figure 4A first block diagram of the control unit is shown.

[0163] Figure 5 A second block diagram of the control unit is shown.

[0164] Figure 6 A first block diagram of the computing unit is shown.

[0165] Figure 7 The first test structure utilizing protective switching equipment is shown.

[0166] Figure 8 A second test structure utilizing protective switching equipment is shown. Detailed Implementation

[0167] Figure 1 A diagram is shown of a protective switching device SG, particularly a fault current protection switch, for protecting low-voltage circuits operating on AC voltage, which has:

[0168] - 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.

[0169] 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.

[0170] Typically, an energy source EQ is connected to the grid side 101.

[0171] Typically, electrical equipment ES is connected to the load side 102;

[0172] - 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 protective switching device) in a low-voltage circuit. That is, especially the instantaneous differential current. ,

[0173] 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.

[0174] 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.

[0175] In a circuit, the magnitude of the phase conductor current (in protective switching equipment) Corresponding to the magnitude of the neutral conductor current (in protective switching equipment) In other words, the magnitude of the differential current Under normal circumstances, it is usually zero.

[0176] - A (two-pole) mechanically separating contact unit MK, which has a closed state of contacts for the current flow of conductors in low-voltage circuits, or an open state of contacts for the separation of current (galvanische) of conductors in low-voltage circuits to prevent current flow.

[0177] The mechanically separating contact unit MK can also be implemented as a single-pole mechanically separating contact unit, i.e., having a 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.

[0178] This arrangement basically corresponds to a conventional fault current protection switch, in which, typically in the case of a fault current line protection switch independent of the mains voltage, the differential current sensor unit ZCT usually controls the mechanically disconnecting contact unit MK through a so-called holding magnet trigger, so that when the magnitude of the differential current exceeds a first current limit or a first current-time limit, the current flow in the low-voltage circuit is prevented by opening the contacts.

[0179] According to the present invention, Figure 1 Protective switchgear, particularly fault current protection switches, is extended to include a voltage sensor unit SUA, which is used to determine the magnitude (particularly instantaneous) of the voltage between the two conductors L and N (connected to the protective switchgear) 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. .

[0180] (According to existing technology, fault current protection switches do not have a voltage sensor unit (voltage is determined).)

[0181] In addition, a control unit SE is provided, which is connected to the differential current sensor unit ZCT, the voltage sensor unit SUA, and the mechanical separation contact unit MK.

[0182] The protective switchgear SG / fault current protection switch, especially the control unit SE, is designed to be controlled by the magnitude of the (instantaneous) voltage. The magnitude of the sum (instantaneous) difference current To determine the differential active current (The effective value).

[0183] The difference in active current (effective value) and first current limit value Compare the (RMS value) or the first current-time limit value.

[0184] Exceeding the first current limit value Or, at the first current-time limit, the avoidance of current flow in the low-voltage circuit is initiated by the control unit SE via the contact disconnect signal open, indicated by the arrow from the control unit SE to the mechanical disconnect contact unit MK.

[0185] Therefore, according to Figure 1 In the example, the avoidance of current flow in the low-voltage circuit is achieved by mechanically separating the open state of the contacts of the contact unit MK.

[0186] 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.

[0187] exist Figure 1 The diagram also shows the individual units of the grid-side energy source EQ. The energy source EQ essentially has a voltage source SQ that provides 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.

[0188] The neutral conductor is grounded on the energy source side, as indicated by the grounding symbol. This grounding has a grounding impedance. ,like Figure 1 As shown.

[0189] according to Figure 1 It serves as a protective earth (PE) connector to provide a neutral conductor connector on the grounding side.

[0190] The energy source EQ is connected to connectors 101 on both grid sides, according to... Figure 1 It is connected to the neutral conductor joint NG on the grid side and the phase conductor joint LG on the grid side.

[0191] exist Figure 1 The 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 It is connected to the neutral conductor connector NL on the load side and the phase conductor connector LL on the load side.

[0192] Typically, protective conductor connections are installed in electrical equipment with a metal casing (or similar casing).

[0193] 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.

[0194] The protective conductor SL has a protective conductor impedance ,like Figure 1 As shown.

[0195] 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.

[0196] Differential current sensor units, in particular, have (conventional) summation current transformers.

[0197] 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.

[0198] Figure 2 It shows that according to Figure 1 The diagram differs in that it depicts the first fault condition, FF1. Based on... Figure 2 In the example, at the output terminal 102 on the load side of the protective switchgear SG, that is, between the output terminal 102 on the load side of the protective switchgear 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 reducing the current in the phase conductors of the protective switching equipment. 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).

[0199] (For illustrative purposes) in Figure 2 Fault condition FF is shown separately. Fault condition FF may also appear in a similar manner in the electrical equipment ES or other locations.

[0200] According to Figure 2 In 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. ).

[0201] Figure 3 It shows that according to Figure 1 or Figure 2 The difference in the diagram is that it depicts the second fault condition, FF2. Based on... Figure 3 In the example, at the output terminal 102 on the load side of the protective switchgear SG, that is, between the output terminal 102 on the load side of the protective switchgear 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, a fault current may flow from the phase conductor connection LL on the load side. (Flowing to the energy source EQ), thereby reducing the current in the phase conductors of the protective switching equipment. 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.

[0202] (For illustrative purposes) in Figure 3 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.

[0203] According to Figure 3 In the example, the generated fault current Corresponding to the differential current determined in the differential current sensor unit ZCT .

[0204] Figure 4 A functional block diagram is shown, illustrating the functions performed in the control unit SE, as illustrated as individual units. Control Unit SE

[0205] - 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

[0206] - Obtain the voltage magnitude from the voltage sensor unit SUA In particular, the instantaneous magnitude of the voltage (instantaneous voltage value).

[0207] Both of these can be fed into the computing unit BE.

[0208] For example, in the calculation unit BE, the magnitude of the (instantaneous) voltage... The instantaneous magnitude of the sum and difference currents Perform differential active current Determination of the effective value. The effective value of the differential active current. With the first current limit value (RMS value) or the first current-time limit (see also) Figure 5 (This is used for comparison. For example, in comparison cell VE. When the first current limit is exceeded...) Alternatively, when the first current-time limit is reached, the control unit SE initiates the avoidance of current flow in the low-voltage circuit by outputting a contact disconnect signal "open" to the mechanical disconnect contact unit MK.

[0209] For example, optionally, when the first current limit value is exceeded. Alternatively, when the first current-time limit is reached, the comparison unit VE can output an exceedance signal trip, which is fed to another optional configuration unit CE, for example, which can be used for adjustment or conversion, and outputs a contact disconnection signal open.

[0210] Figure 5 It shows that according to Figure 4 The illustration differs in that it uses a modified comparison unit. To replace the comparison unit VE. This modified comparison unit... Not only does it perform relative to the first current limit value The comparison, and alternatively or additionally, the comparison is made with respect to the first current-time limit or the current-time limit behavior, which is indicated by a current-time curve in a graph, in which the current limit is plotted on the horizontal X-axis with respect to time t (on the vertical Y-axis). Typically, for example, the current limit decreases as the duration of the fault current increases. That is, the current limit is higher when the differential fault current flows for a very short time compared to for a longer duration (i.e., the current limit is lower in the latter case).

[0211] Figure 6 Another functional block diagram is shown as an example of the function performed in the calculation unit BE, which is illustrated or described as a unit. Specifically, it shows the determination of the effective value of the differential active current. Examples.

[0212] The magnitude of the (instantaneous) difference current Specifically, according to Figure 6 The instantaneous magnitude of the differential current (instantaneous differential current value) and the magnitude of the voltage. Specifically, according to Figure 6 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. .

[0213] 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. .

[0214] The magnitude of the voltage Specifically, according to Figure 6 The instantaneous magnitude of voltage Feed to the effective value unit, according to Figure 6 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 6 The effective value unit consists of three units connected sequentially: the square unit QQ, the second integration unit INT2, and the square root unit QW.

[0215] 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.

[0216] 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. .

[0217]

[0218]

[0219] In other words, the effective value of the voltage (over a period of multiples (1, 2, ... n times) the half-cycle duration of the AC voltage) is determined by the instantaneous voltage value. .

[0220] 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. .

[0221] 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. .

[0222] The effective value of the difference in active current With the first current limit value Alternatively, a first current-time limit can be compared to initiate the avoidance of current flow in the low-voltage circuit if the first current limit or the first current-time limit is exceeded.

[0223] 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.

[0224] 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. .

[0225] 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.

[0226] 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).

[0227] 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.

[0228] 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). The effective value of the reactive current difference. It is compared with a third current limit or a third current-time limit so that current flow in the low-voltage circuit is prevented if the third current limit or the third current-time limit is exceeded.

[0229]

[0230]

[0231]

[0232] 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.

[0233] Furthermore, protective switching equipment or fault current protection switches can be designed or extended to compare the magnitude of the differential current value with a second current limit or a second current-time limit, as a replacement or additional measure for the differential reactive current. When the second current limit or the second current-time limit is exceeded, current flow in the low-voltage circuit is prevented.

[0234] The second or third current limit value, or the second or third current-time limit value, can be greater than the first current limit value or the first current-time limit value. Specifically, it is two, three, four, ... up to ten times the first current limit value. In other applications, it can be up to 20 or 100 times the first current limit value or the first current-time limit value (any intermediate value is acceptable). In particular, this factor is related to the portion on the current limit value side (the current limit value portion) (the magnitude of the current) (i.e., this factor is particularly independent of the time limit value portion).

[0235] In cases where the second (third) current limit or the second (third) current-time limit is exceeded, the effective value of the differential current (differential reactive current) can be used advantageously.

[0236] The current limit value or current-time limit value can be set completely or partially, for example, by means of an input unit or communication unit on the protection switchgear.

[0237] The first current limit or the first current-time limit is advantageously a fault current limit derived from personnel protection. Specifically, it has a value of 30 mA or less on the current limit side (relative to the first current limit or the first current-time limit). Alternatively, it may have a value of 10 mA or less. Alternatively, it may have a value of 6 mA or less.

[0238] The second or third current limit or (second or third) current-time limit (especially the portion on its current limit side) can be, for example, 150 mA or 300 mA.

[0239] In other words, the behavior of the protective switchgear according to the present invention is as follows, for example.

[0240] Figure 7 The test setup (measurement setup) for using the protective switchgear SG / fault current protection switch is shown. On the grid side, the protective switchgear SG is connected to the energy source EQ via a first switch S1 with two poles. On the load side, the load-side phase conductor terminal LL is connected to the grid-side neutral conductor terminal NG 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 terminals NG and LG on the two grid sides of the protective switchgear SG.

[0243] The behavior of conventional fault current protection switches and the protective switchgear SG / fault current protection switch according to the present invention is as follows: when the first and second switches S1 and S2 are closed, and a fault current of, for example, 30 mA (the conventional value, effective value, for fault current protection switches used in personnel protection), set using an adjustable resistor R, is applied. (= Differential current in the test structure of the protective switching device) When the current measuring device AM flows through the current measuring device in this case, the fault current protection switch and the protective switching device SG / fault current protection switch according to the invention interrupt, i.e., trigger the circuit when the current limit or current-time limit (30 mA in this example) is exceeded.

[0244] The fault current can be tested by setting different values ​​of the adjustable resistor R. Therefore, the triggering behavior of the fault current protection switch / protection switchgear SG can be tested. That is, it can be checked whether the fault current protection switch / protection switchgear SG triggers at its pre-given or set current limit value or current-time limit value (e.g., at a maximum of 30 mA).

[0245] Conventional fault current protection switches with current limits or current-time limits of, for example, 30 mA, and the SG / fault current protection switch according to the present invention, must withstand a maximum ohmic fault current (differential active current) of 30 mA set by an adjustable resistor. Down trigger (valid value, note the equipment tolerance range; if the fault current protection switch is measuring the fault current) If, for example, there is a tolerance of + / - 5 mA, then the protective switching device can be configured such that it has been triggered, for example, at 22.5 mA.

[0246] 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).

[0247] 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 the conventional fault current protection switch (according to existing technology) will be interrupted, i.e., the trigger circuit will be activated.

[0248] According to the present invention, the protective switching device SG / fault current protection switch is used in the 30 mA capacitive fault current. (Differential reactive current, RMS value) will not interrupt the circuit.

[0249] If the protective switchgear SG / fault current protection switch according to the present invention is equipped with, for example, a second or third current limit value or a current-time limit value of 300 mA, then the protective switchgear SG / fault current protection switch according to the present invention will withstand a capacitive fault current of 300 mA. (Differential reactive current, RMS value) triggers. However, the SG / fault current protection switch according to the present invention will be triggered under a 30 mA ohmic fault current. Triggered by (differential active current, RMS value).

[0250] 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.

[0251]

[0252] For example,

[0253]

[0254] = 230 volts, f = 50 Hz

[0255] The invention will now be briefly described again using other terms.

[0256] Voltage and the resulting electrical current in the body are dangerous to humans and can quickly lead to injury or death upon contact with voltage. The effects of current and voltage on the human body are now described in international standards such as IEC 60479-1. The hazards to the human body are particularly related to the magnitude and duration of the current. To protect humans from hazards caused by electric current, fault current circuit breakers (RCD protection devices) are now used.

[0257] Nowadays, clock-type voltage converters are increasingly used. These devices cause common-mode current to flow through the protective conductor or to ground potential. This current closes the circuit of any existing fault current protection switch and, in particular, interferes with the proper fault current acquisition and operation of the fault current protection switch. The parasitic capacitance to ground potential from the filter capacitor (i.e., the Y capacitor) or (e.g., in the case of shielded lines) also causes current to flow to the protective conductor, thus causing interference in fault current acquisition. All these currents are acquired as fault current in the differential current transformer, and these currents cause the fault current protection switch to trigger (erroneously).

[0258] The solution and method for fault current assessment according to the present invention can separate the (fault or differential) active current from the (fault or differential) reactive current, and thus react separately to the active current (part) in the (fault or) differential current. Therefore, sensitivity to differential active current can be improved (to achieve enhanced personnel safety), and robustness against parasitic differential current (differential reactive current or so-called leakage current due to operation) can be improved. Therefore, the protection function of fault current protection switches can be improved.

[0259] Therefore, this new differential fault current acquisition takes into account the cause (or effect) of the fault current. If an ohmic connection exists between the phase conductor and ground (or protective conductor) during a fault, active energy from the power grid is transported to the fault location. This current at the fault location is acquired in the equipment via differential current measurement along with all other currents, and this current at the fault location is separated from parasitic differential currents (or leakage currents due to operation) using a new method. The source of the fault current is always the applied grid voltage, which is considered together for further analysis.

[0260] The analysis of differential current is therefore extended to observe differential current power. Here, the applied (instantaneous) (grid) voltage is used. and the measured (instantaneous) difference current Determine the instantaneous difference power (calculate the direction of the difference power) The active power component can be determined from the instantaneous difference power / difference power trend by integration or (especially) averaging. It is appropriate to use it as a multiple of the period duration / basic oscillation duration, or as half of the period duration / basic oscillation duration, for integration or averaging.

[0261] Subsequently, if the determined differential active power is divided by the effective value of the voltage (the applied grid voltage), the effective value of the differential active current is obtained, which represents the active power transmission in the differential current.

[0262] Therefore, the active current (and similarly reactive current) portion of the acquired differential current can be separated, and fault currents (or leakage currents) caused by operation, common-mode current, or leakage current can be separated from the fault current at the ohmic fault location. By performing this separation, more sensitive triggering of fault current protection switches / protective switching devices can be achieved using differential current acquisition, while simultaneously improving robustness against fault currents caused by operation.

[0263] This invention offers the advantage of more sensitive triggering due to ohmic fault current. More sensitive triggering improves electrical safety in low-voltage circuits. Using this new solution and method, for example, protective switching devices can be constructed with triggering characteristics in the AC-2 range (according to IEC_60479-1), thus prohibiting dangerous human body currents (in the AC-3 or AC-4 range). Protective devices with such triggering characteristics provide a new type of electrical safety and are no longer comparable to today's general fault current circuit breakers (RCDs), which cannot ensure that large human body currents will not flow or that small human body currents will not flow over extended periods.

[0264] This invention provides improved robustness against false triggering caused by differential or common-mode currents that meet operating conditions. This improved robustness relative to false triggering increases user satisfaction and reduces complaints arising from false triggering.

[0265] This new solution and approach, for example, enables the use of fault current protection switches in power grids with numerous (power supply units or) converter systems. In these grids, current fault current protection switches are unusable due to high-frequency common-mode currents or differential fault currents, as well as operating conditions-compliant currents on the protective conductors.

[0266] The method according to the invention requires voltage measurement, which can be performed in a cost-effective manner. Because only multiplication and averaging (and RMS calculation) are required in the embodiments, the additional computational overhead is small.

[0267] 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 protective switching device (SG) for protecting a low-voltage circuit using AC voltage, said protective switching device comprising: - A housing having two terminals (LG, NG, LL, NL) for the two conductors of the low-voltage circuit, particularly the phase conductor and the neutral conductor of the low-voltage circuit, on both the grid side and the load side. - 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. - A mechanically disconnecting contact unit (MK) having a closed contact state or a closed contact state, wherein the closed contact state allows current flow in the conductors of the low-voltage circuit, and the open contact state prevents current flow and separation of current in the conductors of the low-voltage circuit. 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 mechanically disconnecting contact unit (MK). The protective switchgear (SG), and in particular the control unit (SE), is designed to be such that, The differential active current is determined based on the magnitude of the voltage and the magnitude of the differential current. The difference in active current is compared with the first current limit or the first current-time limit. When the first current limit or the first current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

2. The protective switchgear (SG) according to claim 1. Its features are, The magnitude of the differential current is compared with the second current limit or the second current-time limit. When the second current limit or the second current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

3. The protective switchgear (SG) according to claim 2. Its features are, The second current limit or the second current-time limit is greater than the first current limit or the first current-time limit, particularly up to 10 times, 20 times or 100 times the first current limit or the first current-time limit.

4. The protective switchgear (SG) according to claim 1, 2 or 3. Its features are, The differential reactive current is determined based on the magnitude of the voltage and the magnitude of the differential current, specifically, the differential reactive current is the portion of the differential reactive current having the fundamental frequency of the voltage in the low-voltage circuit. The difference in reactive current is compared with the third current limit or the third current-time limit. When the third current limit or the third current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

5. The protective switchgear (SG) according to claim 4. Its features are, The third current limit or the third current-time limit is greater than the first current limit or the first current-time limit, particularly up to 10 times, 20 times or 100 times the first current limit or the first current-time limit.

6. The protective switchgear (SG) according to any one of the preceding claims. Its features are, The first current limit or the first current-time limit is the fault current limit in personnel protection, which in particular has a value of 30 mA or less on the current limit side.

7. The protective switchgear (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 compared with the first current limit or the first current-time limit, so that when the first current limit or the first current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

8. The protective switchgear (SG) according to claim 7. Its features are, The difference active power is determined by averaging the product of the instantaneous voltage value and the instantaneous difference current value.

9. The protective switchgear (SG) according to claim 7 or 8. Its features are, The effective value of the difference current is determined from the instantaneous difference current value. The apparent power difference is determined from the effective value of the voltage and the effective value of the differential current.

10. The protective switchgear (SG) according to claim 9. Its features are, 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.

11. The protective switchgear (SG) according to claim 10. Its features are, 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 compared with the third current limit or the third current-time limit, so that when the third current limit or the third current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

12. A method for fault current protection of low-voltage AC circuits. 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 of the low-voltage circuit. The differential active current is determined based on the magnitude of the voltage and the magnitude of the differential current. The difference in active current is compared with the first current limit or the first current-time limit. When the first current limit or the first current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

13. The method according to claim 12, Its features are, The magnitude of the differential current is compared with the second current limit or the second current-time limit. When the second current limit or the second current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

14. The method according to claim 12 or 13, Its features are, The differential reactive current is determined based on the magnitude of the voltage and the magnitude of the differential current. The difference in reactive current is compared with the third current limit or the third current-time limit. When the third current limit or the third current-time limit is exceeded, current flow avoidance in the low-voltage circuit is initiated.

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