Circuit breaker device and method

Abstract

The invention relates to a fault current protection of an electric low-voltage alternating current circuit, comprising a differential current sensor unit (ZCT) for ascertaining the level of a differential current of two conductors of the low-voltage current circuit. A voltage sensor unit (SUA) is provided for ascertaining the level of the voltage of the two conductors of the low-voltage current circuit, and a control unit (SE) is provided which is connected to the differential current sensor unit (ZCT) and to the voltage sensor unit (SUA). A differential active current is ascertained from the level of the voltage and the level of the differential current. The differential active current is compared with a first current threshold or a first current time threshold. If the first current threshold or the first current time threshold is exceeded, a process of preventing a current flow in the low-voltage alternating current circuit is initiated.

Description

[0001] Description

[0002] Protective switching device and procedure

[0003] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0004] The invention relates to the technical field of a protective switching device, in particular a residual current circuit breaker, for protecting an electrical low-voltage alternating current circuit and a method for residual current protection of an electrical low-voltage circuit.

[0005] The term "protective switching device" refers to low-voltage protective switching devices, particularly residual current circuit breakers. Low voltage refers to voltages up to 1000 volts AC or 1500 volts DC. Low voltage refers specifically to voltages higher than extra-low voltage, with values ​​of 50 volts AC or 120 volts DC.

[0006] Low-voltage circuits refer to circuits for currents up to 6300 amps, more specifically currents 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 refer in particular to rated currents (formerly nominal and / or breaking currents), i.e., currents that the circuit or a protective switching device can carry continuously, i.e., without damage, under standardized conditions (such as the connection cross-sections of the copper conductors and their lengths) at a defined ambient temperature (such as 40°C). Such points are specified in relevant product standards (e.g., DIN EN 60947-2 or 60898-1). In colloquial terms, this means the maximum current that is normally carried through the circuit or where the electrical circuit is usually interrupted, for example by a protective switching device such as a circuit breaker or a power switch.

[0007] Residual current circuit breakers are used in particular for rated current ranges of or up to 6, 10, 16, 25, 32, 40, 63, 80 or 125 amperes.

[0008] Residual current circuit breakers for electrical circuits, particularly for low-voltage circuits or systems, are well known. Residual current circuit breakers are also known as residual current devices (RCDs). State-of-the-art residual current circuit breakers are known from the following patent applications: DE 10 2013 219 292 Al; DE 10 2015 224 890 Al; DE 10 2015 225 423 Al; DE 10 2015 225 910 Al; DE 10 2015 218 911 Al; DE 10 2015 215 456 Al; DE 10 2016 213 875 Al; DE 10 2016 205 101 Al; DE 10 2017 217 040 Al; DE 10 2017 217 267 Al; DE 10 2017 217 411 Al; DE 10 2018 200 714 Al.

[0009] Residual current circuit breakers measure the current sum (i.e. a total current or, depending on the current / power flow direction, a differential current) between two or more conductors in an electrical circuit, which is normally zero, and interrupt the electrical circuit when a differential current value is exceeded, i.e. a current sum not equal to zero that exceeds a certain differential current limit (differential current threshold or response current value or fault current value or fault response current value), which is also referred to as tripping. Common differential current thresholds are, for example, 30 mA for personal protection and 300 mA for fire protection (IEC world, 230 volt / 400 volt nominal voltage network). For special requirements for personal protection, a differential current threshold of 10 mA or 6 mA is typical.

[0010] Almost all previous residual current circuit breakers have a summation current transformer, the primary windings of which are formed by the conductors of the circuit and the secondary winding of which outputs the sum current or the differential current or an equivalent of the sum current / the differential current, e.g. in the form of a voltage (or current), which is used directly or indirectly to interrupt the electrical circuit.

[0011] For this purpose, two or more conductors, usually the forward and return conductors or the phase conductor (= outer conductor) and neutral conductor in a single-phase alternating current system, all three phase conductors (= outer conductor) or all three phase conductors (= outer conductor) and the neutral conductor in a three-phase alternating current system, are passed through a current transformer, usually with a ring-shaped core made of ferromagnetic material. Only the differential current from the conductors, i.e. a current that differs from the forward and return current, is converted (or transferred to the secondary winding). The total current in an electrical circuit is usually zero. This allows fault currents to be detected.

[0012] For example, if a current flows to earth on the energy sink or load side, this is referred to as a fault current. This is the case, for example, when a person touches a live phase conductor. In this case, this current to earth is referred to as a fault current.

[0013] In contrast, electrical equipment (such as power supplies or frequency converters) can also discharge a current to ground due to, for example, so-called Y capacitors. This current is typically referred to as leakage current.

[0014] A fault occurs, for example, when there is an electrically conductive connection from a phase conductor or outer conductor of the electrical circuit to earth. For example, when a person touches the phase conductor. In this case, part of the electrical current does not flow back via the neutral conductor or zero conductor as usual, but via the person and the earth. This fault current can now be detected with the help of the summation current transformer, since the recorded sum of the incoming and returning current is not equal to zero. An interruption of the electrical circuit, e.g. at least one, some or all of the lines, is brought about via a holding magnet release (= self-holding magnet) or a relay or a trip coil, generally an interruption unit, for example with connected mechanics and contacts.

[0015] The main function of residual current circuit breakers is to protect people from electrical currents (electric shock), as well as systems, machines or buildings from fire caused by electrical insulation faults.

[0016] If the residual current device or its summation current transformer is designed in such a way that the secondary-side energy is sufficient to actuate a tripping unit or an interruption unit or a release, then such residual current devices are said to be mains voltage independent; otherwise they are said to be mains voltage dependent.

[0017] If a power supply is intended to supply power to a residual current detector, it is a line-voltage-dependent residual current device. These are required, for example, to detect fault currents in DC voltage networks and mixed DC / AC networks, or in high-frequency circuits.

[0018] Residual current circuit breakers are available in different versions, referred to as types, and are identified by letters or letter combinations, such as AC, A, F, G, K, S, B, B+. Each type detects a specific type of residual current. Currently, residual current circuit breakers are available in 2-pole versions for phase and neutral conductors (L+N), 3-pole versions for three phase conductors (LI, L2, L3), and 4-pole versions for three phase conductors and neutral conductors (LI, L2, L3, N).

[0019] For example, type AG only detects purely sinusoidal fault currents. Type A detects both purely sinusoidal alternating currents and pulsating direct residual currents. Type F are mixed-frequency sensitive residual current devices. They detect all types of fault current like type A, but are also suitable for detecting fault currents consisting of a mixture of frequencies up to 1 kHz. Type S are selective residual current circuit breakers which can be graded in terms of both the rated residual current and the tripping time. Type B residual current circuit breakers (= residual current protective devices) are used to detect not only the fault current waveforms of type F but also smooth direct residual currents. They are also suitable for fault currents with frequencies up to 2 kHz. The same conditions apply to type B+ residual current circuit breakers as to type B residual current circuit breakers.Only the frequency range for the detection of fault currents applies for an extended range up to 20 kHz. Type K residual current circuit breakers have the characteristics of type A, but their tripping behavior has a short time delay. Type K is also referred to as super-resistant. They are used because (generally with residual current circuit breakers) it is not possible to distinguish between operational leakage currents and fault currents. The reaction of a residual current circuit breaker is the same for both (operational leakage currents or fault currents). In the case of a brief, high leakage current, switching off the load is neither necessary nor desired. When using electronic equipment which often uses capacitors connected against the protective conductor for interference suppression, this can lead to unwanted tripping of the residual current circuit breaker (= FI circuit breaker) when switched on.To prevent these shutdowns, the use of super-resistant residual current circuit breakers (= residual current devices) is recommended. They have a short time delay in their shutdown behavior (and are designated as Type K).

[0020] The product standards DIN EN 61008-1 (residual current circuit breakers) and DIN EN 61009-1 (residual current / MCBs) describe the behavior of residual current devices, in particular the limit values ​​for tripping times. According to the standard, super-resistant residual current devices (RCDs) are instantaneous versions. Super-resistant Type K residual current devices utilize the maximum permissible tripping range of the standard. They have a minimal time delay. This means that short-term leakage currents and high surge currents are ignored for this period (so that unintentional tripping of the residual current device does not occur). Tripping is only initiated when a fault current flows for longer than the delay time. This residual current device still provides protection against electric shock. The system is protected from unwanted shutdowns - system availability is significantly increased.

[0021] In systems with frequency converters, system availability should be high. This means that nuisance tripping, e.g., due to technical leakage currents, should be avoided. At the same time, personnel protection must be ensured.

[0022] The object of the present invention is to improve a protective switching device, in particular a residual current circuit breaker. More specifically, on the one hand, to ensure personal protection, if possible even at low fault current levels, and on the other hand, to maintain high system availability, i.e., in particular, to avoid false tripping, e.g., due to technically caused leakage currents.

[0023] This object is achieved by a protective switching device having the features of patent claim 1 and a method having the features of patent claim 12.

[0024] According to the invention, a protective switching device, in particular a residual current circuit breaker, for protecting an electrical low-voltage circuit for alternating voltage is proposed, comprising:

[0025] - a housing with at least two mains-side and at least two load-side connections for at least two conductors of the low-voltage circuit, in particular one phase conductor and one neutral conductor of the low-voltage circuit (alternatively for two phase conductors of the low-voltage circuit),

[0026] - a differential current sensor unit for determining the level of a differential current of two conductors (connected to the protective switching device) of the low-voltage circuit (ie the differential current of the phase conductor and neutral conductor (alternatively the differential current of two phase conductors) ),

[0027] - a mechanical isolating contact unit, which has a closed state of the contacts for a current flow of the conductors of the low-voltage circuit or an open state of the contacts for a current flow-preventing galvanic isolation of the conductors of the low-voltage circuit. According to the invention, the protective switching device, in particular residual current circuit breaker, is expanded in such a way that a voltage sensor unit, for determining the level of a voltage of the two (connected to the protective switching device) conductors of the low-voltage circuit (iethe voltage between the phase conductor and the neutral conductor (alternatively the voltage between two phase conductors) ), it is provided that a control unit is provided which is connected to the differential current sensor unit, the voltage sensor unit and the mechanical isolating contact unit, that the protective switching device, in particular the control unit, is designed in such a way that a differential active current is determined from the level of the voltage and the level of the differential current, that the differential active current is compared with a first current limit value or first current-time limit value, that if the first current limit value or first current-time limit value is exceeded, avoidance of a current flow in the low-voltage circuit is initiated. (The first current limit value or first current-time limit value is, for example, a differential current threshold value in accordance with relevant standards. ).

[0028] The prevention of current flow in the low-voltage circuit is preferably initiated by an open state of the contacts. The differential active current refers to the active current component in the differential current, i.e., the ohmic current component (real component) in the differential current, i.e., the current component that, together with the voltage, produces an electrical active power.

[0029] Active power is the electrical power available for conversion into other power (e.g., mechanical, thermal, or chemical). It must be distinguished from reactive power, which cannot be used for this conversion. Furthermore, terms such as active power, reactive power, and apparent power are generally familiar from the fundamentals of AC technology.

[0030] An ohmic resistor as a load or consumer converts the power it absorbs entirely into heat. This is called active power. This power is specified in watts (W). If a consumer has inductive and capacitive components in addition to the ohmic resistance, then a temporal shift occurs between the temporal (especially sinusoidal) curves of current and voltage, also known as a phase shift. In addition to the active power, there is therefore also reactive power (volt-ampere reactive (VAr)) that is not converted into heat. Instead, the reactive power is shifted back and forth at twice the frequency of the alternating voltage. This reactive power is also referred to as oscillation power or displacement reactive power. This type of reactive power should not be confused with so-called distortion reactive power, which in turn is caused by different frequency components in the current and voltage.The reactive power is not consumed (unused "reactive" power).

[0031] If the power consumption of a load / consumer includes both active power and reactive power, the total power is referred to as apparent power. According to DIN 40110-1, apparent power is specified in volt-amperes (VA). Volt-amperes (VA) are used to express that the power includes both active power and reactive power. Apparent power is usually referred to as apparent power for AC and AC voltage consumers.

[0032] The apparent power is usually greater than the active power.

[0033] The current component related to reactive power is referred to as reactive current. In the differential current according to the present invention, this current component is referred to as differential reactive current.

[0034] The current relating to the apparent power is the total current, in this example the total current is the differential current.

[0035] The differential current consists of the differential active current (real part: ohmic component, active power) and the differential reactive current (imaginary part: capacitive or inductive component, reactive power).

[0036] The apparent power S is defined as the product of the effective value of the total current and the effective value of the voltage U. In the example related to the differential current, the apparent power is the product of the effective value of the differential current and the effective value of the voltage U, ie a differential apparent power.

[0037] The apparent power S is composed of the actually converted active power P and the additional reactive power Q.

[0038] In electrical engineering, the root mean square value of a time-varying physical quantity is understood. The term is preferably applied to alternating quantities, generally to quantities in stationary processes. The root mean square value of the variable quantity (in the example, voltage or current) is as large as the value of an equivalent quantity that converts the same electrical power at a resistive load or converts the same electrical energy in a representative period of time as the time-varying quantity. The root mean square value depends on both the peak value and the curve shape. In English, the root mean square value is referred to as RMS (root mean square).

[0039] The present invention relates in particular to low-voltage circuits with an alternating voltage, usually with a time-dependent sinusoidal alternating voltage with the frequency f. The time dependence of the instantaneous voltage value u(t) of the alternating voltage is described by the equation: u(t) = Ua * sin (2n * f * t). Where: u(t) = instantaneous voltage value at time t Ua = amplitude of the voltage

[0040] A harmonic alternating voltage can be represented by the rotation of a pointer whose length corresponds to the amplitude (Ua) of the voltage. The instantaneous deflection is the projection of the pointer onto an axis of the coordinate system (typically the abscissa). One oscillation period corresponds to one full revolution of the pointer, and its full angle is 2n (2Pi) or 360°. The angular frequency is the rate of change of the phase angle of this rotating pointer. The angular frequency of a harmonic oscillation is always 2n times its frequency, i.e.: w = 2n*f = 2n / T = angular frequency of the alternating voltage (T = period of the oscillation)

[0041] Often, the specification of the angular frequency (w) is preferred over the frequency (f), since many formulas of oscillation theory can be represented more compactly using the angular frequency due to the occurrence of trigonometric functions whose period is by definition 2n: u (t) Ua * sin(wt)

[0042] In the case of angular frequencies that are not constant over time, the term instantaneous angular frequency is also used.

[0043] In the case of a sinusoidal, in particular temporally constant, alternating voltage, the time-dependent value of the angular velocity w and the time t corresponds to the time-dependent angle cp ( t ) , which is also referred to as the phase angle cp ( t ). This means that the phase angle cp ( t ) periodically passes through the range O...2n or 0°...360°. This means that the phase angle periodically assumes a value between 0 and 2n or 0° and 360° (cp = n* (0...2n) or cp = n* ( 0 °...360 ° ) , due to periodicity; in short: cp = O...2n or cp = 0°...360° ).

[0044] The instantaneous voltage value u(t) or instantaneous current value or instantaneous differential current value i(t) therefore means the instantaneous value of the voltage / current / differential current at time t, i.e. in the case of a sinusoidal (periodic) alternating voltage, the value of the voltage / current / differential current at the phase angle cp (cp = 0...2n or cp = 0°...360°, of the respective period).

[0045] An effective value of the voltage U can be calculated from instantaneous voltage values ​​u(t), and an effective value of the differential current I can be calculated from instantaneous differential current values ​​i(t). The calculation is usually carried out over at least one period of the voltage or differential current.

[0046] In the patent application, instantaneous values ​​(e.g. instantaneous voltage value u(t) , instantaneous differential current value i(t) , instantaneous differential power p(t) ) are designated with lowercase letters (u, i, ...) and effective values ​​(e.g. effective value of voltage U, effective value of differential current I, ...) are designated with capital letters (U, I, ...). State-of-the-art residual current circuits use the differential current, or more precisely the effective value of the differential current I, for tripping. This means that a residual current circuit with a differential current threshold value of 30 mA, for example, will interrupt the low-voltage circuit if the effective value of the differential current is greater than 30 mA. The effective value of the differential current can contain both active and reactive components (differential active current and differential reactive current components).For example, the effective value of the residual current may consist only of differential active current components; alternatively, the effective value of the residual current may consist only of differential reactive current components; alternatively, or generally, the effective value of the residual current may consist of differential active current components and differential reactive current components. This means that regardless of whether the residual current contains active or reactive current components, a residual current device according to the state of the art "rigidly" (or "stupidly") interrupts the circuit when its differential current threshold is exceeded. Thus, tripping occurs regardless of the type (active or reactive current) of the differential current. In particular, for differential currents with the fundamental frequency (the mains voltage), no distinction is possible today.

[0047] According to the invention, instead of the (effective value of the) differential current, only the differential active current, i.e., the active power component of the differential current, is used. This advantageously provides reliable personal protection, since people typically resemble an ohmic resistance (or always contain an ohmic component)—the IEC 60479-1 standard describes the effect of electrical current on the human body—and, on the other hand, robustness against technically induced leakage currents (which are not critical for personal protection), which are usually capacitive in nature, is provided. This prevents false tripping due to technically induced (capacitive) leakage currents.For this purpose, a voltage sensor unit is advantageously provided in the protective switching device / residual current circuit breaker in order to determine the voltage level, as well as a control unit in order to determine the differential active current from the determined voltage level and the determined differential current level.

[0048] The level of the first current limit or first current-time limit is advantageously adjustable, e.g., on the protective switching device. A current-time limit means that the current must exceed the current limit for a specific period of time before the low-voltage electrical circuit is interrupted.

[0049] In this context, the effective value of the differential active current is advantageously used with regard to the exceedance of the first current limit value or first current time limit value.

[0050] Specifically, differential active current refers to the active current component in the differential current at the (mains) voltage frequency in the low-voltage circuit. This means, for example, that at an alternating voltage frequency of 50 Hz (as is common in Europe), the differential active current is relative to 50 Hz, i.e., the fundamental component.

[0051] In alternating current technology, harmonic oscillations are assumed as a first approximation. This means that a voltage is defined as a harmonic alternating voltage u(t) = Ua * sin(wt)

[0052] (see above) and a current in the same circuit is considered as a harmonic alternating current i (t) I * sin(wt - phi) where phi is the phase shift between (alternating) voltage and (alternating) current (0° to 360° or -180° and +180° etc .).

[0053] The alternating current i (t) = I * sin(wt - phi) can be decomposed (related to the phase angle phi) into two orthogonal components, according to the well-known alternating current theory, into a first component that is in phase with the voltage (phase shift = phase difference 0°) and into a second component with a 90° phase shift with the voltage.

[0054] Bronstein, Pocket Book of Mathematics: sin(a - ß) = cos (ß) * sin(a) + sin(-ß) * cos (a) i (t) = I * sin(wt - phi) a = wt ß ​​= phi i (t) = I * (cos (phi) * sin(wt) + sin(-phi) * cos (wt) )

[0055] The component cos (phi) * sin (wt) is the alternating current component (decomposed alternating current component) that is in phase (phase shift 0°) with the (alternating) voltage (sin (wt)) and is called the active current component (active current component).

[0056] The component sin (-phi) * cos (wt) is the alternating current component (decomposed alternating current component) that is orthogonal (phase shift 90°) to the (alternating) voltage (sin (wt)) and is referred to as the reactive current component (reactive current component), ie the reactive current component with the fundamental frequency (= fundamental oscillation) (e.g. 50 Hz).

[0057] This applies, as already mentioned in the introduction, to a harmonic oscillation / harmonic alternating voltage / harmonic alternating current with a phase shift Phi between voltage and current (between 0° and 360°). In the general case, particularly for sampled, time-varying quantities (instantaneous value curves): - the active current component is the component in the current that transfers active power with the (mains) voltage, - the active current component has the same frequency as the (mains) voltage, in particular the same fundamental frequency (fundamental oscillation) as the (mains) voltage (e.g. 50 Hz), - the active current component has the same phase (or phase position) as the (mains) voltage, in particular the phase shift between the active current component and the fundamental oscillation of the (mains) voltage is 0°.

[0058] The reactive power is shifted back and forth at twice the frequency of the alternating voltage; this is called oscillating power or displacement reactive power.

[0059] For the general case, particularly with sampled, time-varying variables (instantaneous value curves), the following is: -the reactive current component is the component in the current that transfers reactive power with the (mains) voltage, -the reactive current component (also called displacement reactive current component) has the same frequency as the (mains) voltage, in particular the same fundamental frequency (fundamental oscillation) as the (mains) voltage (e.g. 50 Hz), -the reactive current component (displacement reactive current) has a (+ / -) 90° phase shift (or phase position) to the (mains) voltage.

[0060] The di f ference reactive current is the di f ference reactive current component with the fundamental frequency of the voltage in the low-voltage circuit.

[0061] This reactive power should not be confused with the so-called distortion reactive power, which in turn is caused by different frequency components in the current, in particular higher frequency components (relative to the fundamental frequency (fundamental oscillation) of the (mains z-) voltage) in the current. More specifically, the third, fourth, fifth, ... harmonic of the current (relative to the fundamental frequency (fundamental oscillation) of the (mains z-) voltage). More generally, higher (relative to the fundamental frequency) frequency components of the current that are different from the fundamental frequency of the alternating voltage ((mains z-) voltage).

[0062] In the sense of the present invention, reactive power does not mean, in particular, distortion reactive power.

[0063] For the general case, particularly for sampled, time-varying quantities (instantaneous value curves), the following is: -the distortion reactive current component is the component in the current that transmits reactive power with the (network z) voltage, -the distortion reactive current component has a higher frequency compared to the (network z) voltage, particularly to the fundamental frequency (fundamental oscillation) of the (network z) voltage (e.g. 50 Hz).

[0064] Advantageous embodiments of the invention are specified in the subclaims.

[0065] In an advantageous embodiment of the invention, the magnitude of the differential current is compared with a second current limit or second current-time limit. If the second current limit or second current-time limit is exceeded, the prevention of current flow in the low-voltage circuit is initiated.

[0066] This has the particular advantage that in addition to the interruption when the differential active current is exceeded, there is also an interruption when the differential current is exceeded.

[0067] In an advantageous embodiment of the invention, the second current limit value or second current-time limit value is greater than the first current limit value or first current-time limit value, in particular it is up to 10 times or up to 20 times or up to 100 times the first current limit value or first current-time limit value. In particular, the factor is related to the current limit value component (current limit value component) (current level) (i.e. the factor is in particular not related to the time limit value component). This has the particular advantage that safety is provided analogous to classic residual current circuit breakers and the low-voltage circuit is interrupted even if corresponding differential reactive currents are exceeded.

[0068] The level of the second current limit value or second current-time limit value is advantageously adjustable, e.g. adjustable on the protective switching device.

[0069] In this context, the effective value of the residual current is advantageously used to determine when the second current limit or second current-time limit is exceeded. For example, the first current limit for the effective residual current can be 30 mA, 10 mA, or 6 mA to ensure high levels of personal protection, and the second current limit for the effective value of the residual current can be 300 mA to ensure high robustness against false tripping due to operational leakage currents.

[0070] In an advantageous embodiment of the invention, a differential reactive current is determined from the voltage level and the differential current level. The differential reactive current is compared with a third current limit or third current-time limit. If the third current limit or third current-time limit is exceeded, the current flow in the low-voltage circuit is prevented.

[0071] This has the particular advantage that in addition to the interruption when the differential active current is exceeded, there is also an interruption when the differential reactive current is exceeded.

[0072] In an advantageous embodiment of the invention, the third current limit value or third current-time limit value is greater than the first current limit value or first current-time limit value, in particular it is up to 10 times or up to 20 times or up to 100 times the first current limit value or first current-time limit value. In particular, the factor is related to the current-limit-side component (current limit value component) (current level) (i.e. the factor is in particular not related to the time-limit value component). This has the particular advantage that safety is ensured even if the differential reactive currents are too high. If the corresponding differential reactive currents are exceeded, the low-voltage circuit is interrupted.

[0073] The level of the third current limit value or third current-time limit value is advantageously adjustable, e.g. adjustable on the protective switching device.

[0074] In this context, the effective value of the differential reactive current is advantageously used with regard to the exceedance of the third current limit value or third current time limit value.

[0075] Specifically, differential reactive current refers to the reactive current component that results from the total current after subtracting the differential active current at the frequency of the alternating voltage in the low-voltage circuit. This means the differential reactive current that results after subtracting the differential active current at an alternating voltage frequency of, for example, 50 Hz (as is common in Europe). The differential reactive current is the differential reactive current component at the fundamental frequency (Europe, for example, 50 Hz) of the voltage in the low-voltage circuit.

[0076] In an advantageous embodiment of the invention, the first current limit or first current-time limit is a residual current limit used for personal protection. In particular, it has a current limit value of 30 mA or less (relative to the first current limit or first current-time limit). Alternatively, it can also have a value of 6 mA or less.

[0077] This has the particular advantage that the low-voltage circuit is only interrupted in the case of differential active currents, ie in the case of ohmic differential currents (fault currents) caused by people, for example, in compliance with the applicable personal protection regulations.

[0078] In an advantageous embodiment of the invention, the protective switching device is designed such that the differential current sensor unit determines instantaneous differential current values ​​of the magnitude of the differential current, that the voltage sensor unit determines instantaneous voltage values ​​of the magnitude of the voltage, that an effective value of the voltage (in particular over half a period, one or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage) is determined from the instantaneous voltage values, that an instantaneous differential power is determined from the instantaneous voltage values ​​and the instantaneous differential current values; that a differential active power is determined from the instantaneous differential power by averaging (in particular over half a period, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), that from the differential active power,which was determined over half, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), by dividing by the effective value of the voltage (over the same half, one or more (half) periods of the alternating voltage - generally over the same multiple of half the period of the alternating voltage), an (effective value of the) differential active current is determined, that the (effective value of the) differential active current is compared with the first current limit value or first current-time limit value in order to initiate the avoidance of the current flow in the low-voltage circuit if the first current limit value or first current-time limit value is exceeded.

[0079] This has the particular advantage of providing a simple way to determine the differential active current.

[0080] In an advantageous embodiment of the invention, the instantaneous voltage values ​​u(t) (alternatively: u LN ) and the instantaneous differential current values ​​i (t) (alternatively: i a ) by averaging the product of the instantaneous voltage values ​​u(t) and the instantaneous differential current values ​​i(t) (over half, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage) the differential active power Pd (alternatively also: P a ) is determined. This means that from the instantaneous difference power pd(t) (alternatively: p a ) is determined by (especially arithmetic) averaging (ie by integrating the instantaneous difference power pd(t) and dividing by the integration time (t b - t a) ; the integration period is half, one or more (half) periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage) a differential active power Pd is determined.

[0081] From the differential active power Pd (= P a ) can be calculated by dividing by the effective value of the voltage U (alternatively: U LN rms ) the effective value of the differential current I (alternatively: can be determined.

[0082] This has the particular advantage that specific possibilities for determining the differential active power (the (effective value of the) differential active current) are provided, which can be implemented in particular by a control unit having a microprocessor.

[0083] In an advantageous embodiment of the invention, the differential current sensor unit determines instantaneous differential current values ​​of the level of the differential current, from the instantaneous differential current values ​​an effective value of the differential current is determined (over half a period, one or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), the voltage sensor unit determines instantaneous voltage values ​​of the level of the voltage, from the instantaneous voltage values ​​an effective value of the voltage is determined (over half a period, one or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage), that a differential apparent power is determined from the effective value of the voltage and the effective value of the differential current.

[0084] This has the particular advantage that the difference in apparent power can be determined for further embodiments of the invention.

[0085] In an advantageous embodiment of the invention, a differential reactive power is determined from the differential apparent power and the differential active power. The differential reactive current is determined from the differential reactive power.

[0086] This has the particular advantage of showing a possibility for determining the differential reactive current.

[0087] In an advantageous embodiment of the invention, the square root of the difference from the square of the difference apparent power S (alternatively also S ä ) and the square of the difference active power Pd (alternatively P A ) the differential reactive power Q is determined. From the differential reactive power Q a (over half, one or more periods of the alternating voltage - generally over a multiple of half the period of the alternating voltage) is calculated by dividing by the effective value of the voltage U (alternatively: U LNrms) (over the same half, one or more periods of the alternating voltage - generally over the same multiple of half the period of the alternating voltage) an effective value of the differential reactive current The effective value of the differential reactive current 1^, reactive is compared with the third current limit or third current-time limit in order to initiate the prevention of current flow in the low-voltage circuit if the third current limit or third current-time limit is exceeded.

[0088] SU * I (alternatively: S^=U Wrms - 1 rms ) i _

[0089] 'A, blind rr

[0090] '~'LN,rms

[0091] This has the particular advantage that a specific possibility of determining the (effective value of the) differential reactive current is provided, which can be realized in particular by a control unit having a microprocessor.

[0092] In an advantageous embodiment of the invention, the determination of the differential active current, in particular the differential reactive current, is carried out continuously (periodically).

[0093] This has the particular advantage of providing continuous periodic monitoring of the low-voltage circuit.

[0094] According to the invention, a corresponding method for residual current protection of an electrical low-voltage circuit for alternating voltage, especially for a residual current circuit breaker, with the same and further advantages is claimed.

[0095] The method according to the invention for residual current protection of a low-voltage AC electrical circuit comprises:

[0096] - a differential current sensor unit for determining the level of a differential current of two conductors of the low-voltage circuit,

[0097] - a voltage sensor unit for determining the voltage level of the two conductors of the low-voltage circuit,

[0098] - a control unit connected to the differential current sensor unit and the voltage sensor unit. A differential active current is determined from the voltage level and the differential current level. The differential active current is compared with a first current limit or first current-time limit. If the first current limit or first current-time limit is exceeded, the prevention of current flow in the low-voltage AC circuit (of both conductors) is initiated.

[0099] In an advantageous embodiment of the method, the magnitude of the differential current is compared with a second current limit or second current-time limit. If the second current limit or second current-time limit is exceeded, the prevention of current flow in the low-voltage circuit is initiated.

[0100] In an advantageous embodiment of the method, a differential reactive current is determined from the voltage level and the differential current level. The differential reactive current is compared with a third current limit or third current-time limit. If the third current limit or third current-time limit is exceeded, the prevention of current flow in the low-voltage circuit is initiated.

[0101] According to the invention, a corresponding computer program product for a protective switching device, in particular a residual current circuit breaker, is claimed. The computer program product comprises instructions which, when the program is executed by a microprocessor, cause the microprocessor to implement or support the inventive embodiments or methods of the protective switching device.

[0102] In particular, the differential active current is used for comparison with current limit values ​​or current-time limit values. In particular, if these are exceeded, the prevention of current flow in the low-voltage circuit is initiated. The microprocessor is part of the protective switching device, in particular the control unit.

[0103] According to the invention, a corresponding computer-readable storage medium on which the computer program product is stored is claimed.

[0104] According to the invention, a corresponding data carrier signal which transmits the computer program product is claimed.

[0105] All embodiments, both in dependent form referring back to patent claim 1 or 12, and referring back only to individual features or combinations of features of patent claims, in particular also a reference of the dependent arrangement claims to the independent method claim, result in an improvement of a protective switching device, in particular a residual current circuit breaker. Specifically, on the one hand, personal protection is ensured, even at low fault current levels, and on the other hand, system availability is increased by avoiding false triggering due to technically induced leakage currents.

[0106] In general, a new concept for a protective switching device, specifically a residual current device, is provided.

[0107] The described properties, features and advantages of this invention as well as the manner in which these are achieved will become clearer and more clearly understandable in connection with the following description of the embodiments, which are explained in more detail in connection with the drawing.

[0108] The drawing shows:

[0109] Figure 1 shows a first representation with a protective switching device,

[0110] Figure 2 shows a second representation with a protective switching device,

[0111] Figure 3 shows a third representation with a protective switching device, Figure 4 shows a first block diagram for a control unit,

[0112] Figure 5 shows a second block diagram for a control unit,

[0113] Figure 6 shows a first block diagram for a calculation unit,

[0114] Figure 7 a first test setup with a protective switching device,

[0115] Figure 8 shows a second test setup with a protective switching device.

[0116] Figure 1 shows a representation of a protective switching device SG, in particular a residual current circuit breaker, for protecting an electrical low-voltage circuit for alternating voltage, comprising:

[0117] - a housing 103 with two mains-side connections 101 and two load-side connections 102 for two conductors L, N of the low-voltage circuit, in particular a phase conductor L and a neutral conductor N of the low-voltage circuit, according to Figure 1, a mains-side neutral conductor connection NG, a mains-side phase conductor connection LG, a load-side neutral conductor connection NL and a load-side phase conductor connection LL for the two conductors L, N of the low-voltage circuit are provided on the housing 103; an energy source EQ is usually connected to the mains side 101, and a consumer ES is usually connected to the load side 102;

[0118] - a differential current sensor unit ZCT , for determining the level of a differential current i a of the two conductors L, N of the low-voltage circuit (connected to the protective device), i.e. a, in particular instantaneous, differential current i a = i L - IN , where i L is the magnitude of the phase conductor current (in the phase conductor L), i.e. the magnitude of the current flowing between the mains-side phase conductor connection LG and the load-side phase conductor connection LL, and i N is the level of the neutral conductor current, ie the level of the current flowing between the mains-side neutral conductor connection NG and the load-side neutral conductor connection NL.

[0119] In a circuit, the magnitude of the phase conductor current i L (in the protective switching device) the level of the neutral conductor current i N (in the protective switching device), ie the level of the differential current i a = i L - i Nis normally equal to zero.

[0120] - a (two-pole) mechanical isolating contact unit MK, which has a closed state of the contacts for a current flow of the conductors of the low-voltage circuit or an open state of the contacts for a current flow-preventing galvanic isolation of the conductors of the low-voltage circuit; the mechanical isolating contact unit MK can also be designed as a single-pole mechanical isolating contact unit, ie with one contact, wherein the contact is preferably arranged in the phase conductor, ie between the mains-side phase conductor connection LG and the load-side phase conductor connection LL.

[0121] This arrangement essentially corresponds to a classic residual current circuit breaker, whereby the residual current sensor unit ZCT controls the mechanical isolating contact unit MK, usually in the case of mains voltage-independent residual current circuit breakers via a so-called holding magnet release, so that if the level of the residual current exceeds a first current limit value or first current-time limit value, the current flow in the low-voltage circuit is prevented by opening the contacts.

[0122] According to the invention, the protective switching device, in particular residual current circuit breaker, according to Figure 1 is extended in such a way that a voltage sensor unit SUA, for determining the (in particular instantaneous) level of the voltage u LN , the two conductors L, N of the low-voltage circuit (connected to the protective switching device), ie the level of voltage u LNbetween the neutral conductor connection and the phase conductor connection. In the example according to Figure 1, the voltage sensor unit SUA is arranged at or in the area of ​​the mains-side connections 101, ie in this example the level of the voltage u LN between the mains-side neutral conductor connection NG and the mains-side phase conductor connection LG.

[0123] (A residual current device according to the state of the art does not have a voltage sensor unit (voltage detection).)

[0124] Furthermore, a control unit SE is provided, which is connected to the differential current sensor unit ZCT, the voltage sensor unit SUA, and the mechanical isolating contact unit MK. The protective switching device SG / residual current circuit breaker, in particular the control unit SE, is designed such that the level of the (instantaneous) voltage u LN and the level of the (instantaneous) differential current i a (i a = i L - iN ) a determination of an (effective value of the) differential active current I afWlrk is carried out.

[0125] The (effective value of the) differential active current I afWlrk is set to a first current limit I afWirk * (rms value) or first current-time limit value.

[0126] If the first current limit I is exceeded afWirk * or first current-time limit value, avoidance of a current flow in the low-voltage circuit is initiated by the control unit SE, by a contact opening signal open, represented by an arrow from the control unit SE to the mechanical isolating contact unit MK.

[0127] In the example shown in Figure 1, the current flow in the low-voltage circuit is prevented by an open state of the contacts of the mechanical isolating contact unit MK.

[0128] The (effective value) of the differential active current is determined in relation to the frequency of the alternating voltage in the low-voltage circuit. This means that for an alternating voltage frequency of, for example, 50 Hz, the differential active current is determined in relation to 50 Hz. Figure 1 also shows the basic principles of individual units of the grid-side energy source EQ. The energy source EQ essentially comprises a voltage source SQ which provides an alternating voltage, for example in Europe 230 volts phase conductor to neutral conductor or 400 volts between two phase conductors (not shown), effective values ​​of the alternating voltage.

[0129] The neutral conductor is earthed on the energy source side, which is represented by an earth symbol. This earthing has an earth impedance Z PE as shown in Figure 1 .

[0130] The earth-side neutral conductor connection is provided as a protective conductor connection PE (Protective Earth) as shown in Figure 1.

[0131] The energy source EQ is connected to the two mains-side terminals 101, according to Figure 1 to the mains-side neutral conductor terminal NG and the mains-side phase conductor terminal LG.

[0132] Figure 1 also shows the basic principle of the load-side consumer ES. It has a load, in the example a resistor RL. This is connected to the load-side terminals 102, according to Figure 1 to the load-side neutral conductor terminal NL and the load-side phase conductor terminal LL.

[0133] Typically, consumers with a metal housing (or similar) are provided with a protective conductor connection.

[0134] In this example, the metal housing of the consumer ES is connected to the protective conductor terminal PE of the energy source EQ via a protective conductor SL. Alternatively, the housing could also be grounded.

[0135] The protective conductor SL has a protective conductor impedance Z SL as indicated in Figure 1 .

[0136] Depending on the device type, a so-called operational current i flows on the protective conductor SL SL , like a leakage current .

[0137] This can be the case, for example, with a power supply unit containing Y capacitors. The differential current sensor unit, in particular, has a (classic) summation current transformer.

[0138] The two conductors of the low-voltage circuit are routed, for example, through the differential current sensor unit, in particular the summation current transformer. This means that they form the primary winding of the summation current transformer, for example, with a number of turns of 0.5 to 1.

[0139] Figure 2 shows a diagram similar to Figure 1, with the difference that a first fault case FF1 is shown. In the example according to Figure 2, there is an electrical connection from the phase conductor to the protective conductor SL at the load-side output 102 of the protective switching device SG, ie between the load-side output 102 of the protective switching device SG and the load ES. This would be the case, for example, if a person touches the phase conductor and, at the same time, has contact with the protective conductor (e.g., via a metal housing). This means that an electrical fault current i RE1 flow away (to the energy source EQ) so that in the protective switching device the current in the phase conductor i L and the current in the neutral conductor i N is no longer identical, since a fault current i RE1 via the protective conductor SL, here as protective conductor current i SLmarked, can flow to the protective conductor terminal PE of the energy source EQ. The fault case has a resistance value RE1, which can consist of fault resistances (e.g., a person's resistance).

[0140] The fault FF is shown separately in Figure 2 (for explanation). The fault FF can also occur analogously in the consumer ES or elsewhere.

[0141] In the example shown in Figure 2, the resulting fault current i RE1 the differential current i determined in the differential current sensor unit ZCT a (i RE1 = i RE = i a ) (the impedance Z SLof the protective conductor SL is not taken into account in this example; it can be taken into account in an analogous manner). Figure 3 shows a representation according to Figure 1 or 2, with the difference that a second fault case FF2 is shown. In the example according to Figure 3, there is an electrical connection from the phase conductor to earth at the load-side output 102 of the protective switching device SG, ie between the load-side output 102 of the protective switching device SG and the consumer ES. This is the case, for example, if a person touches the phase conductor. This means that an electrical fault current i RE2 flow away (to the energy source EQ) so that in the protective switching device the current in the phase conductor i L and the current in the neutral conductor i N is no longer identical, since a fault current i RE2to earth and then to the energy source EQ or its earth. The second fault case FF2 has a resistance value RE2, which can consist of fault resistances and (if applicable) earth resistances.

[0142] The second fault case FF2 is shown separately in Figure 3 (for explanation). The second fault case FF2 can also occur in an analogous manner at the consumer ES or otherwise.

[0143] In the example shown in Figure 3, the resulting fault current i RE2 the differential current i determined in the differential current sensor unit ZCT a (i RE2 = i a ) .

[0144] Figure 4 shows a functional block diagram of functions executed in the control unit SE, which are represented as units. The control unit SE receives

[0145] - from the differential current sensor unit ZCT the level of the differential current i a(= i (t) ) , in particular the instantaneous level of the differential current (instantaneous differential current values) , and

[0146] - from the voltage sensor unit SUA the level of voltage u LN (= u(t) ) , in particular the instantaneous level of the voltage (instantaneous voltage values) .

[0147] Both can be fed into a calculation unit BE. From the level of the (instantaneous) voltage u LN and the (instantaneous) level of the differential current i a (i a = i L - i N ), for example in the calculation unit BE, a determination of a differential active current I afWlrk (effective value). The (effective value of the) differential active current I &fWlrk is set to a first current limit I a , wir k* (effective value) or the first current-time limit value (see also Fig. 5). For example, in a comparison unit VE. If the first current limit value I a , wlrk* or the first current-time limit value, the control unit SE initiates the prevention of current flow in the low-voltage circuit by sending a contact opening signal (open) to the mechanical isolating contact unit MK. For example, the comparison unit VE can optionally be triggered when the first current limit value I is exceeded. afWirk * or first current time limit value, issue an exceedance signal trip, which is fed to another optional configuration unit CE, with which, for example, an adjustment or conversion can be carried out, which in turn issues the contact opening signal open.

[0148] Figure 5 shows a representation according to Figure 4, with the difference that the comparison unit VE is replaced by a modified comparison unit VE*. The modified comparison unit VE* not only performs a comparison against a first current limit value I afWirk* by, but alternatively or additionally against a first current-time limit value or a current-time limit value behavior, which is indicated by a current-time curve in a diagram in which the current limit value I afWirk * plotted as a function of time t (on the vertical Y-axis). Typically / for example, the current limit decreases with the duration of the flowing fault current. This means that for a very short time during which the differential fault current flows, the current limit is higher than for a longer duration (i.e., in the latter case, the current limit is lower).

[0149] Figure 6 shows a further functional block diagram of an example of functions executed in the calculation unit BE, which are represented or described as units. This is an example of a determination of the (effective value of the) differential active current I &fWirk .

[0150] The magnitude of the (instantaneous) differential current i a , specifically according to Figure 6 the instantaneous level of the differential current (instantaneous differential current values) and the level of the voltage u LN , specifically according to Figure 6 the instantaneous voltage level (instantaneous voltage values) , is fed to a multiplication unit ME, which is calculated by (in-phase) multiplication of the two supplied quantities (differential current i a and tension u LN ) an instantaneous difference power p a (= pd) determined or calculated.

[0151] The instantaneous difference power p a is fed to a first integration unit INTI to determine the difference active power P a , which is obtained by integrating or averaging the instantaneous difference power p aover a multiple of half the period of the alternating voltage, e.g. over half, one, one and a half, ... or several periods of the alternating voltage, a differential active power P a determined or calculated.

[0152] The level of tension u LN , specifically according to Figure 6 the instantaneous level of voltage u LN (= u(t) ) , is fed to an effective value unit, which according to Figure 6 is calculated from the instantaneous level of the voltage u LN an effective value of the voltage U LNfrms determined or calculated. The effective value unit according to Figure 6 consists of three units connected in series: a squaring unit QQ, a second integration unit INT2, and a square root unit QW.

[0153] The squaring unit QQ performs a squaring of the instantaneous level of the voltage u LNThe squared instantaneous voltage level is fed to the second integration unit INT2, which calculates an average value by integrating or, in particular, averaging (the squared instantaneous voltage level) over a multiple of half the period of the alternating voltage, e.g., over half a period, one period, one and a half periods, ... or more periods of the alternating voltage (integration unit INT2 alternatively also means or includes a unit for averaging). The square root unit QW takes the square root of the average value, so that the effective value of the voltage U LNfrmsdetermined or calculated (root mean square, the calculation of an effective value is usually known). It is important that the first integration unit INTI (= mean value unit 1) and the second integration unit INT2 (mean value unit 2) (each) integrate over the same multiple of half the period of the alternating voltage, e.g. over the same half, one, one and a half, ... or more periods of the alternating voltage.

[0154] The differential active power P determined by the first integration unit INTI a and the effective value of the voltage U determined by the three series-connected units (squaring unit QQ, second integration unit INT2, square root unit QW) LNfrms is fed to a division unit DIV, which is calculated by dividing the difference active power P a by the effective value of the voltage U LNfrms the effective value of the differential active current I afWlrkdetermined or calculated.

[0155] This means that from the instantaneous voltage values ​​an effective value of the voltage U is calculated. L N,rms (over a multiple (1, 2, ... n) of half the period of the alternating voltage).

[0156] From the instantaneous voltage values ​​and the instantaneous differential current values, a differential active power P a (over the same multiple of half the period of the alternating voltage).

[0157] The differential active power P a (over the multiple (1, 2, ... n) of half the period of the alternating voltage) is determined by dividing by the effective value of the voltage U L N,rms (over the same multiple (1, 2, ... n) of half the period of the alternating voltage) an effective value of the differential active current I&,wirk is determined.

[0158] The effective value of the differential active current I &fWlrk is set to the first current limit I a , wirk* or first current-time limit value in order to initiate the avoidance of current flow in the low-voltage circuit when the first current limit value or first current-time limit value is exceeded.

[0159] This process, as well as the subsequent processes, can be implemented by a method, algorithm, or computer program product that runs on a microprocessor in the control unit SE. This means that the units are, for example, functions that are executed.

[0160] The instantaneous power p determined from the instantaneous voltage values ​​and the instantaneous differential current values a , from which by integration (over a multiple (such as 1, 2, 3, 4, ... n) of half the period of the alternating voltage) the differential active power P a is determined, can alternatively be determined in another way.

[0161] In an analogous manner, the control unit can determine an effective value of the differential current (over a multiple of half the period of the alternating voltage) from the instantaneous differential current values.

[0162] A differential apparent power is determined by multiplying the effective value of the voltage and the effective value of the differential current (equal times / (multiples of) the period durations are considered in each case).

[0163] The difference in apparent power and the difference in active power are used to calculate the difference in reactive power. The difference in reactive current is calculated from the difference in reactive power.

[0164] More specifically, the differential reactive power is calculated from the square root of the difference between the square of the differential apparent power and the square of the differential active power. From the differential reactive power (a multiple of half the period of the alternating voltage), an effective value of the differential reactive current 1^, reactive is calculated by dividing the differential reactive power (a multiple of half the period of the alternating voltage) by the effective value of the voltage (a multiple of half the period of the alternating voltage). The effective value of the differential reactive current is compared with a third current limit or third current-time limit in order to initiate the avoidance of current flow in the low-voltage circuit if the third current limit or third current-time limit is exceeded.

[0165] The determination of the differential active current, in particular the differential reactive current, is advantageously carried out continuously (periodically), for example with the support of a microprocessor.

[0166] The protective switching device or residual current device can further be designed or enhanced in such a way that, as an alternative to the residual reactive current or in addition to it, the magnitude of the residual current is compared with a second current limit or second current-time limit. If the second current limit or second current-time limit is exceeded, the current flow in the low-voltage circuit is prevented.

[0167] The second or third current limit or second or third current-time limit can be greater than the first current limit or first current-time limit. In particular, it is double, triple, quadruple, ... up to 10 times the first current limit. In other applications, it can be up to 20 times or up to 100 times the first current limit or first current-time limit (any intermediate value is possible). In particular, the factor is related to the current-limit component (current-limit component).

[0168] (Amount of current) (i.e. the factor is not related to the time limit value component).

[0169] Advantageously, the effective value of the differential current (differential reactive current) can be used with regard to the exceedance of the second (third) current limit value or second (third) current time limit value.

[0170] The level of the current limit values ​​or current-time limit values ​​can be fully or partially adjustable, e.g. by means of an input unit or communication unit on the protective switching device.

[0171] The first current limit or first current-time limit is advantageously a residual current limit from personal protection. In particular, on the current limit side (relative to the first current limit or first current-time limit), it has a level of 30 mA or less. Alternatively, it can also have a level of 10 mA or less. Alternatively, it can also have a level of 6 mA or less.

[0172] The second or third current limit value or (second or third) current-time limit value (especially its current limit value component) can be, for example, 150 mA or 300 mA.

[0173] This means that the protective switching device according to the invention behaves, for example, as shown below.

[0174] Figure 7 shows a test setup (measurement setup) with a protective switching device SG / residual current circuit breaker. The protective switching device SG is connected to the energy source EQ on the mains side via a two-pole first switch S1. On the load side, the load-side phase conductor terminal LL is connected to the mains-side neutral conductor terminal NG via an adjustable resistor R, a second switch S2, and an ammeter AM. The load-side neutral conductor terminal NL is not connected in this example.

[0175] A voltage measuring device VN is connected (optionally) between the two mains-side terminals NG, LG of the protective switching device SG.

[0176] A classic residual current device, as well as a protective switching device SG / residual current device according to the invention, behaves in such a way that when the first and second switches SI, S2 are closed and a residual current I set with the adjustable resistor R &fR(= differential current in the test setup via the protective switching device), which in this case flows via the ammeter AM, of for example 30 mA (classic value for residual current circuit breakers in personal protection, effective value) the residual current circuit breaker, as well as the protective switching device SG / residual current circuit breaker according to the invention, interrupts the electrical circuit, i.e. trips, when the current limit value or current time limit value (in the example 30 mA) is exceeded.

[0177] Ohmic test fault currents I &fR Different values ​​can be set using the adjustable resistor R, allowing the residual current device (RCD) / protective switching device (SG) to be tested for its tripping behavior. This means that it can be tested whether the residual current device (RCD) / protective switching device (SG) trips at its specified or set current limit or current-time limit (e.g., at a maximum of 30 mA).

[0178] A classic residual current device, as well as an inventive protective switching device SG / residual current device, with a current limit value or current-time limit value of e.g. 30 mA, must be able to withstand an ohmic residual current (differential active current) I &fR of a maximum of 30 mA (effective value, observe device tolerance ranges, the residual current device has, for example, a tolerance of + / - 5 mA when measuring the residual current I a , R , then the protective switching device could be set so that it already trips at 22.5 mA, for example), set by the adjustable resistor.

[0179] Figure 8 shows a structure / arrangement according to Figure 7, with the difference that instead of the adjustable resistor R, a particularly adjustable, capacitive or inductive component is provided, in the example a capacitor C with a certain capacitance (advantageously variably adjustable).

[0180] If the capacitance of the capacitor C is dimensioned such that a (capacitive) fault current of I &fC of 30 mA in the example flows (effective value, note tolerance ranges), a classic residual current device (according to the state of the art) will interrupt the circuit, ie trip.

[0181] A protective switching device SG / residual current device according to the invention will protect the circuit at this capacitive residual current I &fC (differential reactive current, effective value) of 30 mA.

[0182] If the protective switching device SG / residual current circuit breaker according to the invention is equipped with a second or third current limit value or current-time limit value, e.g. of 300 mA, the protective switching device SG / residual current circuit breaker according to the invention would, in the event of a capacitive residual current I &fC(differential reactive current, effective value) of 300 mA. However, the protective switching device SG / residual current device according to the invention would trigger an ohmic residual current I &fR (differential active current, effective value) of 30 mA.

[0183] The effectiveness of the invention can be easily demonstrated using the test setup mentioned. The capacitance of capacitor C would only need to be dimensioned for corresponding fault currents (depending on the frequency of the low-voltage AC circuit). e.g.

[0184] ULN= 230 Volt, f=50 Hz

[0185] In the following the invention is briefly explained again in other words.

[0186] Electrical voltage and the resulting shock current are dangerous to humans and can quickly lead to injury or death if someone comes into contact with electrical voltage. The effects of current and voltage on the human body are now described in international standards, such as IEC 60479-1. The danger to the human body depends, among other things, on the current magnitude and duration. Residual current devices (RCDs) are used today to protect people from the danger posed by electrical current.

[0187] Nowadays, pulsed voltage transformers are being used more and more often. These devices cause common-mode currents to flow via protective conductors or earth potential. These currents close their circuit via existing residual current circuit breakers and, in particular, disrupt the correct fault current detection and operation of the residual current circuit breaker. Filter capacitors (Y capacitors) or parasitic capacitances to earth potential (e.g. in shielded cables) also lead to a current flow on the protective conductor and, as a result, to a disruption in fault current detection. These currents are all detected as fault currents in the differential current transformers and lead to the (incorrect) tripping of the residual current circuit breaker.

[0188] The inventive solution and method for residual current evaluation can separate the (fault or differential) active current from the (fault or differential) reactive current and thus react separately to the active current (component) in the (fault or differential) current. This increases the sensitivity to a differential active current (to achieve increased personal safety) and simultaneously increases robustness against parasitic differential currents (differential reactive currents, or so-called operational leakage currents). This improves the protective function of a residual current device.

[0189] The new residual current detection method thus considers the cause (or effect) of the fault current. If an ohmic connection exists between the phase conductor and earth (or the protective conductor) in the event of a fault, active energy is transported from the grid to the fault location. This current at the fault location is recorded along with all other currents by the residual current measurement in the device and separated from parasitic residual currents (or operational leakage currents) using the new method. The source of this fault current is always the applied grid voltage, which is also taken into account for further analysis.

[0190] The analysis of the differential current is (thus) extended to include a consideration of the differential current power. Here, the applied (instantaneous) (network z-) voltage u LN (t) and the measured (instantaneous) differential current i (t) (= i a= idiff (t) ) a momentary difference power is determined (a difference power curve pd(t) (= p di f f (t) ) calculated). By means of integration or (in particular) averaging, an effective component P dlff from the instantaneous differential power / the differential power curve. Integration or averaging is conveniently performed as a multiple of the period / fundamental oscillation period, or half of the period / fundamental oscillation period.

[0191] If you then divide the determined differential active power by the effective value of the voltage (applied mains voltage), you get the (effective value of the) differential active current, which characterizes the active power transfer in the differential current.

[0192] This makes it possible to separate the active current (and, analogously, reactive current) components of the detected differential current, and operational fault currents (or leakage currents) due to common-mode currents or leakage currents can be separated from a fault current at an ohmic fault location. This separation enables more sensitive tripping of the residual current circuit breaker / protective switching device with differential current detection, while simultaneously increasing robustness against operational fault currents.

[0193] The invention offers the advantage that more sensitive tripping is possible due to ohmic fault currents. More sensitive tripping enables increased electrical safety in low-voltage circuits. Using the new solution and method, it is possible (e.g.) to build a protective switching device which has a tripping characteristic in the AC-2 range (according to IEC 60479-1) and thus does not allow dangerous body currents (from the AC-3 or AC-4 range). A protective device with such a tripping characteristic offers a new type of electrical safety and can no longer be compared with a residual current device (RCD) typical today, since a residual current device typical today does not ensure that higher body currents or even lower body currents cannot flow for a longer period of time.

[0194] The invention offers increased robustness against false triggering due to operational differential currents or common-mode currents. Increased robustness against false triggering increases customer satisfaction and reduces complaints due to false triggering.

[0195] The new solution and method enables, for example, the use of residual current devices in networks with multiple (power supply units or) converter systems. In these systems, residual current devices cannot currently be used due to high-frequency common-mode currents or differential fault currents, as well as operational currents on the protective conductor.

[0196] The method according to the invention requires a voltage measurement, which can be implemented cost-effectively. The additional computational effort is minimal, since in one exemplary embodiment, only multiplication and averaging (and effective value calculations) are required.

[0197] Although the invention has been illustrated and described in detail by the embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Protective switching device (SG) for protecting an electrical low-voltage circuit for alternating current, comprising: - a housing with two mains-side and two load-side connections (LG, NG, LL, NL) for two conductors of the low-voltage circuit, in particular a phase conductor and a neutral conductor of the low-voltage circuit, - a differential current sensor unit (ZCT) for determining the level of a differential current of the two conductors of the low-voltage circuit, - a mechanical isolating contact unit (MK) which has a closed state of the contacts for a current flow of the conductors of the low-voltage circuit or an open state of the contacts for a current flow-preventing galvanic isolation of the conductors of the low-voltage circuit, characterized in that a voltage sensor unit (SUA) is provided for determining the level of a voltage between the two conductors of the low-voltage circuit, that a control unit (SE) is provided which is connected to the differential current sensor unit (ZCT), the voltage sensor unit (SUA) and the mechanical isolating contact unit (MK), that the protective switching device (SG), in particular the control unit (SE), is designed in such a way that a differential active current is determined from the level of the voltage and the level of the differential current,that the differential active current is compared with a first current limit value or first current-time limit value, that if the first current limit value or first current-time limit value is exceeded, the avoidance of a current flow in the low-voltage circuit is initiated., 2. Protective switching device (SG) according to claim 1, characterized in that that the level of the differential current is compared with a second current limit value or second current-time limit value, that if the second current limit value or second current-time limit value is exceeded, avoidance of a current flow in the low-voltage circuit is initiated.

3. Protective switching device (SG) according to claim 2, characterized in that the second current limit value or second current-time limit value is greater than the first current limit value or first current-time limit value, in particular up to 10 times or up to 20 times or up to 100 times the first current limit value or first current-time limit value.

4. Protective switching device (SG) according to claim 1, 2 or 3, characterized in that a determination of a differential reactive current is carried out from the level of the voltage and the level of the differential current, in particular that the differential reactive current is the differential reactive current component with the fundamental frequency of the voltage in the low-voltage circuit, that the differential reactive current is compared with a third current limit value or third current-time limit value, that if the third current limit value or third current-time limit value is exceeded, avoidance of a current flow in the low-voltage circuit is initiated.

5. Protective switching device (SG) according to claim 4, characterized in that the third current limit value or third current-time limit value is greater than the first current limit value or first current-time limit value, in particular up to 10 times or up to 20 times or up to 100 times the first current limit value or first current-time limit value.

6. Protective switching device (SG) according to one of the preceding claims, characterized in that that the first current limit value or first current-time limit value is a residual current limit value for personal protection, in particular has a current limit value of 30 mA or less.

7. Protective switching device (SG) according to one of the preceding claims, characterized in that the differential current sensor unit (ZCT) determines instantaneous differential current values ​​of the magnitude of the differential current, that the voltage sensor unit (SUA) determines instantaneous voltage values ​​of the magnitude of the voltage, that an effective value of the voltage is determined from the instantaneous voltage values, that a differential active power is determined from the instantaneous voltage values ​​and the instantaneous differential current values; that an effective value of the differential active current is determined from the differential active power by dividing it by the effective value of the voltage, that the effective value of the differential active current is compared with the first current limit value or first current-time limit value in order to initiate the avoidance of the current flow in the low-voltage circuit if the first current limit value or first current-time limit value is exceeded.

8. Protective switching device (SG) according to claim 7, characterized in that the differential active power is determined from the instantaneous voltage values ​​and the instantaneous differential current values ​​by averaging the product of the instantaneous voltage values ​​and the instantaneous differential current values.

9. Protective switching device (SG) according to claims 7 or 8, characterized in that an effective value of the differential current is determined from the instantaneous differential current values, that from the effective value of the voltage and the effective value of the differential current a differential apparent power is determined.

10. Protective switching device (SG) according to claim 9, characterized in that a differential reactive power is determined from the differential apparent power and the differential active power, and that the differential reactive current is determined from the differential reactive power.

11. Protective switching device (SG) according to claim 10, characterized in that the differential reactive power is determined from the square root of the difference between the square of the differential apparent power and the square of the differential active power, that an effective value of the differential reactive current is determined from the differential reactive power by dividing it by the effective value of the voltage, that the effective value of the differential reactive current is compared with the third current limit value or third current time limit value in order to initiate the avoidance of the current flow in the low-voltage circuit if the third current limit value or third current time limit value is exceeded.

12. Method for residual current protection of an electrical low-voltage alternating current circuit, in that the level of a differential current of two conductors of the low-voltage circuit is determined, characterized in that the level of a voltage between the two conductors of the low-voltage circuit is determined, that a differential active current is determined from the level of the voltage and the level of the differential current, that the differential active current is compared with a first current limit value or first current-time limit value, that when the first current limit value or first current-time limit value, an avoidance of current flow in the low-voltage AC circuit is initiated.

13. Method according to claim 12, characterized in that the level of the differential current is compared with a second current limit value or second current-time limit value, and that if the second current limit value or second current-time limit value is exceeded, an avoidance of a current flow in the low-voltage circuit is initiated.

14. Method according to claim 12 or 13, characterized in that a determination of a differential reactive current is carried out from the level of the voltage and the level of the differential current, that the differential reactive current is compared with a third current limit value or third current-time limit value, that if the third current limit value or third current-time limit value is exceeded, avoidance of a current flow in the low-voltage circuit is initiated.

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