PROTECTIVE SWITCH AND PROCEDURES

Description

[0001] The invention relates to the technical field of a protective switching device for a low-voltage circuit with an electronic interruption unit and a method for a protective switching device for a low-voltage circuit with an electronic interruption unit.

[0002] Low voltage refers to voltages up to 1000 volts AC or up to 1500 volts DC. In particular, low voltage refers to voltages higher than extra-low voltage, defined as 50 volts AC or 120 volts DC.

[0003] Low-voltage circuits, networks, or installations refer to circuits with rated currents of up to 125 amperes, or more specifically, up to 63 amperes. Low-voltage circuits also include circuits with rated currents of up to 50 amperes, 40 amperes, 32 amperes, 25 amperes, 16 amperes, or 10 amperes. These current values ​​refer specifically to rated, rated, and / or tripping currents, i.e., the maximum current that normally flows through the circuit or at which the electrical circuit is typically interrupted, for example, by a protective device such as a circuit breaker, miniature circuit breaker, or miniature circuit breaker.

[0004] Miniature circuit breakers (MCBs) are long-established overcurrent protection devices used in low-voltage electrical installations. They protect cables from damage caused by overheating due to excessive current and / or short circuits. A MCB can automatically disconnect the circuit in case of overload and / or short circuit. A MCB is a non-resetting safety device.

[0005] Unlike miniature circuit breakers (MCBs), power circuit breakers are designed for currents greater than 125 A, and sometimes even as low as 63 A. MCBs are therefore simpler and more delicate in design. They typically feature a mounting option for installation on a DIN rail (also known as a top-mounted rail or TH35 rail).

[0006] Miniature circuit breakers (MCBs) are electromechanical devices. They contain a mechanical switching contact or shunt trip within a housing to interrupt (trigger) the electrical current. Typically, a bimetallic element is used for tripping (interruption) in the event of a prolonged overcurrent (overcurrent protection) or thermal overload (overload protection). An electromagnetic trip with a coil is used for momentary tripping when an overcurrent limit is exceeded or in the event of a short circuit (short-circuit protection). One or more arc-quenching chambers or devices are provided. They also include connection elements for conductors of the electrical circuit to be protected.

[0007] Protective switching devices with an electronic interruption unit are relatively new developments. These devices feature a semiconductor-based electronic interruption unit. This means that the electrical current flow of the low-voltage circuit is routed through semiconductor components or semiconductor switches that can interrupt the electrical current flow or be switched to conductivity. Protective switching devices with an electronic interruption unit also frequently feature a mechanical isolating contact system, particularly with isolating characteristics according to relevant standards for low-voltage circuits. The contacts of the mechanical isolating contact system are connected in series with the electronic interruption unit, meaning that the current of the low-voltage circuit to be protected is routed through both the mechanical isolating contact system and the electronic interruption unit.

[0008] In semiconductor-based protective switching devices, also known as solid-state circuit breakers (SSCBs), the switching energy is not converted into an arc as in a mechanical switching device, but rather into heat via an additional circuit called an energy absorber. The switching energy comprises the energy stored in the circuit, i.e., in the network, line, or load impedances (consumer impedances). To reduce the load on the energy absorber, the current flowing at the moment of switching must be as low as possible. This also applies in the case of a short circuit, where the current rises very rapidly. Rapid short-circuit detection allows a short circuit to be identified early and an excessively high short-circuit current to be avoided. The semiconductor-based protective switching device interrupts the circuit almost instantaneously, within microseconds.High currents do not occur, and the load on the energy absorber of a semiconductor-based protective switching device is reduced. Known short-circuit detection and tripping criteria are typically based on determining and evaluating the actual current value.

[0009] The present invention relates to low-voltage alternating current circuits with an alternating voltage, usually a time-dependent sinusoidal alternating voltage with frequency f, typically 50 or 60 Hertz (Hz). The time dependence of the instantaneous voltage value u(t) of the alternating voltage is given by the equation: u t = U * sin 2 π * f * t described. Whereby: u(t) = instantaneous voltage value at time t U = amplitude (maximum value) of the voltage

[0010] A harmonic alternating voltage can be represented by the rotation of a phasor whose length corresponds to the amplitude (U) of the voltage. The instantaneous displacement is the projection of the phasor onto a coordinate system. One oscillation period corresponds to one full rotation of the phasor, and its full angle is 2π (2π) or 360°. The angular frequency is the rate of change of the phase angle of this rotating phasor. The angular frequency of a harmonic oscillation is always 2π times its frequency, i.e., ω = 2 π * f = 2 π / T = Kreisfrequenz der Wechselspannung (T = period of the oscillation)

[0011] The angular frequency (ω) is often preferred over the frequency (f), since many formulas in the theory of oscillations can be represented more compactly using the angular frequency due to the occurrence of trigonometric functions whose period is by definition 2π: u t = U * sin ωt

[0012] In the case of angular frequencies that are not constant over time, the term instantaneous angular frequency is also used.

[0013] For a sinusoidal, especially a time-constant, alternating voltage, the time-dependent value of the angular velocity ω and the time t corresponds to the time-dependent angle φ(t), which is also called the phase angle φ(t). This means that the phase angle φ(t) periodically traverses the range 0...2π or 0°...360°. That is, the phase angle periodically assumes a value between 0 and 2π or 0° and 360° (φ = n*(0...2π) or φ = n*(0°...360°), due to periodicity; simplified: φ = 0...2π or φ = 0°...360°).

[0014] The instantaneous voltage value u(t) therefore refers to the instantaneous value of the voltage at time t, i.e., in the case of a sinusoidal (periodic) alternating voltage, the value of the voltage at the phase angle φ (φ = 0...2π or φ = 0°...360°, of the respective period).

[0015] For example, EP 0 416 569 A2 discloses a mains current monitoring system for uninterruptible power supplies (UPS) which is achieved by adaptively generating a reference waveform against which the current waveform is compared. The reference waveform changes relatively slowly, so that a moderate change in the voltage waveform, indicating a fault, is detected, while the reference can adapt to and adjust to systematic distortions of the power line compared to a pure sine wave, which do not indicate a power line failure, thus avoiding unnecessary UPS switching.

[0016] Furthermore, WO 2015 / 028634 A1 discloses an AC circuit breaker with a live conductor between a live terminal and a live load terminal and a neutral conductor between a neutral supply terminal and a neutral load terminal for connecting an AC load to a mains supply, with a first galvanic disconnector and a bypass switch in the live conductor and a second galvanic disconnector in the neutral conductor and a semiconductor switching element connected in parallel to the bypass switch, wherein the first and second galvanic disconnectors, the bypass switch and the semiconductor switching element are controlled using a processing unit.

[0017] Furthermore, WO 2014 / 084980 A1 discloses a power supply system comprising a user system with a plurality of devices configured to receive power from a power supply line. A power supply module is provided, configured to analyze the power supplied from the power supply line to the user system, and further configured to measure one or more units of actual waveform data corresponding to the supplied power and to compare these one or more units of actual waveform data with one or more units of anomalous waveform data.

[0018] The object of the present invention is to improve a protective switching device of the type mentioned above, in particular to demonstrate a fast and alternative means of short-circuit detection and to ensure a safe interruption.

[0019] This problem is solved by a protective switching device having the features of claim 1, and by a method according to claim 15.

[0020] According to the invention, a protective switching device for the protection of a low-voltage electrical circuit, in particular a low-voltage alternating current circuit, is provided, comprising: A voltage sensor for determining the voltage level of the low-voltage circuit, such that instantaneous / phase-angle-related voltage values ​​are available; an electronic interruption unit, which, by means of semiconductor-based switching elements, has a high-resistance state of the switching elements for interruption and a low-resistance state of the switching elements for current flow in the low-voltage circuit; a control unit, which is connected to the voltage sensor and the interruption unit. According to the invention, the protective switching device is designed such that instantaneous threshold values ​​are available, i.e., that instantaneous threshold values, i.e., phase-angle-related threshold values, are available for each phase angle or phase angle range (multiple phase angles) or phase angle segment (part of a phase angle). The instantaneous voltage values ​​determined by the voltage sensor are compared with the instantaneous phase-angle-related threshold values.A threshold value for a phase angle is compared with the voltage value for the same phase angle.

[0021] Depending on the type of comparison, if the instantaneous thresholds are exceeded or fallen below, an interruption of the low-voltage circuit is initiated to prevent a short circuit. In general, the instantaneous threshold is set lower than the expected instantaneous voltage value. If the instantaneous voltage falls below the instantaneous threshold during the positive half-cycle of the voltage, the low-voltage circuit is interrupted, specifically by the electronic interruption unit. During the negative half-cycle of the voltage, if the instantaneous threshold is exceeded (a higher voltage value (since it is negative), but a lower absolute value), the low-voltage circuit is interrupted to prevent a short circuit, as a short circuit is associated with a voltage drop.Alternatively, an instantaneous differential voltage value is calculated from the current threshold and the current voltage value (continuously). This instantaneous differential voltage value is compared to an absolute or instantaneous differential voltage threshold. If this threshold is exceeded or fallen below, depending on the sign of the differential calculation and the half-wave of the voltage, an interruption of the low-voltage circuit is initiated to prevent a short-circuit current (which is associated with a voltage dip, detected by this solution).

[0022] According to the invention, very rapid detection of short circuits is advantageously possible (within the range of a voltage phase angle or less). Furthermore, no current measurement or current sensor is required (only voltage measurement or a voltage sensor). Short-circuit detection is based on a pure voltage measurement between the (two) conductors of the low-voltage circuit. Thus, for example, short-circuit monitoring can be advantageously integrated retroactively without interrupting any conductors of the low-voltage circuit. Advantageous embodiments of the invention are specified in the dependent claims.

[0023] In an advantageous embodiment of the invention, the instantaneous threshold values ​​are adjusted depending on the amplitude of the voltage of the low-voltage circuit, so that a high instantaneous threshold value is present at a high amplitude of the voltage and a low instantaneous threshold value is present at a low amplitude of the voltage.

[0024] As mentioned earlier, "amplitude" here refers to the maximum value of the voltage. "Depending on the amplitude" further refers to the amplitude of at least one or more complete oscillations (or periods) of the electrical voltage (1...n * 360°). This means that the thresholds should only be adjusted after at least one complete oscillation (360°) (since an amplitude logically only exists after at least one complete oscillation) or after several complete oscillations of the electrical voltage, specifically after 5 to 25 complete oscillations, i.e., after 100 ms to 500 ms (for 50 Hz). Alternatively, adjustment can also be made over a period of seconds, in which case short mains fluctuations have no influence on the thresholds.

[0025] This has the particular advantage that, with regard to long-term voltage changes (i.e., over several periods or oscillations), the instantaneous thresholds are adjusted to achieve accurate and rapid detection of short-circuit-induced voltage dips.

[0026] In an advantageous embodiment of the invention, the magnitudes of the instantaneous voltage values ​​are compared with the (in particular, absolute) instantaneous threshold values ​​in a phase-angle-related manner such that, if the magnitude of the instantaneous threshold value is undershot, or if the differential voltage value is formed from the (in particular, absolute) instantaneous threshold value and the magnitude of the instantaneous voltage value, the differential voltage value is compared with the differential voltage threshold value, and if the threshold value is exceeded, an interruption of the low-voltage circuit is initiated.

[0027] This has the particular advantage that an evaluation of the threshold monitoring can be implemented that is independent of the positive or negative half-wave of the voltage, since only the magnitudes need to be considered.

[0028] In an advantageous embodiment of the invention, the exceedance or fall below a certain threshold is present for a first time interval to initiate an interruption of the low-voltage circuit. The first time interval refers in particular to an exceedance over several phase angles, especially over 0.1° phase angles, or a first time interval greater than 5.6 µs, more specifically from 0.1° phase angle to 2° phase angle – or from 5.6 µs to 111 µs, respectively.

[0029] This has the particular advantage that a robust solution can be implemented which avoids false triggering in the case of short spikes.

[0030] In an advantageous embodiment of the invention, the protective switching device is configured such that the control unit comprises an analog first subunit and a digital second subunit. The first subunit includes a voltage comparator to which the instantaneous voltage values ​​from the voltage sensor and the instantaneous threshold values ​​from the second subunit are supplied. This comparator compares the instantaneous voltage values ​​with the instantaneous threshold values ​​and initiates an interruption of the low-voltage circuit when the threshold is exceeded or fallen below. The instantaneous voltage values ​​are also supplied to the second subunit for determining the instantaneous threshold values.

[0031] This has the distinct advantage of an efficient architecture. The first analog subunit can perform a very fast comparison of instantaneous voltage values ​​and threshold values, enabling rapid short-circuit detection. The second subunit can perform an independent threshold calculation or adjustment, which does not need to be as fast as the detection process. The threshold values ​​can, for example, be buffered for quick comparison. The threshold values ​​do not need to be constantly adjusted.

[0032] In an advantageous embodiment of the invention, the protective switching device is designed such that a grid synchronization unit is provided. The grid synchronization unit can be based on the supplied instantaneous voltage values: The system determines the expected time value (UE), the phase angle (φ(t)), and the amplitude (U) of the voltage. Furthermore, a threshold unit is provided, which receives the expected time value, the phase angle (φ(t)), and the amplitude (U) of the voltage. The threshold unit then determines the instantaneous threshold values. These instantaneous voltage values ​​are compared with the instantaneous threshold values ​​to determine when an interruption is initiated.

[0033] This has the particular advantage of providing a simple comparison and implementation option, especially when using a PLL.

[0034] In an advantageous embodiment of the invention, the protective switching device is designed such that a network synchronization unit is provided which uses the supplied instantaneous voltage values: outputs an expected time value (UE) of the voltage, outputs a phase angle (φ(t)) of the voltage, outputs the amplitude (U) of the voltage.

[0035] A threshold unit is provided to which the phase angle (φ(t)) and the amplitude (U) of the voltage are supplied and which determines the differential voltage threshold, in particular the instantaneous one.

[0036] The instantaneous voltage values ​​and the expected time value of the voltage are fed to a differential unit, which determines a differential voltage value, particularly one that depends on the phase angle. This instantaneous differential voltage value is compared with the differential voltage threshold, also particularly the instantaneous threshold, to determine when an interruption is initiated. This has the particular advantage of providing another simple comparison method and implementation, especially when using a PLL.

[0037] In an advantageous embodiment of the invention, a mechanical disconnect contact system is provided which is connected in series with the electronic interruption unit on the circuit side, so that galvanic isolation can be achieved in the low-voltage circuit. The mechanical disconnect contact system is connected to the control unit. This has the particular advantage that both a rapid interruption of the low-voltage AC circuit by the electronic interruption unit and galvanic isolation, especially with isolating characteristics according to standards, i.e., a complete disconnection, can be achieved. Thus, a comprehensive protective switching device is provided.

[0038] In an advantageous embodiment of the invention, a current sensor is provided for determining the magnitude of the current in the low-voltage circuit.

[0039] This has the particular advantage of enabling further beneficial protection and safeguarding functions.

[0040] In an advantageous embodiment of the invention, galvanic isolation is initiated when a (defective) high-impedance electronic interruption unit is present and a current in the low-voltage circuit exceeds a first current threshold.

[0041] This has the particular advantage that in the event of residual currents or a faulty electronic interruption unit, the circuit is deactivated, i.e., increased safety is provided.

[0042] In an advantageous embodiment of the invention, the determined current level is compared with a second current threshold and, if this threshold is exceeded, an interruption of the low-voltage circuit is initiated, in particular by the mechanical isolating contact system (MK).

[0043] This has the particular advantage that an additional current-based overcurrent or short-circuit detection is implemented, thereby increasing the tripping reliability.

[0044] In an advantageous embodiment of the invention, when an interruption of the low-voltage circuit is initiated by means of the electronic interruption unit and a current flow in the low-voltage circuit exceeds a third current threshold and lasts for a second time period, which is in particular greater than the tripping time by means of the electronic interruption unit, an interruption of the low-voltage circuit is initiated by the mechanical disconnect contact system.

[0045] This has the particular advantage that if the electronic interrupt unit is defective, for example if the semiconductor-based switching elements are through-alloyed, i.e., if an interruption by the electronic interrupt unit has failed, an interruption of the low-voltage circuit is ensured. This preferably occurs after the usual tripping time by the electronic interrupt unit.

[0046] In an advantageous embodiment of the invention, the instantaneous threshold values ​​per phase angle of the voltage of the low-voltage circuit are determined, in particular by the digital second subunit, which performs a digital determination of the instantaneous threshold values ​​with a clock frequency between 10 kHz and 10 MHz, in particular 10 kHz and 1 MHz, more specifically between 10 kHz and 100 kHz, in particular from 18 kHz upwards.

[0047] This has the particular advantage that, on the one hand, it allows for a quick and, on the other hand, not too complex implementation.

[0048] According to the invention, a corresponding method for a protective switching device for a low-voltage circuit with electronic (semiconductor-based) switching elements is claimed, offering the same and further advantages.

[0049] All embodiments, both in dependent form referring back to claim 1 or 15, and in relation only to individual features or combinations of features of claims, result in an improvement of a protective switching device for fast and safe shutdown in the event of short circuits.

[0050] The described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawing.

[0051] The drawing shows: Figure 1 a representation of a protective switching device, Figure 2 a first design of the protective switching device, Figure 3 a second embodiment of the protective switching device, Figure 4 a third design of the protective switching device, Figure 5 Current and voltage waveforms over time, Figure 6 Voltage and threshold curves over time.

[0052] Figure 1 shows a representation of a protective switching device SG for the protection of a low-voltage electrical circuit with a housing GEH, comprising: Connections for conductors of the low-voltage circuit, in particular first connections L1, N1 for a network-side, especially energy source-side, connection EQ of the protective switching device SG and second connections L2, N2 for a load-side, especially energy sink-side - in the case of passive loads, connection ES (consumer-side connection) of the protective switching device SG, wherein phase-side connections L1, L2 and neutral-side connections N1, N2 may be provided; the load-side connection may have a passive load (consumer) and / or an active load ((further) energy source), or a load that may be both passive and active, e.g.in chronological sequence; a voltage sensor SU, for determining the voltage level of the low-voltage circuit, so that instantaneous voltage values ​​(phase-related voltage values) DU are available, an electronic interruption unit EU, which, by means of semiconductor-based switching elements, has a high-resistance state of the switching elements for interruption and a low-resistance state of the switching elements for current flow in the low-voltage circuit, a control unit SE, which is connected to the voltage sensor and the interruption unit.

[0053] The protective switching device SG, in particular the control unit SE, is designed such that instantaneous (phase-angle-related) threshold values ​​are available. For example, in a simple case, the sine wave of the voltage, for example with an RMS value of 230 volts and an amplitude of 325 volts, could be stored as an instantaneous threshold value for each phase angle, with its expected instantaneous voltage value minus a discount of, for example, 10%, or a value between 10 and 30%, or a fixed discount of at least 10 volts, whereby a value of at least 10 volts is used as the minimum instantaneous threshold value (to prevent false tripping). With a reduction of, for example, 10%: 10 volts at 0° (minimum instantaneous threshold), ..., 146.25 volts (162.5 volts - 10%) at 30°, ..., 206.8 volts (229.8 volts - 10%) at 45°, ..., 253.3 volts (281.4 volts - 10%) at 60°, 292.5 volts (325 volts - 10%) at 90°, etc.

[0054] The instantaneous threshold values ​​can be per individual phase angle, a phase angle range (multiple phase angles), e.g. every 2°, or a phase angle segment (a part of a phase angle), e.g. every 0.5°.

[0055] The instantaneous voltage values ​​DU are compared with the instantaneous threshold values ​​with respect to the phase angle. If the instantaneous threshold values ​​are undershot or exceeded, an interruption of the low-voltage circuit is initiated to prevent a short-circuit current. To prevent short-circuit currents in a low-voltage AC circuit, a check is performed during the positive half-cycle for whether the instantaneous threshold values ​​are undershot, and during the negative half-cycle for whether the instantaneous threshold values ​​are exceeded.

[0056] Alternatively, the magnitudes of the instantaneous voltage values ​​DU can also be determined. These magnitudes are then checked against whether they fall below the instantaneous threshold values, thus advantageously eliminating the need to consider the sign. The comparison is performed phase-angle-related, i.e., the instantaneous voltage value of, for example, 30° phase angle is checked against the instantaneous threshold value of 30° phase angle.

[0057] Alternatively, an instantaneous differential voltage value can be calculated (continuously) from the current threshold value (and possibly its magnitude) and the current voltage value DU (and possibly its contribution). This instantaneous differential voltage value is compared to an (absolute or instantaneous) differential voltage threshold value, and if the threshold is exceeded (or fallen below – in the case of a signed comparison), an interruption of the low-voltage circuit is initiated to prevent a short circuit.

[0058] Alternatively, a corridor check can also be performed, i.e., if the current voltage value deviates by more than a certain percentage, in particular 10% (or a value in the range of 5 to 15%), or by a certain + / - voltage amount, in particular a value in the range of 20 to 40 volts, specifically 30 volts, from the expected threshold or expected voltage value, the interruption of the low-voltage circuit is initiated.

[0059] The interruption of the low-voltage circuit is initiated, for example, by a (first) TRIP signal sent from the control unit SE to the electronic interruption unit EU, as shown in Figure 1 marked.

[0060] The undershooting or exceeding can advantageously occur for an initial time period or for a phase angle range or phase angle section in order to initiate an interruption of the low-voltage circuit.

[0061] The electronic interruption unit EU is in accordance with Figure 1 The block is shown in both conductors. In the first variant, this means that neither conductor is interrupted. At least one conductor, in particular the live conductor or phase conductor, has semiconductor-based switching elements. The neutral conductor can be free of switching elements, i.e., without semiconductor-based switching elements. This means the neutral conductor is directly connected and does not become high-impedance. This means there is only a single-pole interruption (of the phase conductor). If further live conductors / phase conductors are present, in a second variant of the electronic interruption unit (EU), the phase conductors have semiconductor-based switching elements. The neutral conductor is directly connected and does not become high-impedance. This is the case, for example, in a three-phase AC circuit.

[0062] In a third variant of the electronic interruption unit EU, the neutral conductor can also have a semiconductor-based switching element, i.e., when the electronic interruption unit EU is interrupted, both conductors become high-resistance.

[0063] The electronic interruption unit EU can comprise semiconductor devices such as bipolar transistors, field-effect transistors (FETs), insulated-gate bipolar transistors (IGBTs), metal-oxide-layer field-effect transistors (MOSFETs), or other (self-commutated) power semiconductors. In particular, IGBTs and MOSFETs are especially well-suited for the protective switching device according to the invention due to their low forward resistance, high junction resistance, and good switching characteristics.

[0064] Additionally, for one embodiment of the invention, a current sensor SI can also be provided to determine the magnitude of the current in the low-voltage circuit, so that current values ​​DI are available, as in the example according to Figure 1 The diagram shows the current sensor SI connected to the control unit SE.

[0065] The protective switching device SG may preferably also include a mechanical isolating contact system MK, in particular with standard-compliant isolating properties, for galvanic isolation of the circuit, especially for standard-compliant disconnection (as opposed to switching off) of the circuit. The mechanical isolating contact system MK may be connected to the control unit SE, as shown in Figure 1 drawn in such a way that the control unit SE can initiate a galvanic isolation of the circuit.

[0066] Specifically, a further evaluation can be implemented that, if other criteria are met, brings about galvanic isolation. For example, overcurrent detection can be provided, for instance in the control unit SE, which, in the event of overcurrents—i.e., when current-time limits are exceeded, i.e., when a current exceeding a current limit is present for a certain time, i.e., when a certain energy threshold is exceeded—in which case a semiconductor-based and / or galvanic interruption of the circuit occurs.

[0067] Alternatively or additionally, galvanic isolation can be initiated, for example, in the event of a detected short circuit.

[0068] The initiation of the galvanic interruption of the low-voltage circuit is effected, for example, by a further (second) signal TRIPG, which is sent from the control unit SE to the mechanical isolating contact system MK, as in Figure 1 marked.

[0069] In a further advantageous embodiment, galvanic isolation can be initiated when a (defective) high-impedance electronic interrupting unit EU is present and a current in the low-voltage circuit, detected in particular by the current sensor SI, exceeds a first current threshold. Depending on the application of the protective switching device, the first current threshold can be in the range of 4 to 6 mA, particularly 5 mA or 6 mA. The first current threshold can be in the range of 26 mA to 30 mA, particularly 28 mA, 29 mA, or 30 mA, especially for personal protection in Europe. The third threshold can be in the range of 290 mA to 300 mA, particularly for fire protection. Each of the aforementioned boundary and intermediate values ​​is disclosed.

[0070] In a further advantageous embodiment, if a determined current level exceeds a second current threshold, an interruption of the low-voltage circuit can be initiated, in particular by the mechanical isolating contact system.

[0071] The second current threshold corresponds, for example, to the standard current (time) limits, i.e., the I-(t) characteristics for protective devices, for example according to standards IEC 60947 or IEC 60898. The selected current (time) limits are chosen by a specialist according to the specific application.

[0072] In a further advantageous embodiment, if an interruption of the low-voltage circuit is initiated by the electronic interruption unit and a current flow in the low-voltage circuit exceeds a third current threshold and persists for a second period, an interruption of the low-voltage circuit can be initiated by the mechanical disconnect contact system. This is done to induce an interruption by the mechanical disconnect contact system in the event of a failed high-resistance test of the electronic interruption unit and thus a failed interruption of the low-voltage circuit. This advantageously increases operational reliability. Such a process can advantageously be indicated on the protective switching device.

[0073] The third current threshold and the second time interval correspond, for example, to the standard current-time limits, i.e., the It characteristics for protective devices, for example according to standards IEC 60947 or IEC 60898. The selected current-time limits are chosen by a specialist according to the specific application.

[0074] The MK mechanical disconnect contact system can, in one variant, interrupt a single pole. This means that only one of the two conductors, specifically the live conductor or phase conductor, is interrupted, i.e., it has a mechanical contact. The neutral conductor is then without contact, i.e., the neutral conductor is directly connected.

[0075] If additional active conductors / phase conductors are provided, in a second variant the phase conductors have mechanical contacts of the mechanical disconnect contact system. In this second variant, the neutral conductor is directly connected. For example, in a three-phase AC circuit.

[0076] In a third variant of the mechanical disconnect contact system MK, the neutral conductor also has mechanical contacts, as in Figure 1 marked.

[0077] The term "MK mechanical disconnect contact system" refers specifically to a (standard-compliant) disconnect function, implemented by the MK disconnect contact system. The following points are included with the disconnect function: Minimum air gap according to standard (minimum distance between contacts), contact position indicator of the contacts of the mechanical disconnect contact system, actuation of the mechanical disconnect contact system always possible (no blockage of the disconnect contact system), meant.

[0078] The minimum air gap between the contacts of the isolating contact system is essentially voltage-dependent. Other parameters include the degree of pollution, the type of field (homogeneous, inhomogeneous), and the air pressure or altitude above sea level.

[0079] There are corresponding regulations and standards for these minimum clearances or creepage distances. For example, these regulations specify the minimum clearance for an inhomogeneous and a homogeneous (ideal) electric field, depending on the degree of pollution, to ensure shock voltage withstand capability. Shock voltage withstand capability is the resistance to being applied when a corresponding shock voltage is applied. Only if this minimum length (minimum distance) is present does the isolating contact system or protective switching device exhibit a disconnecting function (isolating property).

[0080] For the purposes of the invention, the standards DIN EN 60947 and IEC 60947 are relevant for the separator function and its properties, and reference is made to them here.

[0081] The isolating contact system is advantageously characterized by a minimum clearance between the open isolating contacts in the OFF position (open position, contacts open), depending on the rated impulse withstand voltage and the pollution degree. The minimum clearance is, in particular, between 0.01 mm and 14 mm (at a minimum). More advantageously, the minimum clearance is between 0.01 mm at 0.33 kV and 14 mm at 12 kV, especially for pollution degree 1 and particularly for inhomogeneous fields.

[0082] Advantageously, the minimum air gap can have the following values: Table 13 Minimum air distances - Design impulse stress resistance Minimum air distances mm U imp Case A Case B inhomogeneous field homogeneous field, ideal conditions kV (see 3.7.63) (see 3.7.62) Pollution level Pollution level 1 2 3 4 1 2 3 4 0,33 0,01 0,2 0,8 1,6 0,01 0,2 0,8 1,6 0,5 0,04 0,04 0,8 0,1 0,1 1,5 0,5 0,5 0,3 0,3 2,5 1,5 1,5 1,5 0,6 0,6 4,0 3 3 3 3 1,2 1,2 1,2 6,0 5,5 5,5 5,5 5,5 2 2 2 2 8,0 8 8 8 8 3 3 3 3 12 14 14 14 14 4,5 4,5 4,5 4,5 NOTE The specified minimum air gaps are based on the 1.2 / 50 µs shock stress at an air pressure of 80 kPa, which corresponds to the air pressure at 2000 m above sea level.

[0083] The pollution levels and field types correspond to those defined in the standards. This advantageously allows for the creation of a standard-compliant protective switching device dimensioned according to the rated impulse withstand voltage.

[0084] Figure 2 shows a representation according to Figure 1 , with a further detailed embodiment. Here, the control unit SE comprises two subunits: a first subunit SEA, preferably analog, and a second subunit SED, preferably digital. The first subunit SEA includes a voltage comparator CU. The instantaneous voltage values ​​DU from the voltage sensor SU are supplied to the CU. The instantaneous threshold values ​​SWU from the second subunit SED are also supplied to the voltage comparator CU.

[0085] The voltage comparator CU compares the instantaneous voltage values ​​DU with the instantaneous threshold values ​​SWU and, as described, outputs a voltage interruption signal TU to initiate an interruption of the low-voltage circuit when the threshold is exceeded or fallen below.

[0086] The voltage interruption signal TU can be fed to a logic unit LG, which combines it with other interruption signals and outputs the (first) signal TRIP to the electronic interruption unit EU for semiconductor-based interruption or high-impedance interruption.

[0087] In one embodiment, the voltage comparator CU stores the current threshold values ​​SWU in order to have the values ​​constantly available.

[0088] The instantaneous voltage values ​​DU are also fed to the second subunit SED. In a preferred embodiment, the instantaneous voltage values ​​DU are digitized there by an analog-to-digital converter (ADC) and fed to a microprocessor (CPU). The CPU then determines or calculates the instantaneous threshold values ​​SWU. The instantaneous threshold values ​​SWU determined by the second subunit SED, and in particular by the microprocessor CPU, are then fed back to the first subunit SEA, specifically to the voltage comparator CU, to perform the comparison described above.

[0089] Advantageously, the determination of the instantaneous threshold values ​​SWU in the second subunit SED can be carried out digitally, or at a slower processing speed than the continuous comparison of voltage values ​​and threshold values ​​in the first subunit SEA.

[0090] In an advantageous embodiment, in which a current sensor SI is provided that outputs the magnitude of the current, i.e., instantaneous current values ​​DI, the first subunit SEA can have a current comparator CI. The instantaneous current values ​​DI from the current sensor SI are supplied to this comparator. On the other hand, instantaneous current threshold values ​​SWI from the second subunit SED are supplied to the current comparator CI.

[0091] The current comparator CI compares the instantaneous current values ​​DI with the instantaneous current threshold values ​​SWI and, in an analogous manner, outputs a current interruption signal TI if the current exceeds the threshold in magnitude, in order to initiate an interruption of the low-voltage circuit.

[0092] The current interruption signal TI can be fed to the logic unit LG, which combines it with other interruption signals and outputs the (first) signal TRIP to the electronic interruption unit EU for semiconductor-based interruption or high-impedance interruption.

[0093] In one embodiment, the current comparator CI stores the current threshold values ​​SWI in order to have the values ​​constantly available.

[0094] The instantaneous current values ​​DI are also fed to the second subunit SED. In a preferred embodiment, the instantaneous current values ​​DI are digitized there by the analog-to-digital converter ADC and fed to the microprocessor CPU. The CPU then determines or calculates the instantaneous current threshold values ​​SWI. The instantaneous current threshold values ​​SWI determined by the second subunit SED, or more specifically by the microprocessor CPU, are then fed back to the first subunit SEA, in particular to the current comparator CU, to perform the comparison described above.

[0095] Advantageously, the determination of the instantaneous current threshold values ​​SWI in the second subunit SED can be done digitally or with a slower processing speed than the continuous comparison of current values ​​and threshold values ​​in the first subunit SEA.

[0096] Depending on the configuration, a second interruption signal TRIPG can be output from the second subunit SED, in particular from the microprocessor CPU, to the mechanical isolating contact system MK for galvanic interruption of the low-voltage circuit, as shown in Figure 2 marked.

[0097] Figure 3 shows a further design or variant according to Figure 1 and Figure 2 . Figure 3 shows part of a simple variant of the first, preferably analog, subunit SEAE and part of an alternative variant of the second, preferably digital, subunit SEDE.

[0098] The simple version of the first subunit SEAE includes the voltage comparator CU, to which the instantaneous voltage values ​​DU, in particular their magnitude, and the instantaneous threshold values ​​SWU, also in terms of magnitude, are fed. In this example, the voltage comparator CU directly outputs the first signal TRIP to interrupt the low-voltage circuit, analogous to Figure 2 The amount can be calculated using one or more units not shown.

[0099] The alternative version of the second subunit SEDE includes a network synchronization unit NSE. This unit receives the (analog) instantaneous voltage values ​​DU. From these (analog) instantaneous voltage values ​​DU, which are sinusoidal alternating voltages of the low-voltage circuit, the network synchronization unit NSE determines the amplitude U, the phase angle φ(t), and an expected time value of the voltage UE. The expected value of the voltage UE is a type of filtered, regenerated, or generated equivalent instantaneous voltage value DU.

[0100] The expected value of the voltage UE, as well as the amplitude U and the phase angle φ(t), can be determined, for example, by a so-called phase-locked loop (PLL). A PLL is an electronic circuit arrangement that influences the phase and, consequently, the frequency of a variable oscillator via a closed control loop in such a way that the phase deviation between an external periodic reference signal (instantaneous voltage values) and the oscillator or a signal derived from it is as constant as possible.

[0101] This allows, among other things, the determination of the fundamental frequency and its amplitude of the supplied mains voltage, i.e., the determined voltage values, i.e., the (undisturbed or filtered) expected value of the (mains) voltage.

[0102] The amplitude U, phase angle φ(t), and expected time value of the voltage UE, determined by the network synchronization unit NSE, are fed to a threshold unit SWE. The threshold unit SWE modifies the expected value of the voltage UE to an instantaneous threshold SWU, where, for example: a fixed voltage amount can be subtracted from the expected value of the voltage UE, or a phase-angle-dependent voltage amount can be subtracted from the expected value of the voltage UE, or a fixed percentage of the voltage can be subtracted from the expected value of the voltage UE, or a phase-angle-dependent percentage of the voltage can be subtracted from the expected value of the voltage UE to obtain the instantaneous threshold SWU.

[0103] The instantaneous threshold SWU can also be adjusted by the amplitude U of the instantaneous voltage, i.e., a high instantaneous threshold is present at a high amplitude of the voltage and a low instantaneous threshold is present at a low amplitude of the voltage.

[0104] The instantaneous threshold values ​​SWU can be transmitted from the threshold unit SWE to the voltage comparator CU synchronously with the instantaneous voltage DU by virtue of the presence of the phase angle φ(t) in the threshold unit, so that a phase-related (phase-angle-related) comparison between instantaneous threshold value and instantaneous voltage value can be carried out in the voltage comparator CU.

[0105] Figure 4 shows an alternative design according to Figure 3The difference is that the expected value of the voltage UE is not fed to the threshold unit SWE, but to a difference unit DE. Furthermore, the instantaneous voltage value DU is not fed to the voltage comparator CU, but to the difference unit DE. The difference unit DE calculates the difference between the expected value of the voltage UE and the instantaneous voltage value DU, with the calculation being phase-angle accurate. This generates a (phase-angle-dependent) differential voltage value DW, which is fed to the voltage comparator CU. The voltage comparator CU, on the other hand, receives the instantaneous threshold value SWU, which in this example is provided by the threshold unit SWE as a phase-related and amplitude-influenced differential voltage threshold.

[0106] In this example, the expected voltage value UE provided by the grid synchronization unit, particularly in the form of a PLL, is compared with the instantaneous voltage value DU, specifically in a time- or phase-synchronous manner, resulting in a difference of values ​​DW. Often, a PLL itself can perform such a function, i.e., provide the difference, i.e., a differential voltage value DW.

[0107] The differential voltage value DW is then compared, particularly in terms of its magnitude, with the current threshold value SWU, in this case a differential voltage threshold.

[0108] Alternative designs are also conceivable.

[0109] Figure 5The graph shows the curves of current I in amperes A (top) and voltage U in volts V (bottom) – on the vertical y-axis – versus time t in seconds s – on the horizontal x-axis. It depicts a simulated comparison of the time course ERF of the presented invention versus the time course KLA of a simple (classic) overcurrent protection circuit. A short circuit occurs at t = 145 ms. The current I rises sharply, and simultaneously, the measured voltage U drops abruptly.

[0110] The time course of the simple overcurrent protection circuit (KLA), which interrupts the current flow when the current exceeds 200 A. However, due to latencies and shutdown times, the current continues to rise briefly after the limit has been exceeded.

[0111] The temporal response time (ERF) of the short-circuit detection system according to the invention is based on the detection of a sharp drop in the measured voltage, which is detected very quickly by phase-accurate comparison with the expected voltage. The phase angle resolution determines the speed of the threshold calculation. With a phase angle resolution of 1°, i.e., a threshold value is present for every full phase angle of the voltage, meaning an instantaneous threshold value is present approximately every 55.5 µs. The shutdown is preferably carried out via an analog comparator, i.e., continuously, and is therefore significantly faster than the phase angle resolution.

[0112] Alternatively, the following time course applies to fully digital processing. The phase angle resolution determines the detection speed. With a phase angle resolution of 1°, meaning a threshold value exists for each full phase angle of the voltage (i.e., an instantaneous threshold value occurs approximately every 55.5 µs), this means that a shutdown can occur after a minimum of approximately 60 µs. Shorter shutdown times can be achieved with higher phase angle resolutions.

[0113] In this example, the values ​​are then processed at a minimum of 18 kHz.

[0114] Alternatively, the expected value of the voltage can be stored in a table, whereby the respective voltage values ​​are then compared in phase synchrony or a phase-synchronous difference is formed, so that differential voltage values ​​are available.

[0115] Figure 6On the one hand, it shows the course of the voltage Vgrid in volts [V], on the left vertical axis, and on the other hand, a period of a sinusoidal alternating voltage over time t in s [s], on the horizontal axis.

[0116] On the other hand, a phase angle-related or phase angle-dependent instantaneous threshold value, on the right vertical axis, over time t in s [s].

[0117] In this example, the instantaneous threshold is greater than the instantaneous voltage.

[0118] Although the invention has been illustrated and described in detail by the exemplary embodiment, the invention is not limited by the disclosed examples and other variations can be derived from them by the person skilled in the art without leaving the scope of protection of the invention.

Claims

1. Circuit breaker device (SG) for protecting an electrical low-voltage circuit, having: - a housing having connections (L1, N1, L2, N2) for conductors of the low-voltage AC circuit, - a voltage sensor (SU) for ascertaining the level of the voltage of the low-voltage circuit such that instantaneous voltage values (DU) are available, - an electronic interruption unit (EU) that, due to semiconductor-based switching elements, has a high-resistance state of the switching elements for interrupting and a lowresistance state of the switching elements for allowing current to flow in the low-voltage circuit, - a control unit (SE) that is connected to the voltage sensor (SU) and the electronic interruption unit (EU), characterized in that the circuit breaker device (SG) is designed such that instantaneous threshold values (SWU) are available, that the instantaneous voltage values (DU) are compared with the instantaneous threshold values (SWU) in terms of phase angle such that, if the instantaneous threshold values (SWU) are exceeded or undershot, or a differential voltage value (DW) is formed from the instantaneous threshold value (SWU) and the instantaneous voltage value (DU), the differential voltage value (DW) is compared with a differential voltage threshold value (DSW) and, if said threshold value is exceeded or undershot, an interruption of the low-voltage circuit is initiated in order to avoid a short-circuit current.

2. Circuit breaker device (SG) according to Claim 1, characterized in that the instantaneous threshold values (SWU) are adapted on the basis of the amplitude (U) of the voltage of the low-voltage circuit such that there is a high instantaneous threshold value (SWU) in the case of a high amplitude (U) of the voltage and there is a low instantaneous threshold value (SWU) in the case of a low amplitude (U) of the voltage.

3. Circuit breaker device (SG) according to Claim 1 or 2, characterized in that the absolute values of the instantaneous voltage values (DU) are compared with the instantaneous threshold values (SWU) in terms of phase angle such that, if the absolute value of the instantaneous threshold value (SWU) is undershot, or the differential voltage value (DW) is formed from the instantaneous threshold value (SWU) and the absolute value of the instantaneous voltage value (DU), the differential voltage value (DW) is compared with the differential voltage threshold value (DSW) and, if said threshold value is exceeded, an interruption of the low-voltage circuit is initiated.

4. Circuit breaker device (SG) according to one of the preceding claims, characterized in that the exceeding or undershooting must be present for a first time interval in order to initiate an interruption of the low-voltage circuit.

5. Circuit breaker device (SG) according to one of the preceding claims, characterized in that the circuit breaker device (SG) is designed such that the control unit has an analogue first subunit (SEA) and a digital second subunit (SED), that the first subunit (SEA) has a voltage comparator (CU), to which the instantaneous voltage values (DU) from the voltage sensor (SU) and the instantaneous threshold values (SWU) from the second subunit (SED) are supplied, for comparing the instantaneous voltage values (DU) with the instantaneous threshold values (SWU) and initiating an interruption of the low-voltage circuit if said threshold values are exceeded or undershot, that the instantaneous voltage values (DU) are also supplied to the second subunit (SED) in order to ascertain the instantaneous threshold values (SWU).

6. Circuit breaker device (SG) according to one of the preceding claims, characterized in that the circuit breaker device (SG) is designed such that provision is made for a grid synchronization unit (NSE) which, from the supplied instantaneous voltage values (DU): - outputs an expected temporal value (UE) of the voltage, - outputs a phase angle (φ(t)) of the voltage, - outputs the amplitude (U) of the voltage, that provision is made for a threshold value unit (SWE), to which the expected temporal value (UE), the phase angle (φ(t)) and the amplitude (U) of the voltage are supplied and which ascertains the instantaneous threshold values (SWU) therefrom, that the instantaneous voltage values (DU) are compared with the instantaneous threshold values (SWU) in order to ascertain the initiation of an interruption.

7. Circuit breaker device (SG) according to one of the preceding Claims 1 to 5, characterized in that the circuit breaker device (SG) is designed such that provision is made for a grid synchronization unit (NSE) which, from the supplied instantaneous voltage values (DU): - outputs an expected temporal value (UE) of the voltage, - outputs a phase angle (φ(t)) of the voltage, - outputs the amplitude (U) of the voltage, that provision is made for a threshold value unit (SWE), to which the phase angle (φ(t)) and the amplitude (U) of the voltage are supplied and which ascertains differential voltage threshold values (DSW), in particular instantaneous differential voltage threshold values, therefrom, that the instantaneous voltage values (DU) and the expected temporal value (UE) of the voltage are supplied to a differential unit (DE) which ascertains a differential voltage value (DW), in particular a phase angle-dependent differential voltage value, that the instantaneous differential voltage value (DW) is compared with the differential voltage threshold value (DSW), in particular the instantaneous differential voltage threshold value, in order to ascertain the initiation of an interruption.

8. Circuit breaker device (SG) according to one of the preceding claims, characterized in that provision is made for a mechanical isolating contact system (MK) which is connected in series with the electronic interruption unit (EU) on the circuit side such that galvanic isolation can be provided in the low-voltage circuit, in that the mechanical isolating contact system (MK) is connected to the control unit (SE).

9. Circuit breaker device (SG) according to one of the preceding claims, characterized in that, in addition to an interruption by the electronic interruption unit (EU), an electrical interruption by the mechanical isolating contact system (MK) is also initiated.

10. Circuit breaker device (SG) according to one of the preceding claims, characterized in that a current sensor (SI) for ascertaining the level of the current of the low-voltage circuit is provided.

11. Circuit breaker device (SG) according to Claim 10, characterized in that galvanic isolation is initiated in the case of a high-resistance electronic interruption unit (EU) and a current in the low-voltage circuit that exceeds a first current threshold value.

12. Circuit breaker device (SG) according to Claim 10 or 11, characterized in that the ascertained current level is compared with a second current threshold value and an interruption of the low-voltage circuit, in particular by the mechanical isolating contact system (MK), is initiated if said threshold value is exceeded.

13. Circuit breaker device (SG) according to Claim 10, 11 or 12, characterized in that, if an interruption of the low-voltage circuit by means of the electronic interruption unit (EU) is initiated and there is a current flow in the low-voltage circuit that exceeds a third current threshold value and persists for a second time interval, an interruption of the low-voltage circuit by the mechanical isolating contact system (MK) is initiated.

14. Circuit breaker device (SG) according to one of the preceding claims, characterized in that the instantaneous threshold values (SWU) are ascertained for each phase angle of the voltage of the low-voltage circuit, in particular by means of the digital second subunit (SED) which digitally ascertains the instantaneous threshold values (SWU) at a clock frequency of between 10 kHz and 10 MHz, in particular 10 kHz and 1 MHz, more specifically between 10 kHz and 100 kHz, in particular above 18 kHz.

15. Method for protecting an electrical low-voltage circuit, in which: - the level of the voltage of the low-voltage circuit is ascertained such that instantaneous voltage values (DU) are available, characterized - in that instantaneous threshold values (SWU) are available, - in that the instantaneous voltage values (DU) are compared with the instantaneous threshold values (SWU) in terms of phase angle such that, if the instantaneous threshold values are exceeded or undershot, or - a differential voltage value (DW) is formed from the instantaneous threshold value (SWU) and the instantaneous voltage value (DU), the differential voltage value (DW) is compared with a differential voltage threshold value (DSW) and, if said threshold value is exceeded or undershot, - an interruption of the low-voltage circuit is initiated in order to avoid a short-circuit current.