Low-voltage circuit breaker and power measuring arrangement

Abstract

Low-voltage circuit breaker (LS) for a low-voltage AC circuit, comprising: - a voltage sensor (SS) for determining the level of voltage between conductors of the low-voltage AC circuit, - a Rogowski coil (RS1, RS2, RS3, RSN) for determining the magnitude of the electric current of a conductor (L1, L2, L3, N) of the low-voltage alternating current circuit, which outputs an analog voltage (A1, A2, A3, AN) equivalent to the magnitude of the electric current of the conductor, - an interruption unit (UE) with contacts (K) for interrupting the low-voltage alternating current circuit, - a control unit (ETU) connected to the voltage sensor (SS), the Rogowski coil (RS1, RS2, RS3, RSN) and the interruption unit (UE), with a microprocessor (MP), wherein the low-voltage circuit breaker is designed in such a way that if the current and / or current-time limit values ​​of a conductor are exceeded, an interruption of the low-voltage alternating current circuit is initiated, and: - that the Rogowski coil (RS1, RS2, RS3, RSN) is connected to an analog integrator (INT), followed by a first analog-to-digital converter (ADU1) which converts the integrated analog voltage (uc(t)) into a digital signal (P1, P2, P3, PN) so that a sample value of the current is available every X degrees, related to the period of the alternating current, - that the voltage sensor (SS) is connected to a second analog-to-digital converter (ADU2) so that every Y degrees, based on the period of the alternating voltage, a sample value of the voltage (PU) is available which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a sampled value of the current (P1, P2, P3, PN) and an interpolated voltage value, wherein the interpolated voltage value is determined from two successive sampled values ​​of the voltage (PU) in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined.

Description

[0001] The invention relates to the technical field of a low-voltage circuit breaker for a low-voltage AC circuit, a power measuring arrangement for a low-voltage AC circuit, in particular for low-voltage circuit breakers, and a method for determining a power for a low-voltage AC circuit, in particular for a low-voltage circuit breaker.

[0002] Circuit breakers are protective devices that function similarly to a fuse. Circuit breakers monitor the current flowing through them via a conductor and interrupt the electrical current or energy flow to an energy sink or load. This is referred to as tripping when protection parameters, such as current limits or current-time limits, are exceeded. The set current limits or current-time limits are the corresponding tripping reasons. The interruption occurs, for example, when the circuit breaker contacts open.

[0003] Especially for low-voltage circuits, systems, or networks, there are various types of circuit breakers depending on the level of the intended electrical current in the electrical circuit. Circuit breakers within the meaning of the invention refer, in particular, to switches used in low-voltage systems for currents, particularly nominal currents or maximum currents, from 63 to 6300 amperes. Enclosed circuit breakers are used more specifically for currents from 63 to 1600 amperes, particularly from 125 to 630 or 1200 amperes. Open circuit breakers are used particularly for currents from 200 or 630 to 6300 amperes, more specifically from 1200 to 6300 amperes.

[0004] Open circuit breakers are also called air circuit breakers (ACBs) and enclosed circuit breakers are called molded case circuit breakers (MCCBs).

[0005] Low voltage refers to voltages up to 1000 or 1200 volts AC or 1500 volts DC, with particular reference to the effective values ​​of the voltage. Low voltage refers, more specifically, to voltages greater than extra-low voltage, with values ​​of 50 volts AC or 120 volts DC.

[0006] For the purposes of the invention, circuit breakers are understood to mean, in particular, circuit breakers with an electronic trip unit serving as a control unit, also referred to as an Electronic Trip Unit (ETU).

[0007] In low-voltage circuit breakers, the voltage level is typically determined using voltage sensors. So-called Rogowski coils (Rogowoski transformers) are typically used to determine the current level. These emit a voltage proportional to the differentiated current. By integrating this voltage, the current level can be determined.

[0008] Rogowski coils have the disadvantage that the measured current level is not phase-accurate. This is caused by the stray field inductance of the Rogowski coil's coil. Furthermore, both the Rogowski converter and the integrator are not ideal, but real units. After the signal is derived by the Rogowski converter and subsequently integrated by an analog integrator, a (residual) phase error results with respect to the original signal (current in the conductor to be measured). The phase error in the current measurement path distorts all current measurements. Consequently, subsequent quantities such as a power value, which use the current determined by a Rogowski coil (and / or integrator) and which depend, for example, on the phase angle between current and voltage, are distorted.

[0009] German patent DE 10 2012 107 021 B4 describes a device and method for measuring an alternating current. Device (1;400) for measuring an alternating current in a conductor characterized by an alternating voltage with a mains frequency or measured variables derived therefrom, comprising a current channel (2) for detecting a current signal i(t) of the conductor having a mains period, a voltage channel (3) for detecting a voltage signal u(t) of the conductor associated with the current signal i(t), wherein in the voltage channel (3) a first analog-digital converter (7) operating at a sampling frequency fa is provided for converting the voltage signal u(t) into a time-discrete voltage signal u(n), and in the current channel (2) a Rogowski coil (4) in which a Rogowski coil voltage r(t) proportional to the differential of the current signal i(t) is formed, a second analog-digital converter (5) connected to the Rogowski coil (4) for converting the Rogowski coil voltage r(t) into a time-discrete Rogowski coil signal r(n) and an integrator unit (6; 404; 405;406), which determines an integrator signal i(n) proportional to the current signal i(t) on the basis of the Rogowski coil signal r(n), characterized in that a phase-locked loop (8; 407; 408; 409) is arranged in the voltage channel (3), which determines the network period and transmits this to the integrator unit for use in determining the integrator signal i(n).

[0010] The German patent application DE 10 2016 218 960 A1 describes a switch. The patent application concerns a switch for protecting an electrical circuit: - with a release device for interrupting the electrical circuit, - with a summation current transformer through which conductors of the electrical circuit are led to determine differential currents and which has a first winding from which a differential current can be taken, - with a current sensor for determining current values ​​of the electrical circuit, - with a voltage sensor for determining voltage values ​​of the electrical circuit, - with a test button, - with an arc fault simulation unit having one input and two outputs, - with a microprocessor which is connected to the test button, the current sensor, the voltage sensor, the first winding of the summation current transformer, the input of the arc fault simulation unit and the tripping device, and is designed in such a way that if certain current limit values ​​are exceeded or if an arc fault occurs, the electrical circuit is interrupted by the tripping device, wherein the summation current transformer has a second winding which is connected to the microprocessor directly or via a first resistor, wherein the signals of the outputs of the arc fault simulation unit can be fed to the microprocessor by a test signal instead of the current and / or voltage values.

[0011] German patent application DE 10 2015 218 914 A1 describes a fire protection switch. The patent application relates to a fire protection switch for an electrical circuit, comprising: a power supply unit for the power supply, at least one current sensor for continuously determining electrical current values ​​of the electrical circuit, at least one voltage sensor for continuously determining electrical voltage values ​​of the electrical circuit, a control unit comprising an analog-to-digital converter, a processor unit, and a memory in which the determined current and voltage values ​​are digitized and processed, and which is configured such that, upon detection of an arc fault, a signal is emitted to interrupt the electrical circuit.The control unit is further designed such that after detection of an arc fault, the determined current and voltage values ​​are available at an output unit for a first period until the arc fault is detected.

[0012] However, Rogowski coils have the advantage of providing potential isolation, high current capability and small size.

[0013] The object of the present invention is to enable an accurate determination of quantities, in particular power values, based on current and voltage values ​​using Rogowski coils for current determination, in particular for a low-voltage circuit breaker.

[0014] This object is achieved by a low-voltage circuit breaker having the features of patent claim 1, a power measuring arrangement having the features of patent claim 8 or a method having the features of patent claim 9.

[0015] According to the invention, a low-voltage circuit breaker for a low-voltage AC circuit is provided, comprising: - (at least) one voltage sensor to determine the level of voltage between conductors of the low-voltage AC circuit, - (at least) one Rogowski coil for determining the magnitude of the electric current of a conductor of the low-voltage alternating current circuit, which outputs an analogue voltage equivalent to the magnitude of the electric current of the conductor, - an interruption unit with contacts for interrupting the low-voltage alternating current circuit, - a control unit connected to the voltage sensor, the Rogowski coil, and the interruption unit, with a microprocessor, wherein the low-voltage circuit breaker is designed such that, if current and / or current-time limit values ​​of a conductor are exceeded, an interruption of the low-voltage AC circuit is initiated. Furthermore, the low-voltage circuit breaker is designed such that: - (each or) the Rogowski coil is connected to an analog integrator, followed by a first analog-to-digital converter, which converts the integrated analog voltage into a digital signal, so that every X degrees (i.e. a certain fixed number of degrees), related to the period of the alternating current (360°), a sample value of the current is available (related to a period of the alternating current, a first number of digital samples of the alternating current are available) - that the voltage sensor is connected to a second analog-to-digital converter, so that every Y degrees (i.e. a certain fixed number of degrees), related to the period of the alternating voltage (360°), a sample of the voltage is available (related to a period of the alternating voltage, a first or second number of digital samples of the alternating voltage are available), which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a sampled current value and an interpolated voltage value, the interpolated voltage value being determined from two successive sampled voltage values ​​in such a way that a phase error generated by the Rogowski coil and / or the integrator (i.e. the arrangement for determining the level of the current - for example Rogowski coil, integrator and possibly other units), related to the electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined.

[0016] For example, an interpolated voltage value for an intermediate phase angle is determined from two consecutive voltage samples, resulting in interpolated voltage values. A power value is calculated from a sample value corresponding to a phase angle of the first number of current samples and an interpolated voltage value of the same phase angle, resulting in a power determination using current samples and interpolated voltage values ​​with matching phase angles, in order to compensate for a phase error in the current value determination.

[0017] According to the invention, the phase error is advantageously compensated not on the side of the current signal (which causes or has the phase error), but rather the voltage signal is used to compensate for the phase error (of the current). Since the voltage signal is only present at discrete time intervals, which may not correlate with the magnitude of the phase error, interpolated voltage values ​​are determined, which are then correlated with the (phase-errored) current values, so that for a phase angle of current and voltage, the current and voltage values ​​available for this phase angle (i.e. the current value with the phase error and a correlated - interpolated - voltage value) are used, so that an error in a power value calculated from the values ​​is avoided or minimized. In particular, it has been found that compensation of the voltage value is more advantageous, since this often has fewer harmonics.Furthermore, the voltage measurement path (voltage sensor) usually only has linear components, which means that runtime and / or phase errors cannot occur here or are minimized to the utmost.

[0018] Advantageous embodiments of the invention are specified in the subclaims.

[0019] In an advantageous embodiment of the invention, the low-voltage circuit breaker is designed such that the interpolated voltage values ​​are determined by means of a linear interpolation.

[0020] This has the particular advantage of enabling particularly simple and cost-effective interpolation of the voltage values.

[0021] In an advantageous embodiment of the invention, the low-voltage circuit breaker is designed such that the interpolation is carried out in the control unit, in particular in the microprocessor.

[0022] This has the particular advantage of enabling simple and cost-effective interpolation, e.g. in firmware, which can also be easily adapted.

[0023] In an advantageous embodiment of the invention, the low-voltage circuit breaker is designed such that the sampled value of the current and the sampled value of the voltage are each determined at the same time or approximately at the same time.

[0024] This has the particular advantage that a determined phase error of the current can be used directly as a phase difference for the determination or interpolation of the (interpolated) voltage value.

[0025] In an advantageous embodiment of the invention, the low-voltage circuit breaker is designed such that the sampled current value and the sampled voltage value are determined at the same sampling rate, so that the time interval between the sampled current values ​​and the sampled voltage values ​​is the same or, on average, the same.

[0026] This has the particular advantage that compensation for different sampling rates and thus different time intervals is avoided in addition to the phase error correction.

[0027] In an advantageous embodiment of the invention, the low-voltage circuit breaker is designed such that the phase error of the current is determined, particularly during commissioning of the low-voltage circuit breaker, and the phase position of the interpolated voltage value is adjusted, particularly during commissioning of the low-voltage circuit breaker, so that, at least approximately, phase-error-free power values ​​are determined. This has the particular advantage that calibration is performed during commissioning, so that no further calibration is required for an initial accuracy requirement.

[0028] According to the invention, a parallel power measuring arrangement for a low-voltage AC circuit is further claimed. This arrangement comprises: - a voltage sensor for determining the level of voltage between conductors of the low-voltage AC circuit, - a Rogowski coil for determining the magnitude of the electric current of a conductor of the low-voltage alternating current circuit, which outputs an analog voltage equivalent to the magnitude of the electric current of the conductor, - a control unit with a microprocessor connected to the voltage sensor and the Rogowski coil, wherein the power measuring arrangement is designed such that: - the Rogowski coil is connected to an analog integrator, followed by a first analog-to-digital converter, which converts the integrated analog voltage into a digital signal, so that a sample value of the current is available every X degrees, related to the period of the alternating current, - that the voltage sensor is connected to a second analog-to-digital converter so that every Y degrees, relative to the period of the alternating voltage, a sample value of the voltage is available which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a current sample and an interpolated voltage value, with the interpolated voltage value being determined from two consecutive voltage samples in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value that is at least approximately free of phase errors is determined. This has the advantages already described.

[0029] The dependent claims for the low-voltage circuit breaker apply analogously to the power measuring arrangement.

[0030] According to the invention, a parallel method for determining a power value for a low-voltage AC circuit, in particular for a low-voltage circuit breaker, is further claimed, in which: - which is determined from the level of voltage between conductors of the low-voltage alternating current circuit, - the magnitude of the current of at least one conductor is determined by a Rogowski coil which outputs an analog voltage equivalent to the magnitude of the electric current of the conductor, - the analog voltage of the Rogowski coil is integrated and then digitized, so that every X degrees, related to the period of the alternating current, a sample value of the current or its equivalent is available, - the voltage level is digitized so that every Y degrees, related to the period of the alternating voltage, a sample value of the voltage or an equivalent thereof is available, - that a power value is calculated from a current sample and an interpolated voltage value, with the interpolated voltage value being determined from two consecutive voltage samples in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value that is at least approximately free of phase errors is determined. This has the advantages already described.

[0031] The dependent claims relating to the low-voltage circuit breaker apply analogously to the method.

[0032] According to the invention, a computer program product comprising instructions which, when the program is executed by a microprocessor, cause the microprocessor to generate / determine / calculate a power value which is at least approximately free of phase errors is further advantageously claimed.

[0033] The computer program product can advantageously be stored on a computer-readable storage medium, such as a CD, floppy disk, USB stick, etc., in order to enable, for example, a subsequent updating of the firmware of a microprocessor of a low-voltage circuit breaker or a power measuring arrangement.

[0034] The computer program product can advantageously be transmitted by a data carrier signal in order, for example, to enable the firmware to be quickly loaded onto the microprocessor.

[0035] All embodiments, both in dependent form referring back to patent claim 1, 8 or 9, and referring back only to individual features or combinations of features of patent claims, result in an improvement in the determination of quantities from voltage and current measured values ​​in which Rogowski coils are used.

[0036] The described properties, features and advantages of this invention and the manner in which they are achieved will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0037] The accompanying drawing shows: Fig. 1 a block diagram of a low-voltage circuit breaker; Fig. 2 a block diagram of a power measuring arrangement; Fig. 3 a first arrangement according to the invention; Fig. 4 a second arrangement according to the invention.

[0038] Fig. 1 shows a schematic block diagram of a low-voltage circuit breaker LS. Fig. 1 shows electrical conductors L1, L2, L3, N of a low-voltage circuit, for example a three-phase alternating current circuit, wherein the first conductor L1 forms the first phase with the first phase current ip(t), the second conductor L2 forms the second phase with the second phase current, the third conductor L3 forms the third phase with the third phase current and the fourth conductor forms the neutral conductor N with the neutral conductor current of the three-phase alternating current circuit.

[0039] In the example according to Fig. 1, the first conductor L1 is connected to an energy converter EW (for example as part of a converter set) such that at least part of the current, i.e. a partial conductor current, or the entire current of the first conductor L1 flows through the primary side of the energy converter EW. Usually, one conductor, in the example the first conductor L1, forms the primary side of the energy converter EW. The energy converter EW is usually a transformer with a core, e.g. an iron transformer. In one embodiment, an energy converter EW can be provided in each phase or in each conductor of the electrical circuit. The secondary side of the energy converter EW or of each provided energy converter is connected to a power supply NT (or several power supplies), which has a power supply, e.g.provides an internal power supply, for example in the form of a supply voltage, for the units of the low-voltage circuit breaker, in particular an electronic trip unit ETU, represented by a dashed connection of operating voltage conductors BS. The power supply unit NT can also be connected to at least one or all of the power units SE1, SE2, SE3, SEN to supply power to the power units - if necessary.

[0040] Each current unit SE1, SE2, SE3, SEN is connected to a Rogowski coil RS1, RS2, RS3, RSN for determining the magnitude of the electric current in the conductor of the electrical circuit assigned to it. In the example, the first current unit SE1 is assigned to the first conductor L1, i.e., the first phase; the second current unit SE2 to the second conductor L2, i.e., the second phase; the third current unit SE3 to the third conductor L3, i.e., the third phase; and the fourth current unit SEN to the (fourth conductor) neutral conductor N.

[0041] The Rogowski coils RS1, RS2, RS3, RSN provide an analog voltage A1, A2, A3, AN at their output, proportional to the magnitude of the conductor current. This voltage is fed to the first to fourth current units SE1, SE2, SE3, SEN. In the example, the first to fourth current units SE1, SE2, SE3, SEN are part of a control unit ETU. However, they can also be provided as separate units.

[0042] The current units SE1, SE2, SE3, and SEN are used to condition the voltage of the respective Rogowski coils. The current units SE1, SE2, SE3, and SEN supply, for example, a digital signal P1, P2, P3, and NS to a microprocessor MP, which is located, for example, in the electronic trip unit ETU.

[0043] The transmitted digital signals P1, P2, P3, NS are compared in the electronic trip unit ETU with current limit values ​​and / or current-time limit values, which constitute the triggering reasons. If these are exceeded, the electrical circuit is interrupted. This provides overcurrent and / or short-circuit protection. This can be achieved, for example, by providing an interruption unit UE, which is connected to the electronic trip unit ETU on the one hand and has contacts K for interrupting conductors L1, L2, L3, N or other conductors on the other hand. In this case, the interruption unit UE receives an interruption signal to open contacts K.

[0044] The low-voltage circuit breaker LS also has a voltage sensor SS. This can be a separate unit or part of the control unit ETU, as shown in Fig. 1. The voltage sensor SS is connected to the conductors L1, L2, L3, and N. The voltage sensor SS is also connected to the control unit ETU or the microprocessor MP.

[0045] Fig. 2 shows a basic power measurement arrangement SLE, where units according to Fig. 1. The power measuring arrangement SLE comprises at least one Rogowski coil RS1 for determining the magnitude of the electric current of a conductor L1 of the low-voltage AC circuit, which outputs an analog voltage A1 equivalent to the magnitude of the electric current of the conductor L1. The Rogowski coil RS1 is connected to a current unit SE1.

[0046] Furthermore, it has at least one voltage sensor SS for determining the voltage level of the conductors of the low-voltage alternating current circuit, e.g. between the conductors L1 and N (as shown).

[0047] It also has a control unit in the form of a microprocessor MP, which is connected to the current unit SE1 and the voltage sensor SS, wherein the determined current and voltage of the low-voltage alternating current circuit are used to determine the power value by the microprocessor MP. A determined power value SLES can be output. For example, the determined power value can be displayed on the power measuring arrangement SLE or on the low-voltage circuit breaker LS, e.g. via a display unit connected to the control unit ETU or the microprocessor MP. Alternatively or additionally, the power value can be transmitted (wirelessly or wired) via a communication unit connected to the control unit ETU or the microprocessor MP. Alternatively or additionally, the power value can be saved, accumulated or / and retrieved later.

[0048] In the example according to Fig. Figure 2 shows a two-wire circuit. A three-phase alternating current circuit, with or without a neutral conductor, can be provided in a similar manner.

[0049] Fig. 3 shows an embodiment of a power unit SE1 according to Fig. 2 or Fig. 1. This has an analog integrator INT, which is connected to the Rogowski coil RS1. The analog voltage A1 of the Rogowski coil is fed to this integrator. An analog integrator is one that performs integration using discrete components, such as capacitors, inductors, resistors, etc., according to analog circuit technology. That is, an analog signal is integrated.

[0050] The analog integrator INT provides an integrated analog voltage uc(t). In one variant, this voltage is directly converted from analog to digital, e.g., by a first analog-to-digital converter ADU1, which outputs a digital signal P1 to the microprocessor MP.

[0051] In other embodiments according to the invention, a filter FI and / or amplifier V can be provided in any order between the analog integrator INT and the first analog-digital converter ADU1, for example according to Fig. 3. Alternatively, a filter can be provided before the integrator INT.

[0052] Alternatively, the integrator can also be designed as a digital integrator, in which case the first analog-to-digital converter is arranged in front of the integrator.

[0053] The microprocessor MP is designed in such a way that the phase shift / phase error generated by the Rogowski coil RS1 and by the components connected downstream of the Rogowski coil, in particular the integrator INT, if applicable the filter FI and / or amplifier V, is compensated, whereby for this purpose the voltage values ​​determined in an analogous manner (for current value determination) are interpolated free of phase errors, so that phase error-free power values ​​are available.

[0054] Fig. 4 shows an embodiment of a voltage sensor SS according to Fig. 2 or Fig. 1. This has a second analog-to-digital converter ADU2, which outputs a digital signal PU / one sample value of the voltage to the microprocessor MP.

[0055] The second analog-digital converter ADU2 can be preceded by a filter FI and / or amplifier and / or other units, such as in Fig. 4 is shown.

[0056] In the following, the invention will be explained again in other words.

[0057] The most commonly used measuring system in a low-voltage circuit breaker consists of a Rogowski transformer (air-core coil) as the measuring transformer and an analog integrator. The Rogowski coil is a non-closed, toroidal air-core coil with linear characteristics. To measure a current i(t) in a conductor, the ring-shaped coil is wrapped around it. When measuring current using a Rogowski coil, a voltage is induced in the coil that is proportional to the time derivative of the current di(t) / dt.

[0058] To restore the signal from the Rogowski converter to its original signal form before being passed through the converter, the signal must be integrated. This is usually done using an analog integrator (essentially a capacitor) within a power unit or control unit (electronics).

[0059] Both the Rogowski converter and the integrator are not ideal, but real units with non-ideal components. After the signal is derived by the Rogowski converter and subsequently integrated by the analog integrator, a residual phase error with respect to the original signal results. This is a frequency-dependent phase error (phase response). In comparison, the voltage measurement path usually consists only of linear components and therefore exhibits no delay or phase error.

[0060] The phase error in the current measurement path distorts these measured values. Consequently, subsequent variables that depend on the angle between current and voltage, such as power values, are also distorted or inaccurate.

[0061] If the phase difference between current and voltage is large, for example in the range 60 to 90°, the error in determining the power value is particularly large.

[0062] According to the invention, a linear interpolation method for digitally compensating a phase error is proposed to solve the aforementioned problem. The compensation is performed on an analog-to-digital converted signal in the time domain.

[0063] Since the underlying phase error is an angle error between the current and voltage signals, compensation can be performed in both the current and voltage signals. Angle compensation is advantageously performed in the voltage path, as it is generally less subject to harmonics.

[0064] For each sample of the voltage PU (each sample u(t)), a new, interpolated voltage value u'(t) is calculated. Depending on the correction angle, this value can be temporally before or after the original sample of the voltage PU. The calculation of the new value u'(t) is advantageously carried out using the two-point form of the straight line equation, which, according to the ray theorem, allows any point to be determined as a straight line between two points. y=y2−y1x2−x1∗(x−x1)+y1

[0065] Depending on the required compensation angle, the new, interpolated voltage value (new sample) u'(t) is calculated using either the sample u(t), the sample u(t-1) preceding it, or the sample u(t+1) following it. The compensation method therefore has a runtime of one sample. This constant runtime of one sample must be taken into account when calculating the angle-dependent quantities (power values) and when generating the corresponding current / voltage sample pairs.

[0066] Without the angle correction method (which can be implemented as an algorithm, particularly using firmware for the microprocessor), the value pairs would correlate with each other in time, i.e., p(t) = i(t) * u(t), where: p(t) is the power over time, i(t) is the current over time, and u(t) is the voltage over time (each in the low-voltage circuit). The resulting "power sample" at time t is based on the current and voltage samples, also at time t.

[0067] The correction process has a runtime of one sample, meaning the results are always delayed by one sample from the control unit / microprocessor. To maintain the temporal correlation between the angle-corrected voltage samples and the current samples, the current samples must also be delayed by one sample to ensure the correct temporal relationship.

[0068] The resulting “power samples” at time t are based on the current and voltage samples p(t = i(t+1)* u(t+1)) in the past (by one sample).

[0069] Since the individual “performance samples” are often summarized or calculated to form a performance result accumulated over a time window, this temporal shift does not play a (negative) role.

[0070] The angle compensation method proposed here achieves a significant increase in the accuracy of phase-angle-dependent measured values ​​or quantities, such as power values, with minimal expenditure of system resources. The method enables appropriate correction of the phase error individually in each measurement channel (e.g., per phase, i.e., per conductor L1, L2, L3, and possibly N), as required.

[0071] The invention can advantageously be implemented, at least in part, by a computer program product comprising instructions which, when the program is executed by a microprocessor, cause the microprocessor to generate / determine / calculate a power value which is at least approximately free of phase errors.

[0072] The computer program product may advantageously be stored on a computer-readable storage medium, such as a CD, floppy disk, USB stick, etc.

[0073] The computer program product can advantageously be transmitted by a data carrier signal in order to enable rapid loading of the firmware onto the microprocessor.

[0074] 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

[1] Low-voltage circuit breaker (LS) for a low-voltage AC circuit, comprising: - a voltage sensor (SS) for determining the level of voltage between conductors of the low-voltage alternating current circuit, - a Rogowski coil (RS1, RS2, RS3, RSN) for determining the magnitude of the electric current of a conductor (L1, L2, L3, N) of the low-voltage alternating current circuit, which outputs an analog voltage (A1, A2, A3, AN) equivalent to the magnitude of the electric current of the conductor, - an interruption unit (UE) with contacts (K) for interrupting the low-voltage alternating current circuit, - a control unit (ETU) connected to the voltage sensor (SS), the Rogowski coil (RS1, RS2, RS3, RSN) and the interruption unit (UE), with a microprocessor (MP), wherein the low-voltage circuit breaker is designed in such a way that if the current and / or current-time limit values ​​of a conductor are exceeded, an interruption of the low-voltage alternating current circuit is initiated, and: - that the Rogowski coil (RS1, RS2, RS3, RSN) is connected to an analog integrator (INT), followed by a first analog-to-digital converter (ADU1) which converts the integrated analog voltage (uc(t)) into a digital signal (P1, P2, P3, PN) so that a sample value of the current is available every X degrees, related to the period of the alternating current, - that the voltage sensor (SS) is connected to a second analog-to-digital converter (ADU2) so that every Y degrees, based on the period of the alternating voltage, a sample value of the voltage (PU) is available which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a sampled value of the current (P1, P2, P3, PN) and an interpolated voltage value, wherein the interpolated voltage value is determined from two successive sampled values ​​of the voltage (PU) in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined. [2] Low-voltage circuit breaker (LS) according to claim 1, characterized bythat the interpolated voltage values ​​are determined by means of linear interpolation. [3] Low-voltage circuit breaker (LS) according to claim 1 or 2, characterized by that the interpolation is carried out in the control unit (ETU), in particular in the microprocessor (MP). [4] Low-voltage circuit breaker (LS) according to claim 1, 2 or 3, characterized by that the sampled value of the current (P1, P2, P3, PN) and the sampled value of the voltage (PU) are determined at the same time or approximately at the same time. [5] Low-voltage circuit breaker (LS) according to claim 1, 2, 3 or 4, characterized by that the sampled value of the current (P1, P2, P3, PN) and the sampled value of the voltage (PU) are determined with the same sampling rate, so that the time interval between the sampled values ​​of the current (P1, P2, P3, PN) and the sampled values ​​of the voltage (PU) is the same or on average the same. [6] Low-voltage circuit breaker (LS) according to claim 1, 2, 3, 4 or 5, characterized by that the phase error of the current is determined, that the determined phase error is used to determine the interpolated voltage value. [7] Low-voltage circuit breaker (LS) according to claim 1, 2, 3, 4, 5 or 6, characterized by , that the low-voltage circuit breaker is designed in such a way that the phase error of the current is determined, in particular when the low-voltage circuit breaker is put into operation, that the phase position of the interpolated voltage value is adjusted, in particular when commissioning the low-voltage circuit breaker, so that, at least approximately, phase-error-free power values ​​are determined. [8] Power measuring arrangement (SLE) for a low-voltage alternating current circuit, comprising: - a voltage sensor (SS) for determining the level of voltage between conductors of the low-voltage AC circuit, - a Rogowski coil (RS1, RS2, RS3, RSN) for determining the magnitude of the electric current of a conductor (L1, L2, L3, N) of the low-voltage alternating current circuit, which outputs an analog voltage (A1, A2, A3, AN) equivalent to the magnitude of the electric current of the conductor, - a control unit (ETU) with a microprocessor (MP) connected to the voltage sensor (SS) and the Rogowski coil (SE1), wherein the power measuring arrangement is designed such that: - the Rogowski coil (RS1, RS2, RS3, RSN) is connected to an analog integrator (INT), followed by a first analog-to-digital converter (ADU1) which converts the integrated analog voltage (uc(t)) into a digital signal (P1, P2, P3, PN), so that a sample value of the current (P1, P2, P3, PN) is available every X degrees, based on the period of the alternating current, - that the voltage sensor (SS) is connected to a second analog-to-digital converter (ADU2) so that every Y degrees, based on the period of the alternating voltage, a sample value of the voltage (PU) is available which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a sampled value of the current (P1, P2, P3, PN) and an interpolated voltage value, wherein the interpolated voltage value is determined from two successive sampled values ​​of the voltage (PU) in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined. [9] Method for determining a power value for a low-voltage alternating current circuit, in particular for a low-voltage circuit breaker, in which: - which is determined from the level of voltage between conductors of the low-voltage alternating current circuit, - the magnitude of the current of at least one conductor is determined by a Rogowski coil (RS1, RS2, RS3, RSN) which outputs an analog voltage (A1, A2, A3, AN) which is equivalent to the magnitude of the electric current of the conductor, - the analog voltage of the Rogowski coil (RS1, RS2, RS3, RSN) is integrated and then digitized, so that every X degrees, related to the period of the alternating current, a sample value of the current (P1, P2, P3, PN) or an equivalent thereof is available, - the voltage level is digitized so that every Y degrees, related to the period of the alternating voltage, a sample value of the voltage (PU) or an equivalent thereof is available, - that a power value is calculated from a sampled value of the current (P1, P2, P3, PN) and an interpolated voltage value, wherein the interpolated voltage value is determined from two successive sampled values ​​of the voltage (PU) in such a way that a phase error generated by the Rogowski coil and / or the integrator, related to the electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined. [10] Computer program product comprising instructions which, when the program is executed by a microprocessor, cause the microprocessor to generate a power value according to one of claims 1 to 9 which is at least approximately free of phase errors. [11] Computer-readable storage medium on which the computer program product according to claim 10 is stored. [12] Data carrier signal transmitting the computer program product according to claim 10.

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