WO2024083490A1 - Determining a frequency spectrum of an electric current - Google Patents

Determining a frequency spectrum of an electric current Download PDF

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Publication number
WO2024083490A1
WO2024083490A1 PCT/EP2023/077239 EP2023077239W WO2024083490A1 WO 2024083490 A1 WO2024083490 A1 WO 2024083490A1 EP 2023077239 W EP2023077239 W EP 2023077239W WO 2024083490 A1 WO2024083490 A1 WO 2024083490A1
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vector
fourier
current
measurement signal
previous
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PCT/EP2023/077239
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German (de)
French (fr)
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Stefan Schuberth
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Siemens Energy Global GmbH & Co. KG
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Publication of WO2024083490A1 publication Critical patent/WO2024083490A1/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/14—Fourier, Walsh or analogous domain transformations, e.g. Laplace, Hilbert, Karhunen-Loeve, transforms
    • G06F17/141—Discrete Fourier transforms
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/16—Spectrum analysis; Fourier analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
    • G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
    • G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect

Definitions

  • the invention relates to a method and a current analysis device for determining a frequency spectrum of an electric current.
  • the frequency distribution in a current measurement signal is usually determined by a so-called fast Fourier transform (FFT for short), which is an efficient calculation of a so-called discrete Fourier transform (DFT for short). Since the complete calculation of a fast Fourier transform is time-consuming, it usually cannot be carried out after every current measurement, although this would be desirable from a signal processing point of view. For this reason, the frequency amplitude, for example, is only calculated for selected frequencies. This may be sufficient for certain analysis purposes, but a back transformation from the frequency domain to the time domain is not possible.
  • FPGA abbreviation for Field Programmable Gate Array
  • the invention is based on the object of specifying an improved method and an improved current analysis device for determining a frequency spectrum of an electric current.
  • the object is achieved according to the invention by a method having the features of claim 1 and a current analysis device having the features of claim 7.
  • a current measurement signal is recorded by means of a current measuring device at equidistantly successive measurement times.
  • a measurement signal vector is formed from the n most recent current measurement signals, where n is a predetermined number of current measurement signals.
  • a Fourier vector is calculated from the measurement signal vector using a Fourier matrix, which is a discrete Fourier transformation of the measurement signal vector.
  • An updated Fourier vector is formed from the previous Fourier vector by adding to the previous Fourier vector the product of the column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector is added.
  • W ( t 2 ) (w 2 , ..., w k , ..., w n ) denote the measurement signal vector which is formed from the n most recent current measurement signals w 2 ,...,w n recorded up to a measurement time ti (including the measurement time ti), where the k-th component w k is the oldest current measurement signal contained in the measurement signal vector W(t 2 ).
  • the Fourier vector X(t 2 ) for the measurement time t 2 is calculated according to the invention from the Fourier vector X(t 2 ) as follows:
  • X(t 2 ) X(t 2 ) + (M lk , ...,M nk ) - (w 0 -w k ) , where (M lk , ...,M nk ) denotes the k-th column of the Fourier matrix, written as a row vector.
  • the method according to the invention therefore provides for calculating the Fourier vector of a discrete Fourier transformation for a measurement time from the previous Fourier vector, i.e. from the Fourier vector for the previous measurement time, according to the rule described above.
  • the arithmetic operations to be carried out for this rule are proportional to the number n of components of the measurement signal vector and thus enable a more effective (faster) calculation of the Fourier vector than a conventional fast Fourier transformation, the number of arithmetic operations of which scales with n-log(n). This is made possible by the fact that the method according to the invention for calculating the Fourier vector for a measurement time no matrix multiplication of the Fourier matrix with the complete current measurement signal vector is provided.
  • the method according to the invention provides an updating of the previous Fourier vector, which only requires a multiplication of a column of the Fourier matrix with the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector and the addition of the result of this multiplication to the previous Fourier vector.
  • the current measuring device has at least one optical current transformer.
  • An optical current transformer is understood here to be an optical measuring device for measuring an electric current flowing in a current conductor, which is based on the magneto-optical Faraday effect. This effect is understood to be the rotation of the polarization direction of a linearly polarized electromagnetic wave in a medium by a magnetic field parallel to the direction of propagation of the wave. The rotation of the polarization direction is proportional to the magnetic flux density of the magnetic field.
  • linearly polarized light is sent through an optical fiber arranged near the current conductor, which exhibits the Faraday effect. The magnetic field generated by the current in the current conductor causes a rotation of the polarization direction of the light.
  • the current strength can be measured by detecting the rotation of the polarization direction of the light.
  • the light output from the light guide is passed through a polarizer, for example, and a light intensity of the light transmitted by the polarizer is detected.
  • the Fourier vector is a frequency vector whose Components are amplitudes of the current measurement signal depending on frequencies of the current measurement signal.
  • a temporal change in the Fourier vector is continuously calculated, a stability value is calculated from the temporal change in the Fourier vector and the stability value is used to control a protective device of an electrical switchgear.
  • This embodiment of the method according to the invention takes advantage of the fact that large temporal changes in the Fourier vector can indicate, for example, fault currents or damage to an electrical switchgear.
  • the components of a Fourier vector which fall below a threshold value are set to zero.
  • the threshold value is calculated, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector.
  • n is a predetermined number of current measurement signals
  • an updated Fourier vector from the previous Fourier vector is formed by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
  • a current analysis device enables the method according to the invention to be carried out.
  • the advantages of such a current analysis device therefore correspond to the above-mentioned advantages of the method according to the invention.
  • the current measuring device has at least one optical current transformer.
  • the Fourier vector formed by the evaluation unit is a frequency vector whose components are amplitudes of the current measurement signal as a function of frequencies of the current measurement signal.
  • the evaluation unit is set up to continuously calculate a temporal change of the Fourier vector, to calculate a stability value from the temporal change of the Fourier vector and to use the stability value to control a protective device of an electrical switchgear.
  • the Current analysis device is the evaluation unit set up, to set the components of each Fourier vector that fall below a threshold value to zero.
  • the evaluation unit is set up to calculate the threshold value as the product of a predetermined factor and an average value of the components of the Fourier vector.
  • FIG 1 is a block diagram of an embodiment of a current analysis device for determining a frequency spectrum of an electrical current
  • FIG 2 is a flow diagram of an embodiment of a method for determining a frequency spectrum of an electric current.
  • FIG. 1 shows a block diagram of an embodiment of a current analysis device 1 for determining a frequency spectrum of an electrical current.
  • the current analysis device 1 comprises a current measuring device 3 and an evaluation unit 5.
  • the current measuring device 3 is designed to record a current measuring signal at equidistant measuring times.
  • the current measuring device 3 has at least one optical current transformer.
  • the evaluation unit 5 is set up to form a measurement signal vector from the n most recent current measurement signals, where n is a predetermined number of current measurement signals. Furthermore, the evaluation unit 5 is set up to form a Fourier vector which is a discrete Fourier transformation of the measurement signal vector. For this purpose, the evaluation unit 5 is set up to form an updated Fourier vector from the previous Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
  • the evaluation unit 5 can also be configured to set the components of a Fourier vector that fall below a threshold value to zero.
  • the threshold value is calculated by the evaluation unit 5, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector.
  • FIG. 2 shows a flow chart of an embodiment of the method according to the invention for determining a frequency spectrum of an electric current. The method is carried out using a current analysis device 1 described with reference to Figure 1.
  • a current measurement signal is recorded at n consecutive measurement times using the current measuring device 3.
  • a first measurement signal vector is formed from these current measurement signals by the evaluation unit 5.
  • a first Fourier vector is calculated from this measurement signal vector by the evaluation unit 5 by matrix multiplication with a Fourier matrix.
  • a second method step 12 is carried out.
  • the previous Fourier vector is updated.
  • the evaluation unit 5 forms an updated Fourier vector from the previous (previous) Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the current measurement signal recorded in the previous method step 12 (and thus most recent) and the oldest current measurement signal contained in the previous measurement signal vector.
  • the second method step 12 is carried out again.
  • the evaluation unit 5 sets the components of the respective Fourier vector to zero which fall below a threshold value.
  • the threshold value is calculated by the evaluation unit 5, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector.

Abstract

The invention relates to a method for determining a frequency spectrum of an electric current. In the method, at measurement times following another temporally equidistantly, respective current measurement signals are captured. A measurement signal vector is formed from the n latest current measurement signals, n being a specified number of current measurement signals. A Fourier vector is calculated from the measurement signal vector by means of a Fourier matrix. Here, an updated Fourier vector is formed from the preceding Fourier vector in the following manner: the product of the column of the Fourier matrix that corresponds to the earliest current measurement signal contained in the preceding measurement signal vector and of the difference between the latest current measurement signal and the earliest current measurement signal which is contained in the preceding measurement signal vector is added to the preceding Fourier vector.

Description

Beschreibung Description
Ermitteln eines Frequenzspektrums eines elektrischen Stroms Determining a frequency spectrum of an electric current
Die Erfindung betri f ft ein Verfahren und eine Stromanalysevorrichtung zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms . The invention relates to a method and a current analysis device for determining a frequency spectrum of an electric current.
Bei Strommessgeräten, die beispielsweise in der Stromschutztechnik eingesetzt werden, ist es notwendig, das Rauschen in dem Messsignal zu reduzieren, sowie die Frequenz und Phase des Messsignals mit einer hohen Frequenzauflösung und Zeitauflösung zu messen . Werden beispielsweise in einem Übertragungsnetz mehrere Leitungen parallelgeschaltet , so könnte eine Frequenz- oder Phasenabweichung zwischen den Leitungen zu hohen Fehlerströmen oder Schäden an Anlagen führen . Generell wird für eine hohe Frequenzauflösung ein langer Zeitbereich zur Frequenzanalyse benötigt . Idealerweise müsste nach j eder Strommessung eine Frequenzanalyse durchgeführt werden, um einen Frequenzverlauf beziehungsweise ein Spektrum der Frequenzen eines Strommesssignals zu erhalten . Dies übersteigt j edoch die Rechengeschwindigkeit der meisten momentan erhältlichen Auswertungssysteme . For current measuring devices used, for example, in power protection technology, it is necessary to reduce the noise in the measurement signal and to measure the frequency and phase of the measurement signal with a high frequency resolution and time resolution. If, for example, several lines are connected in parallel in a transmission network, a frequency or phase deviation between the lines could lead to high fault currents or damage to systems. In general, a long time range is required for frequency analysis to achieve a high frequency resolution. Ideally, a frequency analysis would have to be carried out after each current measurement in order to obtain a frequency curve or a spectrum of the frequencies of a current measurement signal. However, this exceeds the computing speed of most evaluation systems currently available.
Gegenwärtig wird im Stand der Technik die Frequenzverteilung in einem Strommesssignal in der Regel durch eine so genannte schnelle Fourier-Trans formation ( engl . Fast Fourier Trans form, abgekürzt FFT ) bestimmt , die eine ef fi ziente Berechnung einer so genannten diskreten Fourier- Trans formation ( abgekürzt DFT ) ist . Da die komplette Berechnung einer schnellen Fourier-Trans formation zeitintensiv ist , kann diese meist j edoch nicht nach j eder Strommessung erfolgen, obwohl dies aus Sicht der Signalverarbeitung wünschenswert wäre . Daher wird die Frequenzamplitude beispielsweise nur für ausgewählte Frequenzen berechnet . Für bestimmte Analysezwecke kann dies ausreichen, eine Rücktrans formation vom Frequenzbereich in den Zeitbereich ist damit j edoch nicht möglich . Eine schnelle Fourier-Trans formation wird momentan mit einem so genannten FPGA (Abkürzung für Field Programmable Gate Array) berechnet . Dabei skalieren die notwendigen Rechenoperationen für eine schnelle Fourier-Trans formation mit n - log (n) , wobei n die Anzahl der Frequenzstützstellen der Berechnung ist . Im Vergleich zu der Berechnung einer normalen diskreten Fourier-Trans formation, welche n2 Rechenoperationen benötigt , ist dies bereits ein Vorteil . Selbst dieser Implementierung sind j edoch Grenzen im Zeit- und Frequenzbereich gesetzt . Um das Rauschen in den Messsignalen zu reduzieren, werden meist analoge oder digitale Filter im Zeitbereich auf das Messsignal angewendet . Currently, in the state of the art, the frequency distribution in a current measurement signal is usually determined by a so-called fast Fourier transform (FFT for short), which is an efficient calculation of a so-called discrete Fourier transform (DFT for short). Since the complete calculation of a fast Fourier transform is time-consuming, it usually cannot be carried out after every current measurement, although this would be desirable from a signal processing point of view. For this reason, the frequency amplitude, for example, is only calculated for selected frequencies. This may be sufficient for certain analysis purposes, but a back transformation from the frequency domain to the time domain is not possible. A fast Fourier transformation is currently calculated using a so-called FPGA (abbreviation for Field Programmable Gate Array). The necessary arithmetic operations for a fast Fourier transformation scale with n - log (n), where n is the number of frequency support points in the calculation. Compared to the calculation of a normal discrete Fourier transformation, which requires n 2 arithmetic operations, this is already an advantage. However, even this implementation has limits in the time and frequency domain. In order to reduce the noise in the measurement signals, analog or digital filters in the time domain are usually applied to the measurement signal.
Der Erfindung liegt die Aufgabe zugrunde , ein verbessertes Verfahren und eine verbesserte Stromanalysevorrichtung zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms anzugeben . The invention is based on the object of specifying an improved method and an improved current analysis device for determining a frequency spectrum of an electric current.
Die Aufgabe wird erfindungsgemäß durch ein Verfahren mit den Merkmalen des Anspruchs 1 und eine Stromanalysevorrichtung mit den Merkmalen des Anspruchs 7 gelöst . The object is achieved according to the invention by a method having the features of claim 1 and a current analysis device having the features of claim 7.
Vorteilhafte Ausgestaltungen der Erfindung sind Gegenstand der Unteransprüche . Advantageous embodiments of the invention are the subject of the dependent claims.
Bei dem erfindungsgemäßen Verfahren zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms wird mittels einer Strommessvorrichtung zu zeitlich äquidistant aufeinander folgenden Mess zeitpunkten j eweils ein Strommesssignal erfasst . Aus den j eweils n j üngsten Strommesssignalen wird ein Messsignalvektor gebildet , wobei n eine vorgegebene Anzahl von Strommesssignalen ist . Aus dem Messsignalvektor wird mittels einer Fourier-Matrix ein Fouriervektor berechnet , der eine diskrete Fourier- Trans formation des Messsignalvektors ist . Dabei wird ein aktualisierter Fouriervektor aus dem vorhergehenden Fouriervektor gebildet , indem zu dem vorhergehenden Fouriervektor das Produkt derjenigen Spalte der Fourier- Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert, und der Differenz des jeweils jüngsten Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird. In the method according to the invention for determining a frequency spectrum of an electric current, a current measurement signal is recorded by means of a current measuring device at equidistantly successive measurement times. A measurement signal vector is formed from the n most recent current measurement signals, where n is a predetermined number of current measurement signals. A Fourier vector is calculated from the measurement signal vector using a Fourier matrix, which is a discrete Fourier transformation of the measurement signal vector. An updated Fourier vector is formed from the previous Fourier vector by adding to the previous Fourier vector the product of the column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector is added.
Um das erfindungsgemäße Verfahren im Detail zu erklären, bezeichne W ( t2) = (w2, ..., wk, ..., wn) den Messsignalvektor, der aus den n jüngsten bis zu einem Messzeitpunkt ti (einschließlich des Messzeitpunkts ti) erfassten Strommesssignalen w2,...,wn gebildet wird, wobei die k-te Komponente wk das älteste in dem Messsignalvektor W(t2) enthaltene Strommesssignal ist. Der aus W(t2) gebildete Fouriervektor sei mit X ( t2) = (x2, ..., xn) bezeichnet. w0 bezeichne das zu dem auf den Messzeitpunkt t2 folgenden Messzeitpunkt t2 gemessene Strommesssignal. Der Fouriervektor X(t2) für den Messzeitpunkt t2 wird erfindungsgemäß aus dem Fouriervektor X(t2) folgendermaßen berechnet : In order to explain the method according to the invention in detail, let W ( t 2 ) = (w 2 , ..., w k , ..., w n ) denote the measurement signal vector which is formed from the n most recent current measurement signals w 2 ,...,w n recorded up to a measurement time ti (including the measurement time ti), where the k-th component w k is the oldest current measurement signal contained in the measurement signal vector W(t 2 ). The Fourier vector formed from W(t 2 ) is denoted by X ( t 2 ) = (x 2 , ..., x n ). Let w 0 denote the current measurement signal measured at the measurement time t 2 following the measurement time t 2 . The Fourier vector X(t 2 ) for the measurement time t 2 is calculated according to the invention from the Fourier vector X(t 2 ) as follows:
X(t2) = X(t2) + (Mlk, ...,Mnk) - (w0-wk) , wobei (Mlk, ...,Mnk) die k-te Spalte der Fourier-Matrix, als Zeilenvektor geschrieben, bezeichnet. X(t 2 ) = X(t 2 ) + (M lk , ...,M nk ) - (w 0 -w k ) , where (M lk , ...,M nk ) denotes the k-th column of the Fourier matrix, written as a row vector.
Das erfindungsgemäße Verfahren sieht also vor, den Fouriervektor einer diskreten Fourier-Transformation für einen Messzeitpunkt aus dem vorhergehenden Fouriervektor, das heißt aus dem Fouriervektor für den vorhergehenden Messzeitpunkt, gemäß der oben beschriebenen Vorschrift zu berechnen. Die für diese Vorschrift auszuführenden Rechenoperationen sind proportional zu der Anzahl n der Komponenten des Messsignalvektors und ermöglichen damit eine effektivere (schnellere) Berechnung des Fouriervektors als eine herkömmliche schnelle Fourier-Transformation, deren Anzahl von Rechenoperationen mit n-log(n) skaliert. Dies wird dadurch ermöglicht, dass das erfindungsgemäße Verfahren für die Berechnung des Fouriervektors für einen Messzeitpunkt keine Matrixmultiplikation der Fourier-Matrix mit dem kompletten j eweils aktuellen Messsignalvektor vorsieht . Stattdessen sieht das erfindungsgemäße Verfahren eine Aktualisierung des bisherigen Fouriervektors vor, die lediglich eine Multiplikation einer Spalte der Fourier-Matrix mit der Di f ferenz des j eweils j üngsten Strommesssignals und des ältesten in dem bisherigen Messsignalvektor enthaltenen Strommesssignals und die Addition des Ergebnisses dieser Multiplikation zu dem bisherigen Fouriervektor erfordert . The method according to the invention therefore provides for calculating the Fourier vector of a discrete Fourier transformation for a measurement time from the previous Fourier vector, i.e. from the Fourier vector for the previous measurement time, according to the rule described above. The arithmetic operations to be carried out for this rule are proportional to the number n of components of the measurement signal vector and thus enable a more effective (faster) calculation of the Fourier vector than a conventional fast Fourier transformation, the number of arithmetic operations of which scales with n-log(n). This is made possible by the fact that the method according to the invention for calculating the Fourier vector for a measurement time no matrix multiplication of the Fourier matrix with the complete current measurement signal vector is provided. Instead, the method according to the invention provides an updating of the previous Fourier vector, which only requires a multiplication of a column of the Fourier matrix with the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector and the addition of the result of this multiplication to the previous Fourier vector.
Bei einer Ausgestaltung des erfindungsgemäßen Verfahrens weist die Strommessvorrichtung wenigstens einen optischen Stromwandler auf . Unter einem optischen Stromwandler wird hier eine optische Messvorrichtung zum Messen eines in einem Stromleiter fließenden elektrischen Stroms verstanden, die auf dem magnetooptischen Faraday-Ef fekt beruht . Unter diesem Ef fekt versteht man die Drehung der Polarisationsrichtung einer linear polarisierten elektromagnetischen Welle in einem Medium durch ein zur Ausbreitungsrichtung der Welle paralleles Magnetfeld . Die Drehung der Polarisationsrichtung ist dabei proportional zu der magnetischen Flussdichte des Magnetfelds . Bei einem optischen Stromwandler wird linear polarisiertes Licht durch einen in der Nähe des Stromleiters angeordneten Lichtleiter gesendet , der den Faraday-Ef fekt zeigt . Das von dem Strom in dem Stromleiter erzeugte Magnetfeld bewirkt eine Drehung der Polarisationsrichtung des Lichts . Da die magnetische Flussdichte des Magnetfelds von der Stromstärke des in dem Stromleiter fließenden Stroms abhängt , lässt sich die Stromstärke messen, indem die Drehung der Polarisationsrichtung des Lichts erfasst wird . Um die Drehung der Polarisationsrichtung zu erfassen, wird das von dem Lichtleiter ausgegebene Licht beispielsweise durch einen Polarisator geführt und es wird eine Lichtintensität des von dem Polarisator transmittierten Lichts erfasst . In one embodiment of the method according to the invention, the current measuring device has at least one optical current transformer. An optical current transformer is understood here to be an optical measuring device for measuring an electric current flowing in a current conductor, which is based on the magneto-optical Faraday effect. This effect is understood to be the rotation of the polarization direction of a linearly polarized electromagnetic wave in a medium by a magnetic field parallel to the direction of propagation of the wave. The rotation of the polarization direction is proportional to the magnetic flux density of the magnetic field. In an optical current transformer, linearly polarized light is sent through an optical fiber arranged near the current conductor, which exhibits the Faraday effect. The magnetic field generated by the current in the current conductor causes a rotation of the polarization direction of the light. Since the magnetic flux density of the magnetic field depends on the current strength of the current flowing in the current conductor, the current strength can be measured by detecting the rotation of the polarization direction of the light. In order to detect the rotation of the polarization direction, the light output from the light guide is passed through a polarizer, for example, and a light intensity of the light transmitted by the polarizer is detected.
Bei einer weiteren Ausgestaltung des erfindungsgemäßenIn a further embodiment of the inventive
Verfahrens ist der Fouriervektor ein Frequenzvektor, dessen Komponenten Amplituden des Strommesssignals in Abhängigkeit von Frequenzen des Strommesssignals sind . The Fourier vector is a frequency vector whose Components are amplitudes of the current measurement signal depending on frequencies of the current measurement signal.
Bei einer weiteren Ausgestaltung des erfindungsgemäßen Verfahrens wird fortlaufend eine zeitliche Veränderung des Fouriervektors berechnet , aus der zeitlichen Veränderung des Fouriervektors wird ein Stabilitätswert berechnet und der Stabilitätswert wird verwendet , um eine Schutzeinrichtung einer elektrischen Schaltanlage zu steuern . Diese Ausgestaltung des erfindungsgemäßen Verfahrens nutzt aus , dass große zeitliche Veränderungen des Fouriervektors beispielsweise auf Fehlerströme oder Schäden einer elektrischen Schaltanlage hindeuten können . In a further embodiment of the method according to the invention, a temporal change in the Fourier vector is continuously calculated, a stability value is calculated from the temporal change in the Fourier vector and the stability value is used to control a protective device of an electrical switchgear. This embodiment of the method according to the invention takes advantage of the fact that large temporal changes in the Fourier vector can indicate, for example, fault currents or damage to an electrical switchgear.
Bei einer weiteren Ausgestaltung des erfindungsgemäßen Verfahrens werden die Komponenten eines Fouriervektors Null gesetzt , die einen Schwellenwert unterschreiten . Der Schwellenwert wird beispielsweise als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors berechnet . Diese Ausgestaltung des erfindungsgemäßen Verfahrens ermöglicht vorteilhaft eine Unterdrückung des Einflusses in den Strommesssignalen enthaltenen Rauschens auf die aus den Strommesssignalen gebildeten Fouriervektoren . In a further embodiment of the method according to the invention, the components of a Fourier vector which fall below a threshold value are set to zero. The threshold value is calculated, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector. This embodiment of the method according to the invention advantageously enables the influence of noise contained in the current measurement signals on the Fourier vectors formed from the current measurement signals to be suppressed.
Eine erfindungsgemäße Stromanalysevorrichtung zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms umfasstA current analysis device according to the invention for determining a frequency spectrum of an electric current comprises
- eine Strommessvorrichtung, die eingerichtet ist , zu zeitlich äquidistant aufeinander folgenden Mess zeitpunkten j eweils ein Strommesssignal zu erfassen, und - a current measuring device which is designed to record a current measuring signal at equidistantly successive measuring points in time, and
- eine Auswerteeinheit , die eingerichtet ist , - an evaluation unit which is set up,
- aus den j eweils n j üngsten Strommesssignalen einen Messsignalvektor zu bilden, wobei n eine vorgegebene Anzahl von Strommesssignalen ist , und - to form a measurement signal vector from the n most recent current measurement signals, where n is a predetermined number of current measurement signals, and
- aus dem Messsignalvektor mittels einer Fourier-Matrix einen Fouriervektor zu bilden, der eine diskrete Fourier- Trans formation des Messsignalvektors ist , wobei - to form a Fourier vector from the measurement signal vector using a Fourier matrix, which is a discrete Fourier transformation of the measurement signal vector, where
- ein aktualisierter Fouriervektor aus dem vorhergehenden Fouriervektor gebildet wird, indem zu dem vorhergehenden Fouriervektor das Produkt derj enigen Spalte der Fourier- Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert , und der Di f ferenz des j eweils j üngsten Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird . - an updated Fourier vector from the previous Fourier vector is formed by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
Eine erfindungsgemäße Stromanalysevorrichtung ermöglicht die Durchführung des erfindungsgemäßen Verfahrens . Die Vorteile einer derartigen Stromanalysevorrichtung korrespondieren daher zu den oben genannten Vorteilen des erfindungsgemäßen Verfahrens . Entsprechendes gilt für die folgenden Ausgestaltungen einer erfindungsgemäßen Stromanalysevorrichtung, die zu oben genannten Ausgestaltungen des erfindungsgemäßen Verfahrens korrespondieren . A current analysis device according to the invention enables the method according to the invention to be carried out. The advantages of such a current analysis device therefore correspond to the above-mentioned advantages of the method according to the invention. The same applies to the following embodiments of a current analysis device according to the invention, which correspond to the above-mentioned embodiments of the method according to the invention.
Bei einer Ausgestaltung einer erfindungsgemäßen Stromanalysevorrichtung weist die Strommessvorrichtung wenigstens einen optischen Stromwandler auf . In one embodiment of a current analysis device according to the invention, the current measuring device has at least one optical current transformer.
Bei einer weiteren Ausgestaltung einer erfindungsgemäßen Stromanalysevorrichtung ist der von der Auswerteeinheit gebildete Fouriervektor ein Frequenzvektor, dessen Komponenten Amplituden des Strommesssignals in Abhängigkeit von Frequenzen des Strommesssignals sind . In a further embodiment of a current analysis device according to the invention, the Fourier vector formed by the evaluation unit is a frequency vector whose components are amplitudes of the current measurement signal as a function of frequencies of the current measurement signal.
Bei einer weiteren Ausgestaltung einer erfindungsgemäßen Stromanalysevorrichtung ist die Auswerteeinheit eingerichtet , fortlaufend eine zeitliche Veränderung des Fouriervektors zu berechnen, aus der zeitlichen Veränderung des Fouriervektors einen Stabilitätswert zu berechnen und den Stabilitätswert zu verwenden, um eine Schutzeinrichtung einer elektrischen Schaltanlage zu steuern . In a further embodiment of a current analysis device according to the invention, the evaluation unit is set up to continuously calculate a temporal change of the Fourier vector, to calculate a stability value from the temporal change of the Fourier vector and to use the stability value to control a protective device of an electrical switchgear.
Bei einer weiteren Ausgestaltung einer erfindungsgemäßenIn a further embodiment of an inventive
Stromanalysevorrichtung ist die Auswerteeinheit eingerichtet , die Komponenten j edes Fouriervektors Null zu setzen, die einen Schwellenwert unterschreiten . Beispielsweise ist die Auswerteeinheit dabei eingerichtet , den Schwellenwert als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors zu berechnen . Current analysis device is the evaluation unit set up, to set the components of each Fourier vector that fall below a threshold value to zero. For example, the evaluation unit is set up to calculate the threshold value as the product of a predetermined factor and an average value of the components of the Fourier vector.
Die oben beschriebenen Eigenschaften, Merkmale und Vorteile dieser Erfindung sowie die Art und Weise , wie diese erreicht werden, werden klarer und deutlicher verständlich im Zusammenhang mit der folgenden Beschreibung von Aus führungsbeispielen, die im Zusammenhang mit den Zeichnungen näher erläutert werden . Dabei zeigen : The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of embodiments, which are explained in more detail in connection with the drawings, in which:
FIG 1 ein Blockdiagramm eines Aus führungsbeispiels einer Stromanalysevorrichtung zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms , FIG 1 is a block diagram of an embodiment of a current analysis device for determining a frequency spectrum of an electrical current,
FIG 2 ein Ablauf diagramm eines Aus führungsbeispiels eines Verfahrens zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms . FIG 2 is a flow diagram of an embodiment of a method for determining a frequency spectrum of an electric current.
Figur 1 ( FIG 1 ) zeigt ein Blockdiagramm eines Aus führungsbeispiels einer Stromanalysevorrichtung 1 zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms . Die Stromanalysevorrichtung 1 umfasst eine Strommessvorrichtung 3 und eine Auswerteeinheit 5 . Figure 1 (FIG. 1) shows a block diagram of an embodiment of a current analysis device 1 for determining a frequency spectrum of an electrical current. The current analysis device 1 comprises a current measuring device 3 and an evaluation unit 5.
Die Strommessvorrichtung 3 ist eingerichtet , zu zeitlich äquidistant aufeinander folgenden Mess zeitpunkten j eweils ein Strommesssignal zu erfassen . Beispielsweise weist die Strommessvorrichtung 3 wenigstens einen optischen Stromwandler auf . The current measuring device 3 is designed to record a current measuring signal at equidistant measuring times. For example, the current measuring device 3 has at least one optical current transformer.
Die Auswerteeinheit 5 ist eingerichtet , aus den j eweils n j üngsten Strommesssignalen einen Messsignalvektor zu bilden, wobei n eine vorgegebene Anzahl von Strommesssignalen ist . Ferner ist die Auswerteeinheit 5 eingerichtet , aus dem Messsignalvektor mittels einer Fourier-Matrix einen Fouriervektor zu bilden, der eine diskrete Fourier- Trans formation des Messsignalvektors ist . Zu diesem Zweck ist die Auswerteeinheit 5 eingerichtet , einen aktualisierten Fouriervektor aus dem vorhergehenden Fouriervektor zu bilden, indem zu dem vorhergehenden Fouriervektor das Produkt derj enigen Spalte der Fourier-Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert , und der Di f ferenz des j eweils j üngsten Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird . The evaluation unit 5 is set up to form a measurement signal vector from the n most recent current measurement signals, where n is a predetermined number of current measurement signals. Furthermore, the evaluation unit 5 is set up to form a Fourier vector which is a discrete Fourier transformation of the measurement signal vector. For this purpose, the evaluation unit 5 is set up to form an updated Fourier vector from the previous Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
Die Auswerteeinheit 5 kann ferner eingerichtet sein, die Komponenten eines Fouriervektors Null zu setzen, die einen Schwellenwert unterschreiten . Der Schwellenwert wird von der Auswerteeinheit 5 beispielsweise als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors berechnet . The evaluation unit 5 can also be configured to set the components of a Fourier vector that fall below a threshold value to zero. The threshold value is calculated by the evaluation unit 5, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector.
Figur 2 ( FIG 2 ) zeigt ein Ablauf diagramm eines Aus führungsbeispiels des erfindungsgemäßen Verfahrens zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms . Das Verfahren wird mit einer anhand von Figur 1 beschriebenen Stromanalysevorrichtung 1 durchgeführt . Figure 2 (FIG. 2) shows a flow chart of an embodiment of the method according to the invention for determining a frequency spectrum of an electric current. The method is carried out using a current analysis device 1 described with reference to Figure 1.
In einem ersten Verfahrensschritt 11 wird zu n aufeinander folgenden Mess zeitpunkten mit der Strommessvorrichtung 3 j eweils ein Strommesssignal erfasst . Aus diesen Strommesssignalen wird von der Auswerteeinheit 5 ein erster Messsignalvektor gebildet . Aus diesem Messsignalvektor wird von der Auswerteeinheit 5 durch Matrixmultiplikation mit einer Fourier-Matrix ein erster Fouriervektor berechnet . In a first method step 11, a current measurement signal is recorded at n consecutive measurement times using the current measuring device 3. A first measurement signal vector is formed from these current measurement signals by the evaluation unit 5. A first Fourier vector is calculated from this measurement signal vector by the evaluation unit 5 by matrix multiplication with a Fourier matrix.
Nach dem ersten Verfahrensschritt 11 wird ein zweiter Verfahrensschritt 12 ausgeführt . After the first method step 11, a second method step 12 is carried out.
In dem zweiten Verfahrensschritt 12 wird mit derIn the second process step 12, the
Strommessvorrichtung 3 ein weiteres Strommesssignal erfasst . Nach dem zweiten Verfahrensschritt 12 wird ein dritter Verfahrensschritt 13 ausgeführt . Current measuring device 3 detects a further current measuring signal. After the second method step 12, a third method step 13 is carried out.
In dem dritten Verfahrensschritt 13 wird der bisherige Fouriervektor aktualisiert . Dabei wird von der Auswerteeinheit 5 ein aktualisierter Fouriervektor aus dem vorhergehenden (bisherigen) Fouriervektor gebildet , indem zu dem vorhergehenden Fouriervektor das Produkt derj enigen Spalte der Fourier-Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert , und der Di f ferenz des in dem vorhergehenden Verfahrensschritt 12 erfassten (und somit j üngsten) Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird . In the third method step 13, the previous Fourier vector is updated. In this case, the evaluation unit 5 forms an updated Fourier vector from the previous (previous) Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the current measurement signal recorded in the previous method step 12 (and thus most recent) and the oldest current measurement signal contained in the previous measurement signal vector.
Nach dem dritten Verfahrensschritt 13 wird wieder der zweite Verfahrensschritt 12 ausgeführt . After the third method step 13, the second method step 12 is carried out again.
In den Verfahrensschritt 11 und 13 kann ferner j eweils vorgesehen sein, dass von der Auswerteeinheit 5 die Komponenten des j eweiligen Fouriervektors Null gesetzt werden, die einen Schwellenwert unterschreiten . Der Schwellenwert wird von der Auswerteeinheit 5 beispielsweise als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors berechnet . In method steps 11 and 13, it can also be provided that the evaluation unit 5 sets the components of the respective Fourier vector to zero which fall below a threshold value. The threshold value is calculated by the evaluation unit 5, for example, as the product of a predetermined factor and an average value of the components of the Fourier vector.
Obwohl die Erfindung im Detail durch bevorzugte Aus führungsbeispiele näher illustriert und beschrieben wurde , so ist die Erfindung nicht durch die of fenbarten Beispiele eingeschränkt und andere Variationen können vom Fachmann hieraus abgeleitet werden, ohne den Schutzumfang der Erfindung zu verlassen . Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

Patentansprüche Patent claims
1 . Verfahren zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms , wobei 1 . A method for determining a frequency spectrum of an electric current, wherein
- mittels einer Strommessvorrichtung ( 3 ) zu zeitlich äquidistant aufeinander folgenden Mess zeitpunkten j eweils ein Strommesssignal erfasst wird, - a current measurement signal is recorded by means of a current measuring device ( 3 ) at equidistantly spaced measuring times,
- aus den j eweils n j üngsten Strommesssignalen ein Messsignalvektor gebildet wird, wobei n eine vorgegebene Anzahl von Strommesssignalen ist , und - a measurement signal vector is formed from the n most recent current measurement signals, where n is a predetermined number of current measurement signals, and
- aus dem Messsignalvektor mittels einer Fourier-Matrix ein Fouriervektor berechnet wird, der eine diskrete Fourier- Trans formation des Messsignalvektors ist , wobei - a Fourier vector is calculated from the measurement signal vector using a Fourier matrix, which is a discrete Fourier transformation of the measurement signal vector, where
- ein aktualisierter Fouriervektor aus dem vorhergehenden Fouriervektor gebildet wird, indem zu dem vorhergehenden Fouriervektor das Produkt derj enigen Spalte der Fourier- Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert , und der Di f ferenz des j eweils j üngsten Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird . - an updated Fourier vector is formed from the previous Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the respectively most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
2 . Verfahren nach Anspruch 1 , wobei die Strommessvorrichtung ( 3 ) wenigstens einen optischen Stromwandler aufweist . 2. Method according to claim 1, wherein the current measuring device (3) comprises at least one optical current transformer.
3 . Verfahren nach Anspruch 1 oder 2 , wobei der Fouriervektor ein Frequenzvektor ist . 3. Method according to claim 1 or 2, wherein the Fourier vector is a frequency vector.
4 . Verfahren nach einem der vorhergehenden Ansprüche , wobei fortlaufend eine zeitliche Veränderung des Fouriervektors berechnet wird, aus der zeitlichen Veränderung des Fouriervektors ein Stabilitätswert berechnet wird und der Stabilitätswert verwendet wird, um eine Schutzeinrichtung einer elektrischen Schaltanlage zu steuern . 4. Method according to one of the preceding claims, wherein a temporal change of the Fourier vector is continuously calculated, a stability value is calculated from the temporal change of the Fourier vector and the stability value is used to control a protective device of an electrical switchgear.
5. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Komponenten eines Fouriervektors Null gesetzt werden, die einen Schwellenwert unterschreiten. 5. Method according to one of the preceding claims, wherein the components of a Fourier vector which fall below a threshold value are set to zero.
6. Verfahren nach Anspruch 5, wobei der Schwellenwert als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors berechnet wird. 6. The method of claim 5, wherein the threshold value is calculated as the product of a predetermined factor and an average of the components of the Fourier vector.
7. Stromanalysevorrichtung (1) zum Ermitteln eines Frequenzspektrums eines elektrischen Stroms, umfassend 7. Current analysis device (1) for determining a frequency spectrum of an electric current, comprising
- eine Strommessvorrichtung (3) , die eingerichtet ist, zu zeitlich äquidistant aufeinander folgenden Messzeitpunkten jeweils ein Strommesssignal zu erfassen, und - a current measuring device (3) which is designed to detect a current measuring signal at equidistantly successive measuring times, and
- eine Auswerteeinheit (5) , die eingerichtet ist, - an evaluation unit (5) which is set up,
- aus den jeweils n jüngsten Strommesssignalen einen Messsignalvektor zu bilden, wobei n eine vorgegebene Anzahl von Strommesssignalen ist, und - to form a measurement signal vector from the n most recent current measurement signals, where n is a predetermined number of current measurement signals, and
- aus dem Messsignalvektor mittels einer Fourier-Matrix einen Fouriervektor zu bilden, der eine diskrete Fourier- Transformation des Messsignalvektors ist, wobei - to form a Fourier vector from the measurement signal vector using a Fourier matrix, which is a discrete Fourier transformation of the measurement signal vector, where
- ein aktualisierter Fouriervektor aus dem vorhergehenden Fouriervektor gebildet wird, indem zu dem vorhergehenden Fouriervektor das Produkt derjenigen Spalte der Fourier- Matrix, die zu dem ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignal korrespondiert, und der Differenz des jeweils jüngsten Strommesssignals und des ältesten in dem vorhergehenden Messsignalvektor enthaltenen Strommesssignals addiert wird. - an updated Fourier vector is formed from the previous Fourier vector by adding to the previous Fourier vector the product of that column of the Fourier matrix which corresponds to the oldest current measurement signal contained in the previous measurement signal vector and the difference between the most recent current measurement signal and the oldest current measurement signal contained in the previous measurement signal vector.
8. Stromanalysevorrichtung (1) nach Anspruch 7, wobei die Strommessvorrichtung (3) wenigstens einen optischen Stromwandler aufweist. 8. Current analysis device (1) according to claim 7, wherein the current measuring device (3) comprises at least one optical current transformer.
9. Stromanalysevorrichtung (1) nach Anspruch 7 oder 8, wobei der Fouriervektor ein Frequenzvektor ist. 9. Current analysis device (1) according to claim 7 or 8, wherein the Fourier vector is a frequency vector.
10. Stromanalysevorrichtung (1) nach einem der Ansprüche 7 bis 9, wobei die Auswerteeinheit (5) eingerichtet ist, fortlaufend eine zeitliche Veränderung des Fouriervektors zu berechnen, aus der zeitlichen Veränderung des Fouriervektors einen Stabilitätswert zu berechnen und den Stabilitätswert zu verwenden, um eine Schutzeinrichtung einer elektrischen Schaltanlage zu steuern. 10. Current analysis device (1) according to one of claims 7 to 9, wherein the evaluation unit (5) is arranged to continuously calculate a temporal change of the Fourier vector, to calculate a stability value from the temporal change of the Fourier vector and to use the stability value to control a protective device of an electrical switchgear.
11. Stromanalysevorrichtung (1) nach einem der Ansprüche 7 bis 10, wobei die Auswerteeinheit (5) eingerichtet ist, die Komponenten jedes Fouriervektors Null zu setzen, die einen Schwellenwert unterschreiten. 11. Current analysis device (1) according to one of claims 7 to 10, wherein the evaluation unit (5) is arranged to set to zero the components of each Fourier vector which fall below a threshold value.
12. Stromanalysevorrichtung (1) nach Anspruch 11, wobei die Auswerteeinheit (5) eingerichtet ist, den Schwellenwert als das Produkt eines vorgegebenen Faktors und eines Mittelwerts der Komponenten des Fouriervektors zu berechnen. 12. Current analysis device (1) according to claim 11, wherein the evaluation unit (5) is configured to calculate the threshold value as the product of a predetermined factor and a mean value of the components of the Fourier vector.
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