EP0267498B1 - Flux-compensated current transformer - Google Patents

Flux-compensated current transformer Download PDF

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Publication number
EP0267498B1
EP0267498B1 EP87115924A EP87115924A EP0267498B1 EP 0267498 B1 EP0267498 B1 EP 0267498B1 EP 87115924 A EP87115924 A EP 87115924A EP 87115924 A EP87115924 A EP 87115924A EP 0267498 B1 EP0267498 B1 EP 0267498B1
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Prior art keywords
winding
external
amplifier
current transformer
flux
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EP87115924A
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German (de)
French (fr)
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EP0267498A1 (en
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Gerhard Dipl.-Phys. Fuchs
Manfred Dipl.-Ing. Schwendtner
Gunther Dipl.-Phys. Vieweg
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Siemens AG
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Siemens AG
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/42—Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils
    • H01F27/422—Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils for instrument transformers
    • H01F27/427—Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils for instrument transformers for current transformers

Definitions

  • the invention relates to a flux-compensated current transformer with a primary winding, a secondary winding and a detector winding for the magnetic flux.
  • an external magnetic alternating field causes a measurement error that significantly affects the accuracy of the measurement.
  • External fields can be generated, for example, by adjacent live cables. When used in billing counters, it can also be expected that an attempt will be made to consciously influence the measurement result by external magnetic fields.
  • the object of the invention is therefore to provide a simplified solution for reducing the influence of external magnetic fields on flux-compensated current transformers.
  • an external field detector winding is arranged spatially parallel to the windings, that it is penetrated at least approximately by the same external field as the windings and that the signal present at the external field detector winding influences the measurement signal of the current transformer in such a way that the influence of an external field is compensated.
  • This external field compensation which is easy to carry out, eliminates influences of external magnetic fields on the measurement result.
  • the current transformer 1 has a primary winding 1a, a secondary winding 1c and a detector winding 1b in a known manner. Furthermore, an external field detector winding 2 is provided, which is arranged spatially parallel to the windings 1a to 1c, so that it is penetrated by the same external field as possible as these windings.
  • the detector winding 1b and the external field detector winding 2 are connected in series and connected to the inverting input of an amplifier 3.
  • the series connection of the secondary winding 1c and a load resistor 4 is connected to the output of the amplifier 3, a voltage drop proportional to the input current being generated at the load resistor 4.
  • this circuit has the function of a flow-compensated current transformer known, for example, from the technical measurement atm, 1978, issue 11, pages 407 to 411.
  • the flux passing through the current transformer is detected by the detector winding 1b and the output signal produced at this winding is fed to the secondary winding 1c with the amplifier 3.
  • the current through the secondary winding 1c is set in such a way that the flux caused by the primary winding 1a is just being compensated for, that is to say the converter becomes free of flux.
  • the current flowing through the secondary winding 1c then represents an image of the primary current I 1, the non-linearities of the current transformer core not falsifying the measurement result because of the flux compensation.
  • the external field detector winding 2 which detects such external fields and eliminates their effect on the measurement result by appropriate connection to the signal detected by the detector winding 1b.
  • a field, caused by the primary current to be measured in winding 1a, does not penetrate the winding 2 arranged outside the core and therefore does not induce any voltage dependent on the primary current I 1.
  • the voltage generated in the converter core by the external field and the voltage generated in the external field detector winding must be opposite in the same way.
  • N 1b , N2 the number of turns of the detector winding 1b or the external field detector winding 2 and A 1b , A2 the respective coil surfaces.
  • the external field detector winding 2 is connected to the detector winding 1b via an amplifier 5.
  • This arrangement has the advantage that the external field detector winding 2 must have fewer turns in accordance with the amplification of the amplifier 5. This is particularly advantageous if the external field detector winding 2 is designed as a printed circuit.
  • the same effect can also be achieved if the amplifier 3 is used as a summing amplifier.
  • the detector winding 1b is connected via a resistor 7 and the external field detector winding 2 is connected to the inverting input of the amplifier 3 via an amplifier 5 and a resistor 6.
  • the detector winding 1b is connected to the inverting input of the amplifier 3 and the output of the amplifier 5 to the non-inverting input of the amplifier 3.
  • the polarity of the external field detector winding 2 must of course be reversed.
  • the measurement error caused by the influence of external fields is eliminated in that the signals of the detector winding 1b are reduced by the signal component generated by the influence of the external field.
  • a largely independent external field measurement voltage is obtained at the resistor 4.
  • the one generated by external field effects Flow in the iron of the current transformer is not compensated, however, which can lead to temperature-dependent size and angle errors of the measured value due to hysteresis losses if the external field is extremely high.
  • the current transformer remains free of flux even when exposed to external fields, and the above-mentioned problem is thus avoided.
  • FIG. 5 shows an embodiment of the invention in which the signals of the detector winding 1b are fed to the inverting input of an amplifier 3.
  • the output signal of the amplifier 3 is fed via the secondary winding 1c and a resistor 4 to a first inverting input of a summing amplifier 11.
  • the output signals of the external field detector winding 2 are supplied to the second inverting input of the summing amplifier 11 via an inverting amplifier 5 and a resistor 10.
  • the signals of the detector winding 1b are fed to the secondary coil 1c via the amplifier 3.
  • This circuit measure completely compensates for the flux in the iron of the current transformer 1.
  • This flux is composed of a portion generated by the primary winding 1a and a portion generated by the influence of an external field. A voltage proportional to the primary current and the influence of external fields is thus present at the resistor 4 connected downstream of the secondary coil 1c.
  • a voltage generated by the external field in the external field detector winding 2 and amplified via the amplifier 5 is present at the resistor 10.
  • a current converter 1, 1 ', 1' ' is assigned to each phase.
  • This circuit measure regulates the flow in the iron of each current transformer 1, 1 ', 1' 'to zero.
  • the secondary coils 1c, 1c ', 1c' ' are each followed by a resistor 4,4', 4 '', to which a voltage proportional to the primary current of each phase and the external field effect is applied.
  • each current transformer 1, 1 ', 1' ' can be compensated for by the voltages of only one external field detector winding 2 via an amplifier 5 and a resistor 10, 10', 10 '' per phase of a first inverting one Input of a summing amplifier 11, 11 ', 11' 'are fed to each phase.
  • the resistor 4,4 ', 4' 'of each phase is connected to a second inverting input of the summing amplifier 11, 11', 11 '' of each phase.
  • the alignment of this arrangement is very simple both for single-wire networks and for three-phase networks.
  • the gain of the amplifier 5 is changed under the influence of an external field without primary current until no voltage is present at the output of the summing amplifier 11.
  • the external field detector winding 2 controls a winding 8 wound on the core of the current transformer 1 via an amplifier 5.
  • the turn ratios of the external field detector winding 2 and the winding 8 and the amplification factor of the amplifier 5 it is achieved that the external field detected with the external field detector winding 2 is compensated in the current transformer 1.
  • FIG. 8 shows an example of the arrangement of the external field detector winding 2.
  • an E-shaped core 9 is used, on the inner leg of which the primary winding 1a, the detector winding 1b and the secondary winding 1c are wound.
  • the external field detector winding 2 is applied to the two outer legs of the core 9.
  • the external field detector winding can also be etched into the circuit board in the region of the current transformer.
  • the circuit board is designed, for example, in the region of the current transformer 1 with a conductor with helical windings as an external field detector winding 2. Since only a few turns are possible here, amplification with an amplifier 5 according to the exemplary embodiments according to FIGS. 2 to 7 is necessary.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
  • Transformers For Measuring Instruments (AREA)

Description

Die Erfindung betrifft einen flußkompensierten Stromwandler mit einer Primärwicklung, einer Sekundärwicklung und einer Detektorwicklung für den magnetischen Fluß.The invention relates to a flux-compensated current transformer with a primary winding, a secondary winding and a detector winding for the magnetic flux.

Bei Stromwandlern wird durch ein äußeres magnetisches Wechselfeld (Fremdfeld) ein Meßfehler hervorgerufen, der die Genauigkeit der Messung erheblich beeinträchtigt. Fremdfelder können beispielsweise durch benachbarte stromführende Leitungen erzeugt werden. Bei Anwendung in Verrechnungszählern ist auch damit zu rechnen, daß der Versuch unternommen wird, das Meßergebnis durch äußere magnetische Felder bewußt zu beeinflussen.In current transformers, an external magnetic alternating field (external field) causes a measurement error that significantly affects the accuracy of the measurement. External fields can be generated, for example, by adjacent live cables. When used in billing counters, it can also be expected that an attempt will be made to consciously influence the measurement result by external magnetic fields.

Dieses Problem wurde bisher meist mit magnetischen Abschirmungen gelöst. Derartige Abschirmungen sind jedoch, wenn sie ausreichend wirksam sein sollen, relativ teuer und bedingen oftmals einen nicht unerheblichen zusätzlichen Montageaufwand.So far, this problem has mostly been solved with magnetic shields. Such shields, however, if they are to be sufficiently effective, are relatively expensive and often involve a not inconsiderable additional assembly effort.

Aufgabe der Erfindung ist es daher, eine vereinfachte Lösung zur Verminderung des Einflusses magnetischer Fremdfelder auf flußkompensierte Stromwandler anzugeben.The object of the invention is therefore to provide a simplified solution for reducing the influence of external magnetic fields on flux-compensated current transformers.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß räumlich parallel zu den Wicklungen eine Fremdfelddetektorwicklung angeordnet ist, daß sie zumindest näherungsweise von demselben Fremdfeld durchsetzt wird wie die Wicklungen und daß das an der Fremdfelddetektorwicklung anstehende Signal das Meßsignal des Stromwandlers so beeinflußt, daß der Einfluß eines Fremdfeldes kompensiert wird. Durch diese einfach durchzuführende Fremdfeldkompensation werden Einflüsse magnetischer Fremdfelder auf das Meßergebnis beseitigt.This object is achieved in that an external field detector winding is arranged spatially parallel to the windings, that it is penetrated at least approximately by the same external field as the windings and that the signal present at the external field detector winding influences the measurement signal of the current transformer in such a way that the influence of an external field is compensated. This external field compensation, which is easy to carry out, eliminates influences of external magnetic fields on the measurement result.

Vorteilhafte Ausgestaltungen der Erfindung sind in den Unteransprüchen angegeben.Advantageous embodiments of the invention are specified in the subclaims.

Ausführungsbeispiele der Erfindung werden nachfolgend anhand der Figuren 1 bis 9 näher erläutert.Exemplary embodiments of the invention are explained in more detail below with reference to FIGS. 1 to 9.

FIG 1 zeigt ein erstes Ausführungsbeispiel der Erfindung. Der Stromwandler 1 weist in bekannter Weise eine Primärwicklung 1a, eine Sekundärwicklung 1c und eine Detektorwicklung 1b auf. Ferner ist eine Fremdfelddetektorwicklung 2 vorgesehen, die räumlich parallel zu den Wicklungen 1a bis 1c angeordnet ist, so daß sie möglichst von demselben Fremdfeld durchsetzt wird wie diese Wicklungen. Die Detektorwicklung 1b und die Fremdfelddetektorwicklung 2 sind in Reihe geschaltet und an den invertierenden Eingang eines Verstärkers 3 angeschlossen. An den Ausgang des Verstärkers 3 ist die Reihenschaltung der Sekundärwicklung 1c und eines Lastwiderstands 4 angeschlossen, wobei am Lastwiderstand 4 ein dem Eingangsstrom proportionaler Spannungsabfall erzeugt wird.1 shows a first embodiment of the invention. The current transformer 1 has a primary winding 1a, a secondary winding 1c and a detector winding 1b in a known manner. Furthermore, an external field detector winding 2 is provided, which is arranged spatially parallel to the windings 1a to 1c, so that it is penetrated by the same external field as possible as these windings. The detector winding 1b and the external field detector winding 2 are connected in series and connected to the inverting input of an amplifier 3. The series connection of the secondary winding 1c and a load resistor 4 is connected to the output of the amplifier 3, a voltage drop proportional to the input current being generated at the load resistor 4.

Wenn man die Fremdfelddetektorwicklung 2 zunächst außer Betracht läßt, so weist diese Schaltung die beispielsweise aus der Literaturstelle "Technisches Messen atm", 1978, Heft 11, Seiten 407 bis 411 bekannte Funktion eines flußkompensierten Stromwandlers auf. Der den Stromwandler durchsetzende Fluß wird von der Detektorwicklung 1b erfaßt und das an dieser Wicklung entstehende Ausgangssignal mit dem Verstärker 3 verstärkt der Sekundärwicklung 1c zugeführt. Im Idealfall, d.h. wenn die Verstärkung des Verstärkers 3 gegen unendlich geht, wird der Strom durch die Sekundärwicklung 1c so eingestellt, daß der durch die Primärwicklung 1a verursachte Fluß gerade kompensiert wird, d.h. der Wandler flußfrei wird. Der durch die Sekundärwicklung 1c fließende Strom stellt dann ein Abbild des Primärstroms I₁ dar, wobei wegen der Flußkompensation Nichtlinearitäten des Stromwandlerkerns das Meßergebnis nicht verfälschen.If the external field detector winding 2 is initially disregarded, this circuit has the function of a flow-compensated current transformer known, for example, from the technical measurement atm, 1978, issue 11, pages 407 to 411. The flux passing through the current transformer is detected by the detector winding 1b and the output signal produced at this winding is fed to the secondary winding 1c with the amplifier 3. In the ideal case, ie when the amplification of the amplifier 3 goes towards infinity, the current through the secondary winding 1c is set in such a way that the flux caused by the primary winding 1a is just being compensated for, that is to say the converter becomes free of flux. The current flowing through the secondary winding 1c then represents an image of the primary current I 1, the non-linearities of the current transformer core not falsifying the measurement result because of the flux compensation.

Allerdings gehen Fremdfelder, d.h. äußere magnetische Wechselfelder, die den Stromwandler durchsetzen, ohne entsprechende Kompensationsmaßnahmen voll mit in das Meßergebnis ein.However, foreign fields go, i.e. external alternating magnetic fields that penetrate the current transformer, without corresponding compensation measures, fully into the measurement result.

Um dies zu verhindern, ist die Fremdfelddetektorwicklung 2 vorgesehen, die solche Fremdfelder erfaßt und durch entsprechende Aufschaltung auf das von der Detektorwicklung 1b erfaßte Signal deren Wirkung auf das Meßergebnis eliminiert. Ein Feld, hervorgerufen durch den zu messenden Primärstrom in Wicklung 1a, durchsetzt nicht die außerhalb des Kernes angeordnete Wicklung 2 und induziert deshalb auch keine vom Primärstrom I₁ abhängige Spannung.In order to prevent this, the external field detector winding 2 is provided, which detects such external fields and eliminates their effect on the measurement result by appropriate connection to the signal detected by the detector winding 1b. A field, caused by the primary current to be measured in winding 1a, does not penetrate the winding 2 arranged outside the core and therefore does not induce any voltage dependent on the primary current I 1.

Die im Wandlerkern durch das Fremdfeld erzeugte Spannung und die in der Fremdfelddetektorwicklung erzeugte Spannung müssen entgegengesetzt gleich sein. Die an einer Wicklung erzeugte Spannung U ist proportional der Windungszahl N der Wicklung und deren Fläche A. Für die Spannung U gilt:

U = - dB dt . N . A

Figure imgb0001


Im Falle der Kompensation gilt:

U 1b = U₂
Figure imgb0002

wobei U1b die in der Detektorwicklung 1b induzierte Spannung und U₂ die in der Fremdfelddetektorwicklung 2 erzeugte Spannung ist.The voltage generated in the converter core by the external field and the voltage generated in the external field detector winding must be opposite in the same way. The voltage U generated on a winding is proportional to the number of turns N of the winding and its area A. The following applies to the voltage U:

U = - dB German . N. A
Figure imgb0001

In the case of compensation:

U 1b = U₂
Figure imgb0002

where U 1b is the voltage induced in the detector winding 1b and U₂ is the voltage generated in the external field detector winding 2.

Da die Induktion beim Übergang von einem Medium (Eisenkern des Stromwandlers) zum anderen (Luft zwischen Fremdfelddetektorwicklung 2 und Wandlerkern) konstant ist, folgt:

N 1b . A 1b = N₂ . A₂

Figure imgb0003


Since the induction is constant during the transition from one medium (iron core of the current transformer) to another (air between the external field detector winding 2 and the transformer core), it follows:

N 1b . A 1b = N₂. A₂
Figure imgb0003

Dabei sind N1b,
   N₂ die Windungszahlen der Detektorwicklung 1b bzw. der Fremdfelddetektorwicklung 2 und A1b,
   A₂ die jeweiligen Spulenflächen.Where N 1b ,
N₂ the number of turns of the detector winding 1b or the external field detector winding 2 and A 1b ,
A₂ the respective coil surfaces.

FIG 2 zeigt ein weiteres Ausführungsbeispiel der Erfindung, bei dem die Fremdfelddetektorwicklung 2 über einen Verstärker 5 mit der Detektorwicklung 1b verbunden ist. Diese Anordnung hat den Vorteil, daß die Fremdfelddetektorwicklung 2 entsprechend der Verstärkung des Verstärkers 5 weniger Windungen haben muß. Dies ist insbesondere dann von Vorteil, wenn die Fremdfelddetektorwicklung 2 als gedruckte Schaltung ausgeführt ist.2 shows a further exemplary embodiment of the invention, in which the external field detector winding 2 is connected to the detector winding 1b via an amplifier 5. This arrangement has the advantage that the external field detector winding 2 must have fewer turns in accordance with the amplification of the amplifier 5. This is particularly advantageous if the external field detector winding 2 is designed as a printed circuit.

Anstatt die von der Detektorwicklung 1b und von der Fremdfelddetektorwicklung 2 nach Verstärkung durch den Verstärker 5 gelieferten Spannungen durch Reihenschaltung zu addieren, kann man denselben Effekt auch erreichen, wenn man den Verstärker 3 als Summierverstärker verwendet. Dies kann z.B. gemäß einem Ausführungsbeispiel nach FIG 3 dadurch erfolgen, daß man die Detektorwicklung 1b über einen Widerstand 7 und die Fremdfelddetektorwicklung 2 über einen Verstärker 5 und einen Widerstand 6 mit dem invertierenden Eingang des Verstärkers 3 verbindet.Instead of adding the voltages supplied by the detector winding 1b and by the external field detector winding 2 after amplification by the amplifier 5, the same effect can also be achieved if the amplifier 3 is used as a summing amplifier. This can e.g. According to an exemplary embodiment according to FIG. 3, the detector winding 1b is connected via a resistor 7 and the external field detector winding 2 is connected to the inverting input of the amplifier 3 via an amplifier 5 and a resistor 6.

In einer alternativen Ausführungsform gemäß FIG 4 wird die Detektorwicklung 1b mit dem invertierenden Eingang des Verstärkers 3 und der Ausgang des Verstärkers 5 mit dem nichtinvertierenden Eingang des Verstärkers 3 verbunden. Hierbei muß die Polung der Fremdfelddetektorwicklung 2 selbstverständlich umgekehrt werden.In an alternative embodiment according to FIG. 4, the detector winding 1b is connected to the inverting input of the amplifier 3 and the output of the amplifier 5 to the non-inverting input of the amplifier 3. Here, the polarity of the external field detector winding 2 must of course be reversed.

Bei den bisherigen Ausführungen der Erfindung wird der durch Fremdfeldeinwirkung verursachte Meßfehler dadurch aufgehoben, daß die Signale der Detektorwicklung 1b um den durch die Fremdfeldeinwirkung erzeugten Signalanteil vermindert werden. Am Widerstand 4 wird dadurch eine weitgehend fremdfeldunabhängige Meßspannung erhalten. Der durch Fremdfeldeinwirkung erzeugte Fluß im Eisen des Stromwandlers wird jedoch nicht kompensiert, was bei extrem hoher Fremdfeldeinwirkung durch Hysteresisverluste zu temperaturabhängigen Größen- und Winkelfehlern des Meßwertes führen kann.In the previous embodiments of the invention, the measurement error caused by the influence of external fields is eliminated in that the signals of the detector winding 1b are reduced by the signal component generated by the influence of the external field. A largely independent external field measurement voltage is obtained at the resistor 4. The one generated by external field effects Flow in the iron of the current transformer is not compensated, however, which can lead to temperature-dependent size and angle errors of the measured value due to hysteresis losses if the external field is extremely high.

In weiteren vorteilhaften Ausführungsformen gemäß den FIG 5 und 7 bleibt auch bei Fremdfeldeinwirkung der Stromwandler flußfrei und damit wird das vorstehend genannte Problem vermieden.In further advantageous embodiments according to FIGS. 5 and 7, the current transformer remains free of flux even when exposed to external fields, and the above-mentioned problem is thus avoided.

FIG 5 zeigt ein Ausführungsbeispiel der Erfindung, bei dem die Signale der Detektorwicklung 1b dem invertierenden Eingang eines Verstärkers 3 zugeführt werden. Das Ausgangssignal des Verstärkers 3 wird über die Sekundärwicklung 1c und einen Widerstand 4 einem ersten invertierenden Eingang eines Summierverstärkers 11 zugeführt. Die Ausgangssignale der Fremdfelddetektorwicklung 2 werden über einen invertierenden Verstärker 5 und einen Widerstand 10 dem zweiten invertierenden Eingang des Summierverstärkers 11 zugeführt.5 shows an embodiment of the invention in which the signals of the detector winding 1b are fed to the inverting input of an amplifier 3. The output signal of the amplifier 3 is fed via the secondary winding 1c and a resistor 4 to a first inverting input of a summing amplifier 11. The output signals of the external field detector winding 2 are supplied to the second inverting input of the summing amplifier 11 via an inverting amplifier 5 and a resistor 10.

Die Signale der Detektorwicklung 1b werden über den Verstärker 3 der Sekundärspule 1c zugeführt. Durch diese Schaltungsmaßnahme wird der Fluß im Eisen des Stromwandlers 1 vollständig kompensiert. Dieser Fluß setzt sich aus einem durch die Primärwicklung 1a erzeugten Anteil und aus einem durch Fremdfeldeinwirkung erzeugten Anteil zusammen. Damit liegt an dem der Sekundärspule 1c nachgeschalteten Widerstand 4 eine Spannung proportional zum Primärstrom und zur Fremdfeldeinwirkung an.The signals of the detector winding 1b are fed to the secondary coil 1c via the amplifier 3. This circuit measure completely compensates for the flux in the iron of the current transformer 1. This flux is composed of a portion generated by the primary winding 1a and a portion generated by the influence of an external field. A voltage proportional to the primary current and the influence of external fields is thus present at the resistor 4 connected downstream of the secondary coil 1c.

Am Widerstand 10 liegt eine durch das Fremdfeld in der Fremdfelddetektorwicklung 2 erzeugte und über den Verstärker 5 verstärkte Spannung an.A voltage generated by the external field in the external field detector winding 2 and amplified via the amplifier 5 is present at the resistor 10.

Am Summierpunkt des Summierverstärkers 11 werden die von der Sekundärwicklung 1c und vom Verstärker 5 abgegebenen Spannungen addiert und dem Eingang des Summierverstärkers 11 zugeführt.At the summing point of summing amplifier 11, the voltages emitted by secondary winding 1c and by amplifier 5 are added and fed to the input of summing amplifier 11.

Am Ausgang des Summierverstärkers 11 wird ein zum Primärstrom proportionales und um die Fremdfeldeinwirkung vermindertes Signal erhalten.At the output of the summing amplifier 11, a signal which is proportional to the primary current and reduced by the influence of the external field is obtained.

In einem Drehstromnetz nach FIG 6 ist jeder Phase ein Stromwandler 1,1',1'' zugeordnet. Dabei werden die Signale der Detektorwicklungen 1b,1b',1b'' über die Verstärker 3,3',3'' den Sekundärspulen 1c,1c',1c'' zugeführt. Durch diese Schaltungsmaßnahme wird der Fluß im Eisen jedes Stromwandlers 1,1',1'' zu Null geregelt. Den Sekundärspulen 1c,1c',1c'' ist jeweils ein Widerstand 4,4',4'' nachgeschaltet, an denen eine Spannung proportional zum Primärstrom jeder Phase und zur Fremdfeldeinwirkung anliegt.In a three-phase network according to FIG. 6, a current converter 1, 1 ', 1' 'is assigned to each phase. The signals from the detector windings 1b, 1b ', 1b' 'are fed to the secondary coils 1c, 1c', 1c '' via the amplifiers 3,3 ', 3' '. This circuit measure regulates the flow in the iron of each current transformer 1, 1 ', 1' 'to zero. The secondary coils 1c, 1c ', 1c' 'are each followed by a resistor 4,4', 4 '', to which a voltage proportional to the primary current of each phase and the external field effect is applied.

Im Drehstromnetz können die durch Fremdfeldeinwirkung in jedem Stromwandler 1,1',1'' erzeugten Spannungen dadurch kompensiert werden, daß die Spannungen nur einer Fremdfelddetektorwicklung 2 über einen Verstärker 5 und einen Widerstand 10,10',10'' je Phase einem ersten invertierenden Eingang eines Summierverstärkers 11,11',11'' jeder Phase zugeführt werden. Der Widerstand 4,4',4'' jeder Phase ist mit einem zweiten invertierenden Eingang des Summierverstärkers 11,11',11'' jeder Phase verbunden. Im Summierpunkt der Summierverstärker 11,11',11'' wird die Ausgangsspannung der Sekundärwicklung 1c,1c',1c'' jeder Phase um die Spannung am Ausgang des Verstärkers 5 vermindert, so daß am Ausgang jedes Summierverstärkers 11,11',11'' ein dem Primärstrom jeder Phase proportionales Ausgangssignal erhalten wird.In the three-phase network, the voltages generated by external field effects in each current transformer 1, 1 ', 1' 'can be compensated for by the voltages of only one external field detector winding 2 via an amplifier 5 and a resistor 10, 10', 10 '' per phase of a first inverting one Input of a summing amplifier 11, 11 ', 11' 'are fed to each phase. The resistor 4,4 ', 4' 'of each phase is connected to a second inverting input of the summing amplifier 11, 11', 11 '' of each phase. At the summing point of the summing amplifiers 11, 11 ', 11' ', the output voltage of the secondary winding 1c, 1c', 1c '' of each phase is reduced by the voltage at the output of the amplifier 5, so that at the output of each summing amplifier 11, 11 ', 11' an output signal proportional to the primary current of each phase is obtained.

Der Abgleich dieser Anordnung ist sowohl für Einleiternetze als auch für Drehstromnetze sehr einfach. Die Verstärkung des Verstärkers 5 wird bei Einwirkung eines Fremdfeldes ohne Primärstrom solange verändert, bis am Ausgang der Summierverstärker 11 keine Spannung anliegt.The alignment of this arrangement is very simple both for single-wire networks and for three-phase networks. The gain of the amplifier 5 is changed under the influence of an external field without primary current until no voltage is present at the output of the summing amplifier 11.

Gemäß einem weiteren Ausführungsbeispiel nach FIG 7 steuert die Fremdfelddetektorwicklung 2 über einen Verstärker 5 eine auf den Kern des Stromwandlers 1 gewickelte Wicklung 8 an. Durch entsprechende Dimensionierung der Windungsverhältnisse der Fremdfelddetektorwicklung 2 und der Wicklung 8 sowie des Verstärkungsfaktors des Verstärkers 5 wird erreicht, daß das mit der Fremdfelddetektorwicklung 2 erfaßte Fremdfeld im Stromwandler 1 kompensiert wird.According to a further exemplary embodiment according to FIG. 7, the external field detector winding 2 controls a winding 8 wound on the core of the current transformer 1 via an amplifier 5. By appropriate dimensioning of the turn ratios of the external field detector winding 2 and the winding 8 and the amplification factor of the amplifier 5 it is achieved that the external field detected with the external field detector winding 2 is compensated in the current transformer 1.

FIG 8 zeigt ein Beispiel für die Anordnung der Fremdfelddetektorwicklung 2. Im Ausführungsbeispiel wird ein E-förmiger Kern 9 verwendet, auf dessen Innenschenkel die Primärwicklung 1a, die Detektorwicklung 1b und die Sekundärwicklung 1c aufgewickelt sind. Auf die beiden Außenschenkel des Kerns 9 ist die Fremdfelddetektorwicklung 2 aufgebracht.8 shows an example of the arrangement of the external field detector winding 2. In the exemplary embodiment, an E-shaped core 9 is used, on the inner leg of which the primary winding 1a, the detector winding 1b and the secondary winding 1c are wound. The external field detector winding 2 is applied to the two outer legs of the core 9.

Wenn der Stromwandler auf einer Leiterplatte angeordnet wird, so kann die Fremdfelddetektorwicklung auch in die Leiterplatte im Bereich des Stromwandlers eingeätzt werden. Bei einem in FIG 9 dargestellten Ausführungsbeispiel ist die Leiterplatte beispielsweise im Bereich des Stromwandlers 1 mit einem Leiter mit schneckenförmigen Windungen als Fremdfelddetektorwicklung 2 ausgeführt. Da hierbei nur wenige Windungen möglich sind, ist eine Verstärkung mit einem Verstärker 5 gemäß den Ausführungsbeispielen nach den FIG 2 bis 7 notwendig.If the current transformer is arranged on a circuit board, the external field detector winding can also be etched into the circuit board in the region of the current transformer. In an exemplary embodiment shown in FIG. 9, the circuit board is designed, for example, in the region of the current transformer 1 with a conductor with helical windings as an external field detector winding 2. Since only a few turns are possible here, amplification with an amplifier 5 according to the exemplary embodiments according to FIGS. 2 to 7 is necessary.

Claims (12)

  1. Flux-compensated current transformer having a primary winding (1a), a secondary winding (1c) and a detector winding (1b) for the magnetic flux, characterized in that an external-field detector winding (2) is arranged spatially parallel to the windings (1a - 1c), in that it is exposed at least approximately to the same external field as the windings (1a - 1c) and in that the signal applied to the external-field detector winding (2) influences the measuring signal of the current transformer (1) in such a way that the influence of an external field is compensated.
  2. Flux-compensated current transformer according to claim 1, whereby an amplifier (3) controlled by the detector winding (1b) is connected in series with the secondary winding (1c) on the output side, characterized in that the external-field detector winding (2) is connected in series with the detector winding (1b).
  3. Flux-compensated current transformer according to claim 2, characterized in that an amplifier (5) is controlled by the external-field detector winding (2), which amplifier is connected in series with the detector winding (1b) on the output side.
  4. Flux-compensated current transformer according to claim 2, characterized in that the signals emitted by the detector winding (1b) and by the external-field detector winding (2) are supplied to the amplifier (3) connected as summing amplifier.
  5. Flux-compensated current transformer according to claim 4 for three-phase current, characterized in that per phase a summing amplifier (3) is provided, to which are supplied the signals of the detector winding (1b) of each phase and of an external-field detector winding (2) common to all phases.
  6. Flux-compensated current transformer according to claim 1, characterized in that the signals emitted by the external-field detector winding (2) and the secondary winding (1c) are supplied to the input of an amplifier (11) such that at the output of the amplifier (11) an external-field-compensated signal which is proportional to the primary current is obtained.
  7. Flux-compensated current transformer according to claim 1, whereby an amplifier (3) controlled by the detector winding 1b is connected in series with the secondary winding (1c) on the output side, characterized in that the secondary winding (1c) is connected to a first input of a summing amplifier (11), in that the signal of the external-field detector winding (2) is supplied by way of a further amplifier (5) to a second input of the summing amplifier (11) such that at the output of the summing amplifier (11) an external-field-compensated signal which is proportional to the primary current is obtained.
  8. Flux-compensated current transformer according to claim 7, characterized in that for three-phase current per phase a summing amplifier (11) is provided, to the first input of which in each case the secondary winding (1c) of this phase is connected and in that an external-field detector winding (2) common to all phases with series-connected amplifier (5) is provided, whereby the amplifier (5) is connected to the second inputs of the summing amplifiers (11) of all phases on the output side.
  9. Flux-compensated current transformer according to claim 1, characterized in that the signal emitted by the external-field detector winding (2) controls by way of an amplifier (5) a compensation winding (8) of the current transformer (1) in such a way that the external field in the current transformer (1) is magnetically compensated.
  10. Flux-compensated current transformer according to one of claims 1 to 9, characterized in that the external-field detector winding (2) encloses the entire current transformer (1) spatially.
  11. Flux-compensated current transformer according to claim 10, whereby the current transformer (1) is mounted on a printed-circuit board, characterized in that the external-field detector winding (2) is constructed as a printed circuit on the printed-circuit board.
  12. Flux-compensated current transformer according to one of claims 1 to 9 with a multi-limbed magnetic core (8) [sic], characterized in that the external-field detector winding (2) is fitted to at least one limb of the magnetic core (9).
EP87115924A 1986-11-11 1987-10-29 Flux-compensated current transformer Expired - Lifetime EP0267498B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT87115924T ATE85153T1 (en) 1986-11-11 1987-10-29 FLUX COMPENSATED CURRENT TRANSFORMER.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE3638388 1986-11-11
DE3638388 1986-11-11
DE3718756 1987-06-04
DE3718756 1987-06-04

Publications (2)

Publication Number Publication Date
EP0267498A1 EP0267498A1 (en) 1988-05-18
EP0267498B1 true EP0267498B1 (en) 1993-01-27

Family

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Application Number Title Priority Date Filing Date
EP87115924A Expired - Lifetime EP0267498B1 (en) 1986-11-11 1987-10-29 Flux-compensated current transformer

Country Status (2)

Country Link
EP (1) EP0267498B1 (en)
DE (1) DE3783869D1 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8910570D0 (en) * 1989-05-08 1989-06-21 Wellcome Found Acellular vaccine
DE3918100A1 (en) * 1989-06-02 1990-12-06 Stepper & Co CURRENT TRANSFORMER ARRANGEMENT WITH INCREASED ACCURACY
GB9918539D0 (en) * 1999-08-06 1999-10-06 Sentec Ltd Planar current transformer

Also Published As

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EP0267498A1 (en) 1988-05-18
DE3783869D1 (en) 1993-03-11

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