Device for the isolated measurement of current and a method for the isolated determination of current

Abstract

A device is provided for the isolated measurement of current, comprising a magnetic core that has an opening through which a primary conductor extends, and at least one measurement region that has at least two openings which divide each measurement region into at least three adjacent flux paths. The device additionally comprises a compensator winding that is wound about parts of the core outside of the at least one measurement region, at least two flux paths of the same measurement region, around which at least one exciter winding is wound, as well as at least one measurement winding that is wound about parts of the measurement region. A method is also provided for determining current in an isolated manner using the provided device.

Claims

1. A device (1) for measuring current, comprising: a magnetic core (2) with an opening (3) through which a primary conductor (L.sub.1) is routed, and at least one measuring region (4) with at least two openings (5), which subdivide the measuring region (4) into at least three adjacent flux paths (R.sub.1a, R.sub.1b, R.sub.2, R.sub.2a, R.sub.2b); a compensating winding (L.sub.C), which is wound around parts of the core (2) outside the measuring region (4); at least two flux paths (R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b) of the same measuring region (4), wound by at least one exciter winding (L.sub.S), wherein the at least one exciter winding is one common exciter winding or two individual exciter windings; and at least one measuring winding (L.sub.M), which is wound around parts of the measuring region (4).

2. The device of claim 1, wherein: the at least one measuring region is one measuring region (4) with two openings (5) subdividing the measuring region (4) into the at least three adjacent flux paths (R.sub.1a, R.sub.1b, R.sub.2), the at least one exciter winding (L.sub.S) is one common exciter winding wound with different orientation around two flux paths (R.sub.1a, R.sub.1b) and the at least one measuring winding (L.sub.M) is one measuring winding wound around the other flux path (R.sub.2).

3. The device of claim 1, wherein: the at least one measuring region is two measuring regions (4) with respectively two openings (5) subdividing the measuring regions (4) into three adjacent flux paths (R.sub.1a, R.sub.1b, R.sub.2), the at least one exciter winding is two exciter windings (L.sub.S) wound with different orientation around respectively two flux paths (R.sub.1a, R.sub.1b) of the measuring regions (4), the at least one measuring winding is one measuring winding (L.sub.M) wound around the other flux path (R.sub.2) of one of the measuring regions (4) or one measuring winding (L.sub.M) wound around the other flux path (R.sub.2) of the other measuring region (4).

4. The device of claim 1, wherein: the at least one measuring region is one measuring region (4) with three openings (5) subdividing the measuring region (4) into a first pair of adjacent flux paths (R.sub.1a, R.sub.1b) and a second pair of adjacent flux paths (R.sub.2a, R.sub.2b) and the at least one exciter winding is two exciter windings (L.sub.S) wound with different orientation around respectively one pair of adjacent flux paths (R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b).

5. The device of claim 4, wherein: one measuring winding (L.sub.M) of the at least one measuring winding is wound around the first pair of adjacent flux paths (R.sub.1a, R.sub.1b) or one measuring winding (L.sub.M) of the at least one measuring winding is wound around the second pair of adjacent flux paths (R.sub.2a, R.sub.2b).

6. The device of claim 4, wherein: the middle of the openings (5) has a larger extent than the flux paths (R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b) and thereby defines a first common extension (R.sub.1) of the first pair of adjacent flux paths (R.sub.1a, R.sub.1b) and a second common extension (R.sub.4) of the second pair of adjacent flux paths (R.sub.2a, R.sub.2b), one measuring winding (L.sub.M) of the at least one measuring winding is wound around the first common extension (R.sub.1) or one measuring winding (L.sub.M) of the at least one measuring winding is wound around the second common extension (R.sub.4).

7. The device of claim 1, wherein the at least one exciter winding (L.sub.S) is connected to a modulator unit (M).

8. The device of claim 7, wherein a demodulator (D) is connected to the at least one measuring winding (L.sub.M) and can be synchronized with the modulator unit (M).

9. The device of claim 8, wherein an integrator (I) is connected to the demodulator (D).

10. The device of claim 9, wherein the integrator (I) is connected to the compensating winding (L.sub.C).

11. The device of claim 1, wherein an output (A) is connected directly or indirectly via a first operational amplifier (G) to the compensating winding (L.sub.C).

12. The device of claim 11, wherein the integrator (I) is connected to a second operational amplifier (K), which is connected to the compensating winding (L.sub.C) and the first operational amplifier (G).

13. The device of claim 11, wherein the first operational amplifier (G) and the second operational amplifier (K) are implemented together as digital and analog components.

14. The device of claim 1, wherein the measuring winding (L.sub.M) comprises an analog-to-digital converter (6).

15. A method for determining current using the device of claim 1, the method comprising the following process steps: passing a primary current (I.sub.1) through the primary conductor (L.sub.1) and thereby inducing a magnetic flux in the core (2); passing a compensating current (I.sub.C) through the compensating winding (L.sub.C) and thereby inducing a magnetic flux in the core, in order to counteract the magnetic flux induced by the primary conductor (L.sub.1); periodically energizing the at least one exciter winding (L.sub.S) and thereby, to the extent energized, inducing a magnetic flux in at least two flux paths (R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b) wound by the at least one exciter winding (L.sub.S) and thereby modulating the said flux paths (R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b) magnetically; sensing, by means of the at least one measuring winding (L.sub.M), the change of the magnetic flux between various energization conditions of the exciter winding (L.sub.S), in order to tap a demodulation signal for regulation of the magnetic flux induced by the compensating winding (L.sub.C); setting the compensating current (I.sub.C) to a value such that the change of magnetic flux sensed by the at least one measuring winding (L.sub.M) is minimized; measuring the compensating current (I.sub.C); and calculating the primary current (I.sub.1) from the compensating current (I.sub.C).

16. The method of claim 15, wherein two exciter windings (L.sub.S) of the at least one exciter windings are operated in opposition.

17. The method of claim 15, wherein the ends of the at least one measuring winding (L.sub.M) are connected alternately to the input of an integrator (I).

18. The method of claim 17, wherein a demodulator (D) is synchronized with a modulator unit (M).

19. The method of claim 17, wherein the output signal of a demodulator (D) is converted by means of the integrator (I) into the compensating current (I.sub.C).

20. The method of claim 17, wherein the output signal of a demodulator is converted into the compensating current (I.sub.C) by means of the integrator (I) and the second operational amplifier (K), which receives a feedback signal from the first operational amplifier (G).

21. The method of claim 15, further comprising measurement of inductance of the at least one exciter winding (L.sub.S) and generation of a signal that indicates whether or not the respective measured inductance lies within a specified range.

Description

(1) Exemplary embodiments of the invention are explained in more detail hereinafter on the basis of the drawing, wherein:

(2) FIG. 1 shows a schematic perspective view of an inventive device for measuring current with two openings disposed in a measuring region, two exciter windings wound respectively around one flux path and one measuring winding wound around a third flux path,

(3) FIG. 2 shows a schematic perspective view of a first embodiment of an inventive device for measuring current with one exciter winding wound with different orientation around two flux paths and one measuring winding wound around a third flux path,

(4) FIG. 3 shows a schematic perspective view of a second embodiment of an inventive device for measuring current with two successive measuring regions,

(5) FIG. 4 shows a schematic perspective view of a third embodiment of an inventive device for measuring current with three openings disposed in a measuring region and two measuring windings wound around common extensions of flux paths,

(6) FIG. 5 shows a schematic circuit diagram of a further embodiment of an inventive device for measuring current,

(7) FIG. 6 shows a schematic circuit diagram of an embodiment similar to the embodiment according to FIG. 5, without second operational amplifier,

(8) FIG. 7 shows a schematic circuit diagram of an embodiment similar to the embodiment according to FIG. 6, for direct output of the compensating current, and

(9) FIG. 8 shows a schematic circuit diagram of a further embodiment of an inventive device for measuring current with an analog-to-digital converter and alternatively configured operational amplifiers.

(10) The inventive device 1, illustrated in FIG. 1, for measuring current has a closed magnetic core 2 of generally rectangular shape with an opening 3, through which a primary conductor L.sub.1 is routed. Two openings 5 are disposed in a measuring region 4, subdividing measuring region 4 into three adjacent flux paths R.sub.1a, R.sub.1b, R.sub.2. To illustrate its extent, measuring region 4 is marked off from the rest of the core by a dashed line in FIG. 1. A compensating winding L.sub.C is wound outside measuring region 4 around a leg 6 of core 2. Two exciter windings Ls are wound around two flux paths R.sub.1a, R.sub.1b and one measuring winding L.sub.M is wound around the other flux path R.sub.2.

(11) The first embodiment, illustrated in FIG. 2, of an inventive device 1 for measuring current has a closed magnetic core 2 of generally annular shape, through which a primary conductor L.sub.1 is routed. Two openings 5 are disposed in a measuring region 4, subdividing measuring region 4 into three adjacent flux paths R.sub.1a, R.sub.1b, R.sub.2. A compensating winding L.sub.C is wound outside measuring region 4 around core 2. A single exciter winding L.sub.S is wound with different orientation around two flux paths R.sub.1a, R.sub.1b and one measuring winding is wound around the other flux path R.sub.2.

(12) The second embodiment, illustrated in FIG. 3, of an inventive device 1 for measuring current has a closed magnetic core 2 of generally annular shape, through which a primary conductor L.sub.1 is routed. Two openings 5 respectively are disposed in two identical measuring regions 4, subdividing measuring regions 4 into respectively three adjacent flux paths R.sub.1a, R.sub.1b, R.sub.2. Two exciter windings L.sub.S are wound with different orientation around respectively two flux paths R.sub.1a, R.sub.1b for the purpose of opposite energization and two measuring windings LM are wound around the respective other flux path R.sub.2 of measuring regions 4.

(13) The third embodiment, illustrated in FIG. 4, of an inventive device 1 for measuring current has a closed magnetic core 2 of generally annular shape, through which a primary conductor L.sub.1 is routed. Three openings 5 are disposed in a measuring region 4, subdividing measuring region 4 into a first pair of adjacent flux paths R.sub.1a, R.sub.1b and a second pair of adjacent flux paths R.sub.2a, R.sub.2b. Respectively one exciter winding L.sub.S is wound with different orientation around the first pair of adjacent flux paths R.sub.1a, R.sub.1b and the second pair of adjacent flux paths R.sub.2a, R.sub.2b for the purpose of opposite energization. The middle of the three openings 5 has a greater extent than flux paths R.sub.1a, R.sub.1b, R.sub.2a, R.sub.2b and thereby defines a first common extension R.sub.1 of the first pair of flux paths R.sub.1a, R.sub.1b and a second common extension R.sub.4 for the second pair of adjacent flux paths R.sub.2aa, R.sub.2b. Respectively one measuring winding L.sub.M is wound around the first common extension R.sub.1 and the second common extension R.sub.4.

(14) The circuit diagram, illustrated in FIG. 5, of a further embodiment of a device 1 for measuring current has a primary winding in the form of a primary conductor L.sub.1, which can carry a primary current I.sub.1 and has one turn N.sub.1. To the extent that it carries a primary current I.sub.1, primary conductor L.sub.1 induces a magnetic primary flux .sub.1 proportional to the said current in a closed magnetic core 2. A compensating winding L.sub.C with a plurality of turns N.sub.C, which have a total resistance R.sub.C, is wound around core 2. A compensating current L.sub.C, which induces in the core a magnetic compensating flux .sub.C that counteracts primary flux .sub.1, flows through compensating winding L.sub.C. The difference between primary flux .sub.1 and compensating flux .sub.C is the differential flux , and the difference between primary current I.sub.1 and compensating current I.sub.C is the differential current I.

(15) Core 2 is subdivided in a measuring region 4 into three flux paths R.sub.1, R.sub.2, of which one of the flux paths R.sub.1 comprises two flux paths R.sub.1a, R.sub.1b, not illustrated. An exciter windingas illustrated in FIG. 2, for exampleis wound with different orientation around the two flux paths R.sub.1a, R.sub.1band connected to a modulator unit M. Modulator unit M is designed to energize the exciter winding periodically, in which case the latter in the energized condition induces a magnetic flux in flux paths R.sub.1a, R.sub.1b, as a result of which flux paths R.sub.1a, R.sub.1b become magnetically saturated. The exciter winding is a magnetic switch S, which can open and close flux paths R.sub.1a, R.sub.1b for magnetic flux. If the exciter winding is energized, so that it induces a magnetic flux in flux paths R.sub.1a, R.sub.1b, leading to magnetic saturation thereof, magnetic switch S is said to be open. If the exciter winding is not energized, it does not induce any magnetic flux in flux paths R.sub.1a, R.sub.1b, and so these are not magnetically saturated and magnetic switch S is said to be closed.

(16) A measuring winding L.sub.M is wound with several turns N.sub.M around flux path R.sub.2. A measuring signal in the form of an alternating voltage or alternating current is induced in measuring winding L.sub.M by periodic opening and closing of the magnetic switch (synonymous with periodic energization of the exciter winding). If no compensating current I.sub.C is yet passing through compensating winding L.sub.C, the differential flux corresponds to the primary flux .sub.1. The measuring signal is then proportional to primary current I.sub.1. If a compensating current I.sub.C is passed through compensating winding L.sub.C, the measuring signal is proportional to differential current I.

(17) FIG. 5 shows a very simple embodiment of a demodulator D in the form of an analog reversing switch. The measuring signal of measuring winding L.sub.M is supplied to two inputs D.sub.1, D.sub.2 of demodulator D, which also has two outputs D.sub.3, D.sub.4. The demodulator converts the measuring signal into a demodulated signal. The demodulator can be switched alternately between two switched positions. In a first switched position, input D.sub.1 is connected to output D.sub.4 and input D.sub.2 is connected to output D.sub.3, the signal of which is supplied to a reference signal (ground). In a second switched position, input D.sub.1 is connected to output D.sub.3 and input D.sub.2 is connected to output D.sub.4. The frequency at which demodulator D changes switched positions is synchronized with the energization frequency of modulator unit M. By means of the switching of demodulator D, the phases of the measuring signal are inverted in such a way that a demodulated signal having largely a constant sign is output by demodulator D.

(18) Output D.sub.4 is connected to the input of an integrator I, in the feedback loop of which a capacitor C is disposed. Integrator I functions as a low-pass filter. The output signal of integrator I is a direct current I.sub.2, which is converted by a first operational amplifier G and a second operational amplifier K to a compensating current I.sub.C. First operational amplifier G, which has a resistor R.sub.F in its feedback loop, is connected to one end of compensating winding L.sub.C and it has an amplification factor G. Second operational amplifier K has an amplification factor K and is connected to the other end of compensating winding L.sub.C and the output of integrator I. Direct current I.sub.2 is superposed by the output signal of first operational amplifier G and is then amplified by operational amplifier K with its amplification factor K.

(19) Finally, device 1 has an output A, at the terminals of which an output voltage U.sub.A, which is proportional to primary current I.sub.1 of current-carrying primary conductor L.sub.1, is present. Output voltage U.sub.A has the value U.sub.A=I.sub.1*R.sub.F*N.sub.1/N.sub.C. On the basis of output voltage U.sub.A, primary current I.sub.1 can be measured, calculated and displayed by connecting suitable means (not illustrated).

(20) The circuit diagram, illustrated in FIG. 6, of a further embodiment of a device 1 for measuring current differs from the embodiment shown in FIG. 5 by the fact that a second operational amplifier K is not provided. Furthermore, two individual exciter windings are wound around the two flux paths R.sub.1a, R.sub.1b (as illustrated in FIG. 1) and connected to the modulator unit. The two exciter windings together form a magnetic switch S, which can open and close flux paths R.sub.1a, R.sub.1b for magnetic flux, as in the embodiment according to FIG. 5. Integrator I is connected directly to compensating winding L.sub.C. The functional difference of device 1 consists in the fact that, in the exemplary embodiment shown in FIG. 6, direct current I.sub.2, which is the output signal of integrator I, is supplied directly as compensating current I.sub.C to the compensating winding.

(21) The circuit diagram, illustrated in FIG. 7, of a further embodiment of a device for measuring current differs from the embodiment shown in FIG. 6 by the fact that a first operational amplifier G is not provided, as a result of which compensating current I.sub.C=I.sub.1*N.sub.1/N.sub.C is present directly at output A.

(22) FIG. 8 shows a further exemplary embodiment, similar to the exemplary embodiments illustrated in FIGS. 5 to 7, of inventive device 1 for measuring current. The change of magnetic flux in measuring region 4 of magnetic core 2 is sensed by a measuring winding LM and supplied to an analog-to-digital converter 6 attached to one end of measuring winding L.sub.M. The voltage component of the change of the magnetic flux is converted by analog-to-digital converter 6 into a digital signal. As an example, analog-to-digital converter 6 can be attached by an optional buffer or amplifier, not illustrated, to one end of measuring winding L.sub.M. Analog-to-digital converter 6 is connected on the output side to a digital demodulator D and makes the converted digital signals available thereto.

(23) The digital output signal of digital demodulator D is made available to an integrator I, which can have the form of an I, PI, PID regulator or any other suitable regulator. The output signal of integrator I is a digital signal, which represents direct current I.sub.2 and is supplied to function unit 7. In the illustrated exemplary embodiment, function unit 7 is implemented as a mixed digital and analog component as regards its signals. Function unit 7 comprises operational amplifiers G and K illustrated in FIG. 5 as well as a digital-to-analog converter, not illustrated, which convert the output signal of integrator I into an analog value and can supply the converted signal to first operational amplifier G or second operational amplifier K. As illustrated in FIG. 5, the operational amplifiers supply compensating current I.sub.C for compensating winding L.sub.C. Compensating current L.sub.C is converted by suitable means in function unit 7 into a digital signal, which is available as the output signal at output A. Alternatively, it is also possible to provide that all components downstream from analog-to-digital converter 6, meaning demodulator D, integrator I and operational amplifiers G and K in function unit 7 are implemented as completely digital components.