AU592114B2 - Current transformer for static electricity meter - Google Patents

Description

I

AU-Al 63 3 93/ 86 1 WELTORGA>ZSATION FOR GEISTIGES EIGENTL PCT I~nternatiorndjes Bairo TU INTERNATIONALE ANMELDUNG VEROFFENT LICHT NACH DEM VERTRAG. OBER DIE INTERNATIONALE ZUSAMMENARBEIT AUF DEM GEBIET DES PATENTWESENS (PCT) (51) Internationale Patentklassifikation 4. (11) Internationale Veroffentlichungsnummer: WO 87/ 01812 GOIR 15/02, H01F 40/06 Al (43) Internationaics Veriiffentlichungsdatum: 26. Mdrz 1987 (26.03.87) (21) Internationales Aktenzeichen: PCT/EP86/00515 (74) Anwilte: NONLIST, Hans usw.; LGZ Landis Gyr Zug AG, Konzern-Patentabteilung, CH-6301 Zug (22) Internationales Anmeldedatum: (CH).

8. September 1986 (08.09.86) (81) Bestinimungsstaaten: AT (europdisches Patent), AU, (31) Prioritiitsaktenzeichen: P 35 32911.4 BE (europtiisches Patent), CH (europ~isches Patent), P 35 45 953.0 DE (europaisches Patent), DK, Fl, FR (europdisches P 36 19 423.9 Patent), GB (europaisches Patent), IT (europaiscbes Patent), JP, LU (europiiisches Patent), NL (europdi- (32) Priorititsdaten: 14. September 1985 (14,09.85) sches Patent), NO, SE (europdisches Patent), US.

23. Dezember 1985 (23.12.85) Juni 1986 (10.06.86) Ver'iffentlicht (33) Priorititsland: D E A'!it internationalern Rechechenberich t.

Vor Ablauf derfiir Anderungen der Anspriice z-ugelassenen Frist. Ver~ffentlichung wird wiederholt falls An- (71) Anmielder (ftir alle Bestimrnungsstaaren ausser US): LGZ derungen eintreffen.

LANDIS GYR ZUG AG [CH/CH]; CH-6301 Zug (CH).A.031P 8 (72) Erfinder; und 0S ,AIM Erfinder/Anmelder (nur ftir US) FRIEDL, Richard [DE/DE]; Tiergarten 67, D-3300 Braunschweig (DE).

!"This doctument. contaisthejOFJI aI'1t2: I's 11S iUe under ktioa 41)aztd is coirect for (54) TJ1 qj~ SgA IN ER-OR A STATIC ELECTRICITY COUNTER (54) Bezeichnung: STROMWANDLERANORDNUNG FOR EINEN STATISCREN ELEKTRIZITXTSZXHLER Ii 13a (57) Abstract The current transformer arrangement on the secondary side with an integration stage is provided with a secondary winding consisting of two astatically designed coils (31, 32) lying next to one another and connected in series. A' a result 1 external parasitic magnetic fields have practically no effect on the transmission of the measured viue. A large output sic-I nal from the secondary side is achieved by a large magnetic coupling of the primary conductor and secondary coil without the use of ferromagnetic materials. Preferably, the primary conductor (23) is designed as a flat conductor with suitably arranged slot-shaped recesses (25 to 28), so that primary windings (29a to 29g) are formed by changing the conductor crosssection (Fig. 5, 6, 7).

(57) Zusanmenfassung Die sekundlirseitig mit einer Integrierstufe 'ausgerilstete Stromwandleranordnung ist mit einer Sekunddrwvicklung aus zwei astatisch aufgebauten nebeneinanderliegenden und in Reihe geschalteten Spulen (31, .32) versehen. Hierdurch sind flussere magnetische Stbrfelder praktisch ohe Einfluss auf die Messwe rtilbertragung. Emn grosses sekundS~rseitigres Ausgangssignal wird durch eine grosse magnetische Kopplung des Primdrleiters und der Sekundirspule ohne Verwendung von Ferromagnetika erreicht. Vorzugswveise ist der Primiirleiter (23) als Flachlei~er mit geeignet angodenscitfrgen Ausnehmungen (25 bis 28) ausgebildet, so dass durch Veriinderung der Leiterquerschnitte prim,,re Windungen (29a bis 29g) gebildet wverden (Fig. 5, 6, 7).

la CURRENT TRANSFORMER ARRANGEMENT This invention relates to a current transformer arrangement.

Measuring large currents for determining energy consumption by means of static electricity meters requires the use of current transformers whose output signals must be suitable for further processing in electronic measuring assemblies. The currents to be measured may amount to over 100 amps which must be detected down into the measuring range of milliamps, with low levels of deviation from linearity. Such arrangements must be substantially insensitive in relation to direct current components in the current to be measured.

In addition, the consumption of necessary auxiliary energy for operating the arrangement must be as low as possible.

Furthermore, the requirements set forth in the IEC Publication 521 must be met, in particular galvanic separation with a high level of insulation strength, ability to withstand short-circuiting, I insensitivity in relation to external magnetic interference fields and the suppression of frequency effects.

S- The arrangement disclosed in German AS No 10 79 192, in the form 20 of a magnetic voltmeter, comprises two series-connected secondary coils which surround a bus bar. The secondary sub-windings are short- :circuited at their ends by magnetic material. That provides a closed magnetic circuit (known as a Rogowski coil) which behaves astatically in relation to extraneous fields if the density of turns of the subwindings is sufficiently high and the distribution of turns is uniform.

With high levels of current density in the primary conductor, the secondary coils must be at a certain spacing therefrom in order to ensure satisfactory integration of the sub-voltages of the irregularly distributed winding.

The known current transformer arrangement is provided with an Selectronic integrating stage whose frequency response, which is inversely proportional in respect of its input signal to the output signal, compensates for the proportional frequency dependency of the *voltage induced in the secondary winding by the current to be measured, and which further rotates the input signal with respect to the opposite phase position of its output signal, through a phase angle of 900, rc relative to the current to be measured. The measuring signal at the 2 output of the integrating stage is independent of the measuring frequency and is in phase opposition to the current to be measured, with direct proportionality between the amplitudes.

A disadvantage of the known current transformer arrangement is that the requirement for substantial insensitivity in relation to external magnetic interference fields is not completely met by the use of ferromagnetic materials. Furthermore, the known arrangement delivers very weak output signals as there is only very slight coupling between the fields of the primary conductor and the secondary coils.

That means that that process is not suitable for measuring current strengths of less than about 1 kiloamp.

According to the present invention there is provided a current transformer arrangement comprising a primary conductor for carrying alternating current to be measured and a secondary winding comprising at least two series-connected electrically identical secondary coils having an astatic configuration, the output voltage of the seriesconnected coils being applied to an electronic integration stage on the output side thereof to produce a measurement signal which is independent of frequency, wherein, so as to produce a maximum magnetic et 20 field strength, the primary conductor is formed into at least one °current loop, the turns of at least one of the secondary coils are arranged for maximum magnetic coupling at a minimum spacing relative to the corresponding current loop and engage as completely as possible the magnetic flux produced by the current loop, and the magnetic coupling is effected without magnetic materials, the secondary coils extending Sao.:% in their axial direction over a minimum part of the length of the o magnetic field lines produced by the current in the primary conductor, pand wherein the secondary coils are arranged in closely adjacent juxtaposed relationship for optimum external field compensation.

30 Embodiments of the present invention provide insensitivity to **p.pp external magnetic interference fields as well as a high secondary-side I. output signal, combined with a compact design and the simultaneous use of inexpensive components.

p In the preferred embodiment, the coil carrier has a degree of permeability which is substantially independent of the magnetic field Kof the primary conductor. The secondary winding comprises two seriesconnected coils whose axes extend parallel to each other. The ly___ 3 direction of winding of the coils corresponds to that of a solenoid which is spatially buckled in the centre through 1800. That astatic arrangement of the coils results in a secondary winding which is independent of external homogenous magnetic alternating interference fields as the partial voltages induced by the interference fields in the two coils cancel each other out. While in the known coils consisting of sub-windings, the sub-windings are always brought together to provide a closed integration path corresponding to a Rogowski coil, in the case of embodiments of the present invention the secondary coils, in order to attain small dimensions, each extend only over a part of the length of less than 50% of the magnetic field lines generated by the current in the primary conductor so that no closed integration path is formed. In that arrangement the second secondary coil serves primarily to compensate for the influence of external fields. In regard to achieving the best possible compensation effect, the two secondary coils are of small spatial dimensions and are arranged as closely together as possible.

The secondary coils may be in the form of cylindrical or flat coils having mutually parallel axes, wherein at least one of the two 20 coils is disposed in three-dimensional terms at a location at which the primary current produces the maximum possible field strength. The high '0field strength required for a high secondary-side output signal of the arrangement is produced by shaping of the primary conductor in the form of a loop. In that way the secondary sub-coils only pick up the magnetic field of the primary conductor locally in a punctiform manner, wherein the sum of the voltages induced in the two secondary coils is S°proportional to the primary current to be detected.

A particular feature of the current transformer arrangement °°embodying the invention is the high magnetic coupling thereof between a 30 the primary conductor and the secondary coil, thereby producing high J' °secondary-side output signals which permit the arrangement to be used for linear detection of currents with current strengths of down to a few milliamps, and this is achieved without using ferromagnetic a material. This provides a spatially compact design which permits inexpensive manufacture.

4 In a preferied embodiment, the primtary conductor which is in the form of a loop surrounds the secondary coil in the peripheral direction thereof as closely and as completely as possible. As in that arrangement the secondary coil is arranged with-in a primary conductor which is in the form of an eye, that design provides for opt im~n magnetic coupling with correspondingly high output signals.

In an advantageous embodimrent, the primary conductor encloses boxth secondary coils with two series-connected windings. It is also possible however for the primary conductor to comprise conductor portions which are connected in parallel relationship with each other and the windings of which each enclose one of the coils. In that case, the primary current to be mreasured is distributed to the two windings so that, in the case of a primary conductor which is preferably stampred out of copper, of rectangular cross-section, it is possible to avoid folds where the conductor portions cross over.

A highly advantageous embodiment is character ised by the features of claim 5.1 In that case the primary conductor which is in the form of a flat conductor is folded about a transverse axis through S. an angle of 180 so that the cut and return conductors are disposed 20 at a small spaci ng one above the other; that spacing may be of such a nature, at least n a portion-wise manner, that the resulting space is suitable for acccrmxating the secondary winding. In that embodiment the influence of the magnetic interference field on the measurement result is practically eliminated, even without magnetic materials. The shape and the snall dimensions of the arrangement easily permit fully automatic production.

*gas e~st It is advantageous if the recesses extend substantially fran the centre line to the edge of the primary conductor, in mutually opposite relationship. In that way the electrical current which flows in the longitudinal direction of the flat primary conductor is deflected a to the middle of the primary conductor so that the current paths Pitof 0.J are formed into a loop.

Another embodiment provides that the mutually oppositely disposed portions of the primary conductor each comprise two mutually oppositely directed recesses which are arranged in parallel offset relationship, thereby forming two windings which are disposed in juxtaposed relationship in the longitudinal direction of the primary conductor, wherein the magnetic flux of each winding passes substantially through a respective coil of the secondary winding. In that arrangement the coils of the secondary winding are advantageously disposed between the portions of the primary conductor. As the configuration of the primary conductor results in two juxtaposed windings, the ixes of which are respectively formed by the mutually facing ends of the recesses, each coil of the secondary winding may be associated with a respective primary winding, thus providing for optimum flux linkage.

15 Another advantageous embodiment is provided if the coils of the secondary winding, in a planar technology design, are disposed in one or more layers, possibly also on both sides in the form of spirals, on a substrate. The plate-like substrate may be inserted between the S* spaced-apart conductor portions. The substrate with the two coils 20 of the secondary winding may also be arranged outside the space between the conductor portions above the effective winding areas of the primary conductor.

It is also possible for the substrate to include further electronic components of the electricity meter. They may be for example the S 25 electronic components of the integrating stage and the multiplier stage.

A further embodiment provides that the one conductor portion has two mutually oppositely directed recesses which extend to the edge of the primary conductor on a cammon longitudinal axis, while arranged in parallel therewith is a central recess on the other conductor 30 portion. With that arrangement of the recesses, the current paths are such as to form two turns which are connected in parallel and each 6 of which is linked with the magnetic flux of a coil of the secondary winding.

The invention will be described in greater detail hereinafter by means of embodiments illustrated in the dra.ing. Th known integration circuit has not been illustrated therein.

In the drawing: Figure 1 is a front view of two secondary coils of astatic design, one of which is enclosed by a primary conductor, Figure 2 is a front view of two coils of astatic design, which are enclosed by series-connected turns of the primary conductor, Figure 3 shows an arrangement of the secarrary coils in Figure 2 but with curns of the primary conductor conricted in parallel, Figure 4 is a perspective view of a primar-.' conductor in the form of a flat conductor, in which one of the secondary coils of an astatic design is arranged between oppositely disposed portions of the flat conductor and the other secondary coil is arranged outside the flat conductor, Figure 5 is a perspective view of a prima-. conductor in an emboiment which has been modified in ccmparisc- with Figure 4, .o 20 Figure 6 is a perspective view of the coils, of astatic design, of the secondary winding, with a base plate wh_-ch can be inserted into the primary conductor shown in Figure Figure 7 is a view in cross-saction of the arrangement of Figures and 6 in the operative condition, on a reduced scale, 25 Figure 8 is a perspective view of an embodment of the primary conductor which is modified in comparison with Fiaures 4 and Figure 9 is a perspective view of flat coils of an astatic design, in the form of a secondary winding on a base plate which can be inserted into the primary conductor s1mn in Figure 8, 30 Figure 10 is a perspective view of a primary conductor canparable to that shown in Figure 8, with coils of the secondary winding arranged therein, Shil, I Figure 11 is a plan view of a folded-open primary conductor in the form of a flat condiuctor, Figure 12 is a plan view of the primary conductor shown in Figure 11 in the folded condition, Figure 13 is a plan view of a base plate with flat coils of an astatic design, of a configuration comparable to Figure 9, Figure 14 is a plan view of the folded primary conductor shown in Figure 11, on the oposite side in comparison with Figure 12, andi Figure 15 is a view in cross-section of the arrangement shown in Figure 14.

Figure 1 shows two spaced-apart cylindrical coils 1 and 2, which are of an astatic design, of a secondary winding 3. The coils 1 and 2 which are held by means of a spacer 4 are geanetrically and electrically identical and extend with their cylinder axes parallel to each other. The coils and 2 are arranged in an insulating cylinder 5 and 6. The coil 1 is enclosed by a turn 7a of the prirrary conductor 7 through which the curent Ito be measured flows in the direction *of the indicated arrows. The voltages induced in the coil1s 1 and 2 by the magnetic field of the alternating current flowing in the primarry conductor 7 are added to produce a signal which is proportional to the alternating current 11to be rmeasured. Votlages induced by hcmogeneous; external interference alternating fields have different signs by virtue of the astatic arrangement of the coils 1 and 2, 'S..and cancel each other out in the sun. That arrangement substantially *.25 eliminates the influence of external magnetic alternating fields on correct operation of the current transformer- arrangeent. The influence of external fields may be further reduced by magnetic screening material surrounding the coils.

*:too In Figure 2 the coils 8 and 9 correspond to those shown in Figure 1. The secondary coils 8 and 9 are successively surrounded by the cormin primary conductor 10. That series connection of the primrary turns 10a and l0b results in a measuring signal -which is increased in ccxnparison with the arrangement shown in Figure 1.

In Figure 3 the coils 11 and 12 correspond to the coils 8 and 9 in Figure 2. The primary conductor 13 is brancl.e3: out to provide two conductor portions which are each fourmed into a respective turn 13a and 13b embracing the respective coils 11 and 12. The current11 is branched on to the conductor portions with the turns, 13a and 13b, the sum of the voltages induced in the coils 11 and 12 being proprtional to the current I to be measured. In comparison with the arrangmnt shown in Figure 2, the arrangement shown in Figure 3 has the advantage that, with the primary conductor 13 which is preferably stamped out of copper and -which is of rectangular cross-section (flat conductor), it is possible to avoid folds at the location at which the conductor portions cross over.

In the emoiment shown in Figure 4, a primary conductor 14 is in the form of a flat conductor of rectangular cross-section and which is so folded that mutually oppositely disposed conductor portions 14a and 14b prcduce a square or rectangular cavity 15. Outside the .cavity 15. oppositely disposed portions of the primary conductor 14 separated fran each other by an insulating layer 16. The conductor portion 14a is provided with a slot-like recess 17 which extends from approximately the middle to the edge. A recess 18 which extends in the oposite direction to the edge is provided on the oppositely disposed conductor portion 14b. The recesses 17 and 18 influence the geometrical position of the cur-rent paths of the current which is to be 25 measured, as represented by- the arrows 19 and 20, in such a manner that a turn is formed] for the primary current. The seccondary coil 21 which is shown in broken lines is arranged in the magnetic field of that turn. A second secondary coil 22 is disposed outside the primary conductor, to comnpensate for external magnetic fields.

30 The primary conductor 23 shown in Figure 5 differs fran the embodiment in Figure 4 in that two oppositely directed slot-like 9 recesses 24, 25 and 26, 27 respectively are provided in the mutually oppositely disposed conductor portions 23a and 23b. Each of the laterally open recesses 24 to 27 extends approximately to the middle of the conductor portions 23a and 23b. The recesses 24 and 26 are disposed in the same plane perpendicularly to the primary conductor 23 when it is folded through 1800 in the operative condition, that is to say the conductor portions 23a and 23b extend parallel to each other. In the same manner, the recesses 25 and 27 are arranged in a common plane perpendicularly to the primary conductor 23.

By virtue of the above-indicated configuration of the recesses 24 to 27 the primary current flows along current paths which are indicated by the arrows 29a to 29g. As a result, series-connected primary turns are formed in the planes of the conductor portions 23a and 23b, and secondary coils may be arranged in the magnetic field of the primary turns.

Disposed on the base plate 30 shown in Figure 6 are two astatically arranged secondary coils 31 and 32. In the operative condition, the base plate 30 is located with the coils 31 and 32 between the conductor portions 23a and 23b of the piimary conductor 20 as shown in Figure 5. The position of the coil 31 in Figure 6 is indicated on the conductor portion 23b in Figure 5 by the broken-line circle 33. The coil 32 is disposed in a corresponding manner in Figure 6, in a region represented by the broken-line circle in Figure 25 Figure 7 shows the current transformer arrangement with the primary-side part shown in Figure 5 and the secondary-side part shown to* in Figure 6, in the operative condition. In this case, the upper and lower portions of the primary conductor 23 are separated from each other by an insulating layer 61.

The primary conductor 34 in Figure 8 is comparable to the primary conductor 23 in Figure 5. Only the spacing between the upper conductor portion 34a and the lower conductor portion 34b is smaller p'

*A~

and corresponds to the thickness of the insulating layer The base plate 36 shown in Figure 9 with the secondary coils 38 and 39 arranged thereon is disposed in the operative condition of the current transformer arrangemient between the conductor portions 34a and 34b of the primary conductor 34 shown in Figure 8. The coils 38 and 39 in Figure 9 are of a spiral configuration and are produced by planar technology so that the small space between the conductor portions 34a and 34b as shown in Figure 8 is adequate. In the operative condition the centre point of the coil 38 is disposed approxi-mately at the middle end of the slot-like recess 40 in Figure 8. In a corresponding fashion, the central point of the coil 39 and the middle end of the recess 41 are arranged in approximately coincident positions.

Figure 10 shows a primary conductor 42 which substantially 15 corresponds to the primary conductor 34 in Figure 8. Hovnver the cc:.recesses 44 and 45 are in the formn of holes at their ends which are directed toaards the middle of the primary conductor 42, while secondary coils 46 and 47 of an astatic design are mrounted in the holes.

In the embodiment shown in Figure 11 a primary conductor 48 shown in an open condition, that is to say before being folded about a line 49. In the tlded condition a conductor portion 48a is disposed above a coniductor portion 48b. The conductor portion 48b has recesses 50 and 51 which extend in mutually opposite relationship and on a carmtn longitudinal axis parallel to the fold line 49. Provided 25 on the conductor portion 48a is a recess 52 which extends only in the middle region of the conductor portion 48 and which is at the same spacing frcm the fold line 49 as the recesses 50 and 51. The locations of the secondary coils are illustrated by the broken-line circles 53 and 54. Arranged in mirror image relationship with respect thereto, in to the fold line 49, are the corresponding base areas 55 and 56 for the secondary coils.

Figure 12 shows the primnary conductor 48 of Figure 11 in the folded-together condition, so that the conductor portions 48a and 48b are disposed one above the other. Correspondingly only the recesses 50 and 51 are illustrated, with the locations for the secondary coils, as indicated by the circles 53 arnd 54.

wihFigure 13 shows the secondary coils 56 and 57 of astatic design, whih re ixd t abase pae5.That arrangement which corresponds inpicpet htsonin Figure 9 differs therefran essentially 49 in Figure 13. The coils 56 and 57 may also be produced by a planar technology. In order for both coils to be exposed to the corresponding primary magnetic flux, they may also be arranged outside the space between the folded conductor portions 48a and 48b in Figure 11, if the magnetic coupling involved is sufficient for a high output signal. In that case also, the circles shown in Figures 11 and 12 are the corresponding locations for the seconda-ry coils.

Figure 14 shows the primary conductor 48 in Figure 11 in the a folded-together condition, from the opposite side in cxrnarison with Figure 12. Accordingly only the middle recess 52 can be seen.

20 In Figure 15 also, the primary conductor 48 is shown in the folded-together condition, the spacing between the upper conductor portion 48a and the lower conductor portion 48b being determined by an insulating layer 57. The direction of the primary1 current to be 4**measured is identified by the arrows 58 and 59. The base plate of Figure 13 is inserted into the space SO.

Claims (12)

1. A current transformer arrangement comprising a primary conductor for carrying alternating current to be measured and a seconrdary winding comprising at least two series-connected electrically identical secondary coils having an astatic configuration, the output voltage of the series-connected coils being applied to an electronic integration stage on the output side thereof to produce a measurement signal which is independent of frequency, wherein, so as to produce a maximum magnetic field strength, the primary conductor is formed into at least one current loop, the turns of at least one of the secondary coils are arranged for maximum magnetic coupling at a minimum spacing relative to the corresponding current loop and engage as completely as possible the magnetic flux produced by the current loop, and the magnetic coupling is effected without magnetic materials, the secondary coils extending in their axial direction over a minimum part of the length of the magnetic field lines produced by the current in the primary conductor, and wherein the secondary coils are arranged in closely adjacent juxtaposed relationship for optimum external field compensation.

2. A current transformer arrangement according to claim 1, wherein the current loop closely embraces the at least one secondary coil in "the peripheral direction thereof.

3. A current trai3former arrangement according to claim 1 or claim 2, wherein two current loops are connected in series and each current loop embraces a secondary coil.

4. A current transformer arrangement according to claim 1 or claim S, 30 2, wherein two current loops are connected in parallel with each other 00° and eapih current loop embraces a secondary coil.

A current transformer arrangement according to any one of the preceding claims, wherein the primary conductor is in the form of a 35 folded flat conductor with mutually oppositely disposed conductor portions which, by means of at least one opening, each form at least one portion of the current loop in the plane of the flat conductor. i 13

6. A current transformer arrangement according to claim 5, wherein the openings extend in mutually opposite directions approximately from the centre line to the edge of the flat conductor.

7. A current transformer arrangement according to claim 6, wherein the oppositely disposed conductor portions of the flat conductor each have two mutually oppositely directed openings which are arranged in parallel displaced relationship and thereby form two portions of the current loop which portions are disposed side-by-side in the longitudinal direction of the flat conductor.

8. A current transformer arrangement according to any one of claims to 7, wherein the secondary coils are arranged between the conductor portions of the flat conductor.

9. A current transformer arrangement according to claim 7 or claim 8, wherein the secondary coils are produced by a planar technique and are disposed in one or more layers in the form of spirals on a 20 substrate.

A current transformer arrangement according to claim 5, claim 8 or claim 9, wherein the one conductor portion has two mutually oppositely directed openings which extend to the edge of the flat conductor on a common axis and arranged in parallel therewith on the other conductor portion is an opening which does not extend to the edges.

11. A current transformer arrangement substantially as herein y 30 described with reference to any of Figures I to 5, or Figures 5, 6 and 7, or Figure 8, of Figures 8 and 9, or Figure 10, or Figures 11 to of the accompanying drawings. S

12. A static electricity meter including a current transformer 35 arrangement according to any one of the preceding claims. DATED this 16th day of October, 1989. LGZ LANDIS GYR ZUG AG o By Its Patent Attorneys ARTHUR S CAVE CO 7l