CA1285025C - Folded bar current sensor - Google Patents
Folded bar current sensorInfo
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- CA1285025C CA1285025C CA000561728A CA561728A CA1285025C CA 1285025 C CA1285025 C CA 1285025C CA 000561728 A CA000561728 A CA 000561728A CA 561728 A CA561728 A CA 561728A CA 1285025 C CA1285025 C CA 1285025C
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Abstract
FOLDED BAR CURRENT SENSOR
ABSTRACT OF THE DISCLOSURE
A current sensor employs a folded conductor bar having aligned holes therein to generate magnetic fluxes in the holes proportional to a current flowing in the bar. Each of the two holes has two windings therein wound in opposition to each other but connected for adding their voltages. Corresponding windings in the two holes are wound in opposition to each other and are connected for adding their voltages. The windings in each hole are offset from a center line, whereby magnetic fluxes generated by current flowing in the bar induce voltages in the coils but magnetic fluxes from external sources produce voltages which substantially cancel. A
feedback arrangement is disclosed for creating an opposing magnetic flux such that essentially zero magnetic flux is present in the magnetic cores of the windings. A multi-range current measurement device employs a tapped feedback winding selectively connectable to an output amplifier for producing an output voltage having a range set by the number of turns selected on the tapped feedback winding.
ABSTRACT OF THE DISCLOSURE
A current sensor employs a folded conductor bar having aligned holes therein to generate magnetic fluxes in the holes proportional to a current flowing in the bar. Each of the two holes has two windings therein wound in opposition to each other but connected for adding their voltages. Corresponding windings in the two holes are wound in opposition to each other and are connected for adding their voltages. The windings in each hole are offset from a center line, whereby magnetic fluxes generated by current flowing in the bar induce voltages in the coils but magnetic fluxes from external sources produce voltages which substantially cancel. A
feedback arrangement is disclosed for creating an opposing magnetic flux such that essentially zero magnetic flux is present in the magnetic cores of the windings. A multi-range current measurement device employs a tapped feedback winding selectively connectable to an output amplifier for producing an output voltage having a range set by the number of turns selected on the tapped feedback winding.
Description
l l ~ O
FOLDED BAR CURRENT SE?'SOR
BACXG~OUND OF T~:E INVE~TIOI~ -The present invention rela~es to electrical measuremen~ devlces znd, more pa_.icula-ly, to devices fo_ measuring an elec~ric cur_en~ passing through a conductor.
Many electronic applications such as, for example, electronic metering o_ elect_ic powe~ and energy usagel re~uire means for p-oducing a signal propor~ional to zn elec'ric cu~-ent in a conductor.
Conventional current measuremen~ devices employ a current trznsformer having a p_~mzry winding in se~ies with the cu_ren' to be me~sured. A resis'or in series with a secondary winding of the current ~; trans'ormer produces a vol~age h2ving zn ~mplitude 1~ p~oportional to the current in the primary winding.
This voltzge is then employed as z mezsure of the primzry current.
Conven~ional current mezsurement devices su~fer from a nu~be- of drawbac~;s. Cur~ent t_ansfo~ers are e~per.sive devices znd, when employed in hish-voltage power sources, re~ui~e sul~able insulatlon thus further adding to cost. In additior" an output cur-en~ Oc a cu-rent 'r2ns~0rme_ must be sczled to ,he current-handling cap2bili~y of the circui, ~2~
.
FOLDED BAR CURRENT SE?'SOR
BACXG~OUND OF T~:E INVE~TIOI~ -The present invention rela~es to electrical measuremen~ devlces znd, more pa_.icula-ly, to devices fo_ measuring an elec~ric cur_en~ passing through a conductor.
Many electronic applications such as, for example, electronic metering o_ elect_ic powe~ and energy usagel re~uire means for p-oducing a signal propor~ional to zn elec'ric cu~-ent in a conductor.
Conventional current measuremen~ devices employ a current trznsformer having a p_~mzry winding in se~ies with the cu_ren' to be me~sured. A resis'or in series with a secondary winding of the current ~; trans'ormer produces a vol~age h2ving zn ~mplitude 1~ p~oportional to the current in the primary winding.
This voltzge is then employed as z mezsure of the primzry current.
Conven~ional current mezsurement devices su~fer from a nu~be- of drawbac~;s. Cur~ent t_ansfo~ers are e~per.sive devices znd, when employed in hish-voltage power sources, re~ui~e sul~able insulatlon thus further adding to cost. In additior" an output cur-en~ Oc a cu-rent 'r2ns~0rme_ must be sczled to ,he current-handling cap2bili~y of the circui, ~2~
.
2 11-~E-180 receiving it. Electron~c measurement devices such as, for example, electronic watthour meters, are capable of handling only a few milliamperes of current. Load currents, in contrast, may ~e several hundred amperes. Por e~ample, if a single primary turn is employed in such a current transforme~, on the order of 100,000 ~econdzry tu~ns are reFui_ed to produce a full-scale current in the presence o' a load current of, for example, 300 ~mperes.
Conven~ional toroidal transformer cores do not provide sufficient room for this many turns in a de-.-ice of practical sizeO In.addition, such current transformers require a low value of burden resis'ance to function with adequate accuracy. A wincing with such a large number of tu-ns has an inherently high resistance, thus precluding operation with the re~uired accuracy.
The prior art contains several approaches for dividing a 102d current in order to produce a sample cur-ent or voltage proportional to the load cu_ren~.
A shunt techniue, disclosed in U.S. Patent Nos.
4,182,982 and ~,~92,919, splits the current in a conductor between a main shunt path and a parallel auxiliary path. The auxiliary path contains 2 much 2~ smaller cross section ~han does the m2in shunt path and cur~enl through the combination divides in su~st2n_ially the ratio o~ th~ cross sections.
magnetic core with 2 ~inding of many turns is disposed about the au~iliary path. The auxiliary pzth thus forms a one-turn primary and the many turns z~out it fo~m a seconda~y. A current through the secondary is proportion21 to the current in the 3 11-~E-180 primary divided by the nllmber of turns in the secondary. This technique suffers reduced accuracy from the substantial thermal coefficient of resistance of copper which may be as much as 3D
percen' over the environmental temperature range to which watthour meters are exposed. In addition, it is difficult to obtain a sufficient current divisicn to gi~e the four crders of masnitude reduction in output current compared to load current. Finally, this technique is subject to errors resulti~g from magnetic flux about the cu~rent-carrying conductor ma~ing up the shunt path.
A further technioue, disclosed in U.S. Patent No. 4,~96,932, employs two slits in 2 conductor to p.oduce a measurement conductor be'~ween a pair of shunt conductors. The measuremen~ conductor is deflected, first in one direction, and then in the other, to p-ovide space ~or the pzssage of a one turn 1002 f magnetic core ~ateri21 therethrough. In one em~odiment, the shunts and the measurement conductor a~e folded to 21isn holes in two hzlves thereof. The one-turn loop of magnetic core material is then passed t~._ough the aligned holes for receiving z szmp~e of lea~2ge current produced by the p~esence cf the slits znd the mPzsuremen~ conductor. A second2ry windins of m~ny tu-ns on the co-e locp p~ovides an ou~put. This devlce suffers from the presence of strong mzgnetic fields in its vicinity which are czpable o. saturzting the core 2nd thus int-oducing e--ors or cancelling its ou~put. In addition, no p-o~ision is ~-cvided fo~ cancelling the efSects of non-uniform m2snetic fields orisin2'ing ex.ernal to "
the measurement device, as are r~utinely experienced in wat~hour meters~
Other special problems are encountered in watthour meters. The extern21 conriguration, including the positions of connector blades, is established by rigid industry s~andards. Such industry stand2rds 21so require that crosst21k between adjacen~ phases be held to a very low leve:L.
'.
OBJ:ECTS AND SUMMARY t:)F THE INVr NTIC)N
It is an ~bject of the inven~ion to provide a current sensor which overcomes the drawbacks ~f the prior art.
It is a further object of the inven'ion to pro~ide a current 6ensor that does not require a current trans^ormer.
It is a further object of the invention to provide a current sensor having substantial immunity to external magnetic fields.
It is a still further objec~ of the invention to 2~ provide a cur~ent sensor having 2 plurality of windings, ~11 of the plurality of windings adding ~oltage produced by magnetic fields gene-ated by a current to be measured and subt_zcting voltage generated 2s the results of exte-nal masnetic fields.
It is a still further object of the invention to p-ovide a current sensor having at least first 2nd ;~ second windings on a core disp~sed in 21igned holes ~` in a folded, cu~rer.t-ca-r~ing ba~. The winding directions of the first and seccnd windings are ~ 3~
ll~ME-180 . .
opposite ~hereby current in the two parts of the folded bar add together to produce an ~utput.
It is a still further objec~ of the inven~ion to provide a current sensor having two magnetic cores each containing two, oppositely-wound, windings. The four windings on the two cores produce additi~e output as a result of magnetic ~ields generated by , current passing therepast through the bar bu. cancel ; the e~fects of external ma~netic fields.
It is a still further object of the invention to provide a current sensor employing at least one magnetic core disposed in aligned holes in a folded bar and a feed~ack winding f~o~ an active circuit ef~ecti~e to balance the mas~etic field genera~ed by - -the curren~ through the bar.
Brie,ly stated, the present invention provides a current sensor employing a folded conductor bar having aligned holes therein to generate magr.etic fluxes in the holes proportional to a cu-rent flowing in the bar. ~ach of the two holes has ~wo windings therein wound in opposition to each other but connected fo~ adding their currents. Corr sponding ~
wincinss in the two hc'es are wound in opposition to each o_he_ and are connected for adding their vol'ages. The windings in each hole are o~fset lrom a center line whereby magnetic fluxes generated by cu'rent flowing in the bar induce voltages in the coils but m2gnetic fluxes from exte~nal sources gene~a.e voltages which subs!antially cancel. A
feedback ar-zngement is disclosed for bzlancing the magnetic fluxes in the holes. A .,.ul i-~ange c1rrent meas~rement device em~loys a ta~ed feedb~c~ winding 3~5 6 11-~E-180 selectively connectable to an output am~lifier for producing an output current hzving a range set by the nu~'cer of turns selected on the tapped feedback winding Acco~~ing 'o an em~odiment Oc the invention, there is provided a current senscr for measuring a '-current, comprising a first conductor bar having a firs' ge~erally plan2r surface, a second conduc'or ba~ having a second generally planar sur~ace disposed parallel to the first generally planar surface, a predetermined g2p between the first and second generally planar su~faces, means for connecting adjacent first e~ds of ~he fi-st and second conductor b2rs, means for feeding the current to a second end of the fi~st conductor bar, mezns for receiving the current from a second end of the second conductor bar, a first hole gener211y cen.ered in the first conduc'o- bar and having a first axis substantially normal tD the fi~st gene~ally pl2nar surface, a second hole gene~211y centered in the second conductor bar and having a second a~is substantially no~mzl to the second gene_zlly planar surface, the fi-st and second zxes being collinea~, fi-st and second coils in ~he first hole, third and fou~th ~5 coils in the second hole, mezns for inte connecting the first, sec~nd, third and fou~th coils to produce zn ou_pu_ signal in response to magnetic fields in the firs' and second holes resulting f-om the current in he first and second conduc'cr the, bars first and second coils being wound to add voltages produced by magnetic fields within the fi-st hole and to cancel ~ol.ages produced by manetic fields o-iginating .g~f~ .4.V~
.
outside the first hole, the third znd fourth coils being wound to add voltages produced by magnetic fields within the ~econd hole and to cancel voltages produced by magnetic fields originating outside the second hole, the fi-st and third coils being wound to add voltages produced by magnetic fields within the first and second holes and to cancel voltages produced by magnetic fields orisin2~ing outside the first and second holes, and the second and fourth coils being wound tQ add voltages produced ~y magnetic fields within the first 2nd second holes and to cancel voltages p~oduced ~y masne~ic fields originating outside the firs~ and second holes, whe-eby substzn~ial i~munity to magnetic fields originating ex_ernal ~o the first and second holes is achieved According to a feature of the inven.ion, there is provided ~ coil assembly for a current sensor comprising: first and second collinear windings, the 20 first and second colline2r windings being connec.able in series and having a winding sense effective for c~ncelling voltages p-oduced by magnetic fields 2p~1 ied substanti211y ecually the_e.o, third and fourth collinear windinss, the third and four,h 2~ colline2r windings being conne~able in se-ies and having a winding sense effective for czncelling voltages produced ~y m2snetic fields zpplied su~stantially eoually thereto, means for disposing 2n 2xis of the first znd second collinear windings pzr211el tD an zxis Oc the third znd fourth colline2 windings wit~ the fi-s. 2nd third ~indings z~jacent each other znd the second 2nd four~h windings adjacent each other, the first, second, thi-d and fourth windings being connectable in series, the first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto, and the second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substan.ially eoually thereto.
Acco~ding to a further feature of ~he inven~ion, there is provided a method for measuring a current, comprising: forming a folded bar including a first conductor bar ha~ing a first gene-ally planar surface, disposing a second conducto~ bar having a ~ ~ 15 second gene~ally plzna- su-face parallel to the first :: ~ generally planar surface, spacing the first and second generally planz- sur~aces a predetermined dis,ance apart, connecting zdJacent first ends of the first znd second conductor b2rs, feeding the current 2C to a second end of the first conductor bar, receiving the cu-rent from a second end of the second conductor b2r, fo~ming a fi_st hole generally centered in the first conductor ~r and having a fi-st axis subs~2n~ially no~mal to the first generzlly planar 2~ surface, forming a second hole gener211y cen'ered in the second conductor bar and having 2 second axis substantially normal to the second generally planar ` ~ su-face, the first and second axes being collinear, disposing first and second coils in the firs, hole, disposing third znd four_h coils in the second hole, interconnec~ins the firs., seccnd, third and four~h coils to produce an outpu_ sisn21 in esponse to ~L~ 2 5 . .
magnetic fields in the first and second holes resulting from the cu_rent in the first and second conductor bars, winding the first and sPcond coils to add voltages produce~ by magnetic fields within the first hole and to cancel voltages produced ~y magnetic fields origin2.ing outside the fi-st hole, '-winding the third and fourth coils ~o add voltages produced by magnetic fields within ~he second hole and to cancel voltages produced by m2gnetic fields originating outside the second hole, winding the flrst and third coils to add volt2ges produced by masnetic fields within the first and second holes and to czncel voltages p~oduced by-magnetic fields origina~ing cutside the first and second holes, and winding the second znd fourth coils to add voltages produced by magnetic fields wi,hin the first and sec~nd holes and to c2ncel voltages produced by magnetic fields origina.ing outside the first and second holes, whereby su~stantial immu~ity to magnetic fields origina'ing exte_nal to the firs, 2nd second holes is achieved.
- The a~ove, and o~her objec~s, fea~ures and advan~ages o the present invention will become app2rent from the following d~scription read in conjunction wi~h the ac~ompanying d-awings, in which like reference numer21s designate the same elements.
BRIEF DESCRIPTION OF TX~ DRAWING~
Fig. 1 is a simplified schema.ic diagram of an elect_ic meter ~howing a current senso- according to 10 ll~E-l~O
p-ior ~rt.
Fig. 2 is a pe~spective view of a conductor bar to which reference will be made in describing the principle of operation of the present inventicnO
Fig. 3 is a cross sec~ion ta~en along III-III in Fig. 2.
Fig. 4 is a cross section corresponding to ~is.
3 excep. including two conductor bars and two pai-s of sensing windings.
Fig. 5 is a perspective view of a folded bar current sensor acco~ding to an en~odiment of the invention.
Fig. 6 is 2 perspective view o~ a coil assembly of ~ig. ~. -Fig. 7 is a schematic diag,am of a current measurement system according to an em~odiment of the inven~ion.
Pis. 8 is a si~.~lified schem2tic dias_am of a dual-range current measurement system according to an ~- 20 em~odiment of the invention.
: ' DETAIL~D DESCRIPTION OF T:-'~ PR~PRED ~MBODIM~T
A current sensor accorcing to the present inven~ion m~y be employed for me2suring a curren! in a conductor associaLed with any type of electric21 2~ eouipment. For concreteness, 2 cu--ent sensor in acco-dznce wi.h an e~bodiment of the invention is disclosed in t~e envi-onmen~ OL an electronic w2t.h.0ur mete_. This envi_onmer._ is chosen at le2s~ -pa-ly because pro~lems of meas~ement accuracy, and the ~is.u,bance thereof from external masnetic fields, are more severP than in most other environments.
Also, although the current sensor of the present invention is considered to be especially useful in measuring currents flowing in each of a plurality of ~`
phases of a poly-phase electronic watthour meter, :it is considered that its desc-iption in the environment of a single-phase electronic wa~thour meter avoids unnecessary functional duplication and therefore zids in understanding the invention. Thus, measurement of cu~~en~ in a single-phzse electrcnic wattmeter is described in detail.
Refer~ing now to ~ig. 1, there is shown, generally at 10, a current sensor of the prior art which produces a voltage proportional to a current being fed on an AC line 12 to a load (not shown). A
cur-ent transformer 14 includes a prima~y winding 16 in series with one conduc~o~ o AC line 12. A
second2ry winding 1~ hzs a current therein proportional to the AC cu_rent in primzry winding 16.
The cu~~ent in secondzry windin~ 18 passes th ough a resisto- 20 to develop a voltage thereacross p_oportional to the secondz~y cu_rent. The voltzge is 2p?1ied to inputs of an electronic watthour me~e_ 22. A vol!age ac~oss AC line 12 is connected to elect_onic watthour me.er 22, wherein an electronic multiplication process determines 2n instantaneous vzlue of wat.s consumed by the 102d. A conventional integrating àevice (not shown) in elec~ronic watthou-meter 22 in eg~ates t~.e consumed wzt's t- de-ive the ene~~y consumed.
Electronic watthour meter 22 may be of zny convenient type such as, for example, an electronic watthour meter according to the teaching of U.S.
Patent No. 3,947,763, of common assignee with the present in~en,ion. Such electronic devices require signals proportion21 to load current at values as much as five orders of magnitude smalle_ than the load cu-rent itself. This is difficult to attain in 2 p~ac,ical current tr2nsfo~mer 14. In addition, the need for a cu~-ent transformer 14 adds to ~he over211 cost of the equipment 2nd elimination o- this element is therefore considered desirable.
Referring now to ~ig. 2, there is shown a conductor b2r 24 having an electric current I flowing ,here,~.rough. A hole 26, bored through conductor bzr 2~, sepzrates current I into separ2te cu_rent~ I1 znd I2 on either side of hole 26. Current Il produces a magnetic flux 28 which, in conventional notation, is indicated as flowing into the top of hole 26.
Current I2 produc2s z magnetic flux 30 which, in con~entional notation, is shown flowi~g ou' of the top of hole 26.
Fig. 3 shows a cross sec_ion of conduc~or bar ~ ;
through hole 26 2nd t~znsverse to the direction of cu~rent 1. Magnetic fluY.es 28 and 30 oppose each o,he~ and, if eau21, would cancel ezch o.her along zn zxi5 of hole 26. Conductor bz- 2~ znd hole 26, zlong with first znd second pic};up coils 32 znd 3~ form a cu_rent senso~ 31 zcco-ding ~o 2n em~odiment of the inven'ion. First pickup coil 32 is disposed zlong zn zxis A-A, displaced f~om an zxis of hole 26. Thus, it is inrluenced mo~e by m2snetic flux 3~ znd less by .
magnetic ~lux 28 and a voltase is induced in pic}up :' coil 32 by an AC current in conduc-or ~zr 24. If only a single pickup coil 32 were employed in hole 26, it would be fully responsive to external magne,ic fields. To compensate zt le~st partly for such external magnetic fields, second pickup coil 34 i~
disposed on an z~is A'-A', displaced in the opp~site direc ion from the axis of hole 26. It also has a voltage induced therein. A connec~ion 36 joins one end of pickup coils 32 and 3~. Pickup coils 32 and 34 are wound in opposite direc'ions whereby their voltages, induced by masnetic fluxes 28 and 30~ add togeiher.
The opposite windiny directions of pic};up coi7s 32 and 34 tend to c2ncel the ef~ects of those external magnetic fields which affect them eoually.
This cancellation is more effective as pickup coils 32 and 3~ are brought closer together. Some external masnetic fields may not be oriented to affect pickup coils 32 and 34 equally. In such an event, the voltzges generated in pickup coils 32 and 34 by such ~zgnetic fields do not cancel and inaccuracies in the relationship ~etween output current znd cu-rent I m~y exist. In non-crl .ic21 applicztions, or those in which external masnetic fields zre 5m211, this e~od ment may be czpable of providing suf~icient accuracy.
Since cnly a smzll zmount of flux is induced to enter and leave hole 26, z slbs'zn.izl ratio i5 found be.ween the current lowing in conducto_ bar 2~ and the volt2se across pickup coils 32 and 34. The resulti~s output vcltzge of pickup coils 32 and 3~, ~ 35~3~5 fed on lines 38 and ~0 to e~ternal circuits, may be of a low enough level for direct feedlng to the inpu~
of an electronic watLhour meter without requiring an intermediate current transfD~mer. In this manner, the overall system, inclu~ ~g the electronic watthour meter~ is of reduced complexity and cost. Indeed, such a current ~ensor may be mad~ small enough for inclusion within the housing of a conven'ional electronic watthour ~e.er whcse dimer.sions 2_ e governed by indust~y standards.
~ eferring now to Fis. 4, a cur_en~ senso~ 31' employs a folded concigl~ra~ion in which con~uctor b2r 24 is paralleled by a conductor bar 24' carrying the same urrent I, but in the opposite direction as indicated by conventional indicators of cur-ent Girec.ion. A gap 39 is formed be~ween facing surfaces of conductor bars 24 and 24'. Conductor bar 2~' includes a hole 26' aligned with hole 26 in c~nductor bar 24. A pickup coil 32' in hole 26' is axially ali~ned with pickup coil 32 in hole 26, but is oppositely wound there_~om. As indicated by the direc~ion of masnetic flux 30' in~luencing pickup co~l 32', cur-ents in conductor bz- 24' and conducto-ba_ 2~ add as voltages 2re induced in pickup coils 32 2~ znd 32'. Simila~ly, a pi_kup coil 34' is disposed in hole 26' a~izlly aligned with pic~up coil 34 in hole 26 but opposi~ely wound 'heref-om. I~ will be reco~nized that voltages in pickup coil 34 and pickup coil 34' produced by cu--ent I in conduc.or bzr 24 and conductor bar 24' add togethe-. Connec'ion 36 joins one end of pickup coils 32' ~nd 34' whereby co.~ined voltages from 211 four picku~ coils a_e .
~pplied to lines 38 and ~0.
The presence of oppositely wound pic~up coils 32' and 3~' in hole 2~' cancels voltages produced by e~ternal magnetic fields which affect them equally, in the same ~,znner as the.ir counte~parts in hole 26.
Thus, substantially comple~e cancellation of influences of e~ternal masne~ic fields is attained.
~efer~ing now to ~ig. S, a fDlded bar current sensor ~2 includes conductor bar 24 znd conductor bar 1~ 24' zs previously de cribed, An end tu-n ~4 joins adjacen~ ends o~ conductor b2rs 2~ znd 2~ whereby a cu~rent I flowing in one direction in conducto- bar 24 is identically matched by a current I flowing in the opposite direction in conductor bar 2~'. Aligned holes 26 ard 26' (hole 26' is hidden in thP figure) are disposed ~enerally centrally in conàuctor bz-s 24 znd 2~'. Fi-st and second connector lugs ~6 2nd ~8 provide for connection in a conventional manner to external circuits. A conductor b2r 5D joins connector lug 46 to a free end 52 of conduc'or bar 24. Similzrly, a conductor bzr 54 joins a free end 56 of conduc~or bar 24' to connec_or lug ~8.
In the p~efe~red e~bodiment, connec_o_ lugs 46 <
znd ~8 confo-m in all respects to the ind~st~y s~znd2rds fo~ cirect use in w2t'hou meters. That is, the sizes and sp2cing of connector lugs 46 and ~8 pe~m_t inst211ation of folded b2r cu_rent sensor ~2 within an elec~ric wat~hour mete-. The plane of conduc~or b2rs 24 2nd 2~' are rotated nor~al to the plzne o, cor.ne~~or luss 46 and 43 for convenience 2nd for ensurin~ the fit of folded b2r curren~ sensor within 2 s .andzrd w~,tmete~ housing. The twists .
. .
shown in conductor bars 50 and ~ permit such orientation. Some ins~211ations may permit the plane of c~nductor bzrs 24 and 2~' to lie parallel to that of connector lugs ~6 and ~8. In such installations, the illustrated twists would be omitted.
The physical sizes of conductor bars 24 and 2~' are selected large enough to position holes 26 and 26' fzr enough away from magnetic fields generated in end tu n ~4 and in conducto- bars 50 and 54 to avoid 10 substa,iPl influence of such magnetic fields. In addition, it is believed, without intending to be limited by any theo~, that the amount of flux in holes 26 and 26l is inversely proportional to the widths of conductor bars 2~ and 24'. ~hus, the wid~hs of conductor bars 24 and 24' may be selected on this basis~ A minim~m width dimension transverse to the direc~ion of current flDw may be required by the zmount of metal required to ca~ry the current I.
This ~mount o' met21 is dependent upon the diameters of holes 26 and 26' These dizmeters zre governed, in Lurn, by the sizes of pickup coils 32, 32'/ 34 and 3~'. Prac_ical coil-winding and pacXasing techniues a-e capable of reducing the outside diameter of ~
coil assem~ly to about 0.33 inch. In one embodiment, conductor ba_s 2~ and 24' have cimensions of 0.75 inch wid,h transverse to the direction of current and 1.25 in_h along the di~ection cc cu_-en. flow.
It is clso believed that the amount of magnetic IlUX passing through holes 26 and 26' depends on the wid~h of gap 39. A width of a~ou~ 0.05 inch appea_s to be satis'actory.
Re^e-rins now to Fls. 6, a coil assem~ly 58 is 17 ll-~E-l~0 shown suitable for use in the present invention A~ially aligned masne.ic co-es 60 and 6D' bear pic~up coils 34 and 34', ~espectively Similarly, a~ially aligned magnetic cores 62 and 62' bear pickup coils 32 and 32', respec'ively D-shaped insulating suppo t spacers 64, 66 and 68 are spaced along pickup coils 32 and 32' D-~haped insulating support spacers 70, 72 and 74 are spaced along pickup coils 3~ and 34' with the fla. parts o~ their D shapes facing co--esponding parts of D~shaped insulating suppor_ spacers 6~, 66 and 68, respectively An insulating tu~e 76 includes a circular opening 7~ into which the remainder o~ coil asse~ly 58 ~its snugly An outside diameter of insulating tube 76 fits snugly within hole 26 (Fi~ 5) Although only line 38 and line ~0 Pre shown emersing from coil assembly 5~, it is customary to pe~mit zll ~ight leads o_ pic~up coils 32, 32', 34 and 3~' to extend ou.wzrd from ends of coil assem~ly ~8 for making se-ial and jumper connections external to coil 2ssem~1y 58 Such an P_~angement is assumed but is no. illus-.rated in order to simplify the illustration and descrip.ion OI the invention Re~e~~ing again to Fig 5, I have discovered tha'~ a maximum ou.~u. sisn21 is generated when a plzne se?ara.ing pickup coils 32-32' 2nd pickup coils 3~-3~ ' is pa-2l lel .o a di-ec'ion o~ currert _low in conductor bars 2~ and 2~' As coil assembly 58 is ro,ated ~rom this pæ 211el rel2tisnship, the magnetic flux density in the vicini'y o' the pic~up coils is recuced and thus the output voltage is reduced This reduc.ion in induced ~ol'ages occu-s withou' 18 11-~E-180 noticeable phase e~ror. As the rot2tion of coil assembly 58 passes th ousn go des ees from the above parallel rela.ionship, t~e output passes th-ough a null and then reverses. Such rotation may be used as 2n adjustment fo- setting an ou.put of coil assembly 58 in response to a sLanda~d cu-rent I in conductor bz-s 2~ and 2~'.
The output vcltage of folded bar cu-rent senso~
~2 desc.ibed thus far is propo-tional to the time derivati~e of the cu-rent I passing the-ethrough.
The phase of this voltage is therefore ~isplaced 90 de~rees rela.ive to the cur_ent. Direct use of this ~oltaae in an electron~c watthour meter, such as shown at 22 in Fig. 1, reg~Lires a corrective phase 1~ displacement of 90 àes-ees in the voltage. Circuits for applying such correctiv~ phzse displacements are conventional znd thus do not require Curther attention.
In addition, due to the derivative na8ure of the vol~age signal, any harmonic com?onents of the curren~ I are zmplified in proportion to their harmonic numbe- and may le2d to substantial measurement e-ro.s.
Re e_.ing now to ~iS. 7, a cu~rent measu-ement 2~ system 80 is shown including means for solving the a~ove pro~lems and provi~ing a sisnal proportional to, and in phase wi'h, the cu~rent I. Combined output voltages of pickup coils 32, 32', 3~ 2nd 3~' a~e applied to the in?uts o. an o?erational ampllfier 82. The ou~?ut o, ope~a~ional am?lifier 82 is connected in se-ies through feedback windings 8~, 84', 86 and 86' to an inpu, Oc zn cut?ut ampli'ier ~8 ~ 19 ll-ME-180 .
having a feedbac~ resis~or 9o connected ~e'ween its input and output. Feedback windlngs 8~, 84', 86 and 86' are wound in opposition to pickup coils 32, 32', 34 and 34', respectively, whereby feedback currents produced ~y operational amplifier 82 tend to reduce the magnetic flux to which the cores are subjected.
Due to its high gain, the cu_-rent produced ~y operational amplifier 82 is su.ficient to d_ive the voltage across its inp~ts ve~y close to zero. In effect, this m2in' ains the magnetic flux in the cores nea- zero.
In order for the magnetic ~lux in the cores to be zer~, the ~agnetic flux resulting from the ampere tu-ns in the feedbzck windings ~ust be exactly equal to the magne'ic *lux produced by the current I.
Fur~hermore, this ecuality of flux must be obtained at any instant of time. Thus, t~e feedback current is an accurate represent2tion of the current I in both magnitude and phase~ Amplifier 88 con~er'.s the feedback current into an ~utput ~oltage ~o which is an accurate represen~atiDn of the current I (~ig. ~) p25 ~ coil assembly 5~.
In one embodiment of the invention, a s~rict one-to-one tu-ns rztio is main_zined between pickup 2~ coil 32 and its corresponding feedb2ck winding ~, as well 25 each of the other sets of measu-ement znd feedback windings. T~.is is conveniently achieved using bi-filzr winding technioues. The modification of the apparatus of ~ig. 7 permits achieving an appzratus having 2 plurzlity of ranges without reouiring substzntial increases in equipment complexity.
Referring now to Fig. ~, a duzl-~ange cu-rent measuremert system 92 is shown in which all of the measurement windings are illustrated as a sinsle measurement winding 94 and all of the feed~ack 5 windings are illustrated as a single fee~back winding 96. A tap 98 divides feedback winding 96 into part windings 100 and 102. Tap 98 is connected to a fixst te~.inal 104 of a switch 106. ~n end of pa-~ winding 102 is connected to a second te~minal 108 of switch 106. A movable terminal 110 of switch 106 is connected to the input of output amplifier 88.
The output voltage Vo produced by output ampli~ier 8~ for a given cur-ent I depends on the setting of switch 106. Such output voltage Yaries 1~ according to the turns ratio of pzrt winding 100 to feedback winding 96~ Thus, a fixed sensitivity ratio in two different c~rrent ranges is achieved.
~ aving described p_efe~red embodiments o' the irvention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embDdiments, and that various changes and modifications may be effec~ed the-ein by one skilled in the art without departing f-om the scope or spi-it Oc the inver._ion 2S defined in the zppended claims.
Conven~ional toroidal transformer cores do not provide sufficient room for this many turns in a de-.-ice of practical sizeO In.addition, such current transformers require a low value of burden resis'ance to function with adequate accuracy. A wincing with such a large number of tu-ns has an inherently high resistance, thus precluding operation with the re~uired accuracy.
The prior art contains several approaches for dividing a 102d current in order to produce a sample cur-ent or voltage proportional to the load cu_ren~.
A shunt techniue, disclosed in U.S. Patent Nos.
4,182,982 and ~,~92,919, splits the current in a conductor between a main shunt path and a parallel auxiliary path. The auxiliary path contains 2 much 2~ smaller cross section ~han does the m2in shunt path and cur~enl through the combination divides in su~st2n_ially the ratio o~ th~ cross sections.
magnetic core with 2 ~inding of many turns is disposed about the au~iliary path. The auxiliary pzth thus forms a one-turn primary and the many turns z~out it fo~m a seconda~y. A current through the secondary is proportion21 to the current in the 3 11-~E-180 primary divided by the nllmber of turns in the secondary. This technique suffers reduced accuracy from the substantial thermal coefficient of resistance of copper which may be as much as 3D
percen' over the environmental temperature range to which watthour meters are exposed. In addition, it is difficult to obtain a sufficient current divisicn to gi~e the four crders of masnitude reduction in output current compared to load current. Finally, this technique is subject to errors resulti~g from magnetic flux about the cu~rent-carrying conductor ma~ing up the shunt path.
A further technioue, disclosed in U.S. Patent No. 4,~96,932, employs two slits in 2 conductor to p.oduce a measurement conductor be'~ween a pair of shunt conductors. The measuremen~ conductor is deflected, first in one direction, and then in the other, to p-ovide space ~or the pzssage of a one turn 1002 f magnetic core ~ateri21 therethrough. In one em~odiment, the shunts and the measurement conductor a~e folded to 21isn holes in two hzlves thereof. The one-turn loop of magnetic core material is then passed t~._ough the aligned holes for receiving z szmp~e of lea~2ge current produced by the p~esence cf the slits znd the mPzsuremen~ conductor. A second2ry windins of m~ny tu-ns on the co-e locp p~ovides an ou~put. This devlce suffers from the presence of strong mzgnetic fields in its vicinity which are czpable o. saturzting the core 2nd thus int-oducing e--ors or cancelling its ou~put. In addition, no p-o~ision is ~-cvided fo~ cancelling the efSects of non-uniform m2snetic fields orisin2'ing ex.ernal to "
the measurement device, as are r~utinely experienced in wat~hour meters~
Other special problems are encountered in watthour meters. The extern21 conriguration, including the positions of connector blades, is established by rigid industry s~andards. Such industry stand2rds 21so require that crosst21k between adjacen~ phases be held to a very low leve:L.
'.
OBJ:ECTS AND SUMMARY t:)F THE INVr NTIC)N
It is an ~bject of the inven~ion to provide a current sensor which overcomes the drawbacks ~f the prior art.
It is a further object of the inven'ion to pro~ide a current 6ensor that does not require a current trans^ormer.
It is a further object of the invention to provide a current sensor having substantial immunity to external magnetic fields.
It is a still further objec~ of the invention to 2~ provide a cur~ent sensor having 2 plurality of windings, ~11 of the plurality of windings adding ~oltage produced by magnetic fields gene-ated by a current to be measured and subt_zcting voltage generated 2s the results of exte-nal masnetic fields.
It is a still further object of the invention to p-ovide a current sensor having at least first 2nd ;~ second windings on a core disp~sed in 21igned holes ~` in a folded, cu~rer.t-ca-r~ing ba~. The winding directions of the first and seccnd windings are ~ 3~
ll~ME-180 . .
opposite ~hereby current in the two parts of the folded bar add together to produce an ~utput.
It is a still further objec~ of the inven~ion to provide a current sensor having two magnetic cores each containing two, oppositely-wound, windings. The four windings on the two cores produce additi~e output as a result of magnetic ~ields generated by , current passing therepast through the bar bu. cancel ; the e~fects of external ma~netic fields.
It is a still further object of the invention to provide a current sensor employing at least one magnetic core disposed in aligned holes in a folded bar and a feed~ack winding f~o~ an active circuit ef~ecti~e to balance the mas~etic field genera~ed by - -the curren~ through the bar.
Brie,ly stated, the present invention provides a current sensor employing a folded conductor bar having aligned holes therein to generate magr.etic fluxes in the holes proportional to a cu-rent flowing in the bar. ~ach of the two holes has ~wo windings therein wound in opposition to each other but connected fo~ adding their currents. Corr sponding ~
wincinss in the two hc'es are wound in opposition to each o_he_ and are connected for adding their vol'ages. The windings in each hole are o~fset lrom a center line whereby magnetic fluxes generated by cu'rent flowing in the bar induce voltages in the coils but m2gnetic fluxes from exte~nal sources gene~a.e voltages which subs!antially cancel. A
feedback ar-zngement is disclosed for bzlancing the magnetic fluxes in the holes. A .,.ul i-~ange c1rrent meas~rement device em~loys a ta~ed feedb~c~ winding 3~5 6 11-~E-180 selectively connectable to an output am~lifier for producing an output current hzving a range set by the nu~'cer of turns selected on the tapped feedback winding Acco~~ing 'o an em~odiment Oc the invention, there is provided a current senscr for measuring a '-current, comprising a first conductor bar having a firs' ge~erally plan2r surface, a second conduc'or ba~ having a second generally planar sur~ace disposed parallel to the first generally planar surface, a predetermined g2p between the first and second generally planar su~faces, means for connecting adjacent first e~ds of ~he fi-st and second conductor b2rs, means for feeding the current to a second end of the fi~st conductor bar, mezns for receiving the current from a second end of the second conductor bar, a first hole gener211y cen.ered in the first conduc'o- bar and having a first axis substantially normal tD the fi~st gene~ally pl2nar surface, a second hole gene~211y centered in the second conductor bar and having a second a~is substantially no~mzl to the second gene_zlly planar surface, the fi-st and second zxes being collinea~, fi-st and second coils in ~he first hole, third and fou~th ~5 coils in the second hole, mezns for inte connecting the first, sec~nd, third and fou~th coils to produce zn ou_pu_ signal in response to magnetic fields in the firs' and second holes resulting f-om the current in he first and second conduc'cr the, bars first and second coils being wound to add voltages produced by magnetic fields within the fi-st hole and to cancel ~ol.ages produced by manetic fields o-iginating .g~f~ .4.V~
.
outside the first hole, the third znd fourth coils being wound to add voltages produced by magnetic fields within the ~econd hole and to cancel voltages produced by magnetic fields originating outside the second hole, the fi-st and third coils being wound to add voltages produced by magnetic fields within the first and second holes and to cancel voltages produced by magnetic fields orisin2~ing outside the first and second holes, and the second and fourth coils being wound tQ add voltages produced ~y magnetic fields within the first 2nd second holes and to cancel voltages p~oduced ~y masne~ic fields originating outside the firs~ and second holes, whe-eby substzn~ial i~munity to magnetic fields originating ex_ernal ~o the first and second holes is achieved According to a feature of the inven.ion, there is provided ~ coil assembly for a current sensor comprising: first and second collinear windings, the 20 first and second colline2r windings being connec.able in series and having a winding sense effective for c~ncelling voltages p-oduced by magnetic fields 2p~1 ied substanti211y ecually the_e.o, third and fourth collinear windinss, the third and four,h 2~ colline2r windings being conne~able in se-ies and having a winding sense effective for czncelling voltages produced ~y m2snetic fields zpplied su~stantially eoually thereto, means for disposing 2n 2xis of the first znd second collinear windings pzr211el tD an zxis Oc the third znd fourth colline2 windings wit~ the fi-s. 2nd third ~indings z~jacent each other znd the second 2nd four~h windings adjacent each other, the first, second, thi-d and fourth windings being connectable in series, the first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto, and the second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substan.ially eoually thereto.
Acco~ding to a further feature of ~he inven~ion, there is provided a method for measuring a current, comprising: forming a folded bar including a first conductor bar ha~ing a first gene-ally planar surface, disposing a second conducto~ bar having a ~ ~ 15 second gene~ally plzna- su-face parallel to the first :: ~ generally planar surface, spacing the first and second generally planz- sur~aces a predetermined dis,ance apart, connecting zdJacent first ends of the first znd second conductor b2rs, feeding the current 2C to a second end of the first conductor bar, receiving the cu-rent from a second end of the second conductor b2r, fo~ming a fi_st hole generally centered in the first conductor ~r and having a fi-st axis subs~2n~ially no~mal to the first generzlly planar 2~ surface, forming a second hole gener211y cen'ered in the second conductor bar and having 2 second axis substantially normal to the second generally planar ` ~ su-face, the first and second axes being collinear, disposing first and second coils in the firs, hole, disposing third znd four_h coils in the second hole, interconnec~ins the firs., seccnd, third and four~h coils to produce an outpu_ sisn21 in esponse to ~L~ 2 5 . .
magnetic fields in the first and second holes resulting from the cu_rent in the first and second conductor bars, winding the first and sPcond coils to add voltages produce~ by magnetic fields within the first hole and to cancel voltages produced ~y magnetic fields origin2.ing outside the fi-st hole, '-winding the third and fourth coils ~o add voltages produced by magnetic fields within ~he second hole and to cancel voltages produced by m2gnetic fields originating outside the second hole, winding the flrst and third coils to add volt2ges produced by masnetic fields within the first and second holes and to czncel voltages p~oduced by-magnetic fields origina~ing cutside the first and second holes, and winding the second znd fourth coils to add voltages produced by magnetic fields wi,hin the first and sec~nd holes and to c2ncel voltages produced by magnetic fields origina.ing outside the first and second holes, whereby su~stantial immu~ity to magnetic fields origina'ing exte_nal to the firs, 2nd second holes is achieved.
- The a~ove, and o~her objec~s, fea~ures and advan~ages o the present invention will become app2rent from the following d~scription read in conjunction wi~h the ac~ompanying d-awings, in which like reference numer21s designate the same elements.
BRIEF DESCRIPTION OF TX~ DRAWING~
Fig. 1 is a simplified schema.ic diagram of an elect_ic meter ~howing a current senso- according to 10 ll~E-l~O
p-ior ~rt.
Fig. 2 is a pe~spective view of a conductor bar to which reference will be made in describing the principle of operation of the present inventicnO
Fig. 3 is a cross sec~ion ta~en along III-III in Fig. 2.
Fig. 4 is a cross section corresponding to ~is.
3 excep. including two conductor bars and two pai-s of sensing windings.
Fig. 5 is a perspective view of a folded bar current sensor acco~ding to an en~odiment of the invention.
Fig. 6 is 2 perspective view o~ a coil assembly of ~ig. ~. -Fig. 7 is a schematic diag,am of a current measurement system according to an em~odiment of the inven~ion.
Pis. 8 is a si~.~lified schem2tic dias_am of a dual-range current measurement system according to an ~- 20 em~odiment of the invention.
: ' DETAIL~D DESCRIPTION OF T:-'~ PR~PRED ~MBODIM~T
A current sensor accorcing to the present inven~ion m~y be employed for me2suring a curren! in a conductor associaLed with any type of electric21 2~ eouipment. For concreteness, 2 cu--ent sensor in acco-dznce wi.h an e~bodiment of the invention is disclosed in t~e envi-onmen~ OL an electronic w2t.h.0ur mete_. This envi_onmer._ is chosen at le2s~ -pa-ly because pro~lems of meas~ement accuracy, and the ~is.u,bance thereof from external masnetic fields, are more severP than in most other environments.
Also, although the current sensor of the present invention is considered to be especially useful in measuring currents flowing in each of a plurality of ~`
phases of a poly-phase electronic watthour meter, :it is considered that its desc-iption in the environment of a single-phase electronic wa~thour meter avoids unnecessary functional duplication and therefore zids in understanding the invention. Thus, measurement of cu~~en~ in a single-phzse electrcnic wattmeter is described in detail.
Refer~ing now to ~ig. 1, there is shown, generally at 10, a current sensor of the prior art which produces a voltage proportional to a current being fed on an AC line 12 to a load (not shown). A
cur-ent transformer 14 includes a prima~y winding 16 in series with one conduc~o~ o AC line 12. A
second2ry winding 1~ hzs a current therein proportional to the AC cu_rent in primzry winding 16.
The cu~~ent in secondzry windin~ 18 passes th ough a resisto- 20 to develop a voltage thereacross p_oportional to the secondz~y cu_rent. The voltzge is 2p?1ied to inputs of an electronic watthour me~e_ 22. A vol!age ac~oss AC line 12 is connected to elect_onic watthour me.er 22, wherein an electronic multiplication process determines 2n instantaneous vzlue of wat.s consumed by the 102d. A conventional integrating àevice (not shown) in elec~ronic watthou-meter 22 in eg~ates t~.e consumed wzt's t- de-ive the ene~~y consumed.
Electronic watthour meter 22 may be of zny convenient type such as, for example, an electronic watthour meter according to the teaching of U.S.
Patent No. 3,947,763, of common assignee with the present in~en,ion. Such electronic devices require signals proportion21 to load current at values as much as five orders of magnitude smalle_ than the load cu-rent itself. This is difficult to attain in 2 p~ac,ical current tr2nsfo~mer 14. In addition, the need for a cu~-ent transformer 14 adds to ~he over211 cost of the equipment 2nd elimination o- this element is therefore considered desirable.
Referring now to ~ig. 2, there is shown a conductor b2r 24 having an electric current I flowing ,here,~.rough. A hole 26, bored through conductor bzr 2~, sepzrates current I into separ2te cu_rent~ I1 znd I2 on either side of hole 26. Current Il produces a magnetic flux 28 which, in conventional notation, is indicated as flowing into the top of hole 26.
Current I2 produc2s z magnetic flux 30 which, in con~entional notation, is shown flowi~g ou' of the top of hole 26.
Fig. 3 shows a cross sec_ion of conduc~or bar ~ ;
through hole 26 2nd t~znsverse to the direction of cu~rent 1. Magnetic fluY.es 28 and 30 oppose each o,he~ and, if eau21, would cancel ezch o.her along zn zxi5 of hole 26. Conductor bz- 2~ znd hole 26, zlong with first znd second pic};up coils 32 znd 3~ form a cu_rent senso~ 31 zcco-ding ~o 2n em~odiment of the inven'ion. First pickup coil 32 is disposed zlong zn zxis A-A, displaced f~om an zxis of hole 26. Thus, it is inrluenced mo~e by m2snetic flux 3~ znd less by .
magnetic ~lux 28 and a voltase is induced in pic}up :' coil 32 by an AC current in conduc-or ~zr 24. If only a single pickup coil 32 were employed in hole 26, it would be fully responsive to external magne,ic fields. To compensate zt le~st partly for such external magnetic fields, second pickup coil 34 i~
disposed on an z~is A'-A', displaced in the opp~site direc ion from the axis of hole 26. It also has a voltage induced therein. A connec~ion 36 joins one end of pickup coils 32 and 3~. Pickup coils 32 and 34 are wound in opposite direc'ions whereby their voltages, induced by masnetic fluxes 28 and 30~ add togeiher.
The opposite windiny directions of pic};up coi7s 32 and 34 tend to c2ncel the ef~ects of those external magnetic fields which affect them eoually.
This cancellation is more effective as pickup coils 32 and 3~ are brought closer together. Some external masnetic fields may not be oriented to affect pickup coils 32 and 34 equally. In such an event, the voltzges generated in pickup coils 32 and 34 by such ~zgnetic fields do not cancel and inaccuracies in the relationship ~etween output current znd cu-rent I m~y exist. In non-crl .ic21 applicztions, or those in which external masnetic fields zre 5m211, this e~od ment may be czpable of providing suf~icient accuracy.
Since cnly a smzll zmount of flux is induced to enter and leave hole 26, z slbs'zn.izl ratio i5 found be.ween the current lowing in conducto_ bar 2~ and the volt2se across pickup coils 32 and 34. The resulti~s output vcltzge of pickup coils 32 and 3~, ~ 35~3~5 fed on lines 38 and ~0 to e~ternal circuits, may be of a low enough level for direct feedlng to the inpu~
of an electronic watLhour meter without requiring an intermediate current transfD~mer. In this manner, the overall system, inclu~ ~g the electronic watthour meter~ is of reduced complexity and cost. Indeed, such a current ~ensor may be mad~ small enough for inclusion within the housing of a conven'ional electronic watthour ~e.er whcse dimer.sions 2_ e governed by indust~y standards.
~ eferring now to Fis. 4, a cur_en~ senso~ 31' employs a folded concigl~ra~ion in which con~uctor b2r 24 is paralleled by a conductor bar 24' carrying the same urrent I, but in the opposite direction as indicated by conventional indicators of cur-ent Girec.ion. A gap 39 is formed be~ween facing surfaces of conductor bars 24 and 24'. Conductor bar 2~' includes a hole 26' aligned with hole 26 in c~nductor bar 24. A pickup coil 32' in hole 26' is axially ali~ned with pickup coil 32 in hole 26, but is oppositely wound there_~om. As indicated by the direc~ion of masnetic flux 30' in~luencing pickup co~l 32', cur-ents in conductor bz- 24' and conducto-ba_ 2~ add as voltages 2re induced in pickup coils 32 2~ znd 32'. Simila~ly, a pi_kup coil 34' is disposed in hole 26' a~izlly aligned with pic~up coil 34 in hole 26 but opposi~ely wound 'heref-om. I~ will be reco~nized that voltages in pickup coil 34 and pickup coil 34' produced by cu--ent I in conduc.or bzr 24 and conductor bar 24' add togethe-. Connec'ion 36 joins one end of pickup coils 32' ~nd 34' whereby co.~ined voltages from 211 four picku~ coils a_e .
~pplied to lines 38 and ~0.
The presence of oppositely wound pic~up coils 32' and 3~' in hole 2~' cancels voltages produced by e~ternal magnetic fields which affect them equally, in the same ~,znner as the.ir counte~parts in hole 26.
Thus, substantially comple~e cancellation of influences of e~ternal masne~ic fields is attained.
~efer~ing now to ~ig. S, a fDlded bar current sensor ~2 includes conductor bar 24 znd conductor bar 1~ 24' zs previously de cribed, An end tu-n ~4 joins adjacen~ ends o~ conductor b2rs 2~ znd 2~ whereby a cu~rent I flowing in one direction in conducto- bar 24 is identically matched by a current I flowing in the opposite direction in conductor bar 2~'. Aligned holes 26 ard 26' (hole 26' is hidden in thP figure) are disposed ~enerally centrally in conàuctor bz-s 24 znd 2~'. Fi-st and second connector lugs ~6 2nd ~8 provide for connection in a conventional manner to external circuits. A conductor b2r 5D joins connector lug 46 to a free end 52 of conduc'or bar 24. Similzrly, a conductor bzr 54 joins a free end 56 of conduc~or bar 24' to connec_or lug ~8.
In the p~efe~red e~bodiment, connec_o_ lugs 46 <
znd ~8 confo-m in all respects to the ind~st~y s~znd2rds fo~ cirect use in w2t'hou meters. That is, the sizes and sp2cing of connector lugs 46 and ~8 pe~m_t inst211ation of folded b2r cu_rent sensor ~2 within an elec~ric wat~hour mete-. The plane of conduc~or b2rs 24 2nd 2~' are rotated nor~al to the plzne o, cor.ne~~or luss 46 and 43 for convenience 2nd for ensurin~ the fit of folded b2r curren~ sensor within 2 s .andzrd w~,tmete~ housing. The twists .
. .
shown in conductor bars 50 and ~ permit such orientation. Some ins~211ations may permit the plane of c~nductor bzrs 24 and 2~' to lie parallel to that of connector lugs ~6 and ~8. In such installations, the illustrated twists would be omitted.
The physical sizes of conductor bars 24 and 2~' are selected large enough to position holes 26 and 26' fzr enough away from magnetic fields generated in end tu n ~4 and in conducto- bars 50 and 54 to avoid 10 substa,iPl influence of such magnetic fields. In addition, it is believed, without intending to be limited by any theo~, that the amount of flux in holes 26 and 26l is inversely proportional to the widths of conductor bars 2~ and 24'. ~hus, the wid~hs of conductor bars 24 and 24' may be selected on this basis~ A minim~m width dimension transverse to the direc~ion of current flDw may be required by the zmount of metal required to ca~ry the current I.
This ~mount o' met21 is dependent upon the diameters of holes 26 and 26' These dizmeters zre governed, in Lurn, by the sizes of pickup coils 32, 32'/ 34 and 3~'. Prac_ical coil-winding and pacXasing techniues a-e capable of reducing the outside diameter of ~
coil assem~ly to about 0.33 inch. In one embodiment, conductor ba_s 2~ and 24' have cimensions of 0.75 inch wid,h transverse to the direction of current and 1.25 in_h along the di~ection cc cu_-en. flow.
It is clso believed that the amount of magnetic IlUX passing through holes 26 and 26' depends on the wid~h of gap 39. A width of a~ou~ 0.05 inch appea_s to be satis'actory.
Re^e-rins now to Fls. 6, a coil assem~ly 58 is 17 ll-~E-l~0 shown suitable for use in the present invention A~ially aligned masne.ic co-es 60 and 6D' bear pic~up coils 34 and 34', ~espectively Similarly, a~ially aligned magnetic cores 62 and 62' bear pickup coils 32 and 32', respec'ively D-shaped insulating suppo t spacers 64, 66 and 68 are spaced along pickup coils 32 and 32' D-~haped insulating support spacers 70, 72 and 74 are spaced along pickup coils 3~ and 34' with the fla. parts o~ their D shapes facing co--esponding parts of D~shaped insulating suppor_ spacers 6~, 66 and 68, respectively An insulating tu~e 76 includes a circular opening 7~ into which the remainder o~ coil asse~ly 58 ~its snugly An outside diameter of insulating tube 76 fits snugly within hole 26 (Fi~ 5) Although only line 38 and line ~0 Pre shown emersing from coil assembly 5~, it is customary to pe~mit zll ~ight leads o_ pic~up coils 32, 32', 34 and 3~' to extend ou.wzrd from ends of coil assem~ly ~8 for making se-ial and jumper connections external to coil 2ssem~1y 58 Such an P_~angement is assumed but is no. illus-.rated in order to simplify the illustration and descrip.ion OI the invention Re~e~~ing again to Fig 5, I have discovered tha'~ a maximum ou.~u. sisn21 is generated when a plzne se?ara.ing pickup coils 32-32' 2nd pickup coils 3~-3~ ' is pa-2l lel .o a di-ec'ion o~ currert _low in conductor bars 2~ and 2~' As coil assembly 58 is ro,ated ~rom this pæ 211el rel2tisnship, the magnetic flux density in the vicini'y o' the pic~up coils is recuced and thus the output voltage is reduced This reduc.ion in induced ~ol'ages occu-s withou' 18 11-~E-180 noticeable phase e~ror. As the rot2tion of coil assembly 58 passes th ousn go des ees from the above parallel rela.ionship, t~e output passes th-ough a null and then reverses. Such rotation may be used as 2n adjustment fo- setting an ou.put of coil assembly 58 in response to a sLanda~d cu-rent I in conductor bz-s 2~ and 2~'.
The output vcltage of folded bar cu-rent senso~
~2 desc.ibed thus far is propo-tional to the time derivati~e of the cu-rent I passing the-ethrough.
The phase of this voltage is therefore ~isplaced 90 de~rees rela.ive to the cur_ent. Direct use of this ~oltaae in an electron~c watthour meter, such as shown at 22 in Fig. 1, reg~Lires a corrective phase 1~ displacement of 90 àes-ees in the voltage. Circuits for applying such correctiv~ phzse displacements are conventional znd thus do not require Curther attention.
In addition, due to the derivative na8ure of the vol~age signal, any harmonic com?onents of the curren~ I are zmplified in proportion to their harmonic numbe- and may le2d to substantial measurement e-ro.s.
Re e_.ing now to ~iS. 7, a cu~rent measu-ement 2~ system 80 is shown including means for solving the a~ove pro~lems and provi~ing a sisnal proportional to, and in phase wi'h, the cu~rent I. Combined output voltages of pickup coils 32, 32', 3~ 2nd 3~' a~e applied to the in?uts o. an o?erational ampllfier 82. The ou~?ut o, ope~a~ional am?lifier 82 is connected in se-ies through feedback windings 8~, 84', 86 and 86' to an inpu, Oc zn cut?ut ampli'ier ~8 ~ 19 ll-ME-180 .
having a feedbac~ resis~or 9o connected ~e'ween its input and output. Feedback windlngs 8~, 84', 86 and 86' are wound in opposition to pickup coils 32, 32', 34 and 34', respectively, whereby feedback currents produced ~y operational amplifier 82 tend to reduce the magnetic flux to which the cores are subjected.
Due to its high gain, the cu_-rent produced ~y operational amplifier 82 is su.ficient to d_ive the voltage across its inp~ts ve~y close to zero. In effect, this m2in' ains the magnetic flux in the cores nea- zero.
In order for the magnetic ~lux in the cores to be zer~, the ~agnetic flux resulting from the ampere tu-ns in the feedbzck windings ~ust be exactly equal to the magne'ic *lux produced by the current I.
Fur~hermore, this ecuality of flux must be obtained at any instant of time. Thus, t~e feedback current is an accurate represent2tion of the current I in both magnitude and phase~ Amplifier 88 con~er'.s the feedback current into an ~utput ~oltage ~o which is an accurate represen~atiDn of the current I (~ig. ~) p25 ~ coil assembly 5~.
In one embodiment of the invention, a s~rict one-to-one tu-ns rztio is main_zined between pickup 2~ coil 32 and its corresponding feedb2ck winding ~, as well 25 each of the other sets of measu-ement znd feedback windings. T~.is is conveniently achieved using bi-filzr winding technioues. The modification of the apparatus of ~ig. 7 permits achieving an appzratus having 2 plurzlity of ranges without reouiring substzntial increases in equipment complexity.
Referring now to Fig. ~, a duzl-~ange cu-rent measuremert system 92 is shown in which all of the measurement windings are illustrated as a sinsle measurement winding 94 and all of the feed~ack 5 windings are illustrated as a single fee~back winding 96. A tap 98 divides feedback winding 96 into part windings 100 and 102. Tap 98 is connected to a fixst te~.inal 104 of a switch 106. ~n end of pa-~ winding 102 is connected to a second te~minal 108 of switch 106. A movable terminal 110 of switch 106 is connected to the input of output amplifier 88.
The output voltage Vo produced by output ampli~ier 8~ for a given cur-ent I depends on the setting of switch 106. Such output voltage Yaries 1~ according to the turns ratio of pzrt winding 100 to feedback winding 96~ Thus, a fixed sensitivity ratio in two different c~rrent ranges is achieved.
~ aving described p_efe~red embodiments o' the irvention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embDdiments, and that various changes and modifications may be effec~ed the-ein by one skilled in the art without departing f-om the scope or spi-it Oc the inver._ion 2S defined in the zppended claims.
Claims (11)
1. A current sensor for measuring a current, comprising:
a first conductor bar having a first generally planar surface;
a second conductor bar having a second generally planar surface disposed parallel to said first generally planar surface;
a predetermined gap between said first and second generally planar surfaces;
means for connecting adjacent first ends of said first and second conductor bars;
means for feeding said current to a second end of said first conductor bar;
means for receiving said current from a second end of said second conductor bar;
a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
a second hole generally centered in said second conductor bar and having a second axis substantially normal to said second generally planar surface;
said first and second axes being collinear;
first and second coils in said first hole;
third and fourth coils in said second hole;
means for interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
said first and second coils being wound to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
said third and fourth coils being wound to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
said first and third coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes; and said second and fourth coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved.
a first conductor bar having a first generally planar surface;
a second conductor bar having a second generally planar surface disposed parallel to said first generally planar surface;
a predetermined gap between said first and second generally planar surfaces;
means for connecting adjacent first ends of said first and second conductor bars;
means for feeding said current to a second end of said first conductor bar;
means for receiving said current from a second end of said second conductor bar;
a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
a second hole generally centered in said second conductor bar and having a second axis substantially normal to said second generally planar surface;
said first and second axes being collinear;
first and second coils in said first hole;
third and fourth coils in said second hole;
means for interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
said first and second coils being wound to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
said third and fourth coils being wound to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
said first and third coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes; and said second and fourth coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved.
2. A current sensor according to claim 1, further comprising:
said first, second, third and fourth coils having cores of magnetic material;
at least one feedback coil;
means for feeding a current through said at least one feedback coil; and said current having an amplitude and a sense effective for cancelling a net magnetic field applied to said magnetic material, whereby substantially zero flux is maintained in said magnetic material.
said first, second, third and fourth coils having cores of magnetic material;
at least one feedback coil;
means for feeding a current through said at least one feedback coil; and said current having an amplitude and a sense effective for cancelling a net magnetic field applied to said magnetic material, whereby substantially zero flux is maintained in said magnetic material.
3. A current sensor according to claim 2, further comprising an operational amplifier responsive to said feedback current for producing an output voltage having an amplitude proportional to said feedback current and a phase substantially equal to a phase of said feedback current.
4. A current sensor according to claim 2 wherein said means for feeding a current includes:
an operational amplifier;
means for feeding said output signal to first and second inputs of said operational amplifier;
and means for feeding an output of said operational amplifier through said at least one feedback coil.
an operational amplifier;
means for feeding said output signal to first and second inputs of said operational amplifier;
and means for feeding an output of said operational amplifier through said at least one feedback coil.
5. A current sensor according to claim 3, wherein:
said at least one feedback coil includes at least first and second portions having first and second numbers of turns;
said first and second numbers being different; and means for selectively employing one of said at least first and second portions, whereby an output voltage is scaled according to said first and second numbers.
said at least one feedback coil includes at least first and second portions having first and second numbers of turns;
said first and second numbers being different; and means for selectively employing one of said at least first and second portions, whereby an output voltage is scaled according to said first and second numbers.
6. A current sensor according to claim 5, wherein said means for selectively employing includes a switch.
7. A current sensor for measuring a current, comprising:
a first conductor bar having a first generally planar surface;
a second conductor bar having a second generally planar surface disposed parallel to said first generally planar surface;
a predetermined gap between said first and second generally planar surfaces;
means for connecting adjacent first ends of Claim 7 continued:
said first and second conductor bars;
means for feeding said current to a second end of said first conductor bar;
means for receiving said current from a second end of said second conductor bar;
a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
a second hole generally centered in said second conductor bar and having a second axis substantially normal to said second generally planar surface;
said first and second axes being collinear;
first and second coils in said first hole;
third and fourth coils in said second hole;
means for interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
said first and second coils being wound to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
said third and fourth coils being wound to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
said first and third coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes;
said second and fourth coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved;
said first, second, third and fourth coil shaving cores of magnetic material;
at least one feedback coil;
means for feeding a current through said at least one feedback coil;
said current having an amplitude and a sense effective for cancelling a net magnetic field applied to said magnetic material, whereby substantially zero flux is maintained in said magnetic material;
said means for feeding a current includes an operational amplifier;
means for feeding said output signal to said operational amplifier;
means for feeding an output of said operational amplifier through said at least one feedback coil;
an output amplifier having a first input connected to said at least one feedback coil;
a feedback element connected between an input and an output of said output amplifier; and means for connecting a reference voltage to a second input of said output amplifier, whereby said output amplifier is effective for produciny an output voltage proportional to said current.
a first conductor bar having a first generally planar surface;
a second conductor bar having a second generally planar surface disposed parallel to said first generally planar surface;
a predetermined gap between said first and second generally planar surfaces;
means for connecting adjacent first ends of Claim 7 continued:
said first and second conductor bars;
means for feeding said current to a second end of said first conductor bar;
means for receiving said current from a second end of said second conductor bar;
a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
a second hole generally centered in said second conductor bar and having a second axis substantially normal to said second generally planar surface;
said first and second axes being collinear;
first and second coils in said first hole;
third and fourth coils in said second hole;
means for interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
said first and second coils being wound to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
said third and fourth coils being wound to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
said first and third coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes;
said second and fourth coils being wound to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved;
said first, second, third and fourth coil shaving cores of magnetic material;
at least one feedback coil;
means for feeding a current through said at least one feedback coil;
said current having an amplitude and a sense effective for cancelling a net magnetic field applied to said magnetic material, whereby substantially zero flux is maintained in said magnetic material;
said means for feeding a current includes an operational amplifier;
means for feeding said output signal to said operational amplifier;
means for feeding an output of said operational amplifier through said at least one feedback coil;
an output amplifier having a first input connected to said at least one feedback coil;
a feedback element connected between an input and an output of said output amplifier; and means for connecting a reference voltage to a second input of said output amplifier, whereby said output amplifier is effective for produciny an output voltage proportional to said current.
8. A coil assembly for a current sensor comprising:
first and second collinear windings having collinear axes;
said first and second collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
third and fourth collinear windings having collinear axes;
said third and fourth collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
means for disposing said axes of said first and second collinear windings parallel to said axes of said third and fourth collinear windings with said first and third windings adjacent each other and said second and fourth windings adjacent each other;
said first, second, third and fourth windings being connectable in series;
said first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto: and said second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto.
first and second collinear windings having collinear axes;
said first and second collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
third and fourth collinear windings having collinear axes;
said third and fourth collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
means for disposing said axes of said first and second collinear windings parallel to said axes of said third and fourth collinear windings with said first and third windings adjacent each other and said second and fourth windings adjacent each other;
said first, second, third and fourth windings being connectable in series;
said first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto: and said second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto.
9. A coil assembly for a current sensor comprising:
first and second collinear windings;
said first and second collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
third and fourth collinear windings;
said third and fourth collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
means for disposing an axis of said first and second collinear windings parallel to an axis of said third and fourth collinear windings with said first and third windings adjacent each other and said second and fourth windings adjacent each other;
said first, second, third and fourth windings being connectable in series;
said first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
said second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
at least first and second spacers on said first and second collinear windings;
at least third and fourth spacers on said third and fourth collinear windings;
first and third mutually contacting surfaces on said first and third spacers, and second and fourth mutually contacting surfaces on said second and fourth spacers, whereby axes of said first and second and said third and fourth collinear windings are retained in a predetermined relationship.
first and second collinear windings;
said first and second collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
third and fourth collinear windings;
said third and fourth collinear windings being connectable in series and having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
means for disposing an axis of said first and second collinear windings parallel to an axis of said third and fourth collinear windings with said first and third windings adjacent each other and said second and fourth windings adjacent each other;
said first, second, third and fourth windings being connectable in series;
said first and third windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
said second and fourth windings having a winding sense effective for cancelling voltages produced by magnetic fields applied substantially equally thereto;
at least first and second spacers on said first and second collinear windings;
at least third and fourth spacers on said third and fourth collinear windings;
first and third mutually contacting surfaces on said first and third spacers, and second and fourth mutually contacting surfaces on said second and fourth spacers, whereby axes of said first and second and said third and fourth collinear windings are retained in a predetermined relationship.
10. A coil assembly according to claim 9 wherein said coil assembly further comprises:
a tube;
said tube having a circular opening coaxial therewith;
said at least first, second, third and fourth spacers having an external surface fittable into said circular opening whereby said coil assembly is assembleable into a single unit.
a tube;
said tube having a circular opening coaxial therewith;
said at least first, second, third and fourth spacers having an external surface fittable into said circular opening whereby said coil assembly is assembleable into a single unit.
11. A method for measuring a current, comprising:
forming a folded bar including a first conductor bar having a first generally planar surface;
disposing a second conductor bar having a second generally planar surface parallel to said first generally planar surface;
spacing said first and second generally planar surfaces a predetermined distance apart;
connecting adjacent first ends of said first and second conductor bars;
feeding said current to a second end of said first conductor bar;
receiving said current from a second end of said second conductor bar;
forming a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
forming a second hole generally centered in said second conductor bar and having a second axis substantially normally to said second generally planar surface;
said first and second axes being collinear;
disposing first and second coils in said first hole;
disposing third and fourth coils in said second hole;
interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
Claim 11 continued:
winding said first and second coils to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
winding said third and fourth coils to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
winding said first and third coils to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes; and winding said second and fourth coils to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved.
forming a folded bar including a first conductor bar having a first generally planar surface;
disposing a second conductor bar having a second generally planar surface parallel to said first generally planar surface;
spacing said first and second generally planar surfaces a predetermined distance apart;
connecting adjacent first ends of said first and second conductor bars;
feeding said current to a second end of said first conductor bar;
receiving said current from a second end of said second conductor bar;
forming a first hole generally centered in said first conductor bar and having a first axis substantially normal to said first generally planar surface;
forming a second hole generally centered in said second conductor bar and having a second axis substantially normally to said second generally planar surface;
said first and second axes being collinear;
disposing first and second coils in said first hole;
disposing third and fourth coils in said second hole;
interconnecting said first, second, third and fourth coils to produce an output signal in response to magnetic fields in said first and second holes resulting from said current in said first and second conductor bars;
Claim 11 continued:
winding said first and second coils to add voltages produced by magnetic fields within said first hole and to cancel voltages produced by magnetic fields originating outside said first hole;
winding said third and fourth coils to add voltages produced by magnetic fields within said second hole and to cancel voltages produced by magnetic fields originating outside said second hole;
winding said first and third coils to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes; and winding said second and fourth coils to add voltages produced by magnetic fields within said first and second holes and to cancel voltages produced by magnetic fields originating outside said first and second holes, whereby substantial immunity to magnetic fields originating external to said first and second holes is achieved.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000561728A CA1285025C (en) | 1988-03-17 | 1988-03-17 | Folded bar current sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000561728A CA1285025C (en) | 1988-03-17 | 1988-03-17 | Folded bar current sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1285025C true CA1285025C (en) | 1991-06-18 |
Family
ID=4137659
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000561728A Expired - Fee Related CA1285025C (en) | 1988-03-17 | 1988-03-17 | Folded bar current sensor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1285025C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109148132A (en) * | 2018-08-04 | 2019-01-04 | 安徽华能集团电器有限公司 | A kind of folding mutual inductor |
-
1988
- 1988-03-17 CA CA000561728A patent/CA1285025C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109148132A (en) * | 2018-08-04 | 2019-01-04 | 安徽华能集团电器有限公司 | A kind of folding mutual inductor |
| CN109148132B (en) * | 2018-08-04 | 2023-11-17 | 安徽华能集团电器有限公司 | Foldable transformer |
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