CA2261191A1 - Method, device and sensor for capacitive detecting of field and voltage and use thereof - Google Patents
Method, device and sensor for capacitive detecting of field and voltage and use thereof Download PDFInfo
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- CA2261191A1 CA2261191A1 CA 2261191 CA2261191A CA2261191A1 CA 2261191 A1 CA2261191 A1 CA 2261191A1 CA 2261191 CA2261191 CA 2261191 CA 2261191 A CA2261191 A CA 2261191A CA 2261191 A1 CA2261191 A1 CA 2261191A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/16—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using capacitive devices
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Abstract
A measuring device (10) for measuring voltage in a high-voltage part (22) surrounded by an electric field comprises a capacitive sensor (11) and a signal converter (13). The sensor includes an inner electrode (12) with a surrounding screen electrode (14). In the screen electrode, which is connected to a controllable reference potential, an opening (16) is provided which, during measurement, is directed towards the high-voltage part (22). By sensing a directed part of the electric field penetrating through the opening of the screen electrode into the inner electrode, the voltage of the high-voltage part (22) is measured at insulation distance.
Description
IOD, DEVICE AND SENSOR FOR CAPAClTlVE D~ G OF l;lELD AND VOLTAGE
AND USE THEREOF
TECHNICAL FI~LD
The present in~ention relate~ to a capacitive sensor for sen~ing VariationB in an electric field. The in~ention ai~o relate~ to a measuring de~ice includ~ ng such a ~en~or for measuring voltage at a di~tance from ~igh-vol~age conduc-tors, and to a method for such measurement. The other quantities which are detected by the measurin~ device are transients and ionic discharge. The measuring device i~
partlcularly adapted to measure volta0e in electric power network~, w~ich may comprise one or more pha~es, for control of transmiscion or di~tribution of electric power, or as a ba~is ~or de~iti~g of con~umed energy.
BACKGRO~nND ART
There is often a need of mea~uring the voltage o~ a high-~olt~ge line at a dlstance. This may, for example, be in connection with dis.ribution of el~ctric power with several conductors, where particularly the voltage of one of the conductors i~ to be determined. Su~h voltage measurement is uLed for control of a voltage drop along the distribution chain or for controll~ng that limit values are not exceeded, It may also be a question of calcu}ating the electric ener~y pas6i~s, ba6ed on the measured voltage. In both ca~e~ there i~ a great need of a simple and inexpensive mea~uring device, which i~ flexible and ~ith the aid of which it i~
economically pos~ible to achieve a den5ification of the number of measuring point~ in ~ di~tribution network.
The detectors and mea6uring devices which are currently availa~le are co~tly and com~licated devices which mu~t often be ~rou~ht into ~ontac~ ~ith the ~igh-voltage line, for example a voltage transformer. These 501ution6 entail con~iderable in~restments and therefore imply a great de~artur~ ~rom the lo~7 invectment and flexibility which i8 desira~le.
W O g8/0S974 ~ i/01289 From EP-Bl-~ 181 054, an apparatu~ ~or measurin~ the potential difference betwe0n ground and a power co~ductor, pla~ed above the ground, is previou61y known. The app~atus show~ is intended to be ~ounted on the conductor and generally ha~ ~n~l Ar sha~e. One lim~tation with this apparatus is that it has to be applied onto the conductor, which, ln addition to a great investment co~t, also in~ol~e~
operational distur~ances.
1'0 In an article by P. Sarma Maruvada, R-D. Dallaire and R.
Pedneault, ~Development of field-mill ~n~truments for ground-le~el and,a~ove-ground level elect~ic mea~urement under HVDC transmission lines", IEEE Tran~action~ on Power Apparatus and Systems, Vol. PAS-102, No. 3, pp. 738-744, ~arch 1983, there is shown a device, popularly named "field rnill~ for m~asuring, ae ~round level, an electric field under a high-~roltage conductor. The device comprise~
essentially an electrode, fixed to ground potential, in the form of a cylindrical box with, for example, six sector-s~p~ openings on the upper side thereof, and a rotatin~electrode inside the box but electrlcally insulated from the same. The rotatir~g electrode comprise~ BiX identical lobes formed as a ~ernoulli lemniscate, arranged uni~or~ly around a clrele. The device may be u5ed either at the same level a~
ground-le~el by placing it in a hole dug in the ~round, co~ered wlth a metal-protective plate with an op~i n~ ~or the device. ~he device may also be placed so a~ to project a~ove the ground.
The above-mentinned article al~o ~hows a device for mea~urement above ground level of the electric field under a high-voltage conductor. T~e device comprise~ two metal cylinders, each being di~ided length~i5e into two halves inbul~ted from each other. The cylinder8 hav~ equal or different radii, but different l~ngths- The cylinders rotate at dlfferent speeds and fro~ a mechanica~ point of view it is desirable that the cylinder~ rotate i~ direc~ion~
opposiee to each other.
One problem with the devices described above is that both are sensiti~e to disturbins electri~ fields, which therefore may greatly distort the measurement re,~ult. Another proble~
is that both have a relatively complicated de~ign From US-4,328,46l, an apparatu8 ~or measuring electric fields is ~reviously known. The ta~k of the apparatus is to investigate electrical characterigtics in the atmosphere . during a th~n~Rrstorm. The apparatus is shown in three different en~hoAim~nt:3~ itB ba~ic design comprisinç~ two hemispherical electrodes, between which a devi~e for measuring and generatin~ mea~ured data i~ enclosed. In ~
second ~mh~im~nt~ the mea6uring electrode~ are in the ~orm of two circul~r metal plates, whereby the a~6ociated measurement electronics is arranged be~ween the ~lates and thus at lea~t partly ~reened ~hereby. In a thi~d ~mho~;_ ment, the measuring electrodes are in the form of two ~emi-cylindrical electrodes, insulated from each other, where the electronics, in the ~ame way as above, is located between the electrodes.
The known device for measuring electric fields in ca~e of a stroke of lightning has a certain directional sensitivity becaus~ of it~ twO uniform plates. ~iowever, it is not capable of screening undesired electric ~ields and ~
there~ore not useful in the application sought, where the elec~ric field generated by only one o~ several high-~olta~e part3 i~ to be measured.
SUMMARY OF THE INV~TIO~
The object o~ the prese~t invention is to achieve a measurin~ device, by which may be measured the vDltage in a high-voltage part in an electric power system, which 35 high-voltage part i~ selected from a plurality of ~uch parts and is located at a di~tance. The measuri~g device shall have a simple design, be flexible and ha~e a low ~roducti~n c06t. The measuring device shall be capa~le of screening undesired electric f ields and be capable of ~eing directed, in a simple m~nnfr~ towards a high-volta~e part for mea~uring the magnitude and the frequency ~pectrum of the voltage therein. The measurins de~i~e Bhall al60 detect the pre~ence of 'cransients or ionic discharge of a hi~h-voltage part. This i~ achieved according to the invention by a measuring de~ice compri~ing a ~ensor which detects chan~e~ in a directed part of an electric field and a signal converter, which sen~or and ~ea~uring de~ice, respectively, exhibit the characteristic features descri~ed in the ; n~ep~n~nt claims. The in~ention al~o relates to a method of mea~uring the voltage in ~ high-~oltage part, 5elected from a plurali~y of such parts and located at a distance, in an electric power ~y~tem.
A high-voltage conductor is surrounded ~y an electric field which carries information about the potential o~ the condu~tor, it~ ~ariation and its frequency contents, A
capacitive ~en~or comprising two mirror-symmetrical electrodes which are introduced into this electric field may sense these quantities. One problem, however, i9 that such a capaciti~e sen~or is ~ensitive to changes in all dire~tions of the electric ~ield. Thus, al80 other field-generating o~jects may influence and so~etimes comple~ely ~o~;n~te such a mea~urement. It is, therefore, not possible to distinguish from the measurement result which change belongs to the co~ponent selected for the mea~rement. Since distribution of electric power is normally carried out in three adjacently ext~;n~
conductors, it is thus not po55ible with such a ~en~or to delimit the field which emanates from one o~ ~he conductors.
According to a fir~t aspect, the invention relate~ to a capacitive sensor with two electrodes, adapted for sen~ing changes in a directed part of an electric field. This sensor is also adapted, in such an electric field, to detect ~ransients and ionic discharge from a high-voltage apparatus. According to the invention, a directed part of an electric field i3 sensed by screening the other elec-trode from un~esired electric fields by mean~ of an elec-trode connected to ~round or to some other controllable pote~tial. A ~ensor intended for thi~ purpoBe iS arrang~d with one electrode predominantly surro-~n~i~q the other electrode and ~onnected to ground or to scme other con-trollable potential. In the surrounding electrod~, which hereinafter will be referred ~o a~ a ~creen electrode, an opening is arranged, through which a directed partial amount of the electric field re~ç~ the surrounded electrode, which hereinafter will be re~erred to aq an inne~ electrode. All other directed sub-suantities of the electric field are efficiently prevented by the screen electrode.
In a preferred e~bodiment, the electrodes are insulated from each other by a gaseous dielectric, the capacitance formed by the electrode6 thu~ becoming insensitive to temperature variations. Thu~, the ~en~or may be configured and its capacitance be me~sured in a laboratory and then be used in o~her envlro~ments without ne~ding calibration again. The censor may also be used for ~ long period of time at varying temperature~, in which case no correction has to be made. For the purpose of increa~ing the sensitivity or reinforci~Y the directional effect of the sensor, the inner electrode may be divided into -~ub-electrodes which are insulated with each other and which may be placed both in the lateral and vertical directions.
According to a cecond a6pect, the in~ention relates to a measuring device, including the ~en~or desc~i~ed above, for voltage measurement at insulation di~tance of a high-voleage part in an electric ~ield with a plurality of field-generating components. The measuring device l~
arranged ~y connecting a qignal converter to the sensOr, whereby, when the Qcreen electrode is connected to ground, a mea~uring device i 3 obtained ~y means of which a directional ~ub-quantity of an electric field may be measured, Thi~ measuring device constitutes a 5imple, , . . . .
Wos8tOsg74 PCT/SE97/01289 inexpensive ~nd reliable device for measurin~, in a contactle~s m~ r, an alternating volta~e at a di~tance from a hi~h-voltage conductor. The device is a broad-band de~ice which, within a l~rge frequency range, permit~
m~a~urement in a simple manner al~o of the occurrence and magnit~de of ~rmo~ic components of the ob~ect intended to ~e measured.
The sisnal convert~r includes . mhsrs ~or ;.mr~nce conversion, amplification, and may al~o include ~mherS
fo~ ~ilterin~ and digital converRion, of the measurement signal. 'rhe ~ignal COL-V~r Ler is placed at a-~hort distance ~rom the actual ~ensor, and in a pr~ferred ~bodiment of the invention it i6 integrated with the ~ensor. The lS co~verted, analog or digital, signal may thereafter be transmitted to an analyzer via an electric or optical medium or be transmitted in a contac~le5s ~nnPr via a transmitter and a receiver.
When applying the mea~urlng device to ~oltage measurement, the screen electrode may be con~ected to a controlla~le potential in~tead o~ to ground, in which ca~e, by phase-locking to one of the phases, greater dynamics and higher re~olution of the ~ea~urement may be obt~lnP~. In another pre~erred embodiment of the in~ention, the inner electrode is instead connected to a pha~e lock circuit, in which ca~e the contri~ution ~rom an unwanted field-generatin~
source may be supprsssed. The ~ignal converter is thus brou~ht to include also a ~onductor adapted for sisnals in the opposi~e direction. In the ~ame way, when using ~iltering of the çensed ~ignal, ~he signal converter may include a plurality of condu~ors for transmis~ion of different filtered signals to a ~ulti~Ann~l analyzer.
The mea~urin~ device according to the invention has a wide field of use, especially in connection with measurement o~
alternating ~oltage in high-volt~ge equipment. One such field of use is enclosed or non-enclo~ed 6witchgear in electric power-related distribution ~y~tem~. In a W098/~974 PCT/SE97/01289 preferred use of the measuring de~ice, the device is placed in an enclo~-d switchgear unit at in~ulation distance from each busba~, belonging to the respective - pha~e, for measurement of alternating voltage. In three-phase sy~tems, the measuring devices may be placed at common Foint and be individually directed toward~ a respective h1-~hAr in the switch~ear.
~he measuring method is sensitive to variations in the di~tance between a measuring obj~ct and the measurin~
de~ice. ~owever, thi~ i~ u~ually no problem since such variation~, viewed over a longer perlod of time, tend to become neg-ligi~le. It is advantageous to place the mea~uring device in location~ where the po6ition of the measurin~ object is ~ixed, for example at point~ of attachme~t or ~uspension where the variation in dlstance i~i mi n; m~ l , In di~tribution syste~ ~ith one phase only, the accuracy 2~ is increased in a simple manner by placing a plurallty of measuring de~ices around th~ conductor. In a ~referred use, for example in enclo5ed switchsear wlth one phase only, the accuracy of the voltage meacurement iQ increased by placing four measuring devices rotationally-symmetrically around an extended part o~ the conductor,Since the mea~uring devices are placed equldistantly from the conductor, the correct value of the voltage i~
obtained from the mean value of the four measuring devices .
The ~ensitivity to variations in the distance ~etween the m~a~uring object and the measuring device may be utilized for detecting m~ t of the measuring objQct. By ~lacing at lea6t three mea~u~in~ de~ces in fixed position6 around a hi~h-voltage conductor, it may be detected if the con-ductor i~ moved a~d in which direction this mo~ t ta~eB
place.
W 098t05974 P~l/~h57/01289 A method for obt~i nincl a stable measurement distance to a high-voltage part $~ achieve~ by ar~angin~ the measuring de~ice and the measuring object at e$ther end of an insulator, which may be hollow. In this way, the length of the inculator i5 utilized to constitute a non-varying measurement distance. The ~eas~ring device may ~e placed both outside and inside the insulator ~ody. Amons ~refer~ed ~mho~mPnts may be mentioned suspen~ion insulators, especially in transmi~sion towers, a~d su~
10 i nsulators .
An additional pr.eferred u~e of the ~neasuring device i measurement.of direct volta~e in a high-voltage apparatus.
This i~ made possible by creating, in the i nr~ ~nt rectified electric field entering through the opening in the screen electrode, a known variation which may be detected in a simple ~Anne~. Such a variation of the incident electric field iA achieved by covering the openin~ ln the screen electrode with a ~ta~le frequency by 2~ a conducting ~creen connected to ground. ~his can be performed in the simple~t manner by applying a plate or a plurality of plates to a rotating 6haft connected to ground. Throug~ this rhythmic ~creening of the opening of the surrounding electrode, a varyin~ electric ~ield i~
created, from which the magnitude of a directed part of the direct ~oltage of a high-voltage part can be mea5ured.
Another way of ac~ieving a varying ~ield from which the sou~ht magnitude can ~e mea~ured is to arrange the inner electrode to oscillate with a know~ frequency.
A measuring de~ice according to the invention is also es~ecially suited, in connection with distribution networ3cs, to 211OW to ~ontrol relay protection function-alitie~, in which case the devlce, by it~ low investment cost, may concentrate the mea~uring points and hence increase the ~electi~ity. The measuring device ~s also especially ~uited for measuring voltage in a conductor in connection with debiting o~ energy consumption. ~or thls purpose, the measurement is to be comhine~ h a diffe-W098/~g74 PCT/SE97/01289 ~-rently measured current throu~h the co~ ctor, whereby the electric energy which pa3se~ may be determined, BRIE~ DESCRIPTION OF THE DRAWING~
The invention wlll be explained in greater detail by de~cription of an ~ho~m~nt with prefer~ed PmhO~ nts ehereof with reference to the accompa~ying drawin0s~ wherein ~i~ure 1 show~ a view, partly in section, of a mea~uring de~i~e including a capacitive ~en~or and a ~ign~l co~verter for directed volta~e mea5urement accor-ding to the inventlon;
Figure 2 shows a view, partly in ~ection, of an alternative embodiment of the mea6uring device;
~igure 3 shows a calculated.distribution of an electric field penetrat~ng through the op~n~ n~ o~ the screen electrode;
Figure 4 showfi a view, partl~ i~ section, of an in~ulator with a mea~uring device according to the invention applied thereto ~igure 5 ~hows an explanatory sketch of an enclosed ~witchgear unit with three busbar~ with a mea~uring device according to the invention a~sociated with each of the bus~ars;
Figure 6 ~how~ an explanatory sketch of a transmission tower for tran~mis~ion of three-phase alternating current, on which a measurin~ de~ice according to ~ the invent~on is mounted for voltage measurement;
Fi~ure 7 shows an explanatory sketch of an enclosed ~witchgear unit for a pha~e with a measuring de~ice according to the invention;
~i~ure 8 shows an explanatory sketch o~ an encio~ed switchgear unlt for a phase with four measurin6 d~vices according to the in~ention;
Fi~ure 9 ~ho~ a view, partly in 8ection, of a preferred ~m~o~ment of a measurin~ de~ice with ~he in~er eleetrode di~ded into sub-electrode~ insu~ated from one another; and ~0 Figure 10 shows a vie~, partly in section, of a preferred ~ ;ment of the measurin~ device, which for measurement of dlrect voltage comprise~ a rotating wing ~hlch rhythmically co~er6 the op~n i~ ~n the screen electrode.
DESCRIPTION OF THE PREFERRED E~BODI~:ENTS
Figure 1 showQ a measurin~ device 10 for directed voltage mea~urement according to the present in~ention. ~he measuri~g device 10 is intended to mea~ure alternatin~
voltage at insulation distance ~rom a conductor 22. The me2suring device 10 comprises a capacitive sensor ll and a ~ignal converter 13. The capacitive sen~or ha~ an inner electrode 1~ and a screen electrode 14 which surrounds the inner electrode. The screen electrode is provided with an openin~ 16 intended, durin~ mea~urement, to be directed towards the conductor 22. In the example, the t~o electrode~
are made from a conducting material. However, the electrode~
m~y be made a~ bodies of an arbitrary material as long s their limi~ing 6urfaces are c~nductin~. For example, an electrode may ~e made of a non-conducting material but with a ~urrounding conducting layer, for example a body of plastic, on whlch is applied a conducting coat~ng.
~5 In the example, the ~creen eleetrode h~8 the 6hape o~ a bucket, that is, it has a bottom from which extends a cylindrical or 61i~htly conical ~order. In the example, the inner electrode has a plane extent in a plane parallel to ~he op~n; n9' Of the ~creen eleetrode. The inner electrode is W098/05g74 PCT/SE97/01289 ~ .
insulated from the screen electrode and adjusta~ly fixed thereto ~uch ~ha~ the di6tance between ~he inner electrode 12 and the or~n;~ 16 of the ~creen electrode 14 may be adju~ted, afi indicated by arrow A in Figure 1. In the example, this is ~ade po~sible by means of an insulating tube 17 which extends through the screen elecerode and to which the inner electrode 12 is fixed.
The signal con~erter 13 is placed near the screen electrode 14 and comprise~ m~m~ for i~ro~An e con~ersion ac well a~
amplification. The signal converter may comprise also rh~rs for f~ltering and digit~l conver~lon of the analog ~lgnal from.the ~ensor ll. Primarily. the ~ al i8 adapted to condition the ~ignal from the sen60r, which i~ very di~turbance-prone, into an analog signal or a di~ital pulse train a~apted for transmi6~ion of the measured in~ormation.
Advant~geously, the signal converter i~ provided with a screen connected to ground or, a6 in the ex~mple, enclo~d in a space 21 ~urrounded by a screen 19. The ~ensor 11 and the signal converter 13 are interconnected by mean~ of a conductor 18, which may be ~creened, ru~nlng in the tube 17.
For e~aluation of the ~ignal, the slgnal co~verter i.~
connected to an analyzer 1~, which may be located at a di~tance from the measuring device 1~. The transmission of the signal may be arranged both electrically and optically, but al~o in a contactles~ manner via a tra~mitter and a receiver.
~he capa~itive sensor 11 is capa~le of ~en~ing the electric 3 0 f ield with a large ~andwidth with respect to frequency, u~ually between zero and ~everal thousand Hertz. It i~, therefore, advantageous to arrange a broad-band signal converter 13 to the mea~uring de~ice. The ~h~rs for impedance conver~ion and a~npl~ fication comprised in tho signal converter are thus preferablY arranged ~y a ~o-called video amplifier. A plurality of filters with different filter characteri~tics may also be arranged in the ~ignal co~verter. Such filters may ~e ~ r~s filters or low- or high-pasc filter~. During mea~urement, the~e may ~ach deliver a ~ignal, or be sequentially connected.
Por special applications, it i5 advantaçJeou8 to ronn~t the ~creen electrode, instead of to ground. to a potential which may be locked in relatio~ to, for example, a phase for in~reased dynaml~s and resolution of ~he desired measurement quantlty. The 6ignal converter 13 may therefore comprise a phase lock circuit (not shown) connected to the screen ~0 electrode 14. ~his circuit, a so-called PLh circuit tPulse Locked Loop), makes it possible, for ex~m~le in a three-phase ~yQte;m, to lock the screen electrod~ l4 of the mea~uring device l0 to a potential which ~aries with th~
phase intended to be measured. In thi8 way, the e~ect from the other phases may ~e suppre8sed in the output 8ignal from the signal co,.~L~e~ 13, whlch results in increased measurement accuracy.
During measurement with the mea~uring device l0 for mea~uring alternating voltage at insulation diBtance from a high-voltage conductor 22, the mea~uring device l0 i5 directed towards the conductor Z2. For the inner electro~e tc be able to sen~e a drawn part of the electric ~ield, the desired part of the field mu6t ~e able to fall through the opening in the screen electrode. For thi6 purpo6e, a con-ceived axi~ which passes through the centre of the inner electrode and through the mid-poin~ of the op~n i ng is directed towards ~he measuring object. ~efore the actual measurem~t is ~tarted, the mea~uring de~ice l0 is cali-~rated in situ. The calibration ~s carried out ~y applyin~ a~nown voltage, whereupon measu~ement with the measuring device i~ performed. The measuring de~ice i~ thu~ calibrated by adjusting the m~a~ured ~alue to corre~pond to the kno~n voltage, ~hen this has ~een completed, the actual mea~ure-ment may be ~tarted.
One advanta~e o~ ~he measuring device l0 accordin~ to theinventio~ is that the mea~uring device need not be brought into ~al~anic contact, or e~en in contact with the condu~-tor, the voltage of which i~ to be mea~ured. The mea~urement may instead be performed at insulation distance from the conducSor 22, which meanC that the measuring device is semi-protected for all those who set into contact therewith, This also implies that no installations need ~e made in the immediate vicinity of the conductor, and therefore no operational disturbances need be caueed b~ the measuring method. The measuring devlce ha~ an exceedingly simple de6ign and iQ therefore very in~r~n~ve to manufacture and is also reliable. The measuring device may be advantageously arranged to conctitute a detector, a -Ro-called PD (Partial Dischar~e) dete~tor, for transients and ionic discharge of a measurin~ object. Becau~e of its reliability, it5 broad-band de~ign and slight inve~tment co~t, the measur~ng devlce is exceed~ngly well suited in connection with energy measure-ment for de~iting of consumed electric energy and when functioning as relay protec~ion.
Figure 2 sho~s an alternative ~mho~lmpnt o~ the measuring device lO according to the invention. In the 8ame way a~ in the preceding example, the mea~urin~ device comprises a sensor ll and a signal con~erter 13. A screen electrode 14 surrounds an inner electrode 12, only l~aving an o~ening 16 whioh, during measurement. is directed towardR a measuring object. In this ~mho~imPnt, the screen eleotrode is globular whereas the inner electrode is cup-shaped with the conca~e side facin~ the opening. ~he s~reen ~lectrode may, however, have an arbitrary ~hape and be formed of an arbitrary, den~e or perforated, conducting ma~exial. Likewi~e, the inner electrode may have an arbitrary shape. It iB preferable, however, to arrange the inner electrode with a plane extent which is sub~tantially parallel to the plane of the opening.
The sensor ll is not limited, as indicted in the examples, to exhibi~ a circular sha~e. A narrower opening gives a ~ainter signal ~ut sreater direc~ional sen6itivity. In case of a field-generatin~ line ~ource, it may therefore be advantageous to design the ~ensor with the opening and the inner electrode, respectively, elongated in a direction coinciding with the line source.
W098/05g74 PCT/SE97/01289 Figure 3 shows a calculation of the distribution o~ an ele~trie field pene~rating through the opening o~ a ground-connected screen electrode into an inner electrode 12, The ~igure show6 only part of such a field in the vicinity of the edge of the inner ele~trode. which i~ cup-~haped in the figure. The calculation, which ha~ been veri~ied by experi-ments, show~ that that part of the electric field which penetrates thro~gh the opening initially has a direction parallel to th~ normal to the opening. ~urther ineide the screen elec~rode, the field line5 diver~e out towards the inside of the ~reen electrode and are finally absorbed by the inner ~lectrode 12. The inner electrode 12 has its con-cave ~urface directed towards the op~ n~ in the 6creen electrode. The ad~antage of this geom~try ig that the field distri~ution inside the screen electrode become6 more uni-form. The design of t~ cup-Rhaped inner el~ctrode 12 a~ a cpherically curved plate ~ause~ all the field line~ ~o become incident perpendicularly to the plate. Thi~ provide~
additional advantage~ with a ~tronger output signal from the 2 0 senfior while at the ~a~e time it~ screening properties are maintained .
Fig~re 4 shows an advantageou~ use of a measuring device 1 according to the invention. In the example shown, the mea~uring de~rice i5 applied at the end of a hollow insulator 25. The insulator co~pri~es an insulant 26 of porcelain or other insulating material, as well a~ a fir~t pole 27 and a second pole 28. The first pole is connected to a high-voltage apparatus (not ~hown) w}lereas the ~econd pole i8 connected to ground. The measuriny device i~ applied to the ~econd pole 28 with its screen electrode 14 connected to the pole and with its inner elect~ode 12 insulated and adjus-tably fixed ~o the 6creen electrode 14. By the described u~e, an exac~, non-varying di~tance between the measuring 3~ obje¢t and the mea~u~ing device is obtAi n~ his i~ advan-tageou~ ~ince a ~ariation of the di9tance jeopardizes the accuracy in the voltage mea~urement.
To fur~her scr~en unwanted electric ~ield~, the two pole may be pro~ided with scre-n~ ~not ~hown) in the form of plates of conducting material, extPn~ in the tran~verse direction of the in6ulator, ~hich are connected to the respective pole. In t~e ca6e of hollow in~ulator~ with protecti~e ~as o~ the SFs type, the ~maller insulation distance on the inside of the insulator, which l~ caused by the gas, may be utilized such that the mea~uring device lO
in it~ entirety i~ housed inside the insulator. An ~n~ulator including a device for ~oltage measurement may thuQ be manufactur~d in a ~imple manner a~ a finished product.
Figure 5 ~hows an explanatory sketch of a switrhP~r unit with bu~bars R, S, and T for three-pha~e alterna~ing ~olta~e surrounded by an enclosure 29. Accordins to the figure, in the upper part of the switch~ear and connected to the enclosure 29, there is arran~ed a measurin~ device lO~, lQ6, lOS, intended for each one of the busbars, for directed voltage measurement accarding to the invention. The th~ee measuring devices have been brou~ht together into a common position to achieve a simple installation and wiring, respectively, and each measuring device is directed towards its respective hu~bar. However, each m~asuring device m~y be placed at insulation di6tance in an arbitrary position within the switch~ear. The common locatlon, however, is an advantage since the ~reatest possible anyle between the ~en~itivity directions of the measuring devices may then be achieved. Wit~ this type of use of the measurins device, among other ~hing~, mounting time and space in the enclosure are saved.
An explanatory 6ketch of a trancmission tower with measuring devices 1OR~ 10,, 10~ a~cordin~ to th~ in~ention i~ ~hown in ~isure 6. The t~ansmission tower comprise~ a framework beam 3l supported by ~wo framework column~ 30~, 3 OL and three cu~pension insulntors 32~, 329, 32~, which are arran~ed in the framework beam and each of which supports a hish-voltage conductor 22" 229, 22~. An enlarged pi~turo ~hows, in two side vi~ws, how a measuring device lO~ is ap~lied to the . _ frame~o~k beam 31 clo~e to the fius~en~ion insulator 32T, which ~upports the hig~-voltag~ line 22R. The po6itioning of the measuring device at ~uch a suspension point for the line implie6 that the measurement diRtance be~ome~ defined and not ~ignificantly changed when the.line moves cau~ed ~y wind or any o~her force. ~he measurin~ device may advantageously be integrated also with the in~ulator, as shown in Figure 4.
The converted ~ignal deli~ered from the measuring device may be transmitted to an analyzer ~oth elect~ically, opti~ally and in a wirele~ mAnn~r with the aid o$ telephony~ With a mea~u~in~ method according to the example, by collection of measurement values ~rom a plurality of fixedly installed measuring devices along a netwo~k, the transmiQsion or distribution may be checked in an advanta~eous mAnn~r.
An explanatory ~ketch of a ~witchgear unit with only one pha~e surrounded by an enclosure 29 i~ shown in Figure 7. A
mea~uring de~ice 10 according to the invention for measuring the alternatin~ voltage ~rom one 5ingle busbar 33 may here, in the same ~ay a~ in the example in ~igure 5, be arranged at insulation distance in an arbitrary position within the enclosure. one advantage with thi5 application is that no other electric fields are generated in the enclosure, whi~h permits the positioning of the measuring device to be con-trolled for other reason~. A u~e o~ a measuring deviceaccording ~o the invention in enclosed switchgear with one phase only con3titutes an ex~eedingly simple and co~t-sa~ing in6tallation .
It has been indicated above that a ~oltage measureme~t with a measuring device according to the invention i~ sen~iti~e to variations in the di~tance ~etween the mea~uring de~ice and the mea~uring object. This fact may be u~ilized for the purpose of ~tudying a movement of a measurin~ 0~j2ct. A
method for measuring ~oltage from a mea~u~ing object moving ~tochast~cally around a mid-point ~ay thus be achie~ed in a simple manner. A measurement arrangement whi~h perm~t~, on the one hand, a me~hod for studying the lllo~...,_L~t of a con-ductor and, on the other hand, a method for increasing W098t05974 PCT/SE97101289 mea~urement accuracy is show~ i~ Figure 8- ~ike the pre~ious figure, Figure 8 shows an explanatory sk-tch o~ switchgear with one phase only, sur~ounded by an enclosure 29. Around a centrally placed busbar 33, four measuring devices lOa, lOh, l n~, lOd according to the invention are each arranyed in a corne~ of a cross section o~ the 6witch~ear- ~he converted signal from each one of the mea8uring deviceR iB pre$erably analyzed by a four-rh~nel analyzer ~not shown~. To study the mov_...el~t, the 6ignals are compared, and to increa6e the measurement accuracy, the average Yalue o~ the gisnals are formed.
By geomatrical calculations of st~n~d type from the measurement signals, ehe position of the ~$hAr is lS determined, whereby a measurement of the volta~e i~
corrected ~or the change in position 8uch that a correct mea~u~ement val~e may be a~ri~ed at by calculation. The method m~ly al50 be uqed ~or detecting and correcting the measurement for changes in the electric back~rou3d field, which provides unsymmetrical chan~es in the mea~ured 6ignals. A greater measurement accuracy is obtAlne~ by introducin~ a plurality of mea~uri~g device~ which carry out ~ea~urement on the ~ame object. The mea~uring method~
described are not limited to be applied to enclosed switchgear only, but may al50 be applied to free conductors and to non-enclosed ~witchgear. ~n non-enclosed swltchgear~
it is pa~ticularly ~aluable to be able to correct the measurement value for chan~es in the background field.
An alternative ~mhoA;ment of a sen~or ll ~ncluded in a measuring de~ice according t~ t~e in~ent~on ~s 8hown in Figure 9. The ~en~or ll comprises a ~creen e~ectrode 14 which i~ provided ~i~h an ope~ing 16 and which surrounds a first inner ~ub-electrode 12a and a ~econd inner sub-electrode 12b, which are insulated ~rom each other and whichare each adjustably fixed to the ~creen electrode, In the ~hown case, the openin~ 16 is li~ited ~y a ring 34 of a conducting material, connected to the 8creen ~lectrode, the ta~k of which i8 to equa~ize ~he ele~cric field so as to WOs8/0sg74 PCT/SE97/01289 pre~en~ corona. In the example shown, the inn~r ~ub-electrodes are equally large and ~referably have the 6hape of half a round plate, such that the sub-electrodes together ~Y~h1t the ~hap- of a full round ~late. The inner ~ub-elec~rodes are each connected to a re~pective sign~l con-v~rter (not shown), and, in the ~ame way as in example l, the measuremen~ slgnals are each tranFmitted to a res~ective analyzer, or to a common multl-~h~nnel analyzer, sy dividing the inner electrode into sub-electrode~, the a~ove-mentioned ~ensitivit~ to distance dependence may be further utillzed. ~he electrodes are preferably adjusted to exhibit the same capa~itance, ~hereby, by means o~ a bridge circuit, a comparison between the conve~ted signals from each one of the sub-electrodes may determine, on the one hand, whether by meaF,uring object is in front o~ the senso~
and, on the other hand, whether the measuring ob~ect move~
during the measurement. An electric ~ield generated ~rom another unwanted object ls detec~ed b~ dividing ~he inner electrode ~y comparison~ o~ the mea~urement-Q in an analyzer and may thu~ ~e elimina~ed from the measurement result, According to the invention, the inner ele~trode is divided into an ar~itrary num~er o~ ~ub-electrodeR. E-Q~ecially in cc,nnection with point-shaped high-voltag~ objects, the inner electrode is formed in~o a plurality o~ uniform sectors of a circle. In other ~mho~;mPnts, for example in case of the elongated ~en~or de~cribed above, it is inste~d ad~antageous ~o form the ~ub-electrodes as a plurality of plate~ arranged ~ide-by-side.
An additional al~ernati~e Pm~o~;ment of a ~easuring device according to the invention is ~hown in Figure lO. This exa~ple ~hows a mea~turing device which may co~prise one o~
the lamh~ m~nts according to the exanlple6 in Figure 1, 2 or 9, supplemented ~y a device for creat~ng, at the inner electrode with a known frequency, a variation of a recti ied elec~ric field. A mea~urin~ device lO include~ a sensor ll and a signal converter 13. ~he sensor compri~eF, an inner electrode 12 and a screen electrode 14 surro~ i n~ the inner electrode and pro~ided with an opening 16. The inner electrode i8 fixed to an insulatlng tube 17, which is ad~ustably ~ixed to the screen electrode, Buch that the inner electrode 12 may change in a direccion de~i~nated A.
~he inner electrode is connected tP t~ nal converter 1 by means o~ a conductor 18 dra~n throug~ the tube 17, ~he signal con~erter being arranged in a space 21 ~urrounded ~y a screen 19.
A ~ha~t 36, which is rotated by a drive means (not shown), i5 rotatably fixed to the mE~asurins device, and on this ~haft 36 a disc 35, which i~ parallel to the op~ ng 16, iB
fix~d. The ~haft ~6 and the disc 35 are connected to the same potential a~ the screen electrode 14- During rotation of the shaft 36, the disc 35, which extends, for example, along ~ ~emi-circle, will screen the open~ng ~ith a known fr~uency. Of the rectlfied electric field, a directed part will in thi6 way, with variation between zero and full ~ield strength, penetrate through the openi~g in the screen electrode. From thi~ ~ariation, the magnitude of the directed part o~ the rectified field, which falls through the opening, may be measured.
The disc 35, which is preferably made of metal, will, during rotation, alternately ~over and thu8 6creen the opening and lea~e the op~nin~ unscreened such that a variation o~ the penetratiny stationary field is created ~he invention is not limited to onl~ compr~se a disc but may al~o include a plurality of discs, preferably evenly divided on an axis, 3 0 Al~o, the discs may be formed to com~letely co~er the openin~ 16, or only a part thereof. ~he disc or di~c~ ~ay also be arranged, with the same re~ult, to 8creen the whole sen~or or parts thereof.
The invention is not limited to the embodiments shown, but a plurality of modifications are posBible within the sco~e of the appon~ claim~. Thu~, the screen e~ectrode may, ~or example, comprise a plurality o~ opening~ and, in certain a~plications, be de~lgned fro~ net or a perfora~ed material.
AND USE THEREOF
TECHNICAL FI~LD
The present in~ention relate~ to a capacitive sensor for sen~ing VariationB in an electric field. The in~ention ai~o relate~ to a measuring de~ice includ~ ng such a ~en~or for measuring voltage at a di~tance from ~igh-vol~age conduc-tors, and to a method for such measurement. The other quantities which are detected by the measurin~ device are transients and ionic discharge. The measuring device i~
partlcularly adapted to measure volta0e in electric power network~, w~ich may comprise one or more pha~es, for control of transmiscion or di~tribution of electric power, or as a ba~is ~or de~iti~g of con~umed energy.
BACKGRO~nND ART
There is often a need of mea~uring the voltage o~ a high-~olt~ge line at a dlstance. This may, for example, be in connection with dis.ribution of el~ctric power with several conductors, where particularly the voltage of one of the conductors i~ to be determined. Su~h voltage measurement is uLed for control of a voltage drop along the distribution chain or for controll~ng that limit values are not exceeded, It may also be a question of calcu}ating the electric ener~y pas6i~s, ba6ed on the measured voltage. In both ca~e~ there i~ a great need of a simple and inexpensive mea~uring device, which i~ flexible and ~ith the aid of which it i~
economically pos~ible to achieve a den5ification of the number of measuring point~ in ~ di~tribution network.
The detectors and mea6uring devices which are currently availa~le are co~tly and com~licated devices which mu~t often be ~rou~ht into ~ontac~ ~ith the ~igh-voltage line, for example a voltage transformer. These 501ution6 entail con~iderable in~restments and therefore imply a great de~artur~ ~rom the lo~7 invectment and flexibility which i8 desira~le.
W O g8/0S974 ~ i/01289 From EP-Bl-~ 181 054, an apparatu~ ~or measurin~ the potential difference betwe0n ground and a power co~ductor, pla~ed above the ground, is previou61y known. The app~atus show~ is intended to be ~ounted on the conductor and generally ha~ ~n~l Ar sha~e. One lim~tation with this apparatus is that it has to be applied onto the conductor, which, ln addition to a great investment co~t, also in~ol~e~
operational distur~ances.
1'0 In an article by P. Sarma Maruvada, R-D. Dallaire and R.
Pedneault, ~Development of field-mill ~n~truments for ground-le~el and,a~ove-ground level elect~ic mea~urement under HVDC transmission lines", IEEE Tran~action~ on Power Apparatus and Systems, Vol. PAS-102, No. 3, pp. 738-744, ~arch 1983, there is shown a device, popularly named "field rnill~ for m~asuring, ae ~round level, an electric field under a high-~roltage conductor. The device comprise~
essentially an electrode, fixed to ground potential, in the form of a cylindrical box with, for example, six sector-s~p~ openings on the upper side thereof, and a rotatin~electrode inside the box but electrlcally insulated from the same. The rotatir~g electrode comprise~ BiX identical lobes formed as a ~ernoulli lemniscate, arranged uni~or~ly around a clrele. The device may be u5ed either at the same level a~
ground-le~el by placing it in a hole dug in the ~round, co~ered wlth a metal-protective plate with an op~i n~ ~or the device. ~he device may also be placed so a~ to project a~ove the ground.
The above-mentinned article al~o ~hows a device for mea~urement above ground level of the electric field under a high-voltage conductor. T~e device comprise~ two metal cylinders, each being di~ided length~i5e into two halves inbul~ted from each other. The cylinder8 hav~ equal or different radii, but different l~ngths- The cylinders rotate at dlfferent speeds and fro~ a mechanica~ point of view it is desirable that the cylinder~ rotate i~ direc~ion~
opposiee to each other.
One problem with the devices described above is that both are sensiti~e to disturbins electri~ fields, which therefore may greatly distort the measurement re,~ult. Another proble~
is that both have a relatively complicated de~ign From US-4,328,46l, an apparatu8 ~or measuring electric fields is ~reviously known. The ta~k of the apparatus is to investigate electrical characterigtics in the atmosphere . during a th~n~Rrstorm. The apparatus is shown in three different en~hoAim~nt:3~ itB ba~ic design comprisinç~ two hemispherical electrodes, between which a devi~e for measuring and generatin~ mea~ured data i~ enclosed. In ~
second ~mh~im~nt~ the mea6uring electrode~ are in the ~orm of two circul~r metal plates, whereby the a~6ociated measurement electronics is arranged be~ween the ~lates and thus at lea~t partly ~reened ~hereby. In a thi~d ~mho~;_ ment, the measuring electrodes are in the form of two ~emi-cylindrical electrodes, insulated from each other, where the electronics, in the ~ame way as above, is located between the electrodes.
The known device for measuring electric fields in ca~e of a stroke of lightning has a certain directional sensitivity becaus~ of it~ twO uniform plates. ~iowever, it is not capable of screening undesired electric ~ields and ~
there~ore not useful in the application sought, where the elec~ric field generated by only one o~ several high-~olta~e part3 i~ to be measured.
SUMMARY OF THE INV~TIO~
The object o~ the prese~t invention is to achieve a measurin~ device, by which may be measured the vDltage in a high-voltage part in an electric power system, which 35 high-voltage part i~ selected from a plurality of ~uch parts and is located at a di~tance. The measuri~g device shall have a simple design, be flexible and ha~e a low ~roducti~n c06t. The measuring device shall be capa~le of screening undesired electric f ields and be capable of ~eing directed, in a simple m~nnfr~ towards a high-volta~e part for mea~uring the magnitude and the frequency ~pectrum of the voltage therein. The measurins de~i~e Bhall al60 detect the pre~ence of 'cransients or ionic discharge of a hi~h-voltage part. This i~ achieved according to the invention by a measuring de~ice compri~ing a ~ensor which detects chan~e~ in a directed part of an electric field and a signal converter, which sen~or and ~ea~uring de~ice, respectively, exhibit the characteristic features descri~ed in the ; n~ep~n~nt claims. The in~ention al~o relates to a method of mea~uring the voltage in ~ high-~oltage part, 5elected from a plurali~y of such parts and located at a distance, in an electric power ~y~tem.
A high-voltage conductor is surrounded ~y an electric field which carries information about the potential o~ the condu~tor, it~ ~ariation and its frequency contents, A
capacitive ~en~or comprising two mirror-symmetrical electrodes which are introduced into this electric field may sense these quantities. One problem, however, i9 that such a capaciti~e sen~or is ~ensitive to changes in all dire~tions of the electric ~ield. Thus, al80 other field-generating o~jects may influence and so~etimes comple~ely ~o~;n~te such a mea~urement. It is, therefore, not possible to distinguish from the measurement result which change belongs to the co~ponent selected for the mea~rement. Since distribution of electric power is normally carried out in three adjacently ext~;n~
conductors, it is thus not po55ible with such a ~en~or to delimit the field which emanates from one o~ ~he conductors.
According to a fir~t aspect, the invention relate~ to a capacitive sensor with two electrodes, adapted for sen~ing changes in a directed part of an electric field. This sensor is also adapted, in such an electric field, to detect ~ransients and ionic discharge from a high-voltage apparatus. According to the invention, a directed part of an electric field i3 sensed by screening the other elec-trode from un~esired electric fields by mean~ of an elec-trode connected to ~round or to some other controllable pote~tial. A ~ensor intended for thi~ purpoBe iS arrang~d with one electrode predominantly surro-~n~i~q the other electrode and ~onnected to ground or to scme other con-trollable potential. In the surrounding electrod~, which hereinafter will be referred ~o a~ a ~creen electrode, an opening is arranged, through which a directed partial amount of the electric field re~ç~ the surrounded electrode, which hereinafter will be re~erred to aq an inne~ electrode. All other directed sub-suantities of the electric field are efficiently prevented by the screen electrode.
In a preferred e~bodiment, the electrodes are insulated from each other by a gaseous dielectric, the capacitance formed by the electrode6 thu~ becoming insensitive to temperature variations. Thu~, the ~en~or may be configured and its capacitance be me~sured in a laboratory and then be used in o~her envlro~ments without ne~ding calibration again. The censor may also be used for ~ long period of time at varying temperature~, in which case no correction has to be made. For the purpose of increa~ing the sensitivity or reinforci~Y the directional effect of the sensor, the inner electrode may be divided into -~ub-electrodes which are insulated with each other and which may be placed both in the lateral and vertical directions.
According to a cecond a6pect, the in~ention relates to a measuring device, including the ~en~or desc~i~ed above, for voltage measurement at insulation di~tance of a high-voleage part in an electric ~ield with a plurality of field-generating components. The measuring device l~
arranged ~y connecting a qignal converter to the sensOr, whereby, when the Qcreen electrode is connected to ground, a mea~uring device i 3 obtained ~y means of which a directional ~ub-quantity of an electric field may be measured, Thi~ measuring device constitutes a 5imple, , . . . .
Wos8tOsg74 PCT/SE97/01289 inexpensive ~nd reliable device for measurin~, in a contactle~s m~ r, an alternating volta~e at a di~tance from a hi~h-voltage conductor. The device is a broad-band de~ice which, within a l~rge frequency range, permit~
m~a~urement in a simple manner al~o of the occurrence and magnit~de of ~rmo~ic components of the ob~ect intended to ~e measured.
The sisnal convert~r includes . mhsrs ~or ;.mr~nce conversion, amplification, and may al~o include ~mherS
fo~ ~ilterin~ and digital converRion, of the measurement signal. 'rhe ~ignal COL-V~r Ler is placed at a-~hort distance ~rom the actual ~ensor, and in a pr~ferred ~bodiment of the invention it i6 integrated with the ~ensor. The lS co~verted, analog or digital, signal may thereafter be transmitted to an analyzer via an electric or optical medium or be transmitted in a contac~le5s ~nnPr via a transmitter and a receiver.
When applying the mea~urlng device to ~oltage measurement, the screen electrode may be con~ected to a controlla~le potential in~tead o~ to ground, in which ca~e, by phase-locking to one of the phases, greater dynamics and higher re~olution of the ~ea~urement may be obt~lnP~. In another pre~erred embodiment of the in~ention, the inner electrode is instead connected to a pha~e lock circuit, in which ca~e the contri~ution ~rom an unwanted field-generatin~
source may be supprsssed. The ~ignal converter is thus brou~ht to include also a ~onductor adapted for sisnals in the opposi~e direction. In the ~ame way, when using ~iltering of the çensed ~ignal, ~he signal converter may include a plurality of condu~ors for transmis~ion of different filtered signals to a ~ulti~Ann~l analyzer.
The mea~urin~ device according to the invention has a wide field of use, especially in connection with measurement o~
alternating ~oltage in high-volt~ge equipment. One such field of use is enclosed or non-enclo~ed 6witchgear in electric power-related distribution ~y~tem~. In a W098/~974 PCT/SE97/01289 preferred use of the measuring de~ice, the device is placed in an enclo~-d switchgear unit at in~ulation distance from each busba~, belonging to the respective - pha~e, for measurement of alternating voltage. In three-phase sy~tems, the measuring devices may be placed at common Foint and be individually directed toward~ a respective h1-~hAr in the switch~ear.
~he measuring method is sensitive to variations in the di~tance between a measuring obj~ct and the measurin~
de~ice. ~owever, thi~ i~ u~ually no problem since such variation~, viewed over a longer perlod of time, tend to become neg-ligi~le. It is advantageous to place the mea~uring device in location~ where the po6ition of the measurin~ object is ~ixed, for example at point~ of attachme~t or ~uspension where the variation in dlstance i~i mi n; m~ l , In di~tribution syste~ ~ith one phase only, the accuracy 2~ is increased in a simple manner by placing a plurallty of measuring de~ices around th~ conductor. In a ~referred use, for example in enclo5ed switchsear wlth one phase only, the accuracy of the voltage meacurement iQ increased by placing four measuring devices rotationally-symmetrically around an extended part o~ the conductor,Since the mea~uring devices are placed equldistantly from the conductor, the correct value of the voltage i~
obtained from the mean value of the four measuring devices .
The ~ensitivity to variations in the distance ~etween the m~a~uring object and the measuring device may be utilized for detecting m~ t of the measuring objQct. By ~lacing at lea6t three mea~u~in~ de~ces in fixed position6 around a hi~h-voltage conductor, it may be detected if the con-ductor i~ moved a~d in which direction this mo~ t ta~eB
place.
W 098t05974 P~l/~h57/01289 A method for obt~i nincl a stable measurement distance to a high-voltage part $~ achieve~ by ar~angin~ the measuring de~ice and the measuring object at e$ther end of an insulator, which may be hollow. In this way, the length of the inculator i5 utilized to constitute a non-varying measurement distance. The ~eas~ring device may ~e placed both outside and inside the insulator ~ody. Amons ~refer~ed ~mho~mPnts may be mentioned suspen~ion insulators, especially in transmi~sion towers, a~d su~
10 i nsulators .
An additional pr.eferred u~e of the ~neasuring device i measurement.of direct volta~e in a high-voltage apparatus.
This i~ made possible by creating, in the i nr~ ~nt rectified electric field entering through the opening in the screen electrode, a known variation which may be detected in a simple ~Anne~. Such a variation of the incident electric field iA achieved by covering the openin~ ln the screen electrode with a ~ta~le frequency by 2~ a conducting ~creen connected to ground. ~his can be performed in the simple~t manner by applying a plate or a plurality of plates to a rotating 6haft connected to ground. Throug~ this rhythmic ~creening of the opening of the surrounding electrode, a varyin~ electric ~ield i~
created, from which the magnitude of a directed part of the direct ~oltage of a high-voltage part can be mea5ured.
Another way of ac~ieving a varying ~ield from which the sou~ht magnitude can ~e mea~ured is to arrange the inner electrode to oscillate with a know~ frequency.
A measuring de~ice according to the invention is also es~ecially suited, in connection with distribution networ3cs, to 211OW to ~ontrol relay protection function-alitie~, in which case the devlce, by it~ low investment cost, may concentrate the mea~uring points and hence increase the ~electi~ity. The measuring device ~s also especially ~uited for measuring voltage in a conductor in connection with debiting o~ energy consumption. ~or thls purpose, the measurement is to be comhine~ h a diffe-W098/~g74 PCT/SE97/01289 ~-rently measured current throu~h the co~ ctor, whereby the electric energy which pa3se~ may be determined, BRIE~ DESCRIPTION OF THE DRAWING~
The invention wlll be explained in greater detail by de~cription of an ~ho~m~nt with prefer~ed PmhO~ nts ehereof with reference to the accompa~ying drawin0s~ wherein ~i~ure 1 show~ a view, partly in section, of a mea~uring de~i~e including a capacitive ~en~or and a ~ign~l co~verter for directed volta~e mea5urement accor-ding to the inventlon;
Figure 2 shows a view, partly in ~ection, of an alternative embodiment of the mea6uring device;
~igure 3 shows a calculated.distribution of an electric field penetrat~ng through the op~n~ n~ o~ the screen electrode;
Figure 4 showfi a view, partl~ i~ section, of an in~ulator with a mea~uring device according to the invention applied thereto ~igure 5 ~hows an explanatory sketch of an enclosed ~witchgear unit with three busbar~ with a mea~uring device according to the invention a~sociated with each of the bus~ars;
Figure 6 ~how~ an explanatory sketch of a transmission tower for tran~mis~ion of three-phase alternating current, on which a measurin~ de~ice according to ~ the invent~on is mounted for voltage measurement;
Fi~ure 7 shows an explanatory sketch of an enclosed ~witchgear unit for a pha~e with a measuring de~ice according to the invention;
~i~ure 8 shows an explanatory sketch o~ an encio~ed switchgear unlt for a phase with four measurin6 d~vices according to the in~ention;
Fi~ure 9 ~ho~ a view, partly in 8ection, of a preferred ~m~o~ment of a measurin~ de~ice with ~he in~er eleetrode di~ded into sub-electrode~ insu~ated from one another; and ~0 Figure 10 shows a vie~, partly in section, of a preferred ~ ;ment of the measurin~ device, which for measurement of dlrect voltage comprise~ a rotating wing ~hlch rhythmically co~er6 the op~n i~ ~n the screen electrode.
DESCRIPTION OF THE PREFERRED E~BODI~:ENTS
Figure 1 showQ a measurin~ device 10 for directed voltage mea~urement according to the present in~ention. ~he measuri~g device 10 is intended to mea~ure alternatin~
voltage at insulation distance ~rom a conductor 22. The me2suring device 10 comprises a capacitive sensor ll and a ~ignal converter 13. The capacitive sen~or ha~ an inner electrode 1~ and a screen electrode 14 which surrounds the inner electrode. The screen electrode is provided with an openin~ 16 intended, durin~ mea~urement, to be directed towards the conductor 22. In the example, the t~o electrode~
are made from a conducting material. However, the electrode~
m~y be made a~ bodies of an arbitrary material as long s their limi~ing 6urfaces are c~nductin~. For example, an electrode may ~e made of a non-conducting material but with a ~urrounding conducting layer, for example a body of plastic, on whlch is applied a conducting coat~ng.
~5 In the example, the ~creen eleetrode h~8 the 6hape o~ a bucket, that is, it has a bottom from which extends a cylindrical or 61i~htly conical ~order. In the example, the inner electrode has a plane extent in a plane parallel to ~he op~n; n9' Of the ~creen eleetrode. The inner electrode is W098/05g74 PCT/SE97/01289 ~ .
insulated from the screen electrode and adjusta~ly fixed thereto ~uch ~ha~ the di6tance between ~he inner electrode 12 and the or~n;~ 16 of the ~creen electrode 14 may be adju~ted, afi indicated by arrow A in Figure 1. In the example, this is ~ade po~sible by means of an insulating tube 17 which extends through the screen elecerode and to which the inner electrode 12 is fixed.
The signal con~erter 13 is placed near the screen electrode 14 and comprise~ m~m~ for i~ro~An e con~ersion ac well a~
amplification. The signal converter may comprise also rh~rs for f~ltering and digit~l conver~lon of the analog ~lgnal from.the ~ensor ll. Primarily. the ~ al i8 adapted to condition the ~ignal from the sen60r, which i~ very di~turbance-prone, into an analog signal or a di~ital pulse train a~apted for transmi6~ion of the measured in~ormation.
Advant~geously, the signal converter i~ provided with a screen connected to ground or, a6 in the ex~mple, enclo~d in a space 21 ~urrounded by a screen 19. The ~ensor 11 and the signal converter 13 are interconnected by mean~ of a conductor 18, which may be ~creened, ru~nlng in the tube 17.
For e~aluation of the ~ignal, the slgnal co~verter i.~
connected to an analyzer 1~, which may be located at a di~tance from the measuring device 1~. The transmission of the signal may be arranged both electrically and optically, but al~o in a contactles~ manner via a tra~mitter and a receiver.
~he capa~itive sensor 11 is capa~le of ~en~ing the electric 3 0 f ield with a large ~andwidth with respect to frequency, u~ually between zero and ~everal thousand Hertz. It i~, therefore, advantageous to arrange a broad-band signal converter 13 to the mea~uring de~ice. The ~h~rs for impedance conver~ion and a~npl~ fication comprised in tho signal converter are thus preferablY arranged ~y a ~o-called video amplifier. A plurality of filters with different filter characteri~tics may also be arranged in the ~ignal co~verter. Such filters may ~e ~ r~s filters or low- or high-pasc filter~. During mea~urement, the~e may ~ach deliver a ~ignal, or be sequentially connected.
Por special applications, it i5 advantaçJeou8 to ronn~t the ~creen electrode, instead of to ground. to a potential which may be locked in relatio~ to, for example, a phase for in~reased dynaml~s and resolution of ~he desired measurement quantlty. The 6ignal converter 13 may therefore comprise a phase lock circuit (not shown) connected to the screen ~0 electrode 14. ~his circuit, a so-called PLh circuit tPulse Locked Loop), makes it possible, for ex~m~le in a three-phase ~yQte;m, to lock the screen electrod~ l4 of the mea~uring device l0 to a potential which ~aries with th~
phase intended to be measured. In thi8 way, the e~ect from the other phases may ~e suppre8sed in the output 8ignal from the signal co,.~L~e~ 13, whlch results in increased measurement accuracy.
During measurement with the mea~uring device l0 for mea~uring alternating voltage at insulation diBtance from a high-voltage conductor 22, the mea~uring device l0 i5 directed towards the conductor Z2. For the inner electro~e tc be able to sen~e a drawn part of the electric ~ield, the desired part of the field mu6t ~e able to fall through the opening in the screen electrode. For thi6 purpo6e, a con-ceived axi~ which passes through the centre of the inner electrode and through the mid-poin~ of the op~n i ng is directed towards ~he measuring object. ~efore the actual measurem~t is ~tarted, the mea~uring de~ice l0 is cali-~rated in situ. The calibration ~s carried out ~y applyin~ a~nown voltage, whereupon measu~ement with the measuring device i~ performed. The measuring de~ice i~ thu~ calibrated by adjusting the m~a~ured ~alue to corre~pond to the kno~n voltage, ~hen this has ~een completed, the actual mea~ure-ment may be ~tarted.
One advanta~e o~ ~he measuring device l0 accordin~ to theinventio~ is that the mea~uring device need not be brought into ~al~anic contact, or e~en in contact with the condu~-tor, the voltage of which i~ to be mea~ured. The mea~urement may instead be performed at insulation distance from the conducSor 22, which meanC that the measuring device is semi-protected for all those who set into contact therewith, This also implies that no installations need ~e made in the immediate vicinity of the conductor, and therefore no operational disturbances need be caueed b~ the measuring method. The measuring devlce ha~ an exceedingly simple de6ign and iQ therefore very in~r~n~ve to manufacture and is also reliable. The measuring device may be advantageously arranged to conctitute a detector, a -Ro-called PD (Partial Dischar~e) dete~tor, for transients and ionic discharge of a measurin~ object. Becau~e of its reliability, it5 broad-band de~ign and slight inve~tment co~t, the measur~ng devlce is exceed~ngly well suited in connection with energy measure-ment for de~iting of consumed electric energy and when functioning as relay protec~ion.
Figure 2 sho~s an alternative ~mho~lmpnt o~ the measuring device lO according to the invention. In the 8ame way a~ in the preceding example, the mea~urin~ device comprises a sensor ll and a signal con~erter 13. A screen electrode 14 surrounds an inner electrode 12, only l~aving an o~ening 16 whioh, during measurement. is directed towardR a measuring object. In this ~mho~imPnt, the screen eleotrode is globular whereas the inner electrode is cup-shaped with the conca~e side facin~ the opening. ~he s~reen ~lectrode may, however, have an arbitrary ~hape and be formed of an arbitrary, den~e or perforated, conducting ma~exial. Likewi~e, the inner electrode may have an arbitrary shape. It iB preferable, however, to arrange the inner electrode with a plane extent which is sub~tantially parallel to the plane of the opening.
The sensor ll is not limited, as indicted in the examples, to exhibi~ a circular sha~e. A narrower opening gives a ~ainter signal ~ut sreater direc~ional sen6itivity. In case of a field-generatin~ line ~ource, it may therefore be advantageous to design the ~ensor with the opening and the inner electrode, respectively, elongated in a direction coinciding with the line source.
W098/05g74 PCT/SE97/01289 Figure 3 shows a calculation of the distribution o~ an ele~trie field pene~rating through the opening o~ a ground-connected screen electrode into an inner electrode 12, The ~igure show6 only part of such a field in the vicinity of the edge of the inner ele~trode. which i~ cup-~haped in the figure. The calculation, which ha~ been veri~ied by experi-ments, show~ that that part of the electric field which penetrates thro~gh the opening initially has a direction parallel to th~ normal to the opening. ~urther ineide the screen elec~rode, the field line5 diver~e out towards the inside of the ~reen electrode and are finally absorbed by the inner ~lectrode 12. The inner electrode 12 has its con-cave ~urface directed towards the op~ n~ in the 6creen electrode. The ad~antage of this geom~try ig that the field distri~ution inside the screen electrode become6 more uni-form. The design of t~ cup-Rhaped inner el~ctrode 12 a~ a cpherically curved plate ~ause~ all the field line~ ~o become incident perpendicularly to the plate. Thi~ provide~
additional advantage~ with a ~tronger output signal from the 2 0 senfior while at the ~a~e time it~ screening properties are maintained .
Fig~re 4 shows an advantageou~ use of a measuring device 1 according to the invention. In the example shown, the mea~uring de~rice i5 applied at the end of a hollow insulator 25. The insulator co~pri~es an insulant 26 of porcelain or other insulating material, as well a~ a fir~t pole 27 and a second pole 28. The first pole is connected to a high-voltage apparatus (not ~hown) w}lereas the ~econd pole i8 connected to ground. The measuriny device i~ applied to the ~econd pole 28 with its screen electrode 14 connected to the pole and with its inner elect~ode 12 insulated and adjus-tably fixed ~o the 6creen electrode 14. By the described u~e, an exac~, non-varying di~tance between the measuring 3~ obje¢t and the mea~u~ing device is obtAi n~ his i~ advan-tageou~ ~ince a ~ariation of the di9tance jeopardizes the accuracy in the voltage mea~urement.
To fur~her scr~en unwanted electric ~ield~, the two pole may be pro~ided with scre-n~ ~not ~hown) in the form of plates of conducting material, extPn~ in the tran~verse direction of the in6ulator, ~hich are connected to the respective pole. In t~e ca6e of hollow in~ulator~ with protecti~e ~as o~ the SFs type, the ~maller insulation distance on the inside of the insulator, which l~ caused by the gas, may be utilized such that the mea~uring device lO
in it~ entirety i~ housed inside the insulator. An ~n~ulator including a device for ~oltage measurement may thuQ be manufactur~d in a ~imple manner a~ a finished product.
Figure 5 ~hows an explanatory sketch of a switrhP~r unit with bu~bars R, S, and T for three-pha~e alterna~ing ~olta~e surrounded by an enclosure 29. Accordins to the figure, in the upper part of the switch~ear and connected to the enclosure 29, there is arran~ed a measurin~ device lO~, lQ6, lOS, intended for each one of the busbars, for directed voltage measurement accarding to the invention. The th~ee measuring devices have been brou~ht together into a common position to achieve a simple installation and wiring, respectively, and each measuring device is directed towards its respective hu~bar. However, each m~asuring device m~y be placed at insulation di6tance in an arbitrary position within the switch~ear. The common locatlon, however, is an advantage since the ~reatest possible anyle between the ~en~itivity directions of the measuring devices may then be achieved. Wit~ this type of use of the measurins device, among other ~hing~, mounting time and space in the enclosure are saved.
An explanatory 6ketch of a trancmission tower with measuring devices 1OR~ 10,, 10~ a~cordin~ to th~ in~ention i~ ~hown in ~isure 6. The t~ansmission tower comprise~ a framework beam 3l supported by ~wo framework column~ 30~, 3 OL and three cu~pension insulntors 32~, 329, 32~, which are arran~ed in the framework beam and each of which supports a hish-voltage conductor 22" 229, 22~. An enlarged pi~turo ~hows, in two side vi~ws, how a measuring device lO~ is ap~lied to the . _ frame~o~k beam 31 clo~e to the fius~en~ion insulator 32T, which ~upports the hig~-voltag~ line 22R. The po6itioning of the measuring device at ~uch a suspension point for the line implie6 that the measurement diRtance be~ome~ defined and not ~ignificantly changed when the.line moves cau~ed ~y wind or any o~her force. ~he measurin~ device may advantageously be integrated also with the in~ulator, as shown in Figure 4.
The converted ~ignal deli~ered from the measuring device may be transmitted to an analyzer ~oth elect~ically, opti~ally and in a wirele~ mAnn~r with the aid o$ telephony~ With a mea~u~in~ method according to the example, by collection of measurement values ~rom a plurality of fixedly installed measuring devices along a netwo~k, the transmiQsion or distribution may be checked in an advanta~eous mAnn~r.
An explanatory ~ketch of a ~witchgear unit with only one pha~e surrounded by an enclosure 29 i~ shown in Figure 7. A
mea~uring de~ice 10 according to the invention for measuring the alternatin~ voltage ~rom one 5ingle busbar 33 may here, in the same ~ay a~ in the example in ~igure 5, be arranged at insulation distance in an arbitrary position within the enclosure. one advantage with thi5 application is that no other electric fields are generated in the enclosure, whi~h permits the positioning of the measuring device to be con-trolled for other reason~. A u~e o~ a measuring deviceaccording ~o the invention in enclosed switchgear with one phase only con3titutes an ex~eedingly simple and co~t-sa~ing in6tallation .
It has been indicated above that a ~oltage measureme~t with a measuring device according to the invention i~ sen~iti~e to variations in the di~tance ~etween the mea~uring de~ice and the mea~uring object. This fact may be u~ilized for the purpose of ~tudying a movement of a measurin~ 0~j2ct. A
method for measuring ~oltage from a mea~u~ing object moving ~tochast~cally around a mid-point ~ay thus be achie~ed in a simple manner. A measurement arrangement whi~h perm~t~, on the one hand, a me~hod for studying the lllo~...,_L~t of a con-ductor and, on the other hand, a method for increasing W098t05974 PCT/SE97101289 mea~urement accuracy is show~ i~ Figure 8- ~ike the pre~ious figure, Figure 8 shows an explanatory sk-tch o~ switchgear with one phase only, sur~ounded by an enclosure 29. Around a centrally placed busbar 33, four measuring devices lOa, lOh, l n~, lOd according to the invention are each arranyed in a corne~ of a cross section o~ the 6witch~ear- ~he converted signal from each one of the mea8uring deviceR iB pre$erably analyzed by a four-rh~nel analyzer ~not shown~. To study the mov_...el~t, the 6ignals are compared, and to increa6e the measurement accuracy, the average Yalue o~ the gisnals are formed.
By geomatrical calculations of st~n~d type from the measurement signals, ehe position of the ~$hAr is lS determined, whereby a measurement of the volta~e i~
corrected ~or the change in position 8uch that a correct mea~u~ement val~e may be a~ri~ed at by calculation. The method m~ly al50 be uqed ~or detecting and correcting the measurement for changes in the electric back~rou3d field, which provides unsymmetrical chan~es in the mea~ured 6ignals. A greater measurement accuracy is obtAlne~ by introducin~ a plurality of mea~uri~g device~ which carry out ~ea~urement on the ~ame object. The mea~uring method~
described are not limited to be applied to enclosed switchgear only, but may al50 be applied to free conductors and to non-enclosed ~witchgear. ~n non-enclosed swltchgear~
it is pa~ticularly ~aluable to be able to correct the measurement value for chan~es in the background field.
An alternative ~mhoA;ment of a sen~or ll ~ncluded in a measuring de~ice according t~ t~e in~ent~on ~s 8hown in Figure 9. The ~en~or ll comprises a ~creen e~ectrode 14 which i~ provided ~i~h an ope~ing 16 and which surrounds a first inner ~ub-electrode 12a and a ~econd inner sub-electrode 12b, which are insulated ~rom each other and whichare each adjustably fixed to the ~creen electrode, In the ~hown case, the openin~ 16 is li~ited ~y a ring 34 of a conducting material, connected to the 8creen ~lectrode, the ta~k of which i8 to equa~ize ~he ele~cric field so as to WOs8/0sg74 PCT/SE97/01289 pre~en~ corona. In the example shown, the inn~r ~ub-electrodes are equally large and ~referably have the 6hape of half a round plate, such that the sub-electrodes together ~Y~h1t the ~hap- of a full round ~late. The inner ~ub-elec~rodes are each connected to a re~pective sign~l con-v~rter (not shown), and, in the ~ame way as in example l, the measuremen~ slgnals are each tranFmitted to a res~ective analyzer, or to a common multl-~h~nnel analyzer, sy dividing the inner electrode into sub-electrode~, the a~ove-mentioned ~ensitivit~ to distance dependence may be further utillzed. ~he electrodes are preferably adjusted to exhibit the same capa~itance, ~hereby, by means o~ a bridge circuit, a comparison between the conve~ted signals from each one of the sub-electrodes may determine, on the one hand, whether by meaF,uring object is in front o~ the senso~
and, on the other hand, whether the measuring ob~ect move~
during the measurement. An electric ~ield generated ~rom another unwanted object ls detec~ed b~ dividing ~he inner electrode ~y comparison~ o~ the mea~urement-Q in an analyzer and may thu~ ~e elimina~ed from the measurement result, According to the invention, the inner ele~trode is divided into an ar~itrary num~er o~ ~ub-electrodeR. E-Q~ecially in cc,nnection with point-shaped high-voltag~ objects, the inner electrode is formed in~o a plurality o~ uniform sectors of a circle. In other ~mho~;mPnts, for example in case of the elongated ~en~or de~cribed above, it is inste~d ad~antageous ~o form the ~ub-electrodes as a plurality of plate~ arranged ~ide-by-side.
An additional al~ernati~e Pm~o~;ment of a ~easuring device according to the invention is ~hown in Figure lO. This exa~ple ~hows a mea~turing device which may co~prise one o~
the lamh~ m~nts according to the exanlple6 in Figure 1, 2 or 9, supplemented ~y a device for creat~ng, at the inner electrode with a known frequency, a variation of a recti ied elec~ric field. A mea~urin~ device lO include~ a sensor ll and a signal converter 13. ~he sensor compri~eF, an inner electrode 12 and a screen electrode 14 surro~ i n~ the inner electrode and pro~ided with an opening 16. The inner electrode i8 fixed to an insulatlng tube 17, which is ad~ustably ~ixed to the screen electrode, Buch that the inner electrode 12 may change in a direccion de~i~nated A.
~he inner electrode is connected tP t~ nal converter 1 by means o~ a conductor 18 dra~n throug~ the tube 17, ~he signal con~erter being arranged in a space 21 ~urrounded ~y a screen 19.
A ~ha~t 36, which is rotated by a drive means (not shown), i5 rotatably fixed to the mE~asurins device, and on this ~haft 36 a disc 35, which i~ parallel to the op~ ng 16, iB
fix~d. The ~haft ~6 and the disc 35 are connected to the same potential a~ the screen electrode 14- During rotation of the shaft 36, the disc 35, which extends, for example, along ~ ~emi-circle, will screen the open~ng ~ith a known fr~uency. Of the rectlfied electric field, a directed part will in thi6 way, with variation between zero and full ~ield strength, penetrate through the openi~g in the screen electrode. From thi~ ~ariation, the magnitude of the directed part o~ the rectified field, which falls through the opening, may be measured.
The disc 35, which is preferably made of metal, will, during rotation, alternately ~over and thu8 6creen the opening and lea~e the op~nin~ unscreened such that a variation o~ the penetratiny stationary field is created ~he invention is not limited to onl~ compr~se a disc but may al~o include a plurality of discs, preferably evenly divided on an axis, 3 0 Al~o, the discs may be formed to com~letely co~er the openin~ 16, or only a part thereof. ~he disc or di~c~ ~ay also be arranged, with the same re~ult, to 8creen the whole sen~or or parts thereof.
The invention is not limited to the embodiments shown, but a plurality of modifications are posBible within the sco~e of the appon~ claim~. Thu~, the screen e~ectrode may, ~or example, comprise a plurality o~ opening~ and, in certain a~plications, be de~lgned fro~ net or a perfora~ed material.
Claims (27)
1. A capacitive sensor (11) for detection of a directed part of an electric field comprising an inner electrode (12) and a screen electrode (14), characterized in that the screen electrode (14) surrounds the inner electrode (12) leaving an opening (16), whereby, when the sensor is directed towards a field-generating object, the part of the electric field penetrating through the opening is detected by the inner electrode.
2. A sensor according to claim 1, characterized in that the inner electrode (12) and the screen electrode (14) are insulated from each other by a gaseous dielectric.
3. A sensor according to claim 1 or 2, characterized in that the inner electrode (12) is adjustably fixed to the screen electrode (14).
4. A sensor according to any of the preceding claims, characterized in that the inner electrode (12) has a substantially plane extend, the plane of extend of which being substantially perpendicular to a normal to the opening (16) in the screen electrode (14).
5. A sensor according to any of the preceding claims, characterized in that the inner electrode (12) is cup-shaped.
6. A sensor according to any of the preceding claims, characterized in that the inner electrode (12) comprises a plurality of sub-electrodes (12a, 12b) electrically insulated from each other.
7. A measuring device (10) for measuring of voltage in a high-voltage part (22) surrounded by an electric field, characterized in that the measuring device (10) comprises a capacitive sensor (11), including an inner electrode (12) and a screen electrode (14) connected to a controllable reference potential, the screen electrode being adapted to screen off the inner electrode from a disturbing electric field, whereby the sensor, by sensing a directed part of the electric field penetrating into the inner electrode, at insulation distance measures the voltage of the high-voltage part.
8. A measuring device according to claim 7, characterized in that the screen electrode (14) and the inner electrode (12) are insulated from each other by a gaseous dielectric.
9. A measuring device according to claim 7 or 8, characterized in that the screen electrode (14) surrounds the inner electrode (12) and is arranged with an opening (16), through which the inner electrode senses a directed part of an electric field.
10. A measuring device according to claims 7 - 9, characterized in that the inner electrode (12) includes a plurality of sub-electrodes (12a, 12b).
11. A measuring device according to claims 7 - 10.
characterized in that the measuring device comprises a signal converter (13) which is arranged close to the sensor (11) and comprises members for amplification and impedance conversion of the measurement signal.
characterized in that the measuring device comprises a signal converter (13) which is arranged close to the sensor (11) and comprises members for amplification and impedance conversion of the measurement signal.
12. A measuring device according to claim 11, characterized in that the signal converter (13) includes members for phase locking the screen electrode (14) and/or the inner electrode (12).
13. A measuring device according to any of claims 7 - 12, characterized in that the measuring device (10) is arranged at the grounded part of an insulator.
14. Use of a measuring device (10) according to claims 7 - 13 in switchgear.
15. Use of a measuring device (10) according to claims 7 - 13 in electric power networks for debiting of consumed energy.
16. Use of a measuring device (10) according to claims 7 - 13 in electric power networks for establishing relay functionalities.
17. A method for measuring voltage of a high-voltage part (22) surrounded by an electric field, characterized in that a directed part of the electric field is sensed at insulation distance with at least one capacitive sensor (11).
18. A method according to claim 17, characterized in that the sensor (11) is adapted to comprise an inner electrode (12) and a screen electrode (14) connected to a controllable potential, the screen electrode being adapted to screen off the inner electrode from disturbing electric fields, such that the electric field generated from the high-voltage part is sensed by the inner electrode.
19. A method according to claim 17 or 18, characterized in that the screen electrode (14) is adapted to be insulated from the inner electrode (12) by a gaseous dielectric.
20. A method according to claims 17 - 19, characterized in that the screen electrode (14) is adapted to surround the inner electrode (12), leaving an opening (16) through which a directed part of an electric field is sensed by the inner electrode.
21. A method according to claims 17 - 20, characterized in that a member for phase locking is connected to the sensor (11), by means of which the potential of the screen electrode (14) and/or the inner electrode (12) is locked in relation to the high-voltage part, such that the effect of disturbing electric fields is suppressed.
22. A method according to claims 17 - 21, characterized in that the inner electrode (12) is brought to include a plurality of sub-electrodes (12a, 12b), whereby, by a comparison of the signals from the sub-electrodes, a change in the incident electric field caused by a transfer of the high-voltage part is detected.
23. A method according to claims 17 - 22, characterized in that the sensor (11) is arranged in relation to the high-voltage part (22) at a fixed distance.
24. A method according to claims 17 - 23, characterized in that the sensor (11) is brought to be alternately screened off, whereby a varying electric field is created in the sensor, from which field the direct voltage of a high-voltage part (22) is measured.
25. Use of a method according to claims 17 - 24, in switch-gear.
26. Use of a method according to claims 17 - 24, in an electric power network for debiting consumed energy.
27. Use of a method according to claims 17 - 24, in an electric power network for establishing relay functionalities.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9602785A SE507933C2 (en) | 1996-07-15 | 1996-07-15 | Method, apparatus and sensor for capacitively detecting fields and voltages and their use |
| SE9602785-9 | 1996-07-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2261191A1 true CA2261191A1 (en) | 1998-02-12 |
Family
ID=20403403
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2261191 Abandoned CA2261191A1 (en) | 1996-07-15 | 1997-07-15 | Method, device and sensor for capacitive detecting of field and voltage and use thereof |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0912902A1 (en) |
| JP (1) | JP2000514191A (en) |
| CN (1) | CN1229474A (en) |
| AU (1) | AU719566B2 (en) |
| BR (1) | BR9710724A (en) |
| CA (1) | CA2261191A1 (en) |
| NO (1) | NO990169L (en) |
| SE (1) | SE507933C2 (en) |
| TR (1) | TR199900074T2 (en) |
| WO (1) | WO1998005974A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2768898C2 (en) * | 2017-04-06 | 2022-03-25 | Синаптек Лимитед | Multiphase sensor module, system and method |
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|---|---|---|---|---|
| SE512698C2 (en) * | 1997-11-27 | 2000-05-02 | Abb Ab | Electric system with capacitive contact-free voltage measurement and control unit for reducing harmonics |
| GB0310409D0 (en) * | 2003-05-07 | 2003-06-11 | Koninkl Philips Electronics Nv | Object sensing |
| ITBO20080393A1 (en) * | 2008-06-20 | 2009-12-21 | Alberto Bauer | CAPACITIVE SENSOR TO DETECT AN ELECTRIC FIELD GENERATED BY A CONDUCTOR |
| ITBO20080392A1 (en) | 2008-06-20 | 2009-12-21 | Alberto Bauer | CAPACITIVE SENSOR TO DETECT AN ELECTRIC FIELD GENERATED BY A CONDUCTOR |
| ITBO20080079U1 (en) | 2008-10-30 | 2010-04-30 | Lorenzo Peretto | BUILDING SYSTEM FOR A CAPACITIVE SENSOR. |
| CN103582821B (en) * | 2011-04-14 | 2015-11-25 | 西门子公司 | For contactless device, Electricity testing pliers and the method for determining the current potential of object |
| US9128135B1 (en) | 2013-01-02 | 2015-09-08 | Lockheed Martin Corporation | System, method, and computer program product to provide wireless sensing based on an aggregate electric field reading |
| IT201600103234A1 (en) | 2016-10-14 | 2018-04-14 | Green Seas Ventures Ldt | Constructive system relating to a capacitive voltage sensor |
| CN107192894A (en) * | 2016-11-18 | 2017-09-22 | 国网甘肃省电力公司电力科学研究院 | A kind of alternating current-direct current complex electrical field detector |
| WO2019073497A1 (en) * | 2017-10-13 | 2019-04-18 | Alberto Bauer | Constructive system regarding a capacitive sensor |
| IT201700115489A1 (en) * | 2017-10-13 | 2019-04-13 | Green Seas Ventures Ltd | CONSTRUCTIVE SYSTEM AFFIRMING A CAPACITIVE VOLTAGE SENSOR |
| IT201800004114A1 (en) | 2018-03-30 | 2019-09-30 | Green Seas Ventures Ltd C/O Citco B V I Ltd | CONSTRUCTION SYSTEM WITH A CAPACITIVE VOLTAGE SENSOR |
| US11346876B2 (en) | 2018-12-17 | 2022-05-31 | G & W Electric Company | Electrical sensor assembly |
| CN113196067A (en) | 2018-12-17 | 2021-07-30 | G&W电气公司 | Electric sensor assembly |
| US11415538B2 (en) | 2020-03-06 | 2022-08-16 | Applied Materials, Inc. | Capacitive sensor housing for chamber condition monitoring |
| CN114062794A (en) * | 2021-10-27 | 2022-02-18 | 中国南方电网有限责任公司超高压输电公司贵阳局 | Insulator surface electric field intensity measuring device and insulator system |
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| US3826981A (en) * | 1968-05-03 | 1974-07-30 | H Ross | Solid-state high impedance meter system |
| US4052665A (en) * | 1976-03-30 | 1977-10-04 | Snap-On Tools Corporation | Capacitive pickup device for pulsating high voltage measurements |
| US4328461A (en) * | 1979-07-02 | 1982-05-04 | Mcdonnell Douglas Corporation | Apparatus for and method of measuring a high voltage electric field |
| US4397702A (en) * | 1980-01-09 | 1983-08-09 | Johnson Controls, Inc. | Fabrication of non-conductive charged sensing probe unit |
-
1996
- 1996-07-15 SE SE9602785A patent/SE507933C2/en not_active IP Right Cessation
-
1997
- 1997-07-15 AU AU36396/97A patent/AU719566B2/en not_active Ceased
- 1997-07-15 EP EP97933123A patent/EP0912902A1/en not_active Withdrawn
- 1997-07-15 CN CN 97197676 patent/CN1229474A/en active Pending
- 1997-07-15 BR BR9710724A patent/BR9710724A/en not_active Application Discontinuation
- 1997-07-15 TR TR1999/00074T patent/TR199900074T2/en unknown
- 1997-07-15 CA CA 2261191 patent/CA2261191A1/en not_active Abandoned
- 1997-07-15 JP JP10505939A patent/JP2000514191A/en active Pending
- 1997-07-15 WO PCT/SE1997/001289 patent/WO1998005974A1/en not_active Application Discontinuation
-
1999
- 1999-01-14 NO NO990169A patent/NO990169L/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2768898C2 (en) * | 2017-04-06 | 2022-03-25 | Синаптек Лимитед | Multiphase sensor module, system and method |
Also Published As
| Publication number | Publication date |
|---|---|
| AU3639697A (en) | 1998-02-25 |
| AU719566B2 (en) | 2000-05-11 |
| NO990169L (en) | 1999-03-12 |
| JP2000514191A (en) | 2000-10-24 |
| CN1229474A (en) | 1999-09-22 |
| TR199900074T2 (en) | 1999-03-22 |
| SE9602785D0 (en) | 1996-07-15 |
| SE9602785L (en) | 1998-01-16 |
| NO990169D0 (en) | 1999-01-14 |
| EP0912902A1 (en) | 1999-05-06 |
| BR9710724A (en) | 1999-08-17 |
| SE507933C2 (en) | 1998-07-27 |
| WO1998005974A1 (en) | 1998-02-12 |
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