WO2009008757A2

WO2009008757A2 - Magneto-optical head with adjustable analyzer for current measurements at medium and high voltage

Info

Publication number: WO2009008757A2
Application number: PCT/RS2008/000023
Authority: WO
Inventors: Miodrag Hadzic
Original assignee: Miodrag Hadzic
Priority date: 2007-07-06
Filing date: 2008-07-04
Publication date: 2009-01-15
Also published as: WO2009008757A3; RS20070295A; RS50440B

Abstract

Invention belongs to the field of electrical measuring equipment with measurement error compensators, and concretely relates to magneto- optical head with adjustable analyzer for current measurements at medium and high voltage. The invention furthermore relates to the improved structure of the measuring head used for precise current measurements at medium and high voltage on all standard busbars up to 100 x 10 mm. The measuring head concerned comprises of the following: with plastic of high resistance shielded holder (1) of optical cables (2) and housing (6) of the magnetic concentrator, specially shaped magnetic concentrator (7) with double- segmented side (29) and housing (48) of the magneto-optical crystal (44) with subassembly, which comprises a worm gear (64) for change of the angle of the analyzer (68). Adjusting of the analyzer's (68) angle enables selection of the measuring range and separate calibration of each individual head, which eliminates technological imperfection of LEDs used as light generators.

Description

Miodrag HADZIC, Belgrade, Serbia

MAGNETO-OPTICAL HEAD WITH ADJUSTABLE ANALYZER FOR CURRENT MEASUREMENTS AT MEDIUM AND HIGH VOLTAGE

TECHNICAL FIELD OF THE INVENTION

Subject of invention in general belongs to the field of measuring equipment and measurement procedures for electrical variables, which include different measurement error compensators, and concretely relate to the measuring head with adjustable analyzer of a stationary device for precise measurements of current and monitoring of medium and high voltage at all standard sizes of busbars.

According to the International Patent Classification (IPC, Int. cl⁷) subject of invention has been classified and marked by the basic classification symbol, G 01 R 3/00, which defines devices or procedures specially adjusted for manufacturing measuring instruments; as well as secondary classification symbol, G 01 Rl/38 01 Rl/38, which includes instruments for altering the measuring characteristic.

Due to the specific method of operation, this invention may be classified with another secondary classification symbol G 01 R 33/032, which includes devices or instruments for measuring magnetic variables by magneto-optical devices, for example, the Faraday device.

TECHNICAL PROBLEM

The subject of invention solves a technical problem that consists of the following: how to design a measuring head of variable measuring range with magneto-optical current sensor, which is fixed to the busbar where measuring or monitoring of electrical values is performed, at the control measurement points or monitoring systems, where the signal - primary current ratio is independent from the electromagnetic radiation, with the option of adjusting the device to maximum performance, in order to eliminate reproducible problems as the result of technological imperfection of the magneto-optical crystal sensors and light generators; at the same time, the device should also be reliable, easy to be embedded into a busbar of standard dimensions and 360 kV voltage level, and distinguished by high accuracy and reliability of measured values.

TECHNICAL STATUS

Electric currents in power systems flow through the custom copper or aluminum busbars, and there is great practical interest to perform the current measurement directly on the busbars, wherein the busbar is used as primary conductor of the current sensor.

According to the current technical status, the problem related to elimination of measurement errors depending from the magnetic field strength is successfully settled with optical fibre devices based on the Faraday effect. Such devices have been proved stable and reliable, primarily more precise in comparison with the conventional current transformers.

It has been established by review of domestic and foreign patent documentation that there are numerous inventions based on the magnetic flux rotation of the polarization plane, but majority of these solutions include different fibre optic sensor structures. Inventions which relate to instruments for measuring electrical parameters, current and voltage, found by the author, are mainly based on optical fibre coils into which measuring conductor is inserted for current measurements. Such are the two characteristic patents of the Firm MWB MESSWANDLER-BAU AKTIENGESELLSCHAFT with the same name "A fiber optics arrangement for measuring the intensity of an electric current utilizing the Faraday effect". The first invention, Patent No. 47228, is the device where the light is guided from a light source through a polarizer to a semitransparent plate. From there, the polarized light arrives in an optical fibre, which is partially wound into a coil, a high-voltage conductor extending in its axis and the current to be measured flowing in this conductor, to electronic circuit for forming of a signal shown on display. Patent No. 47724 is a device where light is used in the same way as in the previous patent, but with only one winding of the optical cable, and in the arrangement twisted optical fibre with reflective surface is in question.

Searching through patent documentation, Patent Application of Jovan Radunovic from Belgrade, with the title "Portable device with fiber-optic sensors for measuring electric current intensity on high voltage installations with no interruptions of power supply" was found, but a comparison could not have been made because the application was not published.

The author of the Patent, Miodrag Hadzic, has presented with his Small Patent No. MP -40/07 "Mobile fiber-optic measuring instrument of improved safety and technical characteristics" for measuring the intensity of electrical current with no interruptions in the electric current supply, whose operating is based on the use of magneto-optical arrangements and the Faraday effect, modulation of light under the influence of the magnetic flux, where one of the sides of the magnetic concentrator has a movable axis, thus enabling, for measuring purposes, which are performed without interruption of conductors, placing of the measuring conductor in the central hole of the concentrator.

In further elaborating of this idea, after long experimenting and measuring, during which certain impreciseness of the aforementioned instruments was established, caused by modifications resulting from imperfection of crystal grids of the magneto-optical crystal sensors and serially produced light generators (I-EDs), the author has decided to design a stationary measuring head for high voltage measuring and monitoring, for which, after careful patent documentation search it has been established that it is a novelty, because neither the professional literature nor foreign or domestic patent resources include no relevant technical solution concerning the aforementioned issue.

ESSENCE OF THE INVENTION

The invention completely solves the aforementioned technical problem. The essence of the invention is that the respective measuring head is designed as universal, extremely precise wideband stationary measuring device used for monitoring in electroenergetic facilities equipped by busbars of standard dimensions up to 100 x 10 mm. The device according to the invention enables precise measuring of effective values of current of 50 Hz frequency at 6 kV to 360 kV, and what is particularly important, the device enables precise and reliable measuring of current with values lower than IA.

Novelty of the invention is that the device conducting elements, magnetic concentrator and corresponding measuring equipment, reduce due to embedding the existing distance between the measuring busbars, and are of extremely small dimensions, while the whole measuring surface is shielded with highly-resistant plastic, which completely eliminates possible damages due to big currents and high- voltage breakdowns at measuring locations.

The novelty of the invention is also that the measuring head is easily disassembled; thus, it can be easily and quickly embedded in the existing energetic installations, i.e. dismantled if necessary and moved to other measuring locations with no modifications at the transformer stations.

Significant theoretic and practical novelty of the invention and what makes it essentially different in relation to similar technical solutions, even the previous solution of this author, is eliminating of errors that appear due to technological imperfectness of the material used for making of the ma'gneto-optical crystal as well as errors that appear due to unequal values of light generated by standard light generators, LEDs used within the respective device. This has been achieved when in the sensor assembly a correction sub-assembly has been carried out for adjusting the analyzer's angle, which, after forming of the measuring head and after emitting the light from the optical cables, calibrates the measuring head in such a manner that all measuring instruments have maximum measuring performances.

Novelty of the invention is the possibility to select by changing of the analyzer's angle the measuring range of the measuring head in such a manner as to adjust the maximum instrument sensitivity to the desired area where measuring results are found. To the best knowledge of the authors, compared to the devices invented so far, which perforin measuring of the intensity of the electric current, this invention has a lot of advantages as follows:

- significantly easier for embedding and handling and does not need additional space at the measuring location;

- completely environmentally safe and safe handling;

- explosion resistant (in some cases current transformers are subject to explosion hazards);

- universal use of the invention for measuring on all energetic busbars of standard dimension;

- great operating stability and measurement accuracy;

- maintenance is practically unnecessary;

- extremely high reproducibility.

SHORT DESCRIPTION OF FIGURES AND DRAWINGS

For easier understanding of the invention as well as for demonstration of its practical realization, the author, only as an example, points at the enclosed figures of the drawing that refer to the application in subject and where:

- Fig. 1 represents schematic representation of the measuring head of the respective instrument in horizontal cross-section;

- Fig. 2 represents schematic representation of the measuring head of the respective instrument in vertical cross-section 1-1 ;

- Fig. 3 represents schematic representation of the measuring head of the respective instrument in section B-B;

- Fig. 4 represents hole of the magnetic concentrator with the magneto- optical sensor assembly, in detail;

- Fig. 5 represents vertical cross-section of the assembled magnetic concentrator without the fiber-optical sensor assembly;

- Fig. ^represents view of the magnetic concentrator from the lateral side; - Fig. /represents view of the magnetic concentrator from above;

- Fig. 8 represents axonometric appearance of the assembled measuring head, viewed from the front;

— Fig. 9 represents axonometric appearance of the assembled measuring head, viewed from the back;

- Fig. 10 represents axonometric appearance of the magneto-optical crystal holder;

— Fig. 11 represents longitudinal cross-section of the analyzer's angle adjustment bolt;

— Fig. 12 represents axonometric appearance of the worm gear with the holder of the analyzer.

DETAILED DESCRIPTION OF THE INVENTION

As it can be clearly seen in figures of the drawing the measuring head with adjustable analyzer of the stationary device for precise measuring and monitoring of middle and high voltage on all busbars of standard dimensions, up to 100 x 10 mm, consists of the following: holder (1) of optical cables (2), housing (6) of the magnetic concentrator, magnetic concentrator (7) with assembly (8) of the crystal sensor and elements for fixing (4) of the measuring busbars (5).

Holder (1) of the optical cables (2) is made of high resistance plastic - the most favourable solution - of special mechanical (density 0,94 g/cm³, hardness 64-67 SHORE D), thermal (373 K and 1841 J) and electrical characteristics (dielectric strength 90 kV/mm, specific resistance >10¹⁰ Ohm x cm, surface resistance > 10¹² Ohm and resistance of the stray electrical current KA 3 c). Holder (1) of optical cables (2) is made of base (19) an cover (18) of mutually unique, irregular trapezoidal sections, while on the slanted sides of the base (19) paralel slots are formed by mutually connected holes (10 and 12), shaped in such a manner as to enable inserting of standard connectors (11) of optical cables (2) and their fixing, while in the holes (12) standard connectors (13) of optical cables (2) are placed, which in the part towards the magnetic concentrator (7) enter into slightly curved tubular channels (52), through which pass the optical cables (29), whose ends are inserted into holders (14) of the optical fibre. Paralelly with the longest side of the base (19) a shallow recess (47) is found, of trapezoidal section as well, and along slanting sides of the recess, at equal mutual distance, three slits (16) are found on each side, into which, depending from the dimensions of busbars, fixing elements (4) are inserted, with which the measuring head is fixed to the busbar (5). At the end of the longest side of the base (19) are recesses (22) of shape and dimensions to match with corresponding bulges (25) of the magnetic concentrator housing (6). Cover (18) of the holder is made from the aforementioned plastic consistent material and has the same shape as the base (19). In the interior of the cover (18), along its slanting sides, two prismatic bulges (20) are found one opposite the other, analogously to the holes (10); thus, while placing the cover (18) on the base (19) and after tightening with the bolts (21), the bulges (20) close the holes (10) from the upper side and prevent moving of the connectors (11 and 12) of the optical cables (2). In continuation of the bulge (20), at the very end of the concave edge (23) of the cover (18) fixing elements (24) are found in vertical position with respect to connectors (11 and 12) and when the head is assembled prevent their subsequent pulling out.

The housing (6) of the magnetic concentrator is made from the same thermal resistant and electric resistant plastics as well as holder (1) and is a double-segmented (53 and 54) structure coupled with bolts (52) where a completely shielded magnetic concentrator (7) is placed. The shape of the segment (53) of the housing (6) is adjusted for placing of the side (29) of the yoke and lateral sides (26 and 27), while the assembly (54) serves for placing of the side (28) of the yoke. Segments (53 and 54) are completely shut with covers (17 and 55) and mutually tightened with plastic bolts made from the same material as other elements of the housing (6), which enables complete electrical insulation of the yoke on the measuring location in respect to the other elements of the energetic equipment. At the ends of the strengthened segment (53) are found integrated, diagonally along the longitudinal axis, hollow prismatic channels (56) into which horizontal extensions (39 and 40) of the holders (37 and 38) of the concentrator's yoke are inserted. On the outer side of the channel (56) are lateral bulges (25) in the centre of which tubular openings are made for bolts which fasten together the housing (6) with the holder (1) of the optical cables.

Magnetic concentrator (7) represents a specially designed transformer yoke, made of transformer silicon 4% plates, whose three sides (26, 27 and 28) have the same quadratic section, while the strengthened side (29), made out of two symmetrically placed opposite each other and mutually spaced equal segments (31), is shaped in such a manner as to stick out linearly their outer edges with rounded outer crowns (30) toward the yoke center. Thus, in the magnetic concentrator (7) a prismatic hole (32) is formed, into which assembly (8) of the crystal sensor is inserted. Such shape of the yoke, i.e. side (29) has been selected, and after long testing and calculations it has been achieved that the lines of magnetic force of the secondary, induced magnetic flux in the yoke of the concentrator (7), while entering the magneto-optical crystal (44) are approximately paralel, which is important, according to the example of performance in this technical description, because, thus, the maximum accuracy of the measurement results is achieved. Along the segments (31) tubular openings (33 and 34) through which pass the optical cables (2) are made, and at their ends are tubular extensions (43) into which ends of the holder (35) of crystal sensor (44) are inserted. Transformer plates (37) of the magnetic concentrator (7) are fixed with bolts (36), which are found in the openings on L-shaped holders (45 and 38). These holders are placed laterally on the transformer plates (37) and then- longer arm is fixed in its whole length to lateral sides (26 and 27) of the yoke magnetic concentrator (7), while their horizontal part reaches half of the length of the strengthened segments (31). Through horizontal extensions (39 and 40) of the holders (45 and 38), bilaterally placed by the side (28), are openings through which bolts (46) are inserted, by which side (28) is fixed to the rest of the yoke of the concentrator (7). Since the space in electroenergetic facilities is always used rationally, and is limited as a rule, for preventing possible appearance of breakthrough at measuring locations as well as other possible damages, the magnetic concentrator is completely protected by its plastic housing (6). In the middle of the double-segmented side (29) of the concentrator (7), an opening (32) is found into which housing (48) with magneto-optical crystal (44) positioned in the middle is found. Parallelepiped-shaped housing (48) is made from the most favourable polyacetal and is by its dimensions equal to opening (32). On its sides turned toward the strengthened ends of segments (31) shallow cylindrical outlets are found, into which holders (51) of the housing are inserted. On the housing (48), in the part where the incoming optical cable (2) is found, between the holder (51) and the magneto-optical ciystal (44), in the shallow prismatic recess (64) polarizer (50) is placed and then in the shallow circular recess the aperture (49). Through the housing (48) tubular opening (69) is punched axially, into which, on the one end, holder (57) of the magneto-optical crystal is fixed, and, on the other end, axis movable cylindrical holder (59) of the analyzer (68). Holder (59) has a cylinder shape on which slanted teeth (66) are found; thus, it represents a worm gear. On the upper part of the housing (48) a tubular opening (58) is found radially made, into which worm gear (64) with helical teeth (65) is inserted, coupled with slanted teeth (66) of the cylindrical holder (59), intended for adjusting of the analyzer's (68) angle. On the free side of the worm gear (64) is a transversal slot (60), which serves for its rotation while adjusting the angle of the analyzer (68), during calibration of the measuring head; while on the opposite side, on the end, is a ring-like recess (61), through which passes the cylindrical protector (62) inserted into the narrow tubular opening (63) paralel with the holder (57) of the crystal, which does not allow axial movement of the worm gear (64). Modification of the movement of the holder (59) of the 'analyzer (68) does not mean abandoning protection framework of the present invention.

It is necessary to highlight that such housing (48) performance into which axis movable, adjustable analyzer (68) is inserted, means a significant difference in respect to current technical solutions of the equipment of measuring instruments with optical fibers, even in respect to solutions of this author where fixed analyzers were used. Namely, during the experiment it has been noted that magneto-optical crystals of one production series, made by the same technology on the same raw material basis, under equal conditions, demonstrate different technical characteristics, which is most probably the result of the unequal crystal structure, i.e. technological imperfectness of the very material, which causes, during further measurement, such results that subsequent calibration of the measuring instruments is required. Furthermore, it has been noticed that serially produced LEDs, which are used within the measuring instrument as light generators, have their production tolerance and do not generate light of equal technical characteristics, i.e. the light they generate does not always belong to the same spectra part and are not equally stable, which results more or less in necessary additional calibration of the measuring head to achieve the maximum performance and required measurement preciseness, i.e. projected parameters of the measuring instrument. Such performance of the holder (59) of the analyzer enables adjusting of each instrument after calibration to maximum sensitivity in the desired measuring range, in such a way that the electronic assembly consisting of: phototransistor, microprocessor and data processing assembly, receives the signals with optimal primary current and noise ratio, i.e. signals of fixed wavelength so that all measuring heads have the same starting parameters.

Operating of the device is based on already well known Faraday effect as follows: through the incoming optical cable (2) placed on the holder (51) the light comes through the polarizer (50), through the aperture (49) and comes to the magneto-optical crystal (44) where the light modulates under influence of the magnetic flux induced in the yoke of the concentrator (7) due to flow of the current through busbar (5). Such modulated light through axis movable analyzer (68) and outgoing optical cable (2) passes to phototransistor and then to the receiving electronic assembly where it is processed, turned into digital signal and shown on the instrument display; in order to achieve maximum preciseness of the instrument in final procedure, by rotating of the analyzer (68), the measuring head is calibrated to maximum performance in the desired measuring range.

INDUSTRIAL OR OTHER USE OF THE INVENTION

Industrial production of this invention is absolutely possible in plants for production of electrical measuring instruments on the basis of workshop documentation which could be made by experts in this field by use of drawings and descriptions from this application.

The invention is suitable for serial production and its use - beside current measurement at middle and high voltage, on busbars of all standard dimensions, is recommended in monitoring systems in facilities for measurement of real effective values of current of 50 Hz frequency at middle and high voltage.

This device, according to the invention, is meant to substitute classical measuring current transformers in places which must be^' absolutely safe for the environment and the user because they are explosion resistant and eliminate the risk of damage.

It is necessary to emphasize that the device is small and does not require modification of current transformer stations.

Inventor

Claims

PATENT CLAIMS

1. Measuring magneto-optical head with, adjustable analyzer for current measuring at middle and high voltage, wherein: it consists of holder (1) of the optical cables and housing (6) of the magnetic concentrator, shielded in plastic of high electrical resistance, specially shaped magnetic concentrator (7) with double- segmented side (29) with prismatic opening (32) where housing (48) of the magneto-optical crystal (44) with adjustable analyzer (68) is inserted.

2. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, wherein: through the housing (48), made from the most favourable polyacetal, in the shape of parallelepiped, tubular opening (69) is made axially, into which on one end holder (57) of the magneto- optical crystal is fixed, and, on the other end, axis movable cylindrical holder (59) of the analyzer (68), while in the tubular opening (58), radially made, worm gear (64) with helical teeth (65) is inserted, coupled with slanted teeth (66) of the cylindrical holder (59) of the analyzer (68).

3. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, according to claims 1 and 2, wherein: on sides of the housing (48) turned toward the strengthened ends of the segments (31), shallow cylindrical recesses are made into which holders (51) are inserted, while in the part where the incoming optical cable (2) is found, in the shallow recess (64), first the polarizer (50) is placed and then in the circular recess the aperture (45).

4. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, according to claim 2, wherein: the holder (59) is of cylindrical shape with slanted teeth (66) coupled with helical teeth (65) of the worm gear (64) inserted into tubular opening (58) of the housing (48), whereas on the free sides of the worm gear (64) a ring-like recess (61) is

13 transversally performed, through which passes the cylindrical protector (62) inserted into the narrower tubular opening (63).

5. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, wherein: the holder (1) of optical cables consists of basis (19) and cover (18), where on the slanting sides of the basis (19) slots are formed by mutually connected holes (10) and (12), with such shape to enable inserting of standard connectors (11) and (13) of optical cables (2), which at their ends pass into slightly curved tubular channels (52), while in the centre a shallow recess (47) is found and on its slanted sides at equal mutual distance three slits (16) are found on each side, into which fixing elements (4) are inserted.

6. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, according to claim 1, wherein: the housing (6) of the magnetic concentrator is a double-segmented (53) and (54) structure connected by plastic bolt (52) made form the same material as the holder (1), and the shape of the segment (53) is adjusted for placing of the sides (26), (27) and (29), while segment (54) matches the shape of side (28).

7. Measuring magneto-optical head with adjustable analyzer for current measuring at middle and high voltage, wherein: the magnetic concentrator (7) represents a specially shaped yoke of the transformer, whose three sides (26), (27) and (28) have the same quadratic section, while the strengthened side (29), made out of two symmetrically placed opposite each other and mutually spaced equal segments (31), is shaped in such a manner as to stick out linearly toward the yoke center, thus forming prismatic hole (32), while along segments (31) tubular openings (33) and (34) are made for passing of optical cables (2), with tubular extensions (43) at the end, into which holders (51) are inserted, and the transformer plates (37) are tightened with bolts (46) through openings of the horizontal extensions (39) on (40) the L-shaped holders (37) and (38).

Inventor

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