CN111913024A - High magneto-optical coefficient optical fiber capable of improving performance of all-fiber current transformer - Google Patents
High magneto-optical coefficient optical fiber capable of improving performance of all-fiber current transformer Download PDFInfo
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Abstract
The invention relates to a sensing optical fiber with high magneto-optical coefficient, namely high Field constant, which can be used for an electronic all-Fiber Current Transformer (FCT) to optically measure current to be measured, in particular to measure the current of a high-voltage power transmission network. The sensing optical fiber ring made of the reverse magnetic or paramagnetic material doped with the high-Field constant optical fiber with proper concentration is used for FCT, so that the measured signal intensity is enhanced to improve the FCT measurement accuracy, and the turn number of the sensing optical fiber ring can be reduced to improve indexes such as FCT temperature stability and the like; the complexity and the manufacturing process difficulty of the sensing optical fiber ring structure can be greatly reduced, and the firmness and the consistency of the sensing optical fiber ring are improved; the performance of the electronic all-fiber current transformer is obviously improved, so that the practical application requirement of the power industry is met. The high-Phield constant sensing optical fiber provided by the invention can be used for rapidly measuring the magnetic field in complex extreme conditions by an optical method, such as a rapidly-intensified magnetic field in a Tokamak device for controllable nuclear fusion; the rapid measurement of the rapidly-changed strong magnetic field corresponding to various types of large pulse (or surge) alternating current and direct current large currents such as electromagnetic ejection, electromagnetic weapons and the like can also be realized.
Description
Technical Field
The invention relates to a high magneto-optical coefficient sensing optical fiber, namely a high-field constant (Verdet) sensing optical fiber, which can be applied to an all-fiber current transformer to realize the measurement of a signal generated by current to be measured by an optical method, and is particularly suitable for measuring the current of a high-voltage power transmission network; it can also be used to optically measure magnetic fields in complex extreme conditions, such as rapidly changing magnetic fields in a controlled nuclear fusion tokamak apparatus.
Key words: a special optical fiber; an all-fiber current transformer; sensing by rapidly changing strong magnetic field;
belongs to the field of optical materials, electric power and energy.
Background
An electronic all-fiber current transformer (abbreviated as all-fiber current transformer; abbreviated as FCT) based on Faraday magneto-optical effect belongs to a passive electronic optical current transformer and has incomparable advantages compared with the traditional electromagnetic current transformer. The all-fiber current transformer fully utilizes the excellent characteristics of modern photoelectric and fiber sensing technologies, is safe, reliable, perfect in theory and superior in performance, has incomparable advantages of other various technical schemes, is the development direction of a new generation of optical current transformer, is combined with an electronic optical voltage transformer for application, and forms novel high-end key equipment necessary for a large intelligent power grid.
The principle of the all-fiber current transformer is Faraday magneto-optical effect, that is, the effect that the rotation angle of the polarization plane of the transmitted light beam in the optical fiber is proportional to the effective component of the magnetic field where the transmitted light beam is located.
The sensing fiber currently used in all-fiber current transformers is a fused silica fiber (abbreviated as conventional fiber) in the optical communication industry, or a sensing fiber with improved optical transmission characteristics based on the fused silica fiber, such as a low-birefringence fiber, an elliptic core fiber, and a recently-developed optical fiber (both abbreviated as modified fiber).
All these improved optical fibers for sensing are the same as conventional optical fibers in view of their chemical structural composition; which is also the same as conventional optical fibers in terms of its coefficient of sensitivity to magnetic fields, the fielded (Verdet) constant, is on the order of about 1 microradian (1 μ rad/a.1 turns) per ampere turn of current.
The high magneto-optical coefficient, i.e. high-field constant sensing fiber, means a sensing fiber whose magneto-optical coefficient, i.e. field constant value, is significantly higher than that of a conventional fiber.
Advantages of all-fiber current transformer
The all-fiber current transformer manufactured based on the magneto-optical effect fully utilizes the excellent characteristics of the modern photoelectric and optical fiber sensing technology, and has a series of important advantages as follows:
excellent electrical insulating properties; the high voltage and the low voltage are completely isolated; the interference of stray electromagnetic fields is resisted; no ferromagnetic saturation; the frequency domain width is large; the response speed is high; high accuracy over a large dynamic range; high harmonic accuracy; much lighter weight; a much smaller volume; no insulating materials such as oil, paper, plastic, special gas and the like are needed; the environment is protected; the optical fiber outputs a digital signal; no combustion and explosion hazard and high safety property; no danger of secondary open circuit exists; the operation and maintenance cost is low; resistance to fast transient overvoltage (VFTO) disturbances; the transient characteristic is good; the reliability is strong; the advantages of integration and intellectualization;
the above-mentioned series of important advantages are largely dependent on the sensing fiber: it is welded with the rest part of optical fiber, and combined with few optical fiber devices running on line to penetrate through the whole optical path to form a complete optical fiber. The key part is a sensing optical fiber ring which is closed and surrounds a current-carrying conductor, and the sensing optical fiber ring is formed by closing a sensing optical fiber after being bent and coiled into a plurality of circles.
The sensing fiber ring determines the intensity of the optical signal corresponding to the current (generated magnetic field) acquired by the all-fiber current transformer. The accuracy of the measurement can only be guaranteed if the signal strength is sufficient.
Technical obstacles not yet exceeded
The performance of all-fiber current transformers, FCTs, developed to date has approached the level of practical engineering applications. However, there are some technical obstacles that have not yet been overcome: the sensing optical fiber ring has an excessively complex structure, extremely difficult manufacturing process, very fragile device structure, low benefit of manufactured finished products and unstable temperature characteristics of the finished products; and consistency among finished products cannot be guaranteed. Even the use of the improved optical fiber has not been able to overcome the above technical obstacles. Therefore, the overall accuracy, reliability, stability and consistency of the all-fiber current transformer are affected very adversely. The method comprises the following specific steps:
the temperature characteristic of the sensing fiber loop is not stable enough, that is, mainly because the output signal of the sensing fiber loop changes with the change of the environmental temperature, the overall error of the FCT caused by the error formed by the temperature change is difficult to be reduced to the degree allowed by the national power standard;
the manufactured sensing optical fiber ring has poor consistency and is difficult to improve;
the manufacturing process is rather complicated, difficult and the yield is very low;
the manufactured sensing optical fiber ring is complex in structure, fragile in material and poor in firmness;
too much dependence on the manufacturing process and experience;
even if the overall performance of the FCT can meet the national standard requirements after the application of the so-called improved optical fiber, it is difficult to achieve the standard requirements in practice under certain conditions in various tests, and thus the engineering requirements for the product are not yet met.
In FCT, the sensing fiber loop that closes around the current carrying conductor obeys ampere's law:
θ＝∮VH.dx＝VNI (1)
θ: sensing the phase difference (corresponding to the optical signal of the current) between the two beams of polarized light in the optical fiber;
i: the current flowing through the current carrying conductor (the current being measured);
h: magnetic field strength generated by current flowing through a current carrying conductor;
n: number of turns of sensing fiber ring
V: the field (Verdet) constant (magneto-optical coefficient, i.e., V value);
the conventional optical fiber, which is currently commonly used for manufacturing the sensing optical fiber ring, has a composition based on the fused silica material of the conventional optical fiber, and a corresponding field constant is in a value of about 1 micro radian/1 ampere.1 turn (1 μ rad/a.1 turn), and the corresponding wavelength is as follows: 1310 nm. In the improved sensing optical fiber specially made for the sensing optical fiber ring, although the manufacturing process and the optical fiber structure are various, the Phillid constant of the improved sensing optical fiber for the sensing optical fiber ring is about 1 μ rad/A.1 turn because the used materials are the same. But at this level the sensed current signal strength is significantly too weak to guarantee the accuracy required by the national standards for the full range of measured currents. To achieve the necessary signal strength for this level of accuracy, the sensing fiber loop made of spun fiber made of fused silica material must have many turns.
The best choice for the sensing fiber used to make the sensing fiber ring is the spun fiber (spun fiber) made of fused silica material with improved optical transmission performance, and its feield constant is about 1 μ rad/(ampere.1 turns) at 1310 nm. Although expensive optical fibers are manufactured by very complicated and difficult processes and apparatuses, they have the same feld constant as conventional optical fibers because they are made of fused silica.
The accuracy of such FCT measurements is still not guaranteed to reach the 0.2 level of accuracy. And the measurement accuracy is difficult to be kept in the national standard requirement range in the whole temperature range (-40 ℃ to +70 ℃), which is very marginal, and various tests can actually just meet the standard requirements under specific conditions.
The reason for this is that: since the sensing fiber ring must be bent into a closed circle when being manufactured, the stress distribution inside the fiber is changed, so that the refractive index distribution inside the fiber is changed, and linear birefringence is formed inside the fiber, thereby changing the polarization state of the light beam transmitted in the fiber. The result is a change in the strength of the signal measured by the FCT, thus causing an error in the FCT measurement.
Moreover, because a sensing optical fiber ring has to be manufactured by using a relatively large number of turns of sensing optical fibers, and the diameter of the sensing optical fiber ring is restricted by application conditions and cannot be too large, the bending stress inside the optical fibers is large due to the large number of turns of the small-diameter sensing optical fiber ring, and the corresponding linear birefringence is also large. When the external temperature changes, the larger stress in the optical fibers and the corresponding linear birefringence thereof change along with the external temperature, and what is more difficult to solve is that the linear birefringence also changes along with the change rate of the external temperature, and finally the accuracy of the all-Fiber Current Transformer (FCT) is influenced by the temperature, even the change rate of the temperature along with the time; i.e. influenced by the history of the temperature change. It is very difficult to overcome this effect in a digitally compensated manner so that the signal measured by the FCT for the same current also varies with the ambient temperature.
The results of the linear birefringence as a function of the rate of change of the ambient temperature are: the value of the linear birefringence as a function of temperature is practically difficult to reproduce at the same temperature, and various factors in the test operation, as well as the course of the test experience, have an influence thereon. This makes temperature compensation for the linear birefringence error extremely complex and unstable and uncertain, and thus cannot be reliably implemented in practical applications.
Since the full temperature interval of FCT operation is as high as 110 ℃, the corresponding error value is enough to significantly affect the test accuracy specified by the national standard and cannot be ignored.
Therefore, the high-Field constant sensing optical fiber is developed and applied, so that the number of turns of the sensing optical fiber ring is reduced on the premise of ensuring that the same signal intensity is sensed for the same current to be measured, and the linear birefringence generated by the sensing optical fiber ring is reduced accordingly, so that the error caused by the temperature change to the output signal of the optical fiber sensing ring is obviously reduced, and the instability of the linear birefringence corresponding to the temperature change rate is reduced. FCT thus improves accuracy, repeatability and stability over the full temperature range.
The technical scheme provided by the patent
The all-fiber current transformer applying the high-Field-constant sensing fiber according to the patent not only has the advantages, but also has special advantages:
the whole structure is refined, light, compact and firm;
the sensing optical fiber ring has simple structure and easy manufacture;
reliable long-term operation;
resistance to disturbances such as vibration and temperature;
high reliability, long service life, low cost and long service life.
The scheme that this patent gave: the chemical composition of the material used for the sensing optical fiber is improved, namely, the specific element doping is specifically carried out on the materials of the conventional optical fiber and the improved optical fiber, so as to increase the Phillid constant of the sensing optical fiber. The sensing optical fiber ring formed by the high-Field constant optical fiber can provide enough signal intensity to ensure the measurement accuracy, and can also obviously reduce the number of turns of the sensing optical fiber ring to achieve indexes such as FCT temperature stability and the like; meanwhile, the complexity of the sensing optical fiber ring can be greatly reduced, the manufacturing requirement is simplified, the process difficulty is reduced, the firmness of the sensing optical fiber ring is improved, and the consistency of the manufactured sensing optical fiber ring is increased.
Such doped fiber must not only meet the basic optical characteristic index of the conventional fiber, but also have a much higher field constant than the conventional fiber, so as to manufacture an all-Fiber Current Transformer (FCT) which can finally overcome all the above disadvantages and meet the requirements of engineering manufacture and practical grid operation application.
Method for improving optical fiber field constant used for sensing ring
The technical scheme of the patent provides a technical scheme for enhancing the fiber Field constant used by the fiber sensing ring.
The benefits of high-feld constant fibers:
increasing the signal-to-noise ratio of the test signal so as to achieve the 0.2 s-level metering accuracy specified by the national standard;
allows increased accuracy over a large dynamic range;
reducing the number of turns of the optical fiber sensing ring, and remarkably simplifying the structure of the optical fiber sensing ring;
eliminating a complex packaging structure of the optical fiber sensing ring and a fragile and difficult manufacturing process flow thereof;
increasing the stability of the measurement accuracy of the optical fiber sensing ring along with the change of the temperature;
enhancing the firmness of the sensing optical fiber ring structure;
eliminating a complete set of device subsystems for temperature compensation, comprising the following components:
-a fiber optic temperature sensing head;
-a thermometric signal transmitting optical fiber;
-thermometric signal demodulation electronics module and software;
-a thermometric optical path and its light source;
complex and sensitive temperature compensation coefficient debugging, proofreading and pretesting are avoided;
the reliability, durability and firmness of the whole FCT system are obviously improved;
greatly simplifying the overall structure of the FCT;
significantly reduce the cost of FCT;
allowing the value of the field constant to be adjusted to accommodate the FCT of the measured low current signal;
allowing the values of the field constants to be adjusted to accommodate sensing magnetic fields of different strengths;
finally, the adoption of the high-Field constant sensing optical fiber can enable the all-fiber current transformer to become a high-end equipment product which is really applied to high-voltage power network engineering.
In order to obtain a high-Field-constant sensing fiber, the materials used to make the silica fiber and the glass fiber are doped.
Concrete implementation measures
Current state of the art
The sensing fiber commonly used in making FCTs today is fused silica spun fiber and is single mode fiber. The wavelength of the FCT light source is 1310nm, and the material used for the core (core) and cladding (cladding) through which the light beam passes is typically SiO2 (silica) suitably doped to change the optical refractive index; these silica fibers all have a Phillips coefficient of about 1 μ rad/A.1 turns.
Selecting doping materials for increasing the values of the field constants
The optical materials with high Field constant value (abbreviated as V value) which are manufactured at present are mainly magneto-optical glass.
Magneto-optical glasses can be divided into two categories: paramagnetic glass and diamagnetic glass.
In the formula (1), the magneto-optical glass with the positive Field constant V value is an inverse magnetic material, and the magneto-optical glass with the negative V value is a paramagnetic material.
Paramagnetic glass has a large value of V, but is highly temperature dependent, and the value of V is substantially inversely proportional to temperature.
The inverse magnetic glass has relatively small V value but small temperature dependence, so that it may be used in making stable magneto-optical device for application in special environment.
In order to make paramagnetic glass with high Field constant, rare earth element terbium (Tb) is used; and other various doping elements or compounds that can increase the field constant, such as: praseodymium Pr, cesium Ce, cadmium Nd, dysprosium Dy,. et al, and compounds thereof.
In order to produce a high-Field-constant reverse magnetic glass, it is necessary to use various doping elements or their compounds that can increase the Field constant, such as: lead Pb, boron B, germanium Ge, tellurium Te, antimony Sb, bismuth Bi, Tl thallium.
The optical fiber preform for manufacturing the high-Field-constant doped glass sensing fiber or the quartz sensing fiber needs doped elements and compounds thereof which are similar to the compositions of diamagnetic or paramagnetic doped materials needed by magneto-optical glass, but the corresponding concentration values are different.
In order to achieve the requirement that the FCT operates at ambient temperature, it is preferable to select a doped fiber with a reverse magnetic material that has a stable temperature characteristic with respect to its field constant, which is estimated to be approximately at 1310 nm: -0.015 min/osd.cm; from the above calculations, the corresponding field constant value for the international system of units is approximately: 5 μ rad/A.1 turns. The number of turns of the corresponding doped fiber sensing ring with enough current signal strength to be measured in the FCT can be correspondingly taken as: 2 turns.
Method of implementation
The Diamagnetic Faraday rotator Glass (Diamagnetic Faraday rotator Glass) has a Phield constant hardly influenced by the change of ambient temperature (-55 to +135 ℃). Therefore, it is appropriate to select the diamagnetic material for manufacturing the sensing fiber with high Field constant.
Because the existing inverse magnetic material mainly exists in the form of magneto-optical glass, and the technologies and equipment for manufacturing the doped quartz optical fiber preform and the drawn quartz optical fiber have more complex processes and higher cost, the manufacture of the inverse magnetic material glass optical fiber preform is easier; the drawing of the glass fiber can then be performed. And testing the obtained Fielder constant V value of the glass fiber to determine various process parameters such as doping proportion, doping components and the like. And then, the obtained high-Field-constant V-value glass optical fiber can be made into an optical fiber sensing ring and is subjected to experimental operation in the FCT to detect the practical degree of the glass optical fiber.
After the technology of the glass fiber made of the inverse magnetic material is well mastered, the development of manufacturing the doped quartz fiber preform and drawing the quartz fiber is further developed. Because theory and experience show that the light intensity of light beam loss in the quartz optical fiber is less, and the fusion effect of the quartz optical fiber and the conventional and improved optical fibers which are made of quartz materials is better.
Doping technique
The existing inverse magnetic glass material has been studied and tested, firstly, the necessary field constant value range is determined, meanwhile, the necessary optical, mechanical and thermodynamic characteristics of the manufactured glass optical fiber are considered, and then the basic doping components, the proportion and the amount of the doping materials are calculated or estimated according to experience; and the necessary parameters of the preform process for processing the inverse magnetic material glass optical fiber; and conditions for drawing the glass optical fiber.
The fabrication of the fused silica optical fiber preform is complicated. It should be developed after some experience and basis in the development of reverse magnetic glass optical fiber. Fabrication using MOCVD (metal organic chemical vapor deposition) and like techniques is contemplated.
Choosing a suitably high V value of the Phillips constant
In order to obtain the high-Field constant sensing fiber, the optimal target V value required for manufacturing the doping concentration ratio of the glass material or the quartz material must be determined.
Since an excessive concentration of the dopant material in a specific ratio may degrade optical, mechanical, thermal and magneto-optical properties of the optical fiber, the excellent characteristics of the optical fiber such as: low attenuation of optical intensity, high thermal expansion and thermal stability, good chemical stability, high tensile and bending strength, good flexibility, and good weldability to other types of optical fibers. . . Etc., and good magneto-optical properties and glass formation, while too high a proportional concentration of dopant material is not desirable to achieve too high a field constant.
The rated current of the FCT is 1200A for 220kV voltage class specified by national standard. For such a value of current to be measured, it is sufficient that the Phillips constant of the doped fiber reaches about 5 μ rad/A.1 turns at a wavelength of 1310nm, i.e., it reaches not less than about 0.015 min/Osd.cm.
If the excellent properties of the doped fiber and the good magneto-optical properties and glass formation are not well maintained at this level, it is considered that the doping concentration is further decreased so that the Phillips constant of the doped fiber is not less than about 3 μ rad/A.1 turns, i.e., not less than about 0.009 min/Osd.cm; such doped fibers can also be applied to FCTs of rated current 1200A.
Under the condition that the FIELD constant of the reverse magnetism co-doped optical fiber does not reach the minimum value, a paramagnetic material can be co-doped to manufacture the high FIELD constant optical fiber; and a corresponding digital compensation function is added in the signal processing unit so as to eliminate the large change of the field constant of the paramagnetic material along with the temperature.
In FCT with smaller corresponding rated current of 110kV voltage class, such as 600A (or less), specified by national standard, paramagnetic material co-doped manufactured high-Field constant fiber can also be adopted; when the high-Phillips constant can be met only by doping the reverse magnetic material with larger concentration but the good optical and other physical properties of the doped optical fiber cannot be reserved, the high-Phillips constant optical fiber manufactured by co-doping the paramagnetic material with low doping concentration can be used to reserve the good optical and other physical properties of the doped optical fiber; in both cases, a digital compensation function is required to be added to the signal processing unit so as to eliminate the large temperature-dependent change of the field constant of the paramagnetic material.
A research and development stage;
a, trial preparation of a glass optical fiber preform made of a diamagnetic material and a paramagnetic material;
selecting a type of optical fiber; determining a target parameter;
suitably high Phillips constant
The range of values for the Phillips constant for the International Unit System at a wavelength of 1310nm is approximately: 5.5 +/-0.5 mu rad/A.1 turns; the number of turns of the sensing optical fiber coil is reduced: 2 turns.
It should be noted that excessively high values of the field constants are unacceptable and are not required. For example, beyond a Phillips constant value of about 10 μ rad/A.1 turns, the corresponding dopant concentration may be reduced somewhat.
The selection and control of this parameter of doping concentration can be done by calculation and empirically, with values corresponding to the field constants within the above ranges.
The characteristics of the material;
range of optical parameters
Doping a glass optical fiber preform generally increases the loss of the light beam passing through the fiber being drawn therewith. But the length of the light beam which must pass through the doped fiber is greatly shortened due to the reduction of the number of turns of the sensing fiber coil, so that the unit length propagation loss value of the light beam in the reverse magnetic glass fiber is allowed to be properly higher than that of the existing fused silica spiral fiber. This must be taken into account when manufacturing a reverse magnetic glass optical fiber preform; it is of course preferable to be below or close to this numerical level.
Range of mechanical thermal parameters
Considering that the glass optical fiber preform is used for drawing an optical fiber and the obtained optical fiber must satisfy the requirement of winding a sensing optical fiber coil, the structural strength and the mechanical and thermal properties of the glass optical fiber preform should satisfy the requirement of drawing the optical fiber. And it should be considered that the conditions for fusion splicing of the glass optical fiber and the silica optical fiber are satisfied.
If necessary, a non-fusion optical fiber light-transmitting connection mode can be adopted to realize the optical light-transmitting connection of the sensing optical fiber ring and other optical fibers, especially when the optical and sensing performances of the sensing optical fiber ring are tested in the development process.
B, manufacturing a magneto-optical glass optical fiber preform; drawing glass optical fiber
The raw materials used are doped from the process of making the magneto-optical glass optical fiber preform. The doping process can be referred to in conjunction with the process flow for making magneto-optical glass, with the difference that the desired finished product is changed to a glass optical fiber preform. Only the core (core) portion of the fiber through which the beam passes needs to be doped, and the cladding (cladding) only needs to be of a corresponding undoped glass that is index matched to the fiber.
The preform is then drawn into an optical fiber. The single-mode sensing doped optical fiber is expected to be obtained, because the sensing doped optical fiber is matched with the single-mode sensing doped optical fiber, the single-mode sensing doped optical fiber is welded to the single-mode sensing doped optical fiber, and the loss of the welding position of the optical fiber of the same type is smaller.
If the single-mode glass fiber is difficult to draw, the multi-mode doped glass fiber can be drawn first. The V value is tested by using the multimode glass fibers to determine the proportion and the process of the doped magneto-optical material. The configuration, parameters and drawing process of the glass fiber preform are then further modified to obtain a single mode doped glass fiber.
C, the glass optical fiber should have the performance;
the doped glass fiber used for manufacturing the sensing fiber ring should have the light beam propagation loss as close to the quartz fiber as possible at the wavelength of 1310 nm; the values of the field constants of the doped glass fibers are within the values given above; has a mode field radius close to that of the silica fiber to which it is fusion spliced; the good thermodynamic property ensures that the welding position can be adapted to normal operation in a full temperature range; other advantages of the conventional optical fiber, such as flexibility, are maintained so as to be wound into the optical fiber sensing ring; the tensile property is also used for ensuring the strength of the optical fiber sensing ring; there is also a need to apply suitable coating organic materials and coating processes.
The high-Field constant doped optical fiber can be formed by doping a glass optical fiber preform or a fused silica optical fiber preform; the doped regions in both types of fibers are the core (core) portion through which the light propagates; neither of the cladding (cladding) portions need to be doped.
Under the condition that the FIELD constant of the reverse magnetic co-doped fiber is too low to reach the minimum value (3 mu rad/A. turn), paramagnetic materials can be co-doped to manufacture the high FIELD constant fiber; and a corresponding digital compensation function is added in the signal processing unit so as to eliminate the change of the field constant of the paramagnetic material along with the temperature.
In FCTs with smaller current ratings, such as 600A (or less); when the high-Phillips constant can be met only by doping the reverse magnetic material with larger concentration but the good optical and other physical properties of the doped optical fiber cannot be reserved, the high-Phillips constant optical fiber manufactured by co-doping the paramagnetic material with low doping concentration can be used to reserve the good optical and other physical properties of the doped optical fiber; in both cases, a digital compensation function is required to be added to the signal processing unit so as to eliminate the temperature-dependent change of the field constant of the paramagnetic material.
D, testing the performance of the doped diamagnetic and paramagnetic glass fibers;
the doped glass fiber used to make the sensing fiber loop should be tested at a wavelength of 1310 nm. The main contents of the test are:
-a doped glass fiber field constant value (V value);
-rate of change of values of the field constants with temperature;
-a value of the field constant as a function of the wavelength of the light beam;
-beam propagation losses in doped glass fibers;
additional beam propagation losses after mutual fusion with various different optical fibers;
uniformity of the feld constants throughout the doped glass fiber, i.e. the uniformity of the distribution of the doping over the length of the fiber and in the radial direction of the fiber;
mechanical robustness, flexibility, stability under temperature variations of the optical fibers at the fusion splice after fusion splicing with different optical fibers;
and judging whether the comprehensive performance of the doped reverse magnetic glass fiber reaches the required index for manufacturing the FCT sensing fiber ring or not according to the test result. If the FCT is achieved, the FCT can be tried out for complete machine development, otherwise, research and optimization are carried out from the step A.
E, trial production of a doped diamagnetic and paramagnetic quartz single-mode optical fiber preform;
all the above development processes for glass fibers are repeated and adjusted and optimized according to the characteristics of the single-mode silica fiber until a doped silica single-mode fiber having a suitably high field constant while maintaining other excellent characteristics of the single-mode silica fiber is obtained.
The development of doped silica optical fiber preforms should be carried out after some experience and basis from the development of the reverse magnetic or paramagnetic glass optical fiber. However, the two types of optical fiber preforms may not be produced by the same trial-and-error technique, and a doped quartz optical fiber preform may be produced by a similar well-established technique such as MOCVD (metal organic chemical vapor deposition) and then drawn to produce a doped quartz single mode optical fiber.
Drawings
FIG. 1 is a schematic diagram of a high Field constant fiber application that improves the performance of an all-fiber current transformer.
high-Field constant sensing optical fiber for manufacturing sensing optical fiber ring
The layout of the sensing fiber ring in the FCT complete machine structural block diagram is shown in the figure (figure 1).
The rated current for the 220kV voltage class in the national standard is defined as: 1200A. In a sensing loop made of conventional fiber in FCT, in order to achieve an accuracy of 0.2 level, the number of turns of the sensing fiber loop is usually 8 or more. Nevertheless, the accuracy of such FCT measurements is difficult to guarantee to reach the 0.2s level. And the measurement accuracy is just barely kept within the standard requirement range in the whole temperature range.
On the same premise, the number of turns required by a sensing optical fiber ring adopting the high-Fielder-constant optical fiber is optimally not more than 2 turns, and is generally not more than 3 turns corresponding to the rated current of 1200A; the number of turns is much less than that of the conventional optical fibers of various types currently applied. This allows for a greatly optimized sensing fiber optic ring design.
Designing a sensing optical fiber ring;
the structure and design of the sensing optical fiber ring can be greatly simplified by using the high-Field-constant optical fiber; meanwhile, the performance of the material is obviously improved, and particularly, the stability and consistency of the material to temperature change are improved; and obviously reduce the manufacturing process difficulty of the sensing optical fiber ring.
In addition, other performances of the sensing optical fiber ring, such as vibration resistance, strong external magnetic field interference resistance, reliability of the sensing optical fiber ring and the like, can be improved.
Manufacturing a sensing optical fiber ring;
the sensing optical fiber ring adopting the high-Field constant optical fiber only needs to be wound by a few turns, so that the sensing optical fiber ring and the required optical fiber disc are easy to achieve simple structures, the closing requirement of the sensing optical fiber ring is easy to achieve in the process operation process, the temperature stability is easy to guarantee, the consistency among different sensing optical fiber rings is easy to realize, and the sensing optical fiber ring can be arranged in the optical fiber disc in an accurate, firm, reliable and simple mode.
One end of the nonlinear polarization maintaining fiber of the two sections of tail fibers of the fiber quarter-wave plate forming the sensing fiber ring can be directly connected with a section of doped fiber with high Field constant in a welding mode, and the section of doped fiber with high Field constant is wound to form the sensing fiber ring. If the end is not directly connected to the doped fiber by fusion, the non-doped fiber portion of the sensing fiber loop will cause the sensitivity of the sensing fiber loop to be unbalanced in different orientations due to the relatively low Field constant, so that it is necessary to take the shortest distance and to arrange the non-doped fiber portion corresponding to the orientation where the external interference magnetic field can be ignored.
Since the field constant of the reverse-magnetic high-field-constant optical fiber is expected to be 5 times that of the conventional optical fiber (specific numerical values need to be given in practical tests), the requirement of FCT (magnetic flux temperature) of 220kV grade on the signal intensity generated by magneto-optical effect can be met only by adopting a sensing optical fiber ring of 2 turns. The larger current rating for higher voltage levels also requires only either adjusting the doping concentration or slightly increasing the number of turns of the sensing fiber turns. For different magnetic field strengths needing sensing, the problem can be solved by changing the doping concentration of the sensing optical fiber. Even in special application occasions and operating environments, the method can carry out appropriate precise, quick, easy-to-realize and easy-to-output sensing signal test on the magnetic field.
These all simplify the manufacturing process greatly, eliminated existing numerous and diverse, fragile, the yield is extremely low, technological process and packaging structure that the uniformity is extremely poor, cancelled numerous and expensive optic fibre temperature monitoring subassembly for FCT complete machine performance benefits a lot, is expected to reach and satisfy the compelling demand of real engineering application completely, makes FCT really walk into high-end power equipment market and become the strong fulcrum of smart power grids.
Testing a sensing optical fiber ring;
the test was mainly performed around the temperature characteristics of the sensing fiber loop. According to the temperature cycle test flow specified by the national standard, the temperature characteristic of the sensing optical fiber ring can be good, and the moving edge can meet the strict requirement of the standard.
The performance of the whole machine is improved;
the field constant of the sensing optical fiber is increased by carrying out reverse magnetic or paramagnetic magneto-optical substance doping on the preform raw material for manufacturing the sensing optical fiber, so that the number of turns of the sensing optical fiber ring is greatly reduced on the premise of ensuring the same signal intensity sensed by the same current to be measured, and the error and corresponding instability caused by the temperature change on the output signal of the sensing optical fiber ring can be remarkably reduced. Therefore, the overall error of the FCT can be reduced, the testing accuracy in the whole operating temperature range is improved, and meanwhile, the performance of the FCT whole machine, such as the measuring accuracy of the current to be tested, the stability of the FCT whole machine, the structural simplicity degree, the long-term reliability, the consistency, the structural firmness degree and the like, is remarkably improved.
The sensing optical fiber ring made of the sensing optical fiber with the high Field constant improves the following performances of the electronic all-fiber current transformer-FCT:
-enhancing the stability of the sensing fiber loop against temperature changes to improve the measurement accuracy;
improving the stability of the sensing optical fiber ring of the key part of the all-fiber current transformer;
increase the reliability, consistency, structural robustness of the sensing fiber ring structure, etc.;
the process difficulty of manufacturing the sensing optical fiber ring is obviously reduced;
the packaging structure of the sensing optical fiber ring and the manufacturing process thereof are remarkably simplified;
therefore, the application of the high-field constant sensing optical fiber will become a necessary option for achieving the above excellent performances of the all-fiber current transformer.
The scheme of the invention provides that the sensing optical fiber with high Verdet constant can be combined with an electronic all-fiber current transformer applying the optical fiber to quickly measure the magnetic field in complex extreme conditions by an optical method, such as the rapidly-intensified magnetic field in a Tokamak device used for controllable nuclear fusion; and the rapid-changing strong magnetic field corresponding to various types of pulse (or surge) alternating current and direct current large currents such as electromagnetic ejection, electromagnetic weapons and the like can be rapidly measured by an optical method.
Claims (10)
1. A high-magnetostriction coefficient (hifeld) constant sensing fiber for use in an electronic all-fiber current transformer, comprising:
a sensing optical fiber; the sensing optical fiber is a glass optical fiber doped with a reverse magnetic material or a paramagnetic material; fused silica fibers doped with either a diamagnetic or paramagnetic material; the method is characterized in that: the glass fiber or the quartz fiber can sense a signal generated by current to be measured to a light beam passing through the sensing fiber;
a sensing unit: the sensing unit includes: the sensing optical fiber ring is formed by winding the sensing optical fiber doped with the inverse magnetic material or the paramagnetic material; an optical fiber quarter wave plate made of a specific optical fiber combination; the optical fiber disc is used for packaging the sensing optical fiber ring, and the shell is used for protection;
photoelectric and signal processing unit: the photoelectric and signal processing unit comprises a light source and an optical device for modulating, processing and delaying light beams; a photoelectric detector and a signal processing and output circuit;
the light beam emitted by the light source in the photoelectric and signal processing unit enters the sensing optical fiber ring of the sensing unit through the sensing optical fiber; a signal generated by the current to be measured is sensed to a light beam passing through the sensing optical fiber in the sensing optical fiber ring, and the photoelectric and signal processing unit processes the sensing signal in the light beam to obtain a numerical value of the current to be measured;
the method is characterized in that: after being doped with the inverse magnetic material or the paramagnetic material, the value of the Field constant of the sensing fiber is far higher than that of various quartz fibers which are not doped with the inverse magnetic material or the paramagnetic material and are applied to the current electronic all-fiber current transformer.
2. The electronic all-fiber current transformer (abbreviated as FCT) applying the high-Field constant sensing fiber according to claim 1 is characterized in that: the sensing optical fiber ring of the sensing unit is made of the high-Field-constant sensing optical fiber doped with a diamagnetic or paramagnetic material.
3. The sensing optical fiber ring of the sensing unit according to claim 1 and claim 2 is a high-Field-constant doped optical fiber, characterized in that: the sensing fiber with high FIELD constant is doped with specific diamagnetic or paramagnetic doping elements or compound components when being manufactured, and the proper weight and proportion are taken.
4. The sensing fiber loop of the sensing unit according to claim 1 and claim 3 employs the high-feld constant sensing fiber, characterized in that: when the sensing optical fiber is manufactured or various codopant elements or compounds thereof which can increase the field constant and are necessary for realizing the diamagnetic property are doped, such as: lead Pb, boron B, germanium Ge, tellurium Te, antimony Sb, bismuth Bi, Tl thallium,. et al; or terbium (Tb) element and compound thereof which are necessary for realizing paramagnetic optical materials are doped; and other various doping elements or compounds that can increase the field constant, such as: praseodymium Pr, cesium Ce, cadmium Nd, dysprosium Dy.
5. The sensing fiber ring of the sensing unit according to claim 1 and claim 2, characterized in that: on the premise of obtaining the same strength sensing signal for the same current value to be measured, the number of turns of the sensing optical fiber ring which is made of the high-Fielder-constant sensing optical fiber and needs to be wound is generally not more than 3 turns; this is much less than the number of turns required to wind sensing fiber coils of the various types of undoped silica fibers currently in use.
6. The sensing fiber ring of the sensing unit according to claim 1 and claim 5, characterized in that: the sensing optical fiber ring adopting the high-Field constant sensing optical fiber has few turns to be wound, so the sensing optical fiber ring has simple and reliable structure, easy manufacturing process, easy guarantee of temperature stability, easy realization of consistency among different sensing optical fiber rings, and can be packaged in an optical fiber disc in a precise, firm, reliable and simple mode.
7. The sensing fiber ring of the sensing unit according to claim 1 and claim 3, characterized in that: the high-Phillips constant sensing optical fiber can be formed by doping a glass optical fiber or a fused silica optical fiber; the doped regions in both of these types of sensing fibers are the core (core) portion through which the optical beam propagates.
8. The sensing fiber loop of the sensing unit according to claim 1 and claim 3 employs the high-feld constant sensing fiber, characterized in that: the sensing optical fiber ring is preferably made of an optical fiber doped with a reverse magnetic material, so that the change of the field constant value of the optical fiber sensing ring along with the temperature is small when the ambient temperature changes.
9. The sensing optical fiber ring of the sensing unit according to claim 1 and claim 3 is a high-Field-constant co-doped optical fiber, characterized in that: when the FIELD constant of the reverse magnetic co-doped fiber is too low to meet the application requirement, the high FIELD constant sensing fiber can be manufactured by adopting a paramagnetic material; and the photoelectric and signal processing unit is used for enhancing the corresponding digital compensation function to eliminate the change of the field constant of the paramagnetic material along with the temperature.
10. The sensing fiber ring of the sensing unit according to claim 1 and claim 3 is a co-doped fiber with high Verdet constant, characterized in that: in FCT with smaller rated current and when the inverse magnetic material with larger concentration is doped to meet the high Verdet constant but can not keep the good optical and other physical properties of the doped optical fiber, the high Verdet constant optical fiber manufactured by co-doping the paramagnetic material with low doping concentration can be changed to keep the good optical and other physical properties of the doped optical fiber; in both cases, a digital compensation function is required to be added to the signal processing unit so as to eliminate the temperature-dependent change of the field constant of the paramagnetic material.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1605894A (en) * | 2004-11-18 | 2005-04-13 | 上海大学 | Magneto-optic effect photon crystal fiber and manufacturing method thereof |
| CN203084049U (en) * | 2012-12-20 | 2013-07-24 | 中国科学院西安光学精密机械研究所 | Sensing optical fiber ring and reflection type full-optical-fiber current transformer |
| CN108267631A (en) * | 2016-12-30 | 2018-07-10 | 湾世伟 | A kind of electronic type all-fiber current transformator using high magneto-optic coefficient sensor fibre |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1605894A (en) * | 2004-11-18 | 2005-04-13 | 上海大学 | Magneto-optic effect photon crystal fiber and manufacturing method thereof |
| CN203084049U (en) * | 2012-12-20 | 2013-07-24 | 中国科学院西安光学精密机械研究所 | Sensing optical fiber ring and reflection type full-optical-fiber current transformer |
| CN108267631A (en) * | 2016-12-30 | 2018-07-10 | 湾世伟 | A kind of electronic type all-fiber current transformator using high magneto-optic coefficient sensor fibre |
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