CN217467147U - Measuring device based on wide-range current transformer - Google Patents
Measuring device based on wide-range current transformer Download PDFInfo
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Abstract
The utility model discloses a measuring device based on wide range current transformer belongs to the power measurement technology field. The utility model discloses the system, include: a current transformer, the current transformer comprising: the device comprises a movable magnetic core, a primary winding, a secondary winding and a detection winding; the voltage dividing resistor receives the induced voltage signal and the induced current signal, divides the voltage and transmits the voltage to the signal conditioning circuit; the signal conditioning circuit transmits the induction voltage signal after voltage division to the digital detection module, converts the induction current after voltage division into a voltage signal and transmits the voltage signal to the digital detection module; and the digital detection module determines the higher harmonic content of the current transformer according to the voltage signal, determines the air gap adjustment length of the movable magnetic core according to the higher harmonic content, and determines the secondary current compensated by the current transformer according to the received induced voltage signal. The utility model discloses a wide range of current transformer measurement has ensured current transformer's measurement accuracy again.
Description
Technical Field
The utility model relates to an electric power measurement technical field to more specifically relates to a measuring device based on wide range current transformer.
Background
The current transformer is one of key devices in an electric power system, can convert a large-current signal in a primary system into a secondary side small-current signal in proportion, and plays roles in signal transmission and transformation and safety isolation. The current transformer for metering is an important component of an electric energy metering appliance, has a great amount of application in a power distribution network, and is just and fair in electric energy trade settlement directly related to accuracy or not.
The traditional electromagnetic current transformer adopts a closed magnetic core, and the design method of a closed magnetic circuit can ensure that the magnetic impedance of the current transformer is smaller, obtain better magnetic conductivity, and ensure that primary and secondary currents of the current transformer have better transmission and transformation characteristics.
However, when the primary current is large, the magnetic core is saturated, or when the primary current has a dc component, because the magnetic resistance is very small, the dc magnetic flux in the closed magnetic circuit is very high, the magnetic core also reaches a saturated state, and the secondary current generates a severe distortion phenomenon, which causes a large measurement error of the current transformer, and further causes a significant economic loss.
According to the measured data, when the primary current exceeds 150% of rated current, the current transformer enters a protection state, and the ratio error of 200% of rated current even exceeds 5%. Therefore, when the primary current of the existing metering current transformer is too large, the measurement accuracy can be sharply deteriorated, in order to meet the requirement of accurate electric energy metering, a metering department generally selects a current transformer with the range covering the user electric load range as much as possible, but because the existing metering current transformer only keeps good accuracy within the range of 20% -120% of rated current, the current transformer is difficult to deal with the situation of user load change, and the transformer selection is difficult to some extent. Partial users can select the transformer with the load lower than the actual load of the partial users to reduce the payment of the basic electricity charge, and then the actual operation capacity of the transformer is improved by means of forced cooling and the like, and the maximum operation capacity can even reach 200% of the nominal rated capacity. At the moment, the actual primary current of the current transformer is far larger than the rated current of the current transformer, so that the iron core is rapidly saturated, the current measured by the transformer is far smaller than the actual current, and the electricity stealing event of the type occurs occasionally. The traditional current transformer for metering cannot be completely suitable for all electric energy metering requirements, and can cause less metering of a large amount of electric energy in certain specific scenes, so that electric energy trade settlement is not fair and fair, and the national property loss is caused. Therefore, aiming at the demand of electric power marketing management work, the problem of electric energy measurement loss caused by the limitation of the measurement range of the traditional current transformer for measurement is solved, the research on the wide-range technology of the current transformer for measurement needs to be introduced urgently, the electric energy measurement with higher accuracy in a wider range is realized, and powerful technical support is provided for the electric power marketing work.
In order to solve the problems brought by a closed magnetic circuit, an air gap is reserved on a magnetic circuit of some current transformers, but the air gap is fixed, and the traditional current transformer with the fixed air gap has the advantages that the linearity of a magnetization curve becomes good due to the existence of the air gap, the larger the air gap is, the better the linearity of the magnetization curve is, and on the other hand, the remanence of a magnetic core can be obviously reduced, and the larger the air gap is, the more the remanence of the current transformer is reduced. Therefore, the influence of the residual magnetism on the current transformer with the air gap is smaller than that of the conventional current transformer. The current transformer magnetic core has an air gap, so that saturation magnetic induction intensity is increased, and the larger the air gap is, the more saturation magnetic induction is increased, so that the anti-saturation capacity of the air gap magnetic core is higher than that of a closed magnetic core. However, due to the existence of the air gap, the magnetic permeability of the magnetic core of the current transformer can be significantly reduced, and the larger the air gap is, the more the magnetic permeability is reduced, the error of the current transformer can be increased, which reduces the measurement accuracy of the current transformer, and even makes the current transformer difficult to reach the design accuracy. Because the length of the air gap of the magnetic core of the current transformer is fixed and unchanged, and the traditional fixed air gap current transformer only adopts a compensation measure for changing the number of turns of the secondary winding, when primary current is normal or primary current is small, the error of the current transformer with the fixed air gap relative to the current transformer with the closed magnetic core is large, on the other hand, if a short circuit condition occurs, the primary current is continuously increased, the magnetic core with the fixed air gap still can reach a saturated state, and the secondary current is distorted.
The traditional current transformer structure with the adjustable air gap is used for adjusting the length of the air gap by arranging movable magnetic cores with different lengths in the magnetic cores and controlling the magnetic flux density in the magnetic cores during large current so that the current transformer is always positioned in a linear measurement area. The novel current transformer has the same primary and secondary windings as the traditional structure, and has the difference that the magnetic core consists of a fixed magnetic core and a movable magnetic core, and the air gap length of the magnetic core can be adjusted through a movable magnetic core unit. When the current in the primary winding changes greatly, the magnetic flux density of the magnetic core still does not exceed a saturation value when the primary current is maximum by adjusting the length of the air gap, and the magnetic core characteristic is always located in a linear region so as to widen the measuring range of the current transformer. However, the problem that the precision of the novel air gap adjustable current transformer is not high enough and the adjusting speed is too slow exists, and the movable iron core of the current transformer is in a unit structure, so that when the movable unit of the magnetic core moves, the magnetization curve of the magnetic core can be suddenly changed, the measurement error of the current transformer can also be suddenly changed, a reasonable current compensation measure is not taken, and the precision of the current transformer can be greatly reduced. On the other hand, because of the absence of a monitoring system, the change of the air gap length is not standardized, and a closed system cannot be formed, the adjustment of the air gap is not timely enough and is not accurate enough.
The error of the current transformer is mainly determined by the size of the exciting current, and in order to improve the precision of the current transformer, the exciting current of the current transformer is basically reduced, or the exciting current of the current transformer is extracted and compensated according to the exciting current of the current transformer. However, the method of extracting the exciting current is used for the traditional closed type current transformer and is influenced by the exciting impedance, the exciting impedance of the traditional closed type current transformer is not a fixed value, because the magnetization characteristic of the closed magnetic core is nonlinear, when the magnetic core tends to be saturated, the exciting impedance changes, the exciting current of the current transformer cannot be effective under the condition, and the error of the exciting current can be compensated.
SUMMERY OF THE UTILITY MODEL
To the above problem, the utility model provides a measuring device based on wide range current transformer, include:
a current transformer, the current transformer comprising: the device comprises a movable magnetic core, a primary winding, a secondary winding and a detection winding;
the movable magnetic core adjusts the air gap ratio of the current transformer according to the air gap length determined by the digital detection template;
the primary winding and the detection winding penetrate through the inner part of the movable magnetic core in a through structure, and the secondary winding is uniformly wound on the movable magnetic core; the detection winding outputs an induced voltage signal, and the secondary winding outputs an induced current signal;
the voltage dividing resistor receives the induced voltage signal and the induced current signal, divides the voltage and transmits the voltage to the signal conditioning circuit;
the signal conditioning circuit transmits the induction voltage signal after voltage division to the digital detection module, converts the induction current after voltage division into a voltage signal and transmits the voltage signal to the digital detection module;
and the digital detection module determines the higher harmonic content of the current transformer according to the voltage signal, determines the air gap adjustment length of the movable magnetic core according to the higher harmonic content, and determines the secondary current compensated by the current transformer according to the received induced voltage signal.
Optionally, the movable magnetic core is a UI type magnetic core, and includes a U type magnetic core and an I type magnetic core, the U type magnetic core is used as a fixed part of the movable magnetic core, and the I type magnetic core is used as a movable part of the movable magnetic core.
Optionally, the movable magnetic core is made of permalloy 1J 85.
Optionally, the adjustment length of the movable magnetic core is set to be a maximum adjustment length, and each adjustment does not exceed the maximum adjustment length.
Optionally, the signal conditioning circuit includes two, one of which converts the induced current signal into a voltage signal and transmits the voltage signal to the digital detection module after voltage division, and the other of which transmits the induced voltage signal to the digital detection module.
Optionally, the signal conditioning circuit for converting the divided induced current signal into a voltage signal includes: an integrating circuit, a low-pass filter and a voltage follower;
signal conditioning circuit to sense voltage signal transmission to digital detection module includes: a low pass filter and a voltage follower.
Optionally, the digital detection module includes: the device comprises a signal acquisition circuit and a digital micro-processing unit;
the resolution of the signal sampling circuit is not lower than 8 bits; and the digital micro-processing unit determines the air gap adjustment length and the secondary current compensated by the current transformer.
Optionally, the digital detection module is provided with a high-order harmonic content threshold, if the determined high-order harmonic content is within the threshold, the air gap length is kept unchanged, if the determined high-order harmonic content is greater than the threshold, the air gap length is increased, and if the determined high-order harmonic content is less than the threshold, the air gap length is decreased.
The utility model discloses a current transformer's measuring wide range has ensured current transformer's measurement accuracy again, and air gap length self-adaptation adjustable wide range current transformer is whole, simple structure, and the equipment is convenient, is favorable to equipment and production, and the effectual measurement range who improves current transformer to current transformer's measurement accuracy has been ensured.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 is a graph of magnetization for different air gap ratios for a magnetic core;
FIG. 3 is a graph of compensation current scaling factor versus airgap core airgap ratio.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, which, however, may be embodied in many different forms and are not limited to the embodiments described herein, which are provided for the purpose of thoroughly and completely disclosing the present invention and fully conveying the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments presented in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same unit/element is denoted by the same reference numeral.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
The present invention will be further described with reference to the following examples:
the utility model provides a measuring device based on wide range current transformer, as shown in figure 1, include:
a current transformer, the current transformer comprising: the device comprises a movable magnetic core, a primary winding, a secondary winding and a detection winding;
the movable magnetic core adjusts the air gap ratio of the current transformer according to the air gap length determined by the digital detection template;
the primary winding and the detection winding penetrate through the inner part of the movable magnetic core in a through structure, and the secondary winding is uniformly wound on the movable magnetic core; the detection winding outputs an induced voltage signal, and the secondary winding outputs an induced current signal;
the voltage dividing resistor receives the induction voltage signal and the induction current signal, divides the voltage and transmits the voltage and the induction current signal to the signal conditioning circuit;
the signal conditioning circuit transmits the induction voltage signal after voltage division to the digital detection module, converts the induction current after voltage division into a voltage signal and transmits the voltage signal to the digital detection module;
and the digital detection module determines the higher harmonic content of the current transformer according to the voltage signal, determines the air gap adjustment length of the movable magnetic core according to the higher harmonic content, and determines the secondary current compensated by the current transformer according to the received induced voltage signal.
The movable magnetic core material is selected from permalloy 1J85 material with high magnetic permeability and low coercive force; the magnetic core adopts UI type magnetic core, wherein U type magnetic core part is fixed, and I type magnetic core part accessible magnetic core connects mechanical part moves up and down at minimum within range, changes current transformer's air gap ratio, and primary winding and detection winding adopt the structure of punching to pass from the magnetic core is inside, and secondary winding part is at the fixed magnetic core part of mutual-inductor U type evenly coiling.
The secondary winding output current signal is converted into a voltage signal through a voltage dividing resistor and a signal conditioning circuit and is transmitted into a digital detection module, the digital detection module calculates the content of higher harmonics, the air gap length is automatically adjusted according to the calculation result output signal, the detection winding output current signal is converted into a voltage signal through the signal conditioning circuit after passing through the voltage dividing resistor, the voltage signal is transmitted into the digital detection module, the signal is subjected to proportional operation in the digital detection module to obtain the size of exciting current, and the size of the exciting current is superposed with the size of fundamental wave output by the secondary winding, so that the size of the compensated secondary current can be obtained.
The movable magnetic core can adjust the length of the air gap by moving left and right, the moving distance of the movable magnetic core is limited, the length of the air gap cannot exceed the set maximum length, and when the magnetic core is not in a saturation state and primary current does not contain a direct current component, the length of the air gap is approximately equal to zero.
The signal conditioning circuit comprises an integrating circuit, a low-pass filter circuit and a voltage follower; the signal conditioning circuit connected with the secondary winding comprises a low-pass filter and a voltage follower, and the signal conditioning circuit connected with the detection winding comprises an integrating circuit, a low-pass filter and a voltage follower.
The integrating circuit realizes the integrating function of the output signal, the low-pass filter circuit filters high-frequency noise in the signal, and the voltage follower is used for reducing output impedance.
The digital detection module realizes the functions of rapidly acquiring signals, storing signals, digitally filtering and digitally operating, and consists of a signal acquisition circuit and a digital micro-processing unit.
The signal sampling unit has a high-frequency sampling function and a double-channel sampling function, and the resolution is not lower than 8 bits; the digital micro-processing system receives the data collected by the sampling system, performs digital filtering processing on the signals in the secondary winding, calculates the content of higher harmonics and the fundamental wave peak value of the secondary current, performs proportional operation on the signals in the detection winding and is used for digital compensation of the secondary current, and finally obtains the compensated secondary current value.
The determination of the air gap ratio of the movable magnetic core is as follows:
determining the length of the air gap through the high-order harmonic content calculated by the digital micro-processing system, setting two thresholds for the high-order harmonic content in the digital micro-processing system, and keeping the length of the air gap unchanged when the high-order harmonic content value is between the two thresholds; when the higher harmonic content value is larger than the threshold range, the movable magnetic core moves to increase the length of the air gap, and the higher harmonic content value is gradually reduced along with the increase of the length of the air gap and is finally in the threshold range; when the higher harmonic content value is smaller than the threshold range, the movable magnetic core moves to reduce the length of the air gap, the higher harmonic content value is gradually increased and is finally within the threshold range.
The utility model discloses well air gap magnetic core equivalent permeability's affirmation specifically as follows:
let the exciting current be i 0 Magnetic induction B, magnetic field strength in magnetic core H 0 Magnetic field strength in the air gap is H 1 The equivalent magnetic field strength of the air-gap core is H, and the average magnetic path in the core is l 0 Length of magnetic path in air gap of l 1 Air gap ratio of λ and relative permeability of core of μ r Magnetic permeability in vacuum is mu 0 And the equivalent magnetic permeability of the air-gap magnetic core is mu, then:
i 0 ＝H 0 l 0 +H 1 l 1 (1)
the magnetization curve of the closed core is:
H 0, ＝f(B) (2)
the equivalent magnetic field strength of the airgap core can be expressed as:
H＝i 0 /(l 0 +l 1 ) (3)
thus obtaining:
H(l 0 +l 1 )＝H 0 l 0 +H 1 l 1 (4)
therefore, the following steps are obtained:
H＝f(B)+λB/μ 0 (5)
the equivalent permeability of an airgap core is therefore:
μ＝B/H＝B/(f(B)+λB/μ 0 ) (6)
because of the existence of the air gap, the magnetic permeability of the magnetic core becomes small, the remanence of the magnetic core is obviously reduced at the same time, the excitation impedance is basically unchanged, the anti-saturation capacity of the magnetic core is enhanced, and the value of the higher harmonic content is positioned between two threshold values, so that the magnetization curve of the magnetic core is always positioned in a linear region, under the condition that only the linear region of a B-H curve is considered, the relation between the magnetic field intensity and the magnetic induction intensity can be approximated to a direct proportional function, and if the proportionality coefficient of the closed magnetic core in the linear region is K, the relation between the magnetic field intensity and the magnetic induction intensity of the closed magnetic core can be approximated to:
H＝f(B)＝K B (7)
then:
μ＝B/H＝B/(f(B)+λB/μ 0 )＝B/(K B+λB/μ 0 )＝μ 0 /(μ 0 K+λ) (8)
the symmetric relation between the magnetic field strength and the magnetic induction strength when the air gap ratios are different can be obtained through the calculation, and the equivalent magnetic permeability of the air gap magnetic core when the air gap ratios are different can be further obtained. The magnetization curves for the cores at different air gap ratios are shown in fig. 2.
The extraction of the excitation current (compensation current) is specifically as follows:
the exciting current is the root cause of the work of the current transformer, but the exciting current is the main source of the error of the current transformer, the exciting current of the current transformer is extracted and used for the compensation of the secondary current, and then the secondary current can realize zero error theoretically; on the other hand, because the magnetization curve of the magnetic core is always positioned in a linear region, the nonlinear error of the air-gap magnetic core current transformer can be ignored, and the exciting current can be effectively extracted.
When current passes through the primary winding, voltage is induced in the detection winding due to the existence of the excitation current, and the induced voltage and the excitation current satisfy the following relation:
wherein u is the induced voltage in the detection winding, n is the number of turns of the detection winding, s is the sectional area of the magnetic core, and l is the average magnetic path length of the magnetic core.
Therefore, the signal passes through the signal conditioning circuit to obtain a signal proportional to the exciting current, the signal is acquired by the signal acquisition circuit and transmitted to the digital micro-processing system, the value of the exciting current (compensation current) is obtained through numerical calculation and is used for compensating the secondary current, and a relation graph of the compensation current proportionality coefficient and the air gap ratio of the air gap magnetic core is shown in fig. 3.
The utility model discloses a current transformer's measuring wide range has ensured current transformer's measurement accuracy again, and air gap length self-adaptation adjustable wide range current transformer is whole, simple structure, and the equipment is convenient, is favorable to equipment and production, and the effectual measurement range that improves current transformer to current transformer's measurement accuracy has been ensured.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The embodiment of the present invention provides a scheme that can be implemented by various computer languages, for example, object-oriented programming language Java and direct-translation scripting language JavaScript, etc.
The present invention has been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the appended claims be interpreted as including the preferred embodiment and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (6)
1. A wide range current transformer based measurement device, the device comprising:
a current transformer, the current transformer comprising: the device comprises a movable magnetic core, a primary winding, a secondary winding and a detection winding;
the movable magnetic core adjusts the air gap ratio of the current transformer according to the air gap length determined by the digital detection template;
the primary winding and the detection winding penetrate through the inner part of the movable magnetic core in a through structure, and the secondary winding is uniformly wound on the movable magnetic core; the detection winding outputs an induced voltage signal, and the secondary winding outputs an induced current signal;
the voltage dividing resistor receives the induced voltage signal and the induced current signal, divides the voltage and transmits the voltage to the signal conditioning circuit;
the signal conditioning circuit transmits the induction voltage signal after voltage division to the digital detection module, converts the induction current after voltage division into a voltage signal and transmits the voltage signal to the digital detection module;
and the digital detection module determines the higher harmonic content of the current transformer according to the voltage signal, determines the air gap adjustment length of the movable magnetic core according to the higher harmonic content, and determines the secondary current compensated by the current transformer according to the received induced voltage signal.
2. The apparatus of claim 1, wherein the movable core is a UI-type core, comprising a U-type core as a fixed portion of the movable core and an I-type core as a movable portion of the movable core.
3. The apparatus of claim 1, wherein the movable magnetic core is made of permalloy 1J85 material.
4. The device of claim 1, wherein the adjustment length of the movable core is set to a maximum adjustment length, and each adjustment does not exceed the maximum adjustment length.
5. The apparatus of claim 1, wherein the digital detection module comprises: the device comprises a signal acquisition circuit and a digital micro-processing unit;
the resolution of the signal acquisition circuit is not lower than 8 bits; and the digital micro-processing unit determines the air gap adjustment length and the secondary current compensated by the current transformer.
6. The apparatus of claim 1, wherein the digital detection module is configured with a high harmonic content threshold, and wherein the determined high harmonic content is within the threshold, the air gap length is maintained, if greater than the threshold, the air gap length is increased, and if less than the threshold, the air gap length is decreased.
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| CN115453176A (en) * | 2022-11-07 | 2022-12-09 | 南方电网数字电网研究院有限公司 | Sensitivity-switchable current mutual inductance device and current detection device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115453176A (en) * | 2022-11-07 | 2022-12-09 | 南方电网数字电网研究院有限公司 | Sensitivity-switchable current mutual inductance device and current detection device |
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