CN107356800B - Large current detection device and method for magnetic field cancellation - Google Patents
Large current detection device and method for magnetic field cancellation Download PDFInfo
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- CN107356800B CN107356800B CN201710539565.0A CN201710539565A CN107356800B CN 107356800 B CN107356800 B CN 107356800B CN 201710539565 A CN201710539565 A CN 201710539565A CN 107356800 B CN107356800 B CN 107356800B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
- G01R15/183—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core
- G01R15/185—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core with compensation or feedback windings or interacting coils, e.g. 0-flux sensors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/20—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
- G01R15/202—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices using Hall-effect devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/20—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
- G01R15/207—Constructional details independent of the type of device used
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Abstract
The invention discloses a large current detection device and method for magnetic ring magnetic field cancellation. Two magnetic rings are wound on a current lead to be tested, wherein the winding angles of the two magnetic rings on the lead are different to a certain degree, the two magnetic rings form a structure similar to a concave shape, a large gap is reserved at the intersection of the two magnetic rings, the magnetic force lines are prevented from forming a closed loop in the two magnetic rings respectively, and when the current flows through the lead, the magnetic field generated on the magnetic rings can be offset to reserve the residual magnetic flux. The invention makes the voltage signal output by the magnetic field sensor be zero by adjusting the current wound on the compensation coil on the magnetic ring. The remaining magnetic flux is small and cannot be saturated in the magnetic ring, so that the whole measuring system works in a linear region.
Description
The technical field is as follows:
the invention relates to the field of electrical engineering subjects, instrument science and technology, relates to high-current detection, and particularly relates to a high-current detection device and method for magnetic ring magnetic field cancellation.
Background art:
the measuring method of large current is mainly divided into two categories: one is to determine the magnitude of the measured current according to the voltage drop of the measured current on the resistor, such as a current divider method; the other type is that the current measurement problem is converted into the measurement problem of the magnetic field according to the magnetic field formed by the measured current, and the current magnitude is obtained by measuring the magnetic flux, the magnetic induction intensity or the magnetic potential and then converting. The former has difficulty in meeting the requirements of modern measurement due to the defects of volume, error, loss, insulation, measurement range and the like; from the physical point of view, the latter is classified into a magnetic resonance method, a hall effect method, an electromagnetic induction method, a fluxgate method, an Anisotropic (AMR) method, a giant magnetoresistance effect (GMR) method, a magneto-optical effect method, and the like. In addition, there are a photodiode measurement method, a short pulse discharge method, etc., which are rarely used in engineering practice due to high equipment cost, a complicated structure, etc.
At present, the current measurement methods which are concerned mainly include a hall effect method, a magneto-optical effect method, a rogowski coil method, a transformer method and the like. For general accuracy requirements, a direct amplification (open loop) is often used, while for high accuracy detection, a compensation (closed loop) is often used.
The rogowski coil method is a common means of measuring various varying currents. The method has no magnetic saturation problem, no power and thermal stability problem, is hardly limited by the size of the measured current, and does not need to disconnect the measured circuit during measurement. However, the method is limited by the material of the method, for example, the nonuniformity of the coil frame and the winding brings about a large measurement error, the anti-interference capability of the coil is seriously influenced, the temperature changes the frame of the coil, thereby causing the mutual inductance and the self-inductance coefficient to change, the accuracy of the measurement result is influenced, and the output signal is weaker and is greatly interfered by an external magnetic field. Furthermore, the rogowski coil method can only measure an alternating magnetic field.
The hall current sensor is a commonly used current measuring device, but because the hall element is a semiconductor, the temperature stability and long-term reliability thereof are one of the main reasons that prevent the hall current sensor from being applied to a measuring occasion with high reliability and high accuracy grade requirement. The accuracy grade of the conventional open-loop hall method can only reach 1 grade, and in recent years, with the high integration of semiconductor technology, the linearity and stability of a hall element are greatly improved, but the stability requirement still has many problems. The closed-loop Hall method is stable and reliable, the accuracy grade can reach 0.1 grade and even higher, but the driving capability of the currently adopted balance circuit is limited, the manufacture of the large-current closed-loop Hall current detection device is difficult and high in price, and the defects of large volume, heavy weight, narrow bandwidth and large power consumption exist in a large-current measurement occasion.
The mutual inductor is divided into an alternating current mutual inductor and a direct current mutual inductor, the principle of the alternating current mutual inductor is the same as that of the transformer, and for the detection of large current, the sensor is large in size, heavy in weight and easy to saturate. The direct current transformer utilizes the measured direct current to change the inductive reactance of the iron core choke coil and indirectly changes the current of the auxiliary alternating current circuit, thereby reflecting the magnitude of the measured current. The sensing principle of the method is simple and reliable, the sensing coefficient of the method is only related to the number of turns of the primary side and the secondary side as the alternating current transformer based on the transformer principle, long-term reliability and temperature stability are both guaranteed, and the method is an effective means for detecting direct current large current, but the sensor is also large in size, larger than a closed loop type Hall current sensor, very high in price and required to be supported by an external power supply. The accuracy grade of the conventional direct current transformer is below 0.5 grade, and the accuracy grade can be improved to 0.01 grade or even higher by adopting a compensation method, but the volume and the weight of the transformer are further increased.
The sensitivity of the Anisotropic (AMR) method and the giant magnetoresistance effect (GMR) method is higher, the two methods can adopt a closed loop mode of current compensation to detect a magnetic field generated by large current, and the defect of the method is the same as that of a closed loop Hall current detection method because the magnetic flux in a magnetic ring is 0 when the closed loop current compensation is in a steady state.
The magneto-optical effect method is generally implemented by using an optical fiber, which is a signal transmission component and a sensing component, and is therefore called an all-fiber current sensor. The optical guide material of the magneto-optical effect method has good electrical isolation and insulation performance and good anti-electromagnetic interference characteristic, but the sensor has the stability problems of random drift, signal attenuation and the like because an optical device is exposed outdoors, and the accuracy grade is generally below 0.5 grade, serious vibration interference and poor stability. Meanwhile, the sensing optical fiber is generally imported from foreign countries and is expensive. Therefore, the existing reflection-type all-fiber direct current transformer is not put into use in a large quantity.
In order to overcome the drawbacks of the above-mentioned large current measurement method, patent 201610802270.3 adopts a two-wire magnetic field cancellation method to substantially overcome the problems of large volume and insufficient accuracy of the conventional large current measurement-based device. However, this method is only suitable for use in equipment such as switch cabinets, and for power transmission and distribution lines, it is impossible to lay two parallel wires as required, so that the present invention aims to provide a large current measurement scheme that can be used on the power transmission and distribution lines.
The invention content is as follows:
the invention aims to provide a large-current detection device and a method which are small in size, light in weight, small in power consumption, high in accuracy and good in reliability and can be suitable for magnetic field cancellation of a single wire after being installed.
In order to achieve the purpose, the invention adopts the following technical scheme:
a large current detection device for magnetic ring magnetic field cancellation comprises two magnetic rings sleeved on a lead to be detected, wherein one ends of the two magnetic rings are fixedly connected, the joint of the other ends of the two magnetic rings is provided with an air gap, and a sensor for detecting a magnetic field is arranged at the air gap; and a compensation coil is wound on one of the magnetic rings to compensate residual magnetic flux existing in the magnetic rings when current flows in the lead wires.
The invention has the further improvement that the two magnetic rings are made of high-permeability materials, the diameters and the materials of the two magnetic rings are the same, the winding angles of the two magnetic rings on the tested lead are both larger than 360 degrees but smaller than 540 degrees, the winding angle of one magnetic ring on the lead of the current to be tested is slightly larger than that of the other magnetic ring on the lead of the current to be tested, and the winding modes of the two magnetic rings ensure that the directions of magnetic fields on the two magnetic rings are opposite when the current flows on the lead, so that magnetic field cancellation is formed, and only a small part of magnetic flux is left in the magnetic rings.
The invention has the further improvement that the two magnetic rings are combined into a concave-like structure, and the opening direction of the magnetic rings is vertical to the extending direction of the lead of the current to be measured.
The invention has the further improvement that a distance space is reserved at the respective intersection of the two magnetic rings, so that the magnetic force lines are prevented from forming a closed magnetic loop in the two magnetic rings respectively.
The invention is further improved in that the distance d between the two magnetic rings at the respective junction satisfies the following expression,
d>D2μ0rm/a
wherein r ismIs the magnetic resistance of the magnetic ring, D is the diameter of the magnetic ring, a represents the measurement accuracy level, mu0Is air permeability.
The invention has the further improvement that the large current detection device for magnetic ring magnetic field cancellation also comprises: the magnetic field detection device comprises a signal conditioning circuit, a microprocessor and a compensation current controller, wherein an output signal of a sensor for detecting a magnetic field is connected to the conditioning circuit, an output signal of the conditioning circuit is connected with the microprocessor, the microprocessor outputs a control signal to the compensation current controller, and an output end of the compensation current controller is connected with a compensation coil of a magnetic ring.
When current flows on a tested lead, the magnetic fluxes on the two magnetic rings are different in size and opposite in direction, so that most of the magnetic fluxes formed by the two magnetic rings are mutually counteracted, a small part of the magnetic fluxes is left, and the small part of the magnetic fluxes are acquired and processed by a sensor of the tested magnetic field, and finally the magnetic fluxes generated by the compensating current in the magnetic rings are completely counteracted with the original residual small part of the magnetic fluxes by adjusting the current of a compensating coil on the magnetic rings.
The invention is further improved in that the magnitude of the current to be measured is obtained by multiplying the measured compensation current value by a coefficient, wherein the coefficient is obtained according to the ratio of the given standard current to be measured to the measured compensation current value.
A further improvement of the invention is that the sensor for detecting the magnetic field, placed in the air gap, can be a hall sensor, a giant magneto resistance sensor, a fluxgate sensor, or an anisotropic magnetic field sensor, according to the ampere-loop theorem,
(B1-B2)l/(μ0μr)+(B1-B2)δ/μ0＝I (1)
wherein, B1And B2Respectively the magnetic induction intensity generated by the current I to be measured in the two magnetic ringsL is the total length of the two magnetic rings after combination, and delta is the length of an air gap reserved for detecting the magnetic field intensity, (delta)<<l)，μ0Is air permeability, murFor the relative permeability of a magnetic material, let k be (l/. mu.)r+δ)/μ0Then, a calculation expression of the current I to be measured can be obtained,
I＝k×(B1-B2) (2)
therefore, the voltage collected by the magnetic field sensor passes through the signal conditioning circuit and is input into the microprocessor, the microprocessor outputs a control signal to adjust the current of the compensating circuit, so that the magnetic induction intensity generated by the compensating current in the magnetic ring is equal to the original residual (B)1-B2) And the current to be measured can be calculated by offsetting the current values.
The invention is further improved in that if the alternating current is detected, the following three modes can be adopted:
directly using the output voltage of a compensation coil wound on a magnetic ring as an output signal of large current detection; or
A standard resistor is connected in series with the compensation coil, and the voltage on the resistor is used as output; or
And closing the compensation coil, and directly outputting the current in the compensation coil as an output signal of large current detection.
Compared with the prior art, the invention is characterized in that two magnetic rings are sleeved on a lead of a current to be measured, one ends of the two magnetic rings are fixedly connected with each other, an air gap is reserved at the other end, a magnetic sensor is arranged at the air gap, and a compensation coil is wound on one of the magnetic rings. The winding mode of the two magnetic rings on the lead leads the directions of magnetic fields generated in the two magnetic rings when current flows in the lead to be opposite, but the magnetic fields are slightly different in size, most of magnetic fluxes in the two magnetic rings are mutually offset, only a small part of magnetic fluxes are left, the magnetic induction intensity of the air gap is detected through the magnetic field sensor, finally, the signal output by the magnetic sensor is zero by adjusting the size of the compensating current, and then the current to be detected can be obtained by multiplying the compensating current by a coefficient to be calculated.
Description of the drawings:
fig. 1(a) is a schematic front view of a concave magnetic ring sleeved on a lead to be tested;
fig. 1(b) is a schematic side view of a concave magnetic ring sleeved on a lead to be tested;
FIG. 1(c) is a schematic view of the installation of a wire to be tested and a compensation coil, a Hall piece and a lock catch thereof, which are installed on a magnetic ring shaped like a Chinese character 'ao';
FIG. 2 is a schematic diagram of a current measurement and compensation current control architecture;
FIG. 3 is a schematic diagram of a Hall sensor conditioning circuit;
FIG. 4 is a schematic diagram of a single-conductor magnetic field canceling direct-measurement output current;
FIG. 5 is a schematic diagram of an automatic online detection structure of a single-conductor magnetic field for direct measurement output voltage.
The specific implementation mode is as follows:
embodiments of the present invention will be further illustrated and discussed below in conjunction with the figures and examples.
The invention discloses a large current detection device and a method for magnetic field cancellation of concave-shaped magnetic rings, wherein two high-permeability materials with the same diameter and material are wound on a wire to be detected, the winding angle of one magnetic ring (1) is slightly larger than that of the other magnetic ring, specifically, the winding angles of the two magnetic rings (1) on the wire (L) to be detected are both larger than 360 degrees and smaller than 540 degrees, and the winding angle of one magnetic ring (1) on the wire of the current to be detected is slightly larger than that of the other magnetic ring (1) on the wire of the current to be detected, so that magnetic field cancellation can be formed in the magnetic rings (1) and residual magnetic fields are reserved, and therefore the residual magnetic fields in the magnetic rings (1) are not too large, the magnetic saturation phenomenon cannot occur, and the whole measuring system works in a linear region. The joint of one ends of the two magnetic rings (1) is fixed by a lock catch (7), and an air gap (A) for installing a Hall sensor is reserved at the other end of the two magnetic rings to form a concave magnetic ring, wherein the concave opening is vertical to the extending direction of the lead. If the wire is placed vertically, the opening of the letter "concave" is oriented to the left or right, the opening of the letter "concave" in this embodiment is oriented to the left, and the air gap is provided at the lowermost end of the letter "concave".
The air gap (A) is as small as possible, the magnetic induction intensity of the air gap and the magnetic induction intensity of the inner part of the magnetic ring are approximately equal, and a larger gap d is left at the intersection of the two magnetic rings (the gap satisfies d)>D2μ0rmA, wherein rmThe magnetic resistance of the magnetic rings, D the diameter of the magnetic rings and a the measuring accuracy grade), thus avoiding the magnetic lines of force from forming a closed loop in the two magnetic rings (1) respectively.
The current to be measured can form a part of residual magnetic flux after the part of magnetic flux is offset in a concave magnetic ring with an air gap, the Hall sensor is used for measuring the part of magnetic residual flux, a voltage signal measured by the sensor is input into a microprocessor after being processed by a signal conditioning circuit, a control signal is output to a current compensation controller after being processed and analyzed, and the current in a compensation coil wound on the magnetic ring is adjusted, so that the magnetic flux generated by the compensation current in the magnetic ring is completely offset with the small part of residual magnetic flux which is not offset originally, and the voltage signal output by the Hall sensor is zero.
In this embodiment, the hall sensor 9 is selected to detect the magnetic field, but other magnetic detection devices, such as a giant magnetoresistance sensor, a fluxgate sensor, or an anisotropic sensor, may be used in other embodiments. According to the theory of ampere-loops,
(B1-B2)l/(μ0μr)+(B1-B2)δ/μ0＝I (1)
wherein, B1And B2The magnetic induction intensity generated by the current I to be detected in the two magnetic rings (1) respectively, l is the total length of the two magnetic rings (1) after combination, delta is the length of an air gap left by the magnetic field intensity to be detected, (delta)<<l)，μ0Is air permeability, murFor the relative permeability of a magnetic material, let k be (l/. mu.)r+δ)/μ0Then, a calculation expression of the current I to be measured can be obtained,
I＝k×(B1-B2) (2)
the large current detection device for magnetic ring magnetic field cancellation further comprises: the magnetic field detection device comprises a signal conditioning circuit, a microprocessor and a compensation current controller, wherein an output signal of a sensor for detecting a magnetic field is connected to the conditioning circuit, an output signal of the conditioning circuit is connected with the microprocessor, the microprocessor outputs a control signal to the compensation current controller, and an output end of the compensation current controller is connected with a compensation coil of a magnetic ring. The winding mode of the two magnetic rings sleeved on the lead leads to that the directions of magnetic fields generated in the two magnetic rings are opposite when current flows in the lead, but the magnetic fields are slightly different in size, most of magnetic fluxes in the two magnetic rings are mutually offset, only a small part of magnetic fluxes are left, the magnetic induction intensity of the air gap is detected through the magnetic field sensor, a voltage signal output by the sensor is input into the microprocessor after passing through the conditioning circuit, a control signal is output to the compensation current control loop after being processed by a control algorithm, the size of the compensation current is adjusted, the signal output by the magnetic sensor is zero, and then the current to be detected can be obtained by multiplying the compensation current by a coefficient to be calculated.
Therefore, the voltage collected by the magnetic field sensor passes through the signal conditioning circuit and is input into the microprocessor, the microprocessor outputs a control signal to adjust the current of the compensating circuit, so that the magnetic induction intensity generated by the compensating current in the magnetic ring is equal to the original residual (B)1-B2) And the current to be measured can be calculated by offsetting the current values.
Because the magnetic field in the magnetic ring is offset, the saturation phenomenon can not occur, therefore, for the compensation type, the number of turns and the current of the compensation coil can not be too large, the volume and the weight of the detection device can be made to be very small, and the energy consumed by the compensation coil can also be reduced; for the direct measurement mode, the number of turns and the current of the output coil are not too large, so that the size and the weight of the detection device can be reduced.
In the implementation of the invention, a set of standard test currents I is used1Flowing through the wire and adjusting the compensating current I2So that the voltage signal output by the magnetic field sensor is zero, thus obtaining a test current and a compensation currentCalculating coefficient c ═ I1/I2Thus, for any given test current, the solution can be solved by multiplying the compensation current by a calculation coefficient. In practice, the current measurement can be carried out by direct measurement or by compensation measurement.
[ DIRECT MEASUREMENT ]
The method is mainly used for obtaining the magnitude of the current to be detected by directly winding an output induction coil on a concave magnetic ring when the current to be detected is alternating current, and directly detecting the output current of the induction coil, or by connecting a standard resistor 5 on the induction coil in series and acquiring the magnitude of the current to be detected by acquiring the test voltage value of the resistor. The specific embodiment is shown in figures 4 and 5.
According to the ampere-loop theorem:
(B1-B2)l/(μ0μr)＝I (3)
wherein, B1And B2The magnetic induction intensity generated by the current I to be measured in the two magnetic rings is respectively, l is the total length of the two magnetic rings, mu0Is air permeability, murIs the relative permeability of the magnetic material.
Residual magnetic induction intensity (B) in concave magnetic ring1-B2) The induced current generated on the output induction coil can be directly measured by an ammeter in a manner shown in fig. 4, or can be automatically measured on line in a manner shown in fig. 5, that is, the reading of the ammeter or the reading of an output signal in a processor can be read, so that the alternating current value to be measured can be calculated.
[ Compensation measurement method ]
The measuring method is mainly used for measuring direct current, a Hall sensor is arranged at an air gap of the concave magnetic ring, when the current to be measured flows through the lead, magnetic induction intensity is generated in the concave magnetic ring, the Hall sensor detects the magnetic induction intensity and outputs a voltage signal, the acquired voltage signal passes through the signal conditioning unit, a standard electric signal is input to the microprocessor, a control algorithm is generated by the controller and is output to the current compensation control circuit, wherein the compensation circuit is connected with the compensation coil in series, so as to adjust and generate the compensation current, so that the compensation current generates a magnetic field in the magnetic ring to completely counteract with the original residual small part of the magnetic field, finally, the voltage signal acquired by the Hall sensor is zero, so that the magnitude of the current to be detected can be detected by calculating the magnitude of the compensation current. As described above, according to the ampere-loop theorem, there are:
(B1-B2)l/(μ0μr)+(B1-B2)δ/μ0＝I (2)
wherein, B1And B2The magnetic induction intensity generated by the current I to be measured in the two magnetic rings, l is the total length of the two magnetic rings after combination, delta (delta)<<l) the length of the air gap, μ, left for the detection of the magnetic induction0Is air permeability, murIs the relative permeability of the magnetic material.
Let k equal (l/. mu.r+δ)/μ0Then, a calculation expression of the residual magnetic induction in the magnetic ring can be obtained:
B1-B2＝I/k (4)
here, it is not required to make the number of turns of the compensation coil N, and the compensation current generated by generating a control signal to the compensation circuit via the controller is I', so that when the voltage signal collected by the hall sensor is zero, that is:
NI’＝B1-B2(5)
from equations (4) and (5), the computational expressions for the compensation current and the current to be measured are readily derived:
I＝kNI’ (6)
according to the expression (6), the current to be measured and the compensation current show a linear relationship, and in actual calculation, the current to be measured is not obtained by the expression (6), but a standard current to be measured I is given first1Then adjusting the compensation current and reading the compensation current value I2Then, the calculation coefficient c ═ I can be found1/I2Thus, in the process ofWhen a current to be measured is determined, the magnitude of the current to be measured can be calculated according to the product of the magnitude of the compensation current value and the calculation coefficient.
After the magnetic field in the magnetic ring is offset, the magnetic flux left in the magnetic ring is small, so that the magnetic saturation phenomenon cannot occur in the magnetic ring, and for a compensation measurement method, the compensation current and the number of turns of the compensation coil can be comprehensively considered, so that the size, the weight and the power consumption of a large-current detection device can be greatly reduced, and the effects of high measurement accuracy and good stability are achieved; for direct measurement, the number of turns of the output coil can be reduced significantly, so that the volume and weight of the measuring device can be reduced.
When two magnetic rings are designed, the assumption is not made that the magnetic field intensity formed by the current I to be measured in the first magnetic ring is taken as H1When the magnetic field intensity is equal to 49H, the magnetic field intensity formed in the second magnetic ring is H2When the magnetic field intensity signal is 51H, the magnetic field intensity signal collected by the hall sensor is (H)2-H1) 2H is total magnetic field strength (H)2+H1) The product of the current and the number of turns needed to compensate the magnetic field strength is obviously only 2% of the original value, and the compensation current and the number of turns are reduced, so that the size, the weight and the power consumption of the measuring device can be obviously reduced.
Example (b):
for the implementation of direct current, for convenience of illustration and discussion, the present example uses a hall sensor as a detection unit to illustrate the implementation method of the present invention. The arrangement scheme of a current lead wire to be measured and a concave magnetic ring is shown in figure 1, the system structure diagram of the measuring method is shown in figure 2, the detecting device consists of a magnetic ring made of high magnetic conductive material, a Hall magnetic field sensor and a conditioning circuit thereof, a microprocessor, a compensating coil, a compensating current and a controller thereof and a constant current source, wherein the magnetic ring is sleeved on the lead wire to be measured and is fixed by a lock catch to form a concave magnetic ring with a gap, the Hall magnetic field sensor is arranged in the middle of the gap, the compensating coil is wound on the magnetic ring, and the number of turns of the compensating coil is N2The Hall magnetic field sensor and its conditioning circuit are shown in FIG. 3, and it is used to detect magnetism in the magnetic ringThe small portion of the magnetic field strength remaining after field cancellation is (H) according to the above assumptions2-H1) After the signal collected by the magnetic sensor is inputted into the microprocessor after passing through the conditioning circuit, the signal controls the compensation current outputted by the compensation current controller, and the compensation current is adjusted to make the magnetic field in the magnetic ring reach magnetic balance, namely H ═ I2N2And 2H, namely H' is equal to 2H in size and opposite to the 2H in direction, so that the output of the Hall magnetic field sensor is zero. In practice, a standard current to be measured can be given, the number of turns of the compensation coil is designed, the coefficient can be calculated only by measuring the magnitude of the compensation current, and then for any large current to be measured, the magnitude of the large current to be measured can be calculated by multiplying the coefficient by the compensation current correspondingly measured.
Because the magnetic field intensity in the magnetic ring before compensation is only 0.02 (H)2+H1) Compared with the conventional detection device of the closed-loop Hall current sensor, the current turn product needing to be compensated is reduced by 2%. If the magnitude of the compensation current is not changed, the number of turns of the compensation coil is changed to be 2% of that of the detection device of the conventional Hall current sensor, so that the volume of the measurement device is greatly reduced; if the number of turns of the compensation coil is N2The compensation current of the device of the invention is 2% of the conventional compensation current, the required compensation current is greatly reduced, and considering that the resistance of the compensation coil is R, the power consumed on the compensation coil is P ═ I2 2R, therefore, the improved measurement scheme of the present invention produces only 1/2500% of the power consumption of the compensation coil of the measurement device of the conventional closed-loop hall-method current sensor; if the compensating current is only reduced to 20% of the compensating current of the conventional closed-loop Hall measuring device, the number of turns N of the compensating coil2Can be reduced to 10 percent, thereby reducing the power consumption generated by the device and reducing the volume and the weight of the device. For the large current measuring device of the conventional closed loop Hall method, because the compensation current is large and the power consumption is high, a heat radiating device needs to be considered to be added, otherwise the magnetic conductivity of a magnetic ring is possibly reduced, but the measuring method disclosed by the invention has low power consumption and small volume, and does not need to consider the heat radiating problem at all, because the measuring method disclosed by the invention has low power consumption and small volumeThe device is further reduced in size.
For the ac embodiment, the residual magnetic field strength generated by the current after the cancellation of the magnetic field generated by the magnetic ring in the shape of Chinese character 'ao' is (H) according to the assumption above2-H1) Thus, an output coil is wound on the magnetic ring, and with the structure of fig. 4, an ammeter can be directly connected in series with the output coil, but in practice, it is inconvenient to operate the magnetic ring in this way. Therefore, a precise test resistor can be connected in series to the output coil, the voltage on the test resistor is input to the microprocessor after passing through the signal conditioning unit, and the microprocessor calculates and sends the calculated current value to the remote monitoring system, as shown in fig. 5. Similarly, after the magnetic field of the concave magnetic ring is offset, the magnetic flux in the magnetic ring is greatly reduced, so that the output current of the secondary coil is also greatly reduced, and under the factors of the size and the power consumption of the integrated detection device, the detection device can be smaller in size, lighter in weight and lower in power consumption than the conventional detection method.
The magnetic rings for collecting the magnetic field are formed by combining two magnetic rings with the same diameter and material, and are particularly sleeved on a lead of a current to be measured, wherein the winding angles of the two magnetic rings on the lead have certain difference and form a structure similar to a Chinese character 'ao', compensation coils are wound on the magnetic rings, a larger gap is reserved at the junction of the two magnetic rings to prevent two magnetic lines of force from forming a closed loop in each magnetic ring, so that the magnetic fields formed by the current to be measured in the magnetic rings can be mutually cancelled, and the residual magnetic flux is reserved. And an air gap is reserved when the concave magnetic rings are connected, a magnetic field sensor is arranged in the air gap to detect the residual small part of magnetic flux, a voltage signal acquired by the magnetic field sensor is input to a microprocessor through a signal conditioning circuit, the microprocessor generates a control algorithm, a control signal is output to a compensation control loop, the magnitude of compensation current is adjusted, the output voltage signal of the magnetic field sensor is enabled to be zero, then a standard current to be detected is given, the current in a compensation coil is measured, a proportionality coefficient between the current and the compensation coil can be obtained, and then the magnitude of the current to be detected is obtained by multiplying the current actually adjusted and compensated by the coefficient. The magnetic flux left in the magnetic ring is small when the magnetic ring is designed, so that the magnetic ring cannot be saturated, the whole device works in a linear region, the size, the weight and the power consumption of the large-current sensor can be greatly reduced by the method, and the method is high in measurement accuracy and good in stability.
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A large current detection device for magnetic ring magnetic field cancellation is characterized in that: the winding angle of one magnetic ring on the lead wire of the current to be measured is slightly larger than that of the other magnetic ring on the lead wire of the current to be measured, and the winding mode of the two magnetic rings ensures that the directions of magnetic fields on the two magnetic rings are opposite when the current flows on the lead wire, so that magnetic field cancellation is formed, and only a small part of magnetic flux is left in the magnetic rings; one ends of the two magnetic rings are fixedly connected, an air gap is reserved at the joint of the other ends, and a sensor for detecting a magnetic field is mounted at the air gap; a compensation coil is wound on one of the magnetic rings and used for compensating residual magnetic flux existing in the magnetic rings when current in the lead flows; the two magnetic rings are combined into a concave-like structure, and the opening direction of the magnetic rings is vertical to the extending direction of the lead of the current to be measured;
a distance space is reserved at the respective intersection of the two magnetic rings to prevent magnetic lines of force from forming a closed magnetic loop in each of the two magnetic rings;
distance between two magnetic rings at respective junctiondThe following expression should be satisfied,
d>D 2 m 0 r m /a
wherein the content of the first and second substances,r m is the magnetic resistance of the magnetic ring,Dis the diameter of the magnetic ring,athe level of accuracy of the measurement is indicated,m 0air permeability;
the large current detection device for magnetic ring magnetic field cancellation also comprises: the magnetic field detection device comprises a conditioning circuit, a microprocessor and a compensation current controller, wherein an output signal of a sensor for detecting a magnetic field is connected to the conditioning circuit, an output signal of the conditioning circuit is connected with the microprocessor, the microprocessor outputs a control signal to the compensation current controller, and an output end of the compensation current controller is connected with a compensation coil of a magnetic ring.
2. The large current detection device for magnetic ring magnetic field cancellation as claimed in claim 1, wherein: the two magnetic rings are made of high-permeability materials, and the diameters and the materials are the same.
3. A detection method for a large current detection device based on magnetic ring magnetic field cancellation as claimed in claim 1, is characterized in that: if direct current is detected, when current flows on a lead to be detected, the magnetic fluxes on the two magnetic rings are different in size and opposite in direction, so that most of the magnetic fluxes formed by the two magnetic rings are mutually offset, a small part of the magnetic fluxes is reserved, the small part of the magnetic fluxes are acquired by a sensor of a detected magnetic field and are processed, and finally, the magnetic fluxes generated by the compensation current in the magnetic rings are completely offset with the original remaining small part of the magnetic fluxes by adjusting the current of a compensation coil on the magnetic rings.
4. The large-current detection method for magnetic ring magnetic field cancellation as claimed in claim 3, wherein: the magnitude of the current to be measured can be obtained by multiplying the measured compensation current value by a coefficient, wherein the coefficient is obtained according to the ratio of the given standard current to be measured to the measured compensation current value.
5. The large-current detection method for magnetic ring magnetic field cancellation as claimed in claim 3, wherein: the sensor for detecting a magnetic field placed in the air gap is one of a hall sensor, a giant magnetoresistance sensor, a fluxgate sensor, or an anisotropic magnetic field sensor, according to the ampere-loop theorem,
(B 1-B 2)l/(m 0 m r )+(B 1-B 2)δ/m 0=I(1)
wherein the content of the first and second substances,B 1andB 2respectively is the current to be measuredIThe magnetic induction generated in the two magnetic rings,lthe total length of the two magnetic rings after being combined,δthe length of the air gap left for detecting the magnetic field strength,δ<<l，m 0in order to have a magnetic permeability of air,m r is the relative permeability of the magnetic materialk=(l/m r +δ)/m 0Thus obtaining the current to be measuredIThe expression of (a) is calculated,
I=k´(B 1-B 2) (2)
therefore, the voltage collected by the magnetic field sensor is input to the microprocessor through the conditioning circuit, the microprocessor outputs a control signal to adjust the current of the compensating circuit, so that the magnetic induction intensity generated by the compensating current in the magnetic ring and the original residual (A) and (B) are obtainedB 1-B 2) And offsetting each other, and calculating the magnitude of the current to be measured.
6. The large-current detection method for magnetic ring magnetic field cancellation as claimed in claim 3, wherein: if the alternating current is detected, the following three modes are adopted:
directly using the output voltage of a compensation coil wound on a magnetic ring as an output signal of large current detection; or a standard resistor is connected in series with the compensation coil, and the voltage on the resistor is used as output; or the compensation coil is closed, and the current in the compensation coil is directly output as an output signal of large current detection.
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