CN107807269B - Photoelectric current detection device for various cables and detection method thereof - Google Patents
Photoelectric current detection device for various cables and detection method thereof Download PDFInfo
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Abstract
The invention provides a photoelectric current detection device for various cables and a detection method thereof, belonging to the field of measurement. The upper end cover is fixed with the encapsulation through the coupling bolt, and encapsulation and upper end cover respectively have a semi-cylindrical groove, open the light trap on the encapsulation, the inside of light trap be fixed with the polarizer of light trap size unanimity, cantilever beam and an internal surface fixed connection of encapsulation, it has the piezoelectricity layer to paste at the lower surface of cantilever beam, upper surface fixed with permanent magnet at the cantilever beam, on the both sides face of cantilever beam's free end, be close to the side of light trap and be fixed with the analyzer, another side is fixed with photoelectric conversion element, be fixed with circuit part on the internal surface of encapsulation just right with the light trap. The invention measures direct current and alternating current, is suitable for cables with various internal structures, can be self-powered, and has the characteristics of simple structure, high response speed, convenience in maintenance, wide application range and the like.
Description
Technical Field
The invention belongs to the field of measurement, and particularly relates to a current detection device and a detection method thereof, in particular to a photoelectric current detection device for various cables and a detection method thereof.
Background
Along with the rapid development of the intelligent power grid in China and the proposal of 'China manufacturing 2025', the importance of the dynamic measurement technology is highlighted. The dynamic measurement of current is increasingly required for power transmission cables and various high-precision point devices, so that the development of a current detection device with high response speed has important significance.
According to GB-50217-2007 power cable laying specifications, the cable has single-core, double-core, three-phase three-core, three-phase four-core, three-phase five-core and other structures. The conventional current detection device can only measure the current of one cable, and cannot measure direct current and alternating current at the same time, so that the device has no universality. It is therefore important to develop a current sensing device that accommodates all structural cables and that can measure both dc and ac currents simultaneously.
The current detection device needs current, if a power supply is independently provided, resources are wasted, the battery is required to be replaced manually, and long-term current measurement cannot be performed in occasions such as underground or high altitude where maintenance is inconvenient. Therefore, the self-powered current detection device is developed, not only is manpower and material resources saved, but also the self-powered current detection device can be upgraded into a node of the wireless sensor network later.
The current detection device in the prior art mainly comprises a capacitive current sensor, a cantilever beam resonant current sensor, a Hall current sensor, an all-fiber current sensor, a fluxgate current sensor, a rogowski coil current sensor, a giant magneto-resistance current sensor and the like, and has the problems of complex structure, difficult processing, high cost, small application range and the like. For example, a passive current detection device based on a piezoelectric cantilever structure is developed, and can perform high-precision current measurement on a double-core cable without a driving power supply or stripping a protective layer. However, it cannot measure direct current and alternating current at the same time, and cannot measure current of cables with other structures such as three-core cables, four-core cables, five-core cables and the like, so that the practicability is low.
Disclosure of Invention
The invention provides a photoelectric current detection device for various cables and a detection method thereof, which are used for solving the problems of complex structure, difficult processing, high cost, small application range and the like of the current detection device in the prior art.
The technical scheme adopted by the invention is as follows: the upper end cover is fixed with the encapsulation through the coupling bolt, encapsulation and upper end cover have semicylindrical groove I and semicylindrical groove II respectively, positioning bolt rotates screw in semicylindrical groove I and semicylindrical groove II through the screw hole on the upper end cover, open on the encapsulation has the light trap, be fixed with the polarizer unanimous with the light trap size in the inside of this light trap, cantilever beam and an internal surface fixed connection of encapsulation are fixed with the analyzer near the side of light trap at the free end of cantilever beam, be fixed with photoelectric conversion element at the side that the free end of cantilever beam kept away from the light trap, paste at the lower surface of cantilever beam has the piezoelectricity layer, be fixed with the permanent magnet at the upper surface of cantilever beam, be fixed with circuit part on the internal surface that encapsulation and light trap are just right.
The photoelectric conversion element is a photodiode, a phototriode, a photoresistor or a silicon photocell.
The number of the cantilever beams is a positive integer greater than or equal to 1.
The cantilever beam is in a shape of a long strip, a long strip with a variable cross section, a T shape, a U shape, a V shape, a triangle or a tuning fork shape.
The piezoelectric layer consists of a lower electrode, a piezoelectric sheet and an upper electrode.
A photoelectric current detection method for a plurality of cables, comprising the steps of:
step (1) zeroing the current detection device;
step (2) determining the core number of the tested cable;
the current detection device is fixed on the tested cable through the first semi-cylindrical groove and the second semi-cylindrical groove, the upper end cover and the package are locked by the connecting bolt, and the positioning bolt is screwed in through the threaded hole on the upper end cover;
in the step (4), the permanent magnet is stressed by a magnetic field generated by current in the tested cable, the cantilever beam is bent along with the stress, the angle of the analyzer is changed along with the stress, the polarization direction of the analyzer is changed along with the stress, the light passes through the light transmission port, the polarizer and the analyzer, and then has a new component along the new polarization direction, the illuminance received by the photoelectric conversion element is changed, and the output voltage U of the photoelectric conversion element is changed 1 And then changes; output voltage U of photoelectric conversion element 1 Is an alternating voltage, after passing through the circuit part, the output voltage U of the circuit part is a direct voltage, and the output voltage U of the circuit part and the amplitude I of the current in the tested cable 0 Is in a linear relationship;
step (5) rotating the tested cable or the current detection device around the axis of the tested cable until the position with the maximum output current value is reached, wherein the output current value at the moment is the amplitude I of the current in the tested cable 0 Amplitude I of current in cable under test 0 By means of the output voltage U of the circuit part and the parameter value K of the current detection device S The formula is obtained as follows:
I 0 ＝K S U
for direct current:
for alternating current under symmetrical load:
wherein: e is the elastic modulus of the cantilever beam, I is the moment of inertia of the cantilever Liang Hengjie facing the neutral axis of bending, l is the length of the cantilever beam, m=1 when the I-th core inside the measured cable is the zero line, m=2 when the I-th core inside the measured cable is the live line, μ 0 Is of vacuum permeability, B r For the residual magnetic flux of the permanent magnet, V is the volume of the permanent magnet, a coordinate system is established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet as a z axis and taking a straight line passing through the mass center of the permanent magnet, perpendicular to the z axis and perpendicular to a tested cable as an x axis, and x i 、z i When the output voltage U of the circuit part is maximum, the coordinate of the ith core in the tested cable under the coordinate system is that n is the core number of the tested cable, a is the total number of zero lines and ground lines in the tested cable, ω is the current angular frequency when alternating current is supplied to the interior of the tested cable, t is time,for the initial phase of the ith core inside the tested cable, <>The primary phase of the superimposed alternating current signal at the permanent magnet is for all cores inside the tested cable.
The invention has the advantages that:
(1) The response speed is high: the optical signal is a high-speed signal, the response time of the photoelectric energy conversion element is very short, compared with the traditional non-photoelectric current detection device such as a Hall current sensor, the invention can dynamically measure the current at high response speed, and the response range can be continuously enlarged by improving the natural frequency of the cantilever beam;
(2) The practicability is strong: because the Hall current sensor is limited by a principle, only a single lead current can be measured, the external protective layer is needed to be cut off for the multi-core cable to realize measurement, the lead structure is damaged, and the complexity of current measurement is increased;
(3) Can be self-powered: the piezoelectric layer and the cantilever beam are integrated, so that the self-power supply of the current detection device can be realized, a power supply is not required to be replaced, and the current detection device is convenient for long-time current measurement in the places such as underground or air where maintenance is inconvenient. In the case of insufficient illumination, various light sources such as an infrared light source and an LED light source can be built in, and the self-powered element provides electric energy for the light source.
Drawings
FIG. 1 is an isometric view of the present invention;
FIG. 2 is a front view of the present invention;
FIG. 3 is an isometric view of FIG. 2 taken along the line A-A;
FIG. 4 is an exploded view of the structure of the detection unit of the present invention;
FIG. 5 is an isometric view of the structure of the detection unit of the present invention;
FIG. 6 is a front view of the structure of the detecting unit of the present invention;
FIG. 7 is a cross-sectional view of the detection cell structure of the present invention taken along the plane B-B;
FIG. 8 is an isometric view of a detection unit structure when the longitudinal cross section of the cantilever beam of the present invention is triangular;
FIG. 9 is an isometric view of the structure of the detection unit when the longitudinal section of the cantilever beam of the present invention is in the form of a tuning fork;
FIG. 10 is an isometric view of the structure of the detection unit when the number of cantilevers is 2 in the present invention;
FIG. 11 is an isometric view of the structure of the detection unit when the number of cantilevers is N in accordance with the present invention;
FIG. 12 is a schematic diagram of the present invention for detecting a two-core cable current;
FIG. 13 is a schematic diagram of the present invention for detecting quad cable current;
FIG. 14 is a schematic diagram of the present invention for detecting a core cable current;
fig. 15 is a positional relationship diagram of the present invention, for example, detecting the current of the five-core cable.
Detailed Description
As shown in fig. 1, the upper end cover 9 and the package 8 are fixed by a connecting bolt 10, the package 8 and the upper end cover 9 are respectively provided with a first semi-cylindrical groove 802 and a second semi-cylindrical groove 901, and a positioning bolt 11 is rotated into the first semi-cylindrical groove 802 and the second semi-cylindrical groove 901 by a threaded hole on the upper end cover 9 so as to position a tested cable; as shown in fig. 4, a light hole 801 is formed in a package 8, a polarizer 2 with the same size as the light hole 801 is fixed in the light hole 801, a cantilever beam 1 is fixedly connected with one inner surface of the package 8, an analyzer 3 is fixed on a side surface of a free end of the cantilever beam 1, which is close to the light hole 801, a photoelectric conversion element 4 is fixed on a side surface of the free end of the cantilever beam 1, which is far away from the light hole 801, a piezoelectric layer 6 is stuck on the lower surface of the cantilever beam 1, and a permanent magnet 5 is fixed on the upper surface of the cantilever beam 1; as shown in fig. 3, the circuit portion 7 is fixed to the inner surface of the package 8 facing the light-transmitting hole 801.
The photoelectric conversion element 4 is a photodiode, a phototransistor, a photoresistor, a silicon photocell, or the like, which converts an optical signal into an electrical signal.
The number of the cantilever beams 1 is a positive integer greater than or equal to 1, as shown in fig. 10 and 11.
The cantilever beam 1 is in various shapes such as a long strip shape, a long strip shape with a variable section, a T shape, a U shape, a V shape, a triangle shape, a tuning fork shape and the like, as shown in fig. 8 and 9.
The piezoelectric layer 6 is composed of a lower electrode 601, a piezoelectric sheet 602, and an upper electrode 603, as shown in fig. 4.
As shown in fig. 4, light irradiates the photoelectric conversion element 4 through the light transmitting hole 801, the polarizer 2 and the analyzer 3, voltage is output through the photoelectric conversion element 4, when the electrified cable to be tested is positioned in the first semi-cylindrical groove 802 and the second semi-cylindrical groove 901, the permanent magnet 5 is stressed by a magnetic field generated by current in the cable to be tested, the cantilever beam 1 is bent accordingly, the angle of the analyzer 3 is changed accordingly, the polarization direction of the light passing through the polarizer 2 is changed when passing through the analyzer 3, illuminance received by the photoelectric conversion element 4 is changed, and output voltage of the photoelectric conversion element 4 is changed accordingly. By measuring the output voltage of the photoelectric conversion element 4, the amplitude of the current in the cable to be measured can be reversely calculated, thereby achieving the effect of current detection.
A photoelectric current detection method for a plurality of cables, comprising the steps of:
step (1) zeroing the current detection device;
step (2) determining the core number of the tested cable;
step (3) fixing the current detection device on the tested cable through a first semi-cylindrical groove 802 and a second semi-cylindrical groove 901, locking the upper end cover 9 and the package 8 by using a connecting bolt 10, and screwing in a positioning bolt 11 through a threaded hole on the upper end cover 9;
in the step (4), the permanent magnet 5 is forced by the magnetic field generated by the current in the tested cable, the cantilever beam 1 is bent along with the force, the angle of the analyzer 3 is changed along with the change of the polarization direction, the light has a new component along the new polarization direction after passing through the light-transmitting opening 801, the polarizer 2 and the analyzer 3, the illuminance received by the photoelectric conversion element 4 is changed, and the output voltage U of the photoelectric conversion element 4 is changed 1 And then changes; output voltage U of photoelectric conversion element 4 1 Is an alternating voltage, after passing through the circuit part 7, the output voltage U of the circuit part 7 is a direct voltage, and the output voltage U of the circuit part 7 and the amplitude I of the current in the cable to be tested 0 Is in a linear relationship;
step (5) rotating the tested cable or the current detection device around the axis of the tested cable until the position with the maximum output current value is reached, wherein the output current value at the moment is the amplitude I of the current in the tested cable 0 Amplitude I of current in cable under test 0 The output voltage U of the circuit part 7 and the parameter value K of the current detection device can be used S The formula is obtained as follows:
I 0 ＝K S U
for direct current:
for alternating current under symmetrical load:
wherein: e is the elastic modulus of the cantilever beam 1, I is the moment of inertia of the cross section of the cantilever beam 1 to the bending neutral axis, l is the length of the cantilever beam 1, m=1 when the I-th core inside the tested cable is the zero line, m=2 when the I-th core inside the tested cable is the live line, mu 0 Is of vacuum permeability, B r For the residual magnetic flux of the permanent magnet 5, V is the volume of the permanent magnet 5, a coordinate system is established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet 5 as a z axis and taking a straight line passing through the mass center of the permanent magnet 5, perpendicular to the z axis and orthogonal to a cable to be tested as an x axis, and x i 、z i When the output voltage U of the circuit part 7 is maximum, the coordinate of the ith core in the tested cable under the coordinate system is that n is the core number of the tested cable, a is the total number of zero lines and ground lines in the tested cable, ω is the current angular frequency when alternating current is supplied to the interior of the tested cable, t is time,for the initial phase of the ith core inside the tested cable, <>The primary phase of the superimposed alternating signal at the permanent magnet 5 is for all cores inside the cable under test.
The output voltage U of the circuit portion 7 of the above current detection device prototype and the amplitude I of the measured current 0 The relationship is as follows:
the measured current can be obtained by the following method:
by semi-cylindersThe device is fixed on a tested cable with current of I through a first groove 802 and a second semi-cylindrical groove 901, an upper end cover 9 and a package 8 are locked through a connecting bolt 10, a positioning bolt 11 is screwed in through a threaded hole on the upper end cover 9, the magnetic field force applied to the permanent magnet 5 is obtained, the cantilever beam 1 is bent through the magnetic field force, the polarization direction of the analyzer 3 is changed, the illuminance received by the photoelectric conversion element 4 is changed, the output voltage of the circuit part 7 is changed, and the amplitude I of the current in the tested cable is measured 0 。
The magnetic field intensity and the magnetic field gradient of any position around the tested cable with the core number of n can be obtained according to the following formula:
formula of magnetic field intensity around single wire
The component of the magnetic field strength around the single wire in the z-axis direction is
For direct current, the current i of the ith core firing wire in the tested cable with the core number of n i ＝I 0 Current i of ith core zero line i ＝-I 0 。
For alternating current under symmetrical load, when the ith core in the tested cable with the core number of n is zero line or ground line, the current i i When the ith core in the tested cable is fire wire and the tested cable is=0, the current
Composite magnetic field strength of tested cable with core number of n in z-axis direction
Wherein mu 0 Is vacuum magnetic permeability, r is radial distance from any point in space to single wire, i 0 The current being a single wire, x, z being the current passing through the centre of mass of the permanent magnet 5 and perpendicular to the permanent magnetThe straight line of the upper surface of the permanent magnet 5 is the z axis, and the straight line passing through the mass center of the permanent magnet 5, being perpendicular to the z axis and being orthogonal to the cable to be tested is the coordinate of any point in the coordinate system established by the x axis, x i 、z i When the output voltage U of the circuit part 7 is maximum, the coordinate of the ith core in the tested cable under the coordinate system is that n is the core number of the tested cable, I 0 For the amplitude of the current inside the cable to be measured, ω is the angular frequency of the current when the inside of the cable to be measured is ac, t is time,is the initial phase of the ith core inside the tested cable.
The magnetic field gradient of the single wire in the z-axis direction is
The composite magnetic field gradient of the tested cable with the core number of n in the z-axis direction is
The magnetic field force in the z-axis direction generated by the single wire to the permanent magnet 5 is
The resultant magnetic field force in the z-axis direction generated by the tested cable with the core number of n to the permanent magnet 5 is
Wherein B is r For the residual magnetic flux of the permanent magnet 5, V is the volume of the permanent magnet 5.
The resultant magnetic field force F z Under the action of (a), the bending angle of the cantilever beam 1 is as follows
Under the action of the polarizer 2 and the analyzer 3, the illuminance received by the photoelectric conversion element 4 is
In the linear operation range, the output voltage of the photoelectric conversion element 4 is
Wherein E is the elastic modulus of the cantilever beam 1, I is the moment of inertia of the cross section of the cantilever beam 1 to the bending neutral axis, l is the length of the cantilever beam 1, H 0 For the illuminance of the light emitted by the light source immediately before passing through the polarizer 2, U 0 The illuminance received for the photoelectric conversion element 4 is H 0 Output voltage at that time.
Output voltage U of photoelectric conversion element 4 1 After passing through the circuit portion 7:
for direct current, the output voltage of the circuit portion 7 is u=arccoss (βu 1 -1)
For alternating current, the output voltage of the circuit portion 7 is
Wherein the method comprises the steps ofBeta is the proportionality coefficient after zeroing the current detecting device,/for the current detecting device>The primary phase of the superimposed alternating signal at the permanent magnet 5 is for all cores inside the cable under test.
After substituting the known parameters, the output voltage of the circuit portion 7 for the direct current is:
wherein, m=1 when the i-th core in the tested cable is a zero line, and m=2 when the i-th core in the tested cable is a live line.
After substitution of the known parameters, the output voltage of the circuit part 7 for the alternating current under symmetrical load is:
the above parameters are all known quantities and are simplified as follows: i 0 ＝K S U
Wherein K is S The structure and material parameters of the cantilever beam 1 and the coordinate parameters of each core of the cable to be tested are all known quantities.
For direct current:
for alternating current under symmetrical load:
when the ith core in the tested cable is a live wire, m=2, and a is the total number of the zero wire and the ground wire in the tested cable.
Application example 1:
first, taking a photodiode as a photoelectric conversion element 4, a cantilever beam 1 with a U-shaped longitudinal section is used for detecting direct current in a double-core cable, and the basic principle of the invention is described as follows:
the two-core cable has a live wire and a neutral wire inside, which are opposite in current direction, as shown in fig. 12.
Formula of magnetic field intensity around single wire
The component of the magnetic field strength around the single wire in the z-axis direction is
Resultant magnetic field strength of a two-core cable in the z-axis direction
Current i of zero line in double-core cable 1 ＝-I 0 Current i of live wire 2 ＝I 0 。
Wherein mu 0 Is vacuum magnetic permeability, r is radial distance from any point in space to single wire, i 0 I is the current of a single wire i For the current of the ith core in the tested cable, x and z are the coordinates of any point in a coordinate system established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet 5 as a z axis and taking a straight line passing through the mass center of the permanent magnet 5, perpendicular to the z axis and orthogonal to the tested cable as an x axis, and x is the coordinate i 、z i When the output voltage U of the circuit part 7 is maximum, the coordinate of the ith core in the tested cable under the coordinate system is I 0 Is the magnitude of the current in the cable being measured.
The magnetic field gradient of the single wire in the z-axis direction is
The composite magnetic field gradient of the double-core cable in the z-axis direction is that
The magnetic field force in the z-axis direction generated by the single wire to the permanent magnet 5 is
The resultant magnetic field force in the z-axis direction generated by the twin-core cable to the permanent magnet 5 is
By calculating F z As can be seen from the optimal solution of (a), for a two-core cable, when the z-axis is the symmetry axis of the zero line and the live line, the permanent magnet 5 receives a resultant magnetic field force F z There is a maximum as shown in fig. 12. In order to improve the sensitivity, the invention is symmetrical between the zero line and the fire line in the z-axisWhen the shaft is in use, an electromagnetic field model is built, and the position can be reached to the position of maximum output current by enabling the tested cable to rotate relative to the device so as to achieve calibration.
At this time, the coordinate of the section center of the zero line in the coordinate system is x 1 ＝-r 0 ，z 1 ＝h；
At this time, the coordinate of the section center of the fire wire in the coordinate system is x 2 ＝r 0 ，z 2 ＝h。
Wherein r is 0 For the radius of each core in the tested cable, h is the vertical distance between the center of mass of the permanent magnet 5 and the contact surface of the package 8 and the upper end cover 9, B r For the residual magnetic flux of the permanent magnet 5, V is the volume of the permanent magnet 5.
The resultant magnetic field force F z Under the action of (a), the bending angle of the cantilever beam 1 is as follows
Under the action of the polarizer 2 and the analyzer 3, the illuminance received by the photodiode 4 is
In the linear operating range, the output voltage of the photodiode 4 is
Wherein E is the elastic modulus of the cantilever beam 1, I is the moment of inertia of the cross section of the cantilever beam 1 to the bending neutral axis, l is the length of the cantilever beam 1, H 0 For the illuminance of the light emitted by the light source immediately before passing through the polarizer 2, U 0 The illuminance received for the photodiode is H 0 Output voltage at that time.
Output voltage U of photodiode 4 1 After passing through the circuit portion 7:
the output voltage of the circuit portion 7 is u=arccos (βu 1 -1)
Wherein the method comprises the steps ofBeta is the proportionality coefficient after zeroing the current detection device.
The above parameters are all known quantities and are simplified as follows: i 0 ＝K S U
Wherein K is S The parameter value of the current detection device is determined by the structure and material parameters of the cantilever beam 1 and the coordinate parameters of each core of the cable to be detected. It follows that the output voltage U of the circuit portion 7 and the amplitude I of the current in the cable under test 0 In a linear relationship.
Application example 2:
taking a photodiode as a photoelectric conversion element 4, and using a cantilever beam 1 with a U-shaped longitudinal section to detect three-phase alternating current in a four-core cable as an example, the basic principle of the invention is described as follows:
the four-core cable is generally used for supplying power to three-phase four-wire equipment, three live wires and a zero wire are arranged in the cable, the current in the three live wires has equal amplitude and 120-degree phase difference, and under symmetrical load, the zero wire current is 0, as shown in fig. 13.
Formula of magnetic field intensity around single wire
The component of the magnetic field strength around the single wire in the z-axis direction is
Resultant magnetic field strength of quad cable in z-axis direction
For alternating current under symmetrical load, the current i of the three-phase live wire in the four-core cable 1 ＝I 0 sinωt，i 2 ＝I 0 sin(ωt+120°)，i 3 ＝I 0 sin (ωt+240°), zero line current i 4 ＝0。
Wherein mu 0 Is vacuum magnetic permeability, r is radial distance from any point in space to single wire, i 0 I is the current of a single wire i For the current of the ith core in the tested cable, x and z are the coordinates of any point in a coordinate system established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet 5 as a z axis and taking a straight line passing through the mass center of the permanent magnet 5, perpendicular to the z axis and orthogonal to the tested cable as an x axis, and x is the coordinate i 、z i When the output voltage U of the circuit part 7 is maximum, the coordinate of the ith core in the tested cable under the coordinate system is I 0 For the amplitude of the current in the cable to be measured, ω is the angular frequency of the current when the inside of the cable to be measured is ac current, and t is time.
The magnetic field gradient of the single wire in the z-axis direction is
The four-core cable has a composite magnetic field gradient in the z-axis direction of
The magnetic field force in the z-axis direction generated by the single wire to the permanent magnet 5 is
The resultant magnetic field force in the z-axis direction generated by the four-core cable to the permanent magnet 5 is
By calculating F z As can be seen from the optimal solution of (a) for a four-core cable, if the radius r=10mm of the two semi-cylindrical grooves 802 and 901 in the device and the vertical distance h=23mm between the center of mass of the permanent magnet 5 and the contact surface of the package 8 and the upper end cover 9, then the resultant magnetic field force F applied to the permanent magnet 5 when the symmetry axis and the x axis of the three-phase live wire are angled by 47 degrees z The amplitude in one period is the mostLarge value as shown in fig. 13. In order to improve sensitivity, the electromagnetic field model is built according to the superimposed magnetic field in the 47-degree direction, and the 47-degree angle can be calibrated by enabling the tested cable to rotate relative to the current detection device to reach the position with the maximum output current value.
At the moment, the coordinates of the section center of the three-phase live wire under the coordinate system are
Wherein r is 0 For the radius of each core in the tested cable, h is the vertical distance between the center of mass of the permanent magnet 5 and the contact surface of the package 8 and the upper end cover 9, B r For the residual magnetic flux of the permanent magnet 5, V is the volume of the permanent magnet 5.
The resultant magnetic field force F z Under the action of (a), the bending angle of the cantilever beam 1 is as follows
Under the action of the polarizer 2 and the analyzer 3, the illuminance received by the photodiode 4 is
In the linear operating range, the output voltage of the photodiode 4 is
Wherein E is the elastic modulus of the cantilever beam 1, I is the moment of inertia of the cross section of the cantilever beam 1 to the bending neutral axis, l is the length of the cantilever beam 1, H 0 For the illuminance of the light emitted by the light source immediately before passing through the polarizer 2, U 0 The illuminance received for the photodiode is H 0 Output voltage at that time.
Output voltage U of photodiode 4 1 After passing through the circuit portion 7:
the output voltage of the circuit part 7 is
Wherein the method comprises the steps ofBeta is the proportionality coefficient after zeroing the current detecting device,/for the current detecting device>For the initial phase of the superimposed alternating signal of all cores inside the cable under test at the permanent magnet 5, K 1 ,K 2 ,K 3 Are all constant, and their expressions are:
the above parameters are all known quantities and are simplified as follows: i 0 ＝K S U
Wherein K is S The parameter value of the current detection device is determined by the structure and material parameters of the cantilever beam 1 and the coordinate parameters of each core of the cable to be detected. It follows that the output voltage U of the circuit portion 7 and the amplitude I of the current in the cable under test 0 In a linear relationship.
Application example 3:
taking a photodiode as a photoelectric conversion element 4, and using a cantilever beam 1 with a U-shaped longitudinal section to detect three-phase alternating current in a five-core cable as an example, the basic principle of the invention is described as follows:
the five-core cable is used for supplying power to equipment in a three-phase five-wire system, wherein five cores are three live wires, a zero wire and a ground wire, as shown in fig. 14. Under symmetrical loading, the zero line current is 0. And the ground wire is grounded, so that the current of the ground wire is 0.
Formula of magnetic field intensity around single wire
The component of the magnetic field strength around the single wire in the z-axis direction is
Resultant magnetic field strength of five-core cable in z-axis direction
For alternating current under symmetrical load, the current i of the three-phase live wire in the five-core cable 1 ＝I 0 sinωt，i 2 ＝I 0 sin(ωt+120°)，i 3 ＝I 0 sin (ωt+240°), zero line current i 4 =0, ground current i 5 ＝0。
Wherein mu 0 Is vacuum magnetic permeability, r is radial distance from any point in space to single wire, i 0 I is the current of a single wire i For the current of the ith core in the tested cable, x and z are the coordinates of any point in a coordinate system established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet 5 as a z axis and taking a straight line passing through the mass center of the permanent magnet 5, perpendicular to the z axis and orthogonal to the tested cable as an x axis, and x is the coordinate i 、z i When the output voltage U of the circuit part 7 is maximum, the coordinate of the ith core in the tested cable under the coordinate system is I 0 For the amplitude of the current in the cable to be measured, ω is the current when the interior of the cable to be measured is ACIs time.
The magnetic field gradient of the single wire in the z-axis direction is
The five-core cable has a resultant magnetic field gradient in the z-axis direction of
The magnetic field force in the z-axis direction generated by the single wire to the permanent magnet 5 is/>
The resultant magnetic field force of the five-core cable in the z-axis direction generated by the permanent magnet 5 is
By calculating F z As can be seen from the optimal solution of (a) for a five-core cable, if the radius r=10mm of the two semi-cylindrical grooves 802 and 901 in the device and the vertical distance h=23mm of the centroid of the permanent magnet 5 from the contact surface of the package 8 and the upper end cover 9, then the resultant magnetic field force F applied to the permanent magnet 5 when the symmetry axis of the three-phase live wire forms an angle of 58.4 ° with the x-axis z The amplitude is at a maximum in one cycle as shown in fig. 14. In order to improve the sensitivity, the electromagnetic field model is built according to the superimposed magnetic field in the 58.4-degree direction, and the 58.4-degree angle can reach the position with the maximum output current value by enabling the tested cable to rotate relative to the current detection device so as to achieve calibration.
At the moment, the coordinates of the section center of the three-phase live wire under the coordinate system are
Wherein r is 0 For the radius of each core in the tested cable, h is the vertical distance between the center of mass of the permanent magnet 5 and the contact surface of the package 8 and the upper end cover 9, B r For the residual magnetic flux of the permanent magnet 5, V is the volume of the permanent magnet 5.
The resultant magnetic field force F z Under the action of (a), the bending angle of the cantilever beam 1 is as follows
Under the action of the polarizer 2 and the analyzer 3, the illuminance received by the photodiode 4 is
In the linear operating range, the output voltage of the photodiode 4 is
Wherein E is the elastic modulus of the cantilever beam 1, I is the moment of inertia of the cross section of the cantilever beam 1 to the bending neutral axis, l is the length of the cantilever beam 1, H 0 For the illuminance of the light emitted by the light source immediately before passing through the polarizer 2, U 0 The illuminance received for the photodiode is H 0 Output voltage at that time.
Output voltage U of photodiode 4 1 After passing through the circuit portion 7:
the output voltage of the circuit part 7 is
Wherein the method comprises the steps ofBeta is the proportionality coefficient after zeroing the current detection device,for the initial phase of the superimposed alternating signal of all cores inside the cable under test at the permanent magnet 5, K 1 ,K 2 ,K 3 Are all constant, and their expressions are:
/>
the above parameters are all known quantities and are simplified as follows: i 0 ＝K S U
Wherein K is S The parameter value of the current detection device is determined by the structure and material parameters of the cantilever beam 1 and the coordinate parameters of each core of the cable to be detected. It follows that the output voltage U of the circuit portion 7 and the amplitude I of the current in the cable under test 0 In a linear relationship.
The response range of the current detection device provided by the invention depends on the natural frequency of the cantilever beam 1, and the sensitivity depends on the structure of the cantilever beam 1, the working range of the photoelectric conversion element 4 and the precision error of the circuit part 7. The shape and size of the cantilever beam 1, the operating range of the photoelectric conversion element 4, and the structure of the circuit portion 7 can be improved and adjusted. By optimizing the device, the response range can be further expanded, and the sensitivity can be further improved.
Claims (6)
1. A photoelectric current detection device for multiple cable, its characterized in that: the upper end cover is fixed with the encapsulation through a connecting bolt, the encapsulation and the upper end cover are respectively provided with a semi-cylindrical groove I and a semi-cylindrical groove II, the positioning bolt is rotated into the semi-cylindrical groove I and the semi-cylindrical groove II through a threaded hole on the upper end cover, a light hole is formed in the encapsulation, a polarizer with the same size as the light hole is fixed in the light hole, the cantilever beam is fixedly connected with one inner surface of the encapsulation, an analyzer is fixed on the side surface of the free end of the cantilever beam, which is close to the light hole, a photoelectric conversion element is fixed on the side surface of the free end of the cantilever beam, which is far away from the light hole, a piezoelectric layer is adhered to the lower surface of the cantilever beam, a permanent magnet is fixed on the upper surface of the cantilever beam, and a magnetic field generated by current in a tested cable enables the permanent magnet to be stressed to excite the cantilever beam, and a circuit part is fixed on the inner surface of the encapsulation, which is opposite to the light hole.
2. A photoelectric current detection apparatus for a plurality of cables according to claim 1, wherein: the photoelectric conversion element is a photodiode, a phototriode, a photoresistor or a silicon photocell.
3. A photoelectric current detection apparatus for a plurality of cables according to claim 1, wherein: the number of the cantilever beams is a positive integer greater than or equal to 1.
4. A photoelectric current detection apparatus for a plurality of cables according to claim 1, wherein: the cantilever beam is in a shape of a long strip, a long strip with a variable cross section, a T shape, a U shape, a V shape, a triangle or a tuning fork shape.
5. A photoelectric current detection apparatus for a plurality of cables according to claim 1, wherein: the piezoelectric layer consists of a lower electrode, a piezoelectric sheet and an upper electrode.
6. A detection method using the photoelectric current detection apparatus for a plurality of cables according to claim 1, comprising the steps of:
step (1) zeroing the current detection device;
step (2) determining the core number of the tested cable;
the current detection device is fixed on the tested cable through the first semi-cylindrical groove and the second semi-cylindrical groove, the upper end cover and the package are locked by the connecting bolt, and the positioning bolt is screwed in through the threaded hole on the upper end cover;
in the step (4), the permanent magnet is stressed by a magnetic field generated by current in the tested cable, the cantilever beam is bent along with the stress, the angle of the analyzer is changed along with the stress, the polarization direction of the analyzer is changed along with the stress, the light passes through the light transmission port, the polarizer and the analyzer, and then has a new component along the new polarization direction, the illuminance received by the photoelectric conversion element is changed, and the output voltage U of the photoelectric conversion element is changed 1 And then changes; output voltage U of photoelectric conversion element 1 Is an alternating voltage, after passing through the circuit part, the output voltage U of the circuit part is a direct voltage, and the output voltage U of the circuit part and the amplitude I of the current in the tested cable 0 Is in a linear relationship;
step (5) rotating the tested cable or the current detection device around the axis of the tested cable until the position with the maximum output current value is reached, wherein the output current value at the moment is the amplitude I of the current in the tested cable 0 Amplitude I of current in cable under test 0 By means of the output voltage U of the circuit part and the parameter value K of the current detection device S The formula is obtained as follows:
I 0 ＝K S U
for direct current:
for alternating current under symmetrical load:
wherein: e is the elastic modulus of the cantilever beam, I is the moment of inertia of the cantilever Liang Hengjie facing the neutral axis of bending, l is the length of the cantilever beam, m=1 when the I-th core inside the measured cable is the zero line, and m=1 when the I-th core inside the measured cableM=2, μ for fire wire 0 Is of vacuum permeability, B r For the residual magnetic flux of the permanent magnet, V is the volume of the permanent magnet, a coordinate system is established by taking a straight line passing through the mass center of the permanent magnet 5 and perpendicular to the upper surface of the permanent magnet as a z axis and taking a straight line passing through the mass center of the permanent magnet, perpendicular to the z axis and perpendicular to a tested cable as an x axis, and x i 、z i When the output voltage U of the circuit part is maximum, the coordinate of the ith core in the tested cable under the coordinate system is that n is the core number of the tested cable, a is the total number of zero lines and ground lines in the tested cable, ω is the current angular frequency when alternating current is supplied to the interior of the tested cable, t is time,for the initial phase of the ith core inside the tested cable, <>The primary phase of the superimposed alternating current signal at the permanent magnet is for all cores inside the tested cable.
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| CN109946601A (en) * | 2019-04-18 | 2019-06-28 | 中铁电气化局集团有限公司 | A kind of AC-DC on-line monitoring device |
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