CN114325061A - Piezoelectric current detection device for multiple frequencies and detection method thereof - Google Patents
Piezoelectric current detection device for multiple frequencies and detection method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of current measurement, and particularly relates to a piezoelectric current detection device for multiple frequencies and a detection method thereof; the micro-transducer comprises a cantilever beam, a permanent magnet, a micro-transducer, a mass block, a package, an end cover, a locking mechanism and a circuit part; calibrating the modal frequency of each step of the current detection device, determining the core number of the tested cable, connecting the tested cable into the current detection device, and rotating a handle of a locking mechanism to complete the fixation of the tested cable; when current passes through the tested cable, the output voltage passing through the circuit part and the amplitude of the tested current passing through the tested cable are in a linear relation, and the tested current is calculated according to a given formula: the invention can be used for measuring various alternating current frequency currents, is suitable for cables with various internal structures, and has the characteristics of simple structure, no need of independently equipping a power supply, no need of splitting a lead, large detection range, convenience in installation and the like.
Description
Technical Field
The invention belongs to the technical field of current measurement, and particularly relates to a piezoelectric type current detection device for multiple frequencies and a detection method thereof.
Background
In the measurement of various electrical parameters, the current is the most basic and one of the most important parameters, and the real-time dynamic monitoring is carried out aiming at different characteristics of the current, so that the method has important significance in the aspects of power grid construction, power utilization safety, equipment protection and the like.
The frequency is an important index of current, and the fluctuation of the power grid frequency can not only reduce the quality of electric energy and influence the normal operation of an electric appliance, but also even endanger the normal work of a generator in serious cases, thereby causing the phenomenon of frequency collapse; today, in the field of new energy, the complexity of an electric power system is continuously improved, and new energy such as wind power, photoelectricity and the like is connected to the grid to provide higher requirements for the stability of the power grid. The system monitors the current frequency fluctuation in real time, gives early warning in time and plays an important role in protecting personal and property safety.
The current detection device needs a power supply, and if the power supply is independently equipped, the manufacturing cost is increased, the design structure is complex, the maintenance is difficult, and the current detection device cannot be used for current measurement in extreme environments such as high altitude or underground for a long time. Therefore, the development of the current detection device which is driven without an external power supply has important significance in the aspect of widening application scenes.
The existing current detection device mainly comprises a Hall current sensor, a fluxgate current sensor, a Rogowski coil current sensor, a capacitive current sensor, a giant magnetoresistance current sensor, a resonant current sensor and the like, and has the problems of high processing difficulty, complex structure, large volume, small application range, high energy consumption and the like. The resonant current sensor developed based on the piezoelectric cantilever beam structure does not need to be driven by an external power supply or split by a lead, but can only obtain the maximum output at the resonant frequency, so that the detection range is limited, and the resonant current sensor can only have high sensitivity when detecting a current signal of a certain fixed frequency.
Therefore, under the condition of ensuring that a power supply does not need to be separately equipped and the overall structure of the cable is not damaged, the problem to be solved in the field is to develop a current detection device capable of detecting various frequencies in real time.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a piezoelectric type current detection device for multiple frequencies and a detection method thereof, which are used for measuring multiple alternating current frequency currents, are suitable for cables with various internal structures, and have the characteristics of simple structure, no need of independently equipping a power supply, no need of splitting a lead, large detection range, convenience in installation and the like.
A current detection device for various alternating current frequencies comprises a cantilever beam 1, a permanent magnet 2, a micro transducer 3, a mass block 4, a package 5, an end cover 6, a locking mechanism 7 and a circuit part 9; the bottom of the front side wall of the end cover 6 is provided with a first semicircular hole 601, two sides of the top end of the end cover 6 are respectively provided with a threaded hole, the top of the front side wall of the package 5 is provided with a second semicircular hole 501, the end cover 6 is fixed on the package 5 to cover the package 5, and the first semicircular hole 601 and the second semicircular hole 501 are buckled together to form a circular through hole; a through hole 502 is formed in the left side wall of the package 5, a square groove 503 is formed in the inner side of the left side wall of the package 5, the through hole 502 is communicated with the square groove 503, a long strip-shaped groove 504 is formed in the inner side of the left side wall of the package 5 below the square groove 503, one end of the cantilever beam 1 is fixed in the long strip-shaped groove 504 in the package 5, the micro transducer 3, the permanent magnet 2 and the mass block 4 are fixed on the upper surface of the cantilever beam 1, and the circuit part 9 is fixed on the inner surface of the package 5;
locking mechanism 7 includes handle 701, line ball board 702, spacing post 703, lock nut 704, wherein spacing post 703 is located through-hole 502 and square groove 503, line ball board 702 is located encapsulation 5, and the one end of line ball board 702 penetrates square groove 503 and the laminating is in spacing post 703 top, handle 701 screws in the left screw hole in end cover 6 top in proper order, through-hole 502 on the encapsulation 5, line ball board 702 and spacing post 703, wear out spacing post 703 again and stretch out from encapsulation 5 bottoms through-hole 502, realize handle 701's fastening through lock nut 704 in encapsulation 5 bottoms.
The cantilever beam 1 is in a linear type, a bending type, a one-dimensional variable cross-section type, a U-shaped or T-shaped.
The cantilever beam 1 is of a laminated structure, multiple layers are sequentially arranged in a row, each layer comprises two substrates 101 and one piezoelectric layer 102, one piezoelectric layer 102 is arranged between every two substrates 101, and the piezoelectric layers 102 are connected in series; the relationship between the number of the substrate 101 and the piezoelectric layer 102 is: the number of piezoelectric layers 102 is n, the number of substrates 101 is n +1, and the total number of layers of cantilever beams 1 is 2n + 1.
The micro transducer 3 comprises an upper electrode 301, a piezoelectric film 302 and a lower electrode 303 which are sequentially connected from top to bottom, wherein the piezoelectric film 302 is made of quartz crystal, piezoelectric ceramic and organic piezoelectric materials.
The mass block 4 is a cube, a cuboid or a cylinder and is arranged at any position of the cantilever beam 1.
The circuit part 9 comprises a main processor, an energy storage circuit, a signal sampling circuit, a counter circuit, a communication circuit, an interface and an alarm circuit; the counter circuit and the signal sampling circuit are used for receiving voltage output of the micro transducer 3, the counter circuit and the signal sampling circuit are respectively connected with a main processor, the main processor is simultaneously and respectively connected with the communication circuit, the interface and the alarm circuit, the energy storage circuit is used for receiving voltage output of the upper piezoelectric layer 102 of the cantilever beam 1 and is simultaneously and respectively connected with the signal sampling circuit, the counter circuit, the communication circuit, the interface and the alarm circuit.
A current detection method of the current detection device applying the multiple alternating current frequencies comprises the following steps:
step one, calibrating modal frequencies of various orders of a current detection device:
the modal frequency of each order of the current detection device is
Wherein k isnAnd mnRespectively the equivalent mass and equivalent stiffness of each stage of the device;
modal frequency omega of each order of current detection devicenNear, at 0.8 ωnTo 1.5 omeganThe frequency range of (a) is up-swept by inputting a sweep signal through the electrodes of the micro-transducer 3, and the excitation acceleration is adcos χ t; by adjusting the position of the mass block 4 on the cantilever beam 1, the modal frequency of each order of the current detection device and the estimated frequency range of the current to be detected are enabled to beThe same;
secondly, determining the core number of the tested cable according to specific working conditions;
thirdly, the tested cable is connected into the current detection device through a circular through hole formed by buckling the first semicircular hole 601 and the second semicircular hole 501 together, and the end cover 6 is buckled with the package 5; rotating a handle 701 of the locking mechanism 7 to enable a line pressing plate 702 of the locking mechanism 7 to gradually approach to the end of the cable to be tested until the line pressing plate 702 is contacted with the cable to be tested; then the positioning bolt 8 is screwed in through a threaded hole at the right end of the end cover 6 to complete the fixation of the tested cable;
when current flows through the tested cable, the permanent magnet 2 is stressed by the magnetic field generated by the current, the cantilever beam 1 vibrates along with the magnetic field, the output voltage of the micro transducer 3 changes along with the vibration, and the output voltage passing through the circuit part 9 and the amplitude of the tested current passing through the tested cable form a linear relation;
step five, rotating the package 5 by taking a straight line, perpendicular to the front side wall of the package 5, of the circle center of the circular through hole formed by buckling the first semicircular hole 601 and the second semicircular hole 501 as an axis until the output voltage U of the circuit part 9 is reachedoutThe maximum value is reached, and the amplitude value I of the current in the tested cable is reached0Calculated as follows:
I0＝KSUout
wherein the AC cable Ks：
Wherein k is1Stiffness of the main beam in the cantilever beam 1, CSTheta is the inherent capacitance of the micro transducer 3, theta is the electromechanical coupling coefficient of the micro transducer 3, mu is the ratio of the equivalent mass of the main beam and the auxiliary beam of the cantilever beam 1, and omega is omega/omega1ω is the angular frequency of the measured current, ω1Is the first-order modal frequency, ζ, of the cantilever 11And ζ2Is the first-order and second-order damping ratio of the cantilever beam 3, alpha is the ratio of the second-order modal frequency of the cantilever beam 3, mu0For vacuum permeability, BrIs the remainder of the permanent magnet 2Residual magnetic flux V is the volume of the permanent magnet 2, a straight line passing through the mass center of the permanent magnet 2 and vertical to the upper surface of the permanent magnet 2 is taken as a z-axis, a straight line passing through the mass center of the permanent magnet 2 and vertical to the z-axis and orthogonal to the tested cable is taken as an x-axis to establish a coordinate system, and x isi、ziFor the output voltage U of the circuit part 9outAt the maximum, the coordinate of the ith core in the tested cable under the coordinate system, n is the number of the zero line and the live wire core of the tested cable, t is time, phiiThe initial phase of the ith core in the tested cable is shown.
The invention has the beneficial effects that:
1. the detection range is large: according to the current detection device and the detection method thereof, the response range depends on the range of each order of natural frequency of the cantilever beam, and compared with other resonant current sensors, the current detection device can detect currents to be detected with different frequencies, and the response range is larger; moreover, the response range can be further enlarged by changing the cantilever beam structure and related parameters thereof;
2. the application range is wide: according to the current detection device and the detection method thereof, the cable protective layer does not need to be damaged, the lead does not need to be split, and the detection object can detect various cable currents such as a single-core cable, a double-core cable, a three-phase five-core cable and the like besides a three-phase four-core cable;
3. the power supply is not needed: according to the current detection device and the detection method thereof, the piezoelectric layer is integrated on the cantilever beam structure, and no additional power supply is needed; by designing the optimized circuit part, the whole power consumption is reduced, the self-power supply of the system is realized, and the method can be applied to occasions which are difficult to maintain, such as deep burial, high altitude and the like, and wireless sensing node networks.
Drawings
FIG. 1 is a schematic structural diagram of a piezoelectric current detection device for multiple frequencies according to the present invention;
FIG. 2 is a side view of a piezoelectric current sensing device for multiple frequencies according to the present invention;
FIG. 3 is a top view of the piezoelectric current sensing device for multiple frequencies according to the present invention;
FIG. 4 is a schematic diagram of the internal structure of a piezoelectric current detection device for multiple frequencies according to an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of a cantilever beam when the total number of layers of the laminated structure of the cantilever beam is 3;
FIG. 6 is a schematic diagram of a micro-transducer of a piezoelectric current sensing device for multiple frequencies according to the present invention;
FIG. 7 is a block diagram of the piezoelectric current sensing device circuit portion for multiple frequencies according to the present invention;
FIG. 8 is a schematic structural view of an internal detection unit when the cantilever beam of the present invention is T-shaped;
FIG. 9 is a schematic structural diagram of an internal detection unit according to the present invention when the number of cantilevers is n;
FIG. 10 is a schematic diagram of the detection of the current detection device when the cable to be detected is a single-phase dual-core cable according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of the detection of the current detection device when the cable to be detected is a three-phase five-core cable according to an embodiment of the present invention;
FIG. 12 is a lumped parameter model of a cantilever beam in a piezoelectric current sensing device for multiple frequencies according to an embodiment of the present invention.
Detailed Description
A current detection device for various alternating current frequencies comprises a cantilever beam 1, a permanent magnet 2, a micro transducer 3, a mass block 4, a package 5, an end cover 6, a locking mechanism 7 and a circuit part 9; the bottom of the front side wall of the end cover 6 is provided with a first semicircular hole 601, two sides of the top end of the end cover 6 are respectively provided with a threaded hole, the top of the front side wall of the package 5 is provided with a second semicircular hole 501, the end cover 6 is fixed on the package 5 to cover the package 5, and the first semicircular hole 601 and the second semicircular hole 501 are buckled together to form a circular through hole; a through hole 502 is formed in the left side wall of the package 5, a square groove 503 is formed in the inner side of the left side wall of the package 5, the through hole 502 is communicated with the groove 503, a long strip-shaped groove 504 is formed in the inner side of the left side wall of the package 5 below the square groove 503, one end of the cantilever beam 1 is fixed in the long strip-shaped groove 504 in the package 5, the micro transducer 3, the permanent magnet 2 and the mass block 4 are fixed on the upper surface of the cantilever beam 1, and the circuit part 9 is fixed on the inner surface of the package 5;
locking mechanism 7 includes handle 701, line ball board 702, spacing post 703, lock nut 704, wherein spacing post 703 is located through-hole 502 and square groove 503, line ball board 702 is located encapsulation 5, and the one end of line ball board 702 penetrates square groove 503 and the laminating is in spacing post 703 top, handle 701 screws in the left screw hole in end cover 6 top in proper order, through-hole 502 on the encapsulation 5, line ball board 702 and spacing post 703, wear out spacing post 703 again and stretch out from encapsulation 5 bottoms through-hole 502, realize handle 701's fastening through lock nut 704 in encapsulation 5 bottoms.
The cantilever beam 1 is in a linear type, a bending type, a one-dimensional variable cross-section type, a U-shaped or T-shaped.
The cantilever beam 1 is of a laminated structure, multiple layers are sequentially arranged in a row, each layer comprises two substrates 101 and one piezoelectric layer 102, one piezoelectric layer 102 is arranged between every two substrates 101, and the piezoelectric layers 102 are connected in series; that is, the substrate 101 at the bottom of the upper layer is placed on the substrate 101 at the top of the lower layer in each two-layer structure; the relationship between the number of the substrate 101 and the piezoelectric layer 102 is: the number of piezoelectric layers 102 is n, the number of substrates 101 is n +1, and the total number of layers of cantilever beams 1 is 2n + 1.
The number of the cantilever beams 1 is 1,2,3 to n, and each cantilever beam 1 is provided with a permanent magnet 2 and a mass block 4.
The micro transducer 3 comprises an upper electrode 301, a piezoelectric film 302 and a lower electrode 303 which are sequentially connected from top to bottom, wherein the piezoelectric film 302 is made of quartz crystal, piezoelectric ceramic and organic piezoelectric materials.
The mass block 4 is a cube, a cuboid or a cylinder or an irregular shape and can be arranged at any position of the cantilever beam 1.
The circuit part 9 comprises a main processor, an energy storage circuit, a signal sampling circuit, a counter circuit, a communication circuit, an interface and an alarm circuit; the counter circuit and the signal sampling circuit are used for receiving voltage output of the micro transducer 3, the counter circuit and the signal sampling circuit are respectively connected with a main processor, the main processor is simultaneously and respectively connected with the communication circuit, the interface and the alarm circuit, the energy storage circuit is used for receiving voltage output of the upper piezoelectric layer 102 of the cantilever beam 1 and is simultaneously and respectively connected with the signal sampling circuit, the counter circuit, the communication circuit, the interface and the alarm circuit. The first voltage signal is the voltage output of the micro transducer 3 and is used for detecting the current to be detected, and the second voltage signal is the voltage output of the piezoelectric layer 102 on the cantilever beam 1 and is used for supplying power to the circuit part 9.
A current detection method of the current detection device applying the multiple alternating current frequencies comprises the following steps:
step one, calibrating modal frequencies of various orders of a current detection device:
the modal frequency of each order of the current detection device can be approximately calculated as
Wherein k isnAnd mnRespectively the equivalent mass and equivalent stiffness of each stage of the device; the position of the mass 4 differs by knAnd mnBoth parameters will change, causing the modal frequency to change;
modal frequency omega of each order of current detection devicenNear, at 0.8 ωnTo 1.5 omeganThe frequency range of (a) is up-swept by inputting a sweep signal through the electrodes of the micro-transducer 3, and the excitation acceleration is adcos χ t; the modal frequency of each order of the current detection device is approximately equal to the estimated frequency range of the current to be detected by adjusting the position of the mass block 4 on the cantilever beam 1;
secondly, determining the core number of the tested cable according to specific working conditions;
thirdly, the tested cable is connected into the current detection device through a circular through hole formed by buckling the first semicircular hole 601 and the second semicircular hole 501 together, and the end cover 6 is buckled with the package 5; rotating a handle 701 of the locking mechanism 7 to enable a line pressing plate 702 of the locking mechanism 7 to gradually approach to the end of the cable to be tested until the line pressing plate 702 is contacted with the cable to be tested; then the positioning bolt 8 is screwed in and tightly pressed above the tested cable through a threaded hole at the right end of the end cover 6 to complete the fixation of the tested cable;
when current flows through the tested cable, the permanent magnet 2 is stressed by the magnetic field generated by the current, the cantilever beam 1 vibrates along with the magnetic field, the output voltage of the micro transducer 3 changes along with the vibration, and the output voltage passing through the circuit part 9 and the amplitude of the tested current passing through the tested cable form a linear relation;
step five, slowly rotating the package 5 by taking a straight line, perpendicular to the front side wall of the package 5, of the circle center of the circular through hole formed by buckling the first semicircular hole 601 and the second semicircular hole 501 as an axis until the output voltage U of the circuit part 9 is reachedoutThe maximum value is reached, and the amplitude value I of the current in the tested cable is reached0Can be obtained from the output voltage of the circuit part 9 and the parameters of the current detection means, as calculated by:
I0＝KSUout
wherein the AC cable Ks：
Wherein k is1Stiffness of the main beam in the cantilever beam 1, CSTheta is the inherent capacitance of the micro transducer 3, theta is the electromechanical coupling coefficient of the micro transducer 3, mu is the ratio of the equivalent mass of the main beam and the auxiliary beam of the cantilever beam 1, and omega is omega/omega1Omega is the angular frequency of the measured current (which is the mains frequency and can be measured by a counter circuit of the circuit part 9), omega1Is the first-order modal frequency, ζ, of the cantilever 11And ζ2Is the first-order and second-order damping ratio of the cantilever beam 3, alpha is the ratio of the second-order modal frequency of the cantilever beam 3, mu0For vacuum permeability, BrIs the residual magnetic flux of the permanent magnet 2, V is the volume of the permanent magnet 2, a coordinate system is established by taking a straight line which passes through the mass center of the permanent magnet 2 and is vertical to the upper surface of the permanent magnet 2 as a z-axis and a straight line which passes through the mass center of the permanent magnet 2, is vertical to the z-axis and is orthogonal to a tested cable as an x-axis, and x isi、ziFor the output of the circuit part 9Press UoutAt the maximum, the coordinate of the ith core in the tested cable under the coordinate system, n is the number of the zero line and the live wire core of the tested cable, t is time, phiiThe initial phase of the ith core in the tested cable is shown.
Example 1
A current detection device for a plurality of alternating current frequencies is disclosed, as shown in figures 1-4 and figure 8, and comprises a cantilever beam 1, a permanent magnet 2, a micro transducer 3, a mass block 4, a package 5, an end cover 6, a positioning bolt 8 and a circuit part 9; the bottom of the front side wall of the end cover 6 is provided with a first semicircular hole 601, the top cover of the end cover 6 is provided with a threaded hole, the top of the front side wall of the package 5 is provided with a second semicircular hole 501, the end cover 6 is fixed on the package 5 through a locking mechanism 7, the package 5 is covered, and the first semicircular hole 601 and the second semicircular hole 501 are buckled together to form a circular through hole; the cantilever beam 1 is fixed in the groove of the through hole 502 of the package 5, and the micro transducer 3 is adhered on the upper surface of the cantilever beam 1, as shown in fig. 6, the micro transducer 3 comprises an upper electrode 301, a piezoelectric film 302 and a lower electrode 303 which are sequentially arranged from top to bottom and connected, the upper surface of the cantilever beam 1 is fixed with a permanent magnet 2 and a mass block 4,
a circuit portion 9 is fixed to an inner surface of the package 5;
the locking mechanism 7 comprises a handle 701, a line pressing plate 702, a limiting column 703 and a locking nut 704, wherein a through hole 502 is formed in the left side wall of the package 5, the limiting column 703 is located in the through hole 502, the line pressing plate 702 is located in the package 5, the left end of the line pressing plate 702 penetrates through the through hole 502 and is attached to the upper side of the limiting column 703, the handle 701 is sequentially screwed into a threaded hole in the left side of the top end of the end cover 6, the through hole 502, the line pressing plate 702 and the limiting column 703 on the package 5, penetrates out of the limiting column 703 and extends out of the bottom of the package 5 through the through hole 502, and the fixing of the handle 701 is realized at the bottom of the package 5 through the locking nut 704;
as shown in fig. 7, the circuit portion 9 includes a main processor, a tank circuit, a signal sampling circuit, a counter circuit, a communication circuit and interface, and an alarm circuit; wherein, the voltage signal 1 is the voltage output of the micro transducer and is used for detecting the current to be detected, and the voltage signal 2 is the voltage output of the piezoelectric layer 102 on the cantilever beam 1 and is used for supplying power to the circuit part 9.
As shown in fig. 5, the cantilever 1 has a laminated structure, the upper and lower surfaces are substrates 101, and a piezoelectric layer 102 is disposed between each two substrates 101, where the relationship between the numbers of the two substrates is: the number of piezoelectric layers 102 is n, the number of substrates 101 is n +1, and the total number of layers of cantilever beams 1 is 2n + 1.
The cantilever beam 1 is in a linear type, a bending type, a one-dimensional variable cross-section type, a U-shaped or T-shaped.
The number of the cantilever beams 1 is 1,2,3 to n.
The material of the micro transducer 3 comprises quartz crystal, piezoelectric ceramics and organic piezoelectric materials.
The permanent magnet 2 is in a square, cuboid or cylinder shape and is arranged right below the circular through hole.
The mass block 4 is in a square, cuboid, cylinder or irregular shape and is arranged at any position of the cantilever beam 1.
As shown in fig. 10, a detection method for the current detection device for a plurality of ac frequencies includes the following steps.
the modal frequency of each order of the current detection device can be approximately calculated as
Wherein k isnAnd mnRespectively the equivalent mass and equivalent stiffness of each stage of the device.
Modal frequency omega of each order of current detection devicenNear, at 0.8 ωnTo 1.5 omeganThe frequency range of (a) is up-swept by inputting a sweep signal through the electrodes of the micro-transducer 3, and the excitation acceleration is adcos χ t; the position of the mass block 4 on the cantilever beam 1 is adjusted, so that the modal frequency of each order of the current detection device is approximately equal to the frequency range of the current to be detected;
I0＝KSUout
wherein the AC cable Ks：
Wherein k is1Stiffness of the main beam in the cantilever beam 1, CSTheta is the inherent capacitance of the micro transducer 3, theta is the electromechanical coupling coefficient of the micro transducer 3, mu is the ratio of the equivalent mass of the main beam and the auxiliary beam of the cantilever beam 1, and omega is omega/omega1Omega is the angular frequency of the measured current (which is the mains frequency and can be measured by a counter circuit of the circuit part 9), omega1Is the first-order modal frequency, ζ, of the cantilever 11And ζ2Is the first-order and second-order damping ratio of the cantilever beam 3, alpha is the ratio of the second-order modal frequency of the cantilever beam 3, mu0For vacuum permeability, BrV is the residual magnetic flux of the permanent magnet 2, and V is the volume of the permanent magnet 2, and a line passing through the center of mass of the permanent magnet 2 and perpendicular to the upper surface of the permanent magnet 2 is taken as the z-axis, and a line passing through the center of mass of the permanent magnet 2, perpendicular to the z-axis and perpendicular to the z-axisEstablishing a coordinate system for the x-axis of a straight line orthogonal to the cable to be tested, xi、ziFor the output voltage U of the circuit part 9outAt the maximum, the coordinate of the ith core in the tested cable under the coordinate system, n is the number of the zero line and the live wire core of the tested cable, t is time, phiiThe initial phase of the ith core in the tested cable is shown.
The following formula is used for calculating the force applied by the permanent magnet under the condition that the tested cable with the number of cores n generates the magnetic field:
formula of magnetic field intensity around single wire
The component of the magnetic field strength around a single wire in the z-axis direction is
For the alternating current under the symmetrical load, when the ith core in the tested cable with the core number of n is a zero line or a ground wire, the current iiWhen the ith core in the tested cable is a live wire, the current is equal to 0
The composite magnetic field intensity of the tested cable with the core number n in the z-axis direction
Wherein, mu0For the vacuum permeability, r is the radial distance from any point in space to a single wire, i0The current of a single wire is obtained, x and z are coordinates of any point in a coordinate system which is established by taking a straight line which passes through the mass center of the permanent magnet 2 and is vertical to the upper surface of the permanent magnet 2 as a z axis and taking a straight line which passes through the mass center of the permanent magnet 2, is vertical to the z axis and is orthogonal to a tested cable as an x axis, and the x and z are coordinates of any point in the coordinate systemi、yiFor the output voltage U of the circuit part 9outWhen the maximum value is reached, the ith core in the tested cable is in the coordinate of the coordinate system, n is the core number of the tested cable, I0Is the amplitude of the current in the tested cableOmega is the angular frequency of the current when the inside of the tested cable is the alternating current, t is the time, and phi i is the initial phase of the ith core in the tested cable.
The magnetic field gradient of a single wire in the z-axis direction is
The resultant magnetic field gradient of the tested cable with the core number 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 is
The resultant magnetic field force in the z-axis direction generated by the tested cable with the core number n to the permanent magnet is
Wherein B isrV is the volume of the permanent magnet 2 for the permanent magnet residual magnetic flux.
The following formula is used to calculate the voltage output of the piezoelectric layer 3 via the circuit part 9:
the differential equation of motion of the cantilever 1 and the piezoelectric layer 3 can be expressed as:
the formula is transformed, simultaneous and decoupled through Laplace, and the analytic formula of V can be obtained as follows:
wherein k is1Stiffness of the main beam in the cantilever beam 1, CSIs the clamping capacitance of the piezoelectric layer 3, theta is the electromechanical coupling coefficient of the piezoelectric layer 3, mu cantilever 3, the main beam and the auxiliary beam, etcRatio of effective mass, omega to omega/omega1Omega is the angular frequency of the AC current to be measured, omega1Is the first order natural frequency, ζ, of the cantilever 31And ζ2The first-order and second-order damping ratios of the cantilever beam 3 are shown, and alpha is the ratio of the natural frequencies of the cantilever beam 3.
The above parameters are known quantities, based on the relationship of the current to the output voltage of the piezoelectric layer 3 through the circuit portion 9
I0＝KSUout
Substitution into FzIs simple and easy to obtain
Example 2
The same as in example 1, except that the cantilever beam 1 is T-shaped. As shown in fig. 9, the cantilever beam 1 has a T-shaped symmetrical structure. This structure increases the length of the cross section in the axial direction of the circular through-hole as compared with fig. 4. The root of the cantilever beam 1 is fixed in the strip-shaped groove 504 of the package 5, the upper surface is pasted with the micro transducer 3, and the upper surface is fixed with the permanent magnet 2 and the mass block 4. The basic detection principle of the current detection device in this embodiment is the same as that of the current detection device in embodiment 1, and the lumped parameter model thereof is consistent with fig. 12.
Example 3
The same as in example 1, except that the number of the cantilever beams 1 is n. As shown in fig. 9, the cantilever beam 1 is an array structure arranged along the thin groove of the packaging sidewall, the micro transducer 3 is attached to the upper surface, and the permanent magnet 2 and the mass block 4 in the shape of a cuboid are fixed to the upper surface. The basic detection principle of the current detection device in this embodiment is the same as that of the current detection device in embodiment 1, and the lumped parameter model thereof is consistent with fig. 12.
Example 4
The same as in example 1, except that the cantilever beam 1 has a laminated structure of 7 layers, which is attached in the same manner as in example 1, wherein the piezoelectric layer 102 has 3 layers, and the substrate 101 has 4 layers. Each piezoelectric layer 102 is connected in such a manner that the lower electrode of one layer is connected to the upper electrode of the other layer.
Example 5
The same as example 1, except that the cable to be tested is a three-phase five-core cable, as shown in fig. 11. The tested cable comprises three live wires, a zero wire and a ground wire. The basic principle of the structure of the current detection device is the same as that of embodiment 1.
Claims (8)
1. A current detection device for multiple frequencies is characterized by comprising a cantilever beam (1), a permanent magnet (2), a micro transducer (3), a mass block (4), a package (5), an end cover (6), a locking mechanism (7) and a circuit part (9); the bottom of the front side wall of the end cover (6) is provided with a first semicircular hole (601), two sides of the top end of the end cover (6) are respectively provided with a threaded hole, the top of the front side wall of the package (5) is provided with a second semicircular hole (501), the end cover (6) is fixed on the package (5) to cover the package (5), and the first semicircular hole (601) and the second semicircular hole (501) are buckled together to form a circular through hole; a through hole (502) is formed in the left side wall of the package (5), a square groove (503) is formed in the inner side of the left side wall of the package (5), the through hole (502) is communicated with the square groove (503), a long strip-shaped groove (504) is formed in the inner side of the left side wall of the package (5) below the square groove (503), one end of the cantilever beam (1) is fixed in the long strip-shaped groove (504) in the package (5), the upper surface of the cantilever beam (1) is fixedly provided with the micro transducer (3), the permanent magnet (2) and the mass block (4), and the circuit part (9) is fixed on the inner surface of the package (5);
locking mechanism (7) include handle (701), line ball board (702), spacing post (703), lock nut (704), wherein spacing post (703) are located through-hole (502) and square groove (503), line ball board (702) are located encapsulation (5), and the one end of line ball board (702) penetrates square groove (503) and laminates in spacing post (703) top, handle (701) screw in the left screw hole in end cover (6) top in proper order, through-hole (502) on encapsulation (5), line ball board (702) and spacing post (703), wear out spacing post (703) again and stretch out from encapsulation (5) bottom through-hole (502), realize the fastening of handle (701) through lock nut (704) in encapsulation (5) bottom.
2. A current sensing device for a plurality of ac frequencies according to claim 1, wherein said cantilever beam (1) is of a straight type, a bent type, a one-dimensional variable cross-section type, a U-shape or a T-shape.
3. The current detection device for multiple alternating current frequencies according to claim 2, wherein the cantilever beam (1) is a laminated structure, multiple layers are arranged in sequence, each layer comprises two substrates (101) and one piezoelectric layer (102), one piezoelectric layer (102) is arranged between each two substrates (101), and the piezoelectric layers (102) are connected in series; the number relationship of the substrate (101) and the piezoelectric layer (102) is as follows: the number of the piezoelectric layers (102) is n, the number of the substrates (101) is n +1, and the total layer number of the cantilever beams (1) is 2n + 1.
4. A current detection device for multiple ac frequencies according to claim 3, wherein the micro-transducer (3) comprises an upper electrode (301), a piezoelectric film (302) and a lower electrode (303) connected in sequence from top to bottom, and the piezoelectric film (302) is made of quartz crystal, piezoelectric ceramic or organic piezoelectric material.
5. The current detection device for multiple alternating current frequencies according to claim 4, wherein the permanent magnet (2) is a cube, a cuboid or a cylinder, and the permanent magnet (2) is arranged below a circular through hole formed by buckling the first semicircular hole (601) and the second semicircular hole (501).
6. A current sensing device for multiple AC frequencies according to claim 5, wherein the mass (4) is a cube, a cuboid or a cylinder, and can be placed at any position of the cantilever beam (1).
7. A current sensing device for a plurality of AC frequencies according to claim 6 wherein the circuit portion (9) comprises a main processor, a tank circuit, a signal sampling circuit, a counter circuit, a communication circuit and interface and an alarm circuit; the device comprises a cantilever beam (1), a counter circuit, a signal sampling circuit, an energy storage circuit, a communication circuit, an interface and an alarm circuit, wherein the counter circuit and the signal sampling circuit are used for receiving voltage output of a micro transducer (3), the counter circuit and the signal sampling circuit are respectively connected with a main processor, the main processor is simultaneously and respectively connected with the communication circuit, the interface and the alarm circuit, the energy storage circuit is used for receiving voltage output of an upper piezoelectric layer (102) of the cantilever beam (1), and simultaneously and respectively connected with the signal sampling circuit, the counter circuit, the communication circuit, the interface and the alarm circuit.
8. A current detection method for a current detection device for a plurality of ac frequencies, comprising the steps of:
step one, calibrating modal frequencies of various orders of a current detection device:
the modal frequency of each order of the current detection device is
Wherein k isnAnd mnRespectively the equivalent mass and equivalent stiffness of each stage of the device;
modal frequency omega of each order of current detection devicenNear, at (0) · (8). omeganTo (1) < 5 > omeganThe frequency range of (a) is up-converted by inputting a sweep signal through the electrodes of the micro-transducer (3), and the excitation acceleration is adcos χ t; the position of the mass block (4) on the cantilever beam (1) is adjusted, so that the modal frequency of each order of the current detection device is the same as the estimated frequency range of the current to be detected;
secondly, determining the core number of the tested cable according to specific working conditions;
thirdly, the tested cable is connected into the current detection device through a circular through hole formed by buckling the first semicircular hole (601) and the second semicircular hole (501), and the end cover (6) is buckled with the package (5); rotating a handle (701) of the locking mechanism (7) to enable a wire pressing plate (702) of the locking mechanism (7) to gradually approach to the end of the tested cable until the wire pressing plate (702) is contacted with the tested cable; then the positioning bolt (8) is screwed in through a threaded hole at the right end of the end cover (6) to complete the fixation of the tested cable;
when current flows through the cable to be tested, the permanent magnet (2) is stressed by a magnetic field generated by the current, the cantilever beam (1) vibrates along with the current, the output voltage of the micro transducer (3) changes along with the vibration, and the output voltage of the circuit part (9) and the amplitude of the current to be tested passing through the cable to be tested are in a linear relation;
step five, rotating the package (5) by taking a straight line, perpendicular to the front side wall of the package (5), of the circle center of a circular through hole formed by buckling the first semicircular hole (601) and the second semicircular hole (501) as an axis until the output voltage U of the circuit part (9)outThe maximum value is reached, and the amplitude value I of the current in the tested cable is reached(0)Calculated as follows:
I0＝KSUout
wherein the AC cable Ks：
Wherein k is1Is the rigidity of the main beam in the cantilever beam (1), CSIs the inherent capacitance of the micro transducer (3), theta is the electromechanical coupling coefficient of the micro transducer (3), mu is the ratio of the equivalent mass of the main beam and the auxiliary beam of the cantilever beam (1), and omega is omega/omega1ω is the angular frequency of the measured current, ω1Is the first-order modal frequency, ζ, of the cantilever beam (1)1And ζ2Is the first-order and second-order damping ratio of the cantilever beam (3), alpha is the ratio of the second-order modal frequency of the cantilever beam (3), mu is the vacuum magnetic conductivity, BrIs the residual magnetic flux of the permanent magnet (2), V is the volume of the permanent magnet (2), a coordinate system is established by taking a straight line which passes through the mass center of the permanent magnet (2) and is vertical to the upper surface of the permanent magnet (2) as a z-axis and a straight line which passes through the mass center of the permanent magnet (2), is vertical to the z-axis and is orthogonal to a tested cable as an x-axis, and x isi、ziIs the output voltage U of the circuit part (9)outAt the maximum, the coordinate of the ith core in the tested cable under the coordinate system, n is the number of the zero line and the live wire core of the tested cable, t is time, phiiThe initial phase of the ith core in the tested cable is shown.
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