CN114994147A - Oil-immersed transformer and monitoring sensor based on oil aging automatic monitoring - Google Patents
Oil-immersed transformer and monitoring sensor based on oil aging automatic monitoring Download PDFInfo
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- CN114994147A CN114994147A CN202210935851.XA CN202210935851A CN114994147A CN 114994147 A CN114994147 A CN 114994147A CN 202210935851 A CN202210935851 A CN 202210935851A CN 114994147 A CN114994147 A CN 114994147A
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
- G01N27/226—Construction of measuring vessels; Electrodes therefor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
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- G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
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- G—PHYSICS
- G01—MEASURING; TESTING
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- H01F27/40—Structural association with built-in electric component, e.g. fuse
- H01F27/402—Association of measuring or protective means
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/40—Structural association with built-in electric component, e.g. fuse
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Abstract
The invention discloses an oil-immersed transformer based on automatic oil aging monitoring and a monitoring sensor. The oil-immersed transformer comprises a transformer main body and a health monitoring sensor. The health monitoring sensor is installed in the transformer main body. The health monitoring sensor is used for detecting the aging degree of an insulating medium and comprises an electrode, a molecularly imprinted polymer layer and a capacitance dielectric layer. The molecularly imprinted polymer layer can specifically adsorb 2-furfural molecules. The two electrodes are respectively arranged on the opposite sides of the capacitance dielectric layer. The two molecularly imprinted polymer layers are respectively arranged on the opposite sides of the two electrodes. The smaller the capacitance value of the health monitoring sensor is, the more serious the aging of the insulation medium in the transformer main body is. The invention utilizes the active sites of the molecularly imprinted polymer to detect 2-furfural molecules in furan active substances generated by the aging of the insulating material of the oil-immersed transformer, and judges the aging degree of the insulating material of the oil-immersed transformer according to the detected 2-furfural concentration.
Description
Technical Field
The invention belongs to the technical field of oil-immersed transformers; in particular to an oil-immersed transformer and a monitoring sensor based on automatic oil aging monitoring.
Background
Long-term interruptions of power systems are often due to voltage conversion failures. These failures typically result in significant economic losses. Therefore, oil filled power transformers require a regular monitoring schedule to ensure their continuous operation. The lifetime of such transformers is usually predicted by examining their insulating material. The aging of an insulating material can be determined by its moisture content, dissolved gas analysis, furan content, acidity and dissipation factor of the oil. These parameters are stored in the transformer oil and require pre-measurement and determination of early failure or remaining life or health of the transformer. Therefore, different tests were performed on the oil samples to find out insulation degradation in the transformer. The molecular content of 2-furfural (also known as 2-FAL) in furan is the best parameter for determining solid insulation materials. The existing technology applied to monitoring the service life of the transformer detects the 2-FAL concentration of the transformer through an optical method, but the method has high sensitivity but a small detection range, and the detection concentration range is lower than 1ppm, so that the method can only be used for early warning of the transformer. The 2-FAL molecularly imprinted polymer is prepared on the electrode of the capacitive sensor, so that the 2-FAL molecularly imprinted polymer can be used for detecting 2-FAL molecules with a higher concentration range, the detection concentration range is 0-20ppm, and the 2-FAL molecularly imprinted polymer can be used for long-term monitoring of a transformer.
Disclosure of Invention
The invention aims to provide an oil-immersed transformer and a monitoring sensor based on automatic oil aging monitoring, wherein a molecularly imprinted polymer on the surface of a capacitor is used for reflecting the concentration of 2-furfural in the oil-immersed transformer, and the molecularly imprinted polymer is used for adsorbing capacitance change caused by different amounts of 2-furfural to realize numerical extraction of the change condition of the concentration of 2-furfural so as to reflect the aging degree of an insulating medium in the oil-immersed transformer and monitor the service life of the oil-immersed transformer.
In a first aspect, the invention provides an oil-immersed transformer based on automatic oil aging monitoring, which comprises a transformer main body and a health monitoring sensor. The health monitoring sensor is arranged in the transformer main body and is soaked in an insulating medium in the transformer main body. The health monitoring sensor is used for detecting the aging degree of an insulating medium and comprises an electrode, a molecularly imprinted polymer layer and a capacitance dielectric layer. The molecule capable of being specifically adsorbed by the molecularly imprinted polymer layer is a 2-furfural molecule. The two electrodes are respectively arranged on the opposite sides of the capacitance dielectric layer. The two molecularly imprinted polymer layers are respectively arranged on the opposite sides of the two electrodes. The smaller the capacitance value of the health monitoring sensor is, the more serious the aging of the insulation medium in the transformer main body is.
Preferably, the molecularly imprinted polymer layer, the electrode and the capacitance dielectric layer are all comb-shaped structures.
Preferably, the electrode is a copper sheet. The material of the capacitor dielectric layer is epoxy resin.
Preferably, the molecularly imprinted polymer layer is provided with molecular cavities which are complementary with 2-furfural molecular space. The molecular cavity is obtained by removing 2-furfural molecules after 2-furfural molecules and functional monomers are polymerized together.
Preferably, the material of the molecularly imprinted polymer layer is polydimethylsiloxane.
Preferably, the oil-immersed transformer based on automatic oil aging monitoring further comprises a capacitance reading circuit; the capacitance reading circuit is connected with the two electrodes and is used for reading a capacitance value between the two electrodes; the capacitance reading circuit comprises a capacitance-voltage conversion circuit, an instrument amplification circuit and a peak value detection circuit. The capacitance-voltage conversion circuit is used for reading the change degree of the capacitance between the two electrodes compared with the initial capacitance value and converting the change degree into an alternating current signal; the instrument amplifying circuit is used for amplifying the alternating current signal output by the capacitance-voltage conversion circuit. The peak value detection circuit is used for extracting the amplitude of the alternating current signal output by the instrument amplification circuit.
Preferably, the capacitance-voltage conversion circuit includes a first operational amplifier and a second operational amplifier. The non-inverting input ends of the first operational amplifier and the second operational amplifier are connected with an alternating current input signal Vi. The inverting input terminal of the first operational amplifier is connected with one of the electrodes and one of the ends of the resistor R1 and the resistor R3. The other end of the resistor R1 is connected to ground. The other electrode is connected with one end of a resistor R4. The other ends of the resistor R3 and the resistor R4 are connected to the output end of the first operational amplifier. The inverting input end of the second operational amplifier is connected with one end of the resistor R2, the resistor R6 and the capacitor C1. The other end of the resistor R1 is connected to ground. The capacitor C1 is connected with one end of the resistor R5. The other ends of the resistor R5 and the resistor R6 are connected to the output end of the second operational amplifier. The capacitance of the capacitor C1 is equal to the initial capacitance between the two electrodes. The output ends of the first operational amplifier and the second operational amplifier form an output interface of the capacitance-voltage conversion circuit.
Preferably, the instrument amplification circuit is a precision differential amplifier composed of three operational amplifiers, and the precision differential amplifier comprises a third operational amplifier, a fourth operational amplifier and a fifth operational amplifier. The non-inverting input ends of the third operational amplifier and the fourth operational amplifier are connected with the output interface of the capacitance-voltage conversion circuit. The inverting input terminal of the third operational amplifier is connected with one end of the resistor R7 and one end of the resistor R8. The inverting input terminal of the fourth operational amplifier is connected to one end of the resistor R9 and the other end of the resistor R8. The output end of the third operational amplifier is connected with one end of a resistor R10 and the other end of a resistor R7; the output end of the fourth operational amplifier is connected with one end of a resistor R11 and the other end of a resistor R9. The other end of the resistor R11 is connected to the non-inverting input terminal of the fifth operational amplifier and one end of the resistor R13. The other end of the resistor R13 is connected to ground. The other end of the resistor R10 is connected to the inverting input terminal of the fifth operational amplifier and one end of the resistor R12. The other end of the resistor R12 is connected with the output end of the fifth operational amplifier. And the output end of the fifth operational amplifier is used as the output end of the instrument amplifying circuit.
Preferably, the peak detection circuit includes a sixth operational amplifier and a seventh operational amplifier. And the non-inverting input end of the sixth operational amplifier is connected with the output end of the instrument amplifying circuit. The inverting input of the sixth operational amplifier is connected to the anode of the diode D1 and one end of the resistor R14. The output terminal of the sixth operational amplifier is connected to the anode of the diode D2 and the cathode of the diode D1. The cathode of the diode D2 is connected with one end of the capacitor C2 and the zero clearing switch K and the non-inverting input end of the seventh operational amplifier. The other ends of the capacitor C2 and the zero clearing switch K are grounded. The other end of the resistor R14 is connected with the inverting input end and the output end of the seventh operational amplifier.
In a second aspect, the present invention provides a health monitoring sensor for monitoring the aging degree of an insulating medium in an oil-immersed transformer according to the change of self-capacitance. The health monitoring sensor includes an electrode, a molecularly imprinted polymer layer, and a capacitive dielectric layer. The molecule capable of being specifically adsorbed by the molecularly imprinted polymer layer is a 2-furfural molecule. The two electrodes are respectively arranged on the opposite sides of the capacitance dielectric layer. The two molecularly imprinted polymer layers are respectively arranged on the opposite sides of the two electrodes.
In a third aspect, the present invention provides a method for preparing the health monitoring sensor, which comprises the following steps.
Step one, arranging copper sheets on two sides of epoxy resin to form a flat capacitor. And cutting the flat capacitor into a comb-shaped structure to form the comb-shaped capacitor.
And step two, polishing the surface of the comb-shaped capacitor.
And step three, carrying out ultrasonic cleaning on the comb-shaped capacitor in acetone.
And step four, putting the comb-shaped capacitor into deionized water for cleaning and then drying.
And step five, mixing dimethyl siloxane and a curing agent, and adding a 2-furfural solution.
And step six, defoaming the product obtained in the step five, and coating the product on two side surfaces of the comb capacitor.
And step seven, heating the comb capacitor with the coating layer to cure the coating layer to form the molecularly imprinted polymer layer.
And step eight, cleaning 2-furfural molecules in the molecularly imprinted polymer layer by using an ethanol solution to form molecular cavities in the molecularly imprinted polymer layer, thereby obtaining the health monitoring sensor.
Preferably, in the fifth step, the mass ratio of the dimethyl siloxane to the curing agent to the 2-FAL solution is 10: 1: 4.
the present invention has the following advantageous effects.
1. The method utilizes the active sites of the 2-FAL molecularly imprinted polymer to detect the 2-FAL molecules in furan active substances generated by the aging of the insulating material of the oil-immersed transformer, and judges the aging degree of the insulating material of the oil-immersed transformer according to the concentration of the detected 2-FAL molecules.
2. The method for detecting the concentration of the 2-FAL by using the 2-FAL molecularly imprinted polymer has the capability of quantitatively detecting the concentration of the 2-FAL within a wider concentration range (0-20 ppm), and greatly improves the sustainability of the health detection of the oil-immersed transformer compared with an optical principle detection mode which can only quantitatively detect the 2-FAL with the concentration of less than 1ppm in the prior art.
3. The health monitoring sensor adopts a comb-shaped structure, so that the total edge length of the sensor is increased, the edge capacitance of the sensor is further increased, and the sensitivity of the sensor is improved.
4. The insulating medium of the oil-immersed transformer can generate a plurality of chemical substances after aging, and the 2-FAL molecularly imprinted polymer used in the invention can selectively adsorb a single substance in the insulating medium aiming at a complex oil sample environment, namely, the sensor is only sensitive to the concentration of 2-FAL molecules, so that the detection performance can be effectively improved. In addition, the molecularly imprinted polymer layer used in the invention is made of Polydimethylsiloxane (PDMS) which has hydrophobic property, so that the health monitoring sensor in the invention is insensitive to humidity change in an insulating medium, and the capacitance value of the sensor only changes along with the difference of 2-FAL concentration in oil, thereby improving the reliability of the detection result of the sensor.
5. The invention provides a simple preparation method of a health monitoring sensor, which can effectively reduce the cost and improve the reliability of the sensor. In addition, the invention provides a matched capacitance reading circuit aiming at the monitoring principle and the equivalent circuit of the sensor, thereby effectively improving the practical application level of the invention.
Drawings
Fig. 1 is a schematic view of the overall structure of the present invention.
Fig. 2 is a schematic diagram of the overall structure and equivalent circuit of the health monitoring sensor according to the present invention (a partial enlarged view of a portion a in fig. 1).
Fig. 3 is a schematic diagram of the explosion and size parameters of the health monitoring sensor of the present invention.
FIG. 4 is a simplified process diagram of an equivalent circuit of the health monitoring sensor of the present invention.
FIG. 5 is a schematic diagram of a capacitance reading circuit according to the present invention.
FIG. 6 is a flow chart of the manufacturing process of the health monitoring sensor of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Example 1
As shown in fig. 1 and 2, an oil-immersed transformer based on automatic oil aging monitoring includes a transformer body, a health monitoring sensor, and a capacitance reading circuit. The health monitoring sensor is installed in the transformer body and is soaked in the insulating medium 5 in the transformer body. The health monitoring sensor comprises an electrode 1, a molecularly imprinted polymer layer 2 and a capacitive dielectric layer 6. The molecule capable of being specifically adsorbed by the molecularly imprinted polymer layer 2 is a 2-FAL molecule.
As shown in fig. 2, the two sheets of electrodes 1 are disposed on opposite sides of the capacitor dielectric layer 6, respectively. The two molecularly imprinted polymer layers 2 are respectively disposed on opposite sides of the two sheets of electrodes 1. The cross sections of the molecularly imprinted polymer layer 2, the electrode 1 and the capacitance dielectric layer 6 are all in a comb-shaped structure; in the comb-shaped structure of the electrode 1, the width of comb teeth is 2mm, and the distance between two adjacent outputs is 2 mm; the overall length of the electrode 1 is 50mm and the width 18 mm. The molecularly imprinted polymer layer 2, the electrode 1 and the comb-teeth portion on the capacitance dielectric layer 6 are identical in shape and are laminated together. The entire length of the molecularly imprinted polymer layer 2 was 5mm shorter than the entire length of the electrode 1 so that the outside of the end portion of the electrode 1 was exposed. The molecularly imprinted polymer layer 2 has a thickness of 60 μm.
The inner side surface of the electrode 1 is attached to the capacitance dielectric layer 6, and the outer side surface is attached to the molecularly imprinted polymer layer 2. The electrode 1 is a thin copper sheet. The material of the capacitor dielectric layer 6 is epoxy resin. The molecularly imprinted polymer layer 2 is provided with molecular cavities 4 that are spatially complementary to the target molecules 3. The molecular cavities 4 on the molecularly imprinted polymer layer 2 are formed by pre-assembling the target molecules and the functional monomers by covalent or non-covalent interactions and copolymerizing the target molecules with the cross-linking agent, and then removing the target molecules. The molecular cavities 4 are capable of adsorbing the target molecules 3. The amount of target molecules 3 adsorbed by the molecularly imprinted polymer layer 2 varies with the concentration of the target molecules 3 in the system. When the concentration of the target molecules 3 is between 0 and 20ppm, the capacitance change between the two sheets of electrodes 1 can quantitatively reflect the concentration value of the target molecules 3. The target molecule 3 is 2-FAL molecule, specifically is an organic compound 2-furfural generated by aging of insulating medium in oil-immersed transformer, and its molecular formula is C 5 H 4 O 2 。
As shown in fig. 2 and 3, the molecularly imprinted polymer layer 2 is made of thin and hydrophobic Polydimethylsiloxane (PDMS). The inner side surface of the molecularly imprinted polymer layer 2 is attached to the corresponding electrode 1, and the outer side surface is soaked by an insulating medium 5 of the oil-immersed transformer. The insulating medium 5 is an oil-like environment of the transformer insulating material and has a certain dielectric constant. A certain concentration of 2-FAL molecules is present in the insulating medium 5. The molecular cavities 4 on the imprinted polymer 2 are capable of adsorbing 2-FAL molecules in the insulating medium 5.
In capacitor operation, the capacitor has a capacitive fringe field effect, namely charges are mainly distributed at the edges and the sharp corners of the electrodes, the charges at the edges are higher than those at the center, and the charges at the sharp corners are higher than those at the edges. Therefore, the whole capacitive transformer health monitoring sensor is designed into a comb-shaped structure, so that the increase of the capacitance fringe field capacity is facilitated, the capacity of sensing active molecules is improved, and the sensitivity of the sensor is further improved.
An equivalent circuit schematic diagram of the sensor is shown in fig. 4, where Cz1 is the capacitance between the opposite sides of the two sheet electrodes 1 brought by the capacitive dielectric layer 6 in part (a) of fig. 4; rz1 is the resistance between the opposite sides of the two sheet electrodes 1; cz2 is the capacitance between the opposite sides of the two electrodes 1 brought by the insulating medium 5; rz2 is the resistance between the opposite sides of the two sheet electrodes 1; cz6 and Cz5 are respectively the capacitance between the opposite sides of the two pieces of electrodes 1 brought by the two molecularly imprinted polymer layers 2; cz3 and Cz4 are respectively the capacitance between the opposite sides of the two pieces of electrodes 1 brought by the target molecules adsorbed on the two molecularly imprinted polymer layers 2. The numerical values of Rz1, Rz2, Cz1, Cz2, Cz6 and Cz5 are all constant values; only the values of Cz3 and Cz4 change depending on how many target molecules are adsorbed by the two molecularly imprinted polymer layers 2, forming a variable capacitance reflecting the concentration of 2-FAL molecules in the insulating medium.
As shown in part (b) of fig. 4, the equivalent circuit of the health monitoring sensor is further simplified because the resistance Rz1 of the capacitance dielectric layer 6 and the resistance Rz2 of the insulation medium 5 are large, and therefore can be regarded as an open circuit, and the resistance parallel connection is negligible. In addition, on the basis of part (a) of fig. 4, the same variable capacitances Cz3 and Cz4 are simplified to a variable capacitance Cm, and the capacitances Cz6 and Cz5 are simplified to a constant Cd.
As shown in part (c) of FIG. 4, the equivalent circuit of the health monitoring sensor is further simplified, and the capacitances Cm, Cd and Cz2 in part (b) of FIG. 4 are simplified to a variable capacitance Cz2 -FAL (ii) a The whole sensor is simplified into a parallel circuit of a variable capacitor and a fixed value capacitor. The two parallel capacitances can be considered as the sensor total capacitance Csensor. The capacitance Csensor is the detection capacitance value of the sensor; the Csensor capacitance value decreases when the concentration of 2-FAL molecules in the insulating medium 5 increases.
The initial capacitance value of the health monitoring sensor is 24 pF; when the concentration of 2-FA in the insulating medium reaches 20ppm, the capacitance value of the health monitoring sensor decreases by 3.5 pF.
As shown in fig. 5, the capacitance reading circuit includes a capacitance-voltage conversion circuit 1-1, a meter amplification circuit 1-2, and a peak detection circuit 1-3. The capacitance-voltage conversion circuit 1-1 includes a first in-phase proportional operational amplifier circuit and a second in-phase proportional operational amplifier circuit. The two in-phase proportional operational amplification circuits are respectively connected with the health monitoring sensor and the fixed value capacitor C1. The first comparative operational amplification circuit includes a first operational amplifier a 1. The second in-phase proportional operational amplification circuit includes a second operational amplifier a 2. The non-inverting input terminals of the first operational amplifier a1 and the second operational amplifier a2 are both connected to the ac input signal Vi. The inverting input terminal of the first operational amplifier A1 is connected to one of the electrodes 1 and one of the terminals R1 and R3. The other end of the resistor R1 is connected to ground. The other electrode 1 is connected with one end of a resistor R4. The other ends of the resistor R3 and the resistor R4 are connected to the output Vo1 of the first operational amplifier A1. The inverting input terminal of the second operational amplifier A2 is connected to one terminal of the resistor R2, the resistor R6 and the constant value capacitor C1. The other end of the resistor R1 is connected to ground. The fixed value capacitor C1 is connected with one end of the resistor R5. The other ends of the resistor R5 and the resistor R6 are connected to the output Vo2 of the second operational amplifier A2. The output ends of the first operational amplifier A1 and the second operational amplifier A2 form an output interface of the capacitance-voltage conversion circuit 1-1.
The capacitor under the ac signal has a certain capacitive reactance, and can be regarded as a resistor. Therefore, when the input Vi and the resistors R1 and R4 are not changed, the amplitude change of the output signal at the output terminal Vo1 of the first operational amplifier a1 is in direct proportion to the capacitor Csensor. In addition, the capacitance value of the C1 is fixed, and the capacitance value is the initial value of the capacitance Csense, so the signals of Vo1 and Vo2 are the same in the initial state.
As shown in fig. 5, the meter amplifying circuit 1-2 is a precision differential amplifier composed of three operational amplifiers, which includes a third operational amplifier A3, a fourth operational amplifier a4, and a fifth operational amplifier a 5.
The non-inverting input terminals of the third operational amplifier A3 and the fourth operational amplifier a4 are connected to the output terminal Vo1 of the first operational amplifier a1 and the output terminal Vo2 of the second operational amplifier a2, respectively. The inverting input terminal of the third operational amplifier A3 is connected to one end of the resistor R7 and one end of the resistor R8. The inverting input terminal of the fourth operational amplifier A4 is connected to one terminal of the resistor R9 and the other terminal of the resistor R8. The output end of the third operational amplifier A3 is connected to one end of the resistor R10 and the other end of the resistor R7, and the output end of the fourth operational amplifier A4 is connected to one end of the resistor R11 and the other end of the resistor R9. The other end of the resistor R11 is connected to the non-inverting input terminal of the fifth operational amplifier a5 and one end of the resistor R13. The other end of the resistor R13 is connected to ground. The other end of the resistor R10 is connected to the inverting input terminal of the fifth operational amplifier A5 and one end of the resistor R12. The other end of the resistor R12 is connected to the output Vi2 of the fifth operational amplifier a 5.
The instrument amplifying circuit 1-2 takes a signal Vo2 as a reference input signal, a signal Vo1 as a detection input signal, and a signal Vi2 as an output signal.
Can derive the output voltage signal of the output end of the instrumentation amplifier 1-2V i2 As follows.
V i2 =(1+2R 4 /R 5 )(R 7 /R 6 )(V i1 /jωC 1 R 1 )(ΔC Sensor /(ΔC Sensor +C Sensor ) Equation 1)
Wherein R is 1 、R 4 、R 5 、R 6 、R 7 The resistance values of the resistor R1, the resistor R4, the resistor R5, the resistor R6 and the resistor R7 are respectively; c 1 The capacitance values of the capacitor C1 respectively;jis an imaginary unit;ωfor an ac input signalVi angular frequency.C Sensor Is an initial value of the capacitance of the two electrodes 1; deltaC Sensor Is the value of the change in capacitance of the two electrodes 1.
As shown in fig. 5, the peak detection circuit 1-3 is used to detect the peak magnitude of the ac signal, i.e. convert the ac signal into a dc signal, and the amplitude of the dc signal is the peak magnitude of the ac signal.
The peak detecting circuit 1-3 includes a sixth operational amplifier a6 and a seventh operational amplifier a 7. The non-inverting input of the sixth operational amplifier A6 is connected to the output of the fifth operational amplifier A5. The inverting input of the sixth operational amplifier a6 is connected to the anode of the diode D1 and to one end of the resistor R14. The output terminal of the sixth operational amplifier a6 is connected to the anode of the diode D2 and the cathode of the diode D1. The cathode of the diode D2 is connected to the capacitor C2, one end of the zero clearing switch K, and the non-inverting input terminal of the seventh operational amplifier a 7. Of capacitor C2, zero clearing switch KThe other ends are grounded. The other end of the resistor R14 is connected with the inverting input end and the output end V of the seventh operational amplifier A7 o 。
When the amplitude of the alternating current signal Vi2 output by the peak detection circuit 1-3 gradually becomes larger, the diode D2 charges the capacitor C2 by the analog signal output by the sixth operational amplifier a6 until the peak voltage; when the alternating current signal Vi2 is lower than the peak voltage, the diode D2 is turned off, the capacitor C2 keeps the voltage unchanged, and the diode D1 is turned on. At this time, the circuit formed by the sixth operational amplifier a6 is a voltage follower circuit. In addition, the operational amplifier a7 constitutes a voltage follower circuit, and the voltage value of the forward input end of the voltage follower circuit is the voltage at one end of the capacitor C2, namely the peak voltage, so Vo outputs a direct current analog signal with the amplitude of the peak voltage of the alternating current signal Vi 2. The resistor R14 is an inverting feedback resistor of the sixth operational amplifier a6, so that during the charging process of the capacitor, the operational amplifier a6 also serves as a voltage follower circuit, and the voltage at the output end of the operational amplifier is always the amplitude of the ac signal Vi 2.
Thus, the output signal of the capacitance reading circuitV 0 Peak voltage signal for output signal of instrumentation amplifier 1-2V i2ρ As follows.
V 0 =V i2ρ (formula 2)
Based on the initial capacitance value and the variation range of the health monitoring sensor, the parameter requirements of the components of the reading circuit are provided. The component parameter requirements are as follows: r 1 =R 2 =100kΩ，R 4 =R 5 =10kΩ，R 6 =R 3 =6MΩ，R 7 =R 9 =R 10 =R 11 = R 12 =R 13 =1kΩ，R 8 =200Ω，R 14 =500 Ω. All operational amplifiers are model OP 07.
Example 2
As shown in fig. 6, a method for manufacturing a health monitoring sensor includes the following steps.
Step one, as shown in part a of fig. 6, two copper sheets are separated by using epoxy resin to obtain a plate capacitor with the thickness of 16mm, and the plate capacitor is cut into a comb-shaped structure to form a comb-shaped capacitor 7.
Step two, as shown in part b of fig. 6, the surface and edges of the comb capacitor 7 are treated with files and sandpaper to be smooth.
And step three, as shown in part c of fig. 6, placing the comb-shaped capacitor 7 after cutting and surface treatment into acetone at 60 ℃ for ultrasonic cleaning for 15 minutes.
Step four, as shown in part d of fig. 6, the comb-shaped capacitor 7 cleaned by the ultrasonic cleaning is put into deionized water for cleaning.
And step five, as shown in part e of fig. 6, putting the comb-shaped capacitor 7 into a drying box, and drying for 10 minutes at the temperature of 70 ℃ to form the comb-shaped capacitor 7 consisting of two electrodes 1 and a capacitor dielectric layer 6.
And step six, as shown in parts f and g of fig. 6, mixing and uniformly stirring the PDMS monomer and the curing agent, pouring the 2-FAL solution into the mixture, and stirring the mixture again to form a viscous solution. The mass ratio of the PDMS monomer to the curing agent to the 2-FAL solution is 10: 1: 4.
seventhly, as shown in the h part of fig. 6, the viscous solution obtained in the step seven is placed into a vacuum pump for defoaming treatment.
And step eight, coating the viscous solution on the opposite sides of the two electrodes 1 of the comb capacitor 7 by using a dip coating device, wherein the thickness of the coating layer is 60 microns.
Step nine, as shown in a part j of fig. 6, the coated comb capacitor 7 is placed in a heating box; first at 70 ℃ for 40 minutes and then at 150 ℃ for 3 hours. A molecularly imprinted polymer layer 2 is formed on the surface of the electrode 1.
Step ten, as shown in the part k of fig. 6, cleaning the 2-FAL molecules in the molecularly imprinted polymer layer 2 in an ethanol solution to form molecular cavities 4 in the molecularly imprinted polymer layer 2, thereby obtaining the health monitoring sensor.
Claims (10)
1. An oil-immersed transformer based on automatic oil aging monitoring comprises a transformer main body and a health monitoring sensor; the method is characterized in that: the health monitoring sensor is arranged in the transformer main body and is soaked in an insulating medium (5) in the transformer main body; the health monitoring sensor is used for detecting the aging degree of an insulating medium (5) and comprises an electrode (1), a molecularly imprinted polymer layer (2) and a capacitance dielectric layer (6); the molecule capable of being specifically adsorbed by the molecularly imprinted polymer layer (2) is a 2-furfural molecule; the two electrodes (1) are respectively arranged on the opposite sides of the capacitance dielectric layer (6); the two molecularly imprinted polymer layers (2) are respectively arranged on the opposite sides of the two electrodes (1); the smaller the capacitance value of the health monitoring sensor, the more the insulation medium (5) in the transformer body is aged.
2. The oil-immersed transformer based on automatic oil aging monitoring of claim 1, wherein: the molecularly imprinted polymer layer (2), the electrode (1) and the capacitance dielectric layer (6) are all in a comb-shaped structure.
3. The oil-immersed transformer based on automatic oil aging monitoring of claim 1, wherein: the molecularly imprinted polymer layer (2) is provided with a molecular cavity (4) which is complementary with the 2-furfural molecular space; the molecular cavity (4) is obtained by removing 2-furfural molecules after 2-furfural molecules and functional monomers are polymerized together.
4. The oil-immersed transformer based on automatic oil aging monitoring of claim 1, wherein: the material of the molecularly imprinted polymer layer (2) is polydimethylsiloxane.
5. The oil-filled transformer based on automatic oil aging monitoring of any one of claims 1-4, wherein: the capacitance reading circuit is also included; the capacitance reading circuit is connected with the two electrodes (1) and is used for reading a capacitance value between the two electrodes (1); the capacitance reading circuit comprises a capacitance-voltage conversion circuit (1-1), an instrument amplification circuit (1-2) and a peak value detection circuit (1-3); the capacitance-voltage conversion circuit (1-1) is used for reading the change degree of the capacitance between the two electrodes compared with the initial capacitance value and converting the change degree into an alternating current signal; the instrument amplification circuit (1-2) is used for amplifying the alternating current signal output by the capacitance-voltage conversion circuit (1-1); the peak value detection circuit (1-3) is used for extracting the amplitude of the alternating current signal output by the instrument amplification circuit (1-2).
6. The oil-immersed transformer based on automatic oil aging monitoring according to claim 5, characterized in that: the capacitance-voltage conversion circuit (1-1) comprises a first operational amplifier and a second operational amplifier; the non-inverting input ends of the first operational amplifier and the second operational amplifier are connected with an alternating current input signal Vi; the inverting input end of the first operational amplifier is connected with one end of the resistor R1, one end of the resistor R3 and one electrode (1); the other end of the resistor R1 is grounded; the other electrode (1) is connected with one end of a resistor R4; the other ends of the resistor R3 and the resistor R4 are connected with the output end of the first operational amplifier; the inverting input end of the second operational amplifier is connected with one end of the resistor R2, the resistor R6 and the capacitor C1; the other end of the resistor R1 is grounded; the capacitor C1 is connected with one end of the resistor R5; the other ends of the resistor R5 and the resistor R6 are connected with the output end of the second operational amplifier; the capacitance value of the capacitor C1 is equal to the initial capacitance value between the two electrodes; the output ends of the first operational amplifier and the second operational amplifier form an output interface of the capacitance-voltage conversion circuit (1-1).
7. The oil-immersed transformer based on automatic oil aging monitoring of claim 5, wherein: the instrument amplification circuit (1-2) adopts a precision differential amplifier formed by three operational amplifiers, and comprises a third operational amplifier, a fourth operational amplifier and a fifth operational amplifier; the non-inverting input ends of the third operational amplifier and the fourth operational amplifier are connected with the output interface of the capacitance-voltage conversion circuit (1-1); the inverting input end of the third operational amplifier is connected with one end of the resistor R7 and one end of the resistor R8; the inverting input end of the fourth operational amplifier is connected with one end of a resistor R9 and the other end of a resistor R8; the output end of the third operational amplifier is connected with one end of a resistor R10 and the other end of a resistor R7; the output end of the fourth operational amplifier is connected with one end of a resistor R11 and the other end of a resistor R9; the other end of the resistor R11 is connected with the non-inverting input end of the fifth operational amplifier and one end of the resistor R13; the other end of the resistor R13 is grounded; the other end of the resistor R10 is connected with the inverting input end of the fifth operational amplifier and one end of the resistor R12; the other end of the resistor R12 is connected with the output end of the fifth operational amplifier; the output end of the fifth operational amplifier is used as the output end of the instrument amplifying circuit (1-2).
8. The oil-immersed transformer based on automatic oil aging monitoring of claim 5, wherein: the peak detection circuit (1-3) comprises a sixth operational amplifier and a seventh operational amplifier; the non-inverting input end of the sixth operational amplifier is connected with the output end of the instrument amplifying circuit (1-2); the inverting input end of the sixth operational amplifier is connected with the anode of the diode D1 and one end of the resistor R14; the output end of the sixth operational amplifier is connected with the anode of the diode D2 and the cathode of the diode D1; the negative electrode of the diode D2 is connected with one end of the capacitor C2 and the zero clearing switch K and the non-inverting input end of the seventh operational amplifier; the other ends of the capacitor C2 and the zero clearing switch K are grounded; the other end of the resistor R14 is connected with the inverting input end and the output end of the seventh operational amplifier.
9. A health monitoring sensor for monitoring the aging degree of an insulating medium (5) in an oil-immersed transformer according to the change of self capacitance, characterized in that: the health monitoring sensor comprises an electrode (1), a molecularly imprinted polymer layer (2) and a capacitance dielectric layer (6); the molecule capable of being specifically adsorbed by the molecularly imprinted polymer layer (2) is a 2-furfural molecule; the two electrodes (1) are respectively arranged on the opposite sides of the capacitance dielectric layer (6); the two molecularly imprinted polymer layers (2) are respectively arranged on the opposite sides of the two electrodes (1).
10. A method of making a health monitoring sensor as in claim 9, wherein: the method comprises the following steps:
step one, arranging copper sheets on two sides of epoxy resin to form a flat capacitor; cutting the flat capacitor into a comb-shaped structure to form a comb-shaped capacitor;
step two, polishing the surface of the comb-shaped capacitor;
step three, carrying out ultrasonic cleaning on the comb-shaped capacitor in acetone;
step four, putting the comb capacitor into deionized water for cleaning and then drying;
step five, mixing dimethyl siloxane and a curing agent, and adding a 2-furfural solution;
sixthly, defoaming the product obtained in the fifth step, and coating the product on two side surfaces of the comb capacitor;
heating the comb capacitor with the coating layer to cure the coating layer to form a molecularly imprinted polymer layer;
and step eight, cleaning 2-furfural molecules in the molecularly imprinted polymer layer by using an ethanol solution to form molecular cavities in the molecularly imprinted polymer layer, thereby obtaining the health monitoring sensor.
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