Line type lightning arrester resistive current self-energized monitoring system

Abstract

The invention relates to the technical field of lightning arrester tests, and discloses a line lightning arrester resistive current self-energized monitoring system, which comprises a line voltage sensor, a current sensing circuit, an energy taking circuit and an acquisition unit, the system inducts the voltage of a line where the lightning arrester is located through the induction plate, and the voltage is processed by the conditioning circuit and then collected by the collection unit; collecting by a collecting unit; a total current signal is extracted by an induction coil at the inlet of the current sensing and energy taking circuit, is converted into a voltage signal by a sampling resistor, and is collected by a collection unit; the energy taking circuit rectifies alternating current leakage current, charges a capacitor through over-voltage protection, and then converts the alternating current leakage current into low-voltage alternating current through a DC / DC module to supply power to an acquisition unit and the like. The system can directly obtain the total leakage current and the line voltage on site, so that the accuracy of resistive current extraction is improved; meanwhile, useless leakage current energy on the grounding wire of the lightning arrester is taken by adopting an environment energy taking method, operation of lines and equipment is not affected, and the method is suitable for complex electromagnetic working conditions of working of the lightning arrester.

Description

Technical Field

[0001] The invention relates to the technical field of arrester testing, and in particular to a line-type arrester resistive current self-powered monitoring system. Background Art

[0002] At present, in the power system, the arresters installed on the lines are subject to preventive tests every two years. However, with the continuous expansion of the power grid, the number of arresters installed has increased exponentially. The use of preventive tests and maintenance on arresters is bound to consume huge manpower, material and financial resources. At the same time, some aging and deterioration inside the arrester have no obvious characteristics in daily preventive maintenance and cannot be discovered in time. In order to ensure that the zinc oxide arrester operates in a normal state, the arrester condition needs to be monitored.

[0003] The resistive current of MOA (metal oxide arrester) is an important parameter to measure the state of the arrester. The aging of MOA valve plates under various types of voltages can be attributed to the redistribution of charges near the grain boundary layer of the internal valve plates, which results in the decrease of the Schottky barrier and the increase of the resistive current. Due to the structure without series gaps inside the MOA and the long-term operation of the power frequency current, aging increases the resistive leakage current of the ZnO valve plates; at the same time, the working environment of the arrester is relatively complex, and dirt, moisture, icing, etc. will cause the surface leakage current to increase. At the same time, surface flashovers may cause the insulation structure to be damaged and the insulation performance to decrease, resulting in an increase in the resistive current of MOA. The increase in resistive current increases the heating of MOA. In the early stage of aging and degradation, the self-heating and heat dissipation maintain a balance; but in the later stage, the heat generation is greater than its own heat dissipation, which will eventually lead to the rupture or even explosion of the arrester. Therefore, the resistive current of MOA is monitored.

[0004] MOA resistive current cannot be measured directly. One of the commonly used MOA resistive current extraction methods is the fundamental wave method, which is calculated based on the line voltage and leakage current. The measurement can obtain the synchronous MOA withstand voltage U and full current I MOA Signal. Due to the line voltage U and resistive current I R In phase, resistive current I R With capacitive current I C The phase difference is 90°, and the full current I MOA The phase quantity is equal to the resistive current I R , capacitive current I C The phase sum, such as Figure 1 As shown. Based on the above voltage and current phasor relationship, the MOA resistive current I can be calculated R .

[0005] When using the fundamental wave method, the total current of the arrester can be obtained by measuring the arrester ground wire with a high-precision ammeter. However, for line-type arresters, since they are installed on the crossarm of the tower and work in a complex electromagnetic environment, it is difficult to obtain the line voltage on site. Summary of the invention

[0006] Based on the above situation, the present invention proposes a line arrester resistive current self-powered monitoring system, designs a non-contact inductive measuring device for line voltage suitable for line arresters, and simultaneously takes energy from the leakage current of the arrester grounding wire to supply a low-power device for measuring line voltage and leakage current. The design can directly obtain the full current of leakage current and line voltage on site, which improves the accuracy of resistive current extraction; at the same time, the environment energy extraction method is adopted to extract the useless leakage current energy on the arrester grounding wire, which does not affect the operation of the line and equipment, and is suitable for the complex electromagnetic working conditions of the arrester.

[0007] The technical solution adopted by the present invention is:

[0008] A line arrester resistive current self-powered monitoring system, which is installed on the grounding cross arm of the tower where the arrester is located, and includes a line voltage sensor, a current sensing circuit, an energy taking circuit and a collection unit;

[0009] The line voltage sensor includes an induction plate and a conditioning circuit electrically connected to the induction plate. The induction plate can generate a divided voltage with the line connected to the lightning arrester, and the conditioning circuit is connected to the acquisition unit; the current sensing circuit includes an induction coil and a sampling resistor, the induction coil is installed on the energy extraction circuit, one side of the sampling resistor is connected to the induction coil of the energy extraction circuit, and the other side is connected to the acquisition unit; the energy extraction circuit includes a rectifier bridge, an inductor, a unidirectional transient voltage suppression diode, a voltage stabilizing capacitor and a DC / DC (direct current to direct current) module, the rectifier bridge of the energy extraction circuit is connected in parallel with a ZnO (zinc oxide) varistor and then connected in series to the grounding loop of the lightning arrester, one side of the DC / DC module is connected to the rectifier bridge, and the other side is connected to the acquisition unit, and the inductor, the unidirectional transient voltage suppression diode and the voltage stabilizing capacitor are installed on the connection line between the DC / DC module and the rectifier bridge;

[0010] The line arrester resistive current self-powered monitoring system senses the line voltage of the arrester through the induction plate, and after being processed by the conditioning circuit, it is collected by the acquisition unit; the full current signal is extracted by the current sensor and the induction coil at the entrance of the energy-taking circuit, converted into a voltage signal at the sampling resistor and collected by the acquisition unit; the energy-taking circuit rectifies the AC leakage current, charges the capacitor through voltage protection, and then converts it into low-voltage AC through the DC / DC module to power the acquisition unit, etc.

[0011] Furthermore, the induction plate is set at a certain arc with the line connected to the lightning arrester as the axis, the distance from the arc surface to the line is equal, and the distance from the arc surface to the line is greater than the maximum distance that the air between the line and the induction plate can penetrate; the conditioning circuit includes a grounding capacitor.

[0012] Furthermore, the line voltage sensor is based on the voltage division principle; the distance from the induction plate to the arrester connection line is h, the air stray capacitance between the line and the induction plate is C1, the air stray capacitance C1 forms a capacitive voltage division with the grounding capacitor C2 of the conditioning circuit, and a voltage division voltage U2' is formed on the grounding capacitor C2, that is, voltage measurement.

[0013] Furthermore, during the design process of the line voltage sensor, it is necessary to perform an equivalent estimation of the stray capacitance C1 based on the capacitance equivalent calculation of the arrester connection line;

[0014] The equivalent calculation process of the capacitance of the arrester connection line is as follows:

[0015] Step 1, the transmission line with radius r and length L is equivalent to a long strip with width 2r and length L;

[0016] Step 2, let the length of the induction plate be a and the width be b;

[0017] Step 3: According to dielectric theory, the capacitance of two plates with area S and distance h is calculated as:

[0018] C=εS / h

[0019] Where ε is the dielectric constant;

[0020] Step 4: The equivalent estimation process of stray capacitance C1 is as follows:

[0021] The coordinate axis is established with the center of the sensing plate, and the stray capacitance C1 is equivalent to the integration of multiple differential plate capacitors in series. The stray capacitance C1 is derived and the expression is as follows:

[0022]

[0023] In the formula, ε is the dielectric constant; r and L are the radius and length of the transmission line respectively; a and b are the length and width of the induction plate respectively; h is the distance from the induction plate to the arrester connection line; z is the integral variable, which is a small length along the z axis, varying in the range of 0 to h;

[0024] Step 5: Based on the stray capacitance C1, the size of the sensing plate, the distance h from the sensing plate to the arrester connection line, and the sampling capacitor C2 are designed.

[0025] Furthermore, the line voltage sensor needs to perform induced charge and voltage analysis during the design process, and the analysis process is as follows:

[0026] Step I, Charge and Electric Field:

[0027] When there is no corona discharge in the arrester connection line, the charge is basically bound inside the conductor, and there is no space charge to cause induced voltage; when corona discharge occurs, the space charge will generate induced voltage on the induction plate; Step II, electrostatic field image:

[0028] Using the mirror principle, assuming that the charge per unit length of the line is Q, and the distance from the line to the induction plate is h, the surface density of the induced charge on the induction plate is expressed as:

[0029]

[0030] In the formula, is the potential at any point on the z-axis; ε represents the dielectric constant; z is the length of a small segment along the z-axis, which varies in the range of 0 to the distance h from the induction plate to the arrester connection line;

[0031] The surface density of the induced charge on the induction plate is obtained as s , the calculation formula is as follows:

[0032]

[0033] Ignoring the electrostatic induction of the circuit further away, the amount of induced charge on the surface of the plate is q, and the calculation formula is as follows:

[0034]

[0035] In the formula, S is the area of ​​the sensing plate; θ is the central angle of the arc of the sensing plate; a is the length of the sensing plate;

[0036] Step III, Current and Induced Voltage:

[0037] As the power frequency AC voltage changes, the amount of charge Q on the line changes, and the corresponding amount of induced charge q changes;

[0038] By defining the current I = dq / dt, a current is generated, and an induced voltage is formed on the conditioning circuit connected to the induction plate, based on which the influence of the charge induced voltage on the divided voltage is analyzed;

[0039] Where I is the current intensity, dq is the tiny amount of charge, and dt is the tiny time increment.

[0040] Furthermore, under mA (milliampere) level current, the nonlinear ZnO varistor R1 has an extremely large resistance, close to an open circuit, and the leakage current mainly flows to the current sensing circuit and the energy extraction circuit; when the lightning current passes through the lightning arrester, the ZnO varistor R1 has an extremely small resistance, close to a short circuit, discharging the lightning current and protecting the current sensing circuit and the energy extraction circuit.

[0041] Furthermore, the current sensing circuit is connected in series with an induction coil L1 after the ZnO varistor R1 and before the rectifier circuit B; the induction coil L1 has a magnetic core to enhance the magnetic field; the number of turns n1 of the primary side coil of the induction coil L1 is greater than the number of turns n2 of the secondary side coil;

[0042] According to the relationship between the primary and secondary coil currents, I1n1=I2n2, the current is inversely proportional to the number of turns, that is, the secondary current I2 increases by n1 / n2 times relative to the mA-level I1; at the same time, since the primary current I1 is small, the number of turns n1 takes a larger value;

[0043] Take the precision sampling resistor R2, on which the full current and voltage signals are measured by the acquisition unit;

[0044] The induction coil L1 can electrically isolate the current sensing circuit, the energy extraction circuit and the grounding loop of the lightning arrester.

[0045] Furthermore, the arrester leakage current I1 is rectified by the rectifier bridge B to charge the capacitor C1, and the rectifier bridge B is constructed by a withstand-voltage Schottky diode with a small conduction voltage drop;

[0046] Inductor L limits current mutation;

[0047] A unidirectional transient voltage suppression diode TVS is connected in parallel before capacitor C1 to limit the voltage difference across capacitor C1 so that it does not exceed the upper limit of the DC / DC module input voltage.

[0048] Furthermore, the core of the acquisition unit adopts a low-power acquisition device and is provided with a non-volatile memory.

[0049] The beneficial effects of the present invention are:

[0050] 1. A method of measuring the power frequency voltage of the line by using the stray capacitance of air to form a voltage divider is proposed, and based on the dielectric theory, the design method of the size of the induction plate, the distance from the line, and the sampling capacitor is derived; at the same time, the influence of the induced voltage formed by corona discharge on the phase of the voltage divider is considered.

[0051] 2. A non-contact line voltage sensor is formed without safety risks; at the same time, the sensor and the measuring device are both passive devices and do not require power supply.

[0052] 3. Compared with the long-distance CVT signal acquisition method, the non-contact voltage measurement method can obtain the line voltage at the location of the arrester near the line-type arrester, improve the accuracy of voltage measurement, and calculate the resistive current on the spot, avoiding the interference problem of long-distance transmission of voltage signals.

[0053] 4. It realizes self-power supply suitable for line-type lightning arresters. Under the condition of 10mA leakage current, it can continuously output 5V and 20mW of electric energy. No regular maintenance is required; there is no external power wiring. Compared with the wired power supply method, it can be used for lightning arrester monitoring under complex electromagnetic working conditions; it is installed at the grounding wire position to facilitate the grounding of the metal shielding shell. On the one hand, it shields the electromagnetic field, and on the other hand, it is used as a safe grounding to ensure the safety of personnel during installation and information collection;

[0054] 5. The proposed self-energy supply method is an environmental energy extraction method, which can extract energy from useless mA-level leakage current and utilize waste energy. Compared with the intermittent and unstable energy supply of traditional solar energy and wind energy, the leakage current energy extraction provides stable energy. The energy extraction device is simple in structure and easy to install compared with solar panels for solar energy extraction and wind turbines for wind energy extraction.

[0055] 6. In the overall design of the system, the full current, line voltage measurement circuit and energy acquisition circuit are integrated, with a simple structure and easy practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a schematic diagram for resistive current calculation;

[0057] Figure 2 This is the electrical structure diagram of the CVT;

[0058] Figure 3 This is a schematic diagram of the bushing end-frequency voltage sensor;

[0059] Figure 4 This is a schematic diagram of an inductive power supply;

[0060] Figure 5 This is a schematic diagram of the working power supply of the small current energy-taking system;

[0061] Figure 6 It is a connection diagram of the line arrester resistive current self-powered monitoring system;

[0062] Figure 7 This is a schematic diagram of the installation location of the line arrester resistive current self-powered monitoring system;

[0063] Figure 8 This is a schematic diagram of sensor capacitance voltage division;

[0064] Fig. 9 Schematic diagram of corona discharge charge Q and image charge;

[0065] Fig.10 This is the schematic diagram of the current sensing and energy extraction circuit;

[0066] Fig.11 This is the test induced voltage waveform;

[0067] Fig.12This is a typical circuit diagram of a DC / DC module;

[0068] Fig.13 This is a simulation model diagram of the leakage current energy harvesting circuit;

[0069] Fig.14 Energy extraction results under the conditions of leakage current 10mA and load 500Ω;

[0070] Fig.15 This is the basic circuit diagram of C8051F912;

[0071] Fig.16 Schematic diagram of ferroelectric memory circuit. DETAILED DESCRIPTION

[0072] The following will be combined with the drawings of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0073] At present, the conventional solutions for preventive testing of line-type lightning arresters are: using capacitive voltage transformer (CVT), external voltage division method, inductive energy extraction method, small current energy extraction and other technical means.

[0074] Capacitor Voltage Transformer (CVT): Figure 2 The electrical structure diagram of CVT is shown in Figure 1. The capacitor voltage divider is composed of a high-voltage arm capacitor CH and a low-voltage arm capacitor CL connected in series. The electromagnetic unit is composed of an intermediate transformer T, a compensation reactor L, a damper D, etc., and Z is a secondary load. The line voltage Us is stepped down by the capacitor voltage divider and input into the electromagnetic unit. After the "compensation effect" of the compensation reactor, it is input into the intermediate transformer and then output after the "secondary step-down" of the intermediate transformer. CVT measures line voltage and has problems such as poor transient characteristics. At the same time, in the application scenario of line arresters, the arrester is far away from the CVT or there may be no CVT around, so it is difficult to obtain the line voltage nearby. Even if the voltage signal can be obtained, the signal transmission process over a long distance will be interfered by the electromagnetic field, and it is difficult to guarantee accuracy when used to calculate the resistive current of the arrester.

[0075] External pressure division method: Figure 3As shown in the figure, a method of adding a capacitive sensor to the outside of an existing capacitive device (bushing) has the same principle as a high-voltage voltage divider. The geometric capacitance of the capacitive device is used as an equivalent high-voltage capacitor, and the external capacitor is equivalent to a low-voltage capacitor. The two are connected in series to form a capacitive voltage divider, and the voltage of the additional impedance outside the capacitive device is measured and the line voltage is inversely calculated. This method also has problems such as no available capacitive devices in the immediate surroundings, and because the capacitive device itself has a certain resistance, a voltage phase difference will be introduced. On the other hand, power supply is one of the key issues in the application of lightning arrester monitoring devices. Because the lightning arrester status monitoring devices are widely distributed, there are complex working conditions such as high voltage, strong electric field, and electromagnetic interference at the distribution location. Conventional power supplies are difficult to use, and it is difficult to supply energy to the device and monitoring nodes. Therefore, the difficulty in obtaining power has become one of the important factors restricting the development of online monitoring. The existing energy supply methods mainly include: laser power supply, solar energy supply, inductive energy extraction, etc. Laser power supply requires a low-voltage power supply to generate lasers, which is costly and inefficient; solar energy has low energy density and unstable power supply.

[0076] Induction energy method: Figure 4 As shown, the main coil is used to extract energy. The cross-sectional area is 1.35cm 2 , the number of turns of the main coil is 225 turns of the magnetic core ring. It is concluded that through experimental verification, when the simulated current reaches 3.8A, 5V, 20mW of electrical energy can be output through energy stabilization. Energy is taken from the line through electromagnetic induction, which consumes line energy. At the same time, the coil needs to be closer to the high-voltage line, which poses a safety hazard. At the same time, energy extraction requires the primary side current to reach at least 1A.

[0077] Small current energy extraction: Figure 5 In the area near the grounding wire, electrodes are buried at certain intervals. When a 10mA leakage current passes through, a step potential Ek is formed on the soil resistance R2 between the electrodes. At the same time, a voltage is generated on the energy-taking device Rb connected in series with the contact resistance R0 between the soil, and energy can be supplied through this voltage. Since the line-type lightning arrester is far from the ground, this method cannot be applied to the line-type lightning arrester.

[0078] Based on the above situation, this embodiment proposes a line arrester resistive current self-powered monitoring system, such as Figure 6As shown, the line arrester resistive current self-powered monitoring system includes a line voltage sensor, a current sensing circuit, an energy extraction circuit and a collection unit; the line voltage sensor includes a sensing plate, and a conditioning circuit electrically connected to the sensing plate, the sensing plate can generate a divided voltage with the line connected to the arrester, and the conditioning circuit is connected to the collection unit; the current sensing circuit includes an induction coil and a sampling resistor, the induction coil is installed on the energy extraction circuit, one side of the sampling resistor is connected to the induction coil of the energy extraction circuit, and the other side is connected to the collection unit; the energy extraction circuit includes a rectifier bridge, an inductor, a unidirectional transient voltage suppression diode, a voltage-stabilizing capacitor and a DC / DC (direct current to direct current) module, the rectifier bridge of the energy extraction circuit is connected in parallel with a ZnO (zinc oxide) varistor and then connected in series to the grounding circuit of the arrester, one side of the DC / DC module is connected to the rectifier bridge, and the other side is connected to the collection unit, the inductor, the unidirectional transient voltage suppression diode and the voltage-stabilizing capacitor are installed on the connection line between the DC / DC module and the rectifier bridge. As shown Figure 6 As shown, the line arrester resistive current self-powered monitoring system senses the line voltage of the arrester through the induction plate, and after being processed by the conditioning circuit, it is collected by the acquisition unit; the full current signal is extracted by the current sensor and the induction coil at the entrance of the energy-taking circuit, converted into a voltage signal at the sampling resistor and collected by the acquisition unit; the energy-taking circuit rectifies the AC leakage current, charges the capacitor through voltage protection, and then converts it into low-voltage AC through the DC / DC module to power the acquisition unit, etc.

[0079] The overall installation location of the line arrester resistive current self-powered monitoring system is as follows: Figure 7 As shown in the figure, the traditional arrester is installed on the cross arm of the line tower and the metal bracket, while the line arrester resistive current self-powered monitoring system is installed without changing the arrester installation. The current sensing circuit, energy taking circuit and acquisition unit are connected between the arrester and the metal bracket, and are shielded by the metal grounding shell.

[0080] Furthermore, this embodiment describes in detail the composition, principle, and design process of the line voltage sensor, current sensing circuit, energy acquisition circuit, and acquisition unit as follows:

[0081] ①Line voltage sensor

[0082] The line voltage measurement sensor is mainly composed of a sensing plate and a conditioning circuit. Based on the voltage division principle, the sensing plate generates a divided voltage proportional to the line voltage. The sensing plate is set at a certain arc with the line as the axis, so that the distance from the arc surface to the line is equal, and the distance from the arc surface to the line is greater than the maximum distance that the air can penetrate in the gap between the line and the sensing plate.

[0083] The voltage measurement principle is as follows Fig. 9As shown in the figure, the line voltage measurement is completed by the metal sensing plate and the conditioning circuit. The distance from the sensing plate to the line is h, which is greater than the maximum distance that the air between the line and the sensing plate can penetrate. The core of the conditioning circuit is the grounding capacitor C2. The air stray capacitance between the line and the sensing plate is C1. Due to the short distance, C1 is large enough to form a capacitive voltage divider with capacitor C2, and a voltage divider voltage U2' is formed on C2.

[0084] Estimate the stray capacitance C1. Figure 8 , the transmission line with radius r and length L is equivalent to a long strip with width 2r and length L. The induction plate is a long and b wide. According to dielectric theory, the capacitance calculation formula for two plates with area S and distance h is:

[0085] C=εS / h (1)

[0086] Where ε is the dielectric constant.

[0087] Combined with formula (1), the coordinate axis is established with the center of the sensing plate, and C1 is equivalent to the integration of multiple differential plate capacitors in series. The expression of C1 can be derived as follows:

[0088]

[0089] In the formula, ε is the dielectric constant; r and L are the radius and length of the transmission line respectively; a and b are the length and width of the induction plate respectively; h is the distance from the induction plate to the arrester connection line; z is the integral variable, which is a small length along the z axis, varying in the range of 0 to h;

[0090] According to formula (2), the stray capacitance C1 can be derived, so as to design the size of the sensing plate, the distance h from the sensing plate to the arrester connection line, and the sampling capacitor C2.

[0091] When there is no corona discharge in the line, the charges are basically bound inside the conductor, and there is no space charge to cause induced voltage. However, when corona discharge occurs, the space charge generates induced voltage on the induction plate, and it is necessary to analyze the influence of the induced voltage U2" on the divided voltage U2'.

[0092] The schematic diagram of the cross section of the circuit and the induction board is as follows Fig. 9 As shown, assume that the charge per unit length of the line is Q, and the distance from the line to the induction plate is h. According to the principle of electrostatic field mirror image, the induced charge on the surface of the plate can be equivalent to the action of the opposite charge with the plate as the interface, which is mirror-symmetrical with Q, and -Q is mirror-symmetrical along the induction plate. The center of the Q and -Q axis is the origin, and the axis is the z axis. Then the potential of any point on the z axis is It can be expressed as:

[0093]

[0094] In the formula, is the potential at any point on the z-axis; ε represents the dielectric constant; z is the length of a small segment along the z-axis, which varies in the range of 0 to the distance h from the induction plate to the arrester connection line.

[0095] Furthermore, the surface density of the induced charge on the plate is s for:

[0096]

[0097] Ignoring the electrostatic induction of the circuit further away, the charge q of the induced charge on the surface of the plate is equal to:

[0098]

[0099] Where S is the area of ​​the sensing plate; θ is the central angle of the arc of the sensing plate; and a is the length of the sensing plate.

[0100] As the power frequency AC voltage changes, the charge Q of the line changes, and the corresponding induced charge q changes. I = dq / dt, generating current, and forming an induced voltage on the conditioning circuit connected to the induction board. Based on this, the influence of the induced voltage on the divided voltage is analyzed; in the formula, I represents the current intensity; dq represents the tiny charge; dt represents the tiny time increment.

[0101] The line voltage sensor is based on the induction principle to obtain the line voltage at the line arrester nearby, which solves the problem that it is difficult to obtain the line voltage by using the capacitive voltage transformer (CVT) or external voltage division method, and the long-distance signal transmission process is interfered by the electromagnetic field. It also helps to improve the accuracy of resistive current extraction. At the same time, the line voltage sensor obtains the line voltage in a non-contact manner, which solves the problem that the capacitive voltage transformer (CVT) and other methods directly connect the line and introduce the line voltage, which poses a safety risk.

[0102] ②Current sensing circuit

[0103] The schematic diagram of the current sensing circuit is shown in Fig.10 Under the power frequency working voltage, for a lightning arrester that has aged to a certain extent, the grounding wire leakage current is approximately power frequency AC, with an amplitude of mA (milliampere) level. At the lightning arrester grounding wire (copper busbar) position, the leakage current energy-taking circuit is connected in parallel with the ZnO varistor and then connected in series to the grounding loop. Under mA-level current, the nonlinear ZnO varistor R1 has a very large resistance and is approximately open-circuited, and the leakage current mainly flows to the current sensing circuit and the energy-taking circuit. When MOA passes through the lightning current, the ZnO varistor R1 has a very small resistance, close to a short circuit, discharging the lightning current and protecting the current sensing and energy-taking circuits.

[0104] The current sensing circuit is connected in series with the induction coil L1 after the ZnO varistor R1 and before the rectifier circuit B to measure the full current of mA-level AC. The induction coil L1 has a magnetic core to enhance the magnetic field; the number of turns n1 on the primary side of the induction coil L1 is higher than the number of turns n2 on the secondary side. According to the relationship between the primary and secondary coil currents I1n1=I2n2, the current is inversely proportional to the number of turns, that is, the secondary current I2 increases by n1 / n2 times relative to the mA-level I1. At the same time, since the primary current I1 is small, in order to generate a magnetic field of sufficient strength, the number of turns n1 takes a larger value. The precision sampling resistor R2 is taken, and the full current and voltage signal on it is measured by the acquisition unit. The induction coil L1 plays the role of electrically isolating the measurement circuit and the power supply circuit.

[0105] ③ Energy extraction circuit

[0106] The principle of energy-taking circuit is shown in Fig.10 . The energy-taking circuit mainly includes a rectifier bridge B, an inductor L2, a unidirectional transient voltage suppressor diode TVS, a voltage-stabilizing capacitor C1, and a DC / DC module. The leakage current I1 is rectified by the rectifier bridge B to charge the capacitor C1. The rectifier bridge B is constructed with a withstand-voltage Schottky diode with a small conduction voltage drop. The inductor L plays a role in limiting the current mutation; a unidirectional transient voltage suppressor diode TVS is connected in parallel before the capacitor C1 to limit the voltage difference across C1 so that it does not exceed the upper limit of the DC / DC module input voltage.

[0107] The energy-harvesting circuit is an environmental energy-harvesting method that does not require an external power supply. It solves the technical problem that conventional power supplies cannot be used in line arrester application scenarios where there are complex working conditions such as high voltage, strong electric field, and electromagnetic interference. Energy is harvested from the arrester grounding wire, taking the useless leakage current energy from the arrester grounding wire to solve the problem that the traditional inductive energy-harvesting method loses line energy and has safety hazards; at the same time, the energy-harvesting method is mA-level current energy-harvesting, which solves the problem that the traditional inductive energy-harvesting method requires a wire current of at least 1A, which is not suitable for the arrester leakage current conditions.

[0108] ④ Collection unit

[0109] The core of the acquisition unit can use a low-power acquisition device, such as a single-chip microcomputer. When the leakage current is small, the power supply may be insufficient. To prevent data loss due to power failure, the acquisition power supply accessory circuit uses non-volatile memory such as ferroelectric memory.

[0110] Furthermore, this embodiment also experimentally verifies the above-mentioned line arrester resistive current self-powered monitoring system, and the verification process is as follows:

[0111] Line Voltage Sensor Verification:

[0112] like Fig. 9The principle shown is that under the test conditions, the line diameter is 2.5cm and the length L = 3m. For the induction plate, the distance between the induction plate and the line is designed to be d = 40cm, and the length and width of the induction plate are both 40cm. For the conditioning circuit parameters, according to formula (2), the line-induction plate stray capacitance C1≈5pF. Designed for the 35kV voltage level, C2 uses a 5nF high-voltage capacitor, and the output voltage is lower than 3.5V, which can be directly measured by the acquisition unit (microcontroller C8051F912).

[0113] Voltages of varying magnitudes are applied to the circuit and the induced plate voltage is measured. Fig.11 The voltage waveform of the induction plate under different line voltages. Fig.12 As the voltage applied to the line increases, corona discharge is gradually generated. During the corona discharge, space charge is generated in the space near the line, which is equivalent to increasing the line charge Q. The induced charge q increases, and the induced voltage increases. At this time, the rising rate of the induced voltage waveform is higher than the original sine wave rising rate, resulting in waveform distortion. However, the starting 0 value point of the sine waveform still overlaps, that is, within the loading voltage range, the corona discharge space charge has little effect on the line voltage phase measurement, and can be used for resistive current calculation.

[0114] Energy extraction circuit verification:

[0115] same Fig.10 Principle: Due to the different degradation or aging degree of lightning arresters, the leakage current has certain differences. A DC / DC module with a wide input voltage range is used. After the DC / DC module voltage is converted, a 3V DC voltage is output to supply the signal acquisition unit. When the MK9016 step-down chip is used, the input voltage range is 5V to 100V and the output voltage is 3V. Typical DC / DC module application circuit is as follows: Fig.12 The output voltage of C2 can power the acquisition unit and its accessory circuits. The transient suppression diode TVS uses 5KP100CA; the rectifier bridge diode uses SR120.

[0116] The energy extraction circuit verification simulation model using Matlab / Simulink is as follows Fig.13 As shown in the figure. The model uses an integral-controlled DC / DC buck circuit to replace the MK9016 buck module. In the simulation, a 10mA steady-state DC source is used to simulate the arrester leakage current. The module output is set to 3V. Fig.13 In the energy harvesting circuit, C1=33μF, L2=1μH, L3=100μH, the load side capacitor C2 is 100μF, and the load resistance R0=500Ω (output power is about 20mW). The simulation results of the energy harvesting circuit within a time length of 5s are shown as follows Fig.14 As shown, Fig.14(a), the weak leakage current charges the capacitor C1, and the voltage of C1 gradually rises and finally stabilizes at about 92V, which does not exceed the upper limit of the DC / DC module input voltage. Fig.14 (b) The voltage across the load resistor R0 reaches 3V in about 0.2s, but there is a certain oscillation. A damping resistor R2 = 10Ω is added to the circuit, which plays a certain filtering role together with C2. The simulation proves that the leakage current energy harvesting circuit can work according to the design requirements.

[0117] During the verification process, the core of the acquisition unit uses a low-power microcontroller C8051F912, with power consumption as low as 160μA / MHz in active mode and 10nA in sleep mode with memory retention. The basic circuit is as follows Fig.15 As shown. The power management control word is used to set the power working mode to reduce power consumption. The maximum power-on delay is 2ms, the reset delay time is 10μs, the reset time is 15μs, and the operating speed is 25MIPS. At the same time, when the leakage current is small and the energy-taking circuit is insufficient to supply power, the data needs to be saved after power failure, which requires a non-volatile memory of a certain capacity. The embodiment uses the ferroelectric memory FM3130 of Ramtron Corporation of the United States. The storage circuit circuit diagram is shown in Fig.16 shown.

[0118] In summary, the line arrester resistive current self-powered monitoring system uses air stray capacitance to form a voltage divider to measure the power frequency voltage borne by the line arrester; based on the derivation of dielectric theory, the design method of the induction plate size, the distance from the line, and the sampling capacitor is obtained; based on the induction principle, the method of deducing the influence of the induced voltage formed by corona discharge on the phase of the voltage divider is used. The induction plate and conditioning circuit of the current sensing circuit are non-contact passive sensing devices; the curved surface induction plate is combined with the line structure design. The current sensing circuit is combined with the energy extraction circuit. In order to achieve mA-level current measurement, an induction coil with a magnetic core is used to enhance the magnetic field; the number of turns of the primary side coil n1 is higher than the number of turns of the secondary side coil n2 to increase the current amplitude and reduce the accuracy requirement of the acquisition unit. The full current and line voltage are measured synchronously at the same position of the line, and the resistive current can be calculated on the spot, and the accuracy of the resistive current calculation is improved. The energy-taking circuit is sufficient to supply energy to the low-power measurement circuit, and takes into account the protection of the leakage current energy-taking circuit when transient large current passes through; the energy-taking method is environmental energy-taking, which takes energy from useless leakage current, does not consume line energy, and utilizes waste energy, which is a clean energy method. The line arrester resistive current self-powered monitoring system has a simple structure and a small size, and can be used with a slight modification to the traditional line arrester installation structure.

[0119] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A line arrester resistive current self-powered monitoring system, characterized in that: The line arrester resistive current self-powered monitoring system is installed on the grounding cross arm of the tower where the arrester is located, and includes a line voltage sensor, a current sensing circuit, an energy taking circuit and a collection unit; The line voltage sensor includes an induction plate and a conditioning circuit electrically connected to the induction plate. The induction plate can generate a divided voltage with the line connected to the lightning arrester, and the conditioning circuit is connected to the collection unit; the current sensing circuit includes an induction coil and a sampling resistor, the induction coil is installed on the energy extraction circuit, one side of the sampling resistor is connected to the induction coil of the energy extraction circuit, and the other side is connected to the collection unit; the energy extraction circuit includes a rectifier bridge, an inductor, a unidirectional transient voltage suppression diode, a voltage stabilizing capacitor and a DC / DC module, the rectifier bridge of the energy extraction circuit is connected in parallel with the ZnO varistor and then connected in series to the grounding loop of the lightning arrester, one side of the DC / DC module is connected to the rectifier bridge, and the other side is connected to the collection unit, and the inductor, the unidirectional transient voltage suppression diode and the voltage stabilizing capacitor are installed on the connection line between the DC / DC module and the rectifier bridge; The line arrester resistive current self-powered monitoring system senses the line voltage of the arrester through the induction plate, and after being processed by the conditioning circuit, it is collected by the acquisition unit; the full current signal is extracted by the current sensor and the induction coil at the entrance of the energy-taking circuit, converted into a voltage signal at the sampling resistor and collected by the acquisition unit; the energy-taking circuit rectifies the AC leakage current, charges the capacitor through voltage protection, and then converts it into low-voltage AC through the DC / DC module to power the acquisition unit, etc.

2. The line arrester resistive current self-powered monitoring system according to claim 1, characterized in that: The induction plate is set at a certain arc with the line connected to the arrester as the axis, the distance between the arc surface and the line is equal, and the distance between the arc surface and the line is greater than the maximum distance that the air between the line and the induction plate can penetrate; The conditioning circuit includes a capacitor connected to ground.

3. The line arrester resistive current self-powered monitoring system according to claim 2, characterized in that: The line voltage sensor is based on the voltage division principle; the distance from the induction plate to the arrester connection line is h, the air stray capacitance between the line and the induction plate is C1, the air stray capacitance C1 forms a capacitive voltage division with the grounding capacitor C2 of the conditioning circuit, and a voltage division voltage U2' is formed on the grounding capacitor C2, that is, voltage measurement.

4. The line arrester resistive current self-powered monitoring system according to claim 3, characterized in that: During the design process of the line voltage sensor, it is necessary to perform an equivalent estimation of the stray capacitance C1 based on the capacitance equivalent calculation of the arrester connection line; The equivalent calculation process of the capacitance of the arrester connection line is as follows: Step 1, the transmission line with radius r and length L is equivalent to a long strip with width 2r and length L; Step 2, let the length of the induction plate be a and the width be b; Step 3: According to dielectric theory, the capacitance of two plates with area S and distance h is calculated as: C=εS / h Where ε is the dielectric constant; Step 4: The equivalent estimation process of stray capacitance C1 is as follows: The coordinate axis is established with the center of the sensing plate, and the stray capacitance C1 is equivalent to the integration of multiple differential plate capacitors in series. The stray capacitance C1 is derived and the expression is as follows: In the formula, ε is the dielectric constant; r and L are the radius and length of the transmission line respectively; a and b are the length and width of the induction plate respectively; h is the distance from the induction plate to the arrester connection line; z is the integral variable, which is a small length along the z axis, varying in the range of 0 to h; Step 5: Based on the stray capacitance C1, the size of the sensing plate, the distance h from the sensing plate to the arrester connection line, and the sampling capacitor C2 are designed.

5. The line arrester resistive current self-powered monitoring system according to claim 3, characterized in that: During the design process of the line voltage sensor, the induced charge and voltage analysis needs to be performed, and the analysis process is as follows: Step I, Charge and Electric Field: When there is no corona discharge in the arrester connection line, the charge is basically bound inside the conductor, and there is no space charge to cause induced voltage; when corona discharge occurs, the space charge will generate induced voltage on the induction plate; Step II, electrostatic field mirroring: Using the mirror principle, assuming that the charge per unit length of the line is Q, and the distance from the line to the induction plate is h, the surface density of the induced charge on the induction plate is expressed as: In the formula, is the potential at any point on the z-axis; ε represents the dielectric constant; z is the length of a small segment along the z-axis, which varies in the range of 0 to the distance h from the induction plate to the arrester connection line; The surface density of the induced charge on the induction plate is obtained as s , the calculation formula is as follows: Ignoring the electrostatic induction of the circuit further away, the amount of induced charge on the surface of the plate is q, and the calculation formula is as follows: In the formula, S is the area of ​​the sensing plate; θ is the central angle of the arc of the sensing plate; a is the length of the sensing plate; Step III, Current and Induced Voltage: As the power frequency AC voltage changes, the amount of charge Q on the line changes, and the corresponding amount of induced charge q changes; By defining the current I = dq / dt, a current is generated, and an induced voltage is formed on the conditioning circuit connected to the induction plate, based on which the influence of the charge induced voltage on the divided voltage is analyzed; Where I is the current intensity, dq is the tiny amount of charge, and dt is the tiny time increment.

6. The line arrester resistive current self-powered monitoring system according to claim 1, characterized in that: Under mA-level current, the nonlinear ZnO varistor R1 has a very large resistance value, close to being open-circuited, and the leakage current mainly flows to the current sensing circuit and the energy extraction circuit; when the lightning current passes through the arrester, the ZnO varistor R1 has a very small resistance value, close to being short-circuited, discharging the lightning current and protecting the current sensing circuit and the energy extraction circuit.

7. The line arrester resistive current self-powered monitoring system according to claim 1, characterized in that: The current sensing circuit is connected in series with an induction coil L1 after the ZnO varistor R1 and before the rectifier circuit B; the induction coil L1 has a magnetic core to enhance the magnetic field; the number of turns n1 of the primary side coil of the induction coil L1 is higher than the number of turns n2 of the secondary side coil; According to the relationship between the primary and secondary coil currents, I1n1=I2n2, the current is inversely proportional to the number of turns, that is, the secondary current I2 increases by n1 / n2 times relative to the mA-level I1; at the same time, since the primary current I1 is small, the number of turns n1 takes a larger value; Take the precision sampling resistor R2, on which the full current and voltage signals are measured by the acquisition unit; The induction coil L1 can electrically isolate the current sensing circuit, the energy extraction circuit and the grounding loop of the lightning arrester.

8. The line arrester resistive current self-powered monitoring system according to claim 1, characterized in that: The arrester leakage current I1 is rectified by the rectifier bridge B to charge the capacitor C1. The rectifier bridge B is constructed with a withstand voltage Schottky diode with a small conduction voltage drop. Inductor L limits current mutation; A unidirectional transient voltage suppression diode TVS is connected in parallel before capacitor C1 to limit the voltage difference across capacitor C1 so that it does not exceed the upper limit of the DC / DC module input voltage.

9. The line arrester resistive current self-powered monitoring system according to claim 1, characterized in that: The core of the acquisition unit adopts a low-power acquisition device and is equipped with a non-volatile memory.

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