Transformer substation mutual inductor external insulation current monitoring method based on TMR sensor

Abstract

According to the transformer substation mutual inductor external insulation current monitoring method based on the TMR sensor, a special transformer substation mutual inductor external insulation current monitoring system based on the TMR sensor is used, and the system comprises the TMR sensor, a signal conditioning unit and a control unit. The transformer substation mutual inductor external insulation current monitoring method based on the TMR sensor comprises the following steps: detecting leakage current; noise interference elimination; preprocessing the leakage current signal; analyzing and processing to obtain current monitoring data; and comparing threshold values, judging and sending out an alarm signal. The capacitive equipment leakage current monitoring system can realize high-precision monitoring of the capacitive equipment leakage current, is high in safety and reliability, few in fault and loss, easy to install and maintain, and has relatively high practical value and application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of online monitoring of capacitive equipment in a transformer substation, and in particular to a method for monitoring external insulation current of a transformer in a transformer substation based on a TMR sensor. Background Art

[0002] According to operating experience and statistical data, pollution flashover tripping has always been one of the problems that affect the safe operation of power systems. Affected by factors such as the degree of atmospheric pollution and geographical location (such as coastal areas or chemical parks), the pollution layer deposited on the surface of the insulator is damp, which often causes pollution flashover accidents in substations. After a pollution flashover accident occurs, it often causes the operation of the relay protection device, causing the equipment to trip. Once a pollution flashover accident occurs, it will affect a large area and last for a long time. In severe cases, it may even cause power personal safety accidents. The economic losses and social impacts caused by this are enormous.

[0003] At present, the live detection methods of insulators of power transmission and transformation equipment are divided into two categories, including electrical quantity detection method and non-electrical quantity detection method. Among them, the electrical quantity detection method includes surface leakage current method, insulation resistance method, electric field measurement method and pulse current method, and the non-electrical quantity detection method includes observation method, infrared temperature measurement method, laser Doppler vibration method, etc. Among them, the electric field measurement method is relatively mature.

[0004] People are eager to obtain a substation transformer external insulation current monitoring device based on a TMR sensor with excellent technical effects. Summary of the invention

[0005] The present invention provides a method for monitoring the external insulation current of transformers in substations based on TMR sensors. Aiming at the impact of pollution on the operation safety of substation equipment and the shortcomings of traditional detection methods, research on the detection technology of external insulation pollution current of electrical equipment in substations is carried out based on advanced non-contact measurement technology. Combined with wireless communication technology, live detection and analysis of pollution current and discharge pulse parameters of multiple electrical equipment are carried out at the same time, which can realize active early warning of potential operation risks, greatly improve detection efficiency, effectively prevent the occurrence of pollution flashover accidents, and improve the reliability of system power supply.

[0006] The present invention utilizes the high sensitivity, linearity and resolution of the TMR sensor to realize effective monitoring of the leakage current of high-voltage capacitive equipment in the substation; the weak magnetic field generated by the leakage current of the capacitive equipment is sensed by the TMR sensor, which is converted into an electrical signal, and after signal conditioning and preprocessing, a signal reflecting the current size is finally output.

[0007] The technical solution of the present invention is:

[0008] The technical key of the substation transformer external insulation current monitoring method based on TMR sensor is:

[0009] The substation transformer external insulation current monitoring method based on the TMR sensor uses a special substation transformer external insulation current monitoring system based on the TMR sensor, which includes: a TMR sensor, a signal conditioning unit, and a control unit; wherein: the TMR sensor is connected to the control unit through the signal conditioning unit; the control unit includes a control chip and a data acquisition module;

[0010] The TMR sensor is responsible for sensing the magnetic field and converting it into an electrical signal. The signal conditioning unit pre-processes the electrical signal, and the control unit compensates based on the pre-processed signal and the operating temperature measured by the temperature sensor to ensure the accuracy of the measurement result.

[0011] The substation transformer external insulation current monitoring system based on TMR sensor is a complex and sophisticated electronic system. The various components cooperate with each other to realize the data collection, processing, transmission and reception functions. The wireless communication system design mainly includes the following core parts: microcontroller MCU, analog front end IA, two wireless transceivers nRF24L01 and power module; these components together constitute an efficient and stable wireless communication system; among them:

[0012] (a) Power module: The power module of the system provides a stable 5V DC power supply for the entire system. The power module uses a high-efficiency switching power supply or linear power supply to ensure the stability and reliability of the system. At the same time, the system is also equipped with a microUSB interface for users to facilitate charging and data transmission.

[0013] (b) Data acquisition module, data processing module: The control unit and the control unit together constitute the data acquisition module and the data processing module;

[0014] In the data acquisition module, a 16-bit timer and ADC12 are used; the 16-bit timer has a high-precision timing function and can be used in various application scenarios that require precise timing; and ADC12 is a 12-bit analog-to-digital converter that can convert analog signals into digital signals for use in the subsequent digital signal processing part; the data processing module consists of a signal conditioning unit and a control chip in the controller; the signal conditioning unit is the current sensing amplifier INA, and the control chip in the controller is the msp430f149 chip; INA is used to amplify the weak signal generated by the TMR sensor array to a level that can be processed by subsequent circuits; and the msp430f149 is a low-power microcontroller used to further condition and process the amplified signal, including filtering, amplification, digitization and other operations;

[0015] (c) The specific composition of TMR sensors is the TMR sensor array: the TMR sensor array is one of the key components of the system; the TMR sensor has the advantages of high precision, high sensitivity, and low power consumption, and can accurately detect various environmental parameters; in this system, the TMR sensor array is used to detect environmental changes, including temperature, humidity, pressure and other parameters; changes in temperature, humidity, pressure and other parameters will cause changes in the output signal of the TMR sensor array, which will then be collected and processed by the system;

[0016] (d) Wireless transceiver and signal transmission module: The wireless transceiver part of the system uses two nRF24L01 wireless transceivers; nRF24L01 is a low-power, high-performance 2.4GHz wireless transceiver chip with the advantages of low cost, low power consumption, and high speed. In this system, one nRF24L01 is configured as a transmitter to send processed data; the other is configured as a receiver to receive data from other devices; at the same time, in order to enhance the transmission distance and stability of the signal, the nRF24L01 at the transmitter is also equipped with a power amplifier PA and a low noise amplifier LNA;

[0017] (e) Host computer connection and data receiving unit: Finally, the whole system is connected to the host computer; the host computer is one of the following: PC, smart phone, or other smart device, used to receive and process data from the wireless communication system;

[0018] Through the host computer, users can view and analyze the changes of various environmental parameters in real time, so as to make corresponding decisions and actions;

[0019] The substation transformer external insulation current monitoring method based on the TMR sensor comprises the following steps in sequence:

[0020] Step 1: Use a TMR sensor to detect the leakage current of the capacitive equipment in the substation; wherein the TMR sensor has the advantages of high sensitivity, good linearity, high resolution and wide measurement range, and can effectively reflect the insulation performance of electrical equipment; the high sensitivity, linearity and resolution of the TMR sensor are used to effectively monitor the leakage current of the high-voltage capacitive equipment in the substation;

[0021] The TMR sensor consists of two magnetic layers and a non-magnetic tunnel isolation layer; the two magnetic layers are the fixed layer and the free layer; the magnetization direction of the fixed layer is fixed, while the magnetization direction of the free layer can change with the external magnetic field; the non-magnetic tunnel isolation layer is very thin, allowing electrons to pass through under the quantum tunneling effect; when the external magnetic field changes, the magnetization direction of the free layer changes accordingly, which in turn affects the electron tunneling probability and the sensor resistance, thereby achieving accurate measurement of magnetic field changes;

[0022] TMR sensor (tunneling magnetoresistance current sensor) is a sensor that responds to current changes according to changes in the magnetic field. Compared with Hall sensors, it has lower power consumption, higher sensitivity, better linearity, and a wider measurement range. The basic principle of TMR is to use the tunnel magnetoresistance effect of magnetic multilayer film materials to sense the magnetic field generated by the conductor to be measured. TMR is also called MTJ (magnetic tunnel junction). This sensor has higher accuracy, higher sensitivity, and better temperature stability than Hall sensors. It can also be used without adding a magnetic ring. Compared with AMR sensors, TMR does not require coil settings, and the steps for use are simple. Compared with GMR sensors, TMR's actual performance is more comprehensive, with higher sensitivity, lower power consumption, and better linearity.

[0023] like Figure 2 , Figure 3 It is the equivalent circuit diagram of Wheatstone bridge and the working principle diagram of TMR sensor. Figure 2 As shown, the circuit schematic diagram shows that the following requirements are met:

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] When there is an appropriate external magnetic field, the V CA Proportional to the change of the external magnetic field, the voltage output of the tunnel magnetoresistance sensor is proportional to the external magnetic field; that is, the working principle is: under the action of a magnetic field within a certain range, the resistance of the tunnel magnetoresistance material will change accordingly with the change of the magnetic field. By effectively testing the magnetic field near the current-carrying conductor, the current value can be calculated using the conditioning circuit;

[0030] The internal working principle of TMR sensor is as follows: Figure 3As shown, the TMR sensor works by using the TMR effect, which is a phenomenon related to the spin polarization transport process. The TMR sensor consists of a non-magnetic tunnel isolation layer sandwiched between two magnetic layers, namely the fixed layer and the free layer; the magnetization direction of the fixed layer is fixed during the manufacturing process and will not change with the external magnetic field, while the magnetization direction of the free layer is relatively flexible and can change with the external magnetic field; when there is no magnetic field, the current will pass through the two magnetic layers evenly; when there is a magnetic field, the spin-orbit coupling phenomenon in the non-magnetic tunnel isolation layer occurs, causing the current to tend to pass through the magnetic layer in the same direction as the magnetic field;

[0031] The tunneling probability of electrons from one magnetic layer to another is related to the magnetization directions of the two magnetic layers. If the magnetization directions of the two layers are parallel to each other, then in one magnetic layer, the electrons of the majority spin subband will enter the empty state of the majority spin subband in the other magnetic layer, and the electrons of the minority spin subband will also enter the empty state of the minority spin subband in the other magnetic layer, and the total tunneling current is large. If the magnetization directions of the two magnetic layers are antiparallel, the situation is just the opposite, that is, in one magnetic layer, the electrons of the majority spin subband will enter the empty state of the minority spin subband in the other magnetic layer, and the electrons of the minority spin subband will also enter the empty state of the majority spin subband in the other magnetic layer, and the tunneling current in this state is relatively small. Therefore, the tunneling conductance changes with the change of the magnetization directions of the two ferromagnetic layers, and the conductance when the magnetization vectors are parallel is higher than the conductance when they are antiparallel. The magnetization directions of the two ferromagnetic layers can be changed by applying an external magnetic field, so that the tunneling resistance changes, resulting in the appearance of the TMR effect. Figure 3 As shown, the TMR sensor uses the TMR2905BP sensor, which is powered by 5Vdc. The sensor outputs a 0-50uA current signal, which is converted to a 0-0.5Vdc DC voltage by R1 and R6. The high-frequency filter circuit composed of R2, R4 and C10 is used to filter out the interference signal in the field space; then it enters the amplification through the differential circuit, which consists of two stages of AD628. After amplification, it becomes a 0-5V voltage signal and enters the controller from the SIGAMP end;

[0032] Step 2: To solve the problem that leakage current is interfered by many noises, a Gaussian filter elimination algorithm is used to eliminate the problem. According to the Gaussian filter formula: Among them, Q k+1 (x) is the output value of the original load signal after the k+1th iteration; Q k (a+x) is the input value of the original load signal after the k+1th iteration; is the sum of the weighted coefficients of the filter at the kth iteration; b k(a+x) is the weighting coefficient at the kth iteration point a+x; the initial iteration number k is set to 0, and the number of iterations is set; the collected initial current and voltage data are brought into the formula and iterated to the set number of iterations, and the iteration result is output, which is the filtered value;

[0033] Since the data will be interfered by a lot of noises in the process of measuring data, the size and frequency of these noises will affect the accuracy of the measured data; in order to obtain more accurate measurement data, the data needs to be denoised, and filtering is also called denoising. The filter in the system often cannot remove all the noise, and the filtering function is needed to strengthen the filtering; white noise is a common noise in the power field. Since the power spectrum density width in practice is limited and its average power cannot be estimated, there is no white noise that strictly obeys uniform distribution in practice. Gaussian white noise is ubiquitous, and its one-dimensional probability density is also easy to calculate. Removing these noises is conducive to extracting load characteristics. Convolving the Gaussian function with the original signal is the key to the Gaussian algorithm. Compared with the traditional algorithm, the Gaussian algorithm has the advantages of filtering window and phase shift. It not only retains the mutation signal, does not weaken and eliminate the mutation signal, but also can smooth the mutation data.

[0034] Step 3, preprocessing the leakage current signal detected by the TMR sensor, including signal amplification, filtering and analog-to-digital conversion, for subsequent data processing and analysis;

[0035] Step 4, transmitting the preprocessed signal to a data processing unit for further analysis and processing to obtain current monitoring data of the capacitive device;

[0036] Step 5: compare the current monitoring data with a preset threshold value. If the threshold value is exceeded, an alarm signal is issued to prompt the operation and maintenance personnel to perform inspection and maintenance.

[0037] The method for monitoring the external insulation current of a transformer in a substation based on a TMR sensor of the present invention preferably claims the following technical contents:

[0038] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: In the substation transformer external insulation current monitoring system based on the TMR sensor, the power module is also equipped with a microUSB interface to facilitate users to charge and transmit data;

[0039] In the wireless transceiver and signal transmission module, the wireless transceiver part of the system uses two nRF24L01 wireless transceivers; nRF24L01 is a low-power, high-performance 2.4GHz wireless transceiver chip with the advantages of low cost, low power consumption, and high speed. In this system, one nRF24L01 is configured as a transmitter to send processed data; the other is configured as a receiver to receive data from other devices;

[0040] In the wireless transceiver and signal transmission module, in order to enhance the transmission distance and stability of the signal, the nRF24L01 at the transmitting end is also equipped with a power amplifier PA and a low noise amplifier LNA.

[0041] In step 1 of the substation transformer external insulation current monitoring method based on TMR sensor, the TMR sensor selects TMR2905BP sensor, which is powered by 5Vdc. The sensor outputs 0-50uA current signal, which is converted into 0-0.5Vdc DC voltage by R1 and R6. The high-frequency filter circuit composed of R2, R4 and C10 is used to filter out the interference signal in the field space; then it enters the amplification through the differential circuit, and the amplification consists of two stages of AD628. After amplification, it becomes a 0-5V voltage signal and enters the controller from the SIGAMP end.

[0042] In step 2 of the substation transformer external insulation current monitoring method based on the TMR sensor, the specific requirements for eliminating the current using the Gaussian filter elimination algorithm are:

[0043] According to the Gaussian filter formula: Among them, Q k+1 (x) is the output value of the original load signal after the k+1th iteration; Q k (a+x) is the input value of the original load signal after the k+1th iteration;

[0044] is the sum of the weighted coefficients of the filter at the kth iteration; b k (a+x) is the weighting coefficient at the k-th iteration point a+x; set the initial iteration number k to 0, and set the number of iterations; bring the collected initial current and voltage data into the formula and iterate to the set number of iterations, and output the iterative result, which is the filtered value.

[0045] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements:

[0046] First, during the monitoring process, the working status of the TMR sensor is monitored in real time to ensure its normal operation;

[0047] Second, the TMR sensor should be calibrated and maintained regularly to ensure its measurement accuracy and stability.

[0048] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements:

[0049] The TMR sensor has a closed-loop structure and adopts a closed-loop negative feedback mechanism to improve the measurement accuracy and anti-interference ability of the sensor.

[0050] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: a PC terminal is established to visualize the current monitoring data, alarm signals and other information so that the operation and maintenance personnel can intuitively understand the current status of the capacitive equipment.

[0051] The invention has the advantages of being able to achieve high-precision monitoring of leakage current of capacitive equipment, improving the safety and reliability of substation equipment, and reducing failures and losses caused by reduced insulation performance of equipment. At the same time, the device has a simple structure, is easy to install and maintain, and has high practical value and application prospects.

[0052] The present invention relates to a substation transformer external insulation current monitoring device based on a tunnel magnetoresistance TMR sensor. The method adopts a TMR sensor, and utilizes its high sensitivity and high precision characteristics to directly monitor the leakage current of high-voltage capacitive equipment in the substation. By accurately capturing the weak magnetic field changes generated by the current, the TMR sensor converts the magnetic field signal into an electrical signal, thereby realizing real-time monitoring of the current. The method not only simplifies the complexity of current monitoring, but also significantly improves the accuracy and real-time performance of monitoring, which helps to timely discover and deal with potential faults of substation capacitive equipment and improve the safety and stability of the power system. In addition, the method has the advantages of simple operation, fast response speed, and wide monitoring range. It provides an efficient and reliable measurement device for monitoring the external insulation contamination current of substation capacitive equipment, which is of great significance to ensuring the stable operation of the power system and has broad application prospects and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the structure of the TMR sensor of the present invention;

[0054] Figure 2 It is the pollution current detection bridge and its equivalent circuit diagram;

[0055] Figure 3 This is the schematic diagram of the TMR sensor;

[0056] Figure 4 Schematic diagram for measuring the external insulation current of the transformer;

[0057] Figure 5This is the circuit block diagram of the measurement system. DETAILED DESCRIPTION

[0058] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings, but is not limited thereto.

[0059] Example 1

[0060] Introduction to the capacitive equipment to be tested: Substation transformers such as Figure 4 Other commonly used capacitive devices in substations include capacitors and reactors, which play an important role in power systems. During the operation of substations, capacitive devices will generate dirty currents. The main reason for the generation of dirty currents in capacitive devices is the accumulation of dirt on the surface of the equipment. These dirt may come from dust, particulate matter, chemicals in the atmosphere, etc., which are deposited on the surface of the equipment and gradually form a layer of dirt. When encountering humid weather, the electrolytes in the dirt layer will dissolve and ionize, resulting in an increase in the conductivity of the dirt layer. At this time, if the equipment is in a charged state, the voltage will pass through the dirt layer to form a leakage current, that is, the dirty current. In addition, environmental factors such as humidity and temperature changes, as well as electrical stress factors such as overvoltage, voltage fluctuations, and frequency changes, may all cause leakage currents in capacitive devices.

[0061] Leakage current refers to the tiny induced current generated around the insulating material under the action of the electric field force. In the capacitive equipment of the substation, the leakage current mainly exists in the insulation layer of the components or conductors such as coil windings, capacitors, cables, etc. where current flows. Although the insulation layer is not conductive, there is almost no material that is absolutely non-conductive. Therefore, when a voltage is applied to both ends of the insulating material, a certain current will flow through, which is the source of the leakage current. When the leakage current is too large, it may cause flashover in the insulating material. Flashover refers to the discharge phenomenon in the local area of ​​the insulating material under the action of the electric field, forming a conductive channel, resulting in the degradation or failure of the insulation performance. The occurrence of flashover may cause equipment failure and even cause serious consequences such as fire. As shown in the figure, the capacitive device outputs the change of the magnetic field through the dirty current, and the TMR sensor is a magnetic sensor based on the tunnel effect of magnetic materials. It is very sensitive to the change of the magnetic field, can sense the magnetic field generated by the external insulation current, and convert the change of the magnetic field of the capacitive device (mutual inductor) into an electrical signal output.

[0062] This embodiment provides a method for monitoring the external insulation current of transformers in substations based on TMR sensors. In view of the impact of pollution on the operation safety of substation equipment and the shortcomings of traditional detection methods, research on the detection technology of external insulation pollution current of electrical equipment in substations is carried out based on advanced non-contact measurement technology. Combined with wireless communication technology, live detection and analysis of parameters such as pollution current and discharge pulses of multiple electrical equipment are carried out at the same time, which can realize active early warning of potential operation risks, greatly improve detection efficiency, effectively prevent the occurrence of pollution flash accidents, and improve the reliability of system power supply.

[0063] This embodiment utilizes the high sensitivity, linearity and resolution of the TMR sensor to achieve effective monitoring of the leakage current of high-voltage capacitive equipment in the substation; the TMR sensor senses the weak magnetic field generated by the leakage current of the capacitive equipment, converts it into an electrical signal, and finally outputs a signal reflecting the current size after signal conditioning and preprocessing.

[0064] This embodiment specifically relates to a method for monitoring the external insulation current of a transformer in a substation based on a TMR sensor, the technical key of which is:

[0065] The substation transformer external insulation current monitoring method based on the TMR sensor uses a special substation transformer external insulation current monitoring system based on the TMR sensor, which includes: a TMR sensor, a signal conditioning unit, and a control unit; wherein: the TMR sensor is connected to the control unit through the signal conditioning unit; the control unit includes a control chip and a data acquisition module;

[0066] The TMR sensor is responsible for sensing the magnetic field and converting it into an electrical signal. The signal conditioning unit pre-processes the electrical signal, and the control unit compensates based on the pre-processed signal and the operating temperature measured by the temperature sensor to ensure the accuracy of the measurement result.

[0067] The schematic diagram of the principle of the transformer external insulation current monitoring system based on the TMR sensor is as follows: Figure 5 As shown, from Figure 5 As can be seen in the figure, the system is a complex and sophisticated electronic system. The various components cooperate with each other to realize the functions of data collection, processing, transmission and reception. The wireless communication system design mainly includes the following core parts: microcontroller MCU, analog front end IA, two wireless transceivers nRF24L01 and power module; these components together constitute an efficient and stable wireless communication system; among them:

[0068] First, the power module: The power module of the system provides a stable 5V DC power supply for the entire system; the power module uses a high-efficiency switching power supply or linear power supply to ensure the stability and reliability of the system; at the same time, the system is also equipped with a microUSB interface for users to charge and transmit data;

[0069] Second, data acquisition module and data processing module: the control unit and the control unit together constitute the data acquisition module and the data processing module;

[0070] In the data acquisition module, a 16-bit timer and ADC12 are used; the 16-bit timer has a high-precision timing function and can be used in various application scenarios that require precise timing; and ADC12 is a 12-bit analog-to-digital converter that can convert analog signals into digital signals for use in the subsequent digital signal processing part; the data processing module consists of a signal conditioning unit and a control chip in the controller; the signal conditioning unit is the current sensing amplifier INA, and the control chip in the controller is the msp430f149 chip; INA is used to amplify the weak signal generated by the TMR sensor array to a level that can be processed by subsequent circuits; and the msp430f149 is a low-power microcontroller used to further condition and process the amplified signal, including filtering, amplification, digitization and other operations;

[0071] Third, the TMR sensor specifically constitutes the TMR sensor array: the TMR sensor array is one of the key components of the system; the TMR sensor has the advantages of high precision, high sensitivity, low power consumption, etc., and can realize the accurate detection of various environmental parameters; in this system, the TMR sensor array is used to detect environmental changes, including: temperature, humidity, pressure and other parameters; changes in temperature, humidity, pressure and other parameters will cause changes in the output signal of the TMR sensor array, which will then be collected and processed by the system;

[0072] Fourth, wireless transceiver and signal transmission module: The wireless transceiver part of the system uses two nRF24L01 wireless transceivers; nRF24L01 is a low-power, high-performance 2.4GHz wireless transceiver chip with the advantages of low cost, low power consumption, and high speed. In this system, one nRF24L01 is configured as a transmitter to send processed data; the other is configured as a receiver to receive data from other devices; at the same time, in order to enhance the transmission distance and stability of the signal, the nRF24L01 at the transmitter is also equipped with a power amplifier PA and a low noise amplifier LNA;

[0073] Fifth, host computer connection and data receiving unit: Finally, the whole system is connected to the host computer; the host computer is one of the following: PC, smart phone, or other smart device, used to receive and process data from the wireless communication system;

[0074] Through the host computer, users can view and analyze the changes of various environmental parameters in real time, so as to make corresponding decisions and actions;

[0075] The substation transformer external insulation current monitoring method based on the TMR sensor comprises the following steps in sequence:

[0076] Step 1: Use a TMR sensor to detect the leakage current of the capacitive equipment in the substation; wherein the TMR sensor has the advantages of high sensitivity, good linearity, high resolution and wide measurement range, and can effectively reflect the insulation performance of electrical equipment; the high sensitivity, linearity and resolution of the TMR sensor are used to effectively monitor the leakage current of the high-voltage capacitive equipment in the substation;

[0077] The structure of TMR sensor is shown in the figure Figure 1 , Figure 1 It consists of two magnetic layers and a non-magnetic tunnel isolation layer; the two magnetic layers are the fixed layer and the free layer; the magnetization direction of the fixed layer is fixed, while the magnetization direction of the free layer can change with the external magnetic field; the non-magnetic tunnel isolation layer is very thin, allowing electrons to pass through under the quantum tunneling effect; when the external magnetic field changes, the magnetization direction of the free layer changes accordingly, which in turn affects the electron tunneling probability and the sensor resistance, thereby achieving accurate measurement of magnetic field changes;

[0078] TMR sensor (tunneling magnetoresistance current sensor) is a sensor that responds to current changes according to changes in the magnetic field. Compared with Hall sensors, it has lower power consumption, higher sensitivity, better linearity, and a wider measurement range. The basic principle of TMR is to use the tunnel magnetoresistance effect of magnetic multilayer film materials to sense the magnetic field generated by the conductor to be measured. TMR is also called MTJ (magnetic tunnel junction). This sensor has higher accuracy, higher sensitivity, and better temperature stability than Hall sensors. It can also be used without adding a magnetic ring. Compared with AMR sensors, TMR does not require coil settings, and the steps for use are simple. Compared with GMR sensors, TMR's actual performance is more comprehensive, with higher sensitivity, lower power consumption, and better linearity.

[0079] like Figure 2 , Figure 3 It is the equivalent circuit diagram of Wheatstone bridge and the working principle diagram of TMR sensor. Figure 2 As shown, the circuit schematic diagram shows that the following requirements are met:

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] When there is an appropriate external magnetic field, the V CA Proportional to the change of the external magnetic field, the voltage output of the tunnel magnetoresistance sensor is proportional to the external magnetic field; that is, the working principle is: under the action of a magnetic field within a certain range, the resistance of the tunnel magnetoresistance material will change accordingly with the change of the magnetic field. By effectively testing the magnetic field near the current-carrying conductor, the current value can be calculated using the conditioning circuit;

[0086] The internal working principle of TMR sensor is as follows: Figure 3 As shown, the TMR sensor works by using the TMR effect, which is a phenomenon related to the spin polarization transport process. The TMR sensor consists of a non-magnetic tunnel isolation layer sandwiched between two magnetic layers, namely the fixed layer and the free layer; the magnetization direction of the fixed layer is fixed during the manufacturing process and will not change with the external magnetic field, while the magnetization direction of the free layer is relatively flexible and can change with the external magnetic field; when there is no magnetic field, the current will pass through the two magnetic layers evenly; when there is a magnetic field, the spin-orbit coupling phenomenon in the non-magnetic tunnel isolation layer occurs, causing the current to tend to pass through the magnetic layer in the same direction as the magnetic field;

[0087] The tunneling probability of electrons from one magnetic layer to another is related to the magnetization directions of the two magnetic layers. If the magnetization directions of the two layers are parallel to each other, then in one magnetic layer, the electrons of the majority spin subband will enter the empty state of the majority spin subband in the other magnetic layer, and the electrons of the minority spin subband will also enter the empty state of the minority spin subband in the other magnetic layer, and the total tunneling current is large. If the magnetization directions of the two magnetic layers are antiparallel, the situation is just the opposite, that is, in one magnetic layer, the electrons of the majority spin subband will enter the empty state of the minority spin subband in the other magnetic layer, and the electrons of the minority spin subband will also enter the empty state of the majority spin subband in the other magnetic layer, and the tunneling current in this state is relatively small. Therefore, the tunneling conductance changes with the change of the magnetization directions of the two ferromagnetic layers, and the conductance when the magnetization vectors are parallel is higher than the conductance when they are antiparallel. The magnetization directions of the two ferromagnetic layers can be changed by applying an external magnetic field, so that the tunneling resistance changes, resulting in the appearance of the TMR effect. Figure 3As shown, the TMR sensor uses the TMR2905BP sensor, which is powered by 5Vdc. The sensor outputs a 0-50uA current signal, which is converted to a 0-0.5Vdc DC voltage by R1 and R6. The high-frequency filter circuit composed of R2, R4 and C10 is used to filter out the interference signal in the field space; then it enters the amplification through the differential circuit, which consists of two stages of AD628. After amplification, it becomes a 0-5V voltage signal and enters the controller from the SIGAMP end;

[0088] Step 2: To solve the problem that leakage current is interfered by many noises, a Gaussian filter elimination algorithm is used to eliminate the problem. According to the Gaussian filter formula: Among them, Q k+1 (x) is the output value of the original load signal after the k+1th iteration; Q k (a+x) is the input value of the original load signal after the k+1th iteration; is the sum of the weighted coefficients of the filter at the kth iteration; b k (a+x) is the weighting coefficient at the kth iteration point a+x; the initial iteration number k is set to 0, and the number of iterations is set; the collected initial current and voltage data are brought into the formula and iterated to the set number of iterations, and the iteration result is output, which is the filtered value;

[0089] Since the data will be interfered by a lot of noises in the process of measuring data, the size and frequency of these noises will affect the accuracy of the measured data; in order to obtain more accurate measurement data, the data needs to be denoised, and filtering is also called denoising. The filter in the system often cannot remove all the noise, and the filtering function is needed to strengthen the filtering; white noise is a common noise in the power field. Since the power spectrum density width in practice is limited and its average power cannot be estimated, there is no white noise that strictly obeys uniform distribution in practice. Gaussian white noise is ubiquitous, and its one-dimensional probability density is also easy to calculate. Removing these noises is conducive to extracting load characteristics. Convolving the Gaussian function with the original signal is the key to the Gaussian algorithm. Compared with the traditional algorithm, the Gaussian algorithm has the advantages of filtering window and phase shift. It not only retains the mutation signal, does not weaken and eliminate the mutation signal, but also can smooth the mutation data.

[0090] Step 3, preprocessing the leakage current signal detected by the TMR sensor, including signal amplification, filtering and analog-to-digital conversion, for subsequent data processing and analysis;

[0091] Step 4, transmitting the preprocessed signal to a data processing unit for further analysis and processing to obtain current monitoring data of the capacitive device;

[0092] Step 5: compare the current monitoring data with a preset threshold value. If the threshold value is exceeded, an alarm signal is issued to prompt the operation and maintenance personnel to perform inspection and maintenance.

[0093] The substation transformer external insulation current monitoring method based on TMR sensor also meets the following requirements: first, during the monitoring process, the working status of the TMR sensor is monitored in real time to ensure its normal operation; second, the TMR sensor is regularly calibrated and maintained to ensure its measurement accuracy and stability.

[0094] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: the TMR sensor is a closed-loop structure, and adopts a closed-loop negative feedback mechanism to improve the measurement accuracy and anti-interference ability of the sensor.

[0095] The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: a PC terminal is established to visualize the current monitoring data, alarm signals and other information so that the operation and maintenance personnel can intuitively understand the current status of the capacitive equipment.

[0096] The advantages of this embodiment are that it can realize high-precision monitoring of the leakage current of capacitive equipment, improve the safety and reliability of substation equipment, and reduce failures and losses caused by the degradation of equipment insulation performance. At the same time, the device has a simple structure, is easy to install and maintain, and has high practical value and application prospects.

[0097] This embodiment focuses on a substation transformer external insulation current monitoring device based on a tunnel magnetoresistance TMR sensor. The method uses a TMR sensor, and utilizes its high sensitivity and high precision characteristics to directly monitor the leakage current of high-voltage capacitive equipment in the substation. By accurately capturing the weak magnetic field changes generated by the current, the TMR sensor converts the magnetic field signal into an electrical signal, thereby realizing real-time monitoring of the current. This method not only simplifies the complexity of current monitoring, but also significantly improves the accuracy and real-time performance of monitoring, which helps to timely discover and deal with potential faults of substation capacitive equipment and improve the safety and stability of the power system. In addition, the method has the advantages of simple operation, fast response speed, and wide monitoring range. It provides an efficient and reliable measurement device for monitoring the external insulation pollution current of substation capacitive equipment, which is of great significance to ensuring the stable operation of the power system. It has broad application prospects and practical value.

Claims

1. A method for monitoring external insulation current of transformer in substation based on TMR sensor, characterized in that: The substation transformer external insulation current monitoring method based on the TMR sensor uses a special substation transformer external insulation current monitoring system based on the TMR sensor, which includes: a TMR sensor, a signal conditioning unit, and a control unit; wherein: the TMR sensor is connected to the control unit through the signal conditioning unit; the control unit includes a control chip and a data acquisition module; The TMR sensor is responsible for sensing the magnetic field and converting it into an electrical signal. The signal conditioning unit pre-processes the electrical signal, and the control unit compensates based on the pre-processed signal and the operating temperature measured by the temperature sensor to ensure the accuracy of the measurement result. The substation transformer external insulation current monitoring system based on TMR sensor realizes the functions of data collection, processing, transmission and reception; the wireless communication system design mainly includes the following core parts: microcontroller MCU, analog front end IA, two wireless transceivers nRF24L01 and power module; these components together constitute an efficient and stable wireless communication system; among them: First, power module: The system's power module provides a stable 5V DC power supply for the entire system; Second, data acquisition module and data processing module: the control unit and the control unit together constitute the data acquisition module and the data processing module; In the data acquisition module, a 16-bit timer and ADC12 are used; the data processing module is composed of a signal conditioning unit and a control chip in the controller; the signal conditioning unit is a current sensing amplifier INA, and the control chip in the controller is an msp430f149 chip; Third, the TMR sensor specifically constitutes a TMR sensor array: the TMR sensor array is used to detect environmental changes, including temperature, humidity, and pressure; changes in these parameters will cause changes in the output signal of the TMR sensor array, which will then be collected and processed by the system; Fourth, wireless transceiver and signal transmission module: used to send processed data; also receive data from other devices; Fifth, host computer connection and data receiving unit: Finally, the whole system is connected to the host computer; the host computer is one of the following: PC, smart phone, used to receive and process data from the wireless communication system; Through the host computer, users can view and analyze the changes of various environmental parameters in real time, so as to make corresponding decisions and actions; The substation transformer external insulation current monitoring method based on the TMR sensor comprises the following steps in sequence: Step 1: Use the TMR sensor to detect the leakage current of the capacitive equipment in the substation; use the high sensitivity, linearity and resolution of the TMR sensor to effectively monitor the leakage current of the high-voltage capacitive equipment in the substation; The TMR sensor consists of two magnetic layers and a non-magnetic tunnel isolation layer; the two magnetic layers are the fixed layer and the free layer; the magnetization direction of the fixed layer is fixed, while the magnetization direction of the free layer can change with the external magnetic field; the non-magnetic tunnel isolation layer is very thin, allowing electrons to pass through under the quantum tunneling effect; when the external magnetic field changes, the magnetization direction of the free layer changes accordingly, which in turn affects the electron tunneling probability and the sensor resistance, thereby achieving accurate measurement of magnetic field changes; The Wheatstone bridge equivalent circuit diagram and TMR sensor meet the following requirements: When there is an appropriate external magnetic field, the V CA Proportional to the change of the external magnetic field, the voltage output of the tunnel magnetoresistance sensor is proportional to the external magnetic field; under the action of a magnetic field within a certain range, the resistance of the tunnel magnetoresistance material will change accordingly with the change of the magnetic field. By effectively testing the magnetic field near the current-carrying conductor, the current value can be calculated using the conditioning circuit; The TMR sensor works by using the TMR effect. The TMR sensor consists of a non-magnetic tunnel isolation layer sandwiched between two magnetic layers, namely a fixed layer and a free layer. The magnetization direction of the fixed layer is fixed during the manufacturing process and will not change with the external magnetic field, while the magnetization direction of the free layer is relatively flexible and can change with the external magnetic field. When there is no magnetic field, the current will pass through the two magnetic layers evenly. When there is a magnetic field, the spin-orbit coupling phenomenon in the non-magnetic tunnel isolation layer occurs, causing the current to tend to pass through the magnetic layer in the same direction as the magnetic field. The tunneling probability of electrons from one magnetic layer to another is related to the magnetization directions of the two magnetic layers; the tunneling conductance changes with the change of the magnetization directions of the two ferromagnetic layers, and the conductance when the magnetization vectors are parallel is higher than the conductance when they are antiparallel; the magnetization directions of the two ferromagnetic layers can be changed by applying an external magnetic field, so that the tunneling resistance changes, resulting in the TMR effect; the TMR sensor uses the TMR2905BP sensor, which is powered by 5Vdc. The sensor outputs a 0-50uA current signal, which is converted to a 0-0.5Vdc DC voltage by R1 and R6. The high-frequency filter circuit composed of R2, R4 and C10 is used to filter out the interference signal in the field space; then it enters the amplification through the differential circuit, which consists of two stages of AD628. After amplification, it becomes a 0-5V voltage signal and enters the controller from the SIGAMP end; Step 2: To solve the problem that leakage current is interfered by many noises, a Gaussian filter elimination algorithm is used to eliminate the problem. According to the Gaussian filter formula: Among them, Q k+1 (x) is the output value of the original load signal after the k+1th iteration; Q k (a+x) is the input value of the original load signal after the k+1th iteration; is the sum of the weighted coefficients of the filter at the kth iteration; b k (a+x) is the weighting coefficient at the kth iteration point a+x; the initial iteration number k is set to 0, and the number of iterations is set; the collected initial current and voltage data are brought into the formula and iterated to the set number of iterations, and the iteration result is output, which is the filtered value; Step 3, preprocessing the leakage current signal detected by the TMR sensor, including signal amplification, filtering and analog-to-digital conversion, for subsequent data processing and analysis; Step 4, transmitting the preprocessed signal to a data processing unit for further analysis and processing to obtain current monitoring data of the capacitive device; Step 5: compare the current monitoring data with a preset threshold value. If the threshold value is exceeded, an alarm signal is issued to prompt the operation and maintenance personnel to perform inspection and maintenance.

2. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 1, characterized in that: The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: In the substation transformer external insulation current monitoring system based on the TMR sensor, the power module is also equipped with a microUSB interface to facilitate users to perform charging and data transmission; In the wireless transceiver and signal transmission module, the wireless transceiver part of the system uses two nRF24L01 wireless transceivers; One nRF24L01 is configured as a transmitter to send processed data; the other is configured as a receiver to receive data from other devices.

3. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 1, characterized in that: In the wireless transceiver and signal transmission module, in order to enhance the transmission distance and stability of the signal, the nRF24L01 at the transmitting end is also equipped with a power amplifier PA and a low noise amplifier LNA.

4. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 1, 2 or 3, characterized in that: In step 1 of the substation transformer external insulation current monitoring method based on TMR sensor, the TMR sensor selects TMR2905BP sensor, which is powered by 5Vdc. The sensor outputs 0-50uA current signal, which is converted into 0-0.5Vdc DC voltage by R1 and R6. The high-frequency filter circuit composed of R2, R4 and C10 is used to filter out the interference signal in the field space; then it enters the amplification through the differential circuit, and the amplification consists of two stages of AD628. After amplification, it becomes a 0-5V voltage signal and enters the controller from the SIGAMP end.

5. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 1, 2 or 3, characterized in that: In step 2 of the substation transformer external insulation current monitoring method based on the TMR sensor, the specific requirements for eliminating the current using the Gaussian filter elimination algorithm are: According to the Gaussian filter formula: Among them, Q k+1 (x) is the output value of the original load signal after the k+1th iteration; Q k (a+x) is the input value of the original load signal after the k+1th iteration; is the sum of the weighted coefficients of the filter at the kth iteration; b k (a+x) is the weighting coefficient at the k-th iteration point a+x; set the initial iteration number k to 0, and set the number of iterations; bring the collected initial current and voltage data into the formula and iterate to the set number of iterations, and output the iterative result, which is the filtered value.

6. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 5, characterized in that: The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: First, during the monitoring process, the working status of the TMR sensor is monitored in real time to ensure its normal operation; Second, the TMR sensor should be calibrated and maintained regularly to ensure its measurement accuracy and stability.

7. The method for monitoring the external insulation current of transformer in substation based on TMR sensor according to claim 5, characterized in that: The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: The TMR sensor has a closed-loop structure and adopts a closed-loop negative feedback mechanism to improve the measurement accuracy and anti-interference ability of the sensor.

8. The method for monitoring external insulation current of transformer in substation based on TMR sensor according to claim 7, characterized in that: The substation transformer external insulation current monitoring method based on the TMR sensor also meets the following requirements: a PC terminal is established to visualize the current monitoring data and alarm signals so that operation and maintenance personnel can intuitively understand the current status of the capacitive equipment.

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