Split type on-load tap-changer with current transformer

Abstract

The invention relates to the technical field of transformers, in particular to a split type on-load tap-changer with current transformers, which comprises a switch switching part connected with a switch selection part through a connecting flange, a plurality of current transformers are arranged in the connecting flange, and the current transformers are connected to an intelligent control unit through optical fibers. The intelligent control unit extracts current characteristic data by using a fast Fourier transform algorithm based on original current signals of each converter transformer voltage regulating column acquired by a current transformer, and combines opening and closing position information of a switch switching part and a switch selection part to obtain current characteristic data of the converter transformer voltage regulating column. Extracting a fault mode feature vector by using a pre-trained deep belief network model; and generating a maintenance instruction according to the fault mode feature vector, and controlling the switch switching part to cut off the fault loop through the maintenance instruction. According to the invention, the real-time high-precision monitoring of the current state in the tap switch gear switching process is realized through the technologies of physical isolation, integration of multiple current transformers and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a split on-load tap changer with a current transformer. Background Art

[0002] The converter transformer is the core equipment in the ultra-high voltage direct current (UHVDC) transmission system, responsible for the important tasks of voltage conversion, power distribution and power transmission. The on-load tap changer, as a key component of the converter transformer, can flexibly adjust the DC transmission power by changing the tap position of the converter transformer without interrupting the load current, thereby effectively suppressing large fluctuations in the load center voltage, significantly enhancing the flexibility of the power grid, improving power quality, and optimizing power flow distribution.

[0003] However, the existing on-load tap-changers face many technical difficulties in actual operation, especially the deficiencies in fault detection and isolation. The on-load tap-changers widely used at present mostly adopt an integrated structural design, integrating core components such as the transfer switch and tap selector into the same mechanical system. When faults such as inter-stage short circuit or mechanical jamming occur in the switching part of this design, due to the compact structure, it is difficult to timely and accurately determine the type and location of the fault, resulting in the rapid expansion of the fault range, and eventually triggering the protection action of the converter transformer and cutting off the fault circuit. This delayed reaction not only affects the safe operation of the entire transformer system, but also causes large economic losses. Specifically, due to Due to the lack of effective fault monitoring methods, traditional on-load tap-changers often can only rely on the action of the transformer protection system to cut off the fault when facing a fault. This method is not only delayed, but also unable to accurately locate the fault point, which brings great inconvenience to subsequent maintenance and restoration work. In addition, once an integrated on-load tap-changer fails, it is often necessary to drain the oil and open the cover for maintenance of the entire converter transformer system, which not only increases the complexity and workload of maintenance, but also prolongs the maintenance time and affects the normal operation of the power grid. At the same time, due to the large scope of the fault, the equipment in the main oil tank needs to be fully inspected during the maintenance process, further increasing maintenance costs and risks.

[0004] In summary, the existing on-load tap-changer technology has many shortcomings and cannot meet the high requirements of UHVDC transmission systems for equipment reliability and maintenance efficiency. There is an urgent need for a more efficient and reliable on-load tap-changer technology to ensure the stable operation of converter transformers and the entire transmission system. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a split on-load tap changer with a current transformer.

[0006] In a first aspect, the present invention provides a split-type on-load tap changer with a current transformer, comprising a switch switching portion and a switch selection portion, wherein the switch switching portion is connected to the switch selection portion via a connecting flange, and a plurality of current transformers are disposed in the connecting flange; A plurality of terminals are provided on the surface of the connection flange, at least one of which serves as a neutral point lead-out terminal, and the remaining terminals serve as odd and even terminals of different converter transformer voltage regulating columns. The neutral point lead-out terminal is directly connected to the neutral point circuit and is not connected to the current transformer. The odd and even terminals of each converter transformer voltage regulating column are connected in series with the primary side of the corresponding current transformer. The current transformer is connected to an intelligent control unit via an optical fiber. The intelligent control unit is configured as follows: Based on the original current signals of each converter transformer and voltage regulating column collected by the current transformer, current characteristic data are extracted using a fast Fourier transform algorithm; Obtaining the opening and closing position information of the switch switching part and the switch selection part, and extracting the fault mode feature vector using a pre-trained deep belief network model based on the current characteristic data and the opening and closing position information; A maintenance instruction is generated according to the fault mode characteristic vector, and the switch switching part is controlled by the maintenance instruction to cut off the fault circuit.

[0007] In a further embodiment, the switch switching part is independently installed in the converter transformer auxiliary tank, the switch selection part is independently installed in the converter transformer main tank, and the converter transformer auxiliary tank and the converter transformer main tank are completely separated by a physical isolation structure to control the arc effect generated during the tap gear switching action within the converter transformer auxiliary tank.

[0008] In a further embodiment, the switch switching portion includes a plurality of switches, and the switches are used to control the disconnection or connection of the load switch when the tap changer performs a gear shift; The switch selection part includes a plurality of tap selectors, and the tap selectors are used to preselect a target tap position before switching the current tap position.

[0009] In a further embodiment, the bottom of the switch switching part is connected to one end of the connecting flange through a set of current-carrying conductors, and the other end of the connecting flange is connected to the switch selection part through another set of current-carrying conductors to form a current path across the oil tank.

[0010] In a further embodiment, the current flow direction of the neutral point lead-out terminal is opposite to the current flow direction on the remaining terminals, and the current value of the neutral point lead-out terminal is the vector sum absolute value of the currents of all odd terminals or all even terminals in the converter transformer column.

[0011] In a further embodiment, the switch switching portion uses a dual parallel structure to construct an inter-gear circuit between adjacent tap gears, the dual parallel structure comprising a first branch and a second branch connected in parallel; The first branch is provided with a first vacuum isolation contact, the input end of the first vacuum isolation contact is connected to the current tap position, and the output end of the first vacuum isolation contact is connected to the output end of the switch switching part through a first vacuum tube; the first branch is used to control current transfer through the first vacuum isolation contact and the first vacuum tube when the tap position is changed; The second branch is provided with a second vacuum isolation contact, the input end of the second vacuum isolation contact is connected to the target tap position, and the output end of the second vacuum isolation contact is connected to the output end of the switch switching part through a transition resistor and a parallel vacuum tube branch, wherein the parallel vacuum tube branch includes a second vacuum tube and a third vacuum tube connected in parallel; The second branch is used to control the second vacuum tube and the third vacuum tube to be turned on in stages, and to control the circulating current amplitude during the switching process through the transition resistor, so that no arc is generated during the tap position switching process.

[0012] In a further embodiment, the top of the switch switching part is insulatedly connected to the top of the switch selecting part through an oil-oil bushing.

[0013] In a further embodiment, the connecting flange includes a flange plate and an epoxy resin flange cover; An epoxy resin protective sleeve is provided on the flange cover of the connecting flange, and the epoxy resin protective sleeve is used to protect the terminal.

[0014] In a further embodiment, the current characteristic data includes at least fundamental current amplitude, fundamental frequency and harmonic distortion rate, and the current characteristic data is extracted using a fast Fourier transform algorithm based on the original current signal of each converter transformer and voltage regulating column collected by the current transformer, including: Processing the original current signal using a fast Fourier transform algorithm to obtain spectrum information; Extracting a fundamental component from the frequency spectrum information, and calculating an effective value of the fundamental component to obtain a fundamental current amplitude; Determine the fundamental frequency according to the fundamental peak position in the spectrum information, extract harmonic components from the spectrum information, and calculate the amplitude of each harmonic component; The amplitudes of the harmonic components are compared with the amplitude of the fundamental current, and the harmonic distortion rate of the harmonic components relative to the fundamental current is calculated.

[0015] In a further embodiment, obtaining the opening and closing position information of the switch switching part and the switch selecting part includes: Comparing the fundamental current amplitude with a preset overcurrent protection set value, and determining that an overcurrent abnormality exists if the fundamental current amplitude exceeds the overcurrent protection set value; Comparing the harmonic distortion rate with a preset distortion threshold, and determining that a harmonic anomaly exists if the harmonic distortion rate exceeds the distortion threshold; Detect the current value of the neutral point lead-out terminal. If the current value of the neutral point lead-out terminal is not equal to the vector sum absolute value of the currents of all odd terminals or all even terminals, it is determined that an inter-stage short circuit fault exists. If there is an overcurrent anomaly, harmonic anomaly or inter-stage short circuit fault, the opening and closing position information of the switch switching part and the switch selection part is obtained.

[0016] The present invention provides a split on-load tap changer with a current transformer, the split on-load tap changer comprising a switch switching part and a switch selecting part, the switch switching part being connected to the switch selecting part via a connecting flange, a plurality of current transformers being arranged in the connecting flange; a plurality of terminals being arranged on the surface of the connecting flange, at least one terminal serving as a neutral point lead-out terminal, the remaining terminals serving as odd and even terminals for different converter transformer and voltage-regulating columns, the neutral point lead-out terminal being directly connected to a neutral point loop and not connected to the current transformer, the odd and even terminals of each converter transformer and voltage-regulating column being connected in series with the primary side of the corresponding current transformer; the current transformer being connected to an intelligent control unit via an optical fiber, the intelligent control unit extracting current characteristic data using a fast Fourier transform algorithm based on the original current signals of each converter transformer and voltage-regulating column collected by the current transformer; obtaining opening and closing position information of the switch switching part and the switch selecting part, and extracting a fault mode feature vector based on the current characteristic data and the opening and closing position information using a pre-trained deep belief network model; generating a maintenance instruction based on the fault mode feature vector, and controlling the switch switching part to cut off the fault loop through the maintenance instruction. Compared with the existing technology, this split on-load tap-changer achieves real-time and high-precision monitoring of the current state during the tap-changer gear switching process by physically isolating the switch switching part from the switch selection part, integrating the current transformer in the connecting flange, and combining directional monitoring of the neutral point lead terminal and the odd and even terminals of the voltage regulating column, effectively improving the accuracy and timeliness of fault detection. At the same time, the split structure limits the impact of faults to a local area, effectively solving the fault detection and isolation problems of existing on-load tap-changers, and ensuring the safe and stable operation of the UHVDC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic structural diagram of a split on-load tap changer with a current transformer provided by an embodiment of the present invention; Figure 2 This is a schematic diagram of the connecting flange structure provided by an embodiment of the present invention; Figure 3 This is a schematic diagram of the overcurrent protection action control logic provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be construed as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of protection of the present invention. Many changes may be made to the present invention without departing from the spirit and scope of the present invention.

[0019] refer to Figure 1 , an embodiment of the present invention provides a split on-load tap changer with a current transformer, such as Figure 1 As shown, the split-type on-load tap changer includes a switch switching section 1 and a switch selection section 2. The switch switching section 1 is independently disposed in the converter transformer auxiliary tank, and the switch selection section 2 is independently disposed in the converter transformer main tank. The converter transformer auxiliary tank and the converter transformer main tank are completely separated by a physical isolation structure, ensuring that the switch switching section and the switch selection section operate in independent tanks. This controls the arcing effect generated during the tap position switching operation within the converter transformer auxiliary tank, ensuring that, in the split structure, faults only affect the auxiliary tank and do not require oil draining and maintenance in the main tank. To achieve current transmission and signal detection between the switch switching section 1 and the switch selection section 2, the top of the switch switching section 1 is insulatedly connected to the top of the switch selection section 2 via an oil-oil casing 3. The bottom of the switch switching section 1 is connected to one end of a connecting flange 4 via a set of current-carrying conductors. The other end of the connecting flange 4 is connected to the switch selection section 2 via another set of current-carrying conductors, forming a current path across the tank. Several current transformers 5 are disposed within the connecting flange 4.

[0020] In some embodiments, the switch switching part 1 includes multiple switching switches, and the switching switches are used to control the disconnection or connection of the load switch when the tap changer is switched to a different gear, so as to ensure the safe switching of the circuit. In this embodiment, the switch switching part adopts a dual parallel structure to construct an inter-gear circuit between adjacent tap changer gears, that is, the switch switching part sets up two parallel circuits between adjacent tap changer gears, and the two parallel circuits include a first branch and a second branch connected in parallel, wherein the first branch is provided with a first vacuum isolation contact, the input end of the first vacuum isolation contact is connected to the current tap gear, and the output end of the first vacuum isolation contact is connected to the output end of the switch switching part through a first vacuum tube; the first branch is used to control the current transfer through the first vacuum isolation contact and the first vacuum tube when the tap gear is switched.

[0021] The second branch is provided with a second vacuum isolation contact, the input end of the second vacuum isolation contact is connected to the target tap position, and the output end of the second vacuum isolation contact is connected to the output end of the switch switching part through a transition resistor and a parallel vacuum tube branch, and the parallel vacuum tube branch includes a second vacuum tube and a third vacuum tube connected in parallel; the second branch is used to control the second vacuum tube and the third vacuum tube to be turned on in stages, and to control the circulating current amplitude during the switching process through the transition resistor, so that no arc is generated during the tap position switching process.

[0022] In a specific embodiment, the circuit between the N position and the N+1 position of the switch switching part includes two parallel circuits. In this embodiment, a first main contact is provided between the N position and the output end, and a second main contact is provided between the N+1 position and the output end. When the switch switching part switches between the N position and the N+1 position, this embodiment first closes the first main contact to allow current to flow out through the first main contact. At this time, the switch is in the N position. Then, the first main contact is opened, and the second vacuum tube and the third vacuum tube are closed, so that current flows out through the first vacuum isolation contact and the first vacuum tube. Then, the first vacuum tube is opened, and the first vacuum isolation contact is switched from the N position end to the N position end. Switch to the N+1 gear end, and then close the first vacuum tube. At this time, the current will flow out from the N+1 gear through the first vacuum tube, and at the same time form a circulation with the N gear through the transition resistor; then disconnect the second vacuum tube and the third vacuum tube, and switch the second vacuum isolation contact from the N gear end to the N+1 gear end, and close the second main contact, so that the current will eventually flow out from the second main contact, thereby completing the conversion process from N gear to N+1 gear, ensuring the stability and reliability of the switch conversion process, and providing a strong guarantee for the safe and stable operation of the power system. In addition, in the switch switching part 1, the cross-sectional area between different taps is not less than 400mm 2 The copper busbar is connected in series to the connecting flange to ensure large-capacity current transmission.

[0023] In some embodiments, the switch selection part 2 includes multiple tap selectors, which are used to pre-select and connect the target tap position before the current tap position is switched to ensure the smooth progress of the switching process. In the switch selection part 2, the current-carrying conductor is made of multiple strands of twisted fine copper wire. This structure not only improves the conductive performance of the conductor, but also enhances its mechanical strength and corrosion resistance. In addition, the current-carrying conductor is wrapped with a high-strength glass fiber reinforced insulation layer. The current-carrying conductor is connected to the other end of the connecting flange 4 by welding, ensuring the reliability and stability of current transmission.

[0024] In a specific embodiment, a switch selection part is configured in the main oil tank of the converter transformer. The switch selection part is made of high-temperature resistant alloy material to ensure stable and reliable operation in a working environment of up to 125°C. The contacts of the switch selection part are made of silver-tungsten alloy, and its contact resistance is strictly controlled below 5mΩ to achieve low-loss and high-reliability electrical connection; and a switch switching part is set in the auxiliary oil tank of the converter transformer. The switch switching part adopts a double-breakpoint structure, and the switching time is accurately controlled within 15ms to meet the needs of frequent operations and maintain stable electrical performance. A fluororubber sealing ring is used to seal the main oil tank of the converter transformer and the auxiliary oil tank of the converter transformer. The compression rate of the sealing ring is controlled in the range of 25% to 30% to ensure that it can still operate in a water depth of 10 meters. It can achieve the protection level of IP68 and effectively prevent oil leakage. In addition, the fuel tank is equipped with an oil level sensor, which can monitor the oil height in real time. Once the oil is lower than the preset safety threshold, the system will automatically trigger an alarm and execute corresponding protection measures to prevent the equipment from being damaged due to insufficient oil. In this embodiment, the fuel tank structure can be optimized through finite element analysis method to ensure that when the maximum working pressure reaches 6MPa, the deformation of the fuel tank does not exceed 1mm, thereby further improving the sealing and safety of the equipment. The design of the split-type on-load tap-changer in this embodiment not only realizes the integration of the current transformer and the switch body, but also improves the overall performance and safety of the equipment, meeting the high requirements of the ultra-high voltage direct current transmission project for equipment.

[0025] In some embodiments, a plurality of terminals 6 are provided on the surface of the connecting flange 4, wherein at least one terminal serves as a neutral point lead-out terminal, and all other terminals serve as odd terminals and even terminals of different converter transformer voltage regulating columns, respectively. The odd terminals and even terminals of each converter transformer voltage regulating column are connected in series with the primary side of the current transformer, and the neutral point lead-out terminal is directly connected to the neutral point loop and is not connected to the current transformer. In this embodiment, the current flow direction of the neutral point lead-out terminal is opposite to the current flow direction on the other terminals, and the current value of the neutral point lead-out terminal is the vector sum absolute value of the currents of all odd terminals or all even terminals.

[0026] In this embodiment, the connecting flange 4 includes a flange plate and an epoxy resin flange cover connected to the flange plate. The epoxy resin flange cover is made of epoxy resin. Each terminal 6 is provided with an epoxy resin protective cover. The epoxy resin protective cover is provided on the flange cover of the connecting flange. The epoxy resin protective cover is used to protect the terminal to enhance the insulation performance and mechanical strength, and further protect the terminal from the influence of the external environment.

[0027] like Figure 2As shown, this embodiment is described in detail by taking the five terminals 6 provided on the connecting flange 4 as an example. The five terminals are terminal H0, terminal H1, terminal H2, terminal H3 and terminal H4. Among them, terminal H0 is not connected (displayed in gray) to the current transformer. Terminal H1, terminal H2, terminal H3 and terminal H4 are all equipped with current sensors 5, so that terminal H1, terminal H2, terminal H3 and terminal H4 serve as current measurement points. The monitoring, protection system and recording device of the tap changer are realized through the current sensors. In this embodiment, terminal H Terminals H1 and H2 are the odd and even terminals of the converter transformer voltage regulator I terminal, respectively. Terminals H3 and H4 are the odd and even terminals of the converter transformer voltage regulator II terminal, respectively. Terminal H0 is a neutral point lead-out terminal and is not connected to current transformer 5. At the same time, the current direction of terminal H0 is opposite to the current direction of terminals H1, terminal H2, terminal H3 and terminal H4, and the current direction of terminals H1, terminal H2, terminal H3 and terminal H4 is the same. The current magnitude of terminal H0 is equal to the sum of the currents of terminals H1 and terminal H3 or terminals H2 and terminal H4.

[0028] The current transformer 5 adopts an electromagnetic current transformer. In this embodiment, several electromagnetic current transformers 5 can be configured on the terminal H1, terminal H2, terminal H3 and terminal H4. Each terminal can be configured with 3 or 4 electromagnetic current transformers, which are respectively sent to three sets of control protection and measurement devices to meet the high precision and high reliability requirements of current measurement. The iron core of each current transformer is made of nanocrystalline alloy material. This material has excellent magnetic and mechanical properties and can improve the measurement accuracy and stability of the transformer. In this embodiment, a magnetic permeability meter is used to measure the magnetic permeability of the iron core to ensure that it exceeds 100,000. In the internal space of the connecting flange, the transformer is determined according to the space size and electrical parameters. The number and position of the arrangement ensure the accuracy and safety of the current measurement. In the specific production process, this embodiment needs to install the completed current transformer at the specified position inside the connecting flange and fix the transformer position with bolts. Then, the connection status of all transformers inside the connecting flange is obtained, and the output signals of all transformers are tested by an oscilloscope to ensure that their connection status is normal. When the transformer output signal is abnormal, a magnetic permeability meter is immediately used to detect whether the magnetic permeability of the iron core meets the standard. If it does not meet the requirements, the iron core needs to be remade. After all transformers are installed and tested, this embodiment records the layout information and test data of the transformers in detail in a preset database for subsequent reference.

[0029] The current transformer 5 is fixed in the connecting flange 4 by epoxy resin. In this embodiment, epoxy resin is used as the potting material, and the resin is injected into the current transformer through a vacuum infusion process to ensure that the adhesion between the resin and the iron core, winding and metal terminal reaches 4MPa or more. During the infusion process, this embodiment monitors the flow state of the resin in real time and adjusts the vacuum degree or infusion speed according to the flow state so that the resin evenly covers all parts. For example, if the flow is uneven, the vacuum degree is adjusted between 1 and 0.1MPa or the infusion speed is adjusted between 5 and 5L / min so that the resin evenly covers all parts. During the curing process, this embodiment controls the ambient temperature and humidity within the preset temperature and humidity range. If the preset temperature and humidity range is exceeded, the curing conditions are adjusted by the temperature and humidity controller to ensure that the volume resistivity of the resin after curing is higher than 10 15 Ω·m. After curing, this embodiment uses a tensile tester to test the adhesion of the resin to the iron core, windings and metal terminals. If the adhesion does not meet the standard, re-pouring and curing are performed. At the same time, this embodiment uses a high-precision resistance tester to measure the volume resistivity of the cured resin. If the resistivity does not meet the standard, the resin formula is adjusted or the curing time is extended.

[0030] In addition, this embodiment uses RIP paper-epoxy resin composite material to make oil-oil casing. The two ends of the oil-oil casing are tightly connected to the main and auxiliary oil tanks through a threaded structure. In the design process of the casing, this embodiment first calculates the mechanical properties and electrical properties of the composite material based on the tensile strength, elastic modulus, dielectric constant and other characteristic parameters of RIP paper and epoxy resin. The mechanical properties and electrical properties of the composite material include key indicators such as tensile strength, compressive strength and dielectric strength. Then, using these performance parameters and the power frequency withstand voltage level requirements, the minimum value of the casing wall thickness is calculated to ensure that it meets the withstand voltage requirements of 10kV and above. Next, this embodiment calculates the minimum wall thickness of the casing based on the main and auxiliary oil tanks. The connection requirements set the thread structure at both ends of the casing, determine the thread size and connection method, and ensure that the thread structure perfectly matches the wall thickness design. On this basis, this embodiment uses finite element analysis software to establish a structural model of the casing, analyze its stress distribution and connection stability, and optimize the overall structure of the casing based on the analysis results to meet the requirements of pressure resistance and mechanical strength. Once the casing structure passes the pressure resistance and mechanical strength verification, the manufacturing process parameters of the casing are generated based on the optimized design results, and a detailed production process and strict quality control standards are determined. Finally, according to these manufacturing process parameters, the casing production process is executed to produce oil-oil casing that meets the design standards.

[0031] In addition, the secondary leads of the current transformer are connected to the intelligent control unit through optical fibers, realizing the digital transmission and remote monitoring of the current signal. These current transformers are not only used to detect the current size, but also meet the sensitivity and reliability requirements. At the same time, their size, weight, process, etc. also need to meet the overall requirements of the ultra-high voltage direct current transmission project. In a specific embodiment, the intelligent control unit of the split-type on-load tap changer obtains the connection status of the copper nose of the current transformer and the tinned copper braided wire through a high-precision sensor, and uses the built-in electrical performance evaluation algorithm to determine whether the connection meets the preset electrical performance threshold, thereby ensuring the reliability and safety of the electrical connection. Then, this embodiment determines the optimal fixing method of the tinned copper braided wire through the intelligent control unit based on the structural design of the ceramic terminals in the waterproof junction box, and secures it according to the preset mechanical strength standards. The intelligent control unit can be firmly fixed to ensure the stability and durability of the connection point. At the same time, the intelligent control unit can use sealing performance detection technology to test the sealing performance of the waterproof junction box according to the IP65 protection level required by the terminal. Once the sealing performance is found to be lower than the preset value, the alarm signal will be triggered immediately to remind the operator to take timely measures to repair it, thereby effectively preventing the intrusion of moisture and dust and ensuring the normal operation of the electrical components inside the switch. In addition, the intelligent control unit also collects the measurement data of the switch current in real time through the secondary access point of the current transformer, and uses the built-in current range judgment algorithm to analyze the data to determine whether the current is within the preset safety range. If the current data is abnormal, the intelligent control unit will automatically generate a fault diagnosis report, recording the abnormal data and its possible causes in detail, providing strong support for subsequent troubleshooting and maintenance.

[0032] Based on the above embodiment, in some implementation methods, the current transformer is connected to an intelligent control unit via an optical fiber, and the intelligent control unit is configured as follows: Based on the original current signals of each converter transformer and voltage regulating column collected by the current transformer, current characteristic data are extracted using a fast Fourier transform algorithm, where the current characteristic data includes at least fundamental current amplitude, fundamental frequency and harmonic distortion rate; Obtaining the opening and closing position information of the switch switching part and the switch selection part, and extracting the fault mode feature vector using a pre-trained deep belief network model based on the current characteristic data and the opening and closing position information; Determining the fault type and the fault location according to the fault mode characteristic vector, and generating a maintenance instruction according to the fault type and the fault location; The maintenance instruction controls the switch switching portion to cut off the fault circuit, thereby controlling the fault range within the converter transformer auxiliary tank.

[0033] In some embodiments, the extracting of current characteristic data using a fast Fourier transform algorithm based on the original current signal of each converter transformer and voltage regulating column collected by the current transformer specifically includes: Processing the original current signal using a fast Fourier transform algorithm to obtain spectrum information; Extracting a fundamental component from the frequency spectrum information, and calculating an effective value of the fundamental component to obtain a fundamental current amplitude; Determine the fundamental frequency according to the fundamental peak position in the spectrum information, extract harmonic components from the spectrum information, and calculate the amplitude of each harmonic component; The amplitudes of the harmonic components are compared with the amplitude of the fundamental current, and the harmonic distortion rate of the harmonic components relative to the fundamental current is calculated.

[0034] Specifically, in order to monitor the operating status of the converter transformer (i.e., the converter transformer), the present embodiment installs current transformers on the converter transformer voltage regulating column and the neutral point lead-out terminal. These transformers can collect the current data flowing through these locations in real time and accurately, and convert it into the form of electrical signals, i.e., the original current signal. After receiving the original current signal, the present embodiment uses the fast Fourier transform (FFT) algorithm to process the original current signal to obtain the spectrum information of the original current signal, i.e., the amplitude and phase information of each frequency component in the signal. Then, the present embodiment extracts the fundamental component from the spectrum information. The fundamental component is the component with the lowest frequency and the largest amplitude in the signal, which represents The main characteristics of the signal. This embodiment can determine the fundamental component by searching for the component with the lowest frequency and the largest amplitude in the spectrum information. Then, this embodiment can calculate the effective value of the fundamental component using the root mean square value. The effective value of the fundamental component is the fundamental current amplitude. After determining the fundamental component, this embodiment can determine the frequency of the fundamental by searching for the position of the fundamental peak in the spectrum information. At the same time, the harmonic component is extracted from the spectrum information. The harmonic component is the component in the signal with a frequency higher than the fundamental frequency. They usually appear in the form of integer multiples of the fundamental frequency. This embodiment can find the position of all harmonic components and calculate their amplitudes by traversing the spectrum information.

[0035] After obtaining the fundamental current amplitude and the amplitudes of each harmonic component, this embodiment can calculate the harmonic distortion rate. The harmonic distortion rate is an indicator that measures the size of the harmonic components in the signal relative to the fundamental component. This embodiment calculates the ratio of the sum of the squares of all harmonic component amplitudes to the square of the fundamental current amplitude, and then takes the square root to obtain the harmonic distortion rate. The larger the harmonic distortion rate, the more harmonic components in the signal and the more severe the waveform distortion of the signal.

[0036] In some embodiments, obtaining the opening and closing position information of the switch switching part and the switch selecting part specifically includes: Comparing the fundamental current amplitude with a preset overcurrent protection set value, and determining that an overcurrent abnormality exists if the fundamental current amplitude exceeds the overcurrent protection set value; Comparing the harmonic distortion rate with a preset distortion threshold, and determining that a harmonic anomaly exists if the harmonic distortion rate exceeds the distortion threshold; Detect the current value of the neutral point lead-out terminal. If the current value of the neutral point lead-out terminal is not equal to the vector sum absolute value of the currents of all odd terminals or all even terminals, it is determined that an inter-stage short circuit fault exists. If there is an overcurrent anomaly, harmonic anomaly or inter-stage short circuit fault, the opening and closing position information of the switch switching part and the switch selection part is obtained.

[0037] Specifically, this embodiment compares the calculated fundamental current amplitude with a preset overcurrent protection setting. If the fundamental current amplitude exceeds the overcurrent protection setting, it is determined that an overcurrent anomaly exists. At the same time, the harmonic distortion rate is compared with a preset distortion threshold. If the harmonic distortion rate exceeds the distortion threshold, it is determined that a harmonic anomaly exists. In addition, this embodiment detects the current value of the neutral point lead-out terminal and compares the current value of the neutral point lead-out terminal with the vector sum absolute value of the currents of all odd terminals or all even terminals. If they are not equal, it is determined that an inter-stage short circuit fault exists. For example, this embodiment calculates that the sum of the currents of terminal H1 and terminal H3 is 250A, and the sum of the currents of terminal H2 and terminal H4 is 250A. Then, this embodiment compares these two sums with the current of terminal H0. For example, the current detected at terminal H0 is 280A, which is inconsistent with the calculated 250A, indicating that there is an inter-stage short-circuit fault in the switching part. In order to further verify and diagnose the fault, this embodiment can use the data collected by the current transformer to analyze the current change trend between the various gears of the switching part. For example, between gear N and gear N+1, this embodiment detects that the current suddenly drops from 150A to 50A. This abnormal current change trend indicates that there is a mechanical jamming fault in the switching part. In addition, this embodiment also detects the current of each terminal through an electromagnetic current transformer to determine whether there is a disconnection phenomenon. For example, on terminal H2, the current detected by this embodiment is 0A, which indicates that there is a CT disconnection fault in the switching part.

[0038] like Figure 3As shown, the current detection points defined in this embodiment are specifically: Phase A, Phase B, and Phase C correspond to three independent phases of the three-phase AC system respectively; Terminal H1, Terminal H2, Terminal H3, and Terminal H4 are terminal identifications on the connection flange, wherein Terminal H1 and Terminal H2 are the odd terminal and even terminal of the converter transformer voltage regulator I terminal respectively; Terminal H3 and Terminal H4 are the odd terminal and even terminal of the converter transformer voltage regulator II terminal respectively. At the same time, this embodiment sets the preset overcurrent protection value to Iset, which can be set according to 1.2 times the rated current. T is the delay threshold, which indicates that the current is continuously greater than The time window for triggering the protection action after the overcurrent protection setting value is reached. For each terminal of each phase, H1, H2, H3 and H4, if the current value is detected to be greater than the overcurrent protection setting value and lasts for more than T, it is determined to be an overcurrent abnormality. When any terminal of any phase triggers the overcurrent condition, the intelligent control unit generates an overcurrent protection action instruction, drives the switching part to cut off the corresponding vacuum tube or isolation contact, and isolates the fault circuit to the auxiliary oil tank of the converter transformer. Among them, the execution priority of the protection action is related to the severity of the fault. For example, inter-stage short circuit (excessive current deviation of terminal H0) takes precedence over single terminal overcurrent.

[0039] When any one of overcurrent anomaly, harmonic anomaly or inter-stage short circuit fault is detected, this embodiment immediately obtains the opening and closing position information of the switch switching part and the switch selection part. Then, this embodiment uses a pre-established deep belief network model to diagnose the fault type and location. The specific process is: first, the fundamental current amplitude is obtained, and it is determined whether the fundamental current amplitude is in a serious unbalanced state. If it is in an unbalanced state, the opening and closing position information of the switch switching part and the switch selection part is synchronously collected. Then, the current characteristic data and the opening and closing position information are input into the deep belief network model. The model extracts features and recognizes patterns on the input data, outputs a feature vector, and determines the fault type based on the analysis of the feature vector. Then, this embodiment combines the fault type and the opening and closing position information to determine the specific location where the fault occurs. In order to improve the diagnostic accuracy, this embodiment uses a support vector machine algorithm to perform secondary verification on the fault type and location, and finally obtains an accurate diagnostic result.

[0040] Specifically, this embodiment determines the fault type and location of occurrence based on the fault mode characteristic vector. The fault types include contact erosion, spring fatigue, transmission shaft jamming, etc., and generates targeted maintenance instructions based on the fault type and fault location. The maintenance instruction controls the switch switching part to quickly cut off the fault circuit, effectively controlling the fault range within the converter transformer auxiliary oil tank to prevent the fault from affecting the equipment in the main oil tank. During the fault diagnosis process, if faults such as contact erosion, spring fatigue, or transmission shaft jamming are identified, the corresponding fault severity assessment is determined and relevant maintenance records are retrieved. Specifically, When a contact ablation fault is diagnosed, this embodiment obtains the current data when the contact moves, and uses the integration method to accumulate and calculate the cumulative current impact value. When the cumulative current impact value exceeds the preset cumulative current threshold, an alarm signal is immediately triggered. This embodiment uses a linear regression model to evaluate the degree of contact ablation based on the alarm signal, combined with the number of contact actions and the cumulative current impact value, and matches the evaluation results with the actual action data of the faulty contact to determine the ablation level and generate a contact ablation status diagnostic report. In order to improve the prediction accuracy, this embodiment can use a random forest algorithm to optimize the ablation degree model.

[0041] For spring fatigue failure, this embodiment captures the original displacement data through a spring displacement sensor, and obtains a smooth displacement value through filtering processing. The initial constant of the spring is calculated based on the smooth displacement value, and then the relationship between displacement and force is fitted using the least squares method to determine the spring constant. This embodiment can calculate the average value and standard deviation of the spring constant by multiple measurements and statistics. If the spring constant is lower than the preset threshold, the spring is determined to be in a fatigue failure state. This embodiment calculates the actual fatigue degree based on the decrease ratio of the spring constant, and uses linear regression to fit the relationship between the spring constant and the actual fatigue degree to construct a fatigue model. Based on the fatigue model and the current spring constant, the remaining service life of the spring is judged. At the same time, this embodiment uses a multi-layer perceptron to predict the future fatigue degree of the spring, uses historical fatigue data to train the network, and outputs the prediction result.

[0042] For mechanical jamming of the transmission shaft, this embodiment automatically extracts the usage time and replacement cycle information of the grease from the data storage unit when mechanical jamming is detected. Based on this information, it is determined whether the grease has exceeded the preset replacement cycle threshold. If the grease exceeds the replacement cycle threshold, a grease replacement suggestion is generated. The grease replacement suggestion includes the replacement time and specific operating steps, such as cleaning the lubrication points and injecting new grease, etc., and the grease replacement cycle is recalculated based on the updated maintenance records to generate a new maintenance plan. According to the new grease replacement cycle and maintenance plan, the maintenance strategy and monitoring frequency of the transmission shaft are flexibly adjusted to ensure the timeliness and maintenance efficiency of grease replacement.

[0043] In summary, this embodiment preprocesses the collected original current signal. The preprocessing operation includes filtering to remove noise interference and performing period judgment to determine the periodic characteristics of the data. Then, this embodiment obtains the spectrum information of the original current signal through fast Fourier transform FFT, thereby calculating the amplitude and frequency of the fundamental current. Then, this embodiment will comprehensively evaluate the current state based on the preset overcurrent protection setting and harmonic distortion rate threshold, combined with the current opening and closing position information of the switch switching part and the switch selection part. In this process, if it is detected that the current amplitude is in a serious unbalanced state, the precise opening and closing position information of the switch switching part and the switch selection part will be immediately collected and used. These current amplitude data and opening and closing position information are used as input, and a pre-trained deep belief network model is used to perform feature extraction and pattern recognition. The fault type is determined based on the feature vector output by the model. This embodiment combines the identified fault type with the opening and closing position information to determine the specific location of the fault. At the same time, in order to improve the accuracy of the diagnosis, this embodiment can use a support vector machine algorithm to perform a secondary verification of the fault type and location of the preliminary diagnosis to finally obtain the diagnosis result. When faults such as contact erosion, spring fatigue or drive shaft jamming are diagnosed, this embodiment further determines the severity of the fault and automatically retrieves relevant maintenance records so that corresponding maintenance measures can be taken.

[0044] To further improve the accuracy and stability of current measurement, the intelligent control unit also uses a support vector machine algorithm to classify and process the collected current measurement data to identify the characteristics of the current waveform. By analyzing changes in the current waveform, this embodiment can accurately determine whether there are potential problems such as harmonic interference. Based on the current waveform analysis results, the intelligent control unit will optimize the design of the secondary access point of the current transformer. By adjusting the location and connection method of the access point, the accuracy and stability of current measurement are significantly improved, thereby ensuring that the split on-load tap-changer can demonstrate excellent performance under various operating conditions.

[0045] An embodiment of the present invention provides a split on-load tap changer with a current transformer, the split on-load tap changer includes a switch switching part and a switch selection part, the switch switching part is connected to the switch selection part through a connecting flange, and a plurality of current transformers are arranged in the connecting flange; a plurality of terminals are arranged on the surface of the connecting flange, at least one terminal serving as a neutral point lead-out terminal, and the remaining terminals serving as odd and even terminals of different converter transformer voltage regulating columns, the neutral point lead-out terminal is directly connected to the neutral point circuit and is not connected to the current transformer, and the odd and even terminals of each converter transformer voltage regulating column are connected to the corresponding The primary side of the current transformer is connected in series; the current transformer is connected to an intelligent control unit via an optical fiber. The intelligent control unit extracts current characteristic data using a fast Fourier transform algorithm based on the original current signal of each converter transformer and voltage regulating column collected by the current transformer; obtains the opening and closing position information of the switch switching part and the switch selection part, and extracts the fault mode feature vector based on the current characteristic data and the opening and closing position information using a pre-trained deep belief network model; generates a maintenance instruction based on the fault mode feature vector, and controls the switch switching part to cut off the fault circuit through the maintenance instruction. Compared with the existing technology, this split on-load tap-changer achieves real-time and high-precision monitoring of the current state during the tap-changer gear switching process by physically isolating the switch switching part from the switch selection part, integrating the current transformer in the connecting flange, and combining directional monitoring of the neutral point lead terminal and the odd and even terminals of the voltage regulating column, effectively improving the accuracy and timeliness of fault detection. At the same time, the split structure limits the impact of faults to a local area, effectively solving the fault detection and isolation problems of existing on-load tap-changers, and ensuring the safe and stable operation of the UHVDC transmission system.

[0046] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A split-type on-load tap-changer with a current transformer, characterized in that: It includes a switch switching part and a switch selection part, wherein the switch switching part is connected to the switch selection part via a connecting flange, and a plurality of current transformers are arranged in the connecting flange; A plurality of terminals are provided on the surface of the connection flange, at least one of which serves as a neutral point lead-out terminal, and the remaining terminals serve as odd and even terminals of different converter transformer voltage regulating columns. The neutral point lead-out terminal is directly connected to the neutral point circuit and is not connected to the current transformer. The odd and even terminals of each converter transformer voltage regulating column are connected in series with the primary side of the corresponding current transformer. The current transformer is connected to an intelligent control unit via an optical fiber. The intelligent control unit is configured as follows: Based on the original current signals of each converter transformer and voltage regulating column collected by the current transformer, current characteristic data are extracted using a fast Fourier transform algorithm; Obtaining the opening and closing position information of the switch switching part and the switch selection part, and extracting the fault mode feature vector using a pre-trained deep belief network model based on the current characteristic data and the opening and closing position information; A maintenance instruction is generated according to the fault mode characteristic vector, and the switch switching part is controlled by the maintenance instruction to cut off the fault circuit.

2. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The switch switching part is independently installed in the converter transformer auxiliary tank, and the switch selection part is independently installed in the converter transformer main tank. The converter transformer auxiliary tank and the converter transformer main tank are completely separated by a physical isolation structure to control the arc effect generated during the tap gear switching action within the converter transformer auxiliary tank.

3. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The switch switching part includes a plurality of switches, and the switches are used to control the disconnection or connection of the load switch when the tap switch performs gear conversion; The switch selection part includes a plurality of tap selectors, and the tap selectors are used to preselect a target tap position before switching the current tap position.

4. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The bottom of the switch switching part is connected to one end of the connecting flange through a set of current-carrying conductors, and the other end of the connecting flange is connected to the switch selection part through another set of current-carrying conductors, forming a current path across the oil tank.

5. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The current flow direction of the neutral point lead-out terminal is opposite to the current flow direction on the other terminals, and the current value of the neutral point lead-out terminal is the vector sum absolute value of the currents of all odd terminals or all even terminals in the converter transformer voltage regulating column.

6. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The switch switching part adopts a dual parallel structure to construct an inter-gear circuit between adjacent tap positions, and the dual parallel structure includes a first branch and a second branch connected in parallel; The first branch is provided with a first vacuum isolation contact, the input end of the first vacuum isolation contact is connected to the current tap position, and the output end of the first vacuum isolation contact is connected to the output end of the switch switching part through a first vacuum tube; the first branch is used to control current transfer through the first vacuum isolation contact and the first vacuum tube when the tap position is changed; The second branch is provided with a second vacuum isolation contact, the input end of the second vacuum isolation contact is connected to the target tap position, and the output end of the second vacuum isolation contact is connected to the output end of the switch switching part through a transition resistor and a parallel vacuum tube branch, wherein the parallel vacuum tube branch includes a second vacuum tube and a third vacuum tube connected in parallel; The second branch is used to control the second vacuum tube and the third vacuum tube to be turned on in stages, and to control the circulating current amplitude during the switching process through the transition resistor, so that no arc is generated during the tap position switching process.

7. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The top of the switch switching part is insulatedly connected to the top of the switch selecting part through an oil-oil casing.

8. The split-type on-load tap-changer with a current transformer according to claim 1, characterized in that: The connecting flange includes a flange plate and an epoxy resin flange cover; An epoxy resin protective sleeve is provided on the flange cover of the connecting flange, and the epoxy resin protective sleeve is used to protect the terminal.

9. The split-type on-load tap-changer with current transformer according to claim 1, characterized in that: The current characteristic data includes at least fundamental current amplitude, fundamental frequency and harmonic distortion rate, and the original current signal of each converter transformer and voltage regulating column collected by the current transformer is used to extract the current characteristic data using a fast Fourier transform algorithm, including: processing the original current signal using a fast Fourier transform algorithm to obtain spectrum information; Extracting a fundamental component from the frequency spectrum information, and calculating an effective value of the fundamental component to obtain a fundamental current amplitude; Determine the fundamental frequency according to the fundamental peak position in the spectrum information, extract harmonic components from the spectrum information, and calculate the amplitude of each harmonic component; The amplitudes of the harmonic components are compared with the amplitude of the fundamental current, and the harmonic distortion rate of the harmonic components relative to the fundamental current is calculated.

10. The split-type on-load tap-changer with current transformer according to claim 9, characterized in that: The obtaining of the opening and closing position information of the switch switching part and the switch selecting part includes: Comparing the fundamental current amplitude with a preset overcurrent protection set value, and determining that an overcurrent abnormality exists if the fundamental current amplitude exceeds the overcurrent protection set value; Comparing the harmonic distortion rate with a preset distortion threshold, and determining that a harmonic anomaly exists if the harmonic distortion rate exceeds the distortion threshold; Detect the current value of the neutral point lead-out terminal. If the current value of the neutral point lead-out terminal is not equal to the vector sum absolute value of the currents of all odd terminals or all even terminals, it is determined that an inter-stage short circuit fault exists. If there is an overcurrent anomaly, harmonic anomaly or inter-stage short circuit fault, the opening and closing position information of the switch switching part and the switch selection part is obtained.

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