Split type on-load tap changer with current transformer

Abstract

The present application relates to the technical field of transformer, and especially relates to a split type on-load tap changer with current transformers, which comprises a switch switching part connected to a switch selecting part through a connecting flange, a plurality of current transformers arranged in the connecting flange, and the current transformers connected to an intelligent control unit through optical fibers; the intelligent control unit extracts current characteristic data from original current signals of each converter transformer voltage regulating column collected by the current transformers based on a fast Fourier transform algorithm, extracts a fault mode characteristic vector by using a pre-trained deep belief network model in combination with opening and closing position information of the switch switching part and the switch selecting part; and generates a maintenance instruction according to the fault mode characteristic vector to control the switch switching part to cut off a fault loop through the maintenance instruction. The present application realizes real-time high-precision monitoring of current states in the process of tap changer gear switching by means of physical isolation and integrated multi-current transformers and other technologies.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and more particularly to a split-type on-load tap changer with a current transformer. Background Technology

[0002] Converter transformers are core equipment in ultra-high voltage direct current (UHVDC) transmission systems, undertaking important tasks such as voltage transformation, power distribution, and power transmission. On-load tap changers, as key components of converter transformers, can flexibly adjust the DC transmission power by changing the tap position of the converter transformer without interrupting the load current. This effectively suppresses large fluctuations in load center voltage, significantly improves the flexibility of the power grid, improves power quality, and optimizes power flow distribution.

[0003] However, existing on-load tap changers face numerous technical challenges in actual operation, particularly in fault detection and isolation. Currently, most widely used on-load tap changers employ an integrated design, combining the switching switch and tap selector into a single mechanical system. This design, due to its compact structure, makes it difficult to accurately and promptly determine the fault type and location when inter-stage short circuits or mechanical jamming occur in the switching section. This can lead to a rapid expansion of the fault range, ultimately triggering the converter transformer's protection system and disconnecting the faulty circuit. This delayed response not only affects the safe operation of the entire transformer system but also causes significant economic losses. Specifically, because… Lacking effective fault monitoring methods, traditional on-load tap changers often rely solely on the transformer protection system to disconnect faults when they occur. This approach is not only lagging but also unable to accurately locate the fault point, causing significant inconvenience to subsequent maintenance and restoration work. Furthermore, once an integrated on-load tap changer fails, it often requires draining the oil and opening the cover of the entire converter transformer system for inspection. This not only increases the complexity and workload of maintenance but also prolongs the maintenance time, affecting the normal operation of the power grid. At the same time, due to the large scope of the fault, a comprehensive inspection of the equipment in the main oil tank is required during maintenance, 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] To solve the above technical problems, the present invention provides a split-type 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 current transformers, comprising 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 disposed within the connecting flange.

[0007] The connecting flange surface is provided with multiple terminals, at least one of which serves as a neutral point lead-out terminal, and the remaining terminals serve as odd / even terminals for different converter transformer voltage regulating columns. The neutral point lead-out terminal is directly connected to the neutral point circuit and not connected to the current transformer. The odd / 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 the intelligent control unit via optical fiber. The intelligent control unit is configured as follows:

[0008] Based on the original current signals of each converter transformer voltage regulating column collected by the current transformer, the current feature data is extracted using the fast Fourier transform algorithm.

[0009] Obtain the opening and closing position information of the switch switching section and the switch selection section, and extract the fault mode feature vector using a pre-trained deep belief network model based on the current feature data and the opening and closing position information.

[0010] Based on the fault mode feature vector, a maintenance command is generated, and the fault circuit is cut off by controlling the switch switching part through the maintenance command.

[0011] In a further implementation, the switch switching part is independently installed in the converter transformer auxiliary oil tank, the switch selection part is independently installed in the converter transformer main oil tank, and the converter transformer auxiliary oil tank and the converter transformer main oil tank are completely separated by a physical isolation structure, so as to control the arc effect generated during the tap position switching action within the converter transformer auxiliary oil tank.

[0012] In a further embodiment, the switch switching section includes a plurality of switching switches, which are used to control the load switch to be turned off or on when the tap changer is switching positions.

[0013] The switch selection section includes multiple tap selectors, which are used to pre-select a target tap position before switching to the current tap position.

[0014] In a further embodiment, the bottom of the switch switching section is connected to one end of the connecting flange via a set of current-carrying conductors, and the other end of the connecting flange is connected to the switch selection section via another set of current-carrying conductors, forming a current path across the oil tank.

[0015] In a further 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 and absolute value of the currents of all odd terminals or all even terminals in the converter transformer voltage regulation column.

[0016] In a further embodiment, the switch switching section adopts a dual parallel structure to construct the inter-gear circuit between adjacent tap positions, and the dual parallel structure includes a first branch and a second branch connected in parallel.

[0017] The first branch is equipped 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 the current transfer through the first vacuum isolation contact and the first vacuum tube when the tap position is changed.

[0018] 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. 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. The parallel vacuum tube branch includes a second vacuum tube and a third vacuum tube connected in parallel.

[0019] The second branch is used to control the phased conduction of the second and third vacuum tubes, and to control the circulating current amplitude during the switching process through the transition resistor, so that no electric arc is generated during the tap position switching process.

[0020] In a further embodiment, the top of the switch switching section is insulated from the top of the switch selection section via an oil-oil bushing.

[0021] In a further embodiment, the connecting flange includes a flange plate and an epoxy resin flange cover;

[0022] 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 block.

[0023] In a further implementation, the current characteristic data includes at least the fundamental current amplitude, fundamental frequency, and harmonic distortion rate. The current characteristic data, extracted from the original current signals of each converter transformer voltage regulating column acquired by the current transformer using a fast Fourier transform algorithm, includes:

[0024] The original current signal is processed using a fast Fourier transform algorithm to obtain spectral information;

[0025] The fundamental component is extracted from the spectrum information, and the effective value of the fundamental component is calculated to obtain the fundamental current amplitude.

[0026] The fundamental frequency is determined based on the position of the fundamental peak in the spectrum information, and harmonic components are extracted from the spectrum information to calculate the amplitude of each harmonic component.

[0027] The amplitudes of each harmonic component are compared with the amplitude of the fundamental current to calculate the harmonic distortion rate of the harmonic component relative to the fundamental current.

[0028] In a further implementation, obtaining the opening and closing position information of the switch switching section and the switch selection section includes:

[0029] The fundamental current amplitude is compared with a preset overcurrent protection setting. If the fundamental current amplitude exceeds the overcurrent protection setting, an overcurrent abnormality is determined to exist.

[0030] The harmonic distortion rate is compared with a preset distortion threshold. If the harmonic distortion rate exceeds the distortion threshold, it is determined that there is a harmonic anomaly.

[0031] If the current value at the neutral point terminal is not equal to the vector sum and absolute value of the currents at all odd or even terminals, then an inter-stage short circuit fault is determined to exist.

[0032] If there is an overcurrent anomaly, harmonic anomaly, or inter-stage short circuit fault, the opening and closing position information of the switch switching section and the switch selection section is obtained.

[0033] This invention provides a split-type on-load tap changer with current transformers. The split-type on-load tap changer includes a switch switching section and a switch selection section. The switch switching section is connected to the switch selection section via a connecting flange, and several current transformers are installed inside the connecting flange. Multiple terminals are provided on the surface of the connecting flange, at least one of which serves as a neutral point lead-out terminal, and the remaining terminals serve as odd / even terminals for different converter transformer voltage regulating columns. The neutral point lead-out terminal is directly connected to the neutral point circuit and not connected to the current transformers. The odd / even terminals of each converter transformer voltage regulating column are connected in series with the primary side of the corresponding current transformer. The current transformers are connected to an intelligent control unit via optical fiber. The intelligent control unit extracts current feature data based on the raw current signals of each converter transformer voltage regulating column collected by the current transformers using a fast Fourier transform algorithm. It acquires the opening and closing position information of the switch switching section and the switch selection section, and extracts fault mode feature vectors using a pre-trained deep belief network model based on the current feature data and the opening and closing position information. It generates maintenance commands based on the fault mode feature vectors and controls the switch switching section to disconnect the fault circuit through the maintenance commands. Compared with existing technologies, this split-type on-load tap changer achieves real-time, high-precision monitoring of the current status during tap changer switching by physically isolating the switching section from the selection section and integrating a current transformer within the connecting flange. Combined with directional monitoring of the neutral point lead-out terminal and the odd / even terminals of the voltage regulating column, it effectively improves the accuracy and timeliness of fault detection. At the same time, the split structure limits the impact of faults to a localized area. This split-type on-load tap changer effectively solves the problems of fault detection and isolation in existing on-load tap changers, ensuring the safe and stable operation of the UHVDC transmission system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a split-type on-load tap changer with a current transformer provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the connecting flange structure provided in an embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of the overcurrent protection action control logic provided in an embodiment of the present invention. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0038] refer to Figure 1This invention provides a split-type on-load tap changer with a current transformer, such as... Figure 1 As shown, this 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 located in the auxiliary oil tank of the converter transformer, and the switch selection section 2 is independently located in the main oil tank of the converter transformer. The auxiliary oil tank and the main oil tank of the converter transformer are completely separated by a physical isolation structure, ensuring that the switch switching section and the switch selection section operate in independent oil tanks. This controls the arc effect generated during the tap position switching operation within the auxiliary oil tank of the converter transformer, ensuring that a fault in the split structure only affects the auxiliary oil tank and does not require draining oil from the main oil tank for maintenance. At the same time, in order to realize 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 insulated from the top of the switch selection section 2 through an oil-oil bushing 3. The bottom of the switch switching section 1 is connected to one end of a connecting flange 4 through a set of current-carrying conductors, and the other end of the connecting flange 4 is connected to the switch selection section 2 through another set of current-carrying conductors, forming a current path across the oil tank. Several current transformers 5 are installed inside the connecting flange 4.

[0039] In some embodiments, the switch switching section 1 includes multiple switching switches. These switching switches are used to control the disconnection or connection of the load switch when the tap changer is switching positions, ensuring safe circuit switching. In this embodiment, the switch switching section adopts a double parallel structure to construct the inter-taper circuit between adjacent tap positions. That is, the switch switching section sets two parallel circuits between adjacent tap changer positions. The two parallel circuits include a first branch and a second branch connected in parallel. The first branch is provided with a first vacuum isolation contact. The input terminal of the first vacuum isolation contact is connected to the current tap position, and the output terminal of the first vacuum isolation contact is connected to the output terminal of the switch switching section 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 switched.

[0040] The second branch is equipped with a second vacuum isolation contact. The input end of the second vacuum isolation contact is connected to the target tap position. The output end of the second vacuum isolation contact is connected to the output end of the switch switching section through a transition resistor and a parallel vacuum tube branch. 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 conduct in stages, and to control the circulating current amplitude during the switching process through the transition resistor, so that no electric arc is generated during the tap position switching process.

[0041] In a specific embodiment, the circuit between the N and N+1 positions of the switch switching section includes two parallel circuits. In this embodiment, a first main contact is provided between the N position and the output terminal, and a second main contact is provided between the N+1 position and the output terminal. When the switch switching section switches between the N and N+1 positions, this embodiment first closes the first main contact, allowing 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 and third vacuum tubes are closed, allowing current to flow out through the first vacuum isolation contact and the first vacuum tube. Next, the first vacuum tube is opened, and the first vacuum isolation contact is switched from the N position end. Switching to the N+1 position and then closing the first vacuum tube, current flows from the N+1 position through the first vacuum tube, simultaneously forming a circulating current with the N position via the transition resistor. Then, the second and third vacuum tubes are disconnected, and the second vacuum isolation contact is also switched from the N position to the N+1 position. The second main contact is then closed, allowing current to finally flow out from the second main contact, thus completing the switchover process from N to N+1. This ensures the smoothness and reliability of the switchover process, providing strong support for the safe and stable operation of the power system. Furthermore, in the switchgear section 1, different taps are connected via a cross-sectional area of ​​not less than 400 mm². 2 The copper busbars are connected in series to the connecting flange, ensuring a large capacity of current transmission.

[0042] In some embodiments, the switch selection section 2 includes multiple tap selectors. The tap selectors are used to pre-select and connect the target tap position before switching the current tap position to ensure a smooth switching process. In the switch selection section 2, the current-carrying conductor is made of multi-stranded fine copper wire. This structure not only improves the conductivity 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 to ensure the reliability and stability of current transmission.

[0043] In a specific embodiment, the main oil tank of the converter transformer is equipped with a switch selection section. This switch selection section is made of high-temperature resistant alloy material to ensure stable and reliable operation even in working environments up to 125°C. The contacts of the switch selection section are made of silver-tungsten alloy, and their contact resistance is strictly controlled below 5mΩ to achieve low-loss and high-reliability electrical connections. The auxiliary oil tank of the converter transformer is equipped with a switch switching section. This switch switching section adopts a double-break structure, and the switching time is precisely controlled within 15ms to meet the needs of frequent operation and maintain stable electrical performance. The main oil tank and the auxiliary oil tank of the converter transformer are sealed together using fluororubber sealing rings. The compression rate of the sealing rings is controlled within the range of 25% to 30% to ensure stable operation even in water depths of up to 10 meters. It achieves an IP68 protection rating, effectively preventing oil leakage. Furthermore, the tank is equipped with an oil level sensor that monitors the oil level in real time. If the oil level falls below a preset safety threshold, the system will automatically trigger an alarm and implement corresponding protective measures to prevent damage to the equipment due to insufficient oil. In this embodiment, the tank structure is optimized using finite element analysis to ensure that the tank deformation does not exceed 1mm when the maximum working pressure reaches 6MPa, thereby further improving the equipment's sealing and safety. This split-type on-load tap changer design not only integrates the current transformer and the switch body but also improves the overall performance and safety of the equipment, meeting the high requirements of ultra-high voltage direct current transmission projects.

[0044] In some embodiments, the surface of the connecting flange 4 is provided with a plurality of terminals 6, of which at least one terminal serves as a neutral point lead-out terminal, and all other terminals serve as odd and even terminals of different converter transformer voltage regulating terminals, respectively. The odd and even terminals of each converter transformer voltage regulating terminal are connected in series with the primary side of the current transformer. The neutral point lead-out terminal is directly connected to the neutral point circuit 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 and absolute value of the currents of all odd terminals or all even terminals.

[0045] In this embodiment, the connecting flange 4 includes a flange and an epoxy resin flange cover connected to the flange. The epoxy resin flange cover is made of epoxy resin. Each terminal 6 is provided with an epoxy resin protective sleeve. The epoxy resin protective sleeve is provided on the flange cover of the connecting flange. The epoxy resin protective sleeve is used to protect the terminal to enhance insulation performance and mechanical strength, and further protect the terminal from the influence of the external environment.

[0046] like Figure 2As shown, this embodiment uses a flange 4 with five terminals 6 as an example for detailed explanation. The five terminals are terminals H0, H1, H2, H3, and H4. Terminal H0 is not connected to the current transformer (shown in gray). Terminals H1, H2, H3, and H4 are all equipped with current sensors 5, so that terminals H1, H2, H3, and H4 serve as current measuring points. The current sensors are used to monitor the tap changer, and a protection system and waveform recording device are implemented. In this embodiment, terminal H... Terminals H1 and H2 are the odd and even terminals of the converter transformer voltage regulator I, respectively. Terminals H3 and H4 are the odd and even terminals of the converter transformer voltage regulator II, respectively. Terminal H0 is the neutral point lead-out terminal and is not connected to the current transformer 5. At the same time, the current direction of terminal H0 is opposite to that of terminals H1, H2, H3, and H4, while the current directions of terminals H1, H2, H3, and H4 are the same. The magnitude of the current at terminal H0 is equal to the sum of the currents at terminals H1 and H3 or H2 and H4.

[0047] The current transformer 5 is an electromagnetic current transformer. In this embodiment, several electromagnetic current transformers 5 can be configured on terminals H1, H2, H3, and H4, with 3 or 4 electromagnetic current transformers configured on each terminal. These transformers are then sent to three sets of control, protection, and measurement devices to meet the high accuracy and reliability requirements for current measurement. The core of each current transformer is made of nanocrystalline alloy material, which has excellent magnetic and mechanical properties, improving the measurement accuracy and stability of the transformer. In this embodiment, a permeability meter is used to measure the permeability of the core, ensuring it exceeds 100,000. The transformer is determined based on the space dimensions and electrical parameters within the connecting flange space. The arrangement and location of the current transformers are carefully planned to ensure the accuracy and safety of current measurement. In the specific manufacturing process, this embodiment requires the completed current transformers to be installed in designated positions inside the connecting flange and the transformer positions to be fixed with bolts. Then, the connection status of all transformers inside the connecting flange is obtained, and the output signals of all transformers are tested with an oscilloscope to ensure that their connection status is normal. If an abnormal transformer output signal is detected, the permeability of the iron core is immediately tested with a permeability meter to check whether it meets the standard. If it does not meet the requirements, the iron core needs to be remade. After all transformers are installed and tested successfully, this embodiment records the arrangement information and test data of the transformers in detail in a preset database for future reference.

[0048] The current transformer 5 is fixed inside the connecting flange 4 with 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 potting process to ensure that the adhesion between the resin and the iron core, windings, and metal terminals reaches more than 4 MPa. During the potting process, this embodiment monitors the flow state of the resin in real time and adjusts the vacuum degree or potting speed according to the flow state to ensure that the resin evenly covers all components. For example, if the flow is uneven, the vacuum degree is adjusted to between 1 and 0.1 MPa or the potting speed is adjusted to between 5 and 5 L / min to ensure that the resin evenly covers all components. During the curing process, this embodiment controls the ambient temperature and humidity within a preset temperature and humidity range. If the preset temperature and humidity range is exceeded, the curing conditions are adjusted through a temperature and humidity controller to ensure that the volume resistivity of the cured resin is higher than 10 Ω·cm. 15 After curing, this embodiment uses a tensile tester to test the adhesion between the resin and the iron core, winding and metal terminals. If the adhesion does not meet the standard, the injection and curing process is repeated. 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.

[0049] Furthermore, this embodiment uses a RIP paper-epoxy resin composite material to make an oil-oil bushing. Both ends of the oil-oil bushing are tightly connected to the main and auxiliary oil tanks via threaded structures. In the bushing design process, this embodiment first calculates the mechanical and electrical properties of the composite material based on the tensile strength, elastic modulus, and dielectric constant of the RIP paper and epoxy resin. These mechanical and electrical properties include key indicators such as tensile strength, compressive strength, and dielectric strength. Then, using these performance parameters and the power frequency withstand voltage requirements, the minimum bushing wall thickness is calculated to ensure it meets the withstand voltage requirements of 10kV and above. Next, this embodiment considers the main and auxiliary oil tanks... The connection requirements are set at both ends of the casing to determine the thread structure, thread size, and connection method to ensure a perfect match between the thread structure and the wall thickness design. Based on this, 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 according to 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, a detailed production process and strict quality control standards are determined, and finally, the casing production process is executed according to these manufacturing process parameters to produce an oil-oil casing that meets the design standards.

[0050] Furthermore, the secondary leads of the current transformers are connected to the intelligent control unit via optical fiber, enabling digital transmission and remote monitoring of the current signal. These current transformers not only detect current magnitude but also meet sensitivity and reliability requirements. Their size, weight, and manufacturing process must also comply with the overall requirements of the UHVDC transmission project. In a specific embodiment, the intelligent control unit of the split-type on-load tap changer acquires the connection status of the copper lugs and tinned copper braided wire of the current transformer using a high-precision sensor. It then uses a built-in electrical performance evaluation algorithm to determine whether the connection meets preset electrical performance thresholds, ensuring the reliability and safety of the electrical connection. Next, based on the structural design of the ceramic terminals inside the waterproof junction box, the intelligent control unit determines the optimal fixing method for the tinned copper braided wire and secures it according to preset mechanical strength standards. The system is fixed in place to ensure the stability and durability of the connection points. Simultaneously, the intelligent control unit can perform sealing performance tests on the waterproof junction box using sealing performance testing technology, based on the required IP65 protection level for the terminals. If the sealing performance is found to be lower than the preset value, an alarm signal is immediately triggered, alerting operators to take timely corrective measures. This effectively prevents moisture and dust intrusion, ensuring the normal operation of the electrical components inside the switch. Furthermore, the intelligent control unit also collects real-time measurement data of the switch current through the secondary connection point of the current transformer and analyzes the data using a built-in current range judgment algorithm to determine whether the current is within the preset safe 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 fault diagnosis and maintenance.

[0051] Based on the above embodiments, in some implementations, the current transformer is connected to the intelligent control unit via optical fiber, and the intelligent control unit is configured as follows:

[0052] Based on the original current signals of each converter transformer voltage regulating column collected by the current transformer, the current characteristic data is extracted using the fast Fourier transform algorithm. The current characteristic data includes at least the fundamental current amplitude, fundamental frequency, and harmonic distortion rate.

[0053] Obtain the opening and closing position information of the switch switching section and the switch selection section, and extract the fault mode feature vector using a pre-trained deep belief network model based on the current feature data and the opening and closing position information.

[0054] Based on the fault mode feature vector, the fault type and the location of the fault are determined, and maintenance instructions are generated based on the fault type and the location of the fault.

[0055] The fault circuit is cut off by controlling the switch switching part of the maintenance command, thus controlling the fault range within the converter transformer auxiliary oil tank.

[0056] In some implementations, the extraction of current feature data from the raw current signals of each converter transformer voltage regulating column acquired by the current transformer using a fast Fourier transform algorithm specifically includes:

[0057] The original current signal is processed using a fast Fourier transform algorithm to obtain spectral information;

[0058] The fundamental component is extracted from the spectrum information, and the effective value of the fundamental component is calculated to obtain the fundamental current amplitude.

[0059] The fundamental frequency is determined based on the position of the fundamental peak in the spectrum information, and harmonic components are extracted from the spectrum information to calculate the amplitude of each harmonic component.

[0060] The amplitudes of each harmonic component are compared with the amplitude of the fundamental current to calculate the harmonic distortion rate of the harmonic component relative to the fundamental current.

[0061] Specifically, to monitor the operating status of the converter transformer, this embodiment installs current transformers on the voltage regulating column and neutral point lead-out terminal of the converter transformer. These transformers can collect current data flowing through these locations in real time and accurately, and convert it into an electrical signal, i.e., a raw current signal. After receiving the raw current signal, this embodiment processes it using the Fast Fourier Transform (FFT) algorithm to obtain the spectrum information of the raw current signal, i.e., the amplitude and phase information of each frequency component in the signal. Then, this embodiment extracts the fundamental component from the spectrum information. The fundamental component is the lowest frequency and largest amplitude component in the signal, representing the fundamental frequency. The main characteristics of the signal are as follows: In this embodiment, the fundamental component can be determined by finding the component with the lowest frequency and the largest amplitude in the spectrum information. Then, the effective value of the fundamental component can be calculated using the root mean square value. The effective value of the fundamental component is the amplitude of the fundamental current. After determining the fundamental component, this embodiment can determine the frequency of the fundamental wave by finding the position of the fundamental peak value in the spectrum information. At the same time, harmonic components are extracted from the spectrum information. Harmonic components are components in the signal with frequencies higher than the fundamental frequency. They usually appear in the form of integer multiples of the fundamental frequency. In this embodiment, the positions of all harmonic components can be found by traversing the spectrum information, and their amplitudes can be calculated.

[0062] In this embodiment, after obtaining the amplitude of the fundamental current and the amplitudes of each harmonic component, the harmonic distortion rate can be calculated. The harmonic distortion rate is an indicator that measures the magnitude of the harmonic components in a signal relative to the fundamental component. In this embodiment, the harmonic distortion rate is obtained by calculating the ratio of the sum of the squares of the amplitudes of all harmonic components to the square of the amplitude of the fundamental current, and then taking the square root. The larger the harmonic distortion rate, the more harmonic components there are in the signal, and the more severe the waveform distortion of the signal.

[0063] In some embodiments, obtaining the opening and closing position information of the switch switching section and the switch selection section specifically includes:

[0064] The fundamental current amplitude is compared with a preset overcurrent protection setting. If the fundamental current amplitude exceeds the overcurrent protection setting, an overcurrent abnormality is determined to exist.

[0065] The harmonic distortion rate is compared with a preset distortion threshold. If the harmonic distortion rate exceeds the distortion threshold, it is determined that there is a harmonic anomaly.

[0066] If the current value at the neutral point terminal is not equal to the vector sum and absolute value of the currents at all odd or even terminals, then an inter-stage short circuit fault is determined to exist.

[0067] If there is an overcurrent anomaly, harmonic anomaly, or inter-stage short circuit fault, the opening and closing position information of the switch switching section and the switch selection section is obtained.

[0068] 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, an overcurrent anomaly is determined. Simultaneously, the harmonic distortion rate is compared with a preset distortion threshold. If the harmonic distortion rate exceeds the distortion threshold, a harmonic anomaly is determined. Furthermore, this embodiment detects the current value at the neutral point lead-out terminal and compares it with the vector sum and absolute value of the currents at all odd or even terminals. If they are not equal, an inter-terminal short-circuit fault is determined. For example, this embodiment calculates that the sum of the currents at terminals H1 and H3 is 250A, and the sum of the currents at terminals H2 and H4 is also 250A. Then, this embodiment compares these two sums with the current at terminal H0. The current magnitude is compared. For example, if the current detected at terminal H0 is 280A, which is inconsistent with the calculated 250A, it indicates that there is an inter-stage short circuit fault in the switch switching section. 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 each position of the switch switching section. For example, between the N position and the N+1 position, this embodiment detected that the current suddenly dropped from 150A to 50A. This abnormal current change trend indicates that there is a mechanical jamming fault in the switch switching section. In addition, this embodiment also uses an electromagnetic current transformer to detect the current of each terminal to determine whether there is a broken wire. For example, the current detected at terminal H2 is 0A, which indicates that there is a CT broken wire fault in the switch switching section.

[0069] like Figure 3As shown, in this embodiment, the current detection points are defined as follows: Phase A, Phase B, and Phase C correspond to the three independent phases of the three-phase AC system; terminals H1, H2, H3, and H4 are the terminal markings on the connecting flange, where 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. Furthermore, this embodiment sets a preset overcurrent protection setting of Iset, which can be set according to 1.2 times the rated current. T is the delay threshold, representing the time the current continuously exceeds the rated current. The time window for triggering protection action after the overcurrent protection setting is defined as follows: for each terminal of each phase (H1, H2, H3, and H4), if the detected current value is greater than the overcurrent protection setting and the duration exceeds 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 command, drives the switching section to cut off the corresponding vacuum tube or isolation contact, and isolates the fault circuit to the converter transformer auxiliary oil tank. The execution priority of the protection action is related to the severity of the fault. For example, inter-phase short circuit (current deviation of terminal H0 exceeds the limit) takes precedence over single terminal overcurrent.

[0070] In this embodiment, upon detecting any of the following faults—overcurrent anomaly, harmonic anomaly, or inter-stage short circuit fault—the opening and closing position information of the switch switching section and the switch selection section is immediately acquired. Then, this embodiment utilizes a pre-established deep belief network model to diagnose the fault type and location. The specific process is as follows: First, the fundamental current amplitude is acquired, and it is determined whether the fundamental current amplitude is in a severely unbalanced state. If it is in an unbalanced state, the opening and closing position information of the switch switching section and the switch selection section is simultaneously acquired. Next, the current characteristic data and the opening and closing position information are input into the deep belief network model. This model performs feature extraction and pattern recognition on the input data and outputs a feature vector. Based on the analysis of the feature vector, the fault type is determined. Then, this embodiment combines the fault type and the opening and closing position information to determine the specific location of the fault. To improve diagnostic accuracy, this embodiment uses a support vector machine algorithm to perform secondary verification of the fault type and location, ultimately obtaining an accurate diagnostic result.

[0071] Specifically, this embodiment determines the fault type and its location based on the fault mode feature vector. The fault types include contact erosion, spring fatigue, and drive shaft jamming. Targeted maintenance instructions are generated based on the fault type and location, and the switch switching section is used to quickly disconnect the fault circuit via these instructions. This effectively confines the fault to the auxiliary oil tank of the converter transformer, preventing it from affecting equipment in the main oil tank. During fault diagnosis, if faults such as contact erosion, spring fatigue, or drive shaft jamming are identified, the corresponding fault severity is assessed, and relevant maintenance records are retrieved. When a contact erosion fault is diagnosed, this embodiment acquires the current data during contact operation and calculates the cumulative current impact value using an integral method. When the cumulative current impact value exceeds a preset cumulative current threshold, an alarm signal is immediately triggered. Based on the alarm signal, this embodiment combines the number of contact operations with the cumulative current impact value and uses a linear regression model to evaluate the degree of contact erosion. The evaluation results are matched with the actual operation data of the faulty contact to determine the erosion level and generate a contact erosion status diagnosis report. To improve the accuracy of prediction, this embodiment can use a random forest algorithm to optimize the erosion level model.

[0072] For spring fatigue failure, this embodiment captures raw displacement data through a spring displacement sensor and obtains smoothed displacement values ​​after filtering. The initial spring constant is calculated based on the smoothed displacement values. Then, the relationship between displacement and force is fitted using the least squares method to determine the spring constant. This embodiment can measure and statistically analyze the range of spring constant changes multiple times, calculate its average value and standard deviation. If the spring constant is lower than a preset threshold, the spring is determined to be in a fatigue failure state. This embodiment calculates the actual fatigue degree based on the percentage decrease in the spring constant and uses linear regression to fit the relationship between the spring constant and the actual fatigue degree to construct a fatigue degree model. Based on the fatigue degree model and the current spring constant, the remaining service life of the spring is determined. At the same time, this embodiment uses a multilayer perceptron to predict the future fatigue degree of the spring, trains the network using historical fatigue degree data, and outputs the prediction results.

[0073] For mechanical jamming faults in drive shafts, this embodiment automatically extracts the usage time and replacement cycle information of lubricating grease from the data storage unit when mechanical jamming is detected. Based on this information, it determines whether the lubricating grease has exceeded the preset replacement cycle threshold. If the lubricating grease exceeds the replacement cycle threshold, a lubricating grease replacement suggestion is generated. The lubricating grease replacement suggestion includes the replacement time and specific operating steps, such as cleaning the lubrication points and injecting new lubricating grease. Based on the updated maintenance records, the lubricating grease replacement cycle is recalculated, and a new maintenance plan is generated. Based on the new lubricating grease replacement cycle and maintenance plan, the maintenance strategy and monitoring frequency of the drive shaft are flexibly adjusted to ensure the timeliness of lubricating grease replacement and maintenance efficiency.

[0074] In summary, this embodiment preprocesses the acquired raw current signal. Preprocessing includes filtering to remove noise interference and periodicity determination to identify the periodicity of the data. Then, this embodiment uses Fast Fourier Transform (FFT) to obtain the spectral information of the raw current signal, thereby calculating the amplitude and frequency of the fundamental current. Next, based on preset overcurrent protection settings and harmonic distortion rate thresholds, and combined with the current opening and closing positions of the switch switching section and switch selection section, this embodiment comprehensively evaluates the current state. During this process, if a severe current amplitude imbalance is detected, the precise opening and closing positions of the switch switching section and switch selection section are immediately acquired and processed. Using current amplitude data and circuit breaker position information as input, a pre-trained deep belief network model is used for feature extraction and pattern recognition. The fault type is determined based on the feature vector output by the model. In this embodiment, by combining the identified fault type with the circuit breaker position information, the specific location of the fault can be determined. In order to improve the accuracy of diagnosis, this embodiment can use a support vector machine algorithm to perform secondary verification on the initially diagnosed fault type and location, and 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 in order to take corresponding maintenance measures.

[0075] To further improve the accuracy and stability of current measurement, the intelligent control unit also uses a support vector machine algorithm to classify the collected current measurement data to identify the characteristics of the current waveform. In this embodiment, by analyzing the changes in the current waveform, it can accurately determine whether there are potential problems such as harmonic interference. Based on the analysis results of the current waveform, the intelligent control unit will optimize the design of the secondary access point of the current transformer. By adjusting the position and connection method of the access point, the accuracy and stability of current measurement are significantly improved, thereby ensuring that the split-type on-load tap changer can perform excellently under various operating conditions.

[0076] This invention provides a split-type on-load tap changer with current transformers. The split-type on-load tap changer includes a switch switching section and a switch selection section. The switch switching section is connected to the switch selection section via a connecting flange, and several current transformers are disposed within the connecting flange. Multiple terminals are disposed on the surface of the connecting flange, with at least one terminal serving as a neutral point lead-out terminal, and the remaining terminals serving as odd / even terminals for different converter transformer voltage regulating columns. The neutral point lead-out terminal is directly connected to the neutral point circuit and not connected to the current transformers. The odd / even terminals of each converter transformer voltage regulating column are connected to the corresponding... The primary side of the current transformers is connected in series. The current transformers are connected to the intelligent control unit via optical fiber. Based on the original current signals of each converter transformer voltage regulating column collected by the current transformers, the intelligent control unit extracts current feature data using a fast Fourier transform algorithm; it acquires the opening and closing position information of the switch switching section and the switch selection section, and extracts fault mode feature vectors using a pre-trained deep belief network model based on the current feature data and the opening and closing position information; it generates maintenance instructions based on the fault mode feature vectors, and controls the switch switching section to disconnect the fault circuit through the maintenance instructions. Compared with existing technologies, this split-type on-load tap changer achieves real-time, high-precision monitoring of the current status during tap changer switching by physically isolating the switching section from the selection section and integrating a current transformer within the connecting flange. Combined with directional monitoring of the neutral point lead-out terminal and the odd / even terminals of the voltage regulating column, it effectively improves the accuracy and timeliness of fault detection. At the same time, the split structure limits the impact of faults to a localized area. This split-type on-load tap changer effectively solves the problems of fault detection and isolation in existing on-load tap changers, ensuring the safe and stable operation of the UHVDC transmission system.

[0077] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A split-type on-load tap changer with a current transformer, characterized in that: It includes a switch switching section and a switch selection section. The switch switching section is connected to the switch selection section via a connecting flange, and several current transformers are installed inside the connecting flange. The switch switching section is independently installed in the auxiliary oil tank of the converter transformer, and the switch selection section is independently installed in the main oil tank of the converter transformer. The auxiliary oil tank and the main oil tank of the converter transformer are completely separated by a physical isolation structure to control the arc effect generated during the tap position switching operation within the auxiliary oil tank of the converter transformer. The bottom of the switch switching section is connected to one end of the connecting flange via a set of current-carrying conductors, and the other end of the connecting flange is connected to the switch selection section via another set of current-carrying conductors, forming a current path across the oil tank; the surface of the connecting flange is provided with multiple terminals, at least one of which serves as a neutral point lead-out terminal, and the remaining terminals serve as odd and even terminals for different converter transformer voltage regulating columns, respectively. 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 the intelligent control unit via optical fiber, and the intelligent control unit is configured as follows: Based on the original current signals of each converter transformer voltage regulating column collected by the current transformer, the current feature data is extracted using the fast Fourier transform algorithm. Obtain the opening and closing position information of the switch switching section and the switch selection section, and extract the fault mode feature vector using a pre-trained deep belief network model based on the current feature data and the opening and closing position information. Based on the fault mode feature vector, a maintenance command is generated, and the fault circuit is cut off by controlling the switch switching part through the maintenance command.

2. A split-type on-load tap changer with a current transformer as described in claim 1, characterized in that: The switch switching section includes multiple switching switches, which are used to control the load switch to be turned off or on when the tap changer is switching positions. The switch selection section includes multiple tap selectors, which are used to pre-select a target tap position before switching to the current tap position.

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

4. A split-type on-load tap changer with a current transformer as described in claim 1, characterized in that: The switch switching section adopts a dual parallel structure to construct the inter-gear circuit between adjacent tap positions. The dual parallel structure includes a first branch and a second branch connected in parallel. The first branch is equipped 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 the 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. 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. 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 phased conduction of the second and third vacuum tubes, and to control the circulating current amplitude during the switching process through the transition resistor, so that no electric arc is generated during the tap position switching process.

5. A split-type on-load tap changer with a current transformer as described in claim 1, characterized in that: The top of the switch switching section is insulated from the top of the switch selection section via an oil-oil bushing.

6. A split-type on-load tap changer with a current transformer as described in 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 block.

7. A split-type on-load tap changer with a current transformer as described in claim 1, characterized in that, The current characteristic data includes at least the fundamental current amplitude, fundamental frequency, and harmonic distortion rate. The original current signals from each converter transformer voltage regulation column acquired by the current transformer are used to extract the current characteristic data using a fast Fourier transform algorithm, including: The original current signal is processed using a fast Fourier transform algorithm to obtain spectral information; The fundamental component is extracted from the spectrum information, and the effective value of the fundamental component is calculated to obtain the fundamental current amplitude. The fundamental frequency is determined based on the position of the fundamental peak in the spectrum information, and harmonic components are extracted from the spectrum information to calculate the amplitude of each harmonic component. The amplitudes of each harmonic component are compared with the amplitude of the fundamental current to calculate the harmonic distortion rate of the harmonic component relative to the fundamental current.

8. A split-type on-load tap changer with a current transformer as described in claim 7, characterized in that, The acquisition of the opening and closing position information of the switch switching section and the switch selection section includes: The fundamental current amplitude is compared with a preset overcurrent protection setting. If the fundamental current amplitude exceeds the overcurrent protection setting, an overcurrent abnormality is determined to exist. The harmonic distortion rate is compared with a preset distortion threshold. If the harmonic distortion rate exceeds the distortion threshold, it is determined that there is a harmonic anomaly. If the current value at the neutral point terminal is not equal to the vector sum and absolute value of the currents at all odd or even terminals, then an inter-stage short circuit fault is determined to exist. When there is an overcurrent anomaly, harmonic anomaly, or inter-stage short circuit fault, the current opening and closing position information of the switch switching section and the switch selection section is obtained. During this process, if the fundamental current amplitude is detected to be in a severely unbalanced state, the precise opening and closing position information of the switch switching section and the switch selection section is immediately collected.

Images