Method for transforming 10kV non-excitation transformer into on-load voltage regulating transformer and matched refitting assembly line

Abstract

The invention discloses a method for transforming a 10kV non-excitation transformer into an on-load voltage regulating transformer and a matched refitting assembly line, and relates to the technical field of transformers. According to the method, a tap switch unit is additionally arranged in a winding structure of an original excitation-free transformer, an insulation system is optimized, an intelligent control module is matched, on the premise that a transformer body iron core and an oil tank structure are not changed, the on-load voltage regulation function is achieved, and the problems that a traditional transformation scheme is high in cost and long in construction period are solved; and meanwhile, the requirements of the 10kV power distribution network on the voltage regulation precision and the power supply reliability are met.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and in particular to a method for converting a 10kV off-load transformer into an on-load tap-changing transformer and a corresponding conversion production line. Background Technology

[0002] In today's rapidly developing power distribution networks, voltage stability is crucial for ensuring power quality and the safe operation of equipment. 10kV off-load tap-changing transformers (also known as "no-load tap-changing transformers") have long been widely used in urban and rural power distribution networks due to their significant advantages, including simple structural design, low manufacturing cost, and convenient operation and maintenance. These transformers adjust the number of turns in the high-voltage winding through a tap changer located inside the transformer housing, thereby achieving limited-range regulation of the output voltage. However, a key operational limitation is that all tap changes must be performed manually on-site with the transformer completely de-energized and without load. This "power-off voltage regulation" mode is adequate for traditional industrial or agricultural power supply scenarios where the load is relatively stable and voltage quality requirements are not high.

[0003] However, with the transformation of the socio-economic structure and the upgrading of electricity user demands, the shortcomings of this traditional model have become increasingly prominent. In densely populated urban areas, electricity load exhibits typical diurnal peak-valley fluctuations. In emerging industries such as data centers, precision electronics manufacturing, biomedicine, and high-end laboratories, production equipment and R&D instruments have almost stringent requirements for the stability and purity of the power supply voltage. Even a momentary voltage drop or exceeding of limits can lead to batch scrapping, data loss, or equipment damage, resulting in significant economic losses. Faced with these modern scenarios characterized by "large load fluctuations and high voltage quality requirements," the inherent defect of non-excitation voltage regulating transformers—requiring "power outage adjustment"—makes them completely incapable of handling real-time, dynamic voltage regulation tasks, becoming a bottleneck restricting the improvement of power supply quality.

[0004] The most straightforward traditional solution to this challenge is to replace the existing off-load tap-changing transformers with on-load tap-changing transformers that feature "on-line voltage regulation." On-load tap-changing transformers are equipped with complex and precise on-load tap changers, which can safely and smoothly change the number of winding turns under load through an independent switching mechanism (typically including a selector, a switching switch, and a transition circuit). This achieves automatic and continuous adjustment of the output voltage, perfectly meeting the needs of high power quality scenarios. However, this solution is extremely costly. Purchasing a brand-new on-load tap-changing transformer typically costs more than 80% of the total cost of replacing a conventional transformer of the same capacity, and may even double. Even more challenging is the fact that replacing the transformer itself is a large-scale project, involving multiple stages such as the removal of the old equipment, the installation of the new equipment, testing, and system integration. The entire process often requires a planned power outage of 24 to 48 hours. This is unacceptable for modern commercial and industrial users who demand "uninterrupted power supply," severely impacting power reliability and user experience.

[0005] Therefore, a more economical and feasible technical approach—the "on-load conversion from off-load to on-load" field retrofit technology—has emerged. This technology aims to preserve the original transformer body (core and windings) and tank casing, by removing the existing off-load tap changer and installing a completely new on-load tap changer and its intelligent drive control mechanism on the transformer body. It also modifies the related leads, insulation, and sealing structures, thus giving the old transformer the ability to "regulate voltage without power interruption." Theoretically, this can save significant equipment purchase costs and reduce power outage time to the 8-12 hours required for the retrofit construction.

[0006] However, after years of engineering practice, existing modification technologies have revealed two major shortcomings, which seriously restrict the reliability and safety of their widespread adoption: The first issue concerns the structural compatibility and electrical compatibility between the tap changer and the existing windings. Upgrading is not simply a matter of "replacing the old switch with a new one." On-load tap changers place much higher demands on the transformer windings regarding tap lead-out methods, insulation distances, mechanical strength, and transient overvoltage withstand capabilities during switching compared to off-load tap changers. Existing upgrade solutions often apply a "standardized" approach, failing to fully consider the differences in the original transformer winding design. For example, the taps of the original off-load tap changer may be directly led out from inside the windings, resulting in insufficient insulation margin. Forcibly connecting such a frequently operating, arc-generating on-load tap changer can easily lead to localized aging and deterioration of the insulation at the tap lead or between winding turns under the combined effects of long-term electrical, thermal, and mechanical stress, ultimately causing a major accident involving insulation breakdown. This inherent compatibility issue is a potentially fatal hidden danger within the upgraded transformer.

[0007] Secondly, the lack of targeted high standards and testing systems in the modification process is a problem. Transformer modification is a complex systemic project, especially involving the drilling, welding, sealing, and rearranging of complex internal wiring on the existing tank. Currently, the industry lacks unified and precise process specifications, sealing standards, and acceptance testing standards for the special operation of "converting from no-load to on-load operation." Construction quality highly depends on the technical level and sense of responsibility of on-site personnel, leading to a high degree of arbitrariness. This directly results in two common consequences: first, poor sealing reliability, with oil leakage easily occurring at new interfaces such as new switch flanges, shafts, and lead bushings, which not only pollutes the environment but also threatens the transformer insulation due to oil level drops; second, insufficient voltage regulation accuracy and control stability. Due to insufficient installation accuracy, idle or jammed transmission mechanisms, and failure to accurately calibrate and match the overall electrical parameters and control system after modification, the modified transformer may be able to operate, but the voltage regulation accuracy is substandard, or frequent faults such as failure to operate, malfunction, and continuous operation occur. Statistics show that renovation projects lacking strict guidelines have a failure rate of over 30% in the later stages, resulting in problems such as oil leakage or pressure regulation failure. This significantly reduces the expected economic benefits of the renovation and undermines user confidence.

[0008] In summary, there is an urgent need to upgrade and retrofit 10kV unexcited transformers, but the existing technical approaches have significant deficiencies in the core aspects of "switch-winding" matching and "process-testing" standardization. Summary of the Invention

[0009] The purpose of this invention is to solve the problem of difficulty in modifying existing technologies.

[0010] The specific solution of this invention is: a method for converting a 10kV off-load transformer into an on-load tap-changing transformer, comprising the following steps: (1) Remove the 10kV no-excitation transformer switch: Remove the 10kV no-excitation transformer switch, seal and weld the original switch mounting hole, use cold pressing or soldering process for the original winding joint, install O-type connectors, open the low-voltage side of the 10kV no-excitation transformer, install the load tap changer control connector in the test hole, which is suitable for dyn11 and yyn0 connection methods; (2) Install a new switch: Open an adapter hole in the transformer core clamp and fix the 10kV on-load tap changer in the hole. The rated current of the 10kV on-load tap changer is not less than 1.2 times the rated current of the transformer. Connect the switch terminals to the high-voltage winding group in step (1) through the copper busbar. Seal the switch body and the oil tank with a fluororubber sealing ring. (3) Insulation reinforcement: Two to three layers of epoxy resin glass cloth tube are wrapped between the tap changer and the main insulation of the winding to form strong insulation. Then, a polytetrafluoroethylene insulating partition is added between the tap changer lead and the tank wall. The insulation distance between the epoxy resin glass cloth tube and the polytetrafluoroethylene insulating partition is not less than 15mm. (4) Control integration: An intelligent voltage regulator is installed on the transformer control cabinet. The input end of the controller is connected to the voltage transformer and current transformer signals on the secondary side of the transformer, and the output end is connected to the drive mechanism of the on-load tap changer to realize the function of automatically adjusting the tap position according to the secondary side voltage. (5) Testing: Vacuum oil injection is performed on the switch wiring. After oil injection, the switch is left to stand for 24 hours. Insulation resistance test, transformation ratio test and temperature rise test are performed in sequence.

[0011] In practice, the model of the intelligent voltage regulator is SYYZ-5A.

[0012] This invention also relates to a method for modifying a production line and converting a 10kV off-load transformer into an on-load tap-changing transformer, comprising a conveyor belt, at least one assembly station arranged along the conveyor belt, and a robotic arm, wherein the robotic arm drives the pre-modification equipment on the conveyor belt to the assembly station; wherein the robotic arm includes three degrees of freedom conforming to the Cartesian coordinate system, and the power output terminal of the robotic arm is provided with a clamping claw with a clamping width of 5-15 cm; the assembly station.

[0013] In a specific implementation, the assembly table includes at least two turntables, one of which is responsible for the rotation of the workpiece being modified, and the other turntable is responsible for the rotation of the modification tool.

[0014] In practice, the turntable is equipped with a lifting component that drives its raising and lowering.

[0015] In practice, an extension plate is installed on the turntable, and the modified new equipment is mounted on the extension plate.

[0016] In practice, the conveyor belt is provided with inverted V-shaped protrusions.

[0017] The beneficial effects of this invention are as follows: A complete solution is formed, from winding modification, switch selection, insulation design to intelligent control, which greatly reduces the cost of modification (only 30%-40% of the cost of replacement) and shortens the power outage period to less than 8 hours; The matching modification production line improves modification efficiency and provides a flexible and independent modification space for modification, ensuring structural stability and good sealing performance. Attached Figure Description

[0018] Figure 1This is a three-dimensional structural diagram of the transformer portion of the present invention; Figure 2 This is a perspective view of the modified production line in this invention; Figure 3 This is a front view of the modified production line in this invention; Figure 4 This is a top view of the modified production line in this invention; Figure 5 This is a left view of the modified production line in this invention; Figure 6 This is a right view of the modified production line in this invention; Figure 7 This is a perspective view of the modified production line from another angle in this invention; Figure 8 yes Figure 1 The front view of the structure shown; Figure 9 yes Figure 1 Top view of the structure shown; Figure 10 This is the main view of the modified equipment; In the attached diagram: 1. Driven component; 2. Driving component; 3. Turntable; 4. Modified component; 5. Conveyor belt; 6. Support platform for the robotic arm; 7. Lifting component; 8. Protrusion; 9. Claw; 10. Safety grille; 11. Wiring contact; 12. Dry-type transformer tank; 13. Transformer assembly hole; 14. On-load tap changer; 15. Intelligent tap changer controller; 16. Low-voltage side opening; 17. Off-grid tap changer removed during the modification; 18. O-ring. Detailed Implementation

[0019] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0020] Example 1 A method for converting a 10kV off-load transformer into an on-load tap-changing transformer, see [link to relevant documentation]. Figure 1 The design includes the following steps: (1) Remove the 10kV no-excitation transformer switch: Remove the 10kV no-excitation transformer switch, seal and weld the original switch mounting holes, use cold pressing or soldering process for the original winding joints, install O-type connector 18, open the low-voltage side of the 10kV no-excitation transformer, install the load tap changer control plug in the test hole, which is suitable for dyn11 and yyn0 connection methods; (2) Install the new switch: Open the adapter hole in the transformer core clamp and fix the 10kV on-load tap changer in the hole position, that is, the on-load tap changer 14 is in the dry transformer tank 12, wherein the rated current of the 10kV on-load tap changer is not less than 1.2 times the rated current of the transformer; connect the switch terminal to the high voltage winding tap changer wound in step 1 through the copper busbar, and seal the switch body and the tank with a fluororubber sealing ring. (3) Insulation reinforcement: Two to three layers of epoxy resin glass cloth tube are wrapped between the tap changer and the main insulation of the winding to form strong insulation. Then, a polytetrafluoroethylene insulating partition is added between the tap changer lead and the tank wall. The insulation distance between the epoxy resin glass cloth tube and the polytetrafluoroethylene insulating partition is not less than 15mm. (4) Control integration: An intelligent voltage regulator 15 is installed on the transformer control cabinet. The input end of the controller is connected to the voltage transformer and current transformer signals on the secondary side of the transformer, and the output end is connected to the drive mechanism of the on-load tap changer to realize the function of automatically adjusting the tap position according to the secondary side voltage. (5) Testing: Vacuum oil injection is performed on the switch wiring. After oil injection, the switch is left to stand for 24 hours. Insulation resistance test, transformation ratio test and temperature rise test are performed in sequence.

[0021] The model of the intelligent voltage regulator 15 is SYYZ-5A.

[0022] A method for modifying a production line to convert a 10kV off-load transformer into an on-load tap-changing transformer includes a conveyor belt 5, at least one assembly table and a robotic arm arranged along the conveyor belt 5, wherein the robotic arm drives the original equipment on the conveyor belt to the assembly table; wherein the robotic arm includes three degrees of freedom conforming to the Cartesian coordinate system, and the power output terminal of the robotic arm is provided with a clamping claw with a clamping width of 5~15 cm; the assembly table.

[0023] The assembly table includes at least two turntables 3, one of which is responsible for the rotation of the workpiece being modified, and the other turntable 3 is responsible for the rotation of the modification tool.

[0024] The turntable 3 is equipped with a lifting component 7 that drives its lifting and lowering.

[0025] An extension plate is installed on the turntable 3, and the modified new equipment is mounted on the extension plate. The conveyor belt 5 is provided with an inverted V-shaped protrusion.

[0026] The installation power unit for conveyor belt 5 uses standard components and is not shown. During the operation of the processing workbench, when the transformer needs modification, it moves along with conveyor belt 5. The robotic arm assists the transformer in moving from conveyor belt 5 to the assembly table. After it reaches its position, lifting component 7 is raised. The transformer and other equipment besides lifting component 7 have no support relationship. The lifting component 7 can be steered by the transmission mechanism at the bottom of the lifting component 7. The transmission mechanism here can be a belt drive mechanism, or a gear or friction wheel drive. There are two lifting components 7; the other one is for installing the modification tools used in the assembly, such as the on-load tap changer 14. The extension plate is placed on the lifting component 7 where the modification tools are installed in the working state.

[0027] This product includes multiple workstations, enabling efficient assembly line processing.

[0028] The specific installation process of this invention also includes winding testing steps, including: 1. Disassembling the original tap changer on the transformer, and winding one terminal block at each of the 1 / 5, 2 / 5, 3 / 5, and 4 / 5 positions of the high-voltage winding (rated voltage 10kV, 380 turns). Each tap has 19 turns (corresponding to a voltage regulation range of 2.5%). The conductor is a 120mm² copper conductor consistent with the original winding, and the tap lead is a Φ8mm copper rod wrapped with a 0.5mm thick polyimide film; 2. Tap changer installation: Selecting a vacuum on-load tap changer of model SYYZ-5A (rated current 630A, vacuum degree 5×10). -5A Φ280mm mounting hole is drilled on the side wall of the oil tank 300mm from the top. The switch is fixed by a flange, and a 10mm thick fluororubber sealing ring is installed between the flange and the oil tank. M16 bolts are tightened evenly (torque 35N·m). Then, a 60mm² copper busbar is used to connect the five terminals of the switch to the winding tap changer. A Φ30mm epoxy resin glass cloth tube is fitted on the surface of the copper busbar. 3. Insulation reinforcement: Three layers of epoxy resin glass cloth tube (total thickness 6mm) are wrapped between the tap changer and the main insulation of the winding. A 20mm thick polytetrafluoroethylene partition is installed between the tap changer lead and the oil tank wall to ensure that the lead and the grounding body are in good condition. The insulation distance is not less than 18mm; all insulation parts of the modified parts are dried at 120℃ / 4h to remove moisture; 4. Control module integration: Install a YK-100 intelligent voltage regulator controller 15 in the control cabinet, connect the voltage transformer (400V / 100V ratio) and current transformer (1000A / 5A ratio) signals on the secondary side (0.4kV), set the upper limit of voltage to 1.05Un (420V) and the lower limit to 0.95Un (380V), and connect the controller output to the electric drive mechanism of the tap changer through a cable to realize automatic tap switching when the voltage exceeds the limit. 5. Sealing and Testing: Vacuum oil filling was performed on the modified parts (vacuum degree -0.095MPa, oil filling rate 50L / h). After oil filling, the parts were allowed to stand for 24 hours, and the following tests were conducted sequentially: - Insulation resistance test: Using a 2500V megohmmeter, the high-voltage to ground insulation resistance was measured to be 1500MΩ, which meets the requirements; - Turns ratio test: The turns ratio was measured at each tap position, with errors of +0.2%, 0%, -0.1%, and -0.3%, all ≤±0.5%; - Temperature rise test: After running with a 500kVA rated load for 4 hours, the winding temperature rise was measured to be 58K, which is below the limit of 65K. After the modification, the transformer was put into operation. Within the load fluctuation range (200-500kVA), the secondary voltage remained stable at 380-420V, the voltage regulation response time was ≤10s, and there were no oil leaks or insulation faults after 6 months of continuous operation, meeting the power supply requirements of the distribution network.

[0029] The beneficial effects of this embodiment are as follows: 1. Cost advantage: The renovation cost is about 60,000 yuan, which is only 33% of the cost of replacing the same type of on-load tap-changing transformer (180,000 yuan). A single unit can save more than 120,000 yuan; 2. Efficiency advantage: The renovation downtime is only 8 hours, which is 83% shorter than the replacement plan (48 hours), reducing downtime losses; 3. Performance advantage: Through vacuum arc-extinguishing switch and reinforced insulation design, the voltage regulation accuracy of the renovated transformer is ≤±0.5%, the failure rate is less than 5%, and it supports remote monitoring, which is in line with the development trend of smart distribution networks.

[0030] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for converting a 10kV off-load transformer into an on-load tap-changing transformer, characterized in that, Includes the following steps: (1) Remove the 10kV no-excitation transformer switch: Remove the 10kV no-excitation transformer switch, seal and weld the original switch mounting hole, use cold pressing or soldering process for the original winding joint, install the O-type terminal lug (18), open the low-voltage side of the 10kV no-excitation transformer, install the load tap changer control plug in the test hole, which is suitable for dyn11 and yyn0 connection methods; (2) Install a new switch: Open an adapter hole in the transformer core clamp and fix the 10kV on-load tap changer in the hole. The rated current of the 10kV on-load tap changer shall not be less than 1.2 times the rated current of the transformer. Connect the switch terminals to the high-voltage winding group connector wound in step 1 through the copper busbar. Seal the switch body and the oil tank with a fluororubber sealing ring. (3) Insulation reinforcement: 2-3 layers of epoxy resin glass cloth tube are wrapped between the tap and the main insulation of the winding to form strong insulation. Then, a polytetrafluoroethylene insulating partition is added between the tap switch lead and the oil tank wall. The insulation distance between the epoxy resin glass cloth tube and the polytetrafluoroethylene insulating partition is not less than 15mm. (4) Control integration: An intelligent voltage regulator (15) is installed on the transformer control cabinet. The input end of the controller is connected to the voltage transformer and current transformer signals on the secondary side of the transformer, and the output end is connected to the drive mechanism of the on-load tap changer to realize the function of automatically adjusting the tap position according to the secondary side voltage. (5) Testing: Vacuum oil injection is performed on the switch wiring. After oil injection, the switch is left to stand for 24 hours. Insulation resistance test, transformation ratio test and temperature rise test are performed in sequence.

2. The method for converting a 10kV off-load transformer into an on-load tap-changing transformer as described in claim 1, characterized in that: The model of the intelligent voltage regulator (15) is SYYZ-5A.

3. A method for modifying an assembly line by converting a 10kV off-load transformer into an on-load tap-changing transformer, characterized in that: The device includes a conveyor belt (5), at least one assembly table and a robotic arm arranged along the conveyor belt (5), wherein the robotic arm drives the pre-modification equipment on the transmission belt to the assembly table; wherein the robotic arm includes three degrees of freedom conforming to the Cartesian coordinate system, and the power output terminal of the robotic arm is provided with a gripper with a gripping width of 5 to 15 centimeters.

4. The method for converting a 10kV off-load transformer into an on-load tap-changing transformer as described in claim 3, characterized in that: The assembly table includes at least two turntables (3), one of which is responsible for the rotation of the workpiece being modified, and the other turntable (3) is responsible for the rotation of the modification tool.

5. The method for converting a 10kV off-load transformer into an on-load tap-changing transformer as described in claim 3, characterized in that: The turntable (3) is equipped with a lifting component (7) that drives it to rise and fall.

6. The method for converting a 10kV off-load transformer into an on-load tap-changing transformer as described in claim 3, characterized in that: An extension plate is installed on the turntable (3) on-site, and the modified new equipment is placed on the extension plate.

7. The method for converting a 10kV off-load transformer into an on-load tap-changing transformer as described in claim 3, characterized in that: The conveyor belt (5) is provided with inverted V-shaped protrusions.

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