Method for regulating voltage ratio and impedance of 500kv single-phase autotransformer flexible spare parts

Abstract

The application discloses a 500-kilovolt single-phase self-coupling transformer flexible spare voltage transformation ratio and impedance combined regulation method, relates to the technical field of power transformers, and is used for solving the problem that the existing voltage transformation ratio and impedance are not matched. The method comprises the following steps: constructing a simulation model; based on the simulation model, respectively simulating transformation ratio deviation and impedance deviation, and determining an initial safety threshold according to a simulation result; constructing an adaptive safety boundary; taking the adaptive safety boundary as a safety constraint, constructing a multi-target optimization framework, and obtaining a short-circuit impedance safety threshold; and generating a combined regulation instruction of a voltage regulation winding and an impedance regulation winding according to the voltage transformation ratio safety threshold and the short-circuit impedance safety threshold. The safety threshold is determined through simulation, the combined regulation instruction is generated through multi-target optimization and adaptive boundary constraint, the voltage transformation ratio and the short-circuit impedance can meet the standards at the same time after the flexible spare is replaced.

Description

Technical Field

[0001] This invention relates to the field of power transformer technology, and more particularly to a method for combined adjustment of voltage ratio and impedance of flexible spare parts for a 500 kV single-phase autotransformer. Background Technology

[0002] As a key core piece of equipment in a hub substation, the 500kV transformer plays a vital role in power transmission and voltage transformation within the power grid. Its reliable operation directly impacts the safety and stability of the regional power grid. Currently, most 500kV transformers are single-phase autotransformers. When one of these transformers experiences a major defect or fault that cannot be repaired on-site, the transformer must be returned to the factory for maintenance. Excessive maintenance periods can severely affect the safe operation of the power grid. Therefore, if a transformer fails and needs to be taken out of service, a backup replacement method is typically considered to restore overall operation. This effectively shortens the main transformer outage time and alleviates power supply pressure in the area.

[0003] Due to differences in manufacturing era and design parameters among different transformers, it is difficult to ensure that the spare phase and the original operating transformer are completely identical in core parameters such as voltage ratio and short-circuit impedance. In actual operation, it is often impossible to uniformly configure the spare transformer due to parameter differences. When a spare phase with inconsistent parameters is used to replace the faulty phase, it will lead to an asymmetry in the three-phase parameters of the main transformer. This asymmetry in three-phase parameters will generate circulating current in the delta-connected three-phase windings. Excessive circulating current not only affects the operating characteristics and load capacity of the transformer, but may also pose safety risks.

[0004] Therefore, developing a method to jointly adjust the voltage ratio and impedance of flexible spare parts of a single-phase autotransformer while meeting the circulating current safety margin has become an urgent problem to be solved. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a method for jointly adjusting the voltage ratio and impedance of flexible spare parts of a 500 kV single-phase autotransformer. Based on three-phase transmission line modeling, circulating current multi-parameter constraint analysis, and simulation verification, this method can jointly adjust the voltage ratio and impedance of flexible spare parts of a single-phase autotransformer while meeting the safety margins of multiple parameters such as circulating current.

[0006] This invention is achieved using the following technical solution: A method for jointly adjusting the voltage ratio and impedance of a 500 kV single-phase autotransformer flexible spare part includes the following steps: Construct a power system simulation model that includes a 500 kV autotransformer; Based on the simulation model, the turns ratio deviation and impedance deviation are simulated respectively, and the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold are determined according to the simulation results. An adaptive safety boundary is constructed, wherein the adaptive safety boundary is a circulating safety limit that is dynamically adjusted based on multiple operating state parameters; Using the adaptive safety boundary as a safety constraint, a multi-objective optimization framework is constructed to optimize the initial safety threshold of the short-circuit impedance, thereby obtaining the short-circuit impedance safety threshold. Based on the voltage ratio safety threshold and the short-circuit impedance safety threshold, a joint adjustment command for the voltage regulating winding and the impedance regulating winding is generated. The joint adjustment command is used to control the switching of the tap position of the voltage regulating winding and the impedance regulating winding so that the voltage ratio and short-circuit impedance of the flexible spare part simultaneously meet the safety requirements.

[0007] By determining the safety threshold through simulation and generating joint adjustment commands, the automatic joint adjustment of the voltage transformation ratio and short-circuit impedance of flexible spare parts is realized, fundamentally avoiding the problem of excessive circulating current caused by parameter mismatch.

[0008] Simulations were performed on the turns ratio deviation and impedance deviation respectively. Based on the simulation results, the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold were determined, including: A set of scanning sequences containing multiple preset turns ratio deviation gradient values ​​is input for simulation, and circulating current parameters are extracted from each simulation result. The voltage turns ratio safety threshold is determined based on the circulating current parameters. The turns ratio deviation is fixed to the voltage turns ratio safety threshold. A set of scanning sequences containing multiple preset impedance deviation gradient values ​​is input for simulation. The circulating current parameters in each simulation result are extracted, and the initial safety threshold of the short-circuit impedance is determined based on the circulating current parameters.

[0009] By inputting a preset deviation gradient scanning sequence for simulation, the safe threshold range of voltage transformation ratio and short-circuit impedance was quantitatively determined, providing clear and reproducible constraint boundaries for subsequent joint regulation.

[0010] Furthermore, the circulating current parameter is defined as the circulating current ratio, and a quantifiable safety margin evaluation index is established, providing an objective and unified calculation basis for the determination of the safety threshold. The circulating current parameter is the circulating current ratio, which is the ratio of the effective value of the zero-sequence circulating current in the low-voltage side circuit to the rated current of a single phase in the low-voltage winding.

[0011] To limit the specific structure and parameters of the simulation model, ensure that the simulation results can realistically reflect the electromagnetic transient characteristics of the actual system, and improve the accuracy and reliability of the safety threshold determination, the simulation model includes: The transformer model adopts a three-phase, three-winding structure, with a rated voltage of 525 / 230 / 36kV, a capacity of 334MVA, and a connection method of YNa0d11. System power supply model: Ideal three-phase power supply with infinite capacity and voltage level of 500kV; Load model: Both the 230kV side and the 36kV load adopt the equivalent RLC model with R=1Ω, L=0.1H, C=5uF; Line model: A Π-shaped equivalent model with a length of 1 kilometer is adopted; Monitoring module: Real-time monitoring of circulation values; The multiple operating status parameters include at least circulation, oil temperature, hot spot temperature, dissolved gas information in oil, load rate, power factor, and system short-circuit capacity.

[0012] The adaptive safety boundary is the product of multiple influencing factors, satisfying: , in, =[ , , , , ]T, Let T represent the state vector, and T be the transpose of the vector. Based on the basic circulation limit, The temperature decay factor, T For temperature, Oil temperature This is an estimate of the hotspot temperature. Insulation aging degradation factor, Let be the vector of dissolved gas concentrations in the oil. For load condition factor, For load rate, For power factor, For the system strength factor, This refers to the system short-circuit capacity. By constructing an adaptive safety boundary in the form of a product of multiple influencing factors, the circulating current safety limit can be dynamically adjusted according to operating conditions such as oil temperature, load rate, and system short-circuit capacity, which is more in line with engineering practice than a fixed threshold.

[0013] The multi-objective optimization framework optimizes multiple performance objectives, including: maximizing the fit of the impedance adjustment range to the operating transformer, maximizing the robustness margin of the impedance adjustment range under the worst operating conditions, and minimizing the overall cost associated with the impedance adjustment range. By simultaneously optimizing the three performance objectives of fit, robustness margin, and overall cost, it overcomes the shortcomings of traditional methods that have single or vague objectives, and achieves the selection of the optimal impedance adjustment range that balances economy and safety.

[0014] The computation of the multi-objective optimization framework satisfies: , in, Represents the target vector. To ensure the impedance adjustment range is well-suited for use with transformers in operation, This represents the total cost associated with the impedance adjustment range, including the manufacturing cost of the adjustment device and the expected loss cost. To maximize the robustness margin of the impedance adjustment range under the worst operating conditions, and These are the minimum and maximum short-circuit impedance values ​​that flexible spare parts can achieve, respectively. This indicates the impedance adjustment range to be optimized. Indicates the circulation value. and These represent the 5th and 95th percentiles of the impedance statistics for transformers in operation in the target area, respectively. Represents a time variable. This represents the state vector. By introducing upper and lower limits for the adjustable impedance range and quantile constraints from the actual impedance statistics of operating transformers, we ensure that the optimization solution is both within the range achievable by the physical hardware and meets the actual engineering needs of the target region.

[0015] The joint control command includes: Control the switching of the tap changer winding to determine whether the short-circuit impedance is within the short-circuit impedance safety threshold range, provided that the voltage ratio requirement is met. If the condition is not exceeded, output a completion adjustment signal; If the limit is exceeded, the tap position of the control impedance regulating winding is switched, and it is determined whether the safety requirements of voltage ratio and short-circuit impedance are met simultaneously. If the condition is met, then output the adjustment completion signal; Otherwise, the voltage regulating winding adjustment command is regenerated, and the above judgment and control steps are repeated until both requirements are met. Through the joint adjustment logic of "adjusting voltage first, then impedance, and iterating in a loop if the requirements are not met", the coordinated achievement of the two coupled parameters of voltage ratio and short-circuit impedance is realized, avoiding the problem of one parameter exceeding the limit due to adjusting one parameter alone.

[0016] To optimize the adjustment path, reduce the number of iterations, and improve the execution efficiency of the joint adjustment, the joint adjustment command uses a voltage regulating winding with multiple taps to fine-tune the voltage ratio and coarsely adjust the short-circuit impedance. When the short-circuit impedance does not meet the safety requirements, the impedance regulating winding is used to fine-tune the short-circuit impedance. The fine-tuning range of the voltage ratio is limited to within 20% of the simulated safe threshold range of the voltage ratio, and the coarse-tuning range of the short-circuit impedance is limited to within the simulated safe threshold range of the short-circuit impedance.

[0017] The flexible spare parts for the 500 kV single-phase autotransformer include a core, series winding, common winding, voltage regulating winding, low-voltage winding, and impedance regulating winding. The low-voltage winding is located between the main column of the iron core and the voltage regulating winding, the common winding is located between the voltage regulating winding and the series winding, the series winding is located on the outermost side of the iron core, and the impedance regulating winding is located on the side column of the iron core. The end of the series winding is connected to the beginning of the common winding via a voltage regulating winding, and the end of the common winding is connected to the beginning of the impedance regulating winding. The series winding has a centrally input structure, including an upper series winding and a lower series winding arranged in parallel; The voltage regulating winding is equipped with several taps to adjust the voltage on the medium-voltage side and to change the short-circuit impedance of the transformer synchronously during the voltage ratio adjustment process. The impedance regulating winding is provided with several taps. By switching the connection positions of the end of the common winding and different taps of the impedance regulating winding, the short-circuit impedance of the transformer can be adjusted, and the voltage ratio of the transformer can be changed synchronously during the impedance adjustment process.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, through simulation analysis, pre-determines the influence of voltage ratio and impedance deviation on multiple parameters such as circulating current, and determines the safety threshold range. This provides clear constraint boundaries for the actual adjustment of flexible spare parts, effectively avoiding excessive circulating current and voltage imbalance caused by excessive parameter mismatch in flexible spare parts. A joint adjustment strategy of "coarse adjustment of the voltage regulating winding and fine adjustment of the impedance regulating winding" is adopted. After each adjustment, a safety threshold is determined and cyclically adjusted to ensure that the final tap position simultaneously meets the dual requirements of voltage ratio and short-circuit impedance. This significantly improves the compatibility accuracy and replacement success rate of spare transformers with the parameters of operating transformers. Through a technical architecture of "simulation-predetermined thresholds + adaptive safety boundaries + multi-objective optimization + joint adjustment commands," automated and coordinated compliance of the voltage ratio and short-circuit impedance of flexible spare parts under coupled constraints is achieved. While ensuring the safety margin of the power grid, this improves the compatibility success rate and replacement efficiency of spare parts with transformers of different parameters. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for jointly adjusting the voltage ratio and impedance of a 500 kV single-phase autotransformer flexible spare part according to the present invention. Figure 2 This is a flowchart of the method for joint adjustment of voltage ratio and impedance of flexible spare parts for a 500 kV single-phase autotransformer in Example 1. Figure 3 This is the implementation process of voltage ratio and short-circuit impedance mismatch analysis in Example 1 using a 500kV transmission system model; Figure 4 This is a waveform diagram of the low-voltage side triangular circulating current when the low-voltage side voltage ratio deviates by 0.5% in the embodiment. The horizontal axis represents time, and the vertical axis represents the low-voltage side triangular circulating current in kA.

[0020] Figure 5 This is a waveform diagram of the low-voltage side triangular circulating current when the high-low short-circuit impedance deviation is 0.5% in the embodiment. The horizontal axis represents time, and the vertical axis represents the low-voltage side triangular circulating current in kA.

[0021] Figure 6 This is a schematic diagram of an actual 500kV single-phase autotransformer flexible spare part transformer model. Detailed Implementation

[0022] The present invention will now be described in more detail with reference to the accompanying drawings. It should be noted that the following description of the present invention with reference to the accompanying drawings is merely illustrative and not restrictive. Various embodiments can be combined with each other to form other embodiments not shown in the following description.

[0023] Example 1 Example 1 provides a method for joint adjustment of voltage ratio and impedance of flexible spare parts for a 500 kV single-phase autotransformer. The aim is to determine the safety thresholds of voltage ratio and short-circuit impedance through simulation, establish an adaptive safety boundary based on multiple operating state parameters, and comprehensively optimize the impedance threshold using multi-objective optimization. Finally, a joint adjustment command is generated to control the voltage regulating winding and impedance regulating winding to automatically switch the tap position according to the strategy of "adjusting voltage first and then adjusting impedance, and iterative cycle", so that the two mutually coupled parameters meet the standards at the same time, and solve the problem of excessive circulating current caused by parameter mismatch of flexible spare parts.

[0024] Please refer to Figure 1 As shown, this invention addresses the technical problem of three-phase parameter asymmetry and excessive circulating current caused by the inconsistency between the voltage ratio and short-circuit impedance of the 500kV single-phase autotransformer when replacing a faulty phase with a flexible spare part, which is due to the inconsistency between the voltage ratio and short-circuit impedance and the original operating transformer parameters. The invention proposes a joint adjustment method.

[0025] This method first establishes a power system simulation model based on the PSCAD platform. Simulations are performed by inputting scanning sequences of voltage ratio deviation and impedance deviation to determine the voltage ratio safety threshold and the initial safety threshold of short-circuit impedance, respectively. Based on this, an adaptive safety boundary is constructed, dynamically adjusted by multiple operating state parameters such as oil temperature, hot spot temperature, dissolved gas in the oil, load factor, power factor, and system short-circuit capacity. Using this boundary as a safety constraint, a multi-objective optimization framework is established to further optimize the initial safety threshold of short-circuit impedance, resulting in a short-circuit impedance safety threshold that balances adaptability, robustness margin, and overall cost. Finally, a joint adjustment command is generated based on the two safety thresholds. Following a strategy of "first the voltage regulating winding, then the impedance regulating winding, and iteratively switching if not satisfied," the tap positions of the two windings are controlled to ensure that both the voltage ratio and short-circuit impedance simultaneously meet safety requirements.

[0026] The entire adjustment process is executed automatically by the control system without manual intervention. This method effectively solves the technical challenge of the mutual coupling effect between voltage ratio and short-circuit impedance during the adjustment process, significantly improves the compatibility rate of flexible spare parts with transformers of different parameters in operation, and ensures the safe and stable operation of the power system after replacement.

[0027] Based on the above principles, please refer to Figure 2 As shown, a method for jointly adjusting the voltage ratio and impedance of a 500 kV single-phase autotransformer flexible spare part includes the following steps: S1. Construct a power system simulation model that includes a 500 kV autotransformer; The simulation model in S1 in this embodiment is constructed using the PSCAD platform. Please refer to... Figure 3 The circuit model shown, the simulation model includes: The transformer model adopts a three-phase, three-winding structure, with a rated voltage of 525 / 230 / 36kV, a capacity of 334MVA, and a connection method of YNa0d11. System power supply model: Ideal three-phase power supply with infinite capacity and voltage level of 500kV; Load model: Both the 230kV side and the 36kV load adopt the equivalent RLC model with R=1Ω, L=0.1H, C=5uF; Line model: A Π-shaped equivalent model with a length of 1 km is adopted. For specific values, please refer to the power system design manual. Monitoring module: Real-time monitoring of circulation values.

[0028] According to DL / T 572 "Operating Procedures for Power Transformers" and GB / T 15543 "Power Quality Three-Phase Voltage Imbalance" standards, the standard circulating current ratio for safety margin should be set at ≤5%.

[0029] S2. Based on the simulation model, simulate the turns ratio deviation and impedance deviation respectively, and determine the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold according to the simulation results. In S2, simulations are performed on the turns ratio deviation and impedance deviation respectively. Based on the simulation results, the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold are determined, including: A set of scanning sequences containing multiple preset turns ratio deviation gradient values ​​is input for simulation, and circulating current parameters are extracted from each simulation result. The voltage turns ratio safety threshold is determined based on the circulating current parameters. The turns ratio deviation is fixed to the voltage turns ratio safety threshold. A set of scanning sequences containing multiple preset impedance deviation gradient values ​​is input for simulation. The circulating current parameters in each simulation result are extracted, and the initial safety threshold of the short-circuit impedance is determined based on the circulating current parameters.

[0030] In this embodiment, to ensure that the simulation range covers and exceeds the relevant standards, the transformer ratio deviation gradient is ±0.25%, ±0.5%, ±1.0%, ±2.0%, ±3.0%, ±4.0%, ±5.0%, and the impedance deviation gradient is ±5.0%, ±10.0%, ±20.0%, ±30.0%, ±40.0%, ±50.0%.

[0031] The gradient settings described above, by plotting the characteristic curve from small deviations that meet the standard to large deviations that far exceed the standard, provide a data basis for determining the safety threshold.

[0032] S3. Construct an adaptive safety boundary, wherein the adaptive safety boundary is a circulating safety limit that is dynamically adjusted based on multiple operating state parameters; Based on the three-phase line simulation model established by S1 and S2, the circulating current ratio under different deviations, and multiple operating state parameters such as oil temperature, hot spot temperature, dissolved gas information in oil, load rate, power factor, and system short-circuit capacity under the corresponding deviations, an adaptive safety boundary is established. The adaptive safety boundary is the product of multiple influencing factors and satisfies: , in, =[ , , , , ] T Let T be the state vector, and T be the transpose of the vector. Based on the basic circulation limit, T For temperature, The temperature decay factor, Oil temperature This is an estimate of the hotspot temperature. Insulation aging degradation factor, Let be the vector of dissolved gas concentrations in the oil. This is the load factor, which takes load rate into account. and power factor The function of the degree of core saturation and the change in eddy current loss. For the system strength factor, This refers to the system's short-circuit capacity.

[0033] S4. Using the adaptive safety boundary as a safety constraint, construct a multi-objective optimization framework to optimize the initial safety threshold of the short-circuit impedance, and obtain the short-circuit impedance safety threshold. To address the problem of traditional methods having a single or vague objective, a multi-objective optimization framework is constructed. The problem of determining the impedance adjustment range is formalized into a multi-objective problem that optimizes multiple performance objectives. These multiple performance objectives include: maximizing the adaptability of the impedance adjustment range to the transformer in operation, maximizing the robustness margin of the impedance adjustment range under the worst operating conditions, and minimizing the overall cost associated with the impedance adjustment range.

[0034] Specifically, the computation of the multi-objective optimization framework satisfies: , in, Represents the target vector. To indicate the adaptability of the impedance adjustment range to the transformer in operation, based on historical data statistics, the range is represented as follows. The proportion of operating transformers that can be covered. This represents the total cost associated with the impedance adjustment range, including the manufacturing cost of the adjustment device and the expected loss cost. To maximize the robustness margin of the impedance adjustment range under the worst operating conditions, the minimum distance between the circulating current and the safety boundary under the worst operating conditions is defined. and These are the minimum and maximum short-circuit impedance values ​​that the flexible spare parts can achieve, and are also the core design parameters of the built-in impedance adjustment devices (such as adjustable reactors) in the flexible spare parts. Their adjustment step size is set to no greater than ( ) / 50, response time less than 5 minutes, This indicates the impedance adjustment range to be optimized. Indicates the circulation value. and These represent the 5th and 95th percentiles of the impedance statistics for transformers in operation in the target area, respectively. Represents a time variable. This represents the state vector, while other engineering constraints include size and cost.

[0035] Based on the above multi-objective optimization framework, the maximum deviation between transformer voltage ratio and impedance under multi-objective parameter optimization is obtained.

[0036] S5. Based on the voltage ratio safety threshold and the short-circuit impedance safety threshold, generate a joint adjustment command for the voltage regulating winding and the impedance regulating winding. The joint adjustment command is used to control the switching of the tap position of the voltage regulating winding and the impedance regulating winding so that the voltage ratio and short-circuit impedance of the flexible spare part simultaneously meet the safety requirements.

[0037] The aforementioned joint regulatory directives include: Control the switching of the tap changer winding to determine whether the short-circuit impedance is within the short-circuit impedance safety threshold range, provided that the voltage ratio requirement is met. If the condition is not exceeded, output a completion adjustment signal; If the limit is exceeded, the tap position of the control impedance regulating winding is switched, and it is determined whether the safety requirements of voltage ratio and short-circuit impedance are met simultaneously. If the condition is met, then output the adjustment completion signal; Otherwise, regenerate the voltage regulating winding adjustment command and repeat the above judgment and control steps until both meet the requirements.

[0038] In the joint adjustment command, a voltage regulating winding with multiple taps is used to fine-tune the voltage ratio in small steps and coarse-tune the short-circuit impedance in large steps. When the short-circuit impedance does not meet safety requirements, the impedance regulating winding is used to fine-tune the short-circuit impedance until the safety requirements are met. The fine-tuning range of the voltage ratio is limited to within 20% of the simulated safe threshold range of the voltage ratio, so that the voltage ratio will not exceed the safe threshold when the short-circuit impedance is coarsely adjusted subsequently. The coarse-tune range of the short-circuit impedance is limited to within the simulated safe threshold range of the short-circuit impedance.

[0039] The actual 500 kV single-phase autotransformer flexible spare parts in this embodiment include the core, series winding, common winding, voltage regulating winding, low-voltage winding, and impedance regulating winding. The low-voltage winding is located between the main column of the iron core and the voltage regulating winding, the common winding is located between the voltage regulating winding and the series winding, the series winding is located on the outermost side of the iron core, and the impedance regulating winding is located on the side column of the iron core. The end of the series winding is connected to the beginning of the common winding via a voltage regulating winding, and the end of the common winding is connected to the beginning of the impedance regulating winding. The series winding has a centrally input structure, including an upper series winding and a lower series winding arranged in parallel; The voltage regulating winding is equipped with several taps to adjust the voltage on the medium-voltage side and to change the short-circuit impedance of the transformer synchronously during the voltage ratio adjustment process. The impedance regulating winding is provided with several taps. By switching the connection positions of the end of the common winding and different taps of the impedance regulating winding, the short-circuit impedance of the transformer can be adjusted, and the voltage ratio of the transformer can be changed synchronously during the impedance adjustment process.

[0040] Example 2 Example 2 is an actual test description corresponding to Example 1.

[0041] This embodiment constructs a power system simulation model including a 500 kV autotransformer based on the PSCAD platform. Voltage ratio deviation gradients are set to ±0.25%, ±0.5%, ±1.0%, ±2.0%, ±3.0%, ±4.0%, and ±5.0%, and the changes in circulating current and its proportion are observed. The explanation is based on an example of a 0.5% deviation in the low-voltage side voltage ratio.

[0042] When the turns ratios are inconsistent, the sum of the voltage vectors in the delta-connected three-phase windings is no longer zero. At this time, a residual voltage exists in the circuit. This voltage acts on the sum of the internal impedances of the three-phase windings, generating circulating current. The circulating current ratio is the ratio of the effective value of the zero-sequence circulating current in the delta circuit to the rated current of a single phase of the low-voltage winding, expressed as: Formula 1 Formula 2 Formula 3, Equation 1 is the formula for calculating the rated current of a single phase of the low-voltage winding. The rated current of the delta circuit. This is the rated capacity on the low-voltage side. The rated voltage is the low-voltage side, and Equation 2 is the effective value of the zero-sequence circulating current in the delta circuit. Calculation formula Equation 3 represents the zero-sequence current amplitude and the circulating current ratio. The calculation formula is as follows: when the low-voltage side voltage ratio deviates by 0.5%, the circulating current is as follows: Figure 4 As shown, the effective value is 37A, and the circulating current accounts for 1.33%. The circulating current and circulating current proportion under different voltage ratio deviations obtained by traversing the voltage ratio deviation gradient are shown in Table 1.

[0043] Table 1. Circulating current and circulating current percentage under different voltage ratio deviations obtained by traversing the voltage ratio deviation gradient.

[0044] Based on the above-mentioned maximum voltage ratio deviation of ±3.0% under the premise of ensuring safety, when the low-voltage side voltage ratio deviation is 3%, impedance deviation gradients of ±0.25%, ±0.5%, ±1.0%, ±5.0%, ±10.0%, ±20.0%, ±30.0%, ±40.0%, and ±50.0% are set, and the changes in circulating current and circulating current ratio are observed. The following explanation is based on an example of a 0.5% deviation in high-to-low voltage short-circuit impedance.

[0045] When the high-low short-circuit impedance deviates by 0.5%, the circulating current is as follows: Figure 5 As shown, the effective value is 111.43A, and the circulating current accounts for 4.01%. The circulating current and circulating current proportion under different voltage ratio deviations obtained by traversing the voltage ratio deviation gradient are shown in Table 2.

[0046] Table 2 shows the circulating current and its proportion under different short-circuit impedance deviations obtained by traversing the short-circuit impedance deviation gradient.

[0047] Based on the circulating current ratio obtained above, and combined with the oil temperature, hot spot temperature, dissolved gas information in the oil, load rate, power factor and system short-circuit capacity obtained by actual measurement, an adaptive safety boundary and multi-objective optimization framework is constructed, and the maximum voltage ratio deviation is ±3.0% and the maximum short-circuit impedance deviation is ±30.0%.

[0048] A finite element simulation model was constructed based on an actual 500kV single-phase autotransformer flexible spare transformer to illustrate the feasibility of the combined voltage ratio and impedance regulation method. The transformer model is as follows: Figure 6 As shown. In this embodiment, the 500kV single-phase autotransformer to be replaced has a high-to-medium short-circuit impedance of 16%, a high-to-low short-circuit impedance of 56%, a medium-to-low short-circuit impedance of 36%, and a voltage ratio of 525 / / (230 / ±2×2.5%) / 36kV. Based on requirements, change the tap position of the regulating winding of the 500kV single-phase autotransformer to ensure the medium-voltage ratio meets the range [230 / *(1-3%), 230 / *(1+3%)]. At this point, the transformer short-circuit impedances are: high-medium 28%, high-low 75%, and medium-low 42%. The impedance does not meet the deviation requirements. Further adjust the impedance regulating winding until the short-circuit impedance meets the requirements; at this point, the voltage transformation ratio is still within the acceptable range.

[0049] This demonstrates the effectiveness and practicality of the method of the present invention. Through this systematic approach, the voltage ratio and short-circuit impedance of flexible spare parts can be scientifically adjusted together, ensuring their safe and stable operation after commissioning.

[0050] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A method for jointly adjusting the voltage ratio and impedance of a 500 kV single-phase autotransformer flexible spare part, characterized in that, Includes the following steps: Construct a power system simulation model that includes a 500 kV autotransformer; Based on the simulation model, the turns ratio deviation and impedance deviation are simulated respectively, and the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold are determined according to the simulation results. An adaptive safety boundary is constructed, wherein the adaptive safety boundary is a circulating safety limit that is dynamically adjusted based on multiple operating state parameters; Using the adaptive safety boundary as a safety constraint, a multi-objective optimization framework is constructed to optimize the initial safety threshold of the short-circuit impedance, thereby obtaining the short-circuit impedance safety threshold. Based on the voltage ratio safety threshold and the short-circuit impedance safety threshold, a joint adjustment command for the voltage regulating winding and the impedance regulating winding is generated. The joint adjustment command is used to control the switching of the tap position of the voltage regulating winding and the impedance regulating winding so that the voltage ratio and short-circuit impedance of the flexible spare part simultaneously meet the safety requirements.

2. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, Simulations were performed on the turns ratio deviation and impedance deviation respectively. Based on the simulation results, the voltage turns ratio safety threshold and the initial short-circuit impedance safety threshold were determined, including: A set of scanning sequences containing multiple preset turns ratio deviation gradient values ​​is input for simulation, and circulating current parameters are extracted from each simulation result. The voltage turns ratio safety threshold is determined based on the circulating current parameters. The turns ratio deviation is fixed to the voltage turns ratio safety threshold. A set of scanning sequences containing multiple preset impedance deviation gradient values ​​is input for simulation. The circulating current parameters in each simulation result are extracted, and the initial safety threshold of the short-circuit impedance is determined based on the circulating current parameters.

3. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 2, characterized in that, The circulating current parameter is the circulating current ratio, which is the ratio of the effective value of the zero-sequence circulating current in the low-voltage side circuit to the rated current of a single phase in the low-voltage winding.

4. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, The simulation model includes: The transformer model adopts a three-phase, three-winding structure, with a rated voltage of 525 / 230 / 36kV, a capacity of 334MVA, and a connection method of YNa0d11. System power supply model: Ideal three-phase power supply with infinite capacity and voltage level of 500kV; Load model: Both the 230kV side and the 36kV load adopt the equivalent RLC model with R=1Ω, L=0.1H, C=5uF; Line model: A Π-shaped equivalent model with a length of 1 kilometer; Monitoring module: Real-time monitoring of circulation values; The multiple operating status parameters include at least circulation, oil temperature, hot spot temperature, dissolved gas information in oil, load rate, power factor, and system short-circuit capacity.

5. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, The adaptive safety boundary is the product of multiple influencing factors, satisfying: ， in, =[ , , , , ] T Let T be the state vector, and T be the transpose of the vector. Based on the basic circulation limit, T For temperature, The temperature decay factor, Oil temperature This is an estimate of the hotspot temperature. Insulation aging degradation factor, Let be the vector of dissolved gas concentrations in the oil. For load condition factor, For load rate, For power factor, For the system strength factor, This refers to the system's short-circuit capacity.

6. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, The multi-objective optimization framework optimizes multiple performance objectives, including: maximizing the fit of the impedance adjustment range to the transformer in operation, maximizing the robustness margin of the impedance adjustment range under the worst operating conditions, and minimizing the overall cost associated with the impedance adjustment range.

7. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1 or 6, characterized in that, The computation of the multi-objective optimization framework satisfies: ， in, Represents the target vector. To ensure the impedance adjustment range is well-suited for use with transformers in operation, This indicates the overall cost associated with the impedance adjustment range. To maximize the robustness margin of the impedance adjustment range under the worst operating conditions, and These are the minimum and maximum short-circuit impedance values ​​that flexible spare parts can achieve, respectively. This indicates the impedance adjustment range to be optimized. Indicates the circulation value. and These represent the 5th and 95th percentiles of the impedance statistics for transformers in operation in the target area, respectively. Represents a time variable. This represents the state vector.

8. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, The joint control command includes: Control the switching of the tap changer winding to determine whether the short-circuit impedance is within the short-circuit impedance safety threshold range, provided that the voltage ratio requirement is met. If the condition is not exceeded, output a completion adjustment signal; If the limit is exceeded, the tap position of the control impedance regulating winding is switched, and it is determined whether the safety requirements of voltage ratio and short-circuit impedance are met simultaneously. If the condition is met, then output the adjustment completion signal; Otherwise, regenerate the voltage regulating winding adjustment command and repeat the above judgment and control steps until both meet the requirements.

9. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 8, characterized in that, In the joint adjustment command, the voltage ratio is finely adjusted and the short-circuit impedance is coarsely adjusted using a voltage regulating winding with multiple taps. When the short-circuit impedance does not meet the safety requirements, the impedance regulating winding is used to finely adjust the short-circuit impedance. The fine adjustment range of the voltage ratio is limited to within 20% of the simulated safe threshold range of the voltage ratio, and the coarse adjustment range of the short-circuit impedance is limited to within the simulated safe threshold range of the short-circuit impedance.

10. The method for combined voltage ratio and impedance adjustment of flexible spare parts for a 500 kV single-phase autotransformer as described in claim 1, characterized in that, The flexible spare parts for the 500 kV single-phase autotransformer include a core, series winding, common winding, voltage regulating winding, low-voltage winding, and impedance regulating winding. The low-voltage winding is located between the main column of the iron core and the voltage regulating winding, the common winding is located between the voltage regulating winding and the series winding, the series winding is located on the outermost side of the iron core, and the impedance regulating winding is located on the side column of the iron core. The end of the series winding is connected to the beginning of the common winding via a voltage regulating winding, and the end of the common winding is connected to the beginning of the impedance regulating winding. The series winding has a centrally input structure, including an upper series winding and a lower series winding arranged in parallel; The voltage regulating winding is equipped with several taps to adjust the voltage on the medium-voltage side and to change the short-circuit impedance of the transformer synchronously during the voltage ratio adjustment process. The impedance regulating winding is provided with several taps. By switching the connection positions of the end of the common winding and different taps of the impedance regulating winding, the short-circuit impedance of the transformer can be adjusted, and the voltage ratio of the transformer can be changed synchronously during the impedance adjustment process.

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