Intelligent state monitoring system for box-type substation based on digital twinning

Abstract

The invention discloses a box-type substation intelligent state monitoring system based on digital twinning, and relates to the technical field of state monitoring, and the system comprises a structure parameter obtaining module which is used for calculating a vertical channel ratio based on the clear distance between a ring main unit metal side plate and a corrugated sheet and the equivalent height of a cable trench opening; the structure factor calculation module is used for calculating a structure factor based on the vertical channel ratio and the same-side opening proportion of one side of the ring main unit; the current equivalence module is used for calculating the equivalent current of the transformer winding; and the heat dissipation correction coefficient module is used for determining a backflow cavity correction coefficient of the heat dissipation boundary of the transformer based on the structure factors and the temperature difference asymmetry degree of the corrugated sheets. According to the invention, the operation safety and economy of the power distribution system are improved.

Description

Technical Field

[0001] This invention relates to the field of condition monitoring technology, and in particular to an intelligent condition monitoring system for prefabricated substations based on digital twins. Background Technology

[0002] In urban power distribution networks and industrial park power supply systems, prefabricated substations are widely used due to their compact structure, convenient installation, and flexible operation. These substations typically consist of a high-voltage ring main unit (RNB), a distribution transformer, and low-voltage outgoing line equipment. The distribution transformer uses an oil-immersed structure and achieves heat dissipation through corrugated fins. Due to limited installation space, the RNB is often placed close to the transformer, with a cable trench below for incoming and outgoing lines, and louvered ventilation openings on both sides at the top to introduce cool air and exhaust hot air. In actual operation, this arrangement causes cool air to primarily flow down the narrow channel between the RNB and the corrugated fins and be drawn away by the cable trench, creating a semi-enclosed return path. This results in poor airflow on the side of the RNB closer to the corrugated fins, leading to significantly lower heat dissipation capacity compared to the opposite side. With increasing power loads, especially after the rapid charging of electric vehicles, data centers, and the grid connection of large industrial equipment, the heat generation of transformer windings increases significantly. If the heat dissipation conditions are inaccurate, it will directly affect the accuracy of hot spot temperature assessment and the safe operation of the equipment.

[0003] Current technologies for hotspot temperature assessment generally assume that heat dissipation conditions are the same on both sides of the transformer and calculate based on top oil temperature and load current. This method ignores the uneven heat dissipation caused by the semi-enclosed return current channel, leading to a systematic underestimation of hotspot temperatures. When the actual winding temperature exceeds the insulation allowable value but the monitoring results still show normal, it can easily cause accelerated insulation aging or even sudden failures. Traditional methods lack means to correct for asymmetrical heat dissipation environments when addressing this problem, making it difficult to incorporate the actual airflow distribution in the operating scenario into the assessment. This results in discrepancies between digital monitoring results and actual operating conditions, limiting the reliability of operation control and current limiting management based on real-time monitoring data. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies that make it difficult to incorporate the actual airflow distribution in the operating scenario into the evaluation, thus causing discrepancies between digital monitoring results and actual operating conditions. Therefore, this invention proposes an intelligent condition monitoring system for prefabricated substations based on digital twins.

[0005] To address the problems existing in the prior art, the present invention adopts the following technical solution: A digital twin-based intelligent condition monitoring system for prefabricated substations includes: The structural parameter acquisition module is used to calculate the vertical channel ratio based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening; The structural factor calculation module is used to calculate the structural factor based on the vertical channel ratio and the proportion of openings on the same side of the ring main unit. The current equivalence module is used to calculate the equivalent current of the transformer windings; The heat dissipation correction coefficient module is used to determine the return cavity correction coefficient of the transformer heat dissipation boundary based on the structural factor and the temperature difference asymmetry of the corrugated sheet. The hot spot temperature estimation module is used to calculate the hot spot temperature of the transformer windings based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor. The current limiting control module is used to determine the maximum allowable equivalent current of the transformer winding based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding, and to perform current limiting on the operating load current of the box-type substation based on the maximum allowable equivalent current.

[0006] Preferably, the vertical channel ratio is calculated based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening, including: Measure the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer in the prefabricated substation. Measure the equivalent height of the cable trench opening; The vertical channel ratio is obtained by calculating the ratio of the net clearance to the equivalent height of the cable trench opening.

[0007] Preferably, the structural factor is calculated based on the vertical channel ratio and the proportion of openings on the same side of the ring main unit, including: Measure the area of ​​the first louver opening located on the same side as the ring main unit; Measure the area of ​​the second 100-leaf opening on the opposite side of the ring main unit; The total louver opening area is obtained by summing the opening areas of the first and second louvers. The ratio of the opening area of ​​the first louver to the total opening area of ​​the louvers is calculated to obtain the proportion of the same-side openings on one side of the ring main unit. The structural factor is obtained by multiplying the vertical channel ratio and the proportion of openings on the same side.

[0008] Preferably, calculating the equivalent current of the transformer winding includes: Obtain the harmonic current of the operating circuit in the prefabricated substation; The equivalent current of the transformer winding is obtained by performing RMS synthesis on the harmonic current.

[0009] Preferably, the correction coefficient for the return cavity of the transformer heat dissipation boundary is determined based on the structural factor and the temperature difference asymmetry of the corrugated sheet, including: The temperature difference on the left side is calculated by measuring the temperature difference between the left surface of the corrugated sheet and the air temperature near the left wall. The temperature difference on the right side is calculated by measuring the difference between the surface temperature on the right side of the corrugated sheet and the air temperature near the right wall. Calculate the temperature difference asymmetry of the corrugated sheet based on the temperature difference on the left and right sides; The structural factor and the temperature difference asymmetry are multiplied to obtain the structural temperature difference product. The correction factor for the return cavity of the transformer heat dissipation boundary is determined based on the structural thermo-thermal product.

[0010] Preferably, the formula for calculating the temperature difference asymmetry is as follows: In the formula, It's the temperature difference on the right side. It's the temperature difference on the left side. It is the degree of temperature difference asymmetry.

[0011] Preferably, the hot spot temperature of the transformer winding is calculated based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor, including: The average near-wall temperature of the transformer is obtained by arithmetically averaging the air temperatures near the left and right sides of the corrugated sheet. The difference between the top oil temperature and the average near-wall temperature in the prefabricated substation is calculated to obtain the baseline temperature rise at the oil end. The corrected oil end temperature rise is obtained by multiplying the correction factor of the reflux chamber with the baseline temperature rise of the oil end. Based on the equivalent current and the return cavity correction coefficient, the additional temperature rise of the rated winding hot spot of the transformer winding is corrected to obtain the corrected additional temperature rise of the winding hot spot. The hot spot temperature of the transformer winding is obtained by summing the average near-wall temperature, the corrected oil end temperature rise, and the corrected additional temperature rise of the winding hot spot.

[0012] Preferably, the maximum allowable equivalent current of the transformer winding is determined based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding, including: A numerical comparison was made between the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding: When the hot spot temperature is less than or equal to the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is determined based on the equivalent current of the transformer winding. When the hot spot temperature is greater than the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the return cavity correction factor.

[0013] Preferably, the maximum allowable equivalent current of the transformer winding is calculated based on the transformer oil terminal baseline temperature and the return cavity correction factor, including: The average near-wall temperature and the corrected oil end temperature rise are summed to obtain the transformer oil end baseline temperature. The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature and the return cavity correction factor.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention introduces structural parameter acquisition and structural factor calculation, transforming the net distance between the metal side plate and corrugated sheet of the ring main unit, the equivalent height of the cable trench opening, and the opening area of ​​the ventilation louvers into the vertical channel ratio and the proportion of openings on the same side. Furthermore, it calculates the structural factor, thereby quantifying the impact of the semi-enclosed return channel on airflow organization. This breaks through the limitations of the traditional symmetrical assumption for the heat dissipation environment, allowing the heat dissipation differences caused by the geometric layout of the prefabricated substation to be directly reflected in a parameterized manner during actual operation, providing accurate structural input for subsequent heat dissipation correction and hot spot temperature estimation.

[0015] 2. This invention introduces a recirculation cavity correction coefficient into the heat dissipation correction coefficient module, combining the structural factor with the temperature difference asymmetry on both sides of the corrugated sheet to establish a correction factor that can dynamically reflect uneven heat dissipation. This allows for the simultaneous consideration of structural constraints and heat dissipation differences when estimating hot spot temperatures, avoiding the underestimation of hot spot risk due to neglecting the recirculation channel effect in traditional methods.

[0016] 3. In the current limiting control module, this invention calculates the maximum allowable equivalent current based on the corrected hot spot temperature and the preset upper limit of the hot spot temperature, and implements graded current limiting processing on the operating load current of the prefabricated substation accordingly. This achieves a closed loop from monitoring to control, which not only allows for timely measures to be taken before the hot spot temperature reaches the upper limit, but also accurately determines the current limiting threshold based on the corrected thermal boundary, ensuring that the current limiting action is highly consistent with the actual safe carrying capacity of the transformer. This effectively avoids insulation aging and overheating faults, extends equipment life, and improves the safety and economy of the power distribution system. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a functional block diagram of a digital twin-based intelligent condition monitoring system for prefabricated substations, provided as an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] Example: This example provides an intelligent condition monitoring system for prefabricated substations based on digital twins. See [link to example]. Figure 1 Specifically, including: The structural parameter acquisition module is used to calculate the vertical channel ratio based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening; In embodiments of the present invention, the vertical channel ratio is calculated based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening, including: Measure the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer in the prefabricated substation. Measure the equivalent height of the cable trench opening; The vertical channel ratio is obtained by calculating the ratio of the net clearance to the equivalent height of the cable trench opening.

[0020] Specifically, the metal side panel of the ring main unit in a prefabricated substation is a fixed metal wall located on one side of the transformer. It forms a narrow channel space with the transformer's corrugated sheets; the width of this channel is the clearance. The smaller the clearance, the more restricted the airflow. The equivalent height of the cable trench opening refers to the effective vertical channel size provided by the opening connecting the cable trench at the bottom of the prefabricated substation to the outside, allowing for airflow. The larger this height, the stronger the vertical ventilation and suction capacity. By calculating the ratio of the clearance to the equivalent height of the cable trench opening, the vertical channel ratio can be obtained. This ratio comprehensively reflects the coupling relationship between the lateral slit effect and the vertical suction capacity, characterizing the airflow characteristics within the vertical channel formed between the ring main unit side panel and the corrugated sheets, thus providing fundamental parameters for subsequent heat dissipation performance analysis.

[0021] Specifically, in a prefabricated substation, the first step is to measure the clearance between the metal side plate of the ring main unit and the corrugated sheet of the transformer. This parameter characterizes the width of the narrow passage, and its size directly affects the airflow resistance within the passage. Secondly, the equivalent height of the cable trench opening is measured. This parameter reflects the effective vertical ventilation capacity connecting the lower cable trench to the outside; the greater the height, the more significant the vertical suction and ventilation effects. After obtaining these two data points, the ratio of the equivalent height of the cable trench opening to the clearance between the side plate and the corrugated sheet is calculated to obtain the vertical passage ratio. This ratio comprehensively reflects the relative relationship between the degree of restriction of the narrow passage and the driving force of vertical ventilation. Through this sequential process, spatial geometric features can be quantified into calculable parameters, providing basic data support for subsequent calculations of structural factors based on the ventilation opening area, and forming a logical link that progresses step-by-step from measurement to calculation.

[0022] Specifically, in prefabricated substations, the clearance between the metal side plate of the ring main unit and the transformer corrugated sheets determines the degree of airflow restriction within this narrow channel, while the equivalent height of the cable trench opening determines the suction and exhaust capacity of the vertical channel below. When the clearance is small and the cable trench opening height is large, cold air is more easily washed down along the narrow gaps in the side plate and drawn away, forming a significant vertical airflow path. This causes the corrugated sheets on that side to be in a long-term airflow shielding zone, resulting in a significant reduction in heat dissipation capacity. By calculating the ratio of the clearance and the equivalent height of the cable trench opening, the vertical channel ratio can be obtained, which can quantitatively reflect the relationship between the degree of vertical channel restriction and the suction driving force, thus providing a reliable structural parameter basis for subsequent identification and correction of heat dissipation asymmetry.

[0023] The structural factor calculation module is used to calculate the structural factor based on the vertical channel ratio and the proportion of openings on the same side of the ring main unit. In embodiments of the present invention, the structural factor is calculated based on the vertical channel ratio and the proportion of openings on the same side of the ring main unit, including: Measure the area of ​​the first louver opening located on the same side as the ring main unit; Measure the area of ​​the second 100-leaf opening on the opposite side of the ring main unit; The total louver opening area is obtained by summing the opening areas of the first and second louvers. The ratio of the opening area of ​​the first louver to the total opening area of ​​the louvers is calculated to obtain the proportion of the same-side openings on one side of the ring main unit. The structural factor is obtained by multiplying the vertical channel ratio and the proportion of openings on the same side.

[0024] Specifically, the first louver opening area refers to the effective ventilation area of ​​the ventilation louvers located on the same side as the ring main unit, and its size determines the ability of cold air to enter from that side; the second louver opening area refers to the effective ventilation area of ​​the ventilation louvers located on the opposite side of the ring main unit, used to characterize the air intake capacity of the other side; the total louver opening area is the comprehensive ventilation area obtained by adding the opening areas of both sides, used to describe the overall air intake channel scale; the same-side opening ratio is the ratio of the first louver opening area to the total louver opening area, used to characterize the proportion of cold air mainly entering from the same side of the ring main unit. The larger the ratio, the easier it is for the airflow to concentrate on one side of the ring main unit to form asymmetric heat exchange; the structural factor is the product of the vertical channel ratio and the same-side opening ratio, used to comprehensively reflect the coupling effect of vertical suction capacity and air intake distribution on local heat dissipation conditions, thus providing key parameters for subsequent heat dissipation correction.

[0025] Specifically, firstly, the opening areas of the first louver (located on the same side as the ring main unit) and the second louver (located on the opposite side) are measured. These two data points reflect the air intake capacity of cold air on both sides. Then, the opening areas of the first and second louvers are summed to obtain the total louver opening area, which characterizes the air intake channel scale of the entire prefabricated substation. Based on this, the ratio of the first louver opening area to the total louver opening area is calculated to obtain the proportion of openings on the same side of the ring main unit. This proportion quantitatively reflects the degree to which cold air mainly enters through one side of the ring main unit. Finally, the proportion of openings on the same side is multiplied by the vertical channel ratio obtained in the previous step to obtain the structural factor. This factor comprehensively characterizes the coupling effect of vertical suction and air intake distribution on the transformer's heat dissipation boundary conditions, and therefore can serve as a key parameter for quantifying the asymmetric characteristics of heat dissipation.

[0026] Specifically, in prefabricated substations, the narrow channel formed between the metal side plate of the ring main unit and the corrugated fins of the transformer, together with the opening of the cable trench, determines the vertical flow capacity of cold air, which is characterized by the vertical channel ratio. Simultaneously, the main path for cold air to enter the substation depends on the distribution of the louvered openings. If the louvered opening area ratio on one side of the ring main unit is larger, more cold air will concentrate on entering from that side, thus exacerbating the semi-enclosed return cavity effect on that side. By comprehensively calculating the vertical channel ratio and the proportion of openings on the same side, a structural factor can be obtained, which can simultaneously reflect the coupling effect of the vertical suction effect and the airflow distribution on the heat dissipation boundary. This quantitatively describes the structural characteristics of heat dissipation asymmetry, providing an accurate basis for subsequent hot spot temperature assessment.

[0027] The current equivalence module is used to calculate the equivalent current of the transformer windings; In an embodiment of the present invention, calculating the equivalent current of the transformer winding includes: Obtain the harmonic current of the operating circuit in the prefabricated substation; The equivalent current of the transformer winding is obtained by performing RMS synthesis on the harmonic current.

[0028] Specifically, harmonic current refers to the high-frequency current component caused by nonlinear loads in the operating circuit of a prefabricated substation, in addition to the fundamental current. Its presence leads to additional thermal effects and losses. The operating circuit refers to the electrical circuit inside the prefabricated substation that undertakes the function of power transmission and distribution, and is the main path for current flow and load connection. RMS synthesis is a calculation method that sums the squares of each harmonic current and takes the square root. This method can equivalently reflect the total intensity of the thermal effect of multi-frequency currents. Equivalent current refers to the single current value obtained through RMS synthesis. This current value is equivalent to the combined effect of all harmonic currents in terms of thermal effect and can be used as an important parameter for evaluating the heating level of transformer windings.

[0029] Specifically, when calculating the equivalent current of a transformer winding, the harmonic currents in the operating circuit of the prefabricated substation are first obtained. This data reflects the various high-frequency components generated by nonlinear loads in the electrical system, excluding the fundamental current. Subsequently, the obtained harmonic currents are synthesized using the root mean square (RMS) method. The squares of each harmonic current are summed and then the square root is taken to obtain a single current value. This current value is thermally equivalent to the combined effect of all harmonic currents. Through this sequential process, the complex multi-frequency currents can be transformed into a unified equivalent current, simplifying the calculation and accurately reflecting the heating level of the windings, providing reliable electrical input parameters for subsequent hot spot temperature estimation.

[0030] The heat dissipation correction coefficient module is used to determine the return cavity correction coefficient of the transformer heat dissipation boundary based on the structural factor and the temperature difference asymmetry of the corrugated sheet. In embodiments of the present invention, the correction coefficient for the return cavity of the transformer heat dissipation boundary is determined based on the structural factor and the temperature difference asymmetry of the corrugated sheet, including: The temperature difference on the left side is calculated by measuring the temperature difference between the left surface of the corrugated sheet and the air temperature near the left wall. The temperature difference on the right side is calculated by measuring the difference between the surface temperature on the right side of the corrugated sheet and the air temperature near the right wall. Calculate the temperature difference asymmetry of the corrugated sheet based on the temperature difference on the left and right sides; In an embodiment of the present invention, the formula for calculating the temperature difference asymmetry is as follows: In the formula, It's the temperature difference on the right side. It's the temperature difference on the left side. It is the degree of temperature difference asymmetry.

[0031] Specifically, in calculating the temperature difference asymmetry, the difference between the surface temperature on the left side of the corrugated sheet and the air temperature near the left wall is first obtained as the left-side temperature difference. Then, the difference between the surface temperature on the right side of the corrugated sheet and the air temperature near the right wall is obtained as the right-side temperature difference. These left and right temperature differences are then substituted into the formula, and the temperature difference asymmetry is calculated by the ratio of the difference to the sum of the two temperature differences. When the left and right temperature differences are equal, the result is zero, indicating symmetrical heat dissipation; as the difference between the two sides increases, the result approaches one, indicating severe asymmetry in heat dissipation.

[0032] For example, when the temperature difference on the left is 20 degrees Celsius and the temperature difference on the right is 10 degrees Celsius, the temperature difference asymmetry is 0.23, clearly reflecting the uneven heat dissipation. The beneficial effect of this formula is that it eliminates the influence of absolute temperature differences through normalization, making the result between 0 and 1, which facilitates coupling with structural factors and uniformly quantifies heat dissipation asymmetry. The logic of this step is to first reflect the degree of deviation through the temperature difference, and then normalize the result through the sum of the temperature differences to ensure the universality and comparability of the results, providing direct input for determining the subsequent reflux cavity correction coefficient.

[0033] The structural factor and the temperature difference asymmetry are multiplied to obtain the structural temperature difference product. The correction factor for the return cavity of the transformer heat dissipation boundary is determined based on the structural thermo-thermal product.

[0034] Specifically, the heat dissipation process on both sides of the transformer corrugated sheets is influenced by both spatial geometry and airflow distribution. The vertical airflow formed by the narrow channels and cable trench openings determines the strength of the cold air flow, while the temperature difference between the left and right surfaces and the air near the wall directly reflects the degree of unevenness in heat transfer capacity on both sides. By first calculating the temperature difference asymmetry, the strength of the uneven heat dissipation on both sides can be quantified. Then, multiplying this product by the structural factor yields the structural temperature difference product, thus coupling the two physical effects of geometric constraints and heat dissipation asymmetry together. After converting this product into a return cavity correction coefficient, it can serve as a correction factor for the traditional symmetrical heat dissipation assumption, making the calculated results of oil temperature rise and winding additional temperature rise in hot spot temperature estimation more consistent with the semi-closed return cavity effect existing in actual operation, avoiding systematic overestimation or underestimation of heat dissipation capacity.

[0035] It should be noted that the role of digital twins is to integrate the actual monitored temperature distribution data with the structural factors in the virtual model, enabling the virtual model to dynamically correct the heat dissipation boundary under the traditional symmetry assumption, thereby generating correction coefficients that are consistent with the actual operating conditions, ensuring that the simulation results are highly consistent with the on-site operating conditions.

[0036] Specifically, the left-side temperature difference refers to the difference between the surface temperature on the left side of the transformer corrugated sheet and the air temperature near the left wall, reflecting the heat transfer driving force between the left heat sink and the surrounding air; the right-side temperature difference refers to the difference between the surface temperature on the right side of the corrugated sheet and the air temperature near the right wall, used to characterize the heat transfer intensity on the right side; the temperature difference asymmetry is a dimensionless index based on the degree of temperature difference difference between the left and right sides, and the larger the value, the more uneven the heat dissipation capacity on both sides; the structural factor is a parameter calculated by combining the vertical channel ratio and the proportion of openings on the same side, used to reflect the influence of the geometric layout of the prefabricated substation on the airflow path; the structural temperature difference product is the result of multiplying the structural factor and the temperature difference asymmetry, used to characterize the coupling effect between the structural layout and uneven heat dissipation.

[0037] Specifically, the recirculation cavity correction factor is a dimensionless multiplier used to quantify the influence of the semi-enclosed recirculation cavity on the heat dissipation boundary. Its physical meaning is to amplify or reduce the temperature rise and hot spot estimates under the traditional symmetry assumption when heat exchange on both sides is not asymmetrical under actual ventilation conditions, making the calculation results closer to actual operating conditions. This factor comprehensively reflects two types of effects: one is the structural influence formed by the vertical suction and slit effect determined by the net distance and the cable trench opening height; the other is the degree of uneven heat dissipation reflected by the temperature difference between the left and right sides and the right side surface. When the recirculation cavity effect is weak and the temperature difference on both sides is close, the factor is close to one, indicating that no correction is needed. When the lateral slit is narrow, the suction channel is strong, the proportion of air intake on the same side is high, and the temperature difference on both sides is large, the factor is significantly greater than one, indicating that the temperature rise of the top layer oil and the additional temperature rise of the winding hot spots need to be increased simultaneously to correct the systematic underestimation of the hot spots and provide a reliable thermal boundary input for subsequent current limits and operational control.

[0038] Specifically, in the actual operating environment of a transformer, the heat dissipation process is not only affected by the ventilation geometry within the tank, but also constrained by the difference in heat transfer between the left and right sides of the airflow. Using structural factors alone can only reflect the airflow deviation caused by the vertical channels and air intake distribution, while using temperature difference asymmetry alone can only reflect the degree of uneven heat dissipation on both sides. If these two factors are separated, the actual effect of the semi-enclosed return cavity on the heat dissipation boundary cannot be fully revealed. By combining structural factors with temperature difference asymmetry to calculate the return cavity correction coefficient, the geometric layout and temperature difference performance can be coupled. This corrects the traditional symmetry assumption when estimating hot spot temperatures, ensuring that the calculation results accurately reflect the heat dissipation boundary conditions, avoiding systematic underestimation of hot spot risks, and providing a scientific basis for current limiting and operational control.

[0039] The hot spot temperature estimation module is used to calculate the hot spot temperature of the transformer windings based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor. In embodiments of the present invention, the hot spot temperature of the transformer winding is calculated based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor, including: The average near-wall temperature of the transformer is obtained by arithmetically averaging the air temperatures near the left and right sides of the corrugated sheet. The difference between the top oil temperature and the average near-wall temperature in the prefabricated substation is calculated to obtain the baseline temperature rise at the oil end. The corrected oil end temperature rise is obtained by multiplying the correction factor of the reflux chamber with the baseline temperature rise of the oil end. Specifically, during the heat dissipation process of a transformer, the difference between the top oil temperature and the surrounding air temperature directly reflects the overall heat transfer intensity of the tank. Therefore, the baseline temperature rise at the oil end, obtained by measuring the difference between the top oil temperature and the average near-wall temperature, can characterize the basic oil temperature rise level. However, due to the semi-enclosed reflux cavity effect within the tank, uneven airflow distribution on the left and right sides can lead to differences in heat dissipation capacity compared to actual operating conditions. Relying solely on the baseline temperature rise can easily introduce systematic biases. By multiplying the oil end baseline temperature rise by the reflux cavity correction factor, the effects of structural characteristics and uneven temperature differences can be comprehensively considered. This allows the calculated corrected oil end temperature rise to more accurately reflect the actual interaction between the oil temperature rise and the environment, thus providing a reliable thermal boundary input for hot spot temperature and load capacity assessment.

[0040] Specifically, the average near-wall temperature refers to the value obtained by arithmetically averaging the near-wall air temperatures on the left and right sides of the transformer corrugated sheets. This temperature is used to characterize the overall thermal environment level of the air surrounding the transformer. The oil-end baseline temperature rise is calculated by the difference between the top oil temperature of the prefabricated substation and the average near-wall temperature. This difference reflects the basic heat transfer intensity inside the tank relative to the ambient air. The corrected oil-end temperature rise is the result of multiplying the return cavity correction coefficient by the oil-end baseline temperature rise. Its physical meaning is to amplify or reduce the oil-end temperature rise after considering the semi-enclosed return cavity effect, so that the temperature rise calculation is more in line with the actual operating conditions and avoids underestimation or deviation caused by asymmetrical heat dissipation.

[0041] Based on the equivalent current and the return cavity correction factor, the additional temperature rise of the rated winding hot spot of the transformer winding is corrected to obtain the corrected additional temperature rise of the winding hot spot. The calculation formula for the corrected additional temperature rise of the winding hot spot is as follows: In the formula, It corrects the additional temperature rise caused by hot spots in the winding. It is the correction factor for the reflux chamber. This is the additional temperature rise of the rated winding hot spot. It is the equivalent current. It is the rated current on the nameplate; Specifically, the return cavity correction coefficient in the formula reflects the asymmetric heat dissipation effect caused by the semi-enclosed return cavity, amplifying or reducing the hot spot temperature rise under the traditional symmetric assumption; the rated winding hot spot additional temperature rise is a benchmark value obtained by the manufacturer under rated current conditions, used as a reference starting point for calculation; the equivalent current is a single current value obtained by synthesizing harmonic components and fundamental current, used to truly reflect the load effect under operating conditions; the nameplate rated current is the design current of the transformer under rated conditions, used to compare with the actual load intensity. By squarening the ratio of the equivalent current to the rated current, the physical law that current heating is proportional to the square of the current is introduced. Combined with the return cavity correction coefficient to correct the rated additional temperature rise, a corrected winding hot spot additional temperature rise consistent with the actual heat dissipation boundary and operating current can be obtained, ensuring that the calculation results match the actual operating conditions.

[0042] The hot spot temperature of the transformer winding is obtained by summing the average near-wall temperature, the corrected oil end temperature rise, and the corrected additional temperature rise of the winding hot spot.

[0043] Specifically, the corrected winding hot spot additional temperature rise refers to the additional temperature rise of the winding hot spot relative to the oil end temperature after considering the return cavity effect and the influence of actual current. This value can reflect the additional heat generation level under real operating conditions. The return cavity correction coefficient is a parameter used to correct the traditional symmetrical heat dissipation assumption. It is used to amplify or reduce the additional temperature rise to reflect the impact of uneven heat dissipation. The rated winding hot spot additional temperature rise is the additional temperature rise of the winding hot spot obtained by the manufacturer through testing or design under rated current, and is used as a reference. The equivalent current is a single current value obtained by synthesizing the fundamental current and each harmonic current through the root mean square. It is used to equivalently reflect the comprehensive effect of complex currents on thermal effects. The nameplate rated current is the design current value of the transformer under the conditions specified on the nameplate, and serves as an important basis for calculating the load ratio.

[0044] Specifically, the hot spot temperature of a transformer winding is determined by the average ambient air temperature, the oil end temperature rise, and the additional heat generated by the winding itself. The average near-wall temperature reflects the thermal environment of the external cooling air, the oil end temperature rise reflects the overall temperature rise of the transformer oil under load, and the additional hot spot temperature rise reflects the localized heating effect caused by current flowing through the winding. Due to the semi-enclosed reflux cavity effect in actual operation, the heat dissipation conditions deviate from the traditional symmetrical assumption. Therefore, a reflux cavity correction factor is needed to correct the oil end temperature rise and the additional hot spot temperature rise. The influence of current on heating is reflected by the square ratio of the equivalent current to the rated current. Adding the average near-wall temperature, the corrected oil end temperature rise, and the corrected additional hot spot temperature rise yields the hot spot temperature under actual operating conditions, conforming to the physical essence of heat transfer superposition and the square law of current-induced heating, thus avoiding an underestimation of hot spot risk.

[0045] It should be noted that the semi-enclosed return cavity effect refers to the phenomenon in prefabricated substations where a narrow channel forms between the metal side plate of the ring main unit and the transformer corrugated sheets. This channel interacts with the opening of the cable trench and the louvered ventilation openings on the same side, causing cold air to wash down along the narrow channel and be drawn away by the cable trench. This results in a localized area of ​​sluggish airflow and heat dissipation shielding on that side. This effect causes the corrugated sheets on the side closer to the ring main unit to be in a poorly ventilated environment for a long time, resulting in significantly lower heat dissipation capacity than the opposite side, thus causing a significant asymmetry in heat exchange between the two sides. If this effect is not considered and a symmetrical heat dissipation assumption is directly adopted, the calculated winding hot spot temperature will be systematically underestimated, leading to errors in the operational risk assessment.

[0046] Specifically, the hot spot temperature of transformer windings is not only affected by ambient air temperature, but also closely related to the heating effect of load current and the asymmetry of heat dissipation conditions. Therefore, it is necessary to combine the average near-wall temperature, equivalent current, and return cavity correction factor for calculation. The average near-wall temperature reflects the overall thermal environment around the winding. The equivalent current, through the root mean square method, comprehensively characterizes the actual effect of the fundamental current and each harmonic current on winding heating. The return cavity correction factor is used to correct for uneven heat dissipation caused by the semi-enclosed return cavity, thereby avoiding the underestimation caused by the traditional symmetrical heat dissipation assumption. Through the comprehensive calculation of these three factors, a hot spot temperature consistent with the actual operating conditions can be obtained, providing an accurate basis for assessing insulation life and determining operating limits.

[0047] It should be noted that in calculating the hot spot temperature of the transformer winding, the measured average near-wall temperature is first used as the external environmental input. Then, the oil-end baseline temperature rise is calculated using the difference between the top oil temperature and the near-wall air temperature. This is combined with a return cavity correction coefficient to obtain the corrected oil-end temperature rise. Simultaneously, the rated hot spot additional temperature rise is corrected using the square ratio of the equivalent current and the nameplate rated current, resulting in the corrected winding hot spot additional temperature rise. Finally, the average near-wall temperature, the corrected oil-end temperature rise, and the corrected winding hot spot additional temperature rise are summed to obtain the final hot spot temperature. In this process, the role of the digital twin is demonstrated by continuously correcting the oil-end temperature rise and hot spot additional temperature rise under the traditional symmetry assumption using monitoring data. This allows the virtual model to dynamically map actual operating conditions, thereby obtaining hot spot temperature results that are highly consistent with the actual operating state.

[0048] The current limiting control module is used to determine the maximum allowable equivalent current of the transformer winding based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding, and to perform current limiting on the operating load current of the box-type substation based on the maximum allowable equivalent current.

[0049] In embodiments of the present invention, determining the maximum permissible equivalent current of the transformer winding based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding includes: A numerical comparison was made between the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding: When the hot spot temperature is less than or equal to the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is determined based on the equivalent current of the transformer winding. When the hot spot temperature is greater than the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the return cavity correction factor.

[0050] Specifically, the hot spot temperature limit is the highest permissible temperature that the winding insulation can withstand over a long period, as specified by the manufacturer or industry standards. Exceeding this value will lead to accelerated degradation of the insulation performance. The maximum permissible equivalent current refers to the highest equivalent current that the transformer can safely carry while not exceeding the hot spot temperature limit. It is an important basis for current limiting and load distribution during operation.

[0051] Specifically, the calculated hot spot temperature of the winding is first compared with the preset upper limit of the hot spot temperature to determine whether the current operating state is safe. When the hot spot temperature is less than or equal to the upper limit, it indicates that the transformer winding is still operating within the allowable range. In this case, the equivalent current is directly used as the basis to determine the maximum allowable equivalent current of the transformer winding, thus achieving an uncorrected safety operation assessment. When the hot spot temperature is greater than the upper limit, it indicates that the winding may have overheated, and the traditional limit method needs to be corrected. At this time, the oil end baseline temperature obtained from the difference between the top oil temperature and the average near-wall temperature is introduced, and combined with the return cavity correction coefficient, the maximum allowable equivalent current of the transformer winding is recalculated to avoid underestimation of safety judgment due to uneven heat dissipation. Through this two-level judgment and progressive calculation logic, a dynamic assessment based on multi-parameter correction is realized from single current judgment, effectively ensuring the accuracy of hot spot safety assessment and the reliability of operation control.

[0052] In embodiments of the present invention, the calculation of the maximum permissible equivalent current of the transformer winding based on the transformer oil terminal baseline temperature and the return cavity correction factor includes: The average near-wall temperature and the corrected oil end temperature rise are summed to obtain the transformer oil end baseline temperature. The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature and the return cavity correction factor. The formula for calculating the maximum allowable equivalent current is as follows: In the formula, It is the maximum permissible equivalent current. It is the rated current on the nameplate. It is the upper limit of the standard hotspot temperature. It is the oil end baseline temperature. It is the correction factor for the reflux chamber. It is the additional temperature rise of the rated winding hot spot.

[0053] Specifically, In the formula, the maximum permissible equivalent current represents the highest current value that the transformer winding can safely withstand under current heat dissipation conditions. The nameplate rated current is the standard operating current specified by the manufacturer. The upper limit of the winding hot spot temperature is the highest safe temperature that the insulation material can withstand over a long period. The oil terminal baseline temperature is the reference temperature calculated from the temperature difference between the top oil temperature and the ambient air temperature. The return cavity correction factor is a correction factor used to reflect the heat dissipation asymmetry caused by the semi-enclosed return cavity. The rated winding hot spot additional temperature rise is the temperature rise value of the winding relative to the oil temperature under rated operating conditions. In the calculation, firstly, the upper limit of the hot spot temperature is subtracted from the oil terminal baseline temperature to obtain the usable temperature rise margin. Then, this margin is divided by the corrected rated hot spot additional temperature rise to obtain the square ratio of the current amplification factor. Finally, the maximum permissible equivalent current is obtained by combining it with the nameplate rated current. This combination method follows the physical law that the heating of the winding caused by the increase of current is proportional to the square of the current. By introducing the asymmetry of the heat dissipation boundary through the correction factor, it can accurately reflect the safe bearing limit of the transformer under real environment.

[0054] Specifically, the calculation of the maximum permissible equivalent current is derived based on the thermal effect relationship between hot spot temperature and load current. The formula obtains the allowable additional temperature rise under the current operating conditions by subtracting the oil end baseline temperature from the upper limit of the hot spot temperature. This is then divided by the product of the return cavity correction factor and the additional temperature rise of the rated winding hot spot, thus obtaining the current square ratio. Finally, the maximum permissible equivalent current is obtained by combining this with the rated current. The physical significance of this calculation process is that the increase in hot spot temperature is mainly caused by the heating effect proportional to the square of the current. The return cavity correction factor is used to reflect the amplification effect of heat dissipation asymmetry on the temperature rise. The additional temperature rise of the rated winding hot spot provides a reference under rated conditions. Therefore, through this combination, the limit current that the transformer can withstand under the condition of not exceeding the insulation allowable temperature can be accurately deduced, achieving precise quantification of the safe operating boundary.

[0055] In an embodiment of the present invention, current limiting processing of the operating load current of the prefabricated substation based on the maximum permissible equivalent current includes: Specifically, the maximum permissible equivalent current calculated in the previous stage is obtained as the safety upper limit from the state assessment stage. This is then continuously compared with the equivalent current collected and synthesized in real time. When the equivalent current does not exceed the safety upper limit, the current load state is recorded and the operating mode is maintained. When the equivalent current exceeds or approaches the safety upper limit, the current limiting process is initiated. The control is implemented based on the hot spot temperature and its upper limit determination rules, as well as the safety upper limit current calculated by back-calculating the oil end baseline temperature and the return cavity correction coefficient. The determination and back-calculation rules are described in the corresponding steps and formula clauses of the claims. It is clearly stated that the comparison between the hot spot temperature and the upper limit determines whether to directly use the current equivalent current as the upper limit or to calculate the upper limit current by back-calculating the baseline temperature and the correction coefficient, and finally triggers the current limiting process accordingly. Current limiting measures are implemented in order of priority from low impact to high impact. First, power limits and ramp-up rate constraints are issued to adjustable loads, and hysteresis intervals are set to avoid frequent start-stops. Then, reactive power optimization and voltage constraints are implemented at the feeder level to reduce losses and heat load. Next, load transfer and ring network segmentation or parallel unit number switching are performed according to the distribution structure to distribute the current. If the equivalent current still cannot be reduced below the safe upper limit, power limiting is performed in stages or non-critical loads are disconnected in stages according to the pre-configured peak shaving curve. At the same time, new equivalent current and hot spot temperature are continuously calculated and written back to form a closed loop until the equivalent current stabilizes below the safe upper limit and maintains the minimum necessary margin. After that, the system returns to the monitoring and tracking state and generates event and parameter reports for archiving and auditing.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A digital twin-based intelligent condition monitoring system for prefabricated substations, characterized in that, include: The structural parameter acquisition module is used to calculate the vertical channel ratio based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening; The structural factor calculation module is used to calculate the structural factor based on the vertical channel ratio and the proportion of openings on the same side of the ring main unit. The current equivalence module is used to calculate the equivalent current of the transformer windings; The heat dissipation correction coefficient module is used to determine the return cavity correction coefficient of the transformer heat dissipation boundary based on the structural factor and the temperature difference asymmetry of the corrugated sheet. The hot spot temperature estimation module is used to calculate the hot spot temperature of the transformer windings based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor. The current limiting control module is used to determine the maximum allowable equivalent current of the transformer winding based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding, and to perform current limiting on the operating load current of the box-type substation based on the maximum allowable equivalent current.

2. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, Based on the net distance between the metal side plate and the corrugated sheet of the ring main unit and the equivalent height of the cable trench opening, the vertical channel ratio is calculated, including: Measure the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer in the prefabricated substation. Measure the equivalent height of the cable trench opening; The vertical channel ratio is obtained by calculating the ratio of the net clearance to the equivalent height of the cable trench opening.

3. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, The structural factor is calculated based on the vertical aisle ratio and the proportion of openings on the same side of the ring main unit, including: Measure the area of ​​the first louver opening located on the same side as the ring main unit; Measure the area of ​​the second 100-leaf opening on the opposite side of the ring main unit; The total louver opening area is obtained by summing the opening areas of the first and second louvers. The ratio of the opening area of ​​the first louver to the total opening area of ​​the louvers is calculated to obtain the proportion of the same-side openings on one side of the ring main unit. The structural factor is obtained by multiplying the vertical channel ratio and the proportion of openings on the same side.

4. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, Calculate the equivalent current of the transformer windings, including: Obtain the harmonic current of the operating circuit in the prefabricated substation; The equivalent current of the transformer winding is obtained by performing RMS synthesis on the harmonic current.

5. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, The correction factor for the return cavity of the transformer heat dissipation boundary is determined based on the structural factor and the temperature difference asymmetry of the corrugated sheet, including: The temperature difference on the left side is calculated by measuring the temperature difference between the left surface of the corrugated sheet and the air temperature near the left wall. The temperature difference on the right side is calculated by measuring the difference between the surface temperature on the right side of the corrugated sheet and the air temperature near the right wall. Calculate the temperature difference asymmetry of the corrugated sheet based on the temperature difference on the left and right sides; The structural factor and the temperature difference asymmetry are multiplied to obtain the structural temperature difference product. The correction factor for the return cavity of the transformer heat dissipation boundary is determined based on the structural thermo-thermal product.

6. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 5, characterized in that, The formula for calculating the asymmetry of temperature difference is as follows: In the formula, It's the temperature difference on the right side. It's the temperature difference on the left side. It is the degree of temperature difference asymmetry.

7. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, The hot spot temperature of the transformer winding is calculated based on the transformer's average near-wall temperature, equivalent current, and return cavity correction factor, including: The average near-wall temperature of the transformer is obtained by arithmetically averaging the air temperatures near the left and right sides of the corrugated sheet. The difference between the top oil temperature and the average near-wall temperature in the prefabricated substation is calculated to obtain the baseline temperature rise at the oil end. The corrected oil end temperature rise is obtained by multiplying the correction factor of the reflux chamber with the baseline temperature rise of the oil end. Based on the equivalent current and the return cavity correction coefficient, the additional temperature rise of the rated winding hot spot of the transformer winding is corrected to obtain the corrected additional temperature rise of the winding hot spot. The hot spot temperature of the transformer winding is obtained by summing the average near-wall temperature, the corrected oil end temperature rise, and the corrected additional temperature rise of the winding hot spot.

8. The intelligent condition monitoring system for prefabricated substations based on digital twins according to claim 1, characterized in that, The maximum permissible equivalent current of the transformer winding is determined based on the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding, including: A numerical comparison was made between the hot spot temperature and the upper limit of the hot spot temperature of the transformer winding: When the hot spot temperature is less than or equal to the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is determined based on the equivalent current of the transformer winding. When the hot spot temperature is greater than the upper limit of the hot spot temperature, the maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the return cavity correction factor.

9. The intelligent condition monitoring system for a prefabricated substation based on digital twins according to claim 8, characterized in that, The maximum allowable equivalent current of the transformer windings is calculated based on the transformer oil terminal baseline temperature and the return cavity correction factor, including: The average near-wall temperature and the corrected oil end temperature rise are summed to obtain the transformer oil end baseline temperature. The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature and the return cavity correction factor.

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