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

Abstract

The application discloses a kind of based on digital twinning box-type substation intelligent state monitoring system, it is related to state monitoring technical field, including: structural parameter acquisition module, for based on the net distance between ring main unit metal side plate and corrugated sheet and the equivalent height of cable trench opening, calculate vertical passage ratio;Structural factor calculation module is used to calculate structural factor based on vertical passage ratio and the same side opening proportion of ring main unit one side;Current equivalence module is used to calculate the equivalent current of transformer winding;Heat dissipation correction coefficient module is used to determine the correction coefficient of backflow cavity of transformer heat dissipation boundary based on structural factor and the temperature difference asymmetry of corrugated sheet.The application improves the security and economy of distribution system operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of state monitoring, and particularly relates to an intelligent state monitoring system for box-type substations based on digital twinning. BACKGROUND

[0002] In urban power distribution networks and industrial park power supply systems, box-type substations are widely used due to their compact structure, easy installation and flexible operation. Such substations are usually composed of a high-voltage ring network cabinet, a distribution transformer and a low-voltage outgoing line device. The distribution transformer adopts an oil-immersed structure and achieves heat dissipation through corrugated sheets. Due to limited installation space, the ring network cabinet is often arranged close to the side of the transformer, with a cable trench below for incoming and outgoing lines, and louvered vents on the upper two sides to introduce cold air and exhaust hot air. This arrangement causes cold air to mainly flow down the narrow channel between the ring network cabinet and the corrugated sheets and be drawn away by the cable trench, forming a semi-closed return flow path, which causes the corrugated sheets near the ring network cabinet side to be in a state of poor air flow, with much lower heat dissipation capacity than the opposite side. With the increase of power load, especially after the connection of electric vehicles for rapid charging, data centers and large industrial equipment, the heat generated by the transformer windings increases significantly, and if the heat dissipation conditions are biased, it will directly affect the accuracy of hot spot temperature evaluation and the safe operation of equipment.

[0003] The existing technology generally assumes that the heat dissipation conditions on both sides of the transformer are the same in the evaluation of hot spot temperature, and calculates based on the top oil temperature and load current. This method ignores the uneven heat dissipation caused by the semi-closed return flow channel, resulting in systematic underestimation of the hot spot temperature. When the actual temperature of the winding exceeds the allowable value of the insulation, but the monitoring result still shows normal, it is easy to cause accelerated aging of the insulation and even sudden failure. The traditional method lacks correction means for asymmetric heat dissipation environment and is difficult to incorporate the real air flow distribution in the operating scenario into the evaluation, thus causing a deviation between the digital monitoring results and the actual working conditions, limiting the reliability of operation control and current limiting management based on real-time monitoring data. SUMMARY

[0004] The purpose of the present application is to solve the problem in the prior art that it is difficult to incorporate the real air flow distribution in the operating scenario into the evaluation, thus causing a deviation between the digital monitoring results and the actual working conditions, and to propose an intelligent state monitoring system for box-type substations based on digital twinning.

[0005] In order to solve the problems in the prior art, the present application adopts the following technical solutions:

[0006] An intelligent state monitoring system for box-type substations based on digital twinning, comprising:

[0007] a structure parameter acquisition module, configured to calculate a vertical channel ratio based on a net distance between a metal side plate of the ring main unit and a corrugated sheet and an equivalent height of a cable trench opening;

[0008] a structure factor calculation module, configured to calculate a structure factor based on the vertical channel ratio and a same-side opening proportion of one side of the ring main unit;

[0009] a current equivalence module, configured to calculate an equivalent current of the transformer winding;

[0010] a heat dissipation correction coefficient module, configured to determine a backflow cavity correction coefficient of a heat dissipation boundary of the transformer based on the structure factor and a temperature difference asymmetry of the corrugated sheet;

[0011] a hot spot temperature estimation module, configured to calculate a hot spot temperature of the transformer winding based on an average near-wall temperature of the transformer, the equivalent current and the backflow cavity correction coefficient;

[0012] a current limiting control module, configured to determine a maximum allowable equivalent current of the transformer winding based on the hot spot temperature and an upper limit of the hot spot temperature of the transformer winding, and perform current limiting processing on an operating load current of the box-type substation based on the maximum allowable equivalent current.

[0013] Preferably, the vertical channel ratio is calculated based on the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer and the equivalent height of the cable trench opening, including:

[0014] measuring the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer of the box-type substation;

[0015] measuring the equivalent height of the cable trench opening;

[0016] performing ratio calculation on the net distance and the equivalent height of the cable trench opening to obtain the vertical channel ratio.

[0017] Preferably, the structure factor is calculated based on the vertical channel ratio and the same-side opening proportion of one side of the ring main unit, including:

[0018] measuring a first louver opening area arranged on the same side as the ring main unit;

[0019] measuring a second louver opening area arranged on the opposite side of the ring main unit;

[0020] performing summation on the first louver opening area and the second louver opening area to obtain a total louver opening area;

[0021] performing ratio calculation on the first louver opening area and the total louver opening area to obtain the same-side opening proportion of one side of the ring main unit;

[0022] performing product operation on the vertical channel ratio and the same-side opening proportion to obtain the structure factor.

[0023] Preferably, the equivalent current of the transformer winding is calculated, comprising:

[0024] Harmonic currents of the operating circuit in the box-type substation are obtained;

[0025] The harmonic currents are RMS combined to obtain the equivalent current of the transformer winding.

[0026] Preferably, the backflow cavity correction coefficient of the transformer heat dissipation boundary is determined based on the structure factor and the temperature difference asymmetry of the corrugated sheet, comprising:

[0027] The left side surface temperature of the corrugated sheet and the left side near-wall air temperature are subtracted to obtain the left side temperature difference;

[0028] The right side surface temperature of the corrugated sheet and the right side near-wall air temperature are subtracted to obtain the right side temperature difference;

[0029] Based on the left side temperature difference and the right side temperature difference, the temperature difference asymmetry of the corrugated sheet is calculated;

[0030] The structure factor and the temperature difference asymmetry are multiplied to obtain the structure temperature difference product;

[0031] The backflow cavity correction coefficient of the transformer heat dissipation boundary is determined based on the structure temperature difference product.

[0032] Preferably, the calculation formula of the temperature difference asymmetry is as follows:

[0033]

[0034] In the formula, is the right side temperature difference, is the left side temperature difference, is the temperature difference asymmetry.

[0035] Preferably, the hot spot temperature of the transformer winding is calculated based on the average near-wall temperature of the transformer, the equivalent current and the backflow cavity correction coefficient, comprising:

[0036] The left side near-wall air temperature of the corrugated sheet and the right side near-wall air temperature are arithmetically averaged to obtain the average near-wall temperature of the transformer;

[0037] The top layer oil temperature of the box-type substation and the average near-wall temperature are subtracted to obtain the oil end baseline temperature rise;

[0038] The backflow cavity correction coefficient and the oil end baseline temperature rise are multiplied to obtain the corrected oil end temperature rise;

[0039] Based on the equivalent current and the backflow cavity correction coefficient, the rated winding hot spot additional temperature rise of the transformer winding is corrected to obtain the corrected winding hot spot additional temperature rise;

[0040] Summing up the average near-wall temperature, the corrected oil terminal temperature rise and the corrected winding hot-spot additional temperature rise, the hot-spot temperature of the transformer winding is obtained.

[0041] Preferably, determining 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 comprises:

[0042] Numerically comparing the hot-spot temperature and the upper limit of the hot-spot temperature of the transformer winding:

[0043] When the hot-spot temperature is less than or equal to the upper limit of the hot-spot temperature, then determining the maximum allowable equivalent current of the transformer winding based on the equivalent current of the transformer winding;

[0044] When the hot-spot temperature is greater than the upper limit of the hot-spot temperature, then determining the maximum allowable equivalent current of the transformer winding based on the oil terminal baseline temperature of the transformer and the backflow cavity correction coefficient.

[0045] Preferably, determining the maximum allowable equivalent current of the transformer winding based on the oil terminal baseline temperature of the transformer and the backflow cavity correction coefficient comprises:

[0046] Summing up the average near-wall temperature and the corrected oil terminal temperature rise, the oil terminal baseline temperature of the transformer is obtained.

[0047] Determining the maximum allowable equivalent current of the transformer winding based on the oil terminal baseline temperature and the backflow cavity correction coefficient.

[0048] Compared with the prior art, the present application has the beneficial effects that:

[0049] 1、The present application introduces structure parameter acquisition and structure factor calculation, converts the net distance between the metal side plate of the ring network cabinet and the corrugated sheet, the equivalent height of the cable trench opening and the opening area of the ventilation louver into the vertical channel ratio and the same side opening ratio, and further calculates the structure factor, so that the influence of the semi-closed backflow channel on the air flow organization can be quantified, the limitation of the traditional symmetric assumption for the heat dissipation environment is broken, and the heat dissipation difference of the box-type transformer substation caused by the geometric layout in actual operation can be directly reflected in a parameterized manner, thereby providing accurate structure input for subsequent heat dissipation correction and hot-spot temperature estimation.

[0050] 2、The present application introduces the backflow cavity correction coefficient in the heat dissipation correction coefficient module, combines the structure factor with the temperature difference asymmetry on both sides of the corrugated sheet, establishes a correction factor that can dynamically reflect the uneven heat dissipation, and can consider the structure constraint and the heat dissipation difference at the same time when estimating the hot-spot temperature, thereby avoiding the underestimation of the hot-spot risk due to the neglect of the backflow channel effect in the traditional method.

[0051] 3、The application is based on the corrected hot spot temperature and the preset upper limit of the hot spot temperature in the current limiting control module, reversely calculates the maximum allowed equivalent current, and implements hierarchical current limiting processing on the operation load current of the box-type substation according to the maximum allowed equivalent current, realizes a closed loop from monitoring to control, can take measures in time before the hot spot temperature reaches the upper limit, can accurately determine the current limiting threshold according to the corrected hot boundary, ensures that the current limiting action is highly consistent with the actual safety bearing capacity of the transformer, thereby effectively avoids insulation aging and overheating failure, prolongs the service life of the equipment and improves the safety and economy of the power distribution system operation. BRIEF DESCRIPTION OF DRAWINGS

[0052] The drawings described herein are used to provide further understanding of the present application, constitute a part of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitation on the present application. In the drawings:

[0053] Figure 1 A functional module diagram of an intelligent state monitoring system of a box-type substation based on digital twinning is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0055] Embodiment: The embodiment provides an intelligent state monitoring system of a box-type substation based on digital twinning, referring to Figure 1 , specifically, comprising:

[0056] The structure parameter acquisition module is used to calculate the vertical channel ratio based on the net distance between the metal side plate of the ring network cabinet and the corrugated sheet and the equivalent height of the cable trench opening.

[0057] In the embodiment of the present application, the vertical channel ratio is calculated based on the net distance between the metal side plate of the ring network cabinet and the corrugated sheet and the equivalent height of the cable trench opening, comprising:

[0058] The net distance between the metal side plate of the ring network cabinet and the corrugated sheet of the transformer of the box-type substation is measured.

[0059] The equivalent height of the cable trench opening is measured.

[0060] The net distance and the equivalent height of the cable trench opening are calculated by ratio, and the vertical channel ratio is obtained.

[0061] Specifically, the metal side plate of the ring main unit of the box-type substation is a fixed metal wall surface on the side of the transformer, and a narrow channel space is formed between the metal side plate and the corrugated sheet of the transformer. The width of the channel is the clear distance, and the smaller the clear distance, the more restricted the air flow is. The equivalent height of the cable trench opening refers to the effective vertical channel size provided by the opening of the cable trench at the bottom of the box-type substation in air flow. The greater the height, the stronger the vertical ventilation and suction capacity. By calculating the ratio of the clear distance and the equivalent height of the cable trench opening, the vertical channel ratio can be obtained, which comprehensively reflects the coupling relationship between the lateral slit effect and the vertical suction capacity, and is used to characterize the flow characteristics of air in the vertical channel formed between the side plate and the corrugated sheet of the ring main unit, thereby providing a basic parameter for subsequent heat dissipation performance analysis.

[0062] Specifically, in the box-type substation, the clear distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer is first measured. This parameter is used to characterize the width of the narrow channel, which directly affects the flow resistance of air in the channel. Secondly, the equivalent height of the cable trench opening is measured. This parameter is used to reflect the effective vertical ventilation capacity of the lower cable trench connected to the outside. The greater the height, the more significant the vertical suction and ventilation effect. After obtaining the above two data, the equivalent height of the cable trench opening is calculated by the ratio of the clear distance between the side plate and the corrugated sheet. The vertical channel ratio can comprehensively reflect the relative relationship between the restricted degree of the slit channel and the vertical ventilation driving force. Through the steps realized in this order, the spatial geometric characteristics can be quantified into calculable parameters, providing basic data support for further calculation of the structure factor combined with the ventilation opening area, and forming a logical link from measurement to calculation.

[0063] Specifically, in the box-type substation, the clear distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer determines the restricted degree of air flow in the narrow channel, while the equivalent height of the cable trench opening determines the suction and exhaust capacity of the vertical channel below. When the clear distance is small and the height of the cable trench opening is large, cold air is more easily washed down the side plate slit and sucked away, forming a clear vertical airflow path, which results in the side corrugated sheet being in the airflow shielding area for a long time, and the heat dissipation capacity is significantly weakened. By calculating the ratio of the clear distance and the equivalent height of the cable trench opening, the vertical channel ratio can be obtained, which can quantitatively reflect the relationship between the restricted degree of the vertical channel and the suction driving force, thereby providing reliable structural parameter basis for subsequent identification and correction of heat dissipation asymmetry.

[0064] The structure factor calculation module is configured to calculate a structure factor based on the vertical channel ratio and a same-side opening ratio of one side of the ring main unit.

[0065] In the embodiments of the present application, the structure factor is calculated based on the vertical channel ratio and the same-side opening ratio of one side of the ring main unit, including:

[0066] measure a first louver opening area arranged on the same side as the ring main unit;

[0067] measure a second louver opening area arranged on the opposite side of the ring main unit;

[0068] sum the first louver opening area and the second louver opening area to obtain a total louver opening area;

[0069] calculate a ratio of the first louver opening area and the total louver opening area to obtain a same-side opening ratio of the ring main unit side;

[0070] multiply the vertical channel ratio and the same-side opening ratio to obtain a structure factor.

[0071] Specifically, the first louver opening area refers to the effective ventilation area of the ventilation louver arranged on the same side as the ring main unit, which determines the ability of cold air entering from this side; the second louver opening area refers to the effective ventilation area of the ventilation louver arranged on the opposite side of the ring main unit, which is used to represent the air inlet capacity of the other side; the total louver opening area is the comprehensive ventilation area obtained by adding the opening areas of the two sides, which is used to describe the overall air inlet channel size; the same-side opening ratio is the ratio of the first louver opening area to the total louver opening area, which is used to represent the proportion of cold air entering mainly from the ring main unit side, and the greater the ratio, the easier the airflow is to concentrate on the ring main unit side to form asymmetric heat exchange; the structure factor is the product of the vertical channel ratio and the same-side opening ratio, which is used to comprehensively reflect the coupling effect of vertical suction capacity and air inlet distribution on local heat dissipation conditions, thereby providing key parameters for subsequent heat dissipation correction.

[0072] Specifically, first, the first louver opening area arranged on the same side as the ring main unit and the second louver opening area arranged on the opposite side are measured, and these two data are used to reflect the air inlet capacity of cold air on both sides. Then, the first louver opening area and the second louver opening area are summed to obtain the total louver opening area, which is used to represent the air inlet channel size of the entire box-type substation. On this basis, the ratio of the first louver opening area to the total louver opening area is calculated to obtain the same-side opening ratio of the ring main unit side, which can quantitatively reflect the degree of cold air entering mainly through the ring main unit side. Finally, the same-side opening ratio and the vertical channel ratio obtained in the previous step are multiplied to obtain the structure factor, which comprehensively represents the coupling effect of vertical suction effect and air inlet distribution on the heat dissipation boundary conditions of the transformer, and thus can be used as a key parameter for quantifying the asymmetric characteristics of heat dissipation.

[0073] Specifically, in the box-type substation, the gap channel formed between the metal side plate of the ring network cabinet and the corrugated sheet of the transformer can jointly act with the cable trench opening to determine the flow capacity of cold air in the vertical direction, which is characterized by a vertical channel ratio; at the same time, the main path of cold air entering the substation depends on the distribution of the louver opening, if the area proportion of the louver opening on one side of the ring network cabinet is larger, more cold air will enter from that side, thereby intensifying the semi-closed backflow cavity effect on that side. The structure factor obtained by comprehensively calculating the vertical channel ratio and the opening proportion on the same side can reflect the coupling effect of the vertical suction effect and the air inlet distribution on the heat dissipation boundary, thereby quantitatively describing the structural characteristics of asymmetric heat dissipation and providing an accurate basis for subsequent correction of hot spot temperature evaluation.

[0074] a current equivalent module configured to calculate an equivalent current of the transformer winding;

[0075] In the embodiments of the present application, the equivalent current of the transformer winding is calculated, comprising:

[0076] Harmonic currents in an operating circuit of the box-type substation are obtained.

[0077] The harmonic currents are RMS synthesized to obtain the equivalent current of the transformer winding.

[0078] Specifically, the harmonic current refers to the high-frequency current component caused by the nonlinear load in the operating circuit of the box-type substation in addition to the fundamental current, which can cause additional thermal effects and additional losses; the operating circuit refers to the electrical circuit inside the box-type substation that undertakes the function of power transmission and distribution, which is the main path of current flow and load connection; the RMS synthesis is a calculation method of squaring and summing each harmonic current and taking the square root, which can equivalently reflect the total action strength of multi-frequency currents in thermal effects; the equivalent current refers to a single current value obtained by RMS synthesis, which is equivalent in thermal effects to the combined action of all harmonic currents and can be used as an important parameter for evaluating the heating level of the transformer winding.

[0079] Specifically, in calculating the equivalent current of the transformer winding, first, the harmonic currents in the operating circuit of the box-type substation are obtained, which reflect the high-frequency components produced by the nonlinear load in addition to the fundamental current in the electrical system. Then, the obtained harmonic currents are RMS synthesized, the square sum of each harmonic current is squared and summed, and then the square root is taken, thereby obtaining a single current value, which is equivalent in thermal effects to the combined action of all harmonic currents. Through this sequence of steps, complex multi-frequency currents can be converted into a unified equivalent current, which not only simplifies the calculation, but also accurately reflects the heating level of the winding, providing reliable electrical input parameters for subsequent hot spot temperature estimation.

[0080] The heat dissipation correction coefficient module is configured to determine the correction coefficient of the return flow cavity of the heat dissipation boundary of the transformer based on the structure factor and the temperature difference asymmetry of the corrugated sheet.

[0081] In the embodiment of the present application, the correction coefficient of the return flow cavity of the heat dissipation boundary of the transformer is determined based on the structure factor and the temperature difference asymmetry of the corrugated sheet, comprising:

[0082] The left side surface temperature of the corrugated sheet and the left side near-wall air temperature are subtracted to obtain the left side temperature difference.

[0083] The right side surface temperature of the corrugated sheet and the right side near-wall air temperature are subtracted to obtain the right side temperature difference.

[0084] Based on the left side temperature difference and the right side temperature difference, the temperature difference asymmetry of the corrugated sheet is calculated.

[0085] In the embodiment of the present application, the calculation formula of the temperature difference asymmetry is as follows:

[0086]

[0087] In the formula, is the right side temperature difference, is the left side temperature difference, is the temperature difference asymmetry.

[0088] Specifically, in the calculation of the temperature difference asymmetry, first, the difference between the surface temperature of the left side of the corrugated sheet and the left side near-wall air temperature is obtained as the left side temperature difference, and then the difference between the surface temperature of the right side of the corrugated sheet and the right side near-wall air temperature is obtained as the right side temperature difference. Then, the left and right temperature differences are substituted into the formula, and the temperature difference asymmetry is calculated by the ratio of the difference and the sum of the two side temperature differences. When the left and right temperature differences are equal, the result is zero, indicating that the heat dissipation is symmetrical; when the difference between the two sides increases, the result tends to one, indicating that the heat dissipation is severely asymmetric.

[0089] For example, when the left side temperature difference is 20 degrees Celsius and the right side temperature difference is 10 degrees Celsius, the temperature difference asymmetry is 0.23, which clearly reflects the imbalance of heat dissipation. The beneficial effect of the formula is that the influence of the absolute value difference of temperature is eliminated through normalization processing, so that the result is between 0 and 1, which is convenient for coupling with the structure factor and quantifying the heat dissipation asymmetry. The logic of this step is to reflect the deviation degree through the temperature difference difference, and then to normalize through the temperature difference sum, so as to ensure the universality and comparability of the result, and to provide direct input for the subsequent determination of the correction coefficient of the return flow cavity.

[0090] The structure temperature difference product is obtained by multiplying the structure factor and the temperature difference asymmetry.

[0091] The correction coefficient of the return flow cavity of the heat dissipation boundary of the transformer is determined based on the structure temperature difference product.

[0092] Specifically, the heat dissipation process of both sides of the transformer corrugated sheet is jointly affected by the space geometry layout and air flow distribution. The vertical air flow formed by the narrow channel and the cable trench opening determines the strength of the cold air flow, and the temperature difference between the left and right sides of the surface and the near-wall air directly reflects the imbalance of the heat exchange capacity of both sides. By calculating the temperature difference asymmetry first, the strength of the left and right heat dissipation imbalance can be quantified, and then multiplied by the structure factor to obtain the structure temperature difference product, thereby coupling the geometric constraints and heat dissipation asymmetry two physical effects together. After the product is converted into the backflow cavity correction coefficient, it can be used as a correction factor for the traditional symmetric heat dissipation assumption, so that the calculation results of the oil temperature rise and the winding additional temperature rise in the hot spot temperature estimation are more consistent with the semi-enclosed backflow cavity effect existing in the actual operation, avoiding systematic overestimation or underestimation of the heat dissipation capacity.

[0093] It should be noted that the role of digital twinning is to fuse the actual monitoring temperature distribution data with the structure factor in the virtual model, so that the virtual model can dynamically correct the heat dissipation boundary under the traditional symmetric assumption, thereby generating a correction coefficient consistent with the actual working condition, and ensuring that the simulation result is highly consistent with the field operation state.

[0094] Specifically, the left temperature difference refers to the difference between the surface temperature of the left side of the transformer corrugated sheet and the left side near-wall air temperature, which reflects the heat transfer driving force between the left side of the heat dissipation sheet and the surrounding air. The right temperature difference refers to the difference between the surface temperature of the right side of the corrugated sheet and the right side near-wall air temperature, which is used to represent the heat transfer intensity of the right side. The temperature difference asymmetry is a dimensionless index based on the difference between the left and right temperature differences, and the larger the value, the more unbalanced the heat dissipation capacity of both sides. The structure factor is a parameter calculated by the vertical channel ratio and the same side opening ratio, which is used to reflect the influence of the geometric layout of the box-type substation on the air flow path. The structure temperature difference product is the result of multiplying the structure factor and the temperature difference asymmetry, which is used to represent the coupling effect between the structure layout and the heat dissipation imbalance.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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:

[0099] 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.

[0100] 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.

[0101] 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.

[0102] Specifically, in the heat dissipation process of the transformer, the difference between the top layer oil temperature and the ambient air temperature directly reflects the heat transfer strength of the whole oil tank, and therefore the oil terminal baseline temperature rise obtained by the difference between the top layer oil temperature and the average near-wall temperature can represent the basic oil temperature rise level. However, due to the existence of the semi-closed backflow cavity effect in the tank, the uneven distribution of air flow on the left and right sides will cause differences between the heat dissipation capacity and the actual working condition, and the baseline temperature rise alone is easy to produce systematic deviation. By multiplying the oil terminal baseline temperature rise by the backflow cavity correction coefficient, the influence of the structural characteristics and uneven temperature difference can be comprehensively considered, so that the corrected oil terminal temperature rise can more truly reflect the actual effect of the oil temperature rise and the environmental interaction, thereby providing reliable thermal boundary input for hotspot temperature and load capacity evaluation.

[0103] Specifically, the average near-wall temperature is a value obtained by arithmetically averaging the near-wall air temperatures on the left and right sides of the transformer corrugated sheet, and this temperature is used to represent the overall thermal environment level of the air around the transformer; the oil terminal baseline temperature rise is calculated by the difference between the top layer oil temperature of the tank transformer substation and the average near-wall temperature, and this difference reflects the basic heat transfer strength of the oil tank interior relative to the ambient air; and the corrected oil terminal temperature rise is obtained by multiplying the backflow cavity correction coefficient by the oil terminal baseline temperature rise, and the physical meaning thereof is to amplify or reduce the oil terminal temperature rise after considering the semi-closed backflow cavity effect, so that the temperature rise calculation is more in line with the actual operating state, and underestimation or deviation caused by asymmetric heat dissipation is avoided.

[0104] Based on the equivalent current and the backflow cavity correction coefficient, the rated winding hotspot additional temperature rise of the transformer winding is corrected to obtain a corrected winding hotspot additional temperature rise, wherein the calculation formula of the corrected winding hotspot additional temperature rise is as follows:

[0105]

[0106] In the formula, is the corrected winding hotspot additional temperature rise, is the backflow cavity correction coefficient, is the rated winding hotspot additional temperature rise, is the equivalent current, is the nameplate rated current;

[0107] Specifically, the backflow cavity correction coefficient in the formula is used to reflect the asymmetric heat dissipation effect caused by the semi-closed backflow cavity, and magnifies or reduces the hotspot temperature rise under the traditional symmetric assumption; the rated winding hotspot additional temperature rise is a reference value obtained by the manufacturer under the rated current condition, and is used as a reference starting point for calculation; the equivalent current is a single current value obtained by synthesizing the harmonic component and the fundamental current, and is used to truly reflect the load effect under the operating condition; the nameplate rated current is the design current of the transformer under the rated condition, and is used to compare the actual load strength. By squaring the ratio of the equivalent current to the rated current, the physical law that the current heating is proportional to the square of the current is introduced, and the rated additional temperature rise is corrected by combining the backflow cavity correction coefficient, so that the corrected winding hotspot additional temperature rise consistent with the actual heat dissipation boundary and operating current can be obtained, and the calculation result consistent with the real working condition can be ensured.

[0108] The average near-wall temperature, the corrected oil end temperature rise and the corrected winding hotspot additional temperature rise are summed up to obtain the hotspot temperature of the transformer winding.

[0109] Specifically, the corrected winding hotspot additional temperature rise refers to the additional temperature rise of the winding hotspot relative to the oil end temperature after considering the backflow cavity effect and the actual current influence, which can reflect the additional heating level under the real working condition; the backflow cavity correction coefficient is a parameter for correcting the traditional symmetric heat dissipation assumption, which is used to magnify or reduce the additional temperature rise to reflect the influence of uneven heat dissipation; the rated winding hotspot additional temperature rise is the winding hotspot additional temperature rise obtained by the manufacturer through test or design under the 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, and is used to equivalently reflect the comprehensive effect of complex current on thermal effect; the nameplate rated current is the design current value of the transformer under the nameplate specified condition, and is an important basis for calculating the load ratio.

[0110] Specifically, the hotspot temperature of the transformer winding is determined by the average temperature of the ambient air, the oil end temperature rise and the additional heating of the winding itself, wherein the average near-wall temperature reflects the thermal environment of the external cooling air, the oil end temperature rise reflects the overall temperature rise level of the internal oil body of the transformer under the load effect, and the winding hotspot additional temperature rise reflects the local heating effect caused by the current through the winding. Due to the existence of the semi-closed backflow cavity effect in actual operation, the heat dissipation condition deviates from the traditional symmetric assumption, so it is necessary to introduce the backflow cavity correction coefficient to correct the oil end temperature rise and the winding hotspot additional temperature rise, and reflect the influence of the current on the heating through the square ratio of the equivalent current to the rated current. By adding the average near-wall temperature, the corrected oil end temperature rise and the corrected winding hotspot additional temperature rise, the hotspot temperature under the real operating condition can be obtained, which conforms to the physical nature of the heat transfer superposition and the square law of current heating, thereby avoiding the underestimation of the hotspot risk.

[0111] It should be noted that the semi-closed backflow cavity effect refers to that in the box-type substation, a narrow channel is formed between the metal side plate of the ring network cabinet and the corrugated sheet of the transformer, and interacts with the same side cable trench opening and louvered air vent, so that the cold air is washed down along the narrow channel and is sucked away by the cable trench, thereby causing the phenomenon that a local airflow stagnation zone and a heat dissipation shielding zone are formed on the side of the ring network cabinet. This effect can make the corrugated sheet on the side close to the ring network cabinet be in a poor ventilation environment for a long time, and the heat dissipation capacity is significantly lower than that on the opposite side, thereby causing the heat exchange on both sides to be obviously asymmetric. If the effect is not considered and the symmetric heat dissipation assumption is directly used, the calculation result of the hot spot temperature of the winding will be systematically low, thereby causing errors in the operation risk assessment.

[0112] Specifically, the hot spot temperature of the transformer winding is not only affected by the ambient air temperature, but also closely related to the heating effect caused by the load current and the asymmetry of the heat dissipation condition, so the average near-wall temperature, the equivalent current and the backflow cavity correction coefficient need to be combined for calculation. The average near-wall temperature can reflect the overall thermal environment around the winding, the equivalent current comprehensively represents the actual effect of the fundamental wave current and each harmonic current on the heating of the winding by the root mean square method, and the backflow cavity correction coefficient is used to correct the uneven heat dissipation caused by the semi-closed backflow cavity, thereby avoiding the underestimation caused by the traditional symmetric heat dissipation assumption. Through the comprehensive operation of the three, the hot spot temperature consistent with the actual operating state can be obtained, which provides accurate basis for assessing the insulation life and determining the operating limit.

[0113] It should be noted that in the process of calculating the hot spot temperature of the transformer winding, the measured average near-wall temperature is first taken as the external environment input, then the oil end baseline temperature rise is calculated by the difference between the top oil temperature and the near-wall air temperature, and the corrected oil end temperature rise is obtained by combining the backflow cavity correction coefficient, and the rated hot spot additional temperature rise is corrected by using the square ratio of the equivalent current and the nameplate rated current, to obtain the corrected winding hot spot additional temperature rise. Then the average near-wall temperature, the corrected oil end temperature rise and the corrected winding hot spot additional temperature rise are superimposed and summed to obtain the final hot spot temperature. In this process, the role of digital twinning is embodied in continuously correcting the oil end temperature rise and the hot spot additional temperature rise under the traditional symmetric assumption by using the monitoring data, so that the virtual model can dynamically map the actual working condition, thereby obtaining the hot spot temperature result highly consistent with the real operating state.

[0114] The current limiting control module is configured 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 perform current limiting processing on the operating load current of the box-type substation based on the maximum allowable equivalent current.

[0115] In the embodiment of the present application, 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, comprising:

[0116] Numerical comparison is made between the hotspot temperature and the upper limit of the hotspot temperature of the transformer winding:

[0117] When the hotspot temperature is less than or equal to the upper limit of the hotspot temperature, the maximum allowable equivalent current of the transformer winding is determined based on the equivalent current of the transformer winding;

[0118] When the hotspot temperature is greater than the upper limit of the hotspot temperature, the maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the reflux cavity correction coefficient.

[0119] Specifically, the upper limit of the hotspot temperature is the highest allowable temperature that the winding insulation can withstand for a long time, and exceeding this value will cause accelerated deterioration of the insulation performance. The maximum allowable equivalent current refers to the highest equivalent current that the transformer can carry for safe operation without exceeding the upper limit of the hotspot temperature, and is an important basis for operation current limiting and load distribution.

[0120] Specifically, first, the calculated winding hotspot temperature is compared with the preset upper limit of the hotspot temperature in numerical value to determine whether the current operating state is safe. When the hotspot temperature is less than or equal to the upper limit of the hotspot temperature, it indicates that the operation of the transformer winding is still within the allowable range, and at this time, the equivalent current is directly used as the basis to determine the maximum allowable equivalent current of the transformer winding, thereby realizing safe operation evaluation without correction. When the hotspot temperature is greater than the upper limit of the hotspot temperature, 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 the reflux cavity correction coefficient is combined to recalculate the maximum allowable equivalent current of the transformer winding, so as to avoid the underestimation of safety judgment caused by uneven heat dissipation. Through this two-level judgment and progressive calculation logic, dynamic evaluation based on single current judgment to multi-parameter correction is realized, effectively ensuring the accuracy of hotspot safety evaluation and the reliability of operation control.

[0121] In the embodiment of the present application, the maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the reflux cavity correction coefficient, comprising:

[0122] The average near-wall temperature and the corrected oil end temperature rise are summed to obtain the oil end baseline temperature of the transformer;

[0123] The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature and the reflux cavity correction coefficient, wherein the calculation formula of the maximum allowable equivalent current is as follows:

[0124]

[0125] In the formula, is the maximum allowable equivalent current, is the nameplate rated current, is the standard hotspot temperature upper limit, is the oil end baseline temperature, is the return cavity correction coefficient, is the rated winding hotspot additional temperature rise.

[0126] Specifically, The maximum allowed equivalent current in the formula represents the highest current value that the transformer winding can safely withstand under the current heat dissipation conditions, the nameplate rated current is the standard operating current specified by the manufacturer, the winding hotspot temperature upper limit is the highest safe temperature that the insulation material can withstand for a long time, the oil end baseline temperature is a reference temperature calculated from the difference between the top oil temperature and the ambient air temperature, the return cavity correction coefficient is a correction factor used to reflect the heat dissipation asymmetry caused by the semi-enclosed return cavity, and the rated winding hotspot additional temperature rise is the temperature rise value increased by the winding relative to the oil temperature under the rated operating condition. In the calculation, first, the hotspot temperature upper limit is subtracted from the oil end baseline temperature to obtain the available temperature rise margin, then the margin is divided by the corrected rated hotspot additional temperature rise to obtain the square ratio of the current amplification multiple, and finally, the maximum allowed equivalent current is obtained in combination with the nameplate rated current. This combination follows the physical law that the heat generated by the current increase is proportional to the square of the current, and introduces the non-symmetry of the heat dissipation boundary through the correction coefficient, so it can accurately reflect the safe bearing limit of the transformer in the real environment.

[0127] Specifically, the calculation of the maximum allowed equivalent current is based on the thermal effect relationship between the hotspot temperature and the load current, and the formula obtains the allowed additional temperature rise by subtracting the oil end baseline temperature from the hotspot temperature upper limit under the current operating condition, and then dividing by the product of the return cavity correction coefficient and the rated winding hotspot additional temperature rise, thereby obtaining the square ratio of the current, and finally obtaining the maximum allowed equivalent current in combination with the rated current. The physical meaning of the calculation process is that the increase of the hotspot temperature is mainly caused by the heat generation effect proportional to the square of the current, the return cavity correction coefficient is used to reflect the amplification effect of the heat dissipation asymmetry on the temperature rise, and the rated winding hotspot additional temperature rise provides a reference under the rated condition, so through this combination, the limit current that the transformer can withstand without exceeding the allowable temperature of the insulation can be accurately back calculated, and the safe operating boundary is accurately quantified.

[0128] In the embodiment of the present application, the running load current of the box-type substation is limited based on the maximum allowed equivalent current, which includes:

[0129] Specifically, first, the maximum allowable equivalent current calculated in the state assessment link is obtained as the safety upper limit, and it is continuously compared with the real-time collected and synthesized equivalent current. When the equivalent current does not exceed the safety upper limit, the current load state is recorded and the operation mode is maintained. When the equivalent current exceeds or approaches the safety upper limit, the current limiting disposal process is entered. According to the judgment rule of hotspot temperature and its upper limit and the safety upper limit current calculated by the oil end baseline temperature and the backflow cavity correction coefficient as the control target, the regulation is implemented. The judgment and inverse calculation rule is described in the formula clause of the corresponding steps of the claims, which clearly shows that the comparison of hotspot temperature and upper limit determines whether to directly take the current equivalent current as the upper limit or to calculate the upper limit current according to the baseline temperature and the correction coefficient, and finally triggers the current limiting processing according to this. The current limiting disposal is executed in order of priority from low impact to high impact. First, the power limit and climbing rate constraint are issued to the adjustable load, and the hysteresis interval is set to avoid frequent start and stop. Then, reactive power optimization and voltage constraint are implemented at the feeder level to reduce loss and thermal burden. Then, according to the distribution structure, load transfer and ring network segmentation or parallel number switching are performed to share current. If the equivalent current still cannot be pressed below the safety upper limit, the hierarchical power limiting or phased cut-off of non-critical load is performed according to the pre-configured peak shaving curve, while the new equivalent current and hotspot temperature are continuously calculated and rewritten to form a closed loop until the equivalent current is stable below the safety upper limit and maintains the minimum necessary margin. Thereafter, it is restored to the monitoring and tracking state and generates event and parameter report for archiving and auditing.

[0130] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any skilled person in the art can make equivalent replacement or change according to the technical solution and inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A digital-twin-based intelligent condition monitoring system for a box-type substation, characterized in that, The method comprises the following steps: a structure parameter acquisition module is used to calculate a vertical channel ratio based on the net distance between the metal side plate of the ring main unit and the corrugated sheet and the equivalent height of the cable trench opening; a structure factor calculation module is used to calculate a structure factor based on the vertical channel ratio and the same-side opening proportion of one side of the ring main unit; an equivalent current calculation module is used to calculate the equivalent current of the transformer winding; a heat dissipation correction coefficient module is used to determine the backflow cavity correction coefficient of the transformer heat dissipation boundary based on the structure factor and the temperature difference asymmetry of the corrugated sheet; a hot spot temperature estimation module is used to calculate the hot spot temperature of the transformer winding based on the average near-wall temperature of the transformer, the equivalent current and the backflow cavity correction coefficient; a 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 limit the operating load current of the box-type substation based on the maximum allowable equivalent current.

2. The digital-twin-based intelligent condition monitoring system for a box-type substation according to claim 1, characterized in that, Based on the net distance between the metal side plate of the ring main unit and the corrugated sheet and the equivalent height of the cable trench opening, the vertical channel ratio is calculated, including: measuring the net distance between the metal side plate of the ring main unit and the corrugated sheet of the transformer of the box-type substation; measuring the equivalent height of the cable trench opening; calculating the ratio of the net distance and the equivalent height of the cable trench opening to obtain the vertical channel ratio.

3. The digital-twin-based intelligent condition monitoring system for a box-type substation according to claim 1, characterized in that, Based on the vertical channel ratio and the same-side opening proportion of one side of the ring main unit, the structure factor is calculated, including: measuring the first louver opening area arranged on the same side as the ring main unit; measuring the second louver opening area arranged on the opposite side of the ring main unit; summing the first louver opening area and the second louver opening area to obtain the total louver opening area; calculating the ratio of the first louver opening area and the total louver opening area to obtain the same-side opening proportion of one side of the ring main unit; multiplying the vertical channel ratio and the same-side opening proportion to obtain the structure factor.

4. The digital-twin-based intelligent condition monitoring system for a box-type substation of claim 1, wherein, The equivalent current of the transformer winding is calculated, including: obtaining the harmonic current of the operating loop in the box-type substation; RMS synthesizing the harmonic current to obtain the equivalent current of the transformer winding.

5. The digital-twin-based intelligent condition monitoring system for a box-type substation according to claim 1, characterized in that, Based on the structure factor and the temperature difference asymmetry of the corrugated sheet, the backflow cavity correction coefficient of the transformer heat dissipation boundary is determined, including: calculating the difference between the left side surface temperature of the corrugated sheet and the left side near-wall air temperature to obtain the left side temperature difference; calculating the difference between the right side surface temperature of the corrugated sheet and the right side near-wall air temperature to obtain the right side temperature difference; based on the left side temperature difference and the right side temperature difference, calculating the temperature difference asymmetry of the corrugated sheet; multiplying the structure factor and the temperature difference asymmetry to obtain the structure temperature difference product; determining the backflow cavity correction coefficient of the transformer heat dissipation boundary based on the structure temperature difference product.

6. The digital-twin-based intelligent condition monitoring system for a box-type substation according to claim 5, characterized in that, The calculation formula of the temperature difference asymmetry is as follows: In the formula, is the right side temperature difference, is the left side temperature difference, is the temperature difference asymmetry degree.

7. The digital-twin-based intelligent condition monitoring system for a box-type substation of claim 1, wherein, Based on the average near-wall temperature of the transformer, the equivalent current and the backflow cavity correction coefficient, the hot spot temperature of the transformer winding is calculated, including: arithmetic averaging the left side near-wall air temperature and the right side near-wall air temperature of the corrugated sheet to obtain the average near-wall temperature of the transformer; calculating the difference between the top layer oil temperature of the box-type substation and the average near-wall temperature to obtain the oil end baseline temperature rise; multiplying the backflow cavity correction coefficient and the oil end baseline temperature rise to obtain the corrected oil end temperature rise; The rated winding hot-spot additional temperature rise of the transformer winding is corrected based on the equivalent current and the backflow cavity correction coefficient to obtain a corrected winding hot-spot additional temperature rise; 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 winding hot-spot additional temperature rise.

8. The digital-twin-based intelligent condition monitoring system for a box-type substation of claim 1, wherein, 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: The hot-spot temperature and the upper limit of the hot-spot temperature of the transformer winding are compared numerically: 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 backflow cavity correction coefficient.

9. The digital-twin-based intelligent condition monitoring system for a box-type substation of claim 8, wherein, The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature of the transformer and the backflow cavity correction coefficient, including: The oil end baseline temperature of the transformer is obtained by summing the average near-wall temperature and the corrected oil end temperature rise; The maximum allowable equivalent current of the transformer winding is calculated based on the oil end baseline temperature and the backflow cavity correction coefficient.

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