Method for optimizing structure of pipeline for conveying dry cold air to cooling fins of main transformer of transformer substation

Abstract

The invention relates to a method for optimizing the structure of a pipeline for conveying dry cold air to cooling fins of a main transformer of a transformer substation. The method comprises the following steps of: determining ventilation quantity: calculating the ventilation quantity required by each air outlet and each city according to thermal load calculation and ventilation frequency indexes; determining ejection ports: determining the number, configuration and air volume of the ejection ports according to the number of the radiating fins of the electric appliance; fixed conveying pipelines are determined, wherein the reasonable fixed conveying pipelines connected with all the spraying openings of the air conditioner are determined; determining the passing air volume of each part; the size of a fixed conveying pipeline is determined, and a numerical model is analyzed; simulation is performed through a CFD numerical model to predict a reliable RSM turbulence model; local components and a conveying pipeline are optimized, and the dry cold air amount and the air speed obtained by cooling fins at different positions of the main transformer are uniform and reasonable.

Description

Technical Field

[0001] The present application relates to the field of air conditioning duct design, and in particular to a method for optimizing the duct structure for delivering dry cold air to the heat sink of a main transformer in a substation. Background Art

[0002] If the transformer oil temperature is too high, bubbles will be generated, which will reduce the insulation or cause flashover, causing damage to the transformer. When the upper oil temperature of the main transformer reaches the warning temperature, the temperature relay installed on the main transformer body will send an alarm signal to notify the operation and maintenance personnel for timely processing.

[0003] To reduce the workload of maintenance personnel, a dedicated main transformer cooling device was installed in the main transformer to reduce the temperature according to the main transformer's conditions. The existing piping structure that delivers dry, cold air to the substation's main transformer heat sinks created resistance, increasing vibration and noise, and impacting the efficiency of the entire input system. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a method for optimizing the pipeline structure for delivering dry cold air to the heat sink of the main transformer of a substation. By reasonably optimizing the cold air input pipeline structure, the problem of resistance caused by local components, which increases pipeline vibration and noise and thus affects the efficiency of the entire input system, is solved, so that the amount of dry cold air and the wind speed obtained by the heat sinks at different positions of the main transformer are uniform and reasonable.

[0005] To achieve the above objectives, this application provides the following technical solutions:

[0006] A method for optimizing the structure of a pipeline for delivering dry cold air to a heat sink of a main transformer in a substation, comprising:

[0007] S1: Determination of ventilation volume: Calculate the ventilation volume required for each air outlet and each zone based on heat load calculation and air change frequency index;

[0008] S2: Determine the outlet: The number of outlets, their configuration, and air volume are determined by the number of heat sinks in the transformer.

[0009] S3: Determine the appropriate delivery pipelines connecting the various outlets of the air conditioner;

[0010] S4: Determine the air volume passing through each section. Calculate the air volume passing through each section of the conveying pipeline from each outlet to the main transformer cooling device based on the main transformer oil temperature.

[0011] S5: Determine the dimensions of the transmission duct: Referencing the unit friction loss and the allowable value of the transmission duct wind speed, determine the dimensions of each section of the transmission duct, the diameter of the circular air duct, and the length of the two sides of the rectangular transmission duct. Based on the above conditions, determine the model of the main transformer cooling device, whose main parameters are ventilation resistance and total pressure loss.

[0012] S6: Numerical model analysis: Simulations are performed using CFD numerical models to predict reliable RSM turbulence patterns;

[0013] S7: Optimization of local components and delivery pipelines: Based on the data model predicted by the data model and the actual site requirements, the T-type diversion tee type and the shape of the nozzle are optimized. The straight-through wall is optimized into an arc surface through CFD numerical simulation. The nozzle adopts a nozzle type according to the maximum distance required. It can supply air over long distances and provide the fastest cooling effect for the transformer heat sink. The delivery pipeline adopts a ring structure design.

[0014] The size of the transmission pipeline is determined as follows: the nozzle position is confirmed according to the position of the main transformer heat sink; the inner diameter of the transmission pipeline and the arrangement of the main transformer cooling device are determined according to the air flow velocity; the air supply duct is based on 0.8-1.5Pa / m, and the local resistance is minimized by optimizing the transmission pipeline, including placing the main transformer cooling device as close to the load as possible. The transmission pipeline is planned according to the wind speed, and a large curvature radius is used for the curved part. The design is combined with CFD numerical simulation, and the aspect ratio of the transmission section must be less than 6.

[0015] The numerical model analysis uses CFD numerical simulation and CEM for grid division. The pipeline is structured and the tee is unstructured. The grid adopts the general ANSYS FLUENT 17.0 flow field to analyze the pressure and velocity changes of the fluid in the pipeline. The coupling between pressure / velocity adopts the semi-implicit method of the pressure coupling equation group. The momentum, turbulent kinetic energy, turbulent dissipation rate and Reynolds stress are discretized using the second-order upwind scheme, and the pressure is discretized using the standard form.

[0016] Compared with the prior art, the present invention has the following beneficial effects: by rationally optimizing the cold air input pipe structure, the problem of resistance caused by local components, which increases pipe vibration and noise and thus affects the efficiency of the entire input system, is solved, so that the amount of dry cold air and the wind speed obtained by the heat sinks at different positions of the main transformer are uniform and reasonable. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 A flow chart of the method of this application;

[0019] Figure 2 This is a diagram of the pressure difference before and after the inlet transition pipe under different numbers of grids in this application;

[0020] Figure 3 The optimized rendering for this application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings. It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0022] The terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0023] The terms "first," "second," etc. are only used to distinguish one entity or operation from another entity or operation, and are not to be understood as indicating or implying relative importance, nor are they to be understood as requiring or implying any actual relationship or order between these entities or operations.

[0024] Reference Figures 1 to 3 An embodiment of the present invention provides a method for optimizing the pipeline structure for delivering dry cold air to the heat sink of a main transformer of a substation, comprising:

[0025] S1: Determination of ventilation volume: Calculate the ventilation volume required for each air outlet and each zone based on heat load calculation and air change frequency index;

[0026] S2: Determine the outlet: The number of outlets, their configuration, and air volume are determined by the number of heat sinks in the transformer.

[0027] S3: Determine the appropriate delivery pipelines connecting the various outlets of the air conditioner;

[0028] S4: Determine the air volume passing through each section. Calculate the air volume passing through each section of the conveying pipeline from each outlet to the main transformer cooling device based on the main transformer oil temperature.

[0029] S5: Determine the dimensions of the transmission duct: Referencing the unit friction loss and the allowable value of the transmission duct wind speed, determine the dimensions of each section of the transmission duct, the diameter of the circular air duct, and the length of the two sides of the rectangular transmission duct. Based on the above conditions, determine the model of the main transformer cooling device, whose main parameters are ventilation resistance and total pressure loss.

[0030] S6: Numerical model analysis: Simulations are performed using CFD numerical models to predict reliable RSM turbulence patterns;

[0031] S7: Optimization of local components and delivery pipelines: Based on the data model predicted by the data model and the actual site requirements, the T-type diversion tee type and the shape of the nozzle are optimized. The straight-through wall is optimized into an arc surface through CFD numerical simulation. The nozzle adopts a nozzle type according to the maximum distance required. It can supply air over long distances and provide the fastest cooling effect for the transformer heat sink. The delivery pipeline adopts a ring structure design.

[0032] Example:

[0033] Confirmation of the transmission pipeline: According to the pressure level, the high-pressure pipeline needs to limit the pressure below +2940Pa and below -2450Pa, and the flow velocity in the pipe is below 20m / s. The design is based on the full pressure standard (full pressure = static pressure + dynamic pressure);

[0034] Determination of ventilation volume: Q = 3600q s / C P |t r -t s |

[0035] Where, Q: the ventilation volume required in the air-conditioning equipment Q [m 3 / h];q s : Sensible heat load [kw]; C P : Specific heat of air at constant pressure [kJ / (kg.℃)]; p: density of air [kg / m]; t r : room temperature [℃]; t s : outlet temperature [℃];

[0036] At the same time, it is also necessary to consider whether the main transformer is located indoors or outdoors, and make final confirmation through relevant auxiliary measures.

[0037] Determination of the conveying pipeline: It is necessary to consider the air flow velocity of the conveying pipeline and the aspect ratio of the conveying pipeline: the formula for a circular pipe is r / D = 1.5-2.0 (r: turning radius, D: circular pipe diameter). The design model is as follows:

[0038] The calculation formula of friction loss in the transmission pipeline is:

[0039] Pf = friction coefficient * (pipe length / pipe radius) * (wind speed squared / 2 * 9.8) * air specific gravity. The default value of air specific gravity is usually 1.2 kg / m 3 .

[0040] CFD numerical simulation: CEM is used for grid division, structured grid at the pipe, unstructured grid at the tee, the grid adopts the general ANSYSFLUENT17.0 flow field to analyze the pressure and velocity changes of the fluid in the pipeline, the coupling between pressure / velocity adopts the semi-implicit method for pressure coupled equations (Semi-Implicit Method for Pressure Linked Equations), the discretization of momentum, turbulent kinetic energy, turbulent dissipation rate, and Reynolds stress adopts the second-order upwind scheme, and the discretization of pressure adopts the standard form. In order to ensure the accuracy and reliability of the numerical simulation, it is necessary to verify the relationship between the number of grids and the calculation results. The number of grids generated in sequence is: 3.21 million three-dimensional unstructured grid files, 4.64 million three-dimensional unstructured grid files, 5.4 million three-dimensional unstructured grid files, 6.38 million three-dimensional unstructured grid files, 1017 three-dimensional unstructured grid files,

[0041] Figure 2 The pressure differential across the inlet transition pipe at different grid cell numbers is shown in the figure. The pressure differential at the air conditioner inlet pipe increases with increasing grid cell numbers. However, when the grid cell number increases from 5.6 million to 6.08 million, the pressure differential increases by approximately 1.66%. The pressure differential at the air conditioner inlet pipe remains virtually unchanged. This indicates that the pressure differential at the transition pipe is highly reliable when the grid cell number is 5.6 million, so 5.6 million is selected as the required grid cell number for the calculation.

[0042] Confirmation of nozzle design: mainly based on the main transformer diffusion radius, arrival distance / wind speed. The nozzle shape used this time is slender. The wind speed formula is as follows: Va = passing air volume (m 3 / min) / (60*opening area m 3 ), the effective opening area of ​​the channel is generally less than 65%;

[0043] T-shaped branch pipe design (currently only T-shaped branch pipes are used): The pressure loss formula is:

[0044] ΔP=ξ(ρu 2 / 2)

[0045]

[0046] Where ΔP represents the pressure loss (Pa), ρ represents the density of the fluid (kg / m 3 ), a represents the outlet height, b represents the outlet width, u is the average flow rate of air in the tube, where the design model is as follows:

[0047] According to the CFD data model, the straight pipe wall is optimized as follows:

[0048] H is the height of the cambered surface. As the cambered surface height increases, the local resistance coefficient of the straight-through tube gradually decreases, and the drag reduction gradually increases. When the height is 0.15, it reaches Max (drag reduction rate) = 15.9%; then the drag reduction rate of the straight-through tube gradually decreases. When the height is 0.28, the drag reduction rate = non-positive number, that is, the cambered surface structure no longer reduces drag. It can be seen that the optimal dimension is a cambered surface height of 0.15, and the effect is as follows Figure 3 shown.

[0049] The above measures are used to improve and optimize the pipeline structure for delivering dry cold air to the heat sink of the main transformer of the substation.

[0050] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for optimizing the pipeline structure for delivering dry cold air to the heat sink of the main transformer of a substation, characterized in that: include: S1: Determination of ventilation volume: Calculate the ventilation volume required for each outlet and each area based on heat load calculation and ventilation frequency index; S2: Determine the outlet: The number of outlets, configuration and air volume are determined by the number of heat sinks of the transformer; S3: Determination of fixed delivery pipelines: Determine the reasonable fixed delivery pipelines connecting each spray outlet of the air conditioner; S4: Determine the air volume passing through each part. According to the oil temperature of the main transformer, calculate the air volume passing through each part of the conveying pipeline from each outlet to the main transformer cooling device; S5: Determine the size of the transmission pipeline: refer to the unit friction loss and the allowable value of the transmission pipeline wind speed, determine the size of each part of the transmission pipeline, the diameter of the circular air duct, and the length of the two sides of the rectangular transmission pipeline; based on the above conditions, determine the model of the main transformer cooling device, and its main parameters are ventilation resistance and total pressure loss; S6: Numerical model analysis: Simulations are performed using CFD numerical models to predict reliable RSM turbulence models; S7: Optimization of local components and delivery pipelines: Through the data model predicted by the data model and the actual site requirements, the T-type diversion tee type and the shape of the nozzle are optimized. The straight-through wall is optimized into an arc surface through CFD numerical simulation. The nozzle adopts a nozzle type according to the maximum distance required, and the delivery pipeline adopts a ring structure design.

2. A method for optimizing the pipeline structure for delivering dry cold air to the heat sink of the main transformer of a substation according to claim 1, characterized in that: The size of the delivery pipeline is determined by: confirming the position of the nozzle according to the position of the main transformer heat sink; determining the inner diameter of the delivery pipeline and the arrangement of the main transformer cooling device according to the air flow velocity; the air supply duct is based on 0.8-1.5Pa / m, and the local resistance is minimized by optimizing the delivery pipeline, including the main transformer cooling device being as close to the load as possible, planning the delivery pipeline according to the wind speed, using a large curvature radius for the curved part, and combining CFD numerical simulation for design. The aspect ratio of the delivery section must be less than 6.

3. A method for optimizing the pipeline structure for delivering dry cold air to the heat sink of the main transformer of a substation according to claim 1, characterized in that: The numerical model analysis uses CFD numerical simulation and CEM for grid division. The pipeline is structured and the tee is unstructured. The grid uses the general ANSYS FLUENT 17.0 flow field to analyze the pressure and flow velocity changes of the fluid in the pipeline. The coupling between pressure / flow velocity adopts the semi-implicit method of the pressure coupling equation group. The discretization of momentum, turbulent kinetic energy, turbulent dissipation rate and Reynolds stress adopts the second-order upwind format, and the discretization of pressure adopts the standard form.

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