Design method of transformer accident oil discharge similarity reduced scale model

Abstract

The invention discloses a design method of a transformer accident oil discharge similarity reduced scale model, and aims to solve the problems of high cost, poor repeatability and the like of an existing in-situ or full-scale experiment, the design method is combined with similarity analysis to calculate reduced scale model design parameters under different transformer scales and different similarity ratios. Further calculating the similar scale of the oil discharge process between the reduced scale model and the prototype transformer, and finally manufacturing the reduced scale model according to the design parameters and carrying out an oil discharge experiment. Experimental results show that the method for simulating the oil discharge process of the transformer by adopting the reduced scale model is effective, and the experimental similarity design method provided by the invention can meet the requirements of the reduced scale experiment and can keep a good similarity relationship. In addition, an experimental value obtained by an experiment has good consistency with a theoretical value, and the reduced scale model can be verified by the experiment.

Description

Technical Field

[0001] The invention relates to the field of volume, flow, mass flow or liquid level measurement, and in particular to a design method for a transformer accident oil drainage similarity scale model. Background Art

[0002] After the transformer explodes, stress concentration locations such as the bushing riser are often damaged and cracks are formed. The transformer oil flows out from the cracks to the accident oil pit at the transformer foundation. The oil in the accident oil pit is discharged to the total accident oil pool through the oil discharge pipe at the oil discharge port. Therefore, the leakage and discharge of transformer oil after the transformer explosion can be divided into two stages: (1) the oil in the transformer oil tank is discharged into the accident oil pit, and the accident oil pit is also in the oil discharge stage; (2) the oil in the transformer oil tank is completely discharged, and only the accident oil pit is in the oil discharge stage. In this process, if the leakage flow discharged into the accident oil pit is greater than the discharge volume of the accident oil pit oil, the amount of transformer oil retained in the accident oil pit will increase. When the retained oil volume exceeds the design capacity of the accident oil pit, the transformer oil will overflow to form a flowing fire, and the oil discharge process will fail; on the contrary, the amount of oil retained in the accident oil pit will continue to decrease until it is discharged to the total accident oil pool. The transformer oil will not form a flowing fire, and the oil discharge process will be successful. In order to study the oil discharge process, it is necessary to carry out relevant experiments. However, it is well known that the cost of full-scale model experiments or in-situ experiments is relatively high. If scaled model experiments can be used, the experimental cost can be greatly reduced. However, the biggest problem that needs to be solved in scaled experimental models is the experimental similarity between scaled model experiments and prototype experiments. It is necessary to carry out similarity research on scaled model experiments.

[0003] However, the common research methods for the oil drainage problem after the transformer explosion are full-scale experiments and in-situ experiments, such as transformer accident oil pool fire experiments with different oil pool diameters, and experiments on different fire extinguishing methods for transformer accident oil pool fires. The cost of this experimental method is usually high and not repeatable. Therefore, many scholars have also used numerical simulations, such as using DualSPHysics smooth particle dynamics calculation software to calculate and analyze the transformer oil drainage problem. Although this method is low-cost and highly controllable, it depends on the correctness of the model and the accuracy of the algorithm, and high-precision calculation models require high-performance computers and a long time cost. Therefore, at this stage, it is necessary to combine the advantages and disadvantages of the two and design a scaled model design method to study the oil drainage problem after the transformer explosion. However, the scaled model is not a simple scaling of the geometric dimensions of the actual system, but to keep the key physical properties similar to the original system. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention provides a design method for a transformer accident oil drainage similarity scale model.

[0005] To implement the above technical solution, the specific steps of a design method for a transformer accident oil drainage similarity scale model are as follows:

[0006] S1. Calculate the dimensionless parameters of the prototype transformer and prototype accident oil storage pit;

[0007]

[0008] Where m is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the oil tank, A K is the opening area at the root of the prototype transformer oil tank bushing, A0 is the effective cross-sectional area of ​​the prototype transformer oil tank; n is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the accident oil storage pit, A C is the effective cross-sectional area of ​​the prototype accident oil storage pit; p is the ratio of the effective area of ​​the discharge port of the prototype accident oil storage pit to the effective cross-sectional area of ​​the accident oil storage pit, A P The effective area of ​​the oil outlet of the prototype accident oil storage pit;

[0009] S2. Obtain the similarity relationship m between the scaled model transformer and the prototype transformer based on the dimensionless parameter m, the initial transformer oil level in the prototype transformer and the set similarity ratio. s and H 0s ; According to the dimensionless parameters n, p and the set similarity ratio, the similarity relationship n between the scaled model accident oil storage pit and the prototype accident oil storage pit is obtained s and p s , the specific steps are as follows:

[0010] S2.1. The scale model transformer has the following similarity relationship with the prototype transformer:

[0011]

[0012] In the formula, m s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the oil tank; H0 is the initial transformer oil level height in the prototype transformer; H 0s is the initial transformer oil level in the scaled model; a is the set similarity ratio;

[0013] S2.2. The similarity between the scaled model accident oil storage pit and the prototype accident oil storage pit is as follows:

[0014]

[0015] Where n s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the accident oil storage pit; p sis the ratio of the effective area of ​​the oil outlet of the accident oil storage pit in the scaled model to the effective cross-sectional area of ​​the accident oil storage pit;

[0016] S3. Calculate the design parameters of the scale model transformer and the scale model accident oil storage pit;

[0017] When designing the scaled model, the parameters involved are shown in Table 1;

[0018] Table 1 Scale model design parameters and their descriptions

[0019]

[0020] Among them, H 0s The calculation method of is shown in formula (2), A 0s Determined according to experimental conditions, for the convenience of calculation and model processing, take A 0s =1m 2 ;

[0021] A Ks The calculation method is:

[0022] A Ks =a·m·A 0s (4)

[0023] A Cs The calculation method is:

[0024]

[0025] A Ps The calculation method is:

[0026] A Ps =a·p·A Cs (6)

[0027] S4. Calculate the similarity between the scaled model transformer and the prototype transformer and between the scaled model accident oil storage pit and the prototype accident oil storage pit. The specific steps are as follows:

[0028] S4.1. Calculate the similarity between the scaled model transformer and the prototype transformer, specifically:

[0029] In the prototype system, when the transformer explodes, the transformer oil will leak from the bushing rupture to the accident oil storage pit. At this time, the oil level in the transformer tank obeys the following quadratic function:

[0030]

[0031] Where H1(t) is the height of the oil level of the prototype transformer from the opening; t is time; g is the acceleration of gravity, and C is the flow coefficient;

[0032] Substituting formula (1) into formula (7) we can obtain:

[0033]

[0034] The calculation expression of the time for draining the transformer oil in the oil tank, i.e. the maximum draining time of the transformer, is as follows:

[0035]

[0036] Where, T 1max is the maximum oil draining time of the prototype transformer;

[0037] Substituting formula (1) into formula (9) we can obtain:

[0038]

[0039] For the scaled model transformer, the oil level of the scaled transformer model obeys a quadratic function consistent with the prototype transformer model. The specific expression is:

[0040]

[0041] In the formula, H 1s (t) is the height of the oil level from the opening of the scale model transformer;

[0042] Substituting equations (2)-(6) into equation (11), we can obtain:

[0043]

[0044] It can be seen that the height of the transformer oil level from the opening between the scaled model transformer and the prototype transformer has a similar scale of 1:a 2 ;

[0045] Similarly, the maximum oil draining time of the scale model transformer tank meets the following requirements:

[0046]

[0047] In the formula, is the maximum oil draining time of the scale model transformer;

[0048] Substituting equations (2)-(6) into equation (13), we can obtain:

[0049]

[0050] It can be seen that the maximum oil draining time of the transformer between the scaled model transformer and the prototype transformer has a similar scale of 1:1;

[0051] S4.2. Calculate the similarity between the scaled model accident oil pit and the prototype accident oil pit. Specifically, the oil in the transformer tank is discharged into the accident oil pit. At the same time, the accident oil pit is also in the oil discharge stage (first stage) and the oil in the transformer tank is completely discharged. Only the accident oil pit oil discharge stage (second stage) is analyzed. The specific analysis is as follows:

[0052] S4.2.1. In the prototype system, when the oil in the transformer tank is discharged into the accident oil storage pit, and the accident oil storage pit is also in the oil discharge stage (t≤T max ), the oil level in the accident oil storage pit satisfies the following differential equation:

[0053]

[0054] In the formula, H 2,1 (t) is the height of the liquid level in the prototype accident oil storage pit from the oil discharge port during the first stage;

[0055] Substituting formula (1) into formula (15) we can get:

[0056]

[0057] For the scaled model accident oil storage pit, when the oil in the transformer tank is discharged into the accident oil storage pit and the accident oil storage pit is also in the oil discharge stage, the oil level height of the scaled model accident oil storage pit also satisfies the following differential equation:

[0058]

[0059] Substituting equations (2)-(6) into equation (17), we obtain:

[0060]

[0061] By comparing equation (16) with equation (18), it is not difficult to find that in this stage, the oil level height of the scaled model and the prototype accident oil storage pit has the following similar scale:

[0062]

[0063] It can be seen that in this stage, the liquid level distance from the scaled model accident oil storage pit to the oil discharge port height has a similar scale of 1:a 2 ;

[0064] S4.2.2. In the prototype system, the oil in the transformer tank is completely drained, and only the accident oil storage pit is drained. The oil level height of the accident oil storage pit is expressed as follows:

[0065]

[0066] In the formula, H2,2 (t) is the height of the liquid level in the prototype accident oil storage pit from the oil discharge port during the second stage; H 2max It is T 1max The height of the oil level in the prototype accident oil storage pit at the moment;

[0067] Substituting formula (1) into formula (20) we can obtain:

[0068]

[0069] For the scaled model accident oil storage pit, this stage also satisfies expression (20). From the above analysis, it can be seen that the oil draining of the prototype transformer tank and the scaled model have a similar scale of 1:1 in time. Therefore, when the transformer tank in the scaled model is drained, there is:

[0070]

[0071] From this we can get:

[0072]

[0073] In the formula, is the height of the liquid level in the scaled model accident oil storage pit from the oil discharge port in the second stage. It can be seen that in this stage, the height of the liquid level from the oil discharge port between the scaled model and the prototype accident oil storage pit has a similar scale of 1:a 2 ;

[0074] In the prototype, the maximum oil discharge time of the accident oil storage pit is expressed as:

[0075]

[0076] Where, T 2max is the maximum oil draining time of the prototype system;

[0077] From the above analysis, it can be seen that the maximum oil discharge time expression of the scaled model accident oil storage pit is:

[0078]

[0079] It can be seen that the similarity scale of the maximum oil discharge time between the prototype accident oil storage pit and the scaled model is 1:1;

[0080] Summarizing the above analysis, it can be seen that the liquid level changes between the scaled model transformer and the scaled model accident oil storage pit designed by the present invention and the prototype transformer and the accident oil storage pit have a similar scale of 1:a 2 ; The similarity scale of oil discharge time is 1:1;

[0081] S5. making a scaled model according to the design parameters;

[0082] The scaled model includes: a scaled model transformer and a scaled model accident oil storage pit;

[0083] S6. Carry out scaled-down experiments based on existing transformers to verify the effectiveness of the scaled-down model.

[0084] Beneficial Effects of the Invention

[0085] 1. Replace the currently common full-scale experiments and in-situ experiments, thereby achieving the purpose of reducing costs and repeatable experiments;

[0086] 2. Replace the numerical simulation method, reduce the requirements for personnel and computer equipment, reduce time costs, and also improve the authenticity of the data;

[0087] 3. Through the scaled model experiment, it can provide reference for the design and modification of the accident oil discharge system. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a flow chart of the present invention;

[0089] Figure 2 It is a simplified schematic diagram of oil-immersed transformer and accident oil storage pit;

[0090] Figure 3 This is a schematic diagram of a scaled transformer oil tank;

[0091] Figure 4 This is a scaled-down picture of the transformer oil tank;

[0092] Figure 5 This is a scaled schematic diagram of the accident oil storage pit;

[0093] Figure 6 This is a scaled-down picture of the accident oil storage pit;

[0094] Figure 7 Experimental process of filling the scale transformer oil tank with water to the set water level;

[0095] Figure 8 Drain water from the scale transformer tank and record the liquid level experimental process;

[0096] Fig. 9 The experimental and theoretical values ​​of the change in the oil tank liquid level in the oil draining experiment of the 220kVA transformer scale model;

[0097] Fig.10 The process of water injection experiment for the scaled-down accident oil storage pit;

[0098] Fig.11 Draining the scaled accident oil storage pit and recording the liquid level experimental process;

[0099] Fig.12These are the experimental and theoretical values ​​of the change in liquid level in the accident oil storage pit during the oil drainage experiment of a 220kVA transformer scale model. DETAILED DESCRIPTION

[0100] The present invention is further described in detail below in conjunction with specific embodiments.

[0101] A design method for a transformer accident oil drainage similarity scale model comprises the following steps:

[0102] S1. Calculate the dimensionless parameters of the prototype transformer and prototype accident oil storage pit;

[0103] The calculation method of the dimensionless parameters of the prototype transformer and the prototype accident oil storage pit is:

[0104]

[0105] Where m is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the oil tank, A K is the opening area at the root of the prototype transformer oil tank bushing, A0 is the effective cross-sectional area of ​​the prototype transformer oil tank; n is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the accident oil storage pit, A C is the effective cross-sectional area of ​​the prototype accident oil storage pit; p is the ratio of the effective area of ​​the discharge port of the prototype accident oil storage pit to the effective cross-sectional area of ​​the accident oil storage pit, A P The effective area of ​​the oil outlet of the prototype accident oil storage pit;

[0106] The embodiment of the present invention obtains the prototype design parameters of common transformers and accident oil storage pits. The dimensionless parameters obtained by combining formula (1) are shown in Table 2. The simplified schematic diagram of transformer accident oil drainage is shown in Figure 1 As shown;

[0107] Table 2 Common transformer design parameters and dimensionless parameters

[0108] parameter 500kVA 330kVA 220kVA 110kVA <![CDATA[H0]]> 5.900 5.600 4.790 2.640 <![CDATA[A0]]> 27.100 20.180 19.350 6.856 <![CDATA[A K ]]> 0.205 0.166 0.0995 0.051 <![CDATA[A C ]]> 72.000 51.600 42.00 9.000 <![CDATA[A P ]]> 0.126 0.070 0.070 0.030 <![CDATA[m=A K / A0(10 -3 )]]> 7.565 8.226 5.142 7.439 <![CDATA[n=A K / A C (10 -3 )]]> 2.847 3.217 2.369 5.667 <![CDATA[p=A P / A C (10 -3 )]]> 1.744 1.357 1.667 3.333

[0109] S2. Obtain the similarity relationship m between the scaled model transformer and the prototype transformer based on the dimensionless parameter m, the initial transformer oil level in the prototype transformer and the set similarity ratio. s and H 0s ; According to the dimensionless parameters n, p and the set similarity ratio, the similarity relationship n between the scaled model accident oil storage pit and the prototype accident oil storage pit is obtained s and p s , the specific steps are as follows:

[0110] S2.1. Assume that the scaled model transformer and the prototype transformer have the following similarity relationship:

[0111]

[0112] In the formula, m s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the oil tank; H0 is the initial transformer oil level height in the prototype transformer; H 0s is the initial transformer oil level in the scaled model; a is the set similarity ratio;

[0113] S2.2. Assume that the scaled model accident oil storage pit has the following similarity relationship with the prototype accident oil storage pit:

[0114]

[0115] Where n s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the accident oil storage pit; p s is the ratio of the effective area of ​​the oil outlet of the accident oil storage pit in the scaled model to the effective cross-sectional area of ​​the accident oil storage pit;

[0116] The similarity ratio a is set as required. In the embodiment of the present invention, three common similarity ratios of a=1 / 2, a=1 / 3, and a=1 / 4 are selected to design the scaled model;

[0117] S3. Calculate the design parameters of the scale model transformer and the scale model accident oil storage pit;

[0118] When designing the scaled model, the main parameters involved are shown in Table 1;

[0119] Table 1 Scale model design parameters and their descriptions

[0120]

[0121] Among them, H 0s The calculation method of is shown in formula (2), A 0s Determined according to experimental conditions, for the convenience of calculation and model processing, take A 0s =1m 2 ;

[0122] A Ks The calculation method is:

[0123] A Ks =a·m·A 0s (4)

[0124] A Cs The calculation method is:

[0125]

[0126] A Ps The calculation method is:

[0127] A Ps =a·p·A Cs (6)

[0128] According to formula (2)-formula (6), the scaled model design parameters of transformers of different specifications under different similarity ratios a are calculated. The specific calculation results are shown in Table 3.

[0129] Table 3 Design parameters of scaled models of common transformers at different similarity ratios

[0130]

[0131]

[0132] Table D s is the oil outlet diameter of the accident oil storage pit in the scaled model;

[0133] S4. Calculate the similarity between the scaled model transformer and the prototype transformer and between the scaled model accident oil storage pit and the prototype accident oil storage pit. The specific steps are as follows:

[0134] S4.1. Calculate the similarity between the scaled model transformer and the prototype transformer, specifically:

[0135] In the prototype system, when the transformer explodes, the transformer oil will leak from the bushing rupture to the accident oil storage pit. At this time, the oil level in the transformer tank obeys the following quadratic function:

[0136]

[0137] Where H1(t) is the height of the oil level of the prototype transformer from the opening; t is time; g is the acceleration of gravity, and C is the flow coefficient;

[0138] Substituting formula (1) into formula (7) we can obtain:

[0139]

[0140] The calculation expression of the time for draining the transformer oil in the oil tank, i.e. the maximum draining time of the transformer, is as follows:

[0141]

[0142] Where, T 1max is the maximum oil draining time of the prototype transformer;

[0143] Substituting formula (1) into formula (9) we can obtain:

[0144]

[0145] For the scaled model transformer, the oil level of the scaled transformer model obeys a quadratic function consistent with the prototype transformer model. The specific expression is:

[0146]

[0147] In the formula, H 1s (t) is the height of the oil level from the opening of the scale model transformer;

[0148] Substituting equations (2)-(6) into equation (11), we can obtain:

[0149]

[0150] It can be seen that the height of the transformer oil level from the opening between the scaled model transformer and the prototype transformer has a similar scale of 1:a 2 ;

[0151] Similarly, the maximum oil draining time of the scale model transformer tank meets the following requirements:

[0152]

[0153] In the formula, is the maximum oil draining time of the scale model transformer;

[0154] Substituting equations (2)-(6) into equation (13), we can obtain:

[0155]

[0156] It can be seen that the maximum oil draining time of the transformer between the scaled model transformer and the prototype transformer has a similar scale of 1:1;

[0157] S4.2. Calculate the similarity between the scaled model accident oil pit and the prototype accident oil pit. Specifically, the oil in the transformer tank is discharged into the accident oil pit. At the same time, the accident oil pit is also in the oil discharge stage (first stage) and the oil in the transformer tank is completely discharged. Only the accident oil pit oil discharge stage (second stage) is analyzed. The specific analysis is as follows:

[0158] S4.2.1. In the prototype system, when the oil in the transformer tank is discharged into the accident oil storage pit, and the accident oil storage pit is also in the oil discharge stage (t≤T max ), the oil level in the accident oil storage pit satisfies the following differential equation:

[0159]

[0160] In the formula, H 2,1 (t) is the height of the liquid level in the prototype accident oil storage pit from the oil discharge port during the first stage;

[0161] Substituting formula (1) into formula (15) we can get:

[0162]

[0163] For the scaled model accident oil storage pit, when the oil in the transformer tank is discharged into the accident oil storage pit and the accident oil storage pit is also in the oil discharge stage, the oil level height of the scaled model accident oil storage pit also satisfies the following differential equation:

[0164]

[0165] In the formula, is the height from the liquid level in the scaled model accident oil storage pit to the oil discharge port in the first stage;

[0166] Substituting equations (2)-(6) into equation (17), we obtain:

[0167]

[0168] By comparing equation (16) with equation (18), it is not difficult to find that in this stage, the oil level height of the scaled model and the prototype accident oil storage pit has the following similar scale:

[0169]

[0170] It can be seen that in this stage, the liquid level distance from the scaled model accident oil storage pit to the oil discharge port height has a similar scale of 1:a 2 ;

[0171] S4.2.2. In the prototype system, the oil in the transformer tank is completely drained, and only the accident oil storage pit is drained. The oil level height of the accident oil storage pit is expressed as follows:

[0172]

[0173] In the formula, H 2,2 (t) is the height of the liquid level in the prototype accident oil storage pit from the oil discharge port during the second stage; H 2max It is T 1max The height of the oil level in the prototype accident oil storage pit at the moment;

[0174] Substituting formula (1) into formula (20) we can obtain:

[0175]

[0176] For the scaled model accident oil storage pit, this stage also satisfies expression (20). From the above analysis, it can be seen that the oil draining of the prototype transformer tank and the scaled model have a similar scale of 1:1 in time. Therefore, when the transformer tank in the scaled model is drained, there is:

[0177]

[0178] From this we can get:

[0179]

[0180] In the formula, is the height of the liquid level in the scaled model accident oil storage pit from the oil discharge port in the second stage. It can be seen that in this stage, the height of the liquid level from the oil discharge port between the scaled model and the prototype accident oil storage pit has a similar scale of 1:a 2 ;

[0181] In the prototype, the maximum oil discharge time of the accident oil storage pit is expressed as:

[0182]

[0183] Where, T 2max is the maximum oil draining time of the prototype system;

[0184] From the above analysis, it can be seen that the maximum oil discharge time expression of the scaled model accident oil storage pit is:

[0185]

[0186] It can be seen that the similarity scale of the maximum oil discharge time between the prototype accident oil storage pit and the scaled model is 1:1.

[0187] Summarizing the above analysis, it can be seen that the liquid level changes between the scaled model transformer and the scaled model accident oil storage pit designed by the present invention and the prototype transformer and the accident oil storage pit have a similar scale of 1:a 2 ; The oil discharge time similarity scale is 1:1.

[0188] S5. Make a scaled model according to the design parameters. The specific steps are as follows:

[0189] The scaled model includes: a scaled model transformer and a scaled model accident oil storage pit;

[0190] S5.1. According to the design parameters in S3, the present invention selects a similarity ratio a=1 / 2 to make a scaled model of the transformer and the accident oil storage pit; according to the similarity design parameters given in Table 3, the scaled transformer oil tank model parameters are designed as follows:

[0191] 1.0m long, 1.0m wide, 1.6m high (the height needs to be greater than the initial oil level of 1.475m);

[0192] In order to make the scaled model meet the oil drainage test of four transformer working conditions of 550kVA, 330kVA, 220kVA and 110kVA, four openings are set around, with diameters of 69.4mm, 72.4mm, 57.2mm and 68.8mm respectively, and four initial oil level heights of 1.475m, 1.400m, 1.198m and 0.660m are set; the model designed according to the above parameters is shown in Figure 3 As shown, the actual completed Figure 4 As shown;

[0193] S5.2. According to the similar design parameters given in Table 3, the design parameters of the scaled accident oil storage pit model are: width 1.0m, length 2.657m; in order to make the scaled model meet the oil discharge experiment of four transformer working conditions of 550kVA, 330kVA, 220kVA and 110kVA, three partitions are used to divide the length direction into four compartments, the first partition is located at 2.556m from the end, the second partition is located at 2.170m from the end, and the third partition is located at 1.313m from the end; there are four openings in the compartment, with diameters of 46.76mm, 43.51mm, 43.96mm and 46.10mm respectively;

[0194] When designing the height of the scale model accident oil storage pit, it can be seen from the above that the cross-sectional area A of the transformer oil tank in the scale model 0s Set to 1m 2 According to the initial liquid level of the oil in the oil tank, the transformer oil volumes corresponding to the four working conditions are calculated as follows: 1.475m 2 , 1.400m 2 、1.198m 2 、0.600m 2 ; Assuming that all transformer oil flows into the accident oil storage pit and is not discharged, the maximum oil level height of the accident oil storage pit under four working conditions is: 1.475 / 2.657 = 0.5551m, 1.4 / 2.556 = 0.5477m, 1.198 / 2.17 = 0.5521m, 0.66 / 1.313 = 0.5027m, so when designing the scaled model of the accident oil storage pit, the box height is greater than the above height. The height designed by the present invention is 0.65m; the model designed according to the above parameters is shown in Figure 5 As shown, the actual completed Figure 6 As shown;

[0195] S6. Perform a scaled experiment based on the existing transformer design parameters to verify the effectiveness of the scaled model. The specific steps are as follows:

[0196] S6.1. Taking 220kVA transformer as an example, according to the above scaled model, water is used as the medium to carry out the scaled transformer oil tank draining experiment, and the initial oil level is set to 1.198m; a stopwatch is used to measure the time when the liquid level reaches the upper edge of the opening, and a camera is used to record the change of the liquid level. The test process is shown in Figure 7-Figure 8 The relevant test results are shown in Fig. 9 As shown;

[0197] The main reasons for using water as a medium instead of oil are: 1. Transformer oil is flammable, and water is safer in comparison; 2. Compared with oil, water is more environmentally friendly; 3. When calculating similar scales, the present invention only involves the flow coefficient for the physical properties of the liquid, that is, whether it is oil discharge or water discharge, the correctness of the present invention can be verified;

[0198] Fig. 9 Combined with the real leakage experiment of the scaled model, the time-varying curve of the liquid level calculated by the theoretical scaled model and the time-varying curve of the measured liquid level are compared. The results show that the experimental results are highly consistent with the theoretical calculation results.

[0199] S6.2, taking 220kVA transformer as an example, according to the above scaled model, water is used as the medium to carry out the scaled oil storage pit oil drainage experiment, the plate is placed 2.170m away from the end, and the variable orifice diameter is set to 43.96mm. The specific steps are as follows:

[0200] S6.2.1. Inject water into the scaled oil tank model to the scaled model liquid level specified in Table 3;

[0201] S6.2.2. Install the bottom orifice plate in the accident oil storage tank in place according to the diameter specified in Table 3 and apply sealant to position it;

[0202] S6.2.3. Drain the water in the oil tank and use a camera to observe the liquid level tube on the accident oil storage tank model and record the water level height of the liquid level tube at different times;

[0203] See the test process Figure 10-11 The relevant test results are shown in Fig.12 As shown;

[0204] Fig.12 The liquid level change curve obtained by theoretical calculation of scaled model and the measured liquid level change curve were compared. The results showed that the experimental results were highly consistent with the theoretical calculation results.

[0205] In summary, it is effective to simulate the transformer oil drainage process using a scaled model. The experimental similarity design method proposed in the present invention can meet the requirements of scaled experiments and maintain a good similarity relationship. The theoretical calculation model for transformer oil leakage and accident oil storage tank drainage is effective. The theoretical value of the curve of the liquid level height changing with time in the scaled model of the oil drainage process is in good agreement with the experimental value. The scaled model can be confirmed by experiments.

Claims

1. A design method for a transformer accident oil drainage similarity scale model, characterized in that: The following steps are involved: S1. Calculate the dimensionless parameters of the prototype transformer and prototype accident oil storage pit; The dimensionless parameters include: m, n, p; wherein m is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the prototype transformer oil tank, n is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the accident oil storage pit, and p is the ratio of the effective area of ​​the discharge port of the prototype accident oil storage pit to the effective cross-sectional area of ​​the accident oil storage pit; S2. Obtain the similarity relationship m between the scaled model transformer and the prototype transformer according to the dimensionless parameter m, the initial transformer oil level H0 in the prototype transformer and the set similarity ratio a. s and H 0s ; According to the dimensionless parameters n, p and the set similarity ratio, the similarity relationship n between the scaled model accident oil storage pit and the prototype accident oil storage pit is obtained s and p s ; The m s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the oil tank. 0s is the initial transformer oil level in the scaled model, and n s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the accident oil storage pit. s is the ratio of the effective area of ​​the oil outlet of the accident oil storage pit in the scaled model to the effective cross-sectional area of ​​the accident oil storage pit; S3. Calculate the design parameters of the scale model transformer and the scale model accident oil storage pit; The design parameters include: initial transformer oil level height H 0s , Transformer box effective cross-sectional area A 0s , Transformer bushing root opening area A Ks 、Effective cross-sectional area of ​​accident oil storage pit A Cs 、Effective area of ​​the oil outlet of the accident oil storage pit A Ps ; S4. Calculate the similarity between the scaled model transformer and the prototype transformer and between the scaled model accident oil storage pit and the prototype accident oil storage pit; S5. making a scaled model according to the design parameters; The scaled model includes: a scaled model transformer and a scaled model accident oil storage pit.

2. The design method of a transformer accident oil drainage similarity scale model according to claim 1 is characterized in that: The expression of the dimensionless parameter is as follows: Where m is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the oil tank, A K is the opening area at the root of the prototype transformer oil tank bushing, A0 is the effective cross-sectional area of ​​the prototype transformer oil tank; n is the ratio of the opening area at the root of the prototype transformer oil tank bushing to the effective cross-sectional area of ​​the accident oil storage pit, A C is the effective cross-sectional area of ​​the prototype accident oil storage pit; p is the ratio of the effective area of ​​the discharge port of the prototype accident oil storage pit to the effective cross-sectional area of ​​the accident oil storage pit, A P It is the effective area of ​​the oil discharge outlet of the prototype accident oil storage pit.

3. The design method of a transformer accident oil drainage similarity scale model according to claim 1 is characterized in that: The similarity relationship m between the scaled model transformer and the prototype transformer is obtained according to the dimensionless parameter m, the initial transformer oil level height in the prototype transformer and the set similarity ratio. s and H 0s ; According to the dimensionless parameters n, p and the set similarity ratio, the similarity relationship n between the scaled model accident oil storage pit and the prototype accident oil storage pit is obtained s and p s The steps are as follows: S2.

1. The scale model transformer has the following similarity relationship with the prototype transformer: In the formula, m s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the oil tank; H0 is the initial transformer oil level height in the prototype transformer; H 0s is the initial transformer oil level height in the scaled model; a is the similarity ratio; S2.

2. The similarity between the scaled model accident oil storage pit and the prototype accident oil storage pit is as follows: Where n s is the ratio of the opening area at the root of the oil tank bushing of the scaled model transformer to the effective cross-sectional area of ​​the accident oil storage pit; p s It is the ratio of the effective area of ​​the oil discharge outlet of the scaled accident oil storage pit to the effective cross-sectional area of ​​the accident oil storage pit.

4. The design method of a transformer accident oil drainage similarity scale model according to claim 1 is characterized in that: Among the design parameters, the opening area A at the root of the transformer bushing of the scaled model Ks , Effective cross-sectional area A of the scaled model accident oil storage pit Cs , Effective area A of the oil outlet of the scaled model accident oil storage pit Ps The calculation method is as follows: A Ks The calculation method is: A Ks =a·m·A 0s A Cs The calculation method is: A Ps The calculation method is: A Ps =a·p·A Cs In the formula, A 0s Represents the effective cross-sectional area of ​​the scaled model transformer box.

5. The design method of a transformer accident oil drainage similarity scale model according to claim 1 is characterized in that: The method for calculating the similarity between the scaled model transformer and the prototype transformer, and between the scaled model accident oil storage pit and the prototype accident oil storage pit is as follows: S4.

1. Calculate the similarity between the scaled model transformer and the prototype transformer; The calculation expression of the height of the oil level from the opening of the scaled model transformer is as follows: In the formula, H 1s (t) is the height of the oil level of the scale model transformer from the opening; g is the acceleration of gravity; t is time; C is the flow coefficient; H1(t) is the height of the oil level of the prototype transformer from the opening; The maximum oil draining time calculation expression of the scale model transformer is as follows: In the formula, is the maximum oil draining time of the scale model transformer; T 1max is the maximum oil draining time of the prototype transformer; S4.

2. Calculate the similarity between the scaled model accident oil storage pit and the prototype accident oil storage pit, specifically divided into: (1) the oil in the transformer tank is drained into the accident oil storage pit, and the accident oil storage pit is also in the oil discharge stage; (2) the oil in the transformer tank is completely drained, and only the accident oil storage pit is in the oil discharge stage; S4.2.

1. When the oil in the transformer tank is discharged into the accident oil storage pit and the accident oil storage pit is also in the oil discharge stage, the oil level height of the scaled model accident oil storage pit and the prototype accident oil storage pit has the following similar scale: In the formula, is the height from the liquid level in the scaled model accident oil storage pit to the oil discharge port in the first stage; S4.2.

2. When the oil in the transformer tank is completely drained and only the accident oil storage pit is draining oil, the calculation expression for the height of the liquid level in the accident oil storage pit of the scaled model from the oil drain port is as follows: In the formula, is the height from the liquid level in the scaled model accident oil storage pit to the oil discharge port in the second stage; H 2,2 (t) is the height of the liquid level in the prototype accident oil storage pit from the oil discharge port in the second stage, H 2max It is T 1max The height of the oil level in the prototype accident oil storage pit at the moment; The maximum oil discharge time expression of the scaled model accident oil storage pit is: Where, T 2max is the maximum oil discharge time of the prototype accident oil storage pit, is the maximum oil discharge time of the scaled model accident oil storage pit.

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