A compressed air foam extinguishing system and design method suitable for an extra-high voltage substation

Abstract

The application discloses a compressed air foam fire extinguishing system suitable for an extra-high voltage transformer substation and a design method, and relates to the technical field of fire extinguishing, which comprises a foam generating device, a foam conveying pipe, a first spraying pipe, a second spraying pipe and a nozzle. Near-end firewalls and far-end firewalls are arranged on the two sides of the electric power equipment of the extra-high voltage transformer substation. The foam generating device is connected with the first spraying pipe arranged on the near-end firewall and the second spraying pipe arranged on the far-end firewall through the foam conveying pipe. The length, the aperture and the angle of the nozzle are determined through tests based on the foam spraying track. The foam spraying track is calculated according to a foam track differential equation. The application has the advantage of improving the fire extinguishing efficiency.

Description

Technical Field

[0001] This invention relates to the field of fire extinguishing technology, and in particular to a compressed air foam fire extinguishing system and its design method suitable for ultra-high voltage substations. Background Technology

[0002] Ultra-high voltage (UHV) power transmission, as part of the "new infrastructure" initiative, has matured technologically, enabling efficient power transmission. UHV substations, as a core component of the entire UHV transmission and transformation project, play a crucial role in ensuring power supply. However, transformers within UHV substations are large oil-filled devices, posing a significant fire risk. Once a fire occurs, it burns rapidly, spreads quickly, and is difficult to extinguish manually, resulting in severe losses. Because UHV substations are often located in remote areas, firefighting at these stations relies heavily on self-rescue. Recent fires involving UHV oil-filled equipment highlight the critical role of reliable and efficient firefighting equipment in protecting personnel and equipment safety. Therefore, employing effective fire suppression systems is one of the essential safeguards for the safe operation of UHV substations.

[0003] Foam fire suppression systems, as a highly efficient fire extinguishing method, are widely used in the power industry. The fire extinguishing effect of a foam fire suppression system is inextricably linked to the arrangement of its nozzles. However, traditional nozzle arrangement methods for foam fire suppression systems have certain limitations, such as unreasonable nozzle placement and inaccurate spray angles, leading to reduced fire extinguishing effectiveness. Therefore, optimizing the nozzle arrangement method of foam fire suppression systems is of paramount importance to ensuring and improving their fire extinguishing performance.

[0004] Patent document CN114100044A discloses a sprinkler device for a compressed air foam fire extinguishing system, including a main protective pipe with locally reinforced pipes and branch pipes. Existing compressed air foam fire extinguishing systems, when extinguishing fires in ultra-high voltage substations, struggle to extinguish overflow fires near the near-end firewalls and around bushings. They lack focused protection for key transformer components such as bushings and oil conservators, and their ability to withstand ambient winds is insufficient, resulting in low fire extinguishing efficiency. Furthermore, the existing nozzle arrangement creates a linear foam coverage area, making it difficult to achieve comprehensive coverage. Summary of the Invention

[0005] The technical problem to be solved by this invention is to improve the fire extinguishing efficiency of compressed air foam fire extinguishing systems.

[0006] This invention solves the above-mentioned technical problems through the following technical means: a compressed air foam fire extinguishing system suitable for ultra-high voltage substations, comprising a foam generating device, a foam delivery pipe, a first spray pipe, a second spray pipe, and nozzles; a near-end firewall and a far-end firewall are respectively arranged on both sides of the power equipment in the ultra-high voltage substation; the foam generating device is connected to the first spray pipe installed on the near-end firewall and the second spray pipe installed on the far-end firewall through the foam delivery pipe; the first spray pipe includes a first horizontal pipe and a bend pipe that bends from both ends of the first horizontal pipe toward the side closer to the power equipment, and nozzles are installed on both the first horizontal pipe and the bend pipe; the second spray pipe includes a second horizontal pipe and a vertical pipe connected to the middle section of the second horizontal pipe, and nozzles are installed on both the second horizontal pipe and the vertical pipe;

[0007] The foam jet trajectory is calculated based on the foam trajectory differential equation. Based on the foam jet trajectory, the nozzle length, nozzle orifice diameter, and nozzle angle are determined. The calculation process for the foam jet trajectory is as follows:

[0008]

[0009] Where v is the velocity of the foam, θ is the angle between the direction of the foam velocity and the horizontal ground, x is the horizontal distance between the foam element and the nozzle, y is the height of the foam element above the ground, t is the characteristic time, F is the air resistance, m is the foam mass, g is the acceleration due to gravity, and c is the characteristic time. r d is the foam spray range coefficient during the rising phase. r This is the coefficient for the foam spray range during the descent phase;

[0010] The formula for calculating air resistance F is as follows:

[0011]

[0012] Where, ρ f Let V0 be the foam density, A0 be the initial foam injection velocity, y0 be the nozzle cross-sectional area, and R be the initial height of the foam element. e Let a be the Reynolds number. r br is the coefficient of change of foam cross-section during the rising phase, and br is the coefficient of change of foam cross-section during the falling phase.

[0013] coefficient a r b r c r d r The calculation formula is as follows:

[0014] a r =1281.4285+96.3571M;

[0015] br =4.257 - 0.297M + 0.0052M 2 ;

[0016] c r = -1.5933 - 0.0015L - 0.0856d n +0.0230Q+0.2325R+0.72928M;

[0017] d r = -9.9893 - 0.1417L - 2.1908d n +0.7423Q+2.5514R+6.7995M;

[0018] Where M is the nozzle angle, L is the nozzle length, and d is the nozzle diameter. n Where is the nozzle orifice diameter, Q is the foam flow rate, and R is the gas-liquid ratio.

[0019] As an optimized technical solution, the foam delivery pipe includes a main delivery pipe and branch delivery pipes. The main delivery pipe is connected to two branch delivery pipes through a T-joint, and the two branch delivery pipes are respectively connected to the first spray pipe and the second spray pipe.

[0020] As an optimized technical solution, the main conveying pipe and the branch conveying pipe, the branch conveying pipe and the first spray pipe, and the branch conveying pipe and the second spray pipe are all connected by flanges with internal sealing gaskets.

[0021] As an optimized technical solution, the first spray pipe is provided in two parts, one at the top of the near-end firewall and the other in the middle of the near-end firewall.

[0022] As an optimized technical solution, the vertical pipes are provided in three sections. The ground projection points of the axes of the three vertical pipes are respectively located at the intersection of the perpendicular lines drawn from the ground projection points of the midpoints of the main transformer side bushing, the main transformer oil tank, and the adjustment transformer oil tank of the power equipment to the ground projection of the axis of the second horizontal pipe.

[0023] As an optimized technical solution, both sides of the second transverse duct are extended 1-3 meters beyond the protected area. This can counteract the deflection effect of foam jets under wind and enhance the system's ability to resist ambient wind.

[0024] As an optimized technical solution, the nozzles on the first horizontal pipe, the bend pipe, the second horizontal pipe, and the vertical pipe are all evenly distributed along the pipe extension direction.

[0025] As an optimized technical solution, the first sprinkler pipe is fixedly connected to the near-end firewall via a first bracket, and the second sprinkler pipe is fixedly connected to the far-end firewall via a second bracket.

[0026] A design method for a compressed air foam fire extinguishing system suitable for ultra-high voltage substations, comprising the following steps:

[0027] S1 Data Collection:

[0028] Obtain information on the firewall design and power equipment of the UHV substations that need protection, and determine the areas around the UHV substations where foam generating devices can be placed.

[0029] S2 selects the spray pipe configuration:

[0030] The form of the first and second sprinkler pipes is selected according to the firewall design of the UHV substation.

[0031] S3 determines the number of nozzles, nozzle type, and nozzle arrangement:

[0032] The number, type, and arrangement of sprinklers are determined based on the wind speed in the local environment of the UHV substation and information on the power equipment.

[0033] S4 determines the foam parameters:

[0034] Calculate the foam flow rate based on the number of nozzles determined in step S3, and determine the gas-liquid ratio based on the wind speed of the local ambient wind at the UHV substation and the rated flow rate of the foam generating device.

[0035] S5 determines the nozzle length, nozzle orifice diameter, and nozzle angle:

[0036] The foam jet trajectory is calculated based on the foam trajectory differential equation. Based on the foam jet trajectory, the nozzle length, nozzle orifice diameter, and nozzle angle are determined through experiments.

[0037] S6 setup and commissioning are applicable to compressed air foam fire extinguishing systems in UHV substations:

[0038] Based on S1-S5 and in accordance with relevant standards, design the number of foam generating devices, build a compressed air foam fire extinguishing system suitable for UHV substations, connect the pipelines and conduct an airtightness check.

[0039] As an optimized technical solution, in step S4, the foam flow rate Q is calculated using the following formula:

[0040] Q = n × q;

[0041] Where n is the number of nozzles and q is the minimum foam flow rate of a single nozzle.

[0042] The advantages of this invention are:

[0043] 1. This invention, considering the layout characteristics of power equipment in ultra-high voltage substations and fire scenarios, divides key fire-prone and key protection areas into zones. By arranging a first, angled sprinkler pipe on the near-end firewall close to the foundation pit, overflow fires around the transformer and bushings, which are extremely difficult to extinguish, can be put out, providing key protection for difficult-to-extinguish areas and improving fire extinguishing efficiency. At the same time, the angled sprinkler pipe can also enhance the foam's resistance to ambient wind. By arranging a second, crisscrossing sprinkler pipe on the far-end firewall, key protection is provided for the main transformer's side bushings, main transformer oil conservator, and transformer oil conservator, further improving fire extinguishing efficiency. This invention can significantly improve the fire extinguishing performance of compressed air foam in extinguishing initial fires and fires in areas that are difficult to extinguish, better meeting fire protection requirements, ensuring power transmission safety, and reducing fire losses.

[0044] 2. This invention addresses the phenomenon that ambient wind can cause changes in the foam spray trajectory, thereby reducing fire extinguishing efficiency. It provides a solution by calculating the foam spray trajectory based on the differential equation of the foam trajectory. Based on the foam spray trajectory, the nozzle length, nozzle orifice diameter, and nozzle angle are determined through experiments. By selecting appropriate nozzle length, nozzle orifice diameter, and nozzle angle, the wind resistance of the foam can be improved, the foam coverage area can be increased, and the fire extinguishing efficiency can be improved, thereby quickly extinguishing UHV transformer fires. Attached Figure Description

[0045] Figure 1 This is a structural schematic diagram of a compressed air foam fire extinguishing system applicable to ultra-high voltage substations according to an embodiment of the present invention.

[0046] Figure 2 This is a flowchart illustrating the design method of a compressed air foam fire extinguishing system applicable to ultra-high voltage substations according to an embodiment of the present invention.

[0047] Figure 3 This is a foam spray trajectory diagram of nozzle #2 of the present invention under the action of ambient wind at different wind speeds.

[0048] Figure 4 This is a foam spray trajectory diagram of nozzle #3 of the present invention under the action of ambient wind at different wind speeds.

[0049] Figure 5 This is a foam spray trajectory diagram of nozzle #4 of the present invention under the action of ambient wind at different wind speeds.

[0050] Figure 6 This is a comparison chart of the spray distance and offset distance of different models of nozzles under the action of ambient wind at different wind speeds in embodiments of the present invention.

[0051] Figure 7 This is a diagram showing the foam spray trajectory of the nozzle in an embodiment of the present invention under different wind angles.

[0052] Figure 8 This is a graph showing the relationship between the spray distance and offset distance and the wind direction angle in an embodiment of the present invention.

[0053] Figure 9 This is a diagram showing the foam spray trajectory corresponding to different nozzle angles in an embodiment of the present invention.

[0054] Figure 10 This is a graph showing the change in foam jet aggregation degree with the foam jet angle in an embodiment of the present invention.

[0055] Figure 11 This is a diagram showing the foam jetting trajectory under different gas-liquid ratios in an embodiment of the present invention.

[0056] Figure 12 This is a graph showing the relationship between the injection distance and the gas-liquid ratio in an embodiment of the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0058] like Figure 1 As shown in the figure, this embodiment of the invention discloses a compressed air foam fire extinguishing system suitable for ultra-high voltage substations, including a foam generating device (not shown), a foam delivery pipe 2, a first spray pipe 3, a second spray pipe 4, and a nozzle 5.

[0059] Firewalls are arranged on both sides of the power equipment 1 in the UHV substation. The firewalls adopt an asymmetrical design, that is, the firewalls that are closer to the UHV substation pit and farther from the oil tank end are the near-end firewalls, and the firewalls that are farther from the UHV substation pit and closer to the oil tank end are the far-end firewalls. Ambient wind is easily formed between the near-end firewalls and the far-end firewalls. The effect of ambient wind will cause changes in the foam spray trajectory, thereby reducing the fire extinguishing efficiency.

[0060] The foam generating device is existing technology. It controls an air compressor via a control console to mix foam liquid in a storage tank with air in a storage tank through a gas-liquid mixer to generate foam with preset parameters. The foam generating device is connected via foam delivery pipes 2 to a first spray pipe 3 installed on the near-end firewall and a second spray pipe 4 installed on the far-end firewall. The foam delivery pipes 2 include a main delivery pipe 21 and branch delivery pipes 22. The main delivery pipe 21 delivers compressed air foam to the vicinity of the UHV substation and then connects to two branch delivery pipes 22 via a T-joint, further dividing the foam into two streams which are then delivered to the two branch delivery pipes 22 respectively. The first spray pipe 3 and the second spray pipe 4 are connected; the main conveying pipe 21 and the branch conveying pipe 22 are both made of stainless steel and have a pressure resistance greater than 3MPa. The main conveying pipe 21 is DN200 and the branch conveying pipe 22 is DN150. The main conveying pipe 21 and the branch conveying pipe 22, the branch conveying pipe 22 and the first spray pipe 3, and the branch conveying pipe 22 and the second spray pipe 4 are all connected by flanges with internal sealing gaskets. The foam conveying pipe 2 is arranged according to different UHV substation designs, so that it is connected to the performance-designed first spray pipe 3 and the second spray pipe 4 to ensure the foam spraying effect.

[0061] The first sprinkler pipe 3 is a bend-type sprinkler pipe, including a first horizontal pipe 31 and a bend-type pipe 32 that bends from both ends of the first horizontal pipe 31 toward the side closer to the power equipment 1. Both the first horizontal pipe 31 and the bend-type pipe 32 are equipped with nozzles 5 evenly distributed along the extension direction of the pipes. There are two first sprinkler pipes 3, one set at the top of the near-end firewall and the other set in the middle of the near-end firewall. Considering the structural layout characteristics of the power equipment 1 and the fire scenario, since it is difficult to extinguish the overflow fire at the two corners of the pit, bend-type sprinkler pipes are arranged on the near-end firewall close to the pit. The nozzles 5 on the bend-type pipe 32 extinguish the overflow fire around the transformer and bushing, which is extremely difficult to extinguish. The difficult-to-extinguish parts are given key protection, which improves the fire extinguishing efficiency. At the same time, the bend-type sprinkler pipe can also enhance the performance of foam against ambient wind.

[0062] The second spray pipe 4 adopts a spray pipe with a "Feng" - shaped horizontal and vertical cross - intersection, including a second horizontal pipe 41 and three vertical pipes 42 connected to the middle section of the second horizontal pipe 41. The ground projection points of the axes of the three vertical pipes 42 are respectively located at the intersection positions of the perpendiculars drawn from the mid - point ground projections of the side sleeves of the main transformer of the power equipment 1, the main transformer oil conservator, and the regulating and compensating transformer oil conservator to the ground projection of the axis of the second horizontal pipe 41; Sprayers 5 are uniformly distributed along the extending direction of the pipes on both the second horizontal pipe 41 and the vertical pipes 42. A part of the sprayers 5 on the vertical pipes 42 are located below the second horizontal pipe 41, and another part of the sprayers 5 are located above the second horizontal pipe 41; Both sides of the second horizontal pipe 41 extend to 1 - 3 m beyond the protected area, which can offset the foam spraying deflection effect under the action of wind and enhance the ability of the system to resist environmental wind; Since the sleeves and oil conservators of the power equipment 1 are key parts of the transformer and these parts need to be key - protected, the horizontal and vertical cross - intersection spray pipes are arranged on the distal firewall to conduct key protection on the side sleeves of the main transformer, the main transformer oil conservator, and the regulating and compensating transformer oil conservator, thus improving the fire - extinguishing efficiency.

[0063] The first spray pipe 3 is fixedly connected to the proximal firewall through the first bracket, and the second spray pipe 4 is fixedly connected to the distal firewall through the second bracket. The ends of the first spray pipe 3 and the second spray pipe 4 are both closed.

[0064] The sizes of both the first spray pipe 3 and the second spray pipe 4 are DN150, and the pressure resistance is greater than 3 MPa. The length range of all the sprayers 5 on the first spray pipe 3 and the second spray pipe 4 is 40 - 120 mm, the pore diameter range is 10 - 16 mm, and the sprayer spacing range is 600 - 700 mm. The length, spacing, and pore diameter of each sprayer 5 are the same; The bend angle of the bent - angle pipe 32 is 15 - 45°. There are 3 - 6 sprayers 5 on each bent - angle pipe 32. The sprayers 5 on the top first spray pipe 3 spray horizontally, and the spray angle of the sprayers 5 on the middle first spray pipe 3 is - 15° - 0°; There are 3 - 6 sprayers on each vertical pipe 42. The sprayers on the second horizontal pipe 41 spray horizontally, and the angle of the sprayers 5 on the vertical pipes 42 is - 15° - 5°.

[0065] See Figure 2 This embodiment of the present invention also discloses a design method for a compressed air foam fire - extinguishing system applicable to an UHV substation, which is used to design the compressed air foam fire - extinguishing system applicable to the UHV substation, and includes the following steps:

[0066] S1 Data collection:

[0067] Obtain information such as the firewall design of the UHV substation to be protected, the size, type, and layout of the power equipment 1, and determine the areas around the UHV substation where foam - generating devices can be placed.

[0068] S2 Select the form of the spray pipe:

[0069] Select the forms of the first spray pipe 3 and the second spray pipe 4 according to the firewall design of the UHV substation. For the asymmetric firewall design adopted by most UHV substations in this embodiment, the first spray pipe 3 adopts a bent-angle spray pipe, and the second spray pipe 4 adopts a spray pipe with a "rich" - shaped horizontal and vertical cross - intersection; for the symmetric firewall design, the forms of the first spray pipe 3 and the second spray pipe 4 are the same and symmetrically arranged, and both adopt one or two of a bent - angle spray pipe or a spray pipe with a "rich" - shaped horizontal and vertical cross - intersection.

[0070] S3 Determine the number of nozzles, nozzle type and nozzle arrangement method:

[0071] Determine the number of nozzles, nozzle type and nozzle arrangement method according to the wind speed of the local environment wind in the UHV substation and information such as the size, type and arrangement method of the power equipment 1; the ratio of the total number of nozzles 5 to the total insulating oil volume of the power equipment 1 should be greater than 1.5 nozzles / ton, and the number of nozzles at the foundation pit position should account for more than 90% of the total number of nozzles 5; as the wind speed of the local environment wind in the UHV substation increases, increase the number of nozzles and nozzle aperture on the bent - angle pipe 32, and increase the length of the second horizontal pipe 41; as the height of the power equipment increases, increase the height of the vertical pipe 42, the height of the vertical pipe 42 should be at least 1.2 m higher than the oil pillow, and the injection pressure of the most unfavorable nozzle on the vertical pipe 42 should be greater than or equal to 0.1 MPa.

[0072] S4 Determine the foam parameters:

[0073] According to the number of nozzles determined in step S3, calculate the foam flow rate Q through the following formula:

[0074] Q = n×q;

[0075] Where, n is the number of nozzles, q is the minimum foam flow rate of a single nozzle, and q satisfies not less than 40 L / mmin;

[0076] Determine the gas - liquid ratio according to the wind speed of the local environment wind in the UHV substation and the rated flow rate of the foam - generating device. In the case of a relatively high wind speed of the local environment wind or a relatively high rated flow rate of the foam - generating device, select a lower gas - liquid ratio. A high gas - liquid ratio is not suitable for the case of a relatively high wind speed. However, if the rated flow rate of the foam - generating device is low, the gas - liquid ratio can be appropriately increased to meet the minimum fire - extinguishing flow rate requirement.

[0077] S5 Determine the nozzle length, nozzle aperture and nozzle angle:

[0078] Calculate the foam injection trajectory according to the foam trajectory differential equation. Based on the foam injection trajectory, determine the nozzle length, nozzle aperture and nozzle angle. The foam trajectory differential equation is as follows:

[0079]

[0080] Where v is the velocity of the foam (m / s), θ is the angle between the direction of the foam velocity and the horizontal ground (°), x is the horizontal distance between the foam element and the nozzle (m), y is the height of the foam element above the ground (m), t is the characteristic time (s), F is the air resistance (N), m is the mass of the foam (kg), and g is the acceleration due to gravity (m). 2 / s), c r d is the foam spray range coefficient during the rising phase. r This is the coefficient for the range of foam spraying during the descent phase.

[0081] The formula for calculating air resistance F is as follows:

[0082]

[0083] Where, ρ f Foam density (kg / m³) 3 V0 is the initial foam ejection velocity (m / s), and A0 is the nozzle cross-sectional area (m²). 2 ), y0 is the initial height of the foam element (m), R e Let a be the Reynolds number. r b is the coefficient of change of foam cross section during the rising phase. r This is the coefficient of change in the foam cross-section during the descent phase.

[0084] coefficient a r b r c r d r The calculation formula is as follows:

[0085] a r =1281.4285+96.3571M;

[0086] b r =4.257 - 0.297M + 0.0052M 2 ;

[0087] c r = -1.5933 - 0.0015L - 0.0856d n +0.0230Q+0.2325R+0.72928M;

[0088] d r = -9.9893 - 0.1417L - 2.1908d n +0.7423Q+2.5514R+6.7995M;

[0089] Where M is the nozzle angle (°), L is the nozzle length (m), and dn Let Q be the nozzle orifice diameter (m) and Q be the foam flow rate (m³). 3 / s), where R is the gas-liquid ratio.

[0090] The formula for calculating the foam mass m is as follows:

[0091] m=Q×ρ f ×t;

[0092] The formula for calculating the gas-liquid ratio R is as follows:

[0093]

[0094] Where QL is the flow rate of the foam solution, Q G This refers to the compressed air flow rate.

[0095] Foam density ρ f The calculation formula is as follows:

[0096]

[0097] Where, ρ L p is the density of the foam solution. G This refers to the density of compressed air.

[0098] The formula for calculating the initial foam injection velocity V0 is as follows:

[0099]

[0100] Foam offset distance O and wind speed V W The relationship is as follows:

[0101] O=α×V W +β;

[0102] Wherein, α ranges from 1 to 2, and β ranges from 0.1 to 0.2.

[0103] Foam spray distance D s With wind speed V W The relationship is as follows:

[0104] D s =-κ×V W +ψ;

[0105] Among them, κ ranges from 0.7 to 0.8, and ψ ranges from 10 to 15.

[0106] Foam spray distance D s The relationship between the nozzle angle M and the nozzle angle is as follows:

[0107] D s = 5.6 × (M + 15.5) 0.21 ;

[0108] Foam spray distance D s The relationship with the gas-liquid ratio R is as follows:

[0109] D s =8.95×(R-6.19) 0.15 .

[0110] The nozzle design is based on the experimental results, and the design parameters for different nozzles are shown in Table 1.

[0111]

[0112] To clarify the influence of nozzle length and nozzle orifice diameter on fire extinguishing effect, a series of experiments were conducted, and the corresponding coefficient values ​​of different nozzles in the foam trajectory differential equation were obtained, as shown in Table 2.

[0113]

[0114]

[0115] Figures 3 to 5 The foam ejection trajectories of nozzles #2, #3, and #4 under ambient wind speeds of 2 m / s, 4 m / s, 6 m / s, 8 m / s, and 10 m / s, respectively, are obtained based on the foam trajectory differential equation. The foam ejected from nozzle #2 has the longest offset distance and the shortest jet distance. Nozzles with smaller orifice diameters have shorter offset distances and longer jet distances, while nozzles with larger orifice diameters have longer offset distances and shorter jet distances.

[0116] Figure 6 The relationship between the spray distance and offset distance of nozzles #2, #3, and #4 and the wind speed is shown. Figure 6 Solid symbols represent offset distance, while hollow symbols represent spray distance. The smaller the orifice diameter of the nozzle, the greater the performance degradation with increasing wind speed. This is because nozzles with smaller orifice diameters spray lighter foam. As the nozzle orifice diameter increases, the foam cross-section increases, enhancing its resistance to ambient wind. Extending the nozzle length can increase the stability and decay phases of the sprayed foam, thus improving its stability.

[0117] In addition, the nozzle angle is also an important parameter affecting the foam spray trajectory. Table 3 shows the corresponding coefficient values ​​of different nozzle angles in the foam trajectory differential equation.

[0118]

[0119] Figure 7 The foam spray trajectory of the nozzle under different wind angles. Figure 8The relationship between spray distance, offset distance, and wind direction angle is shown. Under wind conditions, the foam offset distance is shortest when the nozzle deflection angle is -45°, followed by 45°, and the foam offset distance is largest when there is no deflection angle. This is because the velocity at the -45° deflection angle partially cancels out the deflection effect, and since wind speed decreases with increasing distance, the foam at the 45° deflection angle deflects less after a certain distance. The change in foam spray distance is similar to the change in offset distance. The results indicate that designing the deflection angle is beneficial to improving the wind resistance of the foam jet.

[0120] Figure 9 The foam jet trajectory corresponds to different nozzle angles. As the foam jet angle increases, the curvature of the foam trajectory gradually increases, and the maximum distance of foam jetting gradually increases.

[0121] Figure 10 This is a curve showing the change in foam jet concentration as a function of the foam jet angle. As the nozzle angle changes from negative to positive, the foam jetting distance continuously increases, but the rate of increase continuously decreases.

[0122] Figure 11 The foam jetting trajectories are shown for different gas-liquid ratios. As the gas-liquid ratio increases, the curvature of the foam jetting trajectory decreases, while the jetting distance increases.

[0123] Figure 12 The relationship between spray distance and gas-liquid ratio is shown. As the gas-liquid ratio of foam increases, the spray distance of foam gradually increases. This is because the increase in gas-liquid ratio leads to an increase in spray pressure, which in turn leads to an increase in spray distance.

[0124] S6 setup and commissioning are applicable to compressed air foam fire extinguishing systems in UHV substations:

[0125] Based on S1-S5 and in accordance with relevant standards, design the number of foam generating devices, build a compressed air foam fire extinguishing system suitable for UHV substations, connect the pipelines and conduct an airtightness check.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A compressed air foam fire extinguishing system suitable for ultra-high voltage substations, characterized in that: The system includes a foam generating device, a foam delivery pipe, a first spray pipe, a second spray pipe, and nozzles. Near-end firewalls and far-end firewalls are respectively arranged on both sides of the power equipment in the ultra-high voltage substation. The foam generating device is connected to the first spray pipe on the near-end firewall and the second spray pipe on the far-end firewall via the foam delivery pipe. The first spray pipe includes a first horizontal pipe and a bend pipe that bends from both ends of the first horizontal pipe towards the side closer to the power equipment. Nozzles are installed on both the first horizontal pipe and the bend pipe. The second spray pipe includes a second horizontal pipe and a vertical pipe connected to the middle section of the second horizontal pipe. Nozzles are installed on both the second horizontal pipe and the vertical pipe. The foam jet trajectory is calculated based on the foam trajectory differential equation. Based on the foam jet trajectory, the nozzle length, nozzle orifice diameter, and nozzle angle are determined. The calculation process for the foam jet trajectory is as follows: Where v is the velocity of the foam, θ is the angle between the direction of the foam velocity and the horizontal ground, x is the horizontal distance between the foam element and the nozzle, y is the height of the foam element above the ground, t is the characteristic time, F is the air resistance, m is the foam mass, g is the acceleration due to gravity, and c is the characteristic time. r d is the foam spray range coefficient during the rising phase. r This is the coefficient for the foam spray range during the descent phase; The formula for calculating air resistance F is as follows: Where, ρ f Let V0 be the foam density, A0 be the initial foam injection velocity, y0 be the nozzle cross-sectional area, and R be the initial height of the foam element. e Let a be the Reynolds number. r b is the coefficient of change of foam cross section during the rising phase. r The coefficient of change of foam cross section during the descent phase; coefficient a r b r c r d r The calculation formula is as follows: a r =1281.4285+96.3571M; b r =4.257-0.297M+0.0052M 2 ; c r =-1.5933-0.0015L-0.0856d n +0.0230Q+0.2325R+0.72928M; d r =-9.9893-0.1417L-2.1908d n +0.7423Q+2.5514R+6.7995M; Where M is the nozzle angle, L is the nozzle length, and d is the nozzle diameter. n Where is the nozzle orifice diameter, Q is the foam flow rate, and R is the gas-liquid ratio.

2. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The first sprinkler pipe has two parts, one located at the top of the near-end firewall and the other located in the middle of the near-end firewall.

3. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The vertical pipeline consists of three sections. The ground projection points of the axes of the three vertical pipelines are respectively located at the intersection of the perpendicular lines drawn from the ground projection points of the midpoints of the main transformer side bushing, the main transformer oil tank, and the adjustment transformer oil tank of the power equipment to the ground projection points of the axis of the second horizontal pipeline.

4. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The second transverse pipe extends to 1-3m beyond the protected area on both sides.

5. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The foam delivery pipe includes a main delivery pipe and branch delivery pipes. The main delivery pipe is connected to two branch delivery pipes through a T-joint. The two branch delivery pipes are respectively connected to the first spray pipe and the second spray pipe.

6. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 5, characterized in that: The main conveying pipe is connected to the branch conveying pipe, the branch conveying pipe is connected to the first spray pipe, and the branch conveying pipe is connected to the second spray pipe via flanges with internal sealing gaskets.

7. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The nozzles on the first horizontal pipe, the bend pipe, the second horizontal pipe, and the vertical pipe are all evenly distributed along the pipe extension direction.

8. The compressed air foam fire extinguishing system for ultra-high voltage substations according to claim 1, characterized in that: The first sprinkler pipe is fixedly connected to the near-end firewall via a first bracket, and the second sprinkler pipe is fixedly connected to the far-end firewall via a second bracket.

9. A design method for a compressed air foam fire extinguishing system suitable for ultra-high voltage substations, used to design the compressed air foam fire extinguishing system suitable for ultra-high voltage substations according to any one of claims 1-8, characterized in that, Includes the following steps: S1 Data Collection: Obtain information on the firewall design and power equipment of the UHV substations that need protection, and determine the areas around the UHV substations where foam generating devices can be placed. S2 selects the spray pipe configuration: The form of the first and second sprinkler pipes is selected according to the firewall design of the UHV substation. S3 determines the number of nozzles, nozzle type, and nozzle arrangement: The number, type, and arrangement of sprinklers are determined based on the wind speed in the local environment of the UHV substation and information on the power equipment. S4 determines the foam parameters: Calculate the foam flow rate based on the number of nozzles determined in step S3, and determine the gas-liquid ratio based on the wind speed of the local ambient wind at the UHV substation and the rated flow rate of the foam generating device. S5 determines the nozzle length, nozzle orifice diameter, and nozzle angle: The foam jet trajectory is calculated based on the foam trajectory differential equation. Based on the foam jet trajectory, the nozzle length, nozzle orifice diameter, and nozzle angle are determined through experiments. S6 setup and commissioning are applicable to compressed air foam fire extinguishing systems in UHV substations: Based on S1-S5 and in accordance with relevant standards, design the number of foam generating devices, build a compressed air foam fire extinguishing system suitable for UHV substations, connect the pipelines and conduct an airtightness check.

10. The design method for a compressed air foam fire extinguishing system applicable to ultra-high voltage substations according to claim 9, characterized in that: In step S4, the foam flow rate Q is calculated using the following formula: Q = n × q; Where n is the number of nozzles and q is the minimum foam flow rate of a single nozzle.

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