A passive self-phase cancellation muffler for indoor substation and its design method

Abstract

The application discloses a passive self-cancelling muffler for an indoor transformer substation and a design method thereof. The passive self-cancelling muffler comprises a muffling pipeline; the muffling pipeline is divided into a first muffling pipeline and a second muffling pipeline by a partition; the inlet of the first muffling pipeline and the inlet of the second muffling pipeline are respectively used for inputting in-phase sound waves to be muffled; the outlet of the first muffling pipeline and the outlet of the second muffling pipeline are respectively used for outputting first sound waves and second sound waves; a plurality of phase-adjusting guide vanes are arranged in the second muffling pipeline; the phase of the first sound waves and the phase of the second sound waves are 180 degrees different; the outlet of the first muffling pipeline and the outlet of the second muffling pipeline are communicated, and are used for realizing self-cancelling of sound waves based on the opposite-phase superposition of the first sound waves and the second sound waves. The muffler provided by the application can realize self-cancelling of noise of the indoor transformer substation and realize efficient control of emission noise.

Description

Technical Field

[0001] The invention belongs to the technical field of noise control of indoor substations, and in particular relates to a passive self-cancelling muffler for indoor substations and a design method thereof. Background Art

[0002] Indoor substations place important sound source equipment such as transformers inside buildings and dissipate heat through active or passive means. The air inlets and outlets used for heat dissipation in indoor substations are weak links in sound isolation, and sound leakage is likely to occur in these areas, thereby affecting the noise level at the factory boundary and surrounding sensitive points.

[0003] Given the above issues, the current common method is to install silencers at the air inlet and outlet to reduce the impact of air leakage on the outside world. However, traditional classic silencers mainly use internal high-performance sound-absorbing materials to convert internal sound energy into heat energy dissipation. They have a very good absorption and control effect on high-frequency noise, but a general control effect on low-frequency noise. The important noise source equipment in substations is affected by the power frequency, and its noise characteristics show obvious low-frequency line spectrum noise characteristics, and the line spectrum frequency is mainly a multiple of the power frequency. In summary, the current technical problem of poor low-frequency noise control in the main transformer room of indoor substations is that the noise is not well controlled. In addition, the difficulty of controlling low-frequency noise is also an important research focus in the field of vibration and noise reduction. Summary of the Invention

[0004] The present invention aims to provide a passive self-cancelling muffler for indoor substations and its design method to address one or more of the aforementioned technical issues. The muffler provided by the present invention addresses the technical issue of poor low-frequency control achieved by classic mufflers and other existing noise reduction measures. The muffler provided by the present invention achieves self-cancellation of indoor substation noise, effectively controlling emission noise.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a passive self-phase cancellation muffler for an indoor substation, comprising: a muffler pipe;

[0007] The muffler pipe is divided into a first muffler pipe and a second muffler pipe by a partition;

[0008] The inlets of the first and second silencer tubes are respectively used to input the same-phase sound waves to be silenced; the outlets of the first and second silencer tubes are respectively used to output the first and second sound waves; wherein, a plurality of phase-adjusting guide vanes are arranged in the second silencer tube; the phase difference between the first and second sound waves is 180°; the outlets of the first and second silencer tubes are connected, and are used to realize sound wave self-cancellation based on the anti-phase superposition of the first and second sound waves.

[0009] A further improvement of the present invention is that the first silencer is a W-shaped silencer; and the second silencer is a special-shaped silencer with a plurality of phase-adjusting guide plates built in.

[0010] A further improvement of the present invention is that the sound channel distance l1 in the first muffler tube and the sound channel distance l2 in the second muffler tube are expressed as follows:

[0011] Where n is an integer greater than or equal to 0; f 目标 is the low-frequency target frequency to be silenced; c = 343 m / s is the speed of sound in air.

[0012] A further improvement of the present invention is that the inlets of the first muffler pipe and the second muffler pipe are both connected to the inlet of the muffler pipe;

[0013] The inlet of the muffler pipe is provided with an inlet grille and an inlet sound-absorbing grid in sequence along the sound propagation direction.

[0014] A further improvement of the present invention is that the outlets of the first muffler pipe and the second muffler pipe are both connected to the outlet of the muffler pipe;

[0015] The outlet of the muffler pipe is sequentially provided with an outlet sound absorbing grid and an outlet grille along the sound propagation direction.

[0016] A further improvement of the present invention is that an outlet sound baffle is provided between the outlet sound absorbing grid and the outlet grille.

[0017] A further improvement of the present invention is that a plurality of flat filling blocks are provided on the outer wall of the muffler pipe.

[0018] The present invention provides a design method for a passive self-phase cancellation muffler for an indoor substation, comprising the following steps:

[0019] Step 1: Determine the low-frequency target frequency f to be silenced based on the noise characteristics of the indoor substation 目标 ;

[0020] Step 2, initially setting the sound channel distance in the first muffler;

[0021] Step 3, based on the sound channel distance in the first muffler, Determine the sound channel distance in the second muffler; where n is an integer greater than or equal to 0; f 目标 is the low-frequency target frequency to be silenced; c = 343 m / s is the speed of sound in air;

[0022] Step 4: Determine the minimum ventilation area S according to the ventilation and heat dissipation requirements, and initially set the pipe area S1 of the first muffler and the pipe area S2 of the first muffler; calculate the transmission loss of the muffler, and the calculation expression is:

[0023]

[0024] Where, S=S1+S2; is the acoustic wave number, f 目标 is the low-frequency target frequency to be silenced; l1 is the sound channel distance in the first silencer; l2 is the sound channel distance l2 in the second silencer;

[0025] Step 5: Determine whether the obtained transmission loss of the muffler meets the preset noise reduction requirements; if so, complete the muffler design; if not, increase the sound channel length in the first muffler pipe and repeat steps 3 to 5.

[0026] A further improvement of an embodiment of the present invention is that in step 3, after determining the sound channel distance in the second muffler, it also includes: judging whether the sound channel distance in the second muffler is within the designable range of the preset structural dimensions; if so, jump to step 4; otherwise, reduce the length of the sound channel distance in the first muffler, and repeat steps 3 to 5.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In view of the fact that the radiation noise of indoor substations (such as transformers, high-voltage reactors and other important power equipment) presents low-frequency line spectrum characteristics, the silencer provided by the present invention can solve the technical problem that the low-frequency control effect of classic silencers and other existing noise reduction measures is not good; in the silencer provided by the present invention, the self-cancellation of the noise of indoor substations can be achieved through structural design, and the emission noise can be efficiently controlled; the structure is a passive silencer, which does not consume energy and has a controllable ventilation area, and at the same time has a good high-frequency silencer effect, and has a good control effect on indoor substation noise. In summary, in view of the technical problem that it is difficult to control the multi-frequency line spectrum noise of indoor substations, the present invention provides a silencer with high-efficiency low-frequency noise reduction capability, which not only meets the ventilation and heat dissipation requirements of the main transformer room, but also can achieve efficient control of emission noise, ensure the stable and safe operation of the substation, and at the same time, meet the emission standards of noise, and contribute to the harmonious and stable development of society. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 1 is a schematic structural diagram of a passive self-phase cancellation muffler for an indoor substation provided by an embodiment of the present invention;

[0031] Figure 2 In the embodiment of the present invention, Figure 1 Schematic diagram of the exemplary muffler structure used in parallel horizontally;

[0032] Figure 3 In the embodiment of the present invention, Figure 1 A schematic diagram of an exemplary muffler structure used in series longitudinally;

[0033] Figure 4 Schematic diagram of another arrangement of phase-adjusting guide vanes in an embodiment of the present invention;

[0034] Figure 5 Schematic diagram of muffler structures in longitudinal series connection with different phase-adjusting guide vane forms in an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of the structural design process of a passive self-phase cancellation muffler for an indoor substation provided by an embodiment of the present invention;

[0036] Figure 7 1 is a schematic diagram of a transmission loss comparison curve between the muffler structure provided by the present invention and a classic resonant muffler in an embodiment of the present invention;

[0037] In the figure, 1. Inlet grille; 2. Inlet sound-absorbing grid; 3. W-shaped silencer; 4. Flat filling block; 5. Outlet sound-absorbing grid; 6. Outlet grille; 7. Outlet sound baffle; 8. Outlet phase cancellation section; 9. Special-shaped silencer; 10. Phase adjustment guide vane; 11. Inlet rectifier section. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0040] The present invention is described in further detail below with reference to the accompanying drawings:

[0041] See also Figure 1 The embodiment of the present invention provides a passive self-phase cancellation muffler for an indoor substation, which mainly includes an inlet grille 1, an inlet sound absorbing grid 2, an inlet rectifying section 11, a W-shaped muffler 3 (which can be equivalent to a first muffler), a special-shaped muffler 9 (which can be equivalent to a second muffler), a phase-adjusting guide plate 10, an outlet phase cancellation section 8, an outlet sound baffle 7, an outlet sound absorbing grid 5, an outlet grille 6 and a flat filling block 4; wherein, the inlet grille 1 is connected to the flat filling block 4, the inlet sound absorbing grid 2 and the inlet rectifying section 11, and the sound wave to be silenced enters the muffler through the inlet grille 1, a part of which flows into the inlet sound absorbing grid 2 and is absorbed and dissipated by the sound absorbing material inside the sound absorbing grid; the rest of the sound wave enters the inlet rectifying section 11, the inlet part of the inlet rectifying section 11 is connected to the inlet grille 1, the inlet sound absorbing grid 2 and the flat filling block 4, and the outlet of the inlet rectifying section 11 is connected to the inlet of the W-shaped muffler 3 and the special-shaped muffler 9. After mixing and stabilization in the inlet rectifying section 11, the sound wave is divided into The two sound waves enter the W-shaped silencer 3 and the special-shaped silencer 9 respectively, and the inlet rectifying section 11 is divided into two. The two sound waves at the exit are in the same phase; the W-shaped silencer 3 and the special-shaped silencer 9 are arranged in parallel. A flat filling block 4 can be set above the W-shaped silencer 3 to further increase the sound absorption capacity above the pipe, and the pipe wall can be shared with the special-shaped silencer 9 below to save space; a phase-adjusting guide plate 10 is arranged inside the special-shaped silencer 9 to increase the propagation time of the sound wave inside the special-shaped pipe, so as to achieve Adjustment of the relative phase of the sound waves inside the W-shaped silencer 3 and the special-shaped silencer 9; at the outlets of the W-shaped silencer 3 and the special-shaped silencer 9, the sound waves originally in phase at the inlets of the two silencer pipes become out-of-phase sound waves when reaching the outlets. By designing the phase-adjusting guide plates 10 inside the special-shaped silencer 9, the anti-phase intersection of the two sound waves at the outlets of the W-shaped silencer 3 and the special-shaped silencer 9 is achieved; a flat filling block 4 can also be arranged under the special-shaped silencer 9 to increase the sound absorption capacity under the special-shaped silencer 9.

[0042] In the silencer provided by the embodiment of the present invention, during the sound wave propagation process, the relative phase relationship of the sound waves in the W-shaped silencer pipe and the special-shaped silencer pipe is changed through structural design, so that the sound waves of the two silencer pipes are input in the same phase and output in the opposite phase, thereby realizing passive anti-phase cancellation of the sound waves at the outlet, reducing the outward emission of indoor variable noise at a specified frequency, and achieving the purpose of reducing indoor variable noise radiation; the internal phase-adjusting guide plate of the silencer realizes the relative phase adjustment of the sound waves in the special-shaped silencer pipe and the W-shaped silencer pipe, so that after the adjustment, the phase difference at the fusion port of the two pipes is 180°, the two sound waves are superimposed in opposite phases, and the sound wave self-cancellation is realized by using the structure; the silencer not only has a good control effect on the noise at the target frequency, but also has a good control effect on all odd multiples of the target frequency, and can realize simultaneous multi-frequency control.

[0043] See also Figures 2 to 5 Based on the structure provided by the embodiment of the present invention, different target frequency mufflers are used in series to achieve efficient control of noise at multiple set frequencies.

[0044] In an embodiment of the present invention, the W-shaped silencer 3 and the special-shaped silencer 9 are arranged in parallel and contact at the outlet, and an outlet cancellation section 8 is designed at the rear, so that the two sound waves can be superimposed in opposite phases at the inlet of the outlet cancellation section 8, and the two anti-phase sound waves can be fully fused in the outlet cancellation section 8; an acoustic baffle is provided in front of the outlet cancellation section 8, and an outlet sound absorbing grid 5 is provided above it. The outlet sound baffle 7 is used for drainage, the sound reflection inside the muffler is increased, and the outlet sound absorbing grid 5 is used to further improve the absorption of the radiated noise of the indoor substation at the outlet; finally, an outlet grille 6 is arranged at the outlet of the muffler to further achieve noise absorption and directional emission.

[0045] In the embodiment of the present invention, the flat filling block 4 is located above the W-shaped silencer 3 and below the special-shaped silencer 9, mainly utilizing the sound-absorbing filling of the non-pipe vacant area of ​​the silencer to further improve the internal sound absorption capacity, while enhancing the structural strength of the silencer and improving the convenience of transportation and installation.

[0046] In the embodiment of the present invention, the inlet grille 1, the inlet sound absorbing grid 2, the outlet sound absorbing grid 5 and the outlet grille 6 can all adopt a perforated plate-covered sound absorbing cotton structure to increase the sound absorption capacity; the W-shaped silencer 3, the special-shaped silencer 9, the phase-adjusting guide plate 10 and the outlet sound baffle 7 can all adopt a perforated plate-covered sound absorbing cotton combined with a central solid metal plate structure to increase the sound absorption capacity while reducing sound interference on both sides of the structure; the flat filling block 4 can adopt a whole perforated plate-covered sound absorbing cotton structure or a similar hollow sound absorbing grid method.

[0047] See also Figure 6 The embodiment of the present invention provides a design method for a passive self-cancellation indoor substation silencer, and the detailed steps are as follows:

[0048] (1) Determine the low-frequency target frequency f to be silenced based on the noise characteristics of the indoor substation目标 ;

[0049] (2) Preliminary determination of the length l of the W-type muffler pipe W型 ;

[0050] (3) According to the formula Taking different n values, the length of the special-shaped silencer series is preliminarily calculated; where c = 343m / s is the speed of sound in air;

[0051] (4) Determine the minimum ventilation area S based on the actual ventilation and heat dissipation requirements;

[0052] (5) Preliminary determination of the W-type silencer pipe area S W型 and the area of ​​special-shaped silencer pipe S 异型 ;

[0053] (6) Calculate the transmission loss of the existing parameter muffler according to the formula; the transmission loss of the muffler is,

[0054]

[0055] Where S = S W型 +S 异型 ; is the sound wave number, f is the sound wave frequency; l W型 is the length of the W-type muffler pipe, l 异型 It is the length of special-shaped silencer pipe.

[0056] (6) Further determine the length of the special-shaped muffler pipe based on the design range of the actual structural dimensions;

[0057] (7) Determine whether the muffler transmission loss under the above parameters meets the actual noise reduction requirements based on the actual noise reduction requirements;

[0058] (8) If not satisfied, increase the length of the W-shaped muffler pipe, return to step (2), and repeat steps (2) to (7) until the actual requirements are met.

[0059] The working principle of the technical solution provided by the embodiment of the present invention is: the silencer mainly utilizes the sound waves in the W-shaped silencer pipe and the special-shaped silencer pipe during the propagation process, and changes the relative phase relationship of the two sound waves through structural design, so as to achieve the purpose of same-phase input and anti-phase output, realize the passive anti-phase cancellation of the sound waves at the outlet, reduce the outward emission of indoor variable noise at a specified frequency, and achieve the purpose of reducing indoor variable noise radiation. In the technical solution provided by the embodiment of the present invention, the sound wave enters the silencer from the inlet grille, and a part of the energy is absorbed and dissipated in the inlet sound-absorbing grid, and the rest enters the rectifying section. After being mixed and stabilized in the rectifying section, it is divided into two and enters the W-shaped silencer pipe and the special-shaped silencer pipe respectively. The two sound waves at the inlet are the same in phase. In order to achieve the phase adjustment of the sound waves inside the W-shaped silencer pipe and the special-shaped silencer pipe, a phase-adjusting guide plate is arranged inside the special-shaped silencer pipe to increase the propagation time of the sound wave inside the special-shaped pipe. In this way, at the outlet of the W-shaped silencer pipe and the special-shaped pipe, the original in-phase sound waves are changed into out-of-phase sound waves. By designing the phase-adjusting guide plate inside the special-shaped silencer pipe, Realize the anti-phase intersection of two sound waves at the outlet of the W-shaped silencer pipe and the special-shaped pipe; arrange the W-shaped silencer pipe and the special-shaped pipe outlet in parallel and contact, and design an outlet cancellation section at the rear to achieve full fusion of the two anti-phase sound waves, further utilize the outlet sound baffle for drainage, increase the sound reflection inside the silencer, and utilize the outlet sound absorption grid to further improve the absorption of the indoor substation radiation noise at the outlet. Finally, arrange the outlet grille at the outlet of the silencer to further achieve the absorption and directional emission of noise. The flat filling block mainly utilizes the sound absorption filling of the non-pipe vacant area of ​​the silencer to further improve the internal sound absorption capacity, while enhancing the structural strength of the silencer and improving the convenience of transportation and installation.

[0060] In the design method provided in the embodiment of the present invention, the minimum ventilation volume and the minimum ventilation area are determined mainly based on the actual heat dissipation requirements, and the length of the W-shaped silencer pipe is preliminarily determined in combination with the spatial conditions of the indoor substation. Further, based on the target frequency, the length of the W-shaped silencer pipe and the relationship between the length of the special-shaped pipe, the length of the special-shaped pipe is preliminarily calculated to obtain the length of the special-shaped pipe. The noise reduction performance of the silencer is further calculated according to the silencer transmission loss formula. According to the noise reduction requirements of the indoor substation, it is judged whether the design parameters meet the actual requirements. If not, the silencer is redesigned by improving the cross-sectional area ratio of the W-shaped pipe and the special-shaped pipe or the length of the W-shaped pipe until the noise reduction performance of the silencer meets the actual requirements of the indoor substation.

[0061] The actual use steps of the silencer provided in an embodiment of the present invention include: in actual use, the silencer can be installed on the outside of the ventilation opening of a building such as the main transformer room of an indoor substation to eliminate fan noise emissions and indoor noise leakage. The silencer can also be installed on both sides of the ventilation opening of a building such as the main transformer room of an indoor substation to further strengthen the control of indoor leakage noise.

[0062] In the specific embodiment provided by the present invention, according to the spectrum characteristics of indoor variable noise, in the embodiment of the present invention, 100 Hz is used as the target frequency to be silenced, f 目标 =100Hz, set the length of W-type silencer pipe to l W型 =1m, then the length of the special-shaped silencer pipe l is calculated 异型 =2.715m, set the cross-sectional area of ​​the W-type silencer pipe S W型 =0.1m 2 , cross-sectional area of ​​special-shaped silencer pipe S 异型 =0.1m 2 ; Calculate the muffler transmission loss, such as Figure 7 As shown in the figure, under this parameter, the muffler achieves efficient noise reduction at odd multiples of 100Hz, such as 100Hz, 300Hz, and 500Hz, covering many line spectrum frequencies of indoor substations. Figure 7 The paper also presents a classic resonant muffler noise reduction curve. Resonant mufflers achieve significant noise reduction performance at a design frequency of 100Hz, but their effective noise reduction frequency is limited. The present invention achieves highly efficient noise reduction at odd-order multiples of a single design frequency. Connecting mufflers of different design frequencies in series can further extend the target frequency coverage.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A passive self-phase cancellation muffler for indoor substation, characterized in that: include: Silence pipes; The muffler pipe is divided into a first muffler pipe and a second muffler pipe by a partition; The inlets of the first muffler pipe and the second muffler pipe are respectively used to input the same-phase sound waves to be silenced; the outlets of the first muffler pipe and the second muffler pipe are respectively used to output the first sound wave and the second sound wave; wherein a plurality of phase-adjusting guide vanes (10) are provided in the second muffler pipe; the phase difference between the first sound wave and the second sound wave is 180°; the outlets of the first muffler pipe and the second muffler pipe are connected, and are used to realize the self-cancellation of the sound waves based on the anti-phase superposition of the first sound wave and the second sound wave; in, The first silencer is a W-shaped silencer; the second silencer is a special-shaped silencer with a plurality of phase-adjusting guide plates (10) built in; The expressions of the sound channel distance l1 in the first muffler and the sound channel distance l2 in the second muffler are: Where n is an integer greater than or equal to 0; f 目标 is the low-frequency target frequency to be silenced; c = 343 m / s is the speed of sound in air.

2. A passive self-phase cancellation muffler for indoor substation according to claim 1, characterized in that: The inlets of the first muffler pipe and the second muffler pipe are both connected to the inlet of the muffler pipe; The inlet of the muffler pipe is provided with an inlet grille (1) and an inlet sound-absorbing grid (2) in sequence along the sound propagation direction.

3. A passive self-phase cancellation muffler for indoor substation according to claim 1, characterized in that: The outlets of the first muffler pipe and the second muffler pipe are both connected to the outlet of the muffler pipe; The outlet of the muffler pipe is provided with an outlet sound absorbing grid (5) and an outlet grille (6) in sequence along the sound propagation direction.

4. A passive self-phase cancellation muffler for indoor substation according to claim 3, characterized in that: An outlet sound baffle (7) is provided between the outlet sound absorbing grid (5) and the outlet grille (6).

5. A passive self-phase cancellation muffler for indoor substation according to claim 1, characterized in that: The outer wall of the muffler pipe is provided with a plurality of flat filling blocks (4).

6. A design method for a passive self-phase cancellation muffler for an indoor substation according to claim 1, characterized in that: The following steps are involved: Step 1: Determine the low-frequency target frequency f to be silenced based on the noise characteristics of the indoor substation 目标 ; Step 2, initially setting the sound channel distance in the first muffler; Step 3, based on the sound channel distance in the first muffler, Determine the sound channel distance in the second muffler; where n is an integer greater than or equal to 0; f 目标 is the low-frequency target frequency to be silenced; c = 343 m / s is the speed of sound in air; Step 4: Determine the minimum ventilation area S according to the ventilation and heat dissipation requirements, and initially set the pipe area S1 of the first muffler pipe and the pipe area S2 of the second muffler pipe; The transmission loss of the muffler is calculated and the calculation expression is: Where, S=S1+S2; is the acoustic wave number, f 目标 is the low-frequency target frequency to be silenced; l1 is the sound channel distance in the first silencer; l2 is the sound channel distance l2 in the second silencer; Step 5, determine whether the obtained transmission loss of the muffler meets the preset noise reduction requirements; if so, complete the muffler design; if not, increase the length of the sound channel in the first muffler pipe and repeat steps 3 to 5.

7. The design method of a passive self-phase cancellation muffler for an indoor substation according to claim 6, characterized in that: In step 3, after determining the sound channel distance in the second muffler, the method further includes: Determine whether the sound channel distance in the second muffler is within the preset structural size design range. If so, jump to step 4. If not, reduce the sound channel distance length in the first muffler and repeat steps 3 to 5.

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