In order to improve the reliability of urban power supply and improve the quality of power supply and reduce the loss of power transmission, the city network uses a large-scale step-down substation to be built in urban areas. In order to ensure residents are not affected by noise, the power supply department will put forward higher requirements on the noise performance of the transformer. Based on the analysis of the mechanism of vibration and noise generation, the propagation route and various influencing factors, this paper combines the specific manufacturing process of transformers and gives full consideration to economic benefits as a main indicator. The research object of the purpose of transformer vibration reduction and noise reduction, by changing the dynamic characteristics of the transformer tank and adding damping steel plate on the surface of the tank wall, the natural frequency of the fuel tank at home and abroad shows that the root cause of the transformer vibration is: the so-called magnetic When the core is excited, the size of the silicon steel sheet increases along the direction of the magnetic field line, and the size of the silicon steel sheet perpendicular to the direction of the magnetic field line is reduced. This size change is called magnetostriction. Magnetostriction causes the core to periodically vibrate as the excitation frequency changes. The magnetic attraction caused by the magnetic attraction causes the core to vibrate. Reason. It is worth mentioning that when the natural frequency of the core is close to the frequency of the magnetostrictive vibration, or when the natural frequency of the fuel tank and its accessories is close to the vibration frequency from the core, the core or the tank will resonate, making The body noise suddenly increases. Since the variation period of magnetostriction is exactly half a cycle of the power supply frequency, the vibration noise of the transformer body caused by magnetostriction is twice the power frequency as its fundamental frequency. Due to the nonlinearity of the magnetostriction, the different sections of the multi-stage core center column and the corresponding stages of the iron yoke, and the different lengths of the magnetic paths along the inner frame and the outer frame of the core, the magnetic flux is significantly deviated from the sine wave, that is, The component with higher harmonics exists, so that in addition to the fundamental frequency vibration, the vibration spectrum of the core includes high frequency additional vibration whose frequency is an integer multiple of the fundamental frequency. Therefore, in addition to the fundamental frequency noise, the noise spectrum of the transformer core vibration also includes a high iron core whose frequency is an integral multiple of the fundamental frequency and a three-phase transformer core and a winding layout diagram. Where Z is the core column; e is the iron yoke, which closes the magnetic circuit between the two columns. After the core is stacked, it is clamped firmly with the clamp iron and the strap. The windings are wound with a highly conductive copper wire wrapped around a wire with a high strength insulating tape. The windings are placed on the core. For ease of insulation, the low voltage winding is placed against the core and the high voltage winding is placed outside the low voltage winding. The high and low voltage windings of the same phase in the three-phase transformer are placed on the same core column. After the high and low voltage windings are placed on the core, the core and the winding are collectively referred to as the body. The body will be placed in the fuel tank. The fuel tank of the large power transformer is divided into two parts, the upper section and the lower section, and the body is placed in the lower fuel tank, and the iron core is rigidly coupled with the bottom of the tank. Various components of the transformer are arranged on the upper fuel tank. After the upper and lower fuel tanks are assembled and sealed, the oil tank is filled with transformer oil. Transformer oil mainly plays the role of insulation and heat dissipation. 1.2 Mechanism of transformer vibration and noise 11 () When a load current flows through the winding, the leakage current generated by the load current causes vibration of the winding and the tank wall (including magnetic shielding, etc.). In recent years, due to the improvement of the core stacking method (such as the use of step seams, etc.), and the core column and the iron yoke are both tied with epoxy glass tape, the electromagnetic attraction between the seam of the silicon steel sheet and the lamination is The vibration of the core caused by the force is much smaller than that of the magnetostrictive core of the silicon steel sheet. The rated working magnetic density of the transformer is usually 1. 5~1.8T (Tesla). The research and test at home and abroad have proved that in such a magnetic density range, the vibration of the winding, the tank wall (including magnetic shielding, etc.) caused by the leakage current generated by the load current, and the magnetostrictive core vibration of the silicon steel sheet It is much smaller than it can be, and can be ignored. This means that the vibration of the transformer is mainly determined by the vibration of the core, and the vibration of the core can be regarded as completely caused by the magnetostriction of the silicon steel sheet. The magnetostrictive vibration of the core is transmitted to the tank wall through the two steps of the core pad and the insulating oil, so that the tank wall (including the magnetic shield, etc.) vibrates to generate the body noise, and uniformly emits the sound in the form of sound waves, which is the transformer. Machine Noise of Body Noise 1.3 Propeller Vibration and Noise Propagation Path The transformer body noise depends on the magnetostrictive vibration of the core. The magnetostrictive vibration of the core is transmitted to the tank through two paths. One is the solid transfer path. The vibration of the core is transmitted to the tank through its foot; the other is the liquid transfer path. The vibration of the core is transmitted to the tank through the insulating oil. The vibrational energy transmitted by these two paths causes the wall of the tank (including magnetic shielding, etc.) to vibrate to generate bulk noise. Through the air, the bulk noise is uniformly emitted to the surroundings in the form of sound waves. The results of the mortar show that the vibrations transmitted by the solid path and the liquid path are almost equal in energy. Therefore, even if the vibration transmitted by any one of the paths is completely absorbed or attenuated, the bulk noise of the transformer can only be reduced by about 3 dB (A). It can be seen from the above analysis that when the structure, material selection and production assembly process of the transformer cannot be changed by various technical and economic conditions, the transformer tank can be selected as the research object, and the transformer can be suppressed by avoiding the resonance of the fuel tank. The vibration of the fuel tank to reduce the vibration noise of its vibration. 2 Model Transformer Design 2.1 Model Transformer Simplified Real Transformer This article. Iron core silicon steel sheet type is 3ANSYS model structure dynamic characteristics analysis 3.1 Modeling dynamic characteristics analysis The unit used is the shell flat triangular unit, the natural frequency and core excitation of the six fuel tank structures in the ribbed and plate-intensive area unit Frequency frequency natural frequency (Hz) core excitation frequency (Hz) one two three four five six first order 194 0140432415.86308.26351.08353.70405 Note: one model fuel tank structure; two rib thickness is designed to thickness 1. 5 times the fuel tank Structure; the thickness of the tank is 2 times the thickness of the tank structure; the model tank structure of the damper plate is used; the damper plate is reinforced, the rib thickness is 1.5 times the thickness of the tank structure; The rib thickness is a fuel tank structure with a design thickness of 2 times. The method of the steel plate was chosen as a measure to control the vibration and noise of the transformer. Divided into dense, fuel tank caps are divided into '3.2'. Modern large-scale power transformers generally use bell-type fuel tanks. The fuel tanks are divided into upper fuel tanks and lower fuel tanks. The transformer body is installed in the lower fuel tank, between the upper and lower fuel tanks. The joints are bolted and the joints are sealed with oil resistant rubber. When the transformer is installed on site, the lower fuel tank is placed on the foundation of the power station and fastened to the foundation by anchor bolts. The vibration of the iron core is transmitted to the lower fuel tank through the foot between the iron core and the lower fuel tank, and then transmitted to the upper fuel tank through the rigid joint between the upper and lower fuel tanks. The noise of the transformer is mainly the radiation noise of the upper tank wall. Therefore, the prototype of the geometric solid model adopts the upper fuel tank of the model transformer, and the boundary condition is treated as the fastening end. See the model of the fuel tank finite element model, using SHELL93 shell unit. 3.3 Calculation results The model tank structure was calculated in ANSYS software. Considering the influence of model truncation on the calculation accuracy, the number of modals intercepted is twice the number of modals analyzed. The first five natural frequencies of the calculated model transformer tank correspond to the serial number one in Table 1. When the rib thickness is 1.5 times the design thickness, the natural frequency of the model tank corresponds to the serial number 2 in Table 1. The natural frequency of the model tank with the rib thickness of 2 times the design thickness corresponds to the serial number 3 in Table 1. Comparing two and three, it can be seen that the degree of influence of the change of the rib thickness on the frequency of each order is different. Compared with the calculation when the rib thickness is 0.003m, when the rib thickness is increased to IJ0.004m, the first-order natural frequency is added with the third-order natural frequency plus 11.5Hz. This shows that the simple reinforced thickness is inherent to the first step of the fuel tank. The frequency has little effect. In addition, in the engineering practice, the design of the main rib of the large power transformer is 10mm, and the doubling of the rib is more than 2 times, which makes the bending of the rib difficult. Therefore, the use of this method is also limited. of. The natural frequencies of the model tanks with damped steel plates are listed in the table, No. 416. 3.4 Discussion By comparison, the following two conclusions can be drawn: by changing the thickness of the main rib alone, the natural frequencies of each step can be increased, and the welded damping steel plate can reduce the natural frequencies of each step. The combination of the two measures will increase the first-order frequency of the fuel tank and reduce the frequency of the other steps. To avoid resonance of the vibration system, the natural frequency of the system should be higher or lower than 10%~20% of the interference frequency. According to this principle, the natural frequency of the six fuel tank structures can be analyzed, and any fuel tank structure can be found. It is impossible to keep the natural frequency of each step away from the excitation frequency of the core. That is to say, it is entirely possible for the fuel tank to resonate at a certain frequency. Damping must be used to attenuate the amplitude of the resonance. According to the above conclusions, the experimental research method and experimental device for the dynamic characteristics of the welding resistor 4 model transformer on the main rib of the fuel tank. The model transformer adopts the ground support method, which is consistent with the actual installation of the transformer. The hammering method is used when testing the natural frequency of the system. The sound level meter uses BK 2230 precision integral sound level meter. 4.2 Experimental results The frequency spectrum of the model tank can be found on the vibration spectrum map, and there are a large number of other frequency components. It can be found from the noise spectrum that in addition to the complete correlation between the sound spectrum and the vibration spectrum, there is also a power frequency and its frequency doubling component in the sound spectrum, which indicates that the noise generated by the vibration of the core is radiated to the tank wall through the air in the fuel tank, and the transformer This part of the noise component is included in the overall noise. The transformer noise (A sound level) was tested at a distance of 90 cm from the ground and 70 cm from the wall of the box. The frequency values ​​on the vibration self-spectrum of the fuel tank after welding the damping plate are listed in Table 2 and compared with the results of the ANSYS analysis. It can be seen from Table 2 that the first, third, fourth, fifth, sixth, seventh, eighth, nine, ten The eleventh natural frequency calculation results are basically consistent with the experimental results, which indicates that the ANSYS model established during the calculation is of practical value. It can be seen from the forced vibration noise spectrum that the main frequency component in the spectrum is 100 Hz and its multiple frequency, which indicates that the noise main body at this time is the radiation noise of the iron core vibration, and the noise excited by the box vibration has not occupied the main position. . The noise value measured at the same measuring point is 46.7 dB, and the reduction of the noise value also proves that the radiation noise of the tank wall vibration is indeed reduced. Table 2 Model tank natural frequency (HZ) No. Calculated value Actual value 1st order 2nd order 3rd order 4th order 5th order 6th order 7th order 8th order 9th order 10th order 11th order Explanation of the above results The method of welding the damping steel plate on the main rib of the fuel tank is an effective measure for controlling the vibration and noise of the transformer. Compared with the simple reinforced method, this method is more reliable and can be better applied to various transformer tank structures, and has a good engineering application prospect. Silver Face Cotton,Textile Viscose Print,Poplin Shirt Fabric,Rayon Plain Fabric SHAOXING YINGSIPE TEXTILE CO.,LTD , https://www.chinayingsipei.com