4 Ways to reduce no-load noise
4.1 Reduce vibration source noise
(1) The use of high magnetic permeability material with small magnetostriction, such as the selection of 30ZHl20 silicon steel sheet can be compared with other materials of silicon steel sheet noise to reduce noise 4-5dB (A).
(2) Reduce the core magnetic density and reduce noise. Each time the magnetic density is reduced by 0.1T, it can be reduced by 2-3dB (A). Noise, but after reducing the magnetic density, the cross-sectional area of the core, the equivalent capacity and the cost of the transformer are correspondingly increased, which is uneconomical in terms of cost. Therefore, the magnetic density is reduced and cannot exceed 10% of the standard magnetic density.
(3) Improve and reduce the core seam. The core uses multiple levels of seams. The multi-stage seam core has less no-load noise than the two-stage joint, which can reduce the noise by 4-5dB(A). This is because after the multi-stage (fourth grade and above) joints are used, the magnetic flux distribution at the joint is relatively uniform, and the magnetic density in the air gap is greatly reduced, resulting in a decrease in noise caused by magnetic attraction at the joint. reason. In addition, reducing the joint can reduce the amplitude and reduce the excitation capacity and excitation current of the transformer, so that the sound power is greatly reduced, and the no-load noise can be reduced by 4~5dB(A).
(4) Prevent and reduce the mechanical impact of the silicon steel sheet during processing and production, otherwise the magnetostriction of the silicon steel sheet will be increased, thereby increasing the noise of the core.
(5) Applying epoxy glue or polyester glue on the end face of the core can increase the surface tension of the core, and can also reduce the amount of magnetostriction and reduce the noise.
4.2 In terms of absorption of acoustic energy
(1) Part of the noise generated by the core is transmitted through the bottom of the box and the foundation. If a bumper is placed between the body and the fuel tank or between the fuel tank and the foundation, the sound can be attenuated through the buffer. An anti-vibration rubber pad can be placed between the core foot and the magnetic shield and the wall of the box, so that when the vibration of the core and the magnetic shield is transmitted to the oil tank, the steel connection becomes elastic connection, thereby reducing vibration, preventing resonance and reducing noise. the goal of. Can reduce noise by 1-2dB (A).
(2) The sound insulation material in the iron reinforcement of the fuel tank can absorb a part of the vibration energy of the fuel tank, thereby reducing the noise of the body and reducing the noise by 2-3dB (A).
4.3 Add noise layer to reduce noise
According to the structure of the fuel tank, it is divided into two types: combined type and high efficiency type. The combination type is: the sound insulation board can be made into several pieces according to the external structure of the fuel tank, and the sound absorbing material is placed in the steel plate. Sound absorbing materials are: rock wool, fiberglass and the like. The sound insulation wall can reflect some of the noise emitted by the transformer body; and when the noise passes through the sound insulation wall, it can also be absorbed to reduce the noise. The single-piece baffles are bolted to the tank reinforcement iron, which reduces noise by 10-15dB. High-efficiency baffles can also be used, placed between two reinforced irons and secured by thin spring steel plates. The frame-shaped additional weight is used to adjust the vibration characteristics of the high-efficiency baffle, so that its amplitude is significantly lower than the amplitude of the reinforcing iron, thereby effectively shielding the noise emitted by the transformer body and reducing the noise by l0-5dB(A).
4.4 muffling method
Noise reduction is used to reduce noise. That is, a number of noise sounders are placed inside the transformer lm so that the noise they emit and the noise emitted by the transformer cancel each other out. Its principle is to first convert the noise signal of the transformer into an electrical signal, and then amplify the excitation noise sounder, so that the noise emitted by each noise has the same amplitude and opposite phase, which causes the transformer noise to be destructively interfered, which can reduce the noise by 15dB (A )about.
4.5 Other methods
(1) When designing a low no-load noise transformer, use self-cooling as much as possible to remove the noise superimposed between the fan and the oil pump. When the capacity is difficult to meet the needs, in order to meet the heat dissipation of the large-capacity transformer, the low-noise submersible pump and the cooler of the low-rotation fan are selected as much as possible. The use of a low-speed fan can increase the capacity of the self-cooling transformer by 33% and the noise to 69dB (A). A two-speed fan can also be used depending on the situation. When the low-speed fan is started when the load is small, the noise can be reduced accordingly; when the load is large, the high-speed fan can be driven to increase the capacity of the self-cooling transformer by 67%, but the noise is large, reaching 75dB(A).
(2) When arranging transformers indoors, consideration should be given to the increase in noise caused by noise reflected on the wall. This added value is a function of the ratio of the surface area of the transformer to the surface area of the transformer chamber and is related to the sound absorption coefficient of the wall and ceiling. The use of slag wool or similar materials to coat the wall surface can increase the sound absorption coefficient and significantly reduce the noise.