The no-load performance of a five-stage laminated core transformer has been analyzed by Shang Yafei from Xinjiang Special Transformer Co., Ltd., focusing on how this core structure reduces no-load losses, no-load currents, and noise levels. The use of a five-stage seam core significantly enhances the no-load performance of transformers.
Energy conservation and emission reduction are key directions in transformer development, and improving the core lamination structure is a primary way to reduce losses. Many developed countries employ five-stage joint core technology, which shows clear improvements over traditional dual or triple joints in terms of no-load performance. Our factory introduced German Georg Company's TUG M H800×5 000 automatic core cross-cutting line in 1998. This machine can process silicon steel sheets at various angles and automatically cut three-seam, five-seam, and even seven-seam sheets. After adopting the five-stage joint core structure, our product’s no-load loss and no-load current have decreased dramatically, and noise levels have also been reduced. On large capacity transformers, the effect is particularly noticeable. This article will briefly discuss the structural form of the five-stage seam core, its energy-saving mechanisms, and the resulting energy savings.
The no-load loss of a transformer consists mainly of basic loss, joint loss, and shear edge loss. Besides basic loss, joint loss makes up a significant portion, while shear edge loss is relatively small. Joint loss is closely related to local magnetic flux density, especially in the seam areas. Due to the joint gaps, local magnetic density increases, leading to higher localized losses. Thus, reducing this impact is an effective way to lower losses.
Currently, domestic transformer manufacturers typically use dual or triple-stage joint laminations. These laminations are staggered at certain distances, forming two parallel joints in the staggered region. The magnetic flux distribution at the core joint looks like Figure 1, showing that most of the magnetic flux passes through bridging laminations rather than directly through the joints.
For a three-stage seam core where two corresponding seam gaps span two laminates, the magnetic flux at the end of the three-seam silicon steel sheets passes through two layers of bridging laminations. Each layer spans the end of the lamination, resulting in a magnetic density at the B-pillar. The relationship between local magnetic flux density B and the number of joints N is given by the equation. Consequently, the no-load loss and no-load current in the seam area increase significantly.
From equations (6) and (7), it can be seen that as the number of core joints increases, the no-load loss and no-load current in the core joint area gradually decrease. However, the decrease in local loss and no-load current becomes smaller as the number of joints increases. Additionally, the number of laminated sheets increases with the number of lamination stages, which reduces the production efficiency of silicon steel sheet cutting and core lamination. This contradiction can only be resolved through advanced silicon steel sheet cutting equipment and lamination processes, along with selecting the appropriate seam level. After nearly two years of production practice, we believe that kV-class transformers are better suited for five-stage joint single-piece stacking. This approach offers higher production efficiency than ordinary dual or triple joints, meeting production needs effectively.
Comparing the local loss and no-load current of five-stage joints versus three-stage joints, we find that the former shows a significant reduction in no-load loss and current. For a kV-grade product, the total additional coefficient for no-load loss is approximately 1.12. The actual additional coefficient of no-load loss is generally around 1.05, verified across multiple products. Thus, the no-load loss of a five-stage seam core is reduced by 5 to 8 percent on average, and the no-load current is reduced by more than 30 percent, showcasing remarkable energy-saving effects.
Besides reducing no-load loss and current, the five-stage seam core has other notable characteristics compared to traditional dual or triple-stage joints.
Regarding noise, the main cause of transformer noise is the magnetostriction of the silicon steel sheets, but magnetic attraction between the joints and laminations also contributes. The noise level depends on the seam gap length and magnetic density. Based on relevant data, the magnetic field energy differential form of the joint air gap is expressed as dA = FdL. This leads to the magnetic attraction type joint area S and the elastic modulus of the silicon steel sheet in the lamination elongation strain type, causing the corresponding sound intensity level in the core stack. Assuming a working magnetic density of 1.7T, the length of the three-stage joint gap is 0.05cm, and the magnetic density is about 0.4 ton. The five-stage joint core reduces noise by about 3dB compared to the conventional three-stage seam core. Traditional dual and triple-stage joints concentrate the air gap of a certain section of the joint, creating strong alternating electromagnetic forces that cause loud vibrations. In contrast, the five-stage seam core reduces the joint air gap of a section, allowing magnetic lines to smoothly enter adjacent laminations, reducing the no-load current and the electromagnetic force on the yoke, thereby significantly lowering transformer noise.
In terms of production efficiency, many domestic transformer manufacturers often adopt a three-stage seam stacked structure to reduce no-load loss and noise. However, due to equipment limitations, the total number of core cuts per transformer increases, prolonging the time required for core stacking and assembly, reducing overall efficiency. Our factory uses the latest core cross-cutting equipment, which greatly improves cutting efficiency and allows for up to seven-stage single-piece stack seams. Considering the technical aspects of core stacking and insertion, our factory employs a five-stage single-piece laminated seam structure. Core pieces have 20 positioning holes, enabling direct loading with codes, significantly boosting production efficiency.
Material savings are another advantage. Advanced core cross-cutting equipment ensures silicon steel sheet burrs are less than 0.03mm, combined with skilled workers maintaining stacking deviations under 2mm, resulting in very small joint gaps. Optimized core section design has reduced the set gap between transformer windings and the core from 5mm to 2.5mm, decreasing electromagnetic wire usage. Given our factory produces about 100 kV and above transformers annually, the material-saving effect is substantial.
Comparing six kV-class transformers—three using three-stage joints and three using single-piece five-stage joints—the results show the five-stage seam core reduces average no-load loss by 8, no-load current by 50, and noise by 4 dB.
In conclusion, the five-stage seam core boasts low loss, low noise, and excellent processability. Its adoption helps save energy, improve power supply quality, and reduce environmental noise pollution. Notably, our factory’s iron core avoids stacking the yoke, reducing silicon steel sheet damage and further reducing no-load loss by about 2%. Over nearly two years of production practice, our factory’s kV-grade products have seen an average no-load loss reduction of more than 8, a no-load current drop of more than 30, and noise reduction of 4 dB. With current core materials, using a five-stage seam lamination structure is undoubtedly the best production method and an ideal replacement for traditional dual and triple-stage seam cores.
Greeting cards with led lights
Flashing Music Greeting Card, Music Valentine's Day Card, Greeting Card Flashing Led Module
AST Industry Co.,LTD , https://www.astsoundchip.com