Introduction
No-load loss refers to the active power consumed when the secondary winding of a transformer is open-circuited and the primary winding is applied with a rated voltage of sinusoidal waveform at rated frequency. No-load loss is also called constant loss, which is independent of the current passing through but related to the voltage borne by the components. Both 1000kva transformer and 300 kva transformer follow this basic law in terms of no-load loss characteristics. There are many factors affecting the no-load performance of transformers, such as the material performance of silicon steel sheets, processing technology and equipment, and the structural form of the iron core. JINSHANMEN TECHNOLOGY CO., LTD fully considers these factors to optimize the no-load loss performance when producing various transformers.
1. Overview
JINSHANMEN TECHNOLOGY CO., LTD mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment. The company integrates the above no-load loss optimization concepts into the production process of all product lines.
Transformers are one of the most important electrical equipment in the power system, and reducing their power loss is of great economic significance to the power grid. No-load loss is a core parameter of transformers. Once connected to the power grid, no-load loss remains constant regardless of no-load or load magnitude, and has no correlation with the load level of the transformer. In other words, as long as transformers such as 1000kva transformer and 300 kva transformer are connected to the power supply all year round, no-load loss will exist continuously and consume energy, so reducing no-load loss is extremely necessary.
Factors affecting the no-load performance of transformers mainly include the material performance of silicon steel sheets, processing technology and equipment, and the structural form of the iron core. To manufacture transformers with lower no-load loss, on the one hand, silicon steel sheets with lower unit loss can be used; on the other hand, it is necessary to improve the structure and manufacturing process level. However, simply relying on silicon steel sheets with lower unit loss will increase the manufacturing cost of the iron core, while reducing no-load loss by improving the structure and process can not only save materials, but also save costs and energy. Only when structural and process improvements still cannot meet the performance requirements, high-quality silicon steel sheets will be considered.
2. No-Load Loss of Transformers
To reduce the no-load loss of transformers, it is necessary to first clarify their composition and the influencing factors of each part, and then take targeted measures. The no-load loss of transformers is mainly composed of hysteresis loss, eddy current loss and additional loss in the iron core, which is a common feature in both 1000kva transformer and 300 kva transformer.
2.1 Hysteresis Loss
Due to the periodic change of the alternating current on the iron core, the arrangement of dipoles in the ferromagnetic material will change periodically and produce hysteresis phenomenon. The power loss of alternating magnetization of the iron core caused by this is hysteresis loss. Its magnitude is proportional to the area of the hysteresis loop, and the calculation formula is: Pₕ = kₕ·f·B¹·⁶ (kW), where kₕ is the material hysteresis coefficient, f is the frequency, and B is the magnetic flux density.
2.2 Eddy Current Loss
When the magnetic flux passing through the iron core changes, a circular current will be generated in the iron core, which circulates in the plane perpendicular to the magnetic flux vector and is called eddy current. The power loss generated by the eddy current on the iron core resistance is the eddy current loss, and its calculation formula is: Pₑ = kₑ·f²·B²·t² (kW), where t is the thickness of the silicon steel sheet. Modern laser-scribed silicon steel can reduce eddy current loss by 30%-40%.
2.3 Additional Iron Core Loss
The magnitude of the additional loss of the iron core is mainly determined by the following factors: (1) Material characteristics, such as the directional characteristics of silicon steel sheets, processing degradation characteristics and insulation film characteristics; (2) Design structure, such as iron core joint form, iron core lamination mode, iron core lap width, etc.; (3) Process processing, such as the dimensional accuracy and burr size of blanking and shearing processing, the careful handling and lamination of silicon steel sheets during transportation and lamination, and the lamination quality. For 1000kva transformer and 300 kva transformer, reasonable control of these factors can effectively reduce additional losses.
3. Methods to Reduce No-Load Loss
Analysis shows that the hysteresis loss and eddy current loss of the iron core are mainly determined by silicon steel sheet manufacturers, while the additional loss is controlled by transformer manufacturers. The magnetic flux density of the iron core is a key parameter affecting no-load loss. Therefore, on the premise that the effective cross-section of the iron core remains unchanged, it is necessary to make the magnetic flux density distribution of each part of the iron core tend to be uniform and reduce the local magnetic flux density at the corner of the iron core. This optimization idea is applicable to various transformers including 1000kva transformer and 300 kva transformer.
3.1 Changing Staggered Joints to Three-Level Joints
There is a gap in the joint of the silicon steel sheet of the transformer iron core, which will lead to a sudden increase in magnetic resistance when the magnetic flux passes through. The magnetic flux bypasses the gap and passes through the sheets into the adjacent laminations, increasing the local magnetic circuit, increasing the magnetic resistance, and thus increasing the no-load loss and excitation capacity. The more joint levels, the lower the local loss in the joint area, but the reduction range gradually decreases. At the same time, the number of iron core laminations, shearing and lamination man-hours, and process difficulty will increase accordingly.
From a practical perspective, three-level joints are an ideal choice. It is composed of three types of laminations stacked alternately, and only one type of lamination is added to the core column, which slightly increases the process complexity but significantly improves the magnetic performance. Taking 1000kva transformer as an example, using the same design scheme, structure and materials, tests were carried out with staggered joints and three-level joints respectively. The results show that when the cross-section of the core column remains unchanged, the no-load loss of three-level joints is 7%~8% lower than that of staggered joints on average. For 300 kva transformer, the same significant loss reduction effect can be achieved by using this technology.
3.2 Reducing Iron Core Lap Width
At the corner of the iron core lamination, the lap width of the joint area between the core column sheet and the yoke sheet has a direct impact on the no-load performance. The larger the lap area, the larger the area through which the magnetic flux passes, and the no-load loss increases accordingly. Test data shows that for every 1% increase in lap area, the no-load loss of 45° joints increases by 0.3%. Therefore, it is necessary to select the lap area with the best no-load loss and mechanical strength on the premise of meeting the mechanical strength.
JINSHANMEN TECHNOLOGY CO., LTD optimized the distribution transformer, changing the iron core lamination angle from 10mm to 5mm, which increased the cross-sectional area at the triangular cavity of the iron core corner, reduced the local magnetic flux density, and achieved good loss reduction effect. This optimization scheme is applicable to both 300 kva transformer and 1000kva transformer, which can effectively control no-load loss while ensuring structural stability.
3.3 Reasonable Selection of Iron Core Sheet Width
The no-load loss of a transformer is related to the unit iron loss and weight of the iron core. As part of the weight, the iron core corner weight directly affects the no-load loss and manufacturing cost. The selection of iron core sheet width must follow the following premises: (1) The number of iron core levels is equal; (2) When the iron core diameter is D, the main sheet width is selected by subtracting 5mm or 10mm from D to ensure that the maximum difference of the iron core diameter does not exceed +0.3mm, which does not affect the winding assembly; (3) The effective cross-sectional areas of different sheet-shaped iron cores are theoretically equal to ensure consistent magnetic flux density and unit iron loss; (4) The cross-section of the iron core column is consistent with that of the yoke.
Practice shows that after determining the appropriate iron core diameter, selecting the main sheet width of D minus 10mm is better than D minus 5mm, which can realize the gradual decrease of each level of sheet width, reduce the iron core corner weight, and reduce the height of the iron core and oil tank by 10mm, thus saving materials and costs. This method is particularly significant for cost control and no-load loss reduction of 1000kva transformer, and can also achieve considerable energy saving and loss reduction benefits for 300 kva transformer.
4. Summary
(1) The use of multi-level joints can reduce the no-load loss of the transformer iron core. Combined with the actual production (sheet type, man-hour, performance, etc.), three-level joints are generally used. This scheme can achieve significant loss reduction for both 1000kva transformer and 300 kva transformer. (2) Reducing the iron core lap area can effectively reduce no-load loss, and the optimal lap area should be determined according to the product structure. (3) Reasonable selection of iron core sheet width (main sheet width 10mm smaller than diameter is better than 5mm smaller) can reduce iron core corner weight and material consumption, and lower no-load loss.
In addition, during the iron core production process, details such as the burr size of the iron core sheet, the bending and collision degree of the silicon steel sheet during hoisting, and the clamping degree of the iron core sheet will also affect the no-load loss, which need to be strictly controlled. JINSHANMEN TECHNOLOGY CO., LTD fully applies the above optimization technologies and quality control measures to the production of various transformers. With professional design and manufacturing capabilities, it provides customers with low-loss and high-performance power transmission and distribution equipment.