In the field of power transmission and distribution, oil-immersed transformers have always occupied a core position. As a hub for power conversion, it accurately adapts to the needs of various types of electrical equipment by raising and lowering voltage. With the iterative upgrade of the power system and the continuous increase in the requirements for power quality, the design and manufacturing technology of oil-immersed transformers has ushered in new challenges and opportunities. In-depth mastery and optimization of these key technologies can not only significantly improve transformer performance and reduce energy consumption, but also effectively extend the service life of the equipment.
Core technology of oil-immersed transformer design
The design of oil-immersed transformers is a highly complex system engineering, which requires the coordinated optimization of multiple key technologies to maximize performance.
Core design
Core design is the primary link in transformer design, and its quality directly determines the no-load loss and noise level of the transformer. At present, the industry generally uses high-permeability, low-loss oriented silicon steel sheets as core materials, and uses a step-lap process to effectively reduce magnetic resistance and eddy current losses. During the design process, the core cross-sectional area, magnetic flux density and lamination coefficient need to be accurately calculated to minimize iron loss while ensuring that the magnetic circuit is unobstructed. This can lay a solid foundation for the stable operation of the transformer.
Winding structure design
The winding structure design is related to the load loss and short-circuit tolerance of the transformer. High-voltage windings mostly adopt multi-layer cylindrical or segmented structures, while low-voltage windings are commonly spiral or continuous structures. When designing, it is necessary to comprehensively consider factors such as current density, thermal stability and mechanical strength, and then optimize the electric field distribution through scientific transposition and insulation arrangement. With the help of advanced computer-aided design software, the electromagnetic field and temperature field distribution of the winding under different working conditions can be simulated to provide accurate data support for the optimization of the design scheme.
Insulation system design
The insulation system is the key to ensure the long-term stable operation of the transformer. The insulation system of the oil-immersed transformer is mainly oil-paper composite insulation. The heat resistance level, dielectric strength and aging characteristics of the insulation material must be fully considered during design. By rationally planning the main insulation distance, oil channel layout and barrier setting, the electric field strength can be effectively controlled to prevent the risk of local discharge and insulation breakdown. Modern design widely uses electric field finite element analysis technology to finely optimize the insulation structure to ensure that the electric field strength of each part is within the safety threshold.
Cooling system design
The cooling system directly affects the load capacity and service life of the transformer. Common cooling methods include natural oil circulation cooling (ONAN), forced oil circulation air cooling (OFAF) and forced oil circulation water cooling (OFWF). When designing, it is necessary to accurately select the appropriate cooling method based on the transformer capacity and operating environment, and optimize the radiator layout and oil flow path. The application of computational fluid dynamics (CFD) simulation technology enables designers to accurately predict the oil flow distribution and temperature field, effectively avoiding local overheating problems.
Key manufacturing processes for oil-immersed transformers
The manufacturing process of oil-immersed transformers has strict requirements for many key technologies. Only by strict control can product performance and quality be guaranteed.
Material selection
Material selection is the primary task in the manufacturing process and is directly related to the performance and life of the transformer. The core material is mostly made of high magnetic permeability, low loss cold-rolled oriented silicon steel sheets, and its thickness and surface insulation coating must be strictly controlled. The winding conductor is mainly oxygen-free copper or electrical aluminum, which is required to have high purity and excellent conductivity. Insulation materials, such as insulation pressboard, cable paper and insulating oil, must have excellent electrical properties and long-term stability.
Assembly process
The assembly process is the core link of transformer manufacturing, and it has extremely high requirements for precision and cleanliness. The core assembly adopts a step-lap process to ensure that the magnetic circuit is symmetrical and the air gap is minimized; the winding assembly must be carried out in a clean workshop with constant temperature and humidity, and the winding tension and insulation spacing must be strictly controlled. Key processes such as lead welding and tap changer installation require special processes to ensure. Modern manufacturing workshops widely introduce automated equipment and robot-assisted assembly to greatly improve assembly accuracy and consistency.
Vacuum treatment and oil filling process
The vacuum treatment and oil filling process play a decisive role in the insulation performance of the transformer. The assembled transformer needs to undergo strict vacuum drying treatment to completely remove moisture and gas from the insulating material. The vacuum degree is usually maintained below 1Pa, and the duration depends on the transformer capacity. The oil injection process should be carried out in a vacuum environment and uses transformer oil that has been precisely filtered and degassed. After the oil injection, a circulating hot oil treatment should be implemented to ensure that the insulating oil fully penetrates all insulating structures.
Sealing technology and quality control
Sealing technology and quality control are the last line of defense to ensure the long-term reliable operation of the transformer. The transformer oil tank adopts a welded structure, and all flange connections use oil-resistant rubber seals. Before leaving the factory, strict sealing tests such as positive pressure leak detection and negative pressure pressure maintenance are required. Each transformer must also pass comprehensive factory tests such as ratio test, winding resistance measurement, no-load and load loss test, insulation resistance measurement, power frequency withstand voltage test and partial discharge detection to ensure that all performance indicators fully meet the standard requirements.
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