The structure of high-temperature resistant oil-immersed transformers strives to use the mature structure and processes of traditional transformers, retaining the advantages of traditional transformers, such as reliability, good workmanship, and economic efficiency. The biggest difference between these transformers and traditional ones lies in the design's reasonable consideration of the actual temperature field inside the transformer. By rationally using insulation materials of different temperature resistance grades according to the temperature distribution, a mixed insulation system is formed. With the aid of transformer temperature field simulation technology, the temperature distribution of the transformer (mainly the windings and their vicinity) can be accurately determined. According to different temperature ranges, insulation materials of different grades are selected, fully utilizing the high-temperature resistance characteristics of the materials while maintaining good economic efficiency. The maximum operating oil temperature of this oil-immersed transformer is set at 95°C, ensuring good safety, thermal performance margin, and long expected lifespan for the transformer.

For the overall temperature design of the transformer, we propose and implement the concept of "7-level temperature control technology" as a design principle, which involves extending from the hottest point near the winding hotspot to the outer low-temperature area in five levels, and considering short-circuit and overload conditions to form seven thermal states for temperature control design methods:

1. Insulation Temperature Control Technology: Different insulation materials are selected for different parts of the windings and transformer bodies based on their temperatures. This controls the winding hotspot temperature.

2. Liquid Flow Circuit Temperature Control Technology: By comprehensively considering the relationship between liquid flow velocity fields and temperature fields, the temperature of the liquid flow in various parts is determined and controlled. This controls the boundary layer liquid temperature near the winding hotspot and the top-layer liquid temperature.

3. Overload Temperature Control Technology: Temperature rise control for various parts of the transformer under overload conditions. The temperature distribution under overload conditions differs from that during rated load operation, and the design should pay attention to the temperature rise changes under overload conditions.

4. Core Temperature Control Technology: Temperature control of insulation parts in contact with the core.

5. Sealing Temperature Control Technology: The thermal expansion, deformation, strength, etc., of the fully sealed oil tank change with temperature and must be controlled to ensure that the transformer operates normally within its allowable temperature range.

6. Component Temperature Control Technology: Components are equipped with corresponding insulation materials according to their location temperatures, such as sealing gaskets.

7. Short-Circuit Temperature Control Technology: When a transformer experiences a fault short circuit, the short-circuit current flowing through the windings is very large but lasts for a short time. It is usually calculated as an adiabatic process. Under repeated short-circuit reclosure conditions, thermal accumulation, and heat dissipation effects should be considered. Generally, due to the excellent high-temperature resistance, mechanical strength, dielectric coefficient, and minimal change in dielectric loss with temperature of NOMEX® paper, even under repeated short-circuit reclosure conditions, there will be no mechanical damage or electrical faults caused by temperature rise, nor will the lifespan of the insulation material be compromised.