Closed oil immersed transformer

　　Here is the English translation of the provided text about closed oil-immersed transformers:

　　I. Core Design Features

　　Fully Sealed Oil Tank Structure

　　The transformer core and windings are completely submerged in insulating oil, enclosed within a welded steel oil tank designed for sealing to prevent oil leakage and ingress of external contaminants.

　　The typical structure includes the tank shell, cover, and associated accessories (such as oil drain valves, grounding plates, nameplates, etc.), ensuring operational stability.

　　Multi-Functional Insulating Oil

　　Electrical Insulation: The insulating oil fills the gaps between windings and the core, enhancing the equipment's voltage withstand capability and reducing the risk of partial discharge.

　　Heat Dissipation and Cooling: Heat generated by the windings and core is transferred to the outer walls of the oil tank through natural convection or forced circulation, achieving efficient heat dissipation.

　　Anti-Oxidation Protection: The sealed environment minimizes contact between the oil and air, slowing down oil aging and extending maintenance intervals.

　　Key Components Working in Synergy

　　Core: Fabricated from high-permeability cold-rolled silicon steel sheets, reducing hysteresis and eddy current losses.

　　Windings: Wound from copper or aluminum conductors, with interlayer and turn-to-turn insulation provided by insulating paper to ensure efficient voltage transformation.

　　Protective Devices: Integrated with an oil conservator, Buchholz relay, explosion-proof pipe, etc., for real-time monitoring of oil level, temperature, and internal faults, ensuring equipment safety.

　　II. Functional Advantages

　　High Reliability Operation

　　The fully sealed structure reduces interference from the external environment, while the insulating oil provides stable electrical and thermal performance, making it suitable for complex operating conditions.

　　Low Maintenance Costs

　　The sealed design reduces the frequency of oil replacement, extends equipment lifespan, and minimizes manual inspection and maintenance efforts.

　Optimized Heat Dissipation Efficiency

　　The insulating oil directly contacts the heating elements, combined with natural convection cooling from the outer tank walls or forced air cooling, achieving efficient thermal management.

　　Enhanced Safety Performance

　　The Buchholz relay monitors internal faults in real-time, while the explosion-proof pipe releases pressure during abnormal conditions, preventing explosion risks.

　　III. Technical Key Points

　　Materials and Craftsmanship

　　The core selects high-permeability silicon steel sheets, while the windings utilize heat-resistant insulating materials. The oil tank welding process must meet sealing and strength requirements.

　　Cooling System Design

　　Small-capacity transformers rely on natural convection for heat dissipation, while large-capacity transformers require radiators or coolers to enhance heat exchange efficiency.

　　Monitoring and Protection

　　Integrated with oil level indicators, temperature sensors, pressure relief valves, etc., for real-time monitoring of operational status and fault预警 (warning/pre-alarming, depending on context).

　　This translation accurately conveys the technical details and advantages of closed oil-immersed transformers in English while maintaining the original structure and intent.