Enclosed oil-immersed power transformer

　　Analysis of Enclosed Oil-Immersed Power Transformers

　　I. Core Definition and Structural Features

　　An enclosed oil-immersed power transformer is an electrical device that utilizes transformer oil for insulation and cooling. Its core structure includes:

　　1. Core and Windings

　　The core is constructed from high-permeability silicon steel sheets (thickness ≤ 0.35 mm), with a laminated design to minimize eddy current losses.

　　Windings are wound from copper or aluminum conductors, divided into high-voltage and low-voltage windings, enabling voltage transformation through electromagnetic induction.

　　Both windings and the core are fully immersed in transformer oil, creating an enclosed insulating environment.

　　2. Tank and Sealing System

　　The tank features a fully welded, enclosed structure, typically equipped with corrugated fins or conservators to compensate for oil volume changes via elastic expansion, preventing air-oil contact and oxidation.

　　Sealing is achieved using oil-resistant rubber gaskets or welding techniques to ensure leak-free operation, even in harsh outdoor environments.

　　3. Cooling and Protection Devices

　　The cooling system includes radiators or forced-air cooling units, facilitating heat dissipation through oil circulation.

　　Safety devices such as gas relays (Buchholz protection), pressure relief valves, and thermometers are installed to monitor operational status in real time.

　　II. Technical Advantages and Application Scenarios

　　1. Performance Advantages

　　Efficient Heat Dissipation: The high thermal conductivity of transformer oil, combined with cooling systems, enables rapid heat removal, making it ideal for high-capacity, heavy-load applications.

　　Superior Insulation: The oil-immersed structure fully isolates windings from the core, reducing partial discharge and extending insulation lifespan.

　　High Overload Capacity: Short-term overload capability reaches up to 160% of rated capacity (for 15 minutes), accommodating load fluctuations.

　　Low Maintenance Costs: The enclosed design minimizes oil oxidation, extending oil replacement intervals and reducing operational expenses.

　　2. Typical Application Scenarios

　　Industrial Sector: High-capacity power supply for steel mills, chemical plants, and mining operations (e.g., electric arc furnaces, compressors).

　　Power Transmission and Distribution: Voltage transformation and energy distribution in 110 kV and lower-voltage substations and distribution stations.

　　Renewable Energy: Collector lines in wind farms and photovoltaic plants, withstanding harsh outdoor climates.

　　Rural Power Grids: Cost-sensitive regions requiring long-term stability, such as remote substations.

　　III. Comparative Analysis with Dry-Type Transformers

　　IV. Selection and Usage Recommendations

　　1. Capacity Selection

　　Select rated capacity based on load requirements, typically 1.2–1.5 times the calculated load to reserve overload margin.

　　Example: For a 1,000 kVA calculated load, choose a 1,250 kVA or 1,600 kVA transformer.

　　2. Environmental Adaptability

　　For outdoor installations, select IP23 or higher protection ratings, equipped with rain covers and anti-corrosion coatings.

　　In high-altitude areas (>1,000 m), derate capacity or use-type (high-altitude) transformers.

　　3. Maintenance Guidelines

　　Regularly test oil quality (breakdown voltage, moisture content) and perform oil filtration or replacement every 3–5 years.

　　Inspect sealing components for aging and replace rubber gaskets every 5–8 years.

　　Monitor gas relay signals to promptly address internal faults.

　　V. Case Studies

　　Steel Plant Project: A 20,000 kVA enclosed oil-immersed transformer operated at 85% load for 8,000 hours annually. Over 10 years, no insulation failures occurred, and maintenance costs were 40% lower than dry-type alternatives.

　　Wind Farm Collector Lines: A 630 kVA oil-immersed transformer adapted to temperatures ranging from -40°C to +50°C, achieving a fault rate below 0.5%/year and ensuring stable wind farm operation.

　　Conclusion

　　Enclosed oil-immersed power transformers excel in high-capacity, outdoor power transmission due to their efficient cooling, robust insulation, and cost-effectiveness. Proper selection—considering load characteristics, environmental conditions, and economics—combined with scientific maintenance, significantly extends service life and ensures reliable power system support.