Oil-immersed Transformer

　　In-Depth Analysis of Oil-Immersed Transformers

　　1. Core Principles and Functions

　　Oil-immersed transformers are critical equipment in power systems for voltage transformation and electrical energy transmission, operating based on the principle of electromagnetic induction. The transformer core, constructed from laminated silicon steel sheets, minimizes hysteresis and eddy current losses through its high magnetic permeability. The windings are divided into high-voltage (HV) and low-voltage (LV) sides. When the HV side is connected to an AC power source, an alternating magnetic field is induced in the core, which in turn generates an electromotive force in the LV windings, enabling voltage step-up or step-down.

　　Key Functions:

　　Voltage Transformation: Meets diverse voltage requirements for electrical equipment.

　　Power Transmission: Reduces transmission losses by stepping up voltage for long-distance transmission and stepping it down for end-user compatibility.

　　Electrical Isolation: Prevents direct conduction between HV and LV sides using insulating oil and winding insulation structures.2. Technical Characteristics and Advantages

　　Efficient Cooling Design

　　Oil Circulation System: Insulating oil, acting as a cooling medium, transfers heat to radiators via natural convection or forced circulation (e.g., oil pump-driven).

　　Radiator Structure: Utilizes corrugated fin or tubular radiators to increase surface area and enhance heat exchange efficiency.

　　Data Support: Under full load, oil-immersed transformers typically exhibit 10–15°C lower temperature rise compared to dry-type transformers, enabling operation in higher ambient temperatures.Electrical Insulation Performance

　　Insulating Oil Properties: Mineral insulating oil offers a breakdown voltage ≥30 kV/2.5 mm, dielectric loss factor ≤0.5% (at 90°C), providing reliable electrical isolation.

　　Multi-Layer Insulation Structure: Windings are separated by insulating paper, insulating cylinders, and end insulation rings, forming多重防护 (multiple protective layers).

　　High-Voltage Applications: Account for over 80% of transformers in 110 kV and above voltage classes, far exceeding dry-type transformers.Economic Efficiency and Reliability

　　Cost Comparison: Manufacturing costs are 20–30% lower than dry-type transformers for the same capacity, with 15–20% lower maintenance costs.

　　Lifespan: With regular maintenance, lifespan can reach 30–40 years, with a failure rate below 0.5% per year.

　　Overload Capacity: Capable of short-term overload up to 1.3 times rated capacity (for 2 hours), accommodating load fluctuations.

　　3. Structural Components and Key Parts

　　4. Typical Application Scenarios

　　Power Systems

　　Transmission: In 500 kV ultra-high-voltage substations, single units can reach 500 MVA, enhancing transmission efficiency.

　　Distribution: 10 kV oil-immersed transformers supply residential and commercial areas in urban distribution networks.Industrial Sector

　　Heavy Industry: Powers electric arc furnaces in steel mills with transformers up to 100 MVA, tolerating harmonic currents.

　　Chemical Industry: Explosion-proof oil-immersed transformers meet safety requirements in flammable/explosive environments.Renewable Energy

　　Wind Farms: Box-type substations (containing oil-immersed transformers) in 35 kV collector lines step up voltage to 110 kV.

　　Photovoltaic Plants: 10 kV oil-immersed transformers aggregate PV array power for grid connection.Rural Power Grids

　　Pole-Mounted Transformers: Capacities of 50–200 kVA supply remote areas, adapting to harsh environments.

　　5. Comparison of Advantages and Disadvantages

6. Maintenance and Fault Handling

　　Routine Maintenance

　　Oil Quality Testing: Inspect breakdown voltage, water content, and acid value every 6 months; replace oil every 5–10 years.

　　Seal Inspection: Annually check seals on the oil tank, flanges, and valves, with a leakage rate ≤0.1% per year.

　　Electrical Testing: Conduct insulation resistance, DC resistance, and dielectric loss tests every 3 years to prevent insulation aging.Common Faults and Handling

　　Winding Short Circuit: Fault currents exceed 10x rated value; immediate de-energization and winding replacement required.

　　Insulating Oil Deterioration: Perform vacuum oil filtration or regeneration when dielectric loss >5%.

　　Oil Tank Corrosion: Repair welding or replace the tank if thickness reduction exceeds 30%.7. Development Trends

　　Environmentally Friendly Insulating Oils

　　Natural Esters (e.g., Soybean Oil): Biodegradable alternatives to mineral oil, with flash points exceeding 300°C.Intelligent Monitoring

　　Integrated DGA and Partial Discharge Monitoring: Enables fault prediction through real-time analysis.Compact Design

　　Stereoscopic Wound Core: Reduces no-load losses by 15% and volume by 20%.Ultra-High Voltage Levels

　　Development of 1000 kV UHV Oil-Immersed Transformers: Supports large-scale power transmission projects like the West-to-East Electricity Transfer in China.8. Conclusion

　　Oil-immersed transformers dominate in power systems, industry, and renewable energy sectors due to their efficient cooling, reliable insulation, cost-effectiveness, and durability. Despite challenges in fire safety and environmental impact, advancements in eco-friendly oils, intelligent monitoring, and structural optimization ensure a promising future. For scenarios demanding high loads, long lifespans, and low costs, oil-immersed transformers remain the preferred choice.