Closed type power transformer

　　Analysis of Enclosed Power Transformers

　　I. Definition and Core Advantages

　　An enclosed power transformer is a type of transformer in which the core, windings, and insulation materials are completely sealed within an oil tank. Its core advantages include:

　High Protection Rating: The sealed tank design effectively prevents the ingress of moisture, dust, and corrosive gases, making it suitable for harsh environments (e.g., coastal areas, chemical plants).

　　Low Loss and High Efficiency: Utilizing high-quality cold-rolled silicon steel cores and low-loss winding designs, no-load losses are reduced by 10%-20%, achieving energy efficiency ratings up to Grade 1.

　　Low Noise Operation: The fully sealed structure reduces vibration transmission, with noise levels typically below 55dB, meeting the requirements of residential and office areas.

　　Maintenance-Free Design: The internal insulation oil circulates and filters within the tank, eliminating the need for regular oil changes and extending maintenance intervals to over 5 years.II. Technical Classification and Structural Analysis

　　Classification by Insulation Medium:

　　Oil-Immersed Type: Uses mineral oil or vegetable-based insulation oil, offering excellent heat dissipation performance and suitable for voltage levels from 10kV to 500kV.

　　Dry Type (Gas-Insulated): Filled with SF6 or eco-friendly gases (e.g., C5-FK), with outstanding fire resistance, primarily used for indoor power distribution.Cooling Methods:

　　Self-Cooled (ONAN): Relies on natural convection for heat dissipation, suitable for small to medium-capacity transformers (≤6300kVA).

　　Forced-Air Cooled (ONAF): Adds fans for forced heat dissipation, increasing capacity by 30%-50%.

　　Forced-Oil Cooled (OFAF): Uses oil pumps for forced circulation, suitable for large transformers (≥100MVA).Structural Components:

　　Core: Adopts laminated or wound core structures with lamination gaps ≤0.02mm to reduce eddy current losses.

　　Windings: High-voltage windings are layered or disc-type, while low-voltage windings are predominantly foil-type, with short-circuit impedance deviation ≤±7.5%.

　　Oil Tank: Corrugated or radiator-style, with surface corrosion treatment conforming to GB/T 6451 standards.III. Application Scenarios and Selection Guidelines

　　Power Systems:

　　Substations: Main transformers for 220kV and above voltage levels, with capacity ranges of 50MVA-1000MVA.

　　Distribution Networks: 10kV-35kV distribution transformers, with recommended load ratios of 60%-80%.Industrial Applications:

　　Metallurgy/Petrochemicals: Fully sealed structures to withstand high temperatures (≤120°C) and harmonic loads.

　　Rail Transit: Low-noise models (≤50dB) compliant with IEC 60076-11 standards.Selection Parameters:

　　Capacity Calculation: S=η×cosϕP, where η is the load ratio (0.6-0.8) and cosϕ is the power factor (0.8-0.9).

　　Short-Circuit Impedance: Selected based on system short-circuit capacity, typically 4%-10% for distribution transformers or 12%-18% for main transformers.

　　Temperature Rise Limits: Top oil temperature rise ≤55K (oil-immersed), winding temperature rise ≤60K (dry type).IV. Industry Trends and Standards

　　Technological Development Trends:

　　Energy Efficiency Upgrades: Promotion of amorphous alloy core transformers, reducing no-load losses by over 70%.

　　Intelligence: Integration of online monitoring modules (DGA, partial discharge) for remote diagnostics.

　　Environmental Friendliness: Adoption of natural ester insulation oils (e.g., rapeseed oil) with biodegradability >98%.Comparison of Domestic and International Standards:

　　Chinese Standards: GB 1094 series for power transformers, with mandatory certification (CCC).

　　International Standards: IEC 60076 for power transformers, with EU CE certification and US UL certification.

V. Typical Suppliers and Products

　　VI. Selection Recommendations

　　Qualification Verification: Require suppliers to provide type test reports (including short-circuit withstand capacity and temperature rise tests).

　　Energy Efficiency Verification: Check energy efficiency labels (Grade 1 is optimal in China).

　　Environmental Adaptability: Derate capacity in high-altitude areas (reduce capacity by 5%-8% for every 1000m increase in altitude).

　　Operation and Maintenance Support: Confirm the availability of intelligent monitoring systems and full lifecycle services.Conclusion: Enclosed power transformers have become core equipment in modern power grids due to their high reliability, low maintenance requirements, and environmental performance. When selecting, users should consider load characteristics, environmental conditions, and energy efficiency requirements, prioritizing suppliers with international certifications and focusing on total lifecycle cost (TCO) rather than just initial procurement prices.