The 110kV oil-immersed power transformer is the core equipment of the 110kV power transmission and distribution network. It uses mineral insulating oil as the insulation and cooling medium, mainly achieving voltage conversion from 110kV high voltage to 35kV/10kV medium and low voltages. It features large capacity, high reliability, and strong overload capacity, and is widely used in power grid hubs, power plants, large industrial and new energy power stations.

I. Core Parameters (Standard Series)
Rated Capacity: 6300kVA ~ 180000kVA (Mainstream: 10000~63000kVA)
Voltage Combinations

High Voltage: 110 ± 8 × 1.25% kV or 110 ± 2 × 2.5% kV
Low Voltage: 38.5kV / 35kV / 10.5kV / 10kV
Phases / Frequency: Three-phase, 50Hz
Connection Group Number: YNd11 (Two-winding), YNy0d11 (Three-winding)
Short-circuit Impedance: 10% ~ 14% (Dependent on Capacity)
Cooling Method: ONAN (Natural Oil Circulation), OFAF (Forced Oil Circulation Air Cooling)
Voltage Regulation Method: No-excitation Voltage Regulation (±2 × 2.5%), On-load Voltage Regulation (OLTC) (±8 × 1.25%)
Insulation Level: LI480AC200kV (High Voltage), LI200AC85kV (Medium Voltage)

II. Core Structure
1. Core
High-quality cold-rolled grain-oriented silicon steel sheet, fully inclined without holes, multi-level stepped stacking, low no-load loss, low noise.
2. Windings
High voltage: Coiled type / Inner screen continuous type, improves the distribution of impact voltage.
Low voltage: Spiral type / Continuous type, uses self-adhesive interlaced conductors, strong anti-short-circuit ability.
Insulation: High-strength insulating paper / Paperboard + Hard paper tube, overall oil-immersed insulation.
3. Oil tank
Bell jar type / Barrel type, corrugated structure, high mechanical strength.
Sealing: Groove flange, vacuum oil injection, anti-leakage.
4. Main accessories
High-voltage bushing: 3 large porcelain sleeves (110kV grade).
Oil reservoir (oil tank): Adjusts oil volume, slows down oil aging.
Heat exchanger + Fan: OFAF cooling, enhances heat dissipation.
On-load tap changer: On-line voltage adjustment.
Protection: Gas relay, pressure release valve, oil chromatography monitoring, thermometer.

III. Product Features
Low-loss energy-saving: Complies with GB 20052-2020 energy efficiency level 1, S11/S13/S20 series. The no-load loss is 15% - 25% lower than the national standard.
Strong anti-short-circuit capability: The core is tightly pressed, with hard supports, and the overall pressure-drying is constant. It passes the sudden short-circuit test.
Low partial discharge: Partial discharge is ≤ 100 pC, and the insulation life is long.
Low noise: Optimized iron core structure, noise ≤ 60 dB (A).
High reliability: Good sealing, low maintenance, design life ≥ 30 years.
IV. Typical Model Meaning
Take SZ20-31500/110 as an example:
S: Three-phase
Z: On-load voltage regulation
20: Design sequence number (energy-saving type)
31500: Capacity 31500 kVA
110: High-voltage rated voltage 110 kV

V. Application Scenarios
Power Grid Substations: 110kV main transformers, reducing voltage to supply 35kV/10kV distribution networks.
Power Plants: Generator outlets are boosted to 110kV for grid connection.
Large Industries: Steel, chemical, metallurgy, petrochemical main substations.
New Energy: Wind power / solar power stations are boosted to 110kV for grid connection.
Urban / Regional Power Grids: Core hubs, ensuring large-capacity power supply.
VI. Execution Standards
National Standards: GB 1094, GB/T 6451, GB 20052
International: IEC 60076
VII. Selection Key Points
1. Capacity is reserved by 15% - 20% based on load.
2. Select on-load tap-changers when voltage fluctuations are significant.
3. For large capacities, select OFAF cooling.
4. Prioritize S11 and above low-loss models.