The 220kV oil-immersed power transformer is the core equipment of the ultra-high voltage power transmission and transformation system. It is mainly used for power transmission, voltage transformation and power flow distribution between the 220kV power grid and the 110kV/35kV/10kV power grids. It is widely applied in provincial main power grids, hub substations, large power plants, new energy bases and the main step-down stations of heavy industrial enterprises, featuring large capacity, high insulation level, reliable operation and mature technology.

I. Main Technical Parameters
Rated Voltage: High Voltage: 220 kV; Medium Voltage: 110 kV / 35 kV; Low Voltage: 10 kV / 6.3 kV
Voltage Regulation Range: On-load Voltage Regulation: 220 ± 8 × 1.25% kV; No-Excitation Voltage Regulation: 220 ± 2 × 2.5% kV
Rated Capacity: Double-Winding: 90 MVA - 240 MVA; Three-Winding: 120 MVA - 240 MVA and above
Frequency: 50 Hz
Phases: Three-phase
Connection Group Number: Double-Winding: YNd11; Three-Winding: YNy0d11
Cooling Method: ONAN / ONAF / OFAF (Strong Oil Circulation Air Cooling); Large-capacity products commonly use ODAF (Strong Oil Guided Air Cooling)
Insulation Level: High Voltage: LI950AC395 kV; Medium Voltage: LI480AC200 kV

Design life: ≥ 30 years

II. Structural Composition
1. Core
The core is made of high magnetic conductivity grain-oriented cold-rolled silicon steel sheets. It features full bevel joints, no holes for binding, and multi-level laminations, achieving low loss, low noise, and low excitation current.
2. Windings
The high-voltage windings mostly adopt the interwoven type and inner shielding continuous structure;
The medium and low-voltage windings use the spiral or continuous type;
The use of staggered conductors ensures a firm overall compression and strong anti-short-circuit ability.
3. Oil Tank
Mostly bell-shaped oil tanks, with high strength and convenient for lifting and inspecting the tank;
The overall sealing structure effectively prevents oil leakage and moisture absorption.
4. Main Accessories
220kV high-voltage bushing, 110kV/35kV medium and low-voltage bushings
Oil reservoir (oil pillow), capsule / diaphragm seal
Oil-cooling system with forced circulation + fan
On-load tap changer and electric mechanism
Gas relay, pressure release valve
Oil temperature / winding temperature gauge, oil level gauge, desiccant
Can be equipped with online oil chromatography monitoring device

III. Product Features
1. High insulation reliability
Utilizing an oil-paper insulation system, with vacuum injection and hot oil circulation treatment, the partial discharge is low and the insulation performance is stable.
2. Low loss, energy-saving
Compliant with national energy efficiency standards, with low no-load and load losses, the long-term operation has significant economic benefits.
3. Strong short-circuit resistance
The winding support is firm, and the axial and radial compression is reliable, capable of withstanding sudden short-circuit impacts in the system.
4. Safe and stable operation
Comprehensive protection configuration can achieve multiple protections such as over-temperature, light gas, heavy gas, and pressure release.
5. Adapt to outdoor environment
Can operate outdoors for a long time, able to withstand harsh environments such as high and low temperatures, sandstorms, rain, and snow.

IV. Typical Model Examples SFSZ20-180000/220
S: Three-phase
F: Air-cooled
S: Three-winding
Z: On-load voltage regulation
20: Design sequence number
180000: Capacity 180 MVA
220: High-voltage rated voltage 220 kV
V. Application Fields
220 kV hub substations, main transformers of regional power grids
Power generation plants such as thermal, hydropower, and nuclear power plants for voltage boosting
220 kV gathering and voltage boosting stations for new energy sources such as wind power and photovoltaic power
Total step-down transformers for large-scale petrochemical, metallurgical, and coal chemical enterprises with high energy consumption
VI. Execution Standards
GB 1094 "Power Transformers"
GB/T 6451 "Technical Parameters and Requirements for Three-phase Oil-immersed Power Transformers"
GB/T 1094.7 "Load Guidelines for Oil-immersed Power Transformers"
IEC 60076 series international standards