Introduction
Oil immersed power transformers are the most widely used type of power transformer for high voltage and large power applications. This comprehensive guide covers their design, construction, advantages, and applications.
What is an Oil Immersed Transformer?
An oil immersed transformer uses mineral oil (or other insulating fluids) as both the insulating medium and cooling medium. The oil surrounds the core and windings, providing excellent electrical insulation and heat dissipation.
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Construction
Core
- Grain-oriented silicon steel laminations
- Cooled, mitred joints for low no-load loss
- Epoxy coated for corrosion protection
Windings
- Copper or aluminum conductors
- Paper insulation
- Cylindrical or disc winding design
Tank and Accessories
- Welded steel tank
- Radiators for cooling
- Conservator tank for oil expansion
- Buchholz relay for gas protection
- Oil temperature and winding temperature indicators
- Pressure relief device
Cooling Methods
ONAN (Oil Natural Air Natural)
Natural convection of oil and air. Simplest and most reliable. Used for small to medium transformers.
ONAF (Oil Natural Air Forced)
Natural oil convection with forced air cooling via fans. Increases capacity by 30-50%.
OFAF (Oil Forced Air Forced)
Forced oil circulation with pumps and forced air fans. Highest efficiency for large power transformers.
Read our detailed guide on cooling methods.
Advantages
- Excellent heat dissipation
- High dielectric strength
- Suitable for high voltage (up to 765kV+)
- Large power ratings (up to 1000MVA+)
- Long service life (30+ years)
- Proven and reliable technology
Applications
- Power plants – GSU transformers
- Transmission and distribution substations
- Electrical grid and transmission
- Renewable energy projects
Explore our range of large power transformers.
Conclusion
Oil immersed transformers remain the preferred choice for high voltage and large power applications due to their superior cooling and insulation properties. Contact our engineers for custom solutions.