What Is an Oil Immersed Transformer and Why Is It Widely Used in Power Systems?

An oil immersed transformer is a type of electrical transformer where the core and windings are submerged in insulating mineral oil. This oil serves two primary purposes: cooling and insulation. These transformers are essential in medium to high-voltage power transmission and distribution, offering reliable performance and long service life in various industrial and utility applications.

How Does an Oil Immersed Transformer Work?

The transformer core and coils are enclosed in a sealed tank filled with insulating oil. When the transformer operates, electrical losses generate heat. The oil absorbs this heat and circulates either naturally or via pumps to radiators where it cools down. At the same time, the oil insulates high-voltage components, preventing electrical discharges.

What Are the Main Features of Oil Immersed Transformers?

1. High Cooling Efficiency

  The oil effectively transfers heat from the windings to the outer tank, allowing continuous operation even under heavy load.

2. Strong Dielectric Properties

  Mineral oil offers excellent electrical insulation, enhancing safety and performance.

3. Durability

  These transformers are robust and suitable for both indoor and outdoor installations, with lifespans often exceeding 30 years when properly maintained.

4. Cost-Effective for High Power Levels

  For applications above 500 kVA, oil immersed transformers are typically more economical than dry-type alternatives.

Common Types of Oil Immersed Transformers

Distribution Transformers: Step down voltage for local electricity distribution (e.g., 11kV/400V).

Power Transformers: Handle higher voltage transmission between substations.

Sealed vs. Conservator-Type: Sealed types are fully enclosed to reduce oil oxidation, while conservator types use an expansion tank to manage oil volume changes.

Where Are Oil Immersed Transformers Used?

Electric Utility Substations

Industrial Facilities

Commercial Buildings

Renewable Energy Plants

Infrastructure Projects (e.g., Rail, Airports)

Maintenance Considerations

Oil Testing: Periodic oil sampling checks for moisture, acidity, and dielectric strength.

Thermal Monitoring: Ensures the unit doesn’t overheat under load.

Leak Inspection: Prevents environmental damage and ensures safety.

Conclusion

Oil immersed transformers are a trusted solution for medium and high-voltage power distribution due to their excellent cooling, insulation, and long-term performance. Whether in a substation or a factory, these transformers form the backbone of reliable power delivery in modern electrical networks.