What are the advantages of Oil immersed Transformer compared to dry type transformer?

In the realm of electrical power distribution and transmission, selecting the right transformer technology is a critical decision for engineers, grid operators, and industrial facility managers. Two primary technologies dominate the landscape: dry type and oil immersed transformers. While each has its rightful place, the Oil immersed Transformer offers a distinct set of advantages, particularly in demanding, high-capacity applications.

Superior Cooling and Overload Capacity

The most significant advantage of an Oil immersed Transformer is its exceptional heat dissipation capability. The transformer's core and windings are immersed in a specialized insulating oil, which acts as a highly efficient coolant. As the equipment operates, heat is transferred to the oil. Through natural convection or forced circulation, the heated oil moves through radiators, dissipating the thermal energy into the surrounding environment.

This efficient cooling mechanism allows an Oil immersed Transformer to handle higher overloads for shorter durations without sustaining damage. The large thermal mass of the oil provides a buffer against temperature spikes, making it exceptionally robust for applications with fluctuating loads or potential fault conditions.

Enhanced Insulation and Dielectric Strength

The insulating oil in an Oil immersed Transformer serves a dual purpose: cooling and insulation. This oil has a much higher dielectric strength compared to air. By submerging the core and windings, the oil prevents the oxidation of the cellulose-based solid insulation and prevents moisture ingress, which can degrade insulation properties over time. This results in a more reliable and longer-lasting insulation system, capable of withstanding higher voltage stresses andimpulse levels (BIL).

Long Operational Life and Durability

The combination of effective cooling and a well-preserved insulation system directly contributes to an extended operational lifespan. The slow degradation of the cellulose paper insulation is a key factor determining a transformer's life. By keeping operating temperatures stable and protecting the solid insulation from oxygen and moisture, an Oil immersed Transformer is engineered for decades of reliable service, often exceeding 25-30 years with proper maintenance. This makes it a cornerstone asset for utility companies and large industrial plants.

Higher Voltage and Power Rating Capability

Due to its superior cooling and insulation properties, the Oil immersed Transformer is the unequivocal choice for very high voltage and high power applications. It is practically impossible to design a dry type transformer for voltages above 69 kV or for power ratings in the hundreds of MVA. For transmission-level substations, large generator step-up units, and heavy industrial complexes requiring immense power, the Oil immersed Transformer is the only viable technology.

Cost-Effectiveness for Large Ratings

For equivalent voltage and power ratings, an Oil immersed Transformer often presents a lower initial capital cost compared to a dry type unit. This cost advantage becomes increasingly pronounced as the required rating increases. While installation considerations like oil containment systems and potential fire safety measures add to the project cost, the core equipment itself remains a highly economical solution for large-scale power applications.

Considerations and Applications

It is important to note that the advantages of an Oil immersed Transformer come with specific requirements. They typically require a containment berm to manage potential oil leaks, and fire safety codes may dictate the use of fire-resistant fluids or additional suppression systems in indoor installations.

Consequently, the ideal applications for an Oil immersed Transformer are:

Outdoor substations (utility transmission and distribution).

Large industrial plants and generation facilities (e.g., hydroelectric, thermal power plants).

Renewable energy farms (wind and solar) where large units step up voltage for grid connection.

Any location requiring a high-power, high-voltage solution where space and environmental conditions are not a primary constraint.

The Oil immersed Transformer remains a technologically advanced and highly reliable workhorse of the modern electrical grid. Its advantages in cooling efficiency, insulation integrity, power handling capability, and long-term durability make it the preferred solution for high-capacity and high-voltage applications. The choice between transformer types is ultimately dictated by the specific application, budget, environmental conditions, and safety regulations. However, for sheer performance and proven reliability in the most demanding roles, the Oil immersed Transformer continues to hold a critical advantage.