What is an oil-immersed transformer?

Oil-Immersed Transformers: Overview, Features, and Applications

An oil-immersed transformer is a widely used type of power transformer that employs a liquid—typically insulating oil—as both an insulating and cooling medium.

Key Features of Oil-Immersed Transformers:

• Insulating Oil: Insulating oil serves as the primary dielectric medium, electrically isolating the windings from the core and ground. With its high dielectric strength, it effectively prevents electrical breakdown between windings or between windings and the grounded core.

• Cooling Mechanism: In addition to insulation, the oil provides efficient cooling through conduction and natural convection. The windings and core are fully immersed in the oil, which absorbs heat generated during operation. Due to its high thermal capacity, the oil helps transfer and dissipate heat, maintaining safe operating temperatures.

• Pressure Relief Devices: As insulating oil expands when heated during operation, oil-immersed transformers are typically equipped with pressure relief devices. These safety mechanisms release excess oil vapor or pressure in the event of internal overpressure, protecting the tank from rupture or explosion.

• Maintenance and Monitoring: Regular oil sampling and maintenance are essential to ensure the continued performance of the insulating oil. Key tests include dielectric strength, moisture content, and dissolved gas analysis (DGA). Degraded oil should be filtered, reconditioned, or replaced as needed. Transformers are also equipped with monitoring instruments such as oil level indicators, temperature gauges, and pressure sensors to continuously assess operational health.

• Wide Range of Applications: Oil-immersed transformers are extensively used in power transmission and distribution systems, power plants, industrial facilities, and substations. They are available in a broad range of voltage and power ratings, providing stable, reliable, and efficient power supply under diverse operating conditions.

Advantages and Considerations:
Oil-immersed transformers offer excellent insulation performance, high short-circuit withstand capability, effective cooling, and long service life. However, they require more maintenance compared to dry-type transformers, have larger physical dimensions and weight, and pose potential environmental risks in the event of oil leakage. Therefore, careful evaluation of site conditions, environmental regulations, and operational requirements is essential when selecting an oil-immersed transformer for a specific application.