oilfilled

Oil-filled, also described as oil-immersed, refers to components in which insulating oil surrounds the active electrical elements to provide insulation and cooling. The oil acts as a dielectric medium capable of withstanding high voltages while transferring heat away from hot spots. This design is common in equipment that handles significant electrical power.

Common applications include power transformers, high-voltage reactors, and certain capacitors. Mineral oil has historically been the standard insulating fluid, though natural ester and synthetic ester oils are increasingly used for environmental and fire-safety considerations. Oil-filled devices may be designed for outdoor or indoor use and are often chosen where convection cooling or transformer efficiency is critical.

Advantages of oil-filled construction include high dielectric strength, efficient heat removal, and the ability to compactly handle high power densities. Oil also provides a sealing function in some designs, helping to keep moisture and gases out of the active region. Disadvantages include the risk of oil leaks, aging and oxidation of the oil, formation of insulating varnish, and the potential for fire hazards if leaks occur. Environmental concerns require careful handling, containment, and proper recycling or disposal of used oil. Regular maintenance often involves dissolved gas analysis to detect developing faults and monitoring oil quality to determine when reconditioning or replacement is necessary.

In contemporary engineering, there is a trend toward dry-type transformers and ester-based oils to reduce fire risk and environmental impact. Nonetheless, oil-filled insulation remains a foundational technology for many high-power and long-life electrical installations.