For voltages of approximately Um ≤ 36 kV, a simple dry type bushing is commonly used. Dry bushings consist of a conductor surrounded by a high-grade porcelain insulator body. ‘Dry’ indicates that no insulating fluid is used in the bushing construction. The porcelain body surrounds the entire conductor except for the terminal ends.

For higher distribution voltages, Um ≤ 52 kV, electrical grade mineral oil is often used as part of the insulating structure to increase the electrical withstand capabilities of the bushing. In order to achieve this, a void (empty space) is created during the bushing’s manufacture and oil then fills the space between the conductor and insulator (porcelain body).