Which type of bushing is used on higher voltage circuit breakers, usually over 75kV?

The correct answer is the condenser type bushing. This type of bushing is specifically designed to manage the high voltage and electrical insulation requirements found in circuits exceeding 75kV. It functions effectively in high-voltage applications because it provides superior insulation through the use of a series of capacitors, which help to reduce the electric field strength in the bushing and improve the overall thermal performance.

Condenser type bushings are particularly advantageous because they allow for a lighter and more compact design while maintaining efficiency. They are also less susceptible to dielectric breakdown compared to solid or oil-filled options, making them safer for critical applications.

In contrast, solid porcelain bushings, while offering good insulation at lower voltages, may not adequately handle the stress and strain seen in higher voltage systems. Oil-filled bushings, although they can be used in some high voltage applications, are bulkier and can pose environmental hazards if leaks occur. SF6 (sulfur hexafluoride) is a gas that provides excellent insulation and arc-extinguishing properties but is typically utilized in switchgear rather than as a bushing type.