What insulation medium is used for cables over 45 kV?

For cables operating at voltages over 45 kV, oil and gas are commonly used as insulation mediums due to their excellent electrical insulating properties and ability to withstand high voltages. These mediums help in maintaining the stability and efficiency of power transmission by preventing electrical breakdown, which is crucial at higher voltage levels.

Oil, specifically, has been used traditionally in various applications for its dielectric properties and cooling effects. Gas-insulated cables, which utilize gases such as sulfur hexafluoride (SF6), also serve a similar purpose, providing high insulating strength and enabling compact designs.

While air, paper, and rubber can be effective insulators, they are generally not suitable or efficient for use at such high voltage levels. Air can lead to arcing in high voltage scenarios, paper has limitations in moisture absorption and may not provide adequate insulation, and rubber, while useful for lower voltage applications, does not offer the same level of electrical performance required for cables exceeding 45 kV. Therefore, oil and gas stand out as the optimal choices for high-voltage insulation.