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Extra-high Voltage Cables OF Cables

OF cables were developed in the early 1900s as a result of increased demand for cables, and have been widely used due to their high credibility and economic efficiency. OF cables mainly consist of a single or 3-plex structure, and are used for large storage transmission up to ultra-high voltage from 66kV to 765kV. They are widely used in extra-high voltage cables.

Types and Purposes

Extra-high voltage underground cables
•OF Cables:
Mainly used for voltages of 154kV and above to transmit electricity from the power plant to the substation near the usage area. OF cables use paper as their insulator so they are classified as a type of paper insulation cable. They have proven to be the most reliable among all paper insulation cables so therefore are widely used. However, due to the recent commercialization of XLPE cables, usage has been decreasing.


The structure prevents electric degradation of the cable by suppressing gaps due to temperature changes within the cable or the external routing environment. This is achieved through a pressure tank on the exterior of the cable, which is charged through low viscosity insulating oil inside the cable that consistently puts pressure higher than the atmosphere onto the cable.
Paper with a high dielectric constant and electric characteristics is used in the first phase insulation while second phase insulation is maintained through oil pressure using insulating oil.

Main features

• Advanced dielectric strength and reliability
• Compact due to high reliability

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