Which of the following materials is commonly used for high voltage insulation?

The use of EPR, or Ethylene Propylene Rubber, as a material for high voltage insulation is due to its excellent electrical insulating properties, resilience to heat, and resistance to environmental factors, such as moisture and ozone. This makes it highly suitable for applications involving high voltage systems where maintaining electrical insulation integrity is crucial to ensure safety and reliability.

EPR's flexibility and durability allow it to withstand the mechanical stresses that can occur in high voltage environments, which is essential in preventing insulation breakdown. Additionally, its performance across a wide range of temperatures contributes to its effectiveness, making it a preferred choice for insulating cables and other electrical equipment in high voltage applications.

In contrast, the other materials mentioned do not offer the same combination of insulating properties and resilience. Copper, while an excellent conductor of electricity, cannot serve as an insulating material. Steel, similarly, is a conductive material that is often used for structural support or grounding rather than insulation. Fiber materials, depending on their specific type and treatment, may offer some insulating properties but typically do not match the high voltage insulation performance provided by EPR.