What type of cable insulation is made of closely woven cotton cloth coated with insulating varnish and rated from 600 to 23000 volts?

The type of cable insulation made of closely woven cotton cloth coated with insulating varnish, and capable of handling voltages from 600 to 23,000 volts, is indeed varnish-cambric. This material is renowned for its effectiveness in electrical insulation due to the combination of the durable, woven cotton substrate and the varnish that enhances its insulating properties. Varnish-cambric is typically used in applications where flexibility and a certain level of thermal resistance are necessary, making it suitable for various electrical environments.

This insulation type stands out particularly for its historical significance and reliability in various industrial applications, effectively serving its purpose under high voltage conditions. The ability to withstand significant voltage levels indicates its robustness and why it's commonly valued in certain electrical systems.

Comparing to the other types of insulation listed, cross-linked polyethylene is known for its durability and resistance to heat and chemicals but does not utilize a cloth base. Concrete encased pertains to a physical construction method rather than an insulation material, while impregnated-paper insulation involves a different composition that relies heavily on oils or resins rather than a woven fabric structure. These distinctions clarify why varnish-cambric is the correct choice in the context of the question.