New insulating materials for electrical machines

• High dielectric strength.
• It must withstand high temperatures.
• Good thermal conductivity.
• It must not be subjected to thermal oxidation.
• Higher temperatures and repeated thermal cycling should not affect material properties.
• The specific resistance must be high (around 1018 Ωcm).
• Lower energy consumption.
• Low dielectric loss angle.
• It must withstand stresses caused by centrifugal forces, electrodynamic or mechanical forces.
• It must resist vibration, abrasion and bending.
• Do not absorb moisture.
• It has to be flexible and cheap.
• Liquid insulating agents must not evaporate or evaporate.

Properties and types of insulators

Solid

• Fibrous or inorganic materials of animal or vegetable origin, natural or synthetic paper, wood, cardboard, cotton, jute, silk, viscose, nylon, asbestos, fiberglass, etc.
• Plastic or resins. Natural resins – varnish, amber, shellac, etc.,
• Synthetic resins – phenol-formaldehyde, melamine, polyester, epoxy, silicone resins, bakelite, Teflon, PVC, etc.
• Rubber: Natural rubber, synthetic butadiene rubber, silicone rubber, Hypalon, etc.
• Mineral: mica, marble, slate, talcum chloride, etc.
• Ceramics: porcelain, soapstone, alumina, etc.

Glass:

• Non-resinous: mineral waxes, asphalt, bitumen, chlorinated naphthalene, enamel, etc.

Fluid:

• Mineral oil (petroleum by-product).
• Askaris synthetic oil, Pyrazol etc.,
• Varnishes, shellac polishes, epoxy resin varnishes, etc.

Gaseous:

• Air used in switches, air condensers, transmission and distribution lines, etc.,
• Although hydrogen is not used as a dielectric, it often serves as a coolant.
• Use of nitrogen in capacitors, HV gas pressure cables, etc.
• The noble gases neon, argon, mercury and sodium vapor are generally used for neon lamps.
• Halogens, like fluorine, are used in cables under high pressure.
• In practice, no insulating material meets all the desired properties. Therefore, a material that meets most of the desired properties must be selected.

The insulation system (also called insulation grade) for wires used in generators, motors, transformers, and other wound electrical components is divided into several categories depending on the temperature they can safely withstand. Maximum operating temperature is the temperature that the insulation will reach during operation. It is the sum of the standardized ambient temperature, i.e. 40 degrees Celsius, the allowable temperature rise and the tolerance for hot spots in the winding. For example, the maximum temperature of Class B insulation is (ambient temperature 40 + allowable temperature rise 80 + hot spot tolerance 10) = 130°C.