Unleashing the Insulating Materials for Electrical Machines

• High dielectric strength.
• It should withstand high temperatures.
• Good thermal conductivity.
• It should not undergo thermal oxidation.
• It should not deteriorate due to higher temperatures and repeated heat cycles.
• It must have a high value of resistivity (like 1018 Ωcm).
• Less power consumption.
• Low dielectric loss angle.
• It should withstand stresses due to centrifugal forces, electrodynamic or mechanical forces.
• It should withstand vibration, abrasion, and bending.
• Not to absorb moisture.
• It must be flexible and cheap.
• Liquid insulators should not evaporate or volatilize.

Properties and Types of Insulators

Solid

• Fibrous or inorganic animal or plant origin, natural or synthetic paper, wood, cardboard, cotton, jute, silk, rayon, nylon, asbestos, fiberglass, etc.,
• Plastic or resins. Natural resins-lac, amber, shellac, etc.,
• Synthetic resins-phenol formaldehyde, melamine, polyester, epoxy, silicon resins, bake lite, Teflon, PVC, etc.
• Rubber: natural rubber, synthetic rubber-butadiene, silicone rubber, Hypalon, etc.,
• Mineral: mica, marble, slate, talc chloride, etc.,
• Ceramic: porcelain, steatite, alumina, etc.,

Glass:

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

Liquid:

• Mineral oil (petroleum by-product).
• Synthetic oil askaris, pyrazoles, etc.,
• Varnish, French polish, lacquer epoxy resin, etc.,

Gaseous:

• Air used in switches, air condensers, transmission and distribution lines, etc.,
• Hydrogen though not used as a dielectric is generally used as a coolant.
• Nitrogen use in capacitors, HV gas pressure cables, etc.,
• Inert gases neon, argon, mercury, and sodium vapors are generally used for neon sign lamps.
• Halogens, like fluorine, are used under high pressure in cables.
• No insulating material in practice satisfies all the desirable properties. Therefore a material that satisfies most of the desirable properties must be selected.

The insulation system (also called insulation class) for wires utilized in generators, motors transformers, and different wire-wound electrical elements is split into completely different categories according to the temperature they will safely withstand. The maximum operating temperature is the temperature the insulation will reach throughout the operation. It is the summation of standardized ambiance temperature, i.e., 40 degree Celsius, tolerated temperature rise, and allowance tolerance for warm spots in winding. For example, the maximum temperature of sophistication B insulation is (ambient temperature 40 + allowable temperature rise 80 + hot spot tolerance 10) = 130oC.